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<front>
<title abbrev="DetNet Use Cases"> Deterministic Networking Use Cases</title>
<author fullname="Ethan Grossman" initials="E.A.G." role="editor" surname="Grossman">
<organization abbrev="DOLBY">Dolby Laboratories, Inc.</organization>
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<street>1275 Market Street</street>
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<email>ethan.grossman@dolby.com</email>
<uri>http://www.dolby.com</uri>
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</author>
<author fullname="Craig Gunther" initials="C.A.G." surname="Gunther">
<organization abbrev="HARMAN">Harman International</organization>
<address>
<postal>
<street>10653 South River Front Parkway</street>
<city>South Jordan</city>
<region>UT</region>
<code>84095</code>
<country>USA</country>
</postal>
<phone>+1 801 568-7675</phone>
<email>craig.gunther@harman.com</email>
<uri>http://www.harman.com</uri>
</address>
</author>
<author initials="P" surname="Thubert" fullname="Pascal Thubert">
<organization abbrev="CISCO">Cisco Systems, Inc</organization>
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<street>Building D</street>
<street>45 Allee des Ormes - BP1200 </street>
<city>MOUGINS - Sophia Antipolis</city>
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<phone>+33 497 23 26 34</phone>
<email>pthubert@cisco.com</email>
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</author>
<author fullname="Patrick Wetterwald" initials="P" surname="Wetterwald">
<organization abbrev="CISCO"> Cisco Systems </organization>
<address>
<postal>
<street>45 Allees des Ormes</street>
<city>Mougins</city>
<code>06250</code>
<country>FRANCE</country>
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<phone>+33 4 97 23 26 36</phone>
<email>pwetterw@cisco.com</email>
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</author>
<author fullname="Jean Raymond" initials="J" surname="Raymond">
<organization abbrev="HYDRO-QUEBEC"> Hydro-Quebec </organization>
<address>
<postal>
<street>1500 University</street>
<city>Montreal</city>
<code>H3A3S7</code>
<country>Canada</country>
</postal>
<phone>+1 514 840 3000</phone>
<email>raymond.jean@hydro.qc.ca</email>
</address>
</author>
<author fullname="Jouni Korhonen" initials="J." surname="Korhonen">
<organization abbrev="BROADCOM">Broadcom Corporation</organization>
<address>
<postal>
<street>3151 Zanker Road</street>
<city>San Jose</city>
<code>95134</code>
<region>CA</region>
<country>USA</country>
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<email>jouni.nospam@gmail.com</email>
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</author>
<author fullname="Yu Kaneko" initials="Y" surname="Kaneko">
<organization>Toshiba</organization>
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<street>1 Komukai-Toshiba-cho, Saiwai-ku, Kasasaki-shi</street>
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<author fullname="Subir Das" initials="S" surname="Das">
<organization>Applied Communication Sciences</organization>
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<city>New Jersey, 07920, USA</city>
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<email>sdas@appcomsci.com</email>
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<author fullname="Yiyong Zha" initials="Y.Z." surname="Zha">
<organization abbrev="HUAWEI">Huawei Technologies</organization>
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<email>zhayiyong@huawei.com</email>
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</author>
<author fullname="Balázs Varga" initials="B." surname="Varga">
<organization>Ericsson</organization>
<address>
<postal>
<street>Konyves Kálmán krt. 11/B</street>
<city>Budapest</city>
<country>Hungary</country>
<code>1097</code>
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<email>balazs.a.varga@ericsson.com</email>
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</author>
<author fullname="János Farkas" initials="J." surname="Farkas">
<organization>Ericsson</organization>
<address>
<postal>
<street>Konyves Kálmán krt. 11/B</street>
<city>Budapest</city>
<country>Hungary</country>
<code>1097</code>
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<email>janos.farkas@ericsson.com</email>
</address>
</author>
<author fullname="Franz-Josef Goetz" initials="F." surname="Goetz">
<organization>Siemens</organization>
<address>
<postal>
<street>Gleiwitzerstr. 555</street>
<city>Nurnberg</city>
<country>Germany</country>
<code>90475</code>
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<email>franz-josef.goetz@siemens.com</email>
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</author>
<author fullname="Juergen Schmitt" initials="J." surname="Schmitt">
<organization>Siemens</organization>
<address>
<postal>
<street>Gleiwitzerstr. 555</street>
<city>Nurnberg</city>
<country>Germany</country>
<code>90475</code>
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<email>juergen.jues.schmitt@siemens.com</email>
</address>
</author>
<date month="February" year="2016"/>
<area>Routing</area>
<workgroup>Internet Engineering Task Force</workgroup>
<keyword>DetNet</keyword>
<keyword>AVB</keyword>
<keyword>TSN</keyword>
<keyword>SRP</keyword>
<abstract>
<t> This draft documents requirements in several diverse industries to establish multi-hop
paths for characterized flows with deterministic properties. In this context deterministic
implies that streams can be established which provide guaranteed bandwidth and latency which
can be established from either a Layer 2 or Layer 3 (IP) interface, and which can co-exist
on an IP network with best-effort traffic. </t>
<t> Additional requirements include optional redundant paths, very high reliability paths,
time synchronization, and clock distribution. Industries considered include wireless for
industrial applications, professional audio, electrical utilities, building automation
systems, radio/mobile access networks, automotive, and gaming. </t>
<t>For each case, this document will identify the application, identify representative
solutions used today, and what new uses an IETF DetNet solution may enable.</t>
</abstract>
</front>
<middle>
<section title="Introduction">
<t> This draft presents use cases from diverse industries which have in common a need for
deterministic streams, but which also differ notably in their network topologies and
specific desired behavior. Together, they provide broad industry context for DetNet and a
yardstick against which proposed DetNet designs can be measured (to what extent does a
proposed design satisfy these various use cases?) </t>
<t> For DetNet, use cases explicitly do not define requirements; The DetNet WG will consider
the use cases, decide which elements are in scope for DetNet, and the results will be
incorporated into future drafts. Similarly, the DetNet use case draft explicitly does not
suggest any specific design, architecture or protocols, which will be topics of future
drafts. </t>
<t> We present for each use case the answers to the following questions: </t>
<t>
<list style="symbols">
<t> What is the use case? </t>
<t> How is it addressed today? </t>
<t> How would you like it to be addressed in the future? </t>
<t> What do you want the IETF to deliver? </t>
</list>
</t>
<t> The level of detail in each use case should be sufficient to express the relevant elements
of the use case, but not more. </t>
<t> At the end we consider the use cases collectively, and examine the most significant goals
they have in common. </t>
</section>
<section title="Pro Audio Use Cases">
<t>(This section was derived from draft-gunther-detnet-proaudio-req-01) </t>
<section title="Introduction">
<t>The professional audio and video industry includes music and film content creation,
broadcast, cinema, and live exposition as well as public address, media and emergency
systems at large venues (airports, stadiums, churches, theme parks). These industries have
already gone through the transition of audio and video signals from analog to digital,
however the interconnect systems remain primarily point-to-point with a single (or small
number of) signals per link, interconnected with purpose-built hardware.</t>
<t>These industries are now attempting to transition to packet based infrastructure for
distributing audio and video in order to reduce cost, increase routing flexibility, and
integrate with existing IT infrastructure.</t>
<t>However, there are several requirements for making a network the primary infrastructure
for audio and video which are not met by todays networks and these are our concern in this
draft.</t>
<t>The principal requirement is that pro audio and video applications become able to
establish streams that provide guaranteed (bounded) bandwidth and latency from the Layer 3
(IP) interface. Such streams can be created today within standards-based layer 2 islands
however these are not sufficient to enable effective distribution over wider areas (for
example broadcast events that span wide geographical areas).</t>
<t>Some proprietary systems have been created which enable deterministic streams at layer 3
however they are engineered networks in that they require careful configuration to
operate, often require that the system be over designed, and it is implied that all
devices on the network voluntarily play by the rules of that network. To enable these
industries to successfully transition to an interoperable multi-vendor packet-based
infrastructure requires effective open standards, and we believe that establishing
relevant IETF standards is a crucial factor.</t>
<t>It would be highly desirable if such streams could be routed over the open Internet,
however even intermediate solutions with more limited scope (such as enterprise networks)
can provide a substantial improvement over todays networks, and a solution that only
provides for the enterprise network scenario is an acceptable first step.</t>
<t>We also present more fine grained requirements of the audio and video industries such as
safety and security, redundant paths, devices with limited computing resources on the
network, and that reserved stream bandwidth is available for use by other best-effort
traffic when that stream is not currently in use. </t>
</section>
<section title="Fundamental Stream Requirements">
<t>The fundamental stream properties are guaranteed bandwidth and deterministic latency as
described in this section. Additional stream requirements are described in a subsequent
section.</t>
<section title="Guaranteed Bandwidth">
<t>Transmitting audio and video streams is unlike common file transfer activities because
guaranteed delivery cannot be achieved by re-trying the transmission; by the time the
missing or corrupt packet has been identified it is too late to execute a re-try
operation and stream playback is interrupted, which is unacceptable in for example a
live concert. In some contexts large amounts of buffering can be used to provide enough
delay to allow time for one or more retries, however this is not an effective solution
when live interaction is involved, and is not considered an acceptable general solution
for pro audio and video. (Have you ever tried speaking into a microphone through a sound
system that has an echo coming back at you? It makes it almost impossible to speak
clearly).</t>
<t>Providing a way to reserve a specific amount of bandwidth for a given stream is a key
requirement.</t>
</section>
<section title="Bounded and Consistent Latency">
<t>Latency in this context means the amount of time that passes between when a signal is
sent over a stream and when it is received, for example the amount of time delay between
when you speak into a microphone and when your voice emerges from the speaker. Any delay
longer than about 10-15 milliseconds is noticeable by most live performers, and greater
latency makes the system unusable because it prevents them from playing in time with the
other players (see slide 6 of [SRP_LATENCY]).</t>
<t>The 15ms latency bound is made even more challenging because it is often the case in
network based music production with live electric instruments that multiple stages of
signal processing are used, connected in series (i.e. from one to the other for example
from guitar through a series of digital effects processors) in which case the latencies
add, so the latencies of each individual stage must all together remain less than
15ms.</t>
<t>In some situations it is acceptable at the local location for content from the live
remote site to be delayed to allow for a statistically acceptable amount of latency in
order to reduce jitter. However, once the content begins playing in the local location
any audio artifacts caused by the local network are unacceptable, especially in those
situations where a live local performer is mixed into the feed from the remote
location.</t>
<t>In addition to being bounded to within some predictable and acceptable amount of time
(which may be 15 milliseconds or more or less depending on the application) the latency
also has to be consistent. For example when playing a film consisting of a video stream
and audio stream over a network, those two streams must be synchronized so that the
voice and the picture match up. A common tolerance for audio/video sync is one NTSC
video frame (about 33ms) and to maintain the audience perception of correct lip sync the
latency needs to be consistent within some reasonable tolerance, for example 10%.</t>
<t>A common architecture for synchronizing multiple streams that have different paths
through the network (and thus potentially different latencies) is to enable measurement
of the latency of each path, and have the data sinks (for example speakers) buffer
(delay) all packets on all but the slowest path. Each packet of each stream is assigned
a presentation time which is based on the longest required delay. This implies that all
sinks must maintain a common time reference of sufficient accuracy, which can be
achieved by any of various techniques.</t>
<t>This type of architecture is commonly implemented using a central controller that
determines path delays and arbitrates buffering delays.</t>
<section title="Optimizations">
<t>The controller might also perform optimizations based on the individual path delays,
for example sinks that are closer to the source can inform the controller that they
can accept greater latency since they will be buffering packets to match presentation
times of farther away sinks. The controller might then move a stream reservation on a
short path to a longer path in order to free up bandwidth for other critical streams
on that short path. See slides 3-5 of [SRP_LATENCY].</t>
<t>Additional optimization can be achieved in cases where sinks have differing latency
requirements, for example in a live outdoor concert the speaker sinks have stricter
latency requirements than the recording hardware sinks. See slide 7 of
[SRP_LATENCY].</t>
<t>Device cost can be reduced in a system with guaranteed reservations with a small
bounded latency due to the reduced requirements for buffering (i.e. memory) on sink
devices. For example, a theme park might broadcast a live event across the globe via a
layer 3 protocol; in such cases the size of the buffers required is proportional to
the latency bounds and jitter caused by delivery, which depends on the worst case
segment of the end-to-end network path. For example on todays open internet the
latency is typically unacceptable for audio and video streaming without many seconds
of buffering. In such scenarios a single gateway device at the local network that
receives the feed from the remote site would provide the expensive buffering required
to mask the latency and jitter issues associated with long distance delivery. Sink
devices in the local location would have no additional buffering requirements, and
thus no additional costs, beyond those required for delivery of local content. The
sink device would be receiving the identical packets as those sent by the source and
would be unaware that there were any latency or jitter issues along the path.</t>
</section>
</section>
</section>
<section title="Additional Stream Requirements">
<t>The requirements in this section are more specific yet are common to multiple audio and
video industry applications.</t>
<section title="Deterministic Time to Establish Streaming">
<t>Some audio systems installed in public environments (airports, hospitals) have unique
requirements with regards to health, safety and fire concerns. One such requirement is a
maximum of 3 seconds for a system to respond to an emergency detection and begin sending
appropriate warning signals and alarms without human intervention. For this requirement
to be met, the system must support a bounded and acceptable time from a notification
signal to specific stream establishment. For further details see [ISO7240-16].</t>
<t>Similar requirements apply when the system is restarted after a power cycle, cable
re-connection, or system reconfiguration.</t>
<t>In many cases such re-establishment of streaming state must be achieved by the peer
devices themselves, i.e. without a central controller (since such a controller may only
be present during initial network configuration).</t>
<t>Video systems introduce related requirements, for example when transitioning from one
camera feed to another. Such systems currently use purpose-built hardware to switch
feeds smoothly, however there is a current initiative in the broadcast industry to
switch to a packet-based infrastructure (see [STUDIO_IP] and the ESPN DC2 use case
described below).</t>
</section>
<section title="Use of Unused Reservations by Best-Effort Traffic">
<t>In cases where stream bandwidth is reserved but not currently used (or is
under-utilized) that bandwidth must be available to best-effort (i.e.
non-time-sensitive) traffic. For example a single stream may be nailed up (reserved) for
specific media content that needs to be presented at different times of the day,
ensuring timely delivery of that content, yet in between those times the full bandwidth
of the network can be utilized for best-effort tasks such as file transfers.</t>
<t>This also addresses a concern of IT network administrators that are considering adding
reserved bandwidth traffic to their networks that users will just reserve a ton of
bandwidth and then never un-reserve it even though they are not using it, and soon they
will have no bandwidth left.</t>
</section>
<section title="Layer 3 Interconnecting Layer 2 Islands">
<t>As an intermediate step (short of providing guaranteed bandwidth across the open
internet) it would be valuable to provide a way to connect multiple Layer 2 networks.
For example layer 2 techniques could be used to create a LAN for a single broadcast
studio, and several such studios could be interconnected via layer 3 links.</t>
</section>
<section title="Secure Transmission">
<t>Digital Rights Management (DRM) is very important to the audio and video industries.
Any time protected content is introduced into a network there are DRM concerns that must
be maintained (see [CONTENT_PROTECTION]). Many aspects of DRM are outside the scope of
network technology, however there are cases when a secure link supporting authentication
and encryption is required by content owners to carry their audio or video content when
it is outside their own secure environment (for example see [DCI]).</t>
<t>As an example, two techniques are Digital Transmission Content Protection (DTCP) and
High-Bandwidth Digital Content Protection (HDCP). HDCP content is not approved for
retransmission within any other type of DRM, while DTCP may be retransmitted under HDCP.
Therefore if the source of a stream is outside of the network and it uses HDCP
protection it is only allowed to be placed on the network with that same HDCP
protection.</t>
</section>
<section title="Redundant Paths">
<t>On-air and other live media streams must be backed up with redundant links that
seamlessly act to deliver the content when the primary link fails for any reason. In
point-to-point systems this is provided by an additional point-to-point link; the
analogous requirement in a packet-based system is to provide an alternate path through
the network such that no individual link can bring down the system. </t>
</section>
<section title="Link Aggregation">
<t>For transmitting streams that require more bandwidth than a single link in the target
network can support, link aggregation is a technique for combining (aggregating) the
bandwidth available on multiple physical links to create a single logical link of the
required bandwidth. However, if aggregation is to be used, the network controller (or
equivalent) must be able to determine the maximum latency of any path through the
aggregate link (see Bounded and Consistent Latency section above). </t>
</section>
<section title="Traffic Segregation">
<t>Sink devices may be low cost devices with limited processing power. In order to not
overwhelm the CPUs in these devices it is important to limit the amount of traffic that
these devices must process.</t>
<t>As an example, consider the use of individual seat speakers in a cinema. These speakers
are typically required to be cost reduced since the quantities in a single theater can
reach hundreds of seats. Discovery protocols alone in a one thousand seat theater can
generate enough broadcast traffic to overwhelm a low powered CPU. Thus an installation
like this will benefit greatly from some type of traffic segregation that can define
groups of seats to reduce traffic within each group. All seats in the theater must still
be able to communicate with a central controller.</t>
<t>There are many techniques that can be used to support this requirement including (but
not limited to) the following examples.</t>
<section title="Packet Forwarding Rules, VLANs and Subnets">
<t>Packet forwarding rules can be used to eliminate some extraneous streaming traffic
from reaching potentially low powered sink devices, however there may be other types
of broadcast traffic that should be eliminated using other means for example VLANs or
IP subnets.</t>
</section>
<section title="Multicast Addressing (IPv4 and IPv6)">
<t>Multicast addressing is commonly used to keep bandwidth utilization of shared links
to a minimum.</t>
<t>Because of the MAC Address forwarding nature of Layer 2 bridges it is important that
a multicast MAC address is only associated with one stream. This will prevent
reservations from forwarding packets from one stream down a path that has no
interested sinks simply because there is another stream on that same path that shares
the same multicast MAC address.</t>
<t>Since each multicast MAC Address can represent 32 different IPv4 multicast addresses
there must be a process put in place to make sure this does not occur. Requiring use
of IPv6 address can achieve this, however due to their continued prevalence, solutions
that are effective for IPv4 installations are also required.</t>
</section>
</section>
</section>
<section title="Integration of Reserved Streams into IT Networks">
<t>A commonly cited goal of moving to a packet based media infrastructure is that costs can
be reduced by using off the shelf, commodity network hardware. In addition, economy of
scale can be realized by combining media infrastructure with IT infrastructure. In keeping
with these goals, stream reservation technology should be compatible with existing
protocols, and not compromise use of the network for best effort (non-time-sensitive)
traffic.</t>
</section>
<section title="Security Considerations">
<t>Many industries that are moving from the point-to-point world to the digital network
world have little understanding of the pitfalls that they can create for themselves with
improperly implemented network infrastructure. DetNet should consider ways to provide
security against DoS attacks in solutions directed at these markets. Some considerations
are given here as examples of ways that we can help new users avoid common pitfalls. </t>
<section title="Denial of Service">
<t>One security pitfall that this author is aware of involves the use of technology that
allows a presenter to throw the content from their tablet or smart phone onto the A/V
system that is then viewed by all those in attendance. The facility introducing this
technology was quite excited to allow such modern flexibility to those who came to
speak. One thing they hadn't realized was that since no security was put in place around
this technology it left a hole in the system that allowed other attendees to "throw"
their own content onto the A/V system. </t>
</section>
<section title="Control Protocols">
<t>Professional audio systems can include amplifiers that are capable of generating
hundreds or thousands of watts of audio power which if used incorrectly can cause
hearing damage to those in the vicinity. Apart from the usual care required by the
systems operators to prevent such incidents, the network traffic that controls these
devices must be secured (as with any sensitive application traffic). In addition, it
would be desirable if the configuration protocols that are used to create the network
paths used by the professional audio traffic could be designed to protect devices that
are not meant to receive high-amplitude content from having such potentially damaging
signals routed to them.</t>
</section>
</section>
<section title="A State-of-the-Art Broadcast Installation Hits Technology Limits">
<t>ESPN recently constructed a state-of-the-art 194,000 sq ft, $125 million broadcast studio
called DC2. The DC2 network is capable of handling 46 Tbps of throughput with 60,000
simultaneous signals. Inside the facility are 1,100 miles of fiber feeding four audio
control rooms. (See details at [ESPN_DC2] ).</t>
<t>In designing DC2 they replaced as much point-to-point technology as they possibly could
with packet-based technology. They constructed seven individual studios using layer 2 LANS
(using IEEE 802.1 AVB) that were entirely effective at routing audio within the LANs, and
they were very happy with the results, however to interconnect these layer 2 LAN islands
together they ended up using dedicated links because there is no standards-based routing
solution available.</t>
<t>This is the kind of motivation we have to develop these standards because customers are
ready and able to use them.</t>
</section>
<section anchor="Acknowledgements" title="Acknowledgements">
<t>The editors would like to acknowledge the help of the following individuals and the
companies they represent:</t>
<t>Jeff Koftinoff, Meyer Sound</t>
<t>Jouni Korhonen, Associate Technical Director, Broadcom</t>
<t>Pascal Thubert, CTAO, Cisco</t>
<t>Kieran Tyrrell, Sienda New Media Technologies GmbH</t>
</section>
</section>
<section title="Utility Telecom Use Cases">
<t>(This section was derived from draft-wetterwald-detnet-utilities-reqs-02) </t>
<section title="Overview" toc="default">
<t><xref format="default" pageno="false" target="I-D.finn-detnet-problem-statement"/>
defines the characteristics of a deterministic flow as a data communication flow with a
bounded latency, extraordinarily low frame loss, and a very narrow jitter. This document
intends to define the utility requirements for deterministic networking. </t>
<t> Utility Telecom Networks </t>
<t> The business and technology trends that are sweeping the utility industry will
drastically transform the utility business from the way it has been for many decades. At
the core of many of these changes is a drive to modernize the electrical grid with an
integrated telecommunications infrastructure. However, interoperability, concerns, legacy
networks, disparate tools, and stringent security requirements all add complexity to the
grid transformation. Given the range and diversity of the requirements that should be
addressed by the next generation telecommunications infrastructure, utilities need to
adopt a holistic architectural approach to integrate the electrical grid with digital
telecommunications across the entire power delivery chain. </t>
<t> Many utilities still rely on complex environments formed of multiple
application-specific, proprietary networks. Information is siloed between operational
areas. This prevents utility operations from realizing the operational efficiency
benefits, visibility, and functional integration of operational information across grid
applications and data networks. The key to modernizing grid telecommunications is to
provide a common, adaptable, multi-service network infrastructure for the entire utility
organization. Such a network serves as the platform for current capabilities while
enabling future expansion of the network to accommodate new applications and services. </t>
<t> To meet this diverse set of requirements, both today and in the future, the next
generation utility telecommunnications network will be based on open-standards-based IP
architecture. An end-to-end IP architecture takes advantage of nearly three decades of IP
technology development, facilitating interoperability across disparate networks and
devices, as it has been already demonstrated in many mission-critical and highly secure
networks. </t>
<t>IEC (International Electrotechnical Commission) and different National Committees have
mandated a specific adhoc group (AHG8) to define the migration strategy to IPv6 for all
the IEC TC57 power automation standards. IPv6 is seen as the obvious future
telecommunications technology for the Smart Grid. The Adhoc Group has disclosed, to the
IEC coordination group, their conclusions at the end of 2014. </t>
<t> It is imperative that utilities participate in standards development bodies to influence
the development of future solutions and to benefit from shared experiences of other
utilities and vendors. </t>
</section>
<section title="Telecommunications Trends and General telecommunications Requirements">
<t>These general telecommunications requirements are over and above the specific
requirements of the use cases that have been addressed so far. These include both current
and future telecommunications related requirements that should be factored into the
network architecture and design. </t>
<section title="General Telecommunications Requirements">
<t>
<list style="symbols">
<t>IP Connectivity everywhere</t>
<t>Monitoring services everywhere and from different remote centers</t>
<t>Move services to a virtual data center</t>
<t>Unify access to applications / information from the corporate network</t>
<t>Unify services</t>
<t>Unified Communications Solutions</t>
<t>Mix of fiber and microwave technologies - obsolescence of SONET/SDH or TDM</t>
<t>Standardize grid telecommunications protocol to opened standard to ensure
interoperability</t>
<t>Reliable Telecommunications for Transmission and Distribution Substations</t>
<t>IEEE 1588 time synchronization Client / Server Capabilities</t>
<t>Integration of Multicast Design</t>
<t>QoS Requirements Mapping</t>
<t>Enable Future Network Expansion</t>
<t>Substation Network Resilience</t>
<t>Fast Convergence Design</t>
<t>Scalable Headend Design</t>
<t>Define Service Level Agreements (SLA) and Enable SLA Monitoring</t>
<t>Integration of 3G/4G Technologies and future technologies</t>
<t>Ethernet Connectivity for Station Bus Architecture</t>
<t>Ethernet Connectivity for Process Bus Architecture</t>
<t>Protection, teleprotection and PMU (Phaser Measurement Unit) on IP</t>
</list>
</t>
<section title="Migration to Packet-Switched Network">
<t>Throughout the world, utilities are increasingly planning for a future based on smart
grid applications requiring advanced telecommunications systems. Many of these
applications utilize packet connectivity for communicating information and control
signals across the utility's Wide Area Network (WAN), made possible by technologies
such as multiprotocol label switching (MPLS). The data that traverses the utility WAN
includes: <list style="symbols">
<t>Grid monitoring, control, and protection data</t>
<t>Non-control grid data (e.g. asset data for condition-based monitoring)</t>
<t>Physical safety and security data (e.g. voice and video)</t>
<t>Remote worker access to corporate applications (voice, maps, schematics,
etc.)</t>
<t>Field area network backhaul for smart metering, and distribution grid
management</t>
<t>Enterprise traffic (email, collaboration tools, business applications)</t>
</list> WANs support this wide variety of traffic to and from substations, the
transmission and distribution grid, generation sites, between control centers, and
between work locations and data centers. To maintain this rapidly expanding set of
applications, many utilities are taking steps to evolve present time-division
multiplexing (TDM) based and frame relay infrastructures to packet systems.
Packet-based networks are designed to provide greater functionalities and higher
levels of service for applications, while continuing to deliver reliability and
deterministic (real-time) traffic support. </t>
</section>
</section>
<section title="Applications, Use cases and traffic patterns" toc="default">
<t>Among the numerous applications and use cases that a utility deploys today, many rely
on high availability and deterministic behaviour of the telecommunications networks.
Protection use cases and generation control are the most demanding and can't rely on a
best effort approach. </t>
<section title="Transmission use cases" toc="default">
<t>Protection means not only the protection of the human operator but also the
protection of the electric equipments and the preservation of the stability and
frequency of the grid. If a default occurs on the transmission or the distribution of
the electricity, important damages could occured to the human operator but also to
very costly electrical equipments and perturb the grid leading to blackouts. The time
and reliability requirements are very strong to avoid dramatic impacts to the
electrical infrastructure. </t>
<section anchor="simple_list" title="Tele Protection" toc="default">
<t>The key criteria for measuring Teleprotection performance are command transmission
time, dependability and security. These criteria are defined by the IEC standard
60834 as follows: </t>
<t><list style="symbols">
<t>Transmission time (Speed): The time between the moment where state changes at
the transmitter input and the moment of the corresponding change at the receiver
output, including propagation delay. Overall operating time for a Teleprotection
system includes the time for initiating the command at the transmitting end, the
propagation delay over the network (including equipments) and the selection and
decision time at the receiving end, including any additional delay due to a
noisy environment. </t>
<t>Dependability: The ability to issue and receive valid commands in the presence
of interference and/or noise, by minimizing the probability of missing command
(PMC). Dependability targets are typically set for a specific bit error rate
(BER) level. </t>
<t>Security: The ability to prevent false tripping due to a noisy environment, by
minimizing the probability of unwanted commands (PUC). Security targets are also
set for a specific bit error rate (BER) level. </t>
</list> Additional key elements that may impact Teleprotection performance include
bandwidth rate of the Teleprotection system and its resiliency or failure recovery
capacity. Transmission time, bandwidth utilization and resiliency are directly
linked to the telecommunications equipments and the connections that are used to
transfer the commands between relays. </t>
<section title="Latency Budget Consideration" toc="default">
<t>Delay requirements for utility networks may vary depending upon a number of
parameters, such as the specific protection equipments used. Most power line
equipment can tolerate short circuits or faults for up to approximately five power
cycles before sustaining irreversible damage or affecting other segments in the
network. This translates to total fault clearance time of 100ms. As a safety
precaution, however, actual operation time of protection systems is limited to 70-
80 percent of this period, including fault recognition time, command transmission
time and line breaker switching time. Some system components, such as large
electromechanical switches, require particularly long time to operate and take up
the majority of the total clearance time, leaving only a 10ms window for the
telecommunications part of the protection scheme, independent of the distance to
travel. Given the sensitivity of the issue, new networks impose requirements that
are even more stringent: IEC standard 61850 limits the transfer time for
protection messages to 1/4 - 1/2 cycle or 4 - 8ms (for 60Hz lines) for the most
critical messages.</t>
</section>
<section title="Asymetric delay">
<t>In addition to minimal transmission delay, a differential protection
telecommunications channel must be synchronous, i.e., experiencing symmetrical
channel delay in transmit and receive paths. This requires special attention in
jitter-prone packet networks. While optimally Teleprotection systems should
support zero asymmetric delay, typical legacy relays can tolerate discrepancies of
up to 750us.</t>
<t>The main tools available for lowering delay variation below this threshold are: </t>
<t>
<list style="symbols">
<t>A jitter buffer at the multiplexers on each end of the line can be used to
offset delay variation by queuing sent and received packets. The length of the
queues must balance the need to regulate the rate of transmission with the
need to limit overall delay, as larger buffers result in increased latency.
This is the old TDM traditional way to fulfill this requirement.</t>
<t>Traffic management tools ensure that the Teleprotection signals receive the
highest transmission priority and minimize the number of jitter addition
during the path. This is one way to meet the requirement in IP networks.</t>
<t>Standard Packet-Based synchronization technologies, such as 1588-2008
Precision Time Protocol (PTP) and Synchronous Ethernet (Sync-E), can help
maintain stable networks by keeping a highly accurate clock source on the
different network devices involved.</t>
</list>
</t>
<section title="Other traffic characteristics">
<t>
<list style="symbols">
<t>Redundancy: The existence in a system of more than one means of
accomplishing a given function.</t>
<t>Recovery time : The duration of time within which a business process must
be restored after any type of disruption in order to avoid unacceptable
consequences associated with a break in business continuity.</t>
<t>performance management : In networking, a management function defined for
controlling and analyzing different parameters/metrics such as the
throughput, error rate.</t>
<t>packet loss : One or more packets of data travelling across network fail to
reach their destination.</t>
</list>
</t>
</section>
<section title="Teleprotection network requirements">
<t>The following table captures the main network requirements (this is based on
IEC 61850 standard)</t>
<texttable align="center" anchor="table1" style="full" suppress-title="false"
title="Teleprotection network requirements">
<preamble/>
<ttcol align="center">Teleprotection Requirement</ttcol>
<ttcol align="center">Attribute</ttcol>
<c>One way maximum delay</c>
<c>4-10 ms</c>
<c>Asymetric delay required</c>
<c>Yes</c>
<c>Maximum jitter</c>
<c>less than 250 us (750 us for legacy IED)</c>
<c>Topology</c>
<c>Point to point, point to Multi-point</c>
<c>Availability</c>
<c>99.9999</c>
<c>precise timing required</c>
<c>Yes</c>
<c>Recovery time on node failure</c>
<c>less than 50ms - hitless</c>
<c>performance management</c>
<c>Yes, Mandatory</c>
<c>Redundancy</c>
<c>Yes</c>
<c>Packet loss</c>
<c>0.1% to 1%</c>
<postamble/>
</texttable>
</section>
</section>
</section>
<section title="Inter-Trip Protection scheme">
<t>Inter-tripping is the controlled tripping of a circuit breaker to complete the
isolation of a circuit or piece of apparatus in concert with the tripping of other
circuit breakers. The main use of such schemes is to ensure that protection at both
ends of a faulted circuit will operate to isolate the equipment concerned.
Inter-tripping schemes use signaling to convey a trip command to remote circuit
breakers to isolate circuits.</t>
<texttable align="center" anchor="table2" style="full" suppress-title="false"
title="Inter-Trip protection network requirements">
<preamble/>
<ttcol align="center">Inter-Trip protection Requirement</ttcol>
<ttcol align="center">Attribute</ttcol>
<c>One way maximum delay</c>
<c>5 ms</c>
<c>Asymetric delay required</c>
<c>No</c>
<c>Maximum jitter</c>
<c>Not critical</c>
<c>Topology</c>
<c>Point to point, point to Multi-point</c>
<c>Bandwidth</c>
<c>64 Kbps</c>
<c>Availability</c>
<c>99.9999</c>
<c>precise timing required</c>
<c>Yes</c>
<c>Recovery time on node failure</c>
<c>less than 50ms - hitless</c>
<c>performance management</c>
<c>Yes, Mandatory</c>
<c>Redundancy</c>
<c>Yes</c>
<c>Packet loss</c>
<c>0.1%</c>
<postamble/>
</texttable>
</section>
<section title="Current Differential Protection Scheme">
<t>Current differential protection is commonly used for line protection, and is
typical for protecting parallel circuits. A main advantage for differential
protection is that, compared to overcurrent protection, it allows only the faulted
circuit to be de-energized in case of a fault. At both end of the lines, the current
is measured by the differential relays, and based on Kirchhoff's law, both relays
will trip the circuit breaker if the current going into the line does not equal the
current going out of the line. This type of protection scheme assumes some form of
communications being present between the relays at both end of the line, to allow
both relays to compare measured current values. A fault in line 1 will cause
overcurrent to be flowing in both lines, but because the current in line 2 is a
through following current, this current is measured equal at both ends of the line,
therefore the differential relays on line 2 will not trip line 2. Line 1 will be
tripped, as the relays will not measure the same currents at both ends of the line.
Line differential protection schemes assume a very low telecommunications delay
between both relays, often as low as 5ms. Moreover, as those systems are often not
time-synchronized, they also assume symmetric telecommunications paths with constant
delay, which allows comparing current measurement values taken at the exact same
time.</t>
<texttable align="center" anchor="table3" style="full" suppress-title="false"
title="Current Differential Protection requirements">
<preamble/>
<ttcol align="center">Current Differential protection Requirement</ttcol>
<ttcol align="center">Attribute</ttcol>
<c>One way maximum delay</c>
<c>5 ms</c>
<c>Asymetric delay Required</c>
<c>Yes</c>
<c>Maximum jitter</c>
<c>less than 250 us (750us for legacy IED)</c>
<c>Topology</c>
<c>Point to point, point to Multi-point</c>
<c>Bandwidth</c>
<c>64 Kbps</c>
<c>Availability</c>
<c>99.9999</c>
<c>precise timing required</c>
<c>Yes</c>
<c>Recovery time on node failure</c>
<c>less than 50ms - hitless</c>
<c>performance management</c>
<c>Yes, Mandatory</c>
<c>Redundancy</c>
<c>Yes</c>
<c>Packet loss</c>
<c>0.1%</c>
<postamble/>
</texttable>
</section>
<section title="Distance Protection Scheme">
<t>Distance (Impedance Relay) protection scheme is based on voltage and current
measurements. A fault on a circuit will generally create a sag in the voltage level.
If the ratio of voltage to current measured at the protection relay terminals, which
equates to an impedance element, falls within a set threshold the circuit breaker
will operate. The operating characteristics of this protection are based on the line
characteristics. This means that when a fault appears on the line, the impedance
setting in the relay is compared to the apparent impedance of the line from the
relay terminals to the fault. If the relay setting is determined to be below the
apparent impedance it is determined that the fault is within the zone of protection.
When the transmission line length is under a minimum length, distance protection
becomes more difficult to coordinate. In these instances the best choice of
protection is current differential protection.</t>
<texttable align="center" anchor="table4" style="full" suppress-title="false"
title="Distance Protection requirements">
<preamble/>
<ttcol align="center">Distance protection Requirement</ttcol>
<ttcol align="center">Attribute</ttcol>
<c>One way maximum delay</c>
<c>5 ms</c>
<c>Asymetric delay Required</c>
<c>No</c>
<c>Maximum jitter</c>
<c>Not critical</c>
<c>Topology</c>
<c>Point to point, point to Multi-point</c>
<c>Bandwidth</c>
<c>64 Kbps</c>
<c>Availability</c>
<c>99.9999</c>
<c>precise timing required</c>
<c>Yes</c>
<c>Recovery time on node failure</c>
<c>less than 50ms - hitless</c>
<c>performance management</c>
<c>Yes, Mandatory</c>
<c>Redundancy</c>
<c>Yes</c>
<c>Packet loss</c>
<c>0.1%</c>
<postamble/>
</texttable>
</section>
<section title="Inter-Substation Protection Signaling">
<t>This use case describes the exchange of Sampled Value and/or GOOSE (Generic Object
Oriented Substation Events) message between Intelligent Electronic Devices (IED) in
two substations for protection and tripping coordination. The two IEDs are in a
master-slave mode. </t>
<t>The Current Transformer or Voltage Transformer (CT/VT) in one substation sends the
sampled analog voltage or current value to the Merging Unit (MU) over hard wire. The
merging unit sends the time-synchronized 61850-9-2 sampled values to the slave IED.
The slave IED forwards the information to the Master IED in the other substation.
The master IED makes the determination (for example based on sampled value
differentials) to send a trip command to the originating IED. Once the slave
IED/Relay receives the GOOSE trip for breaker tripping, it opens the breaker. It
then sends a confirmation message back to the master. All data exchanges between
IEDs are either through Sampled Value and/or GOOSE messages. </t>
<texttable align="center" anchor="table5" style="full" suppress-title="false"
title="Inter-Substation Protection requirements">
<preamble/>
<ttcol align="center">Inter-Substation protection Requirement</ttcol>
<ttcol align="center">Attribute</ttcol>
<c>One way maximum delay</c>
<c>5 ms</c>
<c>Asymetric delay Required</c>
<c>No</c>
<c>Maximum jitter</c>
<c>Not critical</c>
<c>Topology</c>
<c>Point to point, point to Multi-point</c>
<c>Bandwidth</c>
<c>64 Kbps</c>
<c>Availability</c>
<c>99.9999</c>
<c>precise timing required</c>
<c>Yes</c>
<c>Recovery time on node failure</c>
<c>less than 50ms - hitless</c>
<c>performance management</c>
<c>Yes, Mandatory</c>
<c>Redundancy</c>
<c>Yes</c>
<c>Packet loss</c>
<c>1%</c>
<postamble/>
</texttable>
</section>
<section title="Intra-Substation Process Bus Communications">
<t>This use case describes the data flow from the CT/VT to the IEDs in the substation
via the merging unit (MU). The CT/VT in the substation send the sampled value
(analog voltage or current) to the Merging Unit (MU) over hard wire. The merging
unit sends the time-synchronized 61850-9-2 sampled values to the IEDs in the
substation in GOOSE message format. The GPS Master Clock can send 1PPS or IRIG-B
format to MU through serial port, or IEEE 1588 protocol via network. Process bus
communication using 61850 simplifies connectivity within the substation and removes
the requirement for multiple serial connections and removes the slow serial bus
architectures that are typically used. This also ensures increased flexibility and
increased speed with the use of multicast messaging between multiple devices. </t>
<texttable align="center" anchor="table6" style="full" suppress-title="false"
title="Intra-Substation Protection requirements">
<preamble/>
<ttcol align="center">Intra-Substation protection Requirement</ttcol>
<ttcol align="center">Attribute</ttcol>
<c>One way maximum delay</c>
<c>5 ms</c>
<c>Asymetric delay Required</c>
<c>No</c>
<c>Maximum jitter</c>
<c>Not critical</c>
<c>Topology</c>
<c>Point to point, point to Multi-point</c>
<c>Bandwidth</c>
<c>64 Kbps</c>
<c>Availability</c>
<c>99.9999</c>
<c>precise timing required</c>
<c>Yes</c>
<c>Recovery time on Node failure</c>
<c>less than 50ms - hitless</c>
<c>performance management</c>
<c>Yes, Mandatory</c>
<c>Redundancy</c>
<c>Yes - No</c>
<c>Packet loss</c>
<c>0.1%</c>
<postamble/>
</texttable>
</section>
<section title="Wide Area Monitoring and Control Systems">
<t>The application of synchrophasor measurement data from Phasor Measurement Units
(PMU) to Wide Area Monitoring and Control Systems promises to provide important new
capabilities for improving system stability. Access to PMU data enables more timely
situational awareness over larger portions of the grid than what has been possible
historically with normal SCADA (Supervisory Control and Data Acquisition) data.
Handling the volume and real-time nature of synchrophasor data presents unique
challenges for existing application architectures. Wide Area management System
(WAMS) makes it possible for the condition of the bulk power system to be observed
and understood in real-time so that protective, preventative, or corrective action
can be taken. Because of the very high sampling rate of measurements and the strict
requirement for time synchronization of the samples, WAMS has stringent
telecommunications requirements in an IP network that are captured in the following
table: </t>
<texttable align="center" anchor="table10" style="full" suppress-title="false"
title="WAMS Special Communication Requirements">
<preamble/>
<ttcol align="center">WAMS Requirement</ttcol>
<ttcol align="center">Attribute</ttcol>
<c>One way maximum delay</c>
<c>50 ms</c>
<c>Asymetric delay Required</c>
<c>No</c>
<c>Maximum jitter</c>
<c>Not critical</c>
<c>Topology</c>
<c>Point to point, point to Multi-point, Multi-point to Multi-point</c>
<c>Bandwidth</c>
<c>100 Kbps</c>
<c>Availability</c>
<c>99.9999</c>
<c>precise timing required</c>
<c>Yes</c>
<c>Recovery time on Node failure</c>
<c>less than 50ms - hitless</c>
<c>performance management</c>
<c>Yes, Mandatory</c>
<c>Redundancy</c>
<c>Yes</c>
<c>Packet loss</c>
<c>1%</c>
<postamble/>
</texttable>
</section>
<section title="IEC 61850 WAN engineering guidelines requirement classification">
<t>The IEC (International Electrotechnical Commission) has recently published a
Technical Report which offers guidelines on how to define and deploy Wide Area
Networks for the interconnections of electric substations, generation plants and
SCADA operation centers. The IEC 61850-90-12 is providing a classification of WAN
communication requirements into 4 classes. You will find herafter the table
summarizing these requirements: </t>
<texttable align="center" anchor="table11" style="full" suppress-title="false"
title="61850-90-12 Communication Requirements; Courtesy of IEC">
<preamble/>
<ttcol align="center">WAN Requirement</ttcol>
<ttcol align="center">Class WA</ttcol>
<ttcol align="center">Class WB</ttcol>
<ttcol align="center">Class WC</ttcol>
<ttcol align="center">Class WD</ttcol>
<c>Application field</c>
<c>EHV (Extra High Voltage)</c>
<c>HV (High Voltage)</c>
<c>MV (Medium Voltage)</c>
<c>General purpose</c>
<c>Latency</c>
<c>5 ms</c>
<c>10 ms</c>
<c>100 ms</c>
<c>> 100 ms</c>
<c>Jitter</c>
<c>10 us</c>
<c>100 us</c>
<c>1 ms</c>
<c>10 ms</c>
<c>Latency Asymetry</c>
<c>100 us</c>
<c>1 ms</c>
<c>10 ms</c>
<c>100 ms</c>
<c>Time Accuracy</c>
<c>1 us</c>
<c>10 us</c>
<c>100 us</c>
<c>10 to 100 ms</c>
<c>Bit Error rate</c>
<c>10-7 to 10-6</c>
<c>10-5 to 10-4</c>
<c>10-3</c>
<c> </c>
<c>Unavailability</c>
<c>10-7 to 10-6</c>
<c>10-5 to 10-4</c>
<c>10-3</c>
<c> </c>
<c>Recovery delay</c>
<c>Zero</c>
<c>50 ms</c>
<c>5 s</c>
<c>50 s</c>
<c>Cyber security</c>
<c>extremely high</c>
<c>High</c>
<c>Medium</c>
<c>Medium</c>
<postamble/>
</texttable>
</section>
</section>
<section title="Distribution use case">
<section title="Fault Location Isolation and Service Restoration (FLISR)">
<t>As the name implies, Fault Location, Isolation, and Service Restoration (FLISR)
refers to the ability to automatically locate the fault, isolate the fault, and
restore service in the distribution network. It is a self-healing feature whose
purpose is to minimize the impact of faults by serving portions of the loads on the
affected circuit by switching to other circuits. It reduces the number of customers
that experience a sustained power outage by reconfiguring distribution circuits.
This will likely be the first wide spread application of distributed intelligence in
the grid. Secondary substations can be connected to multiple primary substations.
Normally, static power switch statuses (open/closed) in the network dictate the
power flow to secondary substations. Reconfiguring the network in the event of a
fault is typically done manually on site to operate switchgear to
energize/de-energize alternate paths. Automating the operation of substation
switchgear allows the utility to have a more dynamic network where the flow of power
can be altered under fault conditions but also during times of peak load. It allows
the utility to shift peak loads around the network. Or, to be more precise, alters
the configuration of the network to move loads between different primary
substations. The FLISR capability can be enabled in two modes: </t>
<t>
<list style="symbols">
<t>Managed centrally from DMS (Distribution Management System), or </t>
<t>Executed locally through distributed control via intelligent switches and fault
sensors. </t>
</list>
</t>
<t>There are 3 distinct sub-functions that are performed: </t>
<t>1. Fault Location Identification</t>
<t>This sub-function is initiated by SCADA inputs, such as lockouts, fault
indications/location, and, also, by input from the Outage Management System (OMS),
and in the future by inputs from fault-predicting devices. It determines the
specific protective device, which has cleared the sustained fault, identifies the
de-energized sections, and estimates the probable location of the actual or the
expected fault. It distinguishes faults cleared by controllable protective devices
from those cleared by fuses, and identifies momentary outages and inrush/cold load
pick-up currents. This step is also referred to as Fault Detection Classification
and Location (FDCL). This step helps to expedite the restoration of faulted sections
through fast fault location identification and improved diagnostic information
available for crew dispatch. Also provides visualization of fault information to
design and implement a switching plan to isolate the fault.</t>
<t>2. Fault Type Determination </t>
<t>I. Indicates faults cleared by controllable protective devices by distinguishing
between:</t>
<t>a. Faults cleared by fuses</t>
<t>b. Momentary outages</t>
<t>c. Inrush/cold load current</t>
<t>II. Determines the faulted sections based on SCADA fault indications and protection
lockout signals </t>
<t>III. Increases the accuracy of the fault location estimation based on SCADA fault
current measurements and real-time fault analysis</t>
<t>3. Fault Isolation and Service Restoration </t>
<t>Once the location and type of the fault has been pinpointed, the systems will
attempt to isolate the fault and restore the non-faulted section of the network.
This can have three modes of operation:</t>
<t>I. Closed-loop mode : This is initiated by the Fault location sub-function. It
generates a switching order (i.e., sequence of switching) for the remotely
controlled switching devices to isolate the faulted section, and restore service to
the non-faulted sections. The switching order is automatically executed via SCADA. </t>
<t>II. Advisory mode : This is initiated by the Fault location sub-function. It
generates a switching order for remotely and manually controlled switching devices
to isolate the faulted section, and restore service to the non-faulted sections. The
switching order is presented to operator for approval and execution. </t>
<t>III. Study mode : the operator initiates this function. It analyzes a saved case
modified by the operator, and generates a switching order under the operating
conditions specified by the operator.</t>
<t>With the increasing volume of data that are collected through fault sensors,
utilities will use Big Data query and analysis tools to study outage information to
anticipate and prevent outages by detecting failure patterns and their correlation
with asset age, type, load profiles, time of day, weather conditions, and other
conditions to discover conditions that lead to faults and take the necessary
preventive and corrective measures. </t>
<texttable align="center" anchor="table7" style="full" suppress-title="false"
title="FLISR Communication Requirements">
<preamble/>
<ttcol align="center">FLISR Requirement</ttcol>
<ttcol align="center">Attribute</ttcol>
<c>One way maximum delay</c>
<c>80 ms</c>
<c>Asymetric delay Required</c>
<c>No</c>
<c>Maximum jitter</c>
<c>40 ms</c>
<c>Topology</c>
<c>Point to point, point to Multi-point, Multi-point to Multi-point</c>
<c>Bandwidth</c>
<c>64 Kbps</c>
<c>Availability</c>
<c>99.9999</c>
<c>precise timing required</c>
<c>Yes</c>
<c>Recovery time on Node failure</c>
<c>Depends on customer impact</c>
<c>performance management</c>
<c>Yes, Mandatory</c>
<c>Redundancy</c>
<c>Yes</c>
<c>Packet loss</c>
<c>0.1%</c>
<postamble/>
</texttable>
</section>
</section>
<section title="Generation use case" toc="default">
<section title="Frequency Control / Automatic Generation Control (AGC)">
<t>The system frequency should be maintained within a very narrow band. Deviations
from the acceptable frequency range are detected and forwarded to the Load Frequency
Control (LFC) system so that required up or down generation increase / decrease
pulses can be sent to the power plants for frequency regulation. The trend in system
frequency is a measure of mismatch between demand and generation, and is a necessary
parameter for load control in interconnected systems. </t>
<t>Automatic generation control (AGC) is a system for adjusting the power output of
generators at different power plants, in response to changes in the load. Since a
power grid requires that generation and load closely balance moment by moment,
frequent adjustments to the output of generators are necessary. The balance can be
judged by measuring the system frequency; if it is increasing, more power is being
generated than used, and all machines in the system are accelerating. If the system
frequency is decreasing, more demand is on the system than the instantaneous
generation can provide, and all generators are slowing down. </t>
<t>Where the grid has tie lines to adjacent control areas, automatic generation
control helps maintain the power interchanges over the tie lines at the scheduled
levels. The AGC takes into account various parameters including the most economical
units to adjust, the coordination of thermal, hydroelectric, and other generation
types, and even constraints related to the stability of the system and capacity of
interconnections to other power grids. </t>
<t>For the purpose of AGC we use static frequency measurements and averaging methods
are used to get a more precise measure of system frequency in steady-state
conditions.</t>
<t>During disturbances, more real-time dynamic measurements of system frequency are
taken using PMUs, especially when different areas of the system exhibit different
frequencies. But that is outside the scope of this use case.</t>
<texttable align="center" anchor="table8" style="full" suppress-title="false"
title="FCAG Communication Requirements">
<preamble/>
<ttcol align="center">FCAG (Frequency Control Automatic Generation)
Requirement</ttcol>
<ttcol align="center">Attribute</ttcol>
<c>One way maximum delay</c>
<c>500 ms</c>
<c>Asymetric delay Required</c>
<c>No</c>
<c>Maximum jitter</c>
<c>Not critical</c>
<c>Topology</c>
<c>Point to point</c>
<c>Bandwidth</c>
<c>20 Kbps</c>
<c>Availability</c>
<c>99.999</c>
<c>precise timing required</c>
<c>Yes</c>
<c>Recovery time on Node failure</c>
<c>N/A</c>
<c>performance management</c>
<c>Yes, Mandatory</c>
<c>Redundancy</c>
<c>Yes</c>
<c>Packet loss</c>
<c>1%</c>
<postamble/>
</texttable>
</section>
</section>
</section>
<section title="Specific Network topologies of Smart Grid Applications" toc="default">
<t>Utilities often have very large private telecommunications networks. It covers an
entire territory / country. The main purpose of the network, until now, has been to
support transmission network monitoring, control, and automation, remote control of
generation sites, and providing FCAPS (Fault. Configuration. Accounting. Performance.
Security) services from centralized network operation centers. </t>
<t> Going forward, one network will support operation and maintenance of electrical
networks (generation, transmission, and distribution), voice and data services for ten
of thousands of employees and for exchange with neighboring interconnections, and
administrative services. To meet those requirements, utility may deploy several physical
networks leveraging different technologies across the country: an optical network and a
microwave network for instance. Each protection and automatism system between two points
has two telecommunications circuits, one on each network. Path diversity between two
substations is key. Regardless of the event type (hurricane, ice storm, etc.), one path
shall stay available so the SPS can still operate.</t>
<t>In the optical network, signals are transmitted over more than tens of thousands of
circuits using fiber optic links, microwave and telephone cables. This network is the
nervous system of the utility's power transmission operations. The optical network
represents ten of thousands of km of cable deployed along the power lines.</t>
<t>Due to vast distances between transmission substations (for example as far as 280km
apart), the fiber signal can be amplified to reach a distance of 280 km without
attenuation.</t>
</section>
<section title="Precision Time Protocol">
<t>Some utilities do not use GPS clocks in generation substations. One of the main reasons
is that some of the generation plants are 30 to 50 meters deep under ground and the GPS
signal can be weak and unreliable. Instead, atomic clocks are used. Clocks are
synchronized amongst each other. Rubidium clocks provide clock and 1ms timestamps for
IRIG-B. Some companies plan to transition to the Precision Time Protocol (IEEE 1588),
distributing the synchronization signal over the IP/MPLS network. </t>
<t>The Precision Time Protocol (PTP) is defined in IEEE standard 1588. PTP is applicable
to distributed systems consisting of one or more nodes, communicating over a network.
Nodes are modeled as containing a real-time clock that may be used by applications
within the node for various purposes such as generating time-stamps for data or ordering
events managed by the node. The protocol provides a mechanism for synchronizing the
clocks of participating nodes to a high degree of accuracy and precision. </t>
<t>PTP operates based on the following assumptions : </t>
<t>
<list>
<t>It is assumed that the network eliminates cyclic forwarding of PTP messages within
each communication path (e.g., by using a spanning tree protocol). PTP eliminates
cyclic forwarding of PTP messages between communication paths. </t>
<t>PTP is tolerant of an occasional missed message, duplicated message, or message
that arrived out of order. However, PTP assumes that such impairments are relatively
rare. </t>
<t>PTP was designed assuming a multicast communication model. PTP also supports a
unicast communication model as long as the behavior of the protocol is preserved. </t>
<t>Like all message-based time transfer protocols, PTP time accuracy is degraded by
asymmetry in the paths taken by event messages. Asymmetry is not detectable by PTP,
however, if known, PTP corrects for asymmetry. </t>
</list>
</t>
<t>A time-stamp event is generated at the time of transmission and reception of any event
message. The time-stamp event occurs when the message's timestamp point crosses the
boundary between the node and the network. </t>
<t>IEC 61850 will recommend the use of the IEEE PTP 1588 Utility Profile (as defined in
IEC 62439-3 Annex B) which offers the support of redundant attachment of clocks to
Paralell Redundancy Protcol (PRP) and High-availability Seamless Redundancy (HSR)
networks.</t>
</section>
</section>
<section anchor="IANA" title="IANA Considerations" toc="default">
<t>This memo includes no request to IANA.</t>
</section>
<section anchor="Security" title="Security Considerations" toc="default">
<section title="Current Practices and Their Limitations" toc="default">
<t>Grid monitoring and control devices are already targets for cyber attacks and legacy
telecommunications protocols have many intrinsic network related vulnerabilities. DNP3,
Modbus, PROFIBUS/PROFINET, and other protocols are designed around a common paradigm of
request and respond. Each protocol is designed for a master device such as an HMI (Human
Machine Interface) system to send commands to subordinate slave devices to retrieve data
(reading inputs) or control (writing to outputs). Because many of these protocols lack
authentication, encryption, or other basic security measures, they are prone to
network-based attacks, allowing a malicious actor or attacker to utilize the
request-and-respond system as a mechanism for command-and-control like functionality.
Specific security concerns common to most industrial control, including utility
telecommunication protocols include the following: </t>
<t>
<list style="symbols">
<t>Network or transport errors (e.g. malformed packets or excessive latency) can cause
protocol failure.</t>
<t>Protocol commands may be available that are capable of forcing slave devices into
inoperable states, including powering-off devices, forcing them into a listen-only
state, disabling alarming.</t>
<t>Protocol commands may be available that are capable of restarting communications
and otherwise interrupting processes.</t>
<t>Protocol commands may be available that are capable of clearing, erasing, or
resetting diagnostic information such as counters and diagnostic registers.</t>
<t>Protocol commands may be available that are capable of requesting sensitive
information about the controllers, their configurations, or other need-to-know
information.</t>
<t>Most protocols are application layer protocols transported over TCP; therefore it
is easy to transport commands over non-standard ports or inject commands into
authorized traffic flows.</t>
<t>Protocol commands may be available that are capable of broadcasting messages to
many devices at once (i.e. a potential DoS).</t>
<t>Protocol commands may be available to query the device network to obtain defined
points and their values (i.e. a configuration scan).</t>
<t>Protocol commands may be available that will list all available function codes
(i.e. a function scan).</t>
<t>Bump in the wire (BITW) solutions : A hardware device is added to provide IPSec
services between two routers that are not capable of IPSec functions. This special
IPsec device will intercept then intercept outgoing datagrams, add IPSec protection
to them, and strip it off incoming datagrams. BITW can all IPSec to legacy hosts and
can retrofit non-IPSec routers to provide security benefits. The disadvantages are
complexity and cost.</t>
</list>
</t>
<t> These inherent vulnerabilities, along with increasing connectivity between IT an OT
networks, make network-based attacks very feasible. Simple injection of malicious
protocol commands provides control over the target process. Altering legitimate protocol
traffic can also alter information about a process and disrupt the legitimate controls
that are in place over that process. A man- in-the-middle attack could provide both
control over a process and misrepresentation of data back to operator consoles. </t>
</section>
<section title="Security Trends in Utility Networks" toc="default">
<t> Although advanced telecommunications networks can assist in transforming the energy
industry, playing a critical role in maintaining high levels of reliability,
performance, and manageability, they also introduce the need for an integrated security
infrastructure. Many of the technologies being deployed to support smart grid projects
such as smart meters and sensors can increase the vulnerability of the grid to attack.
Top security concerns for utilities migrating to an intelligent smart grid
telecommunications platform center on the following trends: </t>
<t>
<list style="symbols">
<t>Integration of distributed energy resources</t>
<t>Proliferation of digital devices to enable management, automation, protection, and
control</t>
<t>Regulatory mandates to comply with standards for critical infrastructure
protection</t>
<t>Migration to new systems for outage management, distribution automation,
condition-based maintenance, load forecasting, and smart metering</t>
<t>Demand for new levels of customer service and energy management</t>
</list>
</t>
<t> This development of a diverse set of networks to support the integration of
microgrids, open-access energy competition, and the use of network-controlled devices is
driving the need for a converged security infrastructure for all participants in the
smart grid, including utilities, energy service providers, large commercial and
industrial, as well as residential customers. Securing the assets of electric power
delivery systems, from the control center to the substation, to the feeders and down to
customer meters, requires an end-to-end security infrastructure that protects the myriad
of telecommunications assets used to operate, monitor, and control power flow and
measurement. Cyber security refers to all the security issues in automation and
telecommunications that affect any functions related to the operation of the electric
power systems. Specifically, it involves the concepts of:</t>
<t>
<list style="symbols">
<t>Integrity : data cannot be altered undetectably </t>
<t>Authenticity : the telecommunications parties involved must be validated as genuine </t>
<t>Authorization : only requests and commands from the authorized users can be
accepted by the system </t>
<t>Confidentiality : data must not be accessible to any unauthenticated users </t>
</list>
</t>
<t>When designing and deploying new smart grid devices and telecommunications systems,
it's imperative to understand the various impacts of these new components under a
variety of attack situations on the power grid. Consequences of a cyber attack on the
grid telecommunications network can be catastrophic. This is why security for smart grid
is not just an ad hoc feature or product, it's a complete framework integrating both
physical and Cyber security requirements and covering the entire smart grid networks
from generation to distribution. Security has therefore become one of the main
foundations of the utility telecom network architecture and must be considered at every
layer with a defense-in-depth approach. Migrating to IP based protocols is key to
address these challenges for two reasons:</t>
<t>1. IP enables a rich set of features and capabilities to enhance the security posture </t>
<t>2. IP is based on open standards, which allows interoperability between different
vendors and products, driving down the costs associated with implementing security
solutions in OT networks. </t>
<t>Securing OT (Operation technology) telecommunications over packet-switched IP networks
follow the same principles that are foundational for securing the IT infrastructure,
i.e., consideration must be given to enforcing electronic access control for both
person-to-machine and machine-to-machine communications, and providing the appropriate
levels of data privacy, device and platform integrity, and threat detection and
mitigation. </t>
</section>
</section>
<section anchor="Acknowledgements2" title="Acknowledgements" toc="default">
<t>Faramarz Maghsoodlou, Ph. D. IoT Connected Industries and Energy Practice Cisco </t>
<t>Pascal Thubert, CTAO Cisco</t>
</section>
</section>
<section title="Building Automation Systems Use Cases">
<section title="Introduction">
<t> Building Automation System (BAS) is a system that manages various equipment and sensors
in buildings (e.g., heating, cooling and ventilating) for improving residents' comfort,
reduction of energy consumption and automatic responses in case of failure and emergency.
For example, BAS measures temperature of a room by using various sensors and then controls
the HVAC (Heating, Ventilating, and air Conditioning) system automatically to maintain the
temperature level and minimize the energy consumption. </t>
<t> There are typically two layers of network in a BAS. Upper one is called management
network and the lower one is called field network. In management networks, an IP-based
communication protocol is used while in field network, non-IP based communication
protocols (a.k.a., field protocol) are mainly used.
<!-- Those field protocols must guarantee communication requirements, for instance, sensor measurement interval should be less than 50 milliseconds. -->
</t>
<t> There are many field protocols used in today's deployment in which some medium access
control and physical layers protocols are standards-based and others are proprietary
based. Therefore the BAS needs to have multiple MAC/PHY modules and interfaces to make use
of multiple field protocols based devices. This situation not only makes BAS more
expensive with large development cycle of multiple devices but also creates the issue of
vendor lock-in with multiple types of management applications. </t>
<t> The other issue with some of the existing field networks and protocols are security.
When these protocols and network were developed, it was assumed that the field networks
are isolated physically from external networks and therefore the network and protocol
security was not a concern. However, in today's world many BASes are managed remotely and
is connected to shared IP networks and it is also not uncommon that same IT infrastructure
is used be it office, home or in enterprise networks. Adding network and protocol security
to existing system is a non-trivial task. </t>
<t> This document first describes the BAS functionalities, its architecture and current
deployment models. Then we discuss the use cases and field network requirements that need
to be satisfied by deterministic networking. </t>
</section>
<section title="BAS Functionality">
<t>
<!-- summary of BAS functionality --> Building Automation System (BAS) is a system that
manages various devices in buildings automatically. BAS primarily performs the following
functions: <list style="symbols">
<t> Measures states of devices in a regular interval. For example, temperature or
humidity or illuminance of rooms, on/off state of room lights, open/close state of
doors, FAN speed, valve, running mode of HVAC, and its power consumption. </t>
<t> Stores the measured data into a database (Note: The database keeps the data for
several years). </t>
<t> Provides the measured data for BAS operators for visualization. </t>
<t> Generates alarms for abnormal state of devices (e.g., calling operator's cellular
phone, sending an e-mail to operators and so on). </t>
<t>Controls devices on demand.</t>
<t>Controls devices with a pre-defined operation schedule (e.g., turn off room lights at
10:00 PM).</t>
</list>
</t>
</section>
<section title="BAS Architecture">
<t> A typical BAS architecture is described below in <xref target="localbas"/>. There are
several elements in a BAS. </t>
<figure title="BAS architecture" anchor="localbas">
<artwork align="center">
+----------------------------+
| |
| BMS HMI |
| | | |
| +----------------------+ |
| | Management Network | |
| +----------------------+ |
| | | |
| LC LC |
| | | |
| +----------------------+ |
| | Field Network | |
| +----------------------+ |
| | | | | |
| Dev Dev Dev Dev |
| |
+----------------------------+
BMS := Building Management Server
HMI := Human Machine Interface
LC := Local Controller
</artwork>
</figure>
<t>
<!-- about HMI --> Human Machine Interface (HMI): It is commonly a computing platform
(e.g., desktop PC) used by operators. Operators perform the following operations through
HMI. <list style="symbols">
<t> Monitoring devices: HMI displays measured device states. For example, latest device
states, a history chart of states, a popup window with an alert message. Typically,
the measured device states are stored in BMS (Building Management Server). </t>
<t> Controlling devices: HMI provides ability to control the devices. For example, turn
on a room light, set a target temperature to HVAC. Several parameters (a target
device, a control value, etc.), can be set by the operators which then HMI sends to a
LC (Local Controller) via the management network. </t>
<t> Configuring an operational schedule: HMI provides scheduling capability through
which operational schedule is defined. For example, schedule includes 1) a time to
control, 2) a target device to control, and 3) a control value. A specific operational
example could be turn off all room lights in the building at 10:00 PM. This schedule
is typically stored in BMS. </t>
</list>
</t>
<t>
<!-- about BMS --> Building Management Server (BMS) collects device states from LCs (Local
Controllers) and stores it into a database. According to its configuration, BMS executes
the following operation automatically. <list style="symbols">
<t> BMS collects device states from LCs in a regular interval and then stores the
information into a database. </t>
<t> BMS sends control values to LCs according to a pre-configured schedule. </t>
<t> BMS sends an alarm signal to operators if it detects abnormal devices states. For
example, turning on a red lamp, calling operators' cellular phone, sending an e-mail
to operators. </t>
</list>
</t>
<t>
<!-- LC --> BMS and HMI communicate with Local Controllers (LCs) via IP-based
communication protocol standardized by <xref target="bacnetip">BACnet/IP</xref>, <xref
target="knx">KNX/IP</xref>. These protocols are commonly called as management protocols.
LCs measure device states and provide the information to BMS or HMI. These devices may
include HVAC, FAN, doors, valves, lights, sensors (e.g., temperature, humidity, and
illuminance). LC can also set control values to the devices. LC sometimes has additional
functions, for example, sending a device state to BMS or HMI if the device state exceeds a
certain threshold value, feedback control to a device to keep the device state at a
certain state. Typical example of LC is a PLC (Programmable Logic Controller).
<!--
Typically, single IP-based communication protocol is used in the management network.
Hereafter we call protocols used in the management network as "management protocol".
-->
</t>
<t> Each LC is connected with a different field network and communicates with several tens
or hundreds of devices via the field network. Today there are many field protocols used in
the field network. Based on the type of field protocol used, LC interfaces and its
hardware/software could be different. Field protocols are currently non-IP based in which
some of them are standards-based (e.g., <xref target="lontalk">LonTalk</xref>, <xref
target="modbus">Modbus</xref>, <xref target="profibus">Profibus</xref>, <xref
target="flnet">FL-net</xref>,) and others are proprietary. </t>
<!--
<t>
LCs measure device states and provide it to BMS or HMI.
There are several kinds of devices in buildings, for example, HVAC, FAN, doors, valves, lights, sensors (temperature, humidity, illuminance, etc.).
LC also sets control values received from BMS or HMI to devices.
LC sometimes has additional functions, for example, sending a device state to BMS or HMI immediately if the device state beyond a certain threshold, feedback control to a device to keep the state of the device at a certain state.
Programmable Logic Controller (PLC) is a type of LC.
</t>
<t>
Each LC is connected with a different field network and communicates with several tens or hundred devices via the field network.
Field protocols used in field networks may be different.
Some of field protocols are non-IP-based protocol.
<xref target="lontalk">LonTalk</xref>, <xref target="modbus">Modbus</xref>, <xref target="flnet">FL-net</xref>, <xref target="profibus">Profibus</xref>, are examples of standardized field protocols, but there are some proprietary field protocols.
</t>
-->
<!--
<section title="Remote BAS">
<t>
<figure title="Remote BAS architecture" anchor="remotebas">
<artwork><![CDATA[
]]></artwork>
</figure>
</t>
<t>
For small buildings, sometimes BAS functionality are provided from a remote data center or cloud environment.
We call this type BAS as "remote BAS".
</t>
<t>
<xref target="remotebas" /> shows remote BAS architecture.
MS and HMI are located at far from a building, for example, a data center, cloud environment.
Their functions are same as that of the case of local BAS.
However, a communication protocol of the remote network is sometimes different.
For example, BACnet/WS, IEEE1888, is used in the remote network.
</t>
<t>
Gateway (GW) converts a remote network protocol and a management network protocol.
If the same protocol (BACnet/IP, Modbus TCP, etc.) is used in both networks, the GW does not need to converts protocols.
</t>
</section>
-->
</section>
<section title="Deployment Model">
<t> An example BAS system deployment model for medium and large buildings is depicted in
<xref target="deploy-localbas"/> below. In this case the physical layout of the entire
system spans across multiple floors in which there is normally a monitoring room where the
BAS management entities are located. Each floor will have one or more LCs depending upon
the number of devices connected to the field network. </t>
<figure title="Deployment model for Medium/Large Buildings" anchor="deploy-localbas">
<artwork align="center">
+--------------------------------------------------+
| Floor 3 |
| +----LC~~~~+~~~~~+~~~~~+ |
| | | | | |
| | Dev Dev Dev |
| | |
|--- | ------------------------------------------|
| | Floor 2 |
| +----LC~~~~+~~~~~+~~~~~+ Field Network |
| | | | | |
| | Dev Dev Dev |
| | |
|--- | ------------------------------------------|
| | Floor 1 |
| +----LC~~~~+~~~~~+~~~~~+ +-----------------|
| | | | | | Monitoring Room |
| | Dev Dev Dev | |
| | | BMS HMI |
| | Management Network | | | |
| +--------------------------------+-----+ |
| | |
+--------------------------------------------------+
</artwork>
</figure>
<t> Each LC is then connected to the monitoring room via the management network. In this
scenario, the management functions are performed locally and reside within the building.
In most cases, fast Ethernet (e.g. 100BASE-TX) is used for the management network. In the
field network, variety of physical interfaces such as RS232C, and RS485 are used. Since
management network is non-real time, Ethernet without quality of service is sufficient for
today's deployment. However, the requirements are different for field networks when they
are replaced by either Ethernet or any wireless technologies supporting real time
requirements (Section 3.4). </t>
<t>
<xref target="deploy-remotebas"/> depicts a deployment model in which the management can
be hosted remotely. This deployment is becoming popular for small office and residential
buildings whereby having a standalone monitoring system is not a cost effective solution.
In such scenario, multiple buildings are managed by a remote management monitoring system. </t>
<figure title="Deployment model for Small Buildings" anchor="deploy-remotebas">
<artwork align="center">
+---------------+
| Remote Center |
| |
| BMS HMI |
+------------------------------------+ | | | |
| Floor 2 | | +---+---+ |
| +----LC~~~~+~~~~~+ Field Network| | | |
| | | | | | Router |
| | Dev Dev | +-------|-------+
| | | |
|--- | ------------------------------| |
| | Floor 1 | |
| +----LC~~~~+~~~~~+ | |
| | | | | |
| | Dev Dev | |
| | | |
| | Management Network | WAN |
| +------------------------Router-------------+
| |
+------------------------------------+
</artwork>
</figure>
<t> In either case, interoperability today is only limited to the management network and its
protocols. In existing deployment, there are limited interoperability opportunity in the
field network due to its nature of non-IP-based design and requirements. </t>
</section>
<section title="Use cases and Field Network Requirements">
<!-- explain requirements for each function -->
<t> In this section, we describe several use cases and corresponding network requirements. </t>
<section title="Environmental Monitoring">
<t> In this use case, LCs measure environmental data (e.g. temperatures, humidity,
illuminance, CO2, etc.) from several sensor devices at each measurement interval. LCs
keep latest value of each sensor. BMS sends data requests to LCs to collect the latest
values, then stores the collected values into a database. Operators check the latest
environmental data that are displayed by the HMI. BMS also checks the collected data
automatically to notify the operators if a room condition was going to bad (e.g., too
hot or cold). The following table lists the field network requirements in which the
number of devices in a typical building will be ~100s per LC. </t>
<texttable title="Field Network Requirements for Environmental Monitoring"
anchor="reqs-temp-mon">
<ttcol>Metric</ttcol>
<ttcol>Requirement</ttcol>
<!-- <c>number of devices</c><c>~ several hundreds per LC</c> -->
<c>Measurement interval</c>
<c>100 msec</c>
<c/>
<c/>
<c>Availability</c>
<c>99.999 %</c>
</texttable>
<t> There is a case that BMS sends data requests at each 1 second in order to draw a
historical chart of 1 second granularity. Therefore 100 msec measurement interval is
sufficient for this use case, because typically 10 times granularity (compared with the
interval of data requests) is considered enough accuracy in this use case. A LC needs to
measure values of all sensors connected with itself at each measurement interval. Each
communication delay in this scenario is not so critical. The important requirement is
completing measurements of all sensor values in the specified measurement interval. The
availability in this use case is very high (Three 9s).
<!--
If LC has a function to store multiple values with timestamps, 1 second measurement interval is sufficient for this use case.
-->
</t>
<!--
<t>
There are several measurement intervals, for example, 1 second, 10 seconds, 1 minute, 10 minutes, 30 minutes, 1 hour.
Operators can configure the measurement interval for each device.
For most of BAS, the minimum measurement interval is 1 second.
Therefore several hundred millisecond interval is required in this use case.
It means that a LC needs to measure data from all sensors connected with itself at each measurement interval.
</t>
-->
<!--
<t>
Communication delay of field networks is not so important because there are no real-time requirements in this use case.
</t>
-->
</section>
<section title="Fire Detection">
<t> In the case of fire detection, HMI needs to show a popup window with an alert message
within a few seconds after an abnormal state is detected. BMS needs to do some
operations if it detects fire. For example, stopping a HVAC, closing fire shutters, and
turning on fire sprinklers. The following table describes requirements in which the
number of devices in a typical building will be ~10s per LC. </t>
<texttable title="Field Network Requirements for Fire Detection" anchor="reqs-fire-alarm">
<ttcol>Metric</ttcol>
<ttcol>Requirement</ttcol>
<!-- <c>number of devices</c><c>several tens per LC</c> -->
<c>Measurement interval</c>
<c>10s of msec</c>
<c/>
<c/>
<c>Communication delay</c>
<c>< 10s of msec</c>
<c/>
<c/>
<c>Availability</c>
<c>99.9999 %</c>
</texttable>
<t> In order to perform the above operation within a few seconds (1 or 2 seconds) after
detecting fire, LCs should measure sensor values at a regular interval of less than 10s
of msec. If a LC detects an abnormal sensor value, it sends an alarm information to BMS
and HMI immediately. BMS then controls HVAC or fire shutters or fire sprinklers. HMI
then displays a pop up window and generates the alert message. Since the management
network does not operate in real time, and software run on BMS or HMI requires 100s of
ms, the communication delay should be less than ~10s of msec. The availability in this
use case is very high (Four 9s). </t>
</section>
<section title="Feedback Control">
<t> Feedback control is used to keep a device state at a certain value. For example,
keeping a room temperature at 27 degree Celsius, keeping a water flow rate at 100 L/m
and so on. The target device state is normally pre-defined in LCs or provided from BMS
or from HMI. </t>
<t> In feedback control procedure, a LC repeats the following actions at a regular
interval (feedback interval). <list style="numbers">
<t>The LC measures device states of the target device.</t>
<t>The LC calculates a control value by considering the measured device state.</t>
<t>The LC sends the control value to the target device.</t>
</list> The feedback interval highly depends on the characteristics of the device and a
target quality of control value. While several tens of milliseconds feedback interval is
sufficient to control a valve that regulates a water flow, controlling DC motors
requires several milliseconds interval. The following table describes the field network
requirements in which the number of devices in a typical building will be ~10s per LC. </t>
<texttable title="Field Network Requirements for Feedback Control"
anchor="reqs-fb-control">
<ttcol>Metric</ttcol>
<ttcol>Requirement</ttcol>
<c>Feedback interval</c>
<c>~10ms - 100ms</c>
<c/>
<c/>
<c>Communication delay</c>
<c>< 10s of msec</c>
<c/>
<c/>
<c>Communication jitter</c>
<c>< 1 msec</c>
<c/>
<c/>
<c>Availability</c>
<c>99.9999 %</c>
</texttable>
<t> Small communication delay and jitter are required in this use case in order to provide
high quality of feedback control. This is currently offered in production environment
with hgh availability (Four 9s).
<!--
There are a lot of feedback control research that assume large communication delay and jitter.
Some of them have achieved high quality of feedback control over the internet.
However, small delay and jitter are expected in most of real production environments.
-->
</t>
</section>
</section>
<!--
<section title="Issues to be Addressed">
<t>
There are many protocols in the field network.
Some of them are standardized but some of them are proprietary.
Some of them uses different MAC/PHY layer specifications.
This situation leads vendors to develop variety of products (e.g. LCs and devices).
One of those products is compliant with a part of field protocols, and another one is compliant with another field protocol.
It would causes low interoperability, vendor lock in, high development cost for products, finally result in expensive BAS.
</t>
<t>
Some field network protocols do not have security mechanism.
It was maybe not an issue when BAS was completely isolated with external networks, e.g. the internet.
However situation have changed.
Recently, several security incidents were happened in industrial systems.
</t>
<t>
We needs an open standardized IP-based protocol that can satisfy requirements of field networks.
It would address the issues about low interoperability and high development cost.
Using IP is important to address security issues because there are a lot of security technologies like <xref target="RFC2865">RADIUS</xref> that assume IP.
</t>
</section>
-->
<section title="Security Considerations">
<t> Both network and physical security of BAS are important. While physical security is
present in today's deployment, adequate network security and access control are either not
implemented or configured properly. This was sufficient in networks while they are
isolated and not connected to the IT or other infrastructure networks but when IT and OT
(Operational Technology) are connected in the same infrastructure network, network
security is essential. The management network being an IP-based network does have the
protocols and knobs to enable the network security but in many cases BAS for example, does
not use device authentication or encryption for data in transit. On the contrary, many of
today's field networks do not provide any security at all. Following are the high level
security requirements that the network should provide: <list style="symbols">
<t> Authentication between management and field devices (both local and remote) </t>
<t> Integrity and data origin authentication of communication data between field and
management devices </t>
<t> Confidentiality of data when communicated to a remote device </t>
<t> Availability of network data for normal and disaster scenario </t>
</list>
</t>
</section>
</section>
<section title="Wireless for Industrial Use Cases">
<t>(This section was derived from draft-thubert-6tisch-4detnet-01) </t>
<section title="Introduction">
<t> The emergence of wireless technology has enabled a variety of new devices to get
interconnected, at a very low marginal cost per device, at any distance ranging from Near
Field to interplanetary, and in circumstances where wiring may not be practical, for
instance on fast-moving or rotating devices. </t>
<t> At the same time, a new breed of Time Sensitive Networks is being developed to enable
traffic that is highly sensitive to jitter, quite sensitive to latency, and with a high
degree of operational criticality so that loss should be minimized at all times. Such
traffic is not limited to professional Audio/ Video networks, but is also found in command
and control operations such as industrial automation and vehicular sensors and actuators. </t>
<t> At IEEE802.1, the <xref target="IEEE802.1TSNTG">Audio/Video Task Group </xref> Time
Sensitive Networking (TSN) to address Deterministic Ethernet. The Medium access Control
(MAC) of IEEE802.15.4 <xref target="IEEE802154"/> has evolved with the new <xref
target="RFC7554"> TimeSlotted Channel Hopping (TSCH)</xref> mode for deterministic
industrial-type applications. TSCH was introduced with the IEEE802.15.4e <xref
target="IEEE802154e"/> amendment and will be wrapped up in the next revision of the
IEEE802.15.4 standard. For all practical purpose, this document is expected to be
insensitive to the future versions of the IEEE802.15.4 standard, which is thus referenced
undated. </t>
<t> Though at a different time scale, both TSN and TSCH standards provide Deterministic
capabilities to the point that a packet that pertains to a certain flow crosses the
network from node to node following a very precise schedule, as a train that leaves
intermediate stations at precise times along its path. With TSCH, time is formatted into
timeSlots, and an individual cell is allocated to unicast or broadcast communication at
the MAC level. The time-slotted operation reduces collisions, saves energy, and enables to
more closely engineer the network for deterministic properties. The channel hopping aspect
is a simple and efficient technique to combat multi-path fading and co-channel
interferences (for example by Wi-Fi emitters). </t>
<t> The <xref target="I-D.ietf-6tisch-architecture"> 6TiSCH Architecture </xref> defines a
remote monitoring and scheduling management of a TSCH network by a Path Computation
Element (PCE), which cooperates with an abstract Network Management Entity (NME) to manage
timeSlots and device resources in a manner that minimizes the interaction with and the
load placed on the constrained devices. </t>
<t> This Architecture applies the concepts of Deterministic Networking on a TSCH network to
enable the switching of timeSlots in a G-MPLS manner. This document details the
dependencies that 6TiSCH has on <xref target="PCE">PCE</xref> and <xref
target="I-D.finn-detnet-architecture">DetNet</xref> to provide the necessary
capabilities that may be specific to such networks. In turn, DetNet is expected to
integrate and maintain consistency with the work that has taken place and is continuing at
IEEE802.1TSN and AVnu. </t>
</section>
<section title="Terminology">
<t> Readers are expected to be familiar with all the terms and concepts that are discussed
in <xref target="I-D.ietf-ipv6-multilink-subnets"> "Multi-link Subnet Support in
IPv6"</xref>. </t>
<t> The draft uses terminology defined or referenced in <xref
target="I-D.ietf-6tisch-terminology"/> and <xref
target="I-D.ietf-roll-rpl-industrial-applicability"/>. </t>
<t> The draft also conforms to the terms and models described in <xref target="RFC3444"/>
and uses the vocabulary and the concepts defined in <xref target="RFC4291"/> for the IPv6
Architecture. </t>
</section>
<section title="6TiSCH Overview">
<t> The scope of the present work is a subnet that, in its basic configuration, is made of a
<xref target="RFC7554">TSCH</xref> MAC Low Power Lossy Network (LLN). </t>
<t>
<figure anchor="fig1" title="Basic Configuration of a 6TiSCH Network">
<artwork><![CDATA[
---+-------- ............ ------------
| External Network |
| +-----+
+-----+ | NME |
| | LLN Border | |
| | router +-----+
+-----+
o o o
o o o o
o o LLN o o o
o o o o
o
]]></artwork>
</figure>
</t>
<t> In the extended configuration, a Backbone Router (6BBR) federates multiple 6TiSCH in a
single subnet over a backbone. 6TiSCH 6BBRs synchronize with one another over the
backbone, so as to ensure that the multiple LLNs that form the IPv6 subnet stay tightly
synchronized. </t>
<t>
<figure anchor="fig2" title="Extended Configuration of a 6TiSCH Network">
<artwork><![CDATA[
---+-------- ............ ------------
| External Network |
| +-----+
| +-----+ | NME |
+-----+ | +-----+ | |
| | Router | | PCE | +-----+
| | +--| |
+-----+ +-----+
| |
| Subnet Backbone |
+--------------------+------------------+
| | |
+-----+ +-----+ +-----+
| | Backbone | | Backbone | | Backbone
o | | router | | router | | router
+-----+ +-----+ +-----+
o o o o o
o o o o o o o o o o o
o o o LLN o o o o
o o o o o o o o o o o o
]]></artwork>
</figure>
</t>
<t> If the Backbone is Deterministic, then the Backbone Router ensures that the end-to-end
deterministic behavior is maintained between the LLN and the backbone. This SHOULD be done
in conformance to the <xref target="I-D.finn-detnet-architecture">DetNet
Architecture</xref> which studies Layer-3 aspects of Deterministic Networks, and covers
networks that span multiple Layer-2 domains. One particular requirement is that the PCE
MUST be able to compute a deterministic path and to end across the TSCH network and an
IEEE802.1 TSN Ethernet backbone, and DetNet MUST enable end-to-end deterministic
forwarding. </t>
<t> 6TiSCH defines the concept of a Track, which is a complex form of a uni-directional
Circuit (<xref target="I-D.ietf-6tisch-terminology"/>). As opposed to a simple circuit
that is a sequence of nodes and links, a Track is shaped as a directed acyclic graph
towards a destination to support multi-path forwarding and route around failures. A Track
may also branch off and rejoin, for the purpose of the so-called Packet Replication and
Elimination (PRE), over non congruent branches. PRE may be used to complement layer-2
Automatic Repeat reQuest (ARQ) to meet industrial expectations in Packet Delivery Ratio
(PDR), in particular when the Track extends beyond the 6TiSCH network. </t>
<t>
<figure anchor="fig3" title="End-to-End deterministic Track">
<artwork><![CDATA[
+-----+
| IoT |
| G/W |
+-----+
^ <---- Elimination
| |
Track branch | |
+-------+ +--------+ Subnet Backbone
| |
+--|--+ +--|--+
| | | Backbone | | | Backbone
o | | | router | | | router
+--/--+ +--|--+
o / o o---o----/ o
o o---o--/ o o o o o
o \ / o o LLN o
o v <---- Replication
o
]]></artwork>
</figure>
</t>
<t>In the example above, a Track is laid out from a field device in a 6TiSCH network to an
IoT gateway that is located on a IEEE802.1 TSN backbone. </t>
<t> The Replication function in the field device sends a copy of each packet over two
different branches, and the PCE schedules each hop of both branches so that the two copies
arrive in due time at the gateway. In case of a loss on one branch, hopefully the other
copy of the packet still makes it in due time. If two copies make it to the IoT gateway,
the Elimination function in the gateway ignores the extra packet and presents only one
copy to upper layers. </t>
<t> At each 6TiSCH hop along the Track, the PCE may schedule more than one timeSlot for a
packet, so as to support Layer-2 retries (ARQ). It is also possible that the field device
only uses the second branch if sending over the first branch fails. </t>
<t> In current deployments, a TSCH Track does not necessarily support PRE but is
systematically multi-path. This means that a Track is scheduled so as to ensure that each
hop has at least two forwarding solutions, and the forwarding decision is to try the
preferred one and use the other in case of Layer-2 transmission failure as detected by
ARQ. </t>
<section title="TSCH and 6top">
<t> 6top is a logical link control sitting between the IP layer and the TSCH MAC layer,
which provides the link abstraction that is required for IP operations. The 6top
operations are specified in <xref target="I-D.wang-6tisch-6top-sublayer"/>. </t>
<t> The 6top data model and management interfaces are further discussed in <xref
target="I-D.ietf-6tisch-6top-interface"/> and <xref target="I-D.ietf-6tisch-coap"/>. </t>
<t> The architecture defines "soft" cells and "hard" cells. "Hard" cells are owned and
managed by an separate scheduling entity (e.g. a PCE) that specifies the
slotOffset/channelOffset of the cells to be added/moved/deleted, in which case 6top can
only act as instructed, and may not move hard cells in the TSCH schedule on its own. </t>
</section>
<section anchor="slotFrames" title="SlotFrames and Priorities">
<t>A slotFrame is the base object that the PCE needs to manipulate to program a schedule
into an LLN node. Elaboration on that concept can be found in section "SlotFrames and
Priorities" of the 6TiSCH architecture <xref target="I-D.ietf-6tisch-architecture"/>.
The architecture also details how the schedule is constructed and how transmission
resources called cells can be allocated to particular transmissions so as to avoid
collisions. </t>
</section>
<section anchor="schd" title="Schedule Management by a PCE">
<t> 6TiSCH supports a mixed model of centralized routes and distributed routes.
Centralized routes can for example be computed by a entity such as a PCE. Distributed
routes are computed by RPL. </t>
<t> Both methods may inject routes in the Routing Tables of the 6TiSCH routers. In either
case, each route is associated with a 6TiSCH topology that can be a RPL Instance
topology or a track. The 6TiSCH topology is indexed by a Instance ID, in a format that
reuses the RPLInstanceID as defined in <xref target="RFC6550">RPL</xref>. </t>
<t> Both RPL and PCE rely on shared sources such as policies to define Global and Local
RPLInstanceIDs that can be used by either method. It is possible for centralized and
distributed routing to share a same topology. Generally they will operate in different
slotFrames, and centralized routes will be used for scheduled traffic and will have
precedence over distributed routes in case of conflict between the slotFrames. </t>
<t> Section "Schedule Management Mechanisms" of the 6TiSCH architecture describes 4
paradigms to manage the TSCH schedule of the LLN nodes: Static Scheduling,
neighbor-to-neighbor Scheduling, remote monitoring and scheduling management, and
Hop-by-hop scheduling. The Track operation for DetNet corresponds to a remote monitoring
and scheduling management by a PCE. </t>
<t> The 6top interface document <xref target="I-D.ietf-6tisch-6top-interface"/> specifies
the generic data model that can be used to monitor and manage resources of the 6top
sublayer. Abstract methods are suggested for use by a management entity in the device.
The data model also enables remote control operations on the 6top sublayer. </t>
<t>
<xref target="I-D.ietf-6tisch-coap"/> defines an mapping of the 6top set of commands,
which is described in <xref target="I-D.ietf-6tisch-6top-interface"/>, to CoAP
resources. This allows an entity to interact with the 6top layer of a node that is
multiple hops away in a RESTful fashion. </t>
<t>
<xref target="I-D.ietf-6tisch-coap"/> also defines a basic set CoAP resources and
associated RESTful access methods (GET/PUT/POST/DELETE). The payload (body) of the CoAP
messages is encoded using the CBOR format. The PCE commands are expected to be issued
directly as CoAP requests or to be mapped back and forth into CoAP by a gateway function
at the edge of the 6TiSCH network. For instance, it is possible that a mapping entity on
the backbone transforms a non-CoAP protocol such as PCEP into the RESTful interfaces
that the 6TiSCH devices support. This architecture will be refined to comply with <xref
target="I-D.finn-detnet-architecture">DetNet</xref> when the work is formalized. </t>
</section>
<section anchor="fwd" title="Track Forwarding">
<t> By forwarding, this specification means the per-packet operation that allows to
deliver a packet to a next hop or an upper layer in this node. Forwarding is based on
pre-existing state that was installed as a result of the routing computation of a Track
by a PCE. The 6TiSCH architecture supports three different forwarding model, G-MPLS
Track Forwarding (TF), 6LoWPAN Fragment Forwarding (FF) and IPv6 Forwarding (6F) which
is the classical IP operation. The DetNet case relates to the Track Forwarding operation
under the control of a PCE. </t>
<t> A Track is a unidirectional path between a source and a destination. In a Track cell,
the normal operation of IEEE802.15.4 Automatic Repeat-reQuest (ARQ) usually happens,
though the acknowledgment may be omitted in some cases, for instance if there is no
scheduled cell for a retry. </t>
<t> Track Forwarding is the simplest and fastest. A bundle of cells set to receive
(RX-cells) is uniquely paired to a bundle of cells that are set to transmit (TX-cells),
representing a layer-2 forwarding state that can be used regardless of the network layer
protocol. This model can effectively be seen as a Generalized Multi-protocol Label
Switching (G-MPLS) operation in that the information used to switch a frame is not an
explicit label, but rather related to other properties of the way the packet was
received, a particular cell in the case of 6TiSCH. As a result, as long as the TSCH MAC
(and Layer-2 security) accepts a frame, that frame can be switched regardless of the
protocol, whether this is an IPv6 packet, a 6LoWPAN fragment, or a frame from an
alternate protocol such as WirelessHART or ISA100.11a. </t>
<t> A data frame that is forwarded along a Track normally has a destination MAC address
that is set to broadcast - or a multicast address depending on MAC support. This way,
the MAC layer in the intermediate nodes accepts the incoming frame and 6top switches it
without incurring a change in the MAC header. In the case of IEEE802.15.4, this means
effectively broadcast, so that along the Track the short address for the destination of
the frame is set to 0xFFFF. </t>
<t> A Track is thus formed end-to-end as a succession of paired bundles, a receive bundle
from the previous hop and a transmit bundle to the next hop along the Track, and a cell
in such a bundle belongs to at most one Track. For a given iteration of the device
schedule, the effective channel of the cell is obtained by adding a pseudo-random number
to the channelOffset of the cell, which results in a rotation of the frequency that used
for transmission. The bundles may be computed so as to accommodate both variable rates
and retransmissions, so they might not be fully used at a given iteration of the
schedule. The 6TiSCH architecture provides additional means to avoid waste of cells as
well as overflows in the transmit bundle, as follows: </t>
<t> In one hand, a TX-cell that is not needed for the current iteration may be reused
opportunistically on a per-hop basis for routed packets. When all of the frame that were
received for a given Track are effectively transmitted, any available TX-cell for that
Track can be reused for upper layer traffic for which the next-hop router matches the
next hop along the Track. In that case, the cell that is being used is effectively a
TX-cell from the Track, but the short address for the destination is that of the
next-hop router. It results that a frame that is received in a RX-cell of a Track with a
destination MAC address set to this node as opposed to broadcast must be extracted from
the Track and delivered to the upper layer (a frame with an unrecognized MAC address is
dropped at the lower MAC layer and thus is not received at the 6top sublayer). </t>
<t>On the other hand, it might happen that there are not enough TX-cells in the transmit
bundle to accommodate the Track traffic, for instance if more retransmissions are needed
than provisioned. In that case, the frame can be placed for transmission in the bundle
that is used for layer-3 traffic towards the next hop along the track as long as it can
be routed by the upper layer, that is, typically, if the frame transports an IPv6
packet. The MAC address should be set to the next-hop MAC address to avoid confusion. It
results that a frame that is received over a layer-3 bundle may be in fact associated to
a Track. In a classical IP link such as an Ethernet, off-track traffic is typically in
excess over reservation to be routed along the non-reserved path based on its QoS
setting. But with 6TiSCH, since the use of the layer-3 bundle may be due to transmission
failures, it makes sense for the receiver to recognize a frame that should be
re-tracked, and to place it back on the appropriate bundle if possible. A frame should
be re-tracked if the Per-Hop-Behavior group indicated in the Differentiated Services
Field in the IPv6 header is set to Deterministic Forwarding, as discussed in <xref
target="pmh"/>. A frame is re-tracked by scheduling it for transmission over the
transmit bundle associated to the Track, with the destination MAC address set to
broadcast. </t>
<t> There are 2 modes for a Track, transport mode and tunnel mode. </t>
<section title="Transport Mode">
<t> In transport mode, the Protocol Data Unit (PDU) is associated with flow-dependant
meta-data that refers uniquely to the Track, so the 6top sublayer can place the frame
in the appropriate cell without ambiguity. In the case of IPv6 traffic, this flow
identification is transported in the Flow Label of the IPv6 header. Associated with
the source IPv6 address, the Flow Label forms a globally unique identifier for that
particular Track that is validated at egress before restoring the destination MAC
address (DMAC) and punting to the upper layer. </t>
<t>
<figure title="Track Forwarding, Transport Mode">
<artwork><![CDATA[
| ^
+--------------+ | |
| IPv6 | | |
+--------------+ | |
| 6LoWPAN HC | | |
+--------------+ ingress egress
| 6top | sets +----+ +----+ restores
+--------------+ dmac to | | | | dmac to
| TSCH MAC | brdcst | | | | self
+--------------+ | | | | | |
| LLN PHY | +-------+ +--...-----+ +-------+
+--------------+
]]></artwork>
</figure>
</t>
</section>
<section title="Tunnel Mode">
<t> In tunnel mode, the frames originate from an arbitrary protocol over a compatible
MAC that may or may not be synchronized with the 6TiSCH network. An example of this
would be a router with a dual radio that is capable of receiving and sending
WirelessHART or ISA100.11a frames with the second radio, by presenting itself as an
access Point or a Backbone Router, respectively. </t>
<t> In that mode, some entity (e.g. PCE) can coordinate with a WirelessHART Network
Manager or an ISA100.11a System Manager to specify the flows that are to be
transported transparently over the Track. </t>
<t>
<figure anchor="fig6" title="Track Forwarding, Tunnel Mode">
<artwork><![CDATA[
+--------------+
| IPv6 |
+--------------+
| 6LoWPAN HC |
+--------------+ set restore
| 6top | +dmac+ +dmac+
+--------------+ to|brdcst to|nexthop
| TSCH MAC | | | | |
+--------------+ | | | |
| LLN PHY | +-------+ +--...-----+ +-------+
+--------------+ | ingress egress |
| |
+--------------+ | |
| LLN PHY | | |
+--------------+ | |
| TSCH MAC | | |
+--------------+ | dmac = | dmac =
|ISA100/WiHART | | nexthop v nexthop
+--------------+
]]></artwork>
</figure>
</t>
<t> In that case, the flow information that identifies the Track at the ingress 6TiSCH
router is derived from the RX-cell. The dmac is set to this node but the flow
information indicates that the frame must be tunneled over a particular Track so the
frame is not passed to the upper layer. Instead, the dmac is forced to broadcast and
the frame is passed to the 6top sublayer for switching. </t>
<t> At the egress 6TiSCH router, the reverse operation occurs. Based on metadata
associated to the Track, the frame is passed to the appropriate link layer with the
destination MAC restored. </t>
</section>
<section title="Tunnel Metadata">
<t> Metadata coming with the Track configuration is expected to provide the destination
MAC address of the egress endpoint as well as the tunnel mode and specific data
depending on the mode, for instance a service access point for frame delivery at
egress. If the tunnel egress point does not have a MAC address that matches the
configuration, the Track installation fails. </t>
<t> In transport mode, if the final layer-3 destination is the tunnel termination, then
it is possible that the IPv6 address of the destination is compressed at the 6LoWPAN
sublayer based on the MAC address. It is thus mandatory at the ingress point to
validate that the MAC address that was used at the 6LoWPAN sublayer for compression
matches that of the tunnel egress point. For that reason, the node that injects a
packet on a Track checks that the destination is effectively that of the tunnel egress
point before it overwrites it to broadcast. The 6top sublayer at the tunnel egress
point reverts that operation to the MAC address obtained from the tunnel metadata. </t>
</section>
</section>
</section>
<section anchor="detnet" title="Operations of Interest for DetNet and PCE">
<t>In a classical system, the 6TiSCH device does not place the request for bandwidth between
self and another device in the network. Rather, an Operation Control System invoked
through an Human/Machine Interface (HMI) indicates the Traffic Specification, in
particular in terms of latency and reliability, and the end nodes. With this, the PCE must
compute a Track between the end nodes and provision the network with per-flow state that
describes the per-hop operation for a given packet, the corresponding timeSlots, and the
flow identification that enables to recognize when a certain packet belongs to a certain
Track, sort out duplicates, etc... </t>
<t> For a static configuration that serves a certain purpose for a long period of time, it
is expected that a node will be provisioned in one shot with a full schedule, which
incorporates the aggregation of its behavior for multiple Tracks. 6TiSCH expects that the
programing of the schedule will be done over COAP as discussed in <xref
target="I-D.ietf-6tisch-coap">6TiSCH Resource Management and Interaction using
CoAP</xref>. </t>
<t> But an Hybrid mode may be required as well whereby a single Track is added, modified, or
removed, for instance if it appears that a Track does not perform as expected for, say,
PDR. For that case, the expectation is that a protocol that flows along a Track (to be),
in a fashion similar to classical Traffic Engineering (TE) <xref target="CCAMP"/>, may be
used to update the state in the devices. 6TiSCH provides means for a device to negotiate a
timeSlot with a neighbor, but in general that flow was not designed and no protocol was
selected and it is expected that DetNet will determine the appropriate end-to-end
protocols to be used in that case. </t>
<figure title="Stream Management Entity" align="center" anchor="NorthSouth">
<artwork><![CDATA[
Operational System and HMI
-+-+-+-+-+-+-+ Northbound -+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
PCE PCE PCE PCE
-+-+-+-+-+-+-+ Southbound -+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
--- 6TiSCH------6TiSCH------6TiSCH------6TiSCH--
6TiSCH / Device Device Device Device \
Device- - 6TiSCH
\ 6TiSCH 6TiSCH 6TiSCH 6TiSCH / Device
----Device------Device------Device------Device--
]]></artwork>
</figure>
<section anchor="pmh" title="Packet Marking and Handling">
<t> Section "Packet Marking and Handling" of <xref target="I-D.ietf-6tisch-architecture"/>
describes the packet tagging and marking that is expected in 6TiSCH networks. </t>
<section anchor="pmhft" title="Tagging Packets for Flow Identification">
<t> For packets that are routed by a PCE along a Track, the tuple formed by the IPv6
source address and a local RPLInstanceID is tagged in the packets to identify uniquely
the Track and associated transmit bundle of timeSlots. </t>
<t> It results that the tagging that is used for a DetNet flow outside the 6TiSCH LLN
MUST be swapped into 6TiSCH formats and back as the packet enters and then leaves the
6TiSCH network. </t>
<t> Note: The method and format used for encoding the RPLInstanceID at 6lo is
generalized to all 6TiSCH topological Instances, which includes Tracks. </t>
</section>
<section anchor="pmhrre" title="Replication, Retries and Elimination">
<t>6TiSCH expects elimination and replication of packets along a complex Track, but has
no position about how the sequence numbers would be tagged in the packet. </t>
<t> As it goes, 6TiSCH expects that timeSlots corresponding to copies of a same packet
along a Track are correlated by configuration, and does not need to process the
sequence numbers. </t>
<t> The semantics of the configuration MUST enable correlated timeSlots to be grouped
for transmit (and respectively receive) with a 'OR' relations, and then a 'AND'
relation MUST be configurable between groups. The semantics is that if the transmit
(and respectively receive) operation succeeded in one timeSlot in a 'OR' group, then
all the other timeSLots in the group are ignored. Now, if there are at least two
groups, the 'AND' relation between the groups indicates that one operation must
succeed in each of the groups. </t>
<t> On the transmit side, timeSlots provisioned for retries along a same branch of a
Track are placed a same 'OR' group. The 'OR' relation indicates that if a transmission
is acknowledged, then further transmissions SHOULD NOT be attempted for timeSlots in
that group. There are as many 'OR' groups as there are branches of the Track departing
from this node. Different 'OR' groups are programmed for the purpose of replication,
each group corresponding to one branch of the Track. The 'AND' relation between the
groups indicates that transmission over any of branches MUST be attempted regardless
of whether a transmission succeeded in another branch. It is also possible to place
cells to different next-hop routers in a same 'OR' group. This allows to route along
multi-path tracks, trying one next-hop and then another only if sending to the first
fails. </t>
<t> On the receive side, all timeSlots are programmed in a same 'OR' group. Retries of a
same copy as well as converging branches for elimination are converged, meaning that
the first successful reception is enough and that all the other timeSlots can be
ignored. </t>
</section>
<section anchor="pmhds" title="Differentiated Services Per-Hop-Behavior">
<t> Additionally, an IP packet that is sent along a Track uses the Differentiated
Services Per-Hop-Behavior Group called Deterministic Forwarding, as described in <xref
target="I-D.svshah-tsvwg-deterministic-forwarding"/>. </t>
</section>
</section>
<section anchor="topo" title="Topology and capabilities">
<t>6TiSCH nodes are usually IoT devices, characterized by very limited amount of memory,
just enough buffers to store one or a few IPv6 packets, and limited bandwidth between
peers. It results that a node will maintain only a small number of peering information,
and will not be able to store many packets waiting to be forwarded. Peers can be
identified through MAC or IPv6 addresses, but a Cryptographically Generated Address
<xref target="RFC3972"/> (CGA) may also be used. </t>
<t> Neighbors can be discovered over the radio using mechanism such as beacons, but,
though the neighbor information is available in the 6TiSCH interface data model, 6TiSCH
does not describe a protocol to pro-actively push the neighborhood information to a PCE.
This protocol should be described and should operate over CoAP. The protocol should be
able to carry multiple metrics, in particular the same metrics as used for RPL
operations <xref target="RFC6551"/>
</t>
<t> The energy that the device consumes in sleep, transmit and receive modes can be
evaluated and reported. So can the amount of energy that is stored in the device and the
power that it can be scavenged from the environment. The PCE SHOULD be able to compute
Tracks that will implement policies on how the energy is consumed, for instance balance
between nodes, ensure that the spent energy does not exceeded the scavenged energy over
a period of time, etc... </t>
</section>
</section>
<section anchor="sec" title="Security Considerations">
<t>On top of the classical protection of control signaling that can be expected to support
DetNet, it must be noted that 6TiSCH networks operate on limited resources that can be
depleted rapidly if an attacker manages to operate a DoS attack on the system, for
instance by placing a rogue device in the network, or by obtaining management control and
to setup extra paths. </t>
</section>
<section title="Acknowledgments">
<t>This specification derives from the 6TiSCH architecture, which is the result of multiple
interactions, in particular during the 6TiSCH (bi)Weekly Interim call, relayed through the
6TiSCH mailing list at the IETF. </t>
<t> The authors wish to thank: Kris Pister, Thomas Watteyne, Xavier Vilajosana, Qin Wang,
Tom Phinney, Robert Assimiti, Michael Richardson, Zhuo Chen, Malisa Vucinic, Alfredo
Grieco, Martin Turon, Dominique Barthel, Elvis Vogli, Guillaume Gaillard, Herman Storey,
Maria Rita Palattella, Nicola Accettura, Patrick Wetterwald, Pouria Zand, Raghuram
Sudhaakar, and Shitanshu Shah for their participation and various contributions. </t>
</section>
</section>
<section title="Cellular Radio Use Cases">
<t>(This section was derived from draft-korhonen-detnet-telreq-00) </t>
<section anchor="intro" title="Introduction and background">
<t>The recent developments in telecommunication networks, especially in the cellular domain,
are heading towards transport networks where precise time synchronization support has to
be one of the basic building blocks. While the transport networks themselves have
practically transitioned to all-AP packet based networks to meet the bandwidth and cost
requirements, a highly accurate clock distribution has become a challenge. Earlier the
transport networks in the cellular domain were typically time division and multiplexing
(TDM) -based and provided frequency synchronization capabilities as a part of the
transport media. Alternatively other technologies such as Global Positioning System (GPS)
or Synchronous Ethernet (SyncE) <xref target="SyncE"/> were used. New radio access network
deployment models and architectures may require time sensitive networking services with
strict requirements on other parts of the network that previously were not considered to
be packetized at all. The time and synchronization support are already topical for
backhaul and midhaul packet networks <xref target="MEF"/>, and becoming a real issue for
fronthaul networks. Specifically in the fronthaul networks the timing and synchronization
requirements can be extreme for packet based technologies, for example, in order of sub
+-20 ns packet delay variation (PDV) and frequency accuracy of +0.002 PPM <xref
target="Fronthaul"/>. </t>
<t>Both Ethernet and IP/MPLS <xref target="RFC3031"/> (and PseudoWires (PWE) <xref
target="RFC3985"/> for legacy transport support) have become popular tools to build and
manage new all-IP radio access networks (RAN) <xref target="I-D.kh-spring-ip-ran-use-case"
/>. Although various timing and synchronization optimizations have already been proposed
and implemented including 1588 PTP enhancements <xref
target="I-D.ietf-tictoc-1588overmpls"/><xref target="I-D.mirsky-mpls-residence-time"/>,
these solution are not necessarily sufficient for the forthcoming RAN architectures or
guarantee the higher time-synchronization requirements <xref target="CPRI"/>. There are
also existing solutions for the TDM over IP <xref target="RFC5087"/>
<xref target="RFC4553"/> or Ethernet transports <xref target="RFC5086"/>. The really
interesting and important existing work for time sensitive networking has been done for
Ethernet <xref target="TSNTG"/>, which specifies the use of IEEE 1588 time precision
protocol (PTP) <xref target="IEEE1588"/> in the context of IEEE 802.1D and IEEE 802.1Q.
While IEEE 802.1AS <xref target="IEEE8021AS"/> specifies a Layer-2 time synchronizing
service other specification, such as IEEE 1722 <xref target="IEEE1722"/> specify
Ethernet-based Layer-2 transport for time-sensitive streams. New promising work seeks to
enable the transport of time-sensitive fronthaul streams in Ethernet bridged networks
<xref target="IEEE8021CM"/>. Similarly to IEEE 1722 there is an ongoing standardization
effort to define Layer-2 transport encapsulation format for transporting radio over
Ethernet (RoE) in IEEE 1904.3 Task Force <xref target="IEEE19043"/>. </t>
<t>As already mentioned all-IP RANs and various "haul" networks would benefit from time
synchronization and time-sensitive transport services. Although Ethernet appears to be the
unifying technology for the transport there is still a disconnect providing Layer-3
services. The protocol stack typically has a number of layers below the Ethernet Layer-2
that shows up to the Layer-3 IP transport. It is not uncommon that on top of the lowest
layer (optical) transport there is the first layer of Ethernet followed one or more layers
of MPLS, PseudoWires and/or other tunneling protocols finally carrying the Ethernet layer
visible to the user plane IP traffic. While there are existing technologies, especially in
MPLS/PWE space, to establish circuits through the routed and switched networks, there is a
lack of signaling the time synchronization and time-sensitive stream
requirements/reservations for Layer-3 flows in a way that the entire transport stack is
addressed and the Ethernet layers that needs to be configured are addressed. Furthermore,
not all "user plane" traffic will be IP. Therefore, the same solution need also address
the use cases where the user plane traffic is again another layer or Ethernet frames.
There is existing work describing the problem statement <xref
target="I-D.finn-detnet-problem-statement"/> and the architecture <xref
target="I-D.finn-detnet-architecture"/> for deterministic networking (DetNet) that
eventually targets to provide solutions for time-sensitive (IP/transport) streams with
deterministic properties over Ethernet-based switched networks. </t>
<t>This document describes requirements for deterministic networking in a cellular telecom
transport networks context. The requirements include time synchronization, clock
distribution and ways of establishing time-sensitive streams for both Layer-2 and Layer-3
user plane traffic using IETF protocol solutions. </t>
<t>The recent developments in telecommunication networks, especially in the cellular domain,
are heading towards transport networks where precise time synchronization support has to
be one of the basic building blocks. While the transport networks themselves have
practically transitioned to all-AP packet based networks to meet the bandwidth and cost
requirements, a highly accurate clock distribution has become a challenge. Earlier the
transport networks in the cellular domain were typically time division and multiplexing
(TDM) -based and provided frequency synchronization capabilities as a part of the
transport media. Alternatively other technologies such as Global Positioning System (GPS)
or Synchronous Ethernet (SyncE) <xref target="SyncE"/> were used. New radio access network
deployment models and architectures may require time sensitive networking services with
strict requirements on other parts of the network that previously were not considered to
be packetized at all. The time and synchronization support are already topical for
backhaul and midhaul packet networks <xref target="MEF"/>, and becoming a real issue for
fronthaul networks. Specifically in the fronthaul networks the timing and synchronization
requirements can be extreme for packet based technologies, for example, in order of sub
+-20 ns packet delay variation (PDV) and frequency accuracy of +0.002 PPM <xref
target="Fronthaul"/>. </t>
<t>Both Ethernet and IP/MPLS <xref target="RFC3031"/> (and PseudoWires (PWE) <xref
target="RFC3985"/> for legacy transport support) have become popular tools to build and
manage new all-IP radio access networks (RAN) <xref target="I-D.kh-spring-ip-ran-use-case"
/>. Although various timing and synchronization optimizations have already been proposed
and implemented including 1588 PTP enhancements <xref
target="I-D.ietf-tictoc-1588overmpls"/><xref target="I-D.mirsky-mpls-residence-time"/>,
these solution are not necessarily sufficient for the forthcoming RAN architectures or
guarantee the higher time-synchronization requirements <xref target="CPRI"/>. There are
also existing solutions for the TDM over IP <xref target="RFC5087"/>
<xref target="RFC4553"/> or Ethernet transports <xref target="RFC5086"/>. The really
interesting and important existing work for time sensitive networking has been done for
Ethernet <xref target="TSNTG"/>, which specifies the use of IEEE 1588 time precision
protocol (PTP) <xref target="IEEE1588"/> in the context of IEEE 802.1D and IEEE 802.1Q.
While IEEE 802.1AS <xref target="IEEE8021AS"/> specifies a Layer-2 time synchronizing
service other specification, such as IEEE 1722 <xref target="IEEE1722"/> specify
Ethernet-based Layer-2 transport for time-sensitive streams. New promising work seeks to
enable the transport of time-sensitive fronthaul streams in Ethernet bridged networks
<xref target="IEEE8021CM"/>. Similarly to IEEE 1722 there is an ongoing standardization
effort to define Layer-2 transport encapsulation format for transporting radio over
Ethernet (RoE) in IEEE 1904.3 Task Force <xref target="IEEE19043"/>. </t>
<t>As already mentioned all-IP RANs and various "haul" networks would benefit from time
synchronization and time-sensitive transport services. Although Ethernet appears to be the
unifying technology for the transport there is still a disconnect providing Layer-3
services. The protocol stack typically has a number of layers below the Ethernet Layer-2
that shows up to the Layer-3 IP transport. It is not uncommon that on top of the lowest
layer (optical) transport there is the first layer of Ethernet followed one or more layers
of MPLS, PseudoWires and/or other tunneling protocols finally carrying the Ethernet layer
visible to the user plane IP traffic. While there are existing technologies, especially in
MPLS/PWE space, to establish circuits through the routed and switched networks, there is a
lack of signaling the time synchronization and time-sensitive stream
requirements/reservations for Layer-3 flows in a way that the entire transport stack is
addressed and the Ethernet layers that needs to be configured are addressed. Furthermore,
not all "user plane" traffic will be IP. Therefore, the same solution need also address
the use cases where the user plane traffic is again another layer or Ethernet frames.
There is existing work describing the problem statement <xref
target="I-D.finn-detnet-problem-statement"/> and the architecture <xref
target="I-D.finn-detnet-architecture"/> for deterministic networking (DetNet) that
eventually targets to provide solutions for time-sensitive (IP/transport) streams with
deterministic properties over Ethernet-based switched networks. </t>
<t>This document describes requirements for deterministic networking in a cellular telecom
transport networks context. The requirements include time synchronization, clock
distribution and ways of establishing time-sensitive streams for both Layer-2 and Layer-3
user plane traffic using IETF protocol solutions. </t>
</section>
<!--section title="Terminology">
<t>The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in <xref
target="RFC2119"></xref>.</t>
</section-->
<section title="Network architecture">
<t>Figure <xref target="arch"/> illustrates a typical, 3GPP defined, cellular network
architecture, which also has fronthaul and midhaul network segments. The fronthaul refers
to the network connecting base stations (base band processing units) to the remote radio
heads (antennas). The midhaul network typically refers to the network inter-connecting
base stations (or small/pico cells). </t>
<t> Fronthaul networks build on the available excess time after the base band processing of
the radio frame has completed. Therefore, the available time for networking is actually
very limited, which in practise determines how far the remote radio heads can be from the
base band processing units (i.e. base stations). For example, in a case of LTE radio the
Hybrid ARQ processing of a radio frame is allocated 3 ms. Typically the processing
completes way earlier (say up to 400 us, could be much less, though) thus allowing the
remaining time to be used e.g. for fronthaul network. 200 us equals roughly 40 km of
optical fiber based transport (assuming round trip time would be total 2*200 us). The base
band processing time and the available "delay budget" for the fronthaul is a subject to
change, possibly dramatically, in the forthcoming "5G" to meet, for example, the
envisioned reduced radio round trip times, and other architecural and service requirements
<xref target="NGMN"/>. </t>
<t>The maximum "delay budget" is then consumed by all nodes and required buffering between
the remote radio head and the base band processing in addition to the distance incurred
delay. Packet delay variation (PDV) is problematic to fronthaul networks and must be
minimized. If the transport network cannot guarantee low enough PDV additional buffering
has to be introduced at the edges of the network to buffer out the jitter. Any buffering
will eat up the total available delay budget, though. Section <xref target="sync"/> will
discuss the PDV requirements in more detail. </t>
<figure
title="Generic 3GPP-based cellular network architecture with Front/Mid/Backhaul networks"
anchor="arch">
<artwork><![CDATA[
Y (remote radios)
\
Y__ \.--. .--. +------+
\_( `. +---+ _(Back`. | 3GPP |
Y------( Front )----|eNB|----( Haul )----| core |
( ` .Haul ) +---+ ( ` . ) ) | netw |
/`--(___.-' \ `--(___.-' +------+
Y_/ / \.--. \
Y_/ _( Mid`. \
( Haul ) \
( ` . ) ) \
`--(___.-'\_____+---+ (small cells)
\ |SCe|__Y
+---+ +---+
Y__|eNB|__Y
+---+
Y_/ \_Y ("local" radios)
]]></artwork>
</figure>
</section>
<section title="Time synchronization requirements" anchor="sync">
<t>Cellular networks starting from long term evolution (LTE) <xref target="TS36300"/>
<xref target="TS23401"/> radio the phase synchronization is also needed in addition to the
frequency synchronization. The commonly referenced fronthaul network synchronization
requirements are typically drawn from the common public radio interface (CPRI) <xref
target="CPRI"/> specification that defines the transport protocol between the base band
processing - radio equipment controller (REC) and the remote antenna - radio equipment
(RE). However, the fundamental requirements still originate from the respective cellular
system and radio specifications such as the 3GPP ones <xref target="TS25104"/><xref
target="TS36104"/><xref target="TS36211"/>
<xref target="TS36133"/>. </t>
<t>The fronthaul time synchronization requirements for the current 3GPP LTE-based networks
are listed below: <list style="hanging">
<t hangText="Transport link contribution to radio frequency error:">
<vspace blankLines="1"/>+-2 PPB. The given value is considered to be "available" for
the fronthaul link out of the total 50 PPB budget reserved for the radio interface. </t>
<t hangText="Delay accuracy:">
<vspace blankLines="1"/> +-8.138 ns i.e. +-1/32 Tc (UMTS Chip time, Tc, 1/3.84 MHz) to
downlink direction and excluding the (optical) cable length in one direction. Round
trip accuracy is then +-16.276 ns. The value is this low to meet the 3GPP timing
alignment error (TAE) measurement requirements. </t>
<t hangText="Packet delay variation (PDV):">
<list style="symbols">
<t>For multiple input multiple output (MIMO) or TX diversity transmissions, at each
carrier frequency, TAE shall not exceed 65 ns (i.e. 1/4 Tc).</t>
<t>For intra-band contiguous carrier aggregation, with or without MIMO or TX
diversity, TAE shall not exceed 130 ns (i.e. 1/2 Tc).</t>
<t>For intra-band non-contiguous carrier aggregation, with or without MIMO or TX
diversity, TAE shall not exceed 260 ns (i.e. one Tc).</t>
<t>For inter-band carrier aggregation, with or without MIMO or TX diversity, TAE
shall not exceed 260 ns.</t>
</list>
</t>
</list>
</t>
<t>The above listed time synchronization requirements are hard to meet even with point to
point connected networks, not to mention cases where the underlying transport network
actually constitutes of multiple hops. It is expected that network deployments have to
deal with the jitter requirements buffering at the very ends of the connections, since
trying to meet the jitter requirements in every intermediate node is likely to be too
costly. However, every measure to reduce jitter and delay on the path are valuable to make
it easier to meet the end to end requirements. </t>
<t>In order to meet the timing requirements both senders and receivers must is perfect sync.
This asks for a very accurate clock distribution solution. Basically all means and
hardware support for guaranteeing accurate time synchronization in the network is needed.
As an example support for 1588 transparent clocks (TC) in every intermediate node would be
helpful. </t>
</section>
<section title="Time-sensitive stream requirements">
<t>In addition to the time synchronization requirements listed in Section <xref
target="sync"/> the fronthaul networks assume practically error free transport. The
maximum bit error rate (BER) has been defined to be 10^-12. When packetized that would
equal roughly to packet error rate (PER) of 2.4*10^-9 (assuming ~300 bytes packets).
Retransmitting lost packets and/or using forward error coding (FEC) to circumvent bit
errors are practically impossible due additional incurred delay. Using redundant streams
for better guarantees for delivery is also practically impossible due to high bandwidth
requirements fronthaul networks have. For instance, current uncompressed CPRI bandwidth
expansion ratio is roughly 20:1 compared to the IP layer user payload it carries in a
"radio sample form". </t>
<t>The other fundamental assumption is that fronthaul links are symmetric. Last, all
fronthaul streams (carrying radio data) have equal priority and cannot delay or pre-empt
each other. This implies the network has always be sufficiently under subscribed to
guarantee each time-sensitive flow meets their schedule. </t>
<t>Mapping the fronthaul requirements to <xref target="I-D.finn-detnet-architecture"/>
Section 3 "Providing the DetNet Quality of Service" what is seemed usable are: <list
style="none">
<t>(a) Zero congestion loss.</t>
<t>(b) Pinned-down paths.</t>
</list>
</t>
<t>The current time-sensitive networking features may still not be sufficient for fronthaul
traffic. Therefore, having specific profiles that take the requirements of fronthaul into
account are deemed to be useful <xref target="IEEE8021CM"/>. </t>
<t>The actual transport protocols and/or solutions to establish required transport
"circuits" (pinned-down paths) for fronthaul traffic are still undefined. Those are likely
to include but not limited to solutions directly over Ethernet, over IP, and
MPLS/PseudoWire transport. </t>
</section>
<section title="Security considerations">
<t>Establishing time-sensitive streams in the network entails reserving networking resources
sometimes for a considerable long time. It is important that these reservation requests
must be authenticated to prevent malicious reservation attempts from hostile nodes or even
accidental misconfiguration. This is specifically important in a case where the
reservation requests span administrative domains. Furthermore, the reservation information
itself should be digitally signed to reduce the risk where a legitimate node pushed a
stale or hostile configuration into the networking node. </t>
</section>
</section>
<section title="Industrial M2M">
<t>(This section was derived from draft-varga-industrial-m2m-00) </t>
<section anchor="introm2m" title="Introduction">
<t> Traditional "industrial automation" and terminology usually refers to automation of
manufacturing, quality control and material processing. In practice, it means that machine
units in a plant floor need cyclic control data exchange to upstream or downstream machine
modules or to a supervisory control in a local network, which is often based on
proprietary networking technologies today.</t>
<t> For such communication between industrial entities, it is critical to ensure proper and
deterministic end to end delivery time of messages with (very) high reliability and
robustness, especially in closed loop automation control. </t>
<t> Moreover, the recent trend is to use standard networking technologies in the local
network and for connecting remote industrial automation sites, e.g., over an enterprise or
metro network which also carries other types of traffic. Therefore, deterministic flows
should be guaranteed regardless of the amount of other flows in those networks for the
deployment of future industrial automation.</t>
<t> This document covers a selected industrial application, identifies representative
solutions used today, and points on new use cases an IETF DetNet solution may enable. </t>
</section>
<section title="Terminology and Definitions">
<t><list style="hanging">
<t hangText="DetNet:">Deterministic Networking. <xref target="IETFDetNet"/></t>
<t hangText="M2M:">Machine to Machine. </t>
<t hangText="MES:">Manufacturing-Execution-System. </t>
<t hangText="PLC:">Programmable Logic Control. </t>
<t hangText="S-PLC:">Supervisory Programmable Logic Control. </t>
</list></t>
</section>
<section anchor="sec_m2m" title="Machine to Machine communication over IP networks">
<t> In case of industrial automation, the actors of Machine to Machine (M2M) communication
are Programmable Logic Controls (PLC). The communication between PLCs and between PLCs and
the supervisory PLC (S-PLC) is achieved via critical Control-Data-Streams <xref
target="fig_indm2m"/>. This draft focuses on PLC related communications and
communication to Manufacturing-Execution-System (MES) are out-of-scope. The PLC related
Control-Data-Streams are transmitted periodically and they are established either with (i)
a pre-configured payload or (ii) a payload configuration during runtime.</t>
<figure title="Current generic industrial M2M network architecture" anchor="fig_indm2m">
<artwork><![CDATA[
S (Sensor)
\ +-----+
PLC__ \.--. .--. ---| MES |
\_( `. _( `./ +-----+
A------( Local )-------------( L2 )
( Net ) ( Net ) +-------+
/`--(___.-' `--(___.-' ----| S-PLC |
S_/ / PLC .--. / +-------+
A_/ \_( `.
(Actuator) ( Local )
( Net )
/`--(___.-'\
/ \ A
S A
]]></artwork>
</figure>
<t> The network topologies used today by applications of industrial automation are (i) daisy
chain, (ii) ring and (iii) hub and spoke. Such topologies are often used in
telecommunication networks too. In industrial networks comb (being a subset of
daisy-chain) is also used.</t>
<t> Some industrial applications require Time Synchronization (Sync) to end nodes, which is
also similar to some telecommunication networks, e.g., mobile Radio Access Networks. For
such time coordinated PLCs, accuracy of 1 microseconds is required. In case of non-time
coordinated PLCs, a requirement for Time Sync may still exist, e.g., for time stamping of
collected measurement (sensor) data.</t>
</section>
<section anchor="sec_m2mreq" title="Machine to Machine communication requirements">
<t> The requirements listed here refer to critical Control-Data-Streams. Non-critical
traffic of industrial automation applications can be served with currently available
prioritizing techniques. </t>
<t> In an industrial environment, non-time-critical traffic is related to (i) communication
of state, configuration, set-up, etc., (ii) connection to Manufacturing-Execution-System
(MES) and (iii) database communication. Such type of traffic can use up to 80% of the
available bandwidth. There is a subset of non-time-critical traffic that their bandwidth
should be guaranteed.</t>
<t> The rest of this chapter is dealing only with time-critical traffic.</t>
<section anchor="sec_m2mtr" title="Transport parameters">
<t> The Cycle Time defines the frequency of message(s) between industrial entities. The
Cycle Time is application dependent, it is in the range of 1ms - 100ms for critical
Control-Data-Streams.</t>
<t> As industrial applications assume deterministic transport instead of defining latency
and delay variation parameters for critical Control-Data-Stream parameters, it is enough
to fulfill the upper bound of latency (maximum latency). The communication must ensure a
maximum end to end delivery time of messages in the range of 100 microseconds to 50
milliseconds depending on the control loop application.</t>
<t> Bandwidth requirements of Control-Data-Streams are usually calculated directly from
the bytes per cycle parameter of the control loop. For PLC to PLC communication one can
expect 2 - 32 streams with packet size in the range of 100 - 700 bytes. For S-PLC to
PLCs the number of streams is higher up-to 256 streams need to be supported. Usually no
more than 20% of available bandwidth is used for critical Control-Data-Streams in
today's networks, which comprise Gbps links.</t>
<t> Usual PLC control loops are rather tolerant for packet loss. Critical
Control-Data-Streams accept no more than 1 packet loss per consecutive communication
cycles. The required network availability is rather high, it hits the 5 nines
(99,999%).</t>
<t> Based on the above parameters, it can be concluded that some form of redundancy might
be required for M2M communication. The actual solution depends on several parameters,
like cycle time, delivery time, etc. </t>
</section>
<section anchor="sec_m2mfm" title="Flow maintenance">
<t> Most Critical Control-Data-Streams get created at startup, however, flexibility is
also needed during runtime (e.g. add / remove machine). In an industrial environment,
critical Control-Data-Streams are created rather infrequent: ~10 times per day / week /
month. With the future advent of flexible production systems, flow maintenance
parameters are expected to increase significantly.</t>
</section>
</section>
<section anchor="sec_sum" title="Summary">
<t>This document specifies an industrial machine-to-machine use-case in the DetNet
context.</t>
</section>
<section anchor="Securitym2m" title="Security Considerations">
<t> Industrial network scenarios require advanced security solutions. Many of the current
industrial production networks are physically separated. Protection of critical flows are
handled today by gateways / firewalls. </t>
</section>
<section title="Acknowledgements">
<t>The authors would like to thank Feng Chen and Marcel Kiessling for their comments and
suggestions.</t>
</section>
</section>
<section title="Other Use Cases">
<t>(This section was derived from draft-zha-detnet-use-case-00) </t>
<section title="Introduction">
<t> The rapid growth of the today's communication system and its access into almost all
aspects of daily life has led to great dependency on services it provides. The
communication network, as it is today, has applications such as multimedia and
peer-to-peer file sharing distribution that require Quality of Service (QoS) guarantees in
terms of delay and jitter to maintain a certain level of performance. Meanwhile, mobile
wireless communications has become an important part to support modern sociality with
increasing importance over the last years. A communication network of hard real-time and
high reliability is essential for the next concurrent and next generation mobile wireless
networks as well as its bearer network for E-2-E performance requirements. </t>
<t> Conventional transport network is IP-based because of the bandwidth and cost
requirements. However the delay and jitter guarantee becomes a challenge in case of
contention since the service here is not deterministic but best effort. With more and more
rigid demand in latency control in the future network [METIS], deterministic networking
[I-D.finn-detnet-architecture] is a promising solution to meet the ultra low delay
applications and use cases. There are already typical issues for delay sensitive
networking requirements in midhaul and backhaul network to support LTE and future 5G
network [net5G]. And not only in the telecom industry but also other vertical industry has
increasing demand on delay sensitive communications as the automation becomes critical
recently. </t>
<t> More specifically, CoMP techniques, D-2-D, industrial automation and gaming/media
service all have great dependency on the low delay communications as well as high
reliability to guarantee the service performance. Note that the deterministic networking
is not equal to low latency as it is more focused on the worst case delay bound of the
duration of certain application or service. It can be argued that without high certainty
and absolute delay guarantee, low delay provisioning is just relative [rfc3393], which is
not sufficient to some delay critical service since delay violation in an instance cannot
be tolerated. Overall, the requirements from vertical industries seem to be well aligned
with the expected low latency and high determinist performance of future networks </t>
<t> This document describes several use cases and scenarios with requirements on
deterministic delay guarantee within the scope of the deterministic network
[I-D.finn-detnet-problem-statement]. </t>
</section>
<section title="Critical Delay Requirements">
<t> Delay and jitter requirement has been take into account as a major component in QoS
provisioning since the birth of Internet. The delay sensitive networking with increasing
importance become the root of mobile wireless communications as well as the applicable
areas which are all greatly relied on low delay communications. Due to the best effort
feature of the IP networking, mitigate contention and buffering is the main solution to
serve the delay sensitive service. More bandwidth is assigned to keep the link low loaded
or in another word, reduce the probability of congestion. However, not only lack of
determinist but also has limitation to serve the applications in the future communication
system, keeping low loaded cannot provide deterministic delay guarantee. Take the [METIS]
that documents the fundamental challenges as well as overall technical goal of the 5G
mobile and wireless system as the starting point. It should supports: -1000 times higher
mobile data volume per area, -10 times to 100 times higher typical user data rate, -10
times to 100 times higher number of connected devices, -10 times longer battery life for
low power devices, and -5 times reduced End-to-End (E2E) latency, at similar cost and
energy consumption levels as today's system. Taking part of these requirements related to
latency, current LTE networking system has E2E latency less than 20ms [LTE-Latency] which
leads to around 5ms E2E latency for 5G networks. It has been argued that fulfill such
rigid latency demand with similar cost will be most challenging as the system also
requires 100 times bandwidth as well as 100 times of connected devices. As a result to
that, simply adding redundant bandwidth provisioning can be no longer an efficient
solution due to the high bandwidth requirements more than ever before. In addition to the
bandwidth provisioning, the critical flow within its reserved resource should not be
affected by other flows no matter the pressure of the network. Robust defense of critical
flow is also not depended on redundant bandwidth allocation. Deterministic networking
techniques in both layer-2 and layer-3 using IETF protocol solutions can be promising to
serve these scenarios. </t>
</section>
<section title="Coordinated multipoint processing (CoMP)">
<t> In the wireless communication system, Coordinated multipoint processing (CoMP) is
considered as an effective technique to solve the inter-cell interference problem to
improve the cell-edge user throughput [CoMP]. </t>
<section title="CoMP Architecture">
<figure title="Framework of CoMP Technology" anchor="compa">
<artwork><![CDATA[
+--------------------------+
| CoMP |
+--+--------------------+--+
| |
+----------+ +------------+
| Uplink | | Downlink |
+-----+----+ +--------+---+
| |
------------------- -----------------------
| | | | | |
+---------+ +----+ +-----+ +------------+ +-----+ +-----+
| Joint | | CS | | DPS | | Joint | | CS/ | | DPS |
|Reception| | | | | |Transmission| | CB | | |
+---------+ +----+ +-----+ +------------+ +-----+ +-----+
| |
|----------- |-------------
| | | |
+------------+ +---------+ +----------+ +------------+
| Joint | | Soft | | Coherent | | Non- |
|Equalization| |Combining| | JT | | Coherent JT|
+------------+ +---------+ +----------+ +------------+
]]></artwork>
</figure>
<t> As shown in <xref target="compa"/>, CoMP reception and transmission is a framework
that multiple geographically distributed antenna nodes cooperate to improve the
performance of the users served in the common cooperation area. The design principal of
CoMP is to extend the current single-cell to multi-UEs transmission to a multi-cell-
to-multi-UEs transmission by base station cooperation. In contrast to single-cell
scenario, CoMP has critical issues such as: Backhaul latency, CSI (Channel State
Information) reporting and accuracy and Network complexity. Clearly the first two
requirements are very much delay sensitive and will be discussed in next section. </t>
</section>
<section title="Delay Sensitivity in CoMP">
<t> As the essential feature of CoMP, signaling is exchanged between eNBs, the backhaul
latency is the dominating limitation of the CoMP performance. Generally, JT and JP may
benefit from coordinating the scheduling (distributed or centralized) of different cells
in case that the signaling exchanging between eNBs is limited to 4-10ms. For C-RAN the
backhaul latency requirement is 250us while for D-RAN it is 4-15ms. And this delay
requirement is not only rigid but also absolute since any uncertainty in delay will down
the performance significantly. Note that, some operator's transport network is not build
to support Layer-3 transfer in aggregation layer. In such case, the signaling is
exchanged through EPC which means delay is supposed to be larger. CoMP has high
requirement on delay and reliability which is lack by current mobile network systems and
may impact the architecture of the mobile network. </t>
</section>
</section>
<section title="Industrial Automation">
<t> Traditional "industrial automation" terminology usually refers to automation of
manufacturing, quality control and material processing. "Industrial internet" and
"industrial 4.0" [EA12] is becoming a hot topic based on the Internet of Things. This high
flexible and dynamic engineering and manufacturing will result in a lot of so-called smart
approaches such as Smart Factory, Smart Products, Smart Mobility, and Smart
Home/Buildings. No doubt that ultra high reliability and robustness is a must in data
transmission, especially in the closed loop automation control application where delay
requirement is below 1ms and packet loss less than 10E-9. All these critical requirements
on both latency and loss cannot be fulfilled by current 4G communication networks.
Moreover, the collaboration of the industrial automation from remote campus with cellular
and fixed network has to be built on an integrated, cloud-based platform. In this way, the
deterministic flows should be guaranteed regardless of the amount of other flows in the
network. The lack of this mechanism becomes the main obstacle in deployment on of
industrial automation. </t>
</section>
<section title="Vehicle to Vehicle">
<t> V2V communication has gained more and more attention in the last few years and will be
increasingly growth in the future. Not only equipped with direct communication system
which is short ranged, V2V communication also requires wireless cellular networks to cover
wide range and more sophisticated services. V2V application in the area autonomous driving
has very stringent requirements of latency and reliability. It is critical that the timely
arrival of information for safety issues. In addition, due to the limitation of processing
of individual vehicle, passing information to the cloud can provide more functions such as
video processing, audio recognition or navigation systems. All of those requirements lead
to a highly reliable connectivity to the cloud. On the other hand, it is natural that the
provisioning of low latency communication is one of the main challenges to be overcome as
a result of the high mobility, the high penetration losses caused by the vehicle itself.
As result of that, the data transmission with latency below 5ms and a high reliability of
PER below 10E-6 are demanded. It can benefit from the deployment of deterministic
networking with high reliability. </t>
</section>
<section title="Gaming, Media and Virtual Reality">
<t> Online gaming and cloud gaming is dominating the gaming market since it allow multiple
players to play together with more challenging and competing. Connected via current
internet, the latency can be a big issue to degrade the end users' experience. There
different types of games and FPS (First Person Shooting) gaming has been considered to be
the most latency sensitive online gaming due to the high requirements of timing precision
and computing of moving target. Virtual reality is also receiving more interests than ever
before as a novel gaming experience. The delay here can be very critical to the
interacting in the virtual world. Disagreement between what is seeing and what is feeling
can cause motion sickness and affect what happens in the game. Supporting fast, real-time
and reliable communications in both PHY/MAC layer, network layer and application layer is
main bottleneck for such use case. The media content delivery has been and will become
even more important use of Internet. Not only high bandwidth demand but also critical
delay and jitter requirements have to be taken into account to meet the user demand. To
make the smoothness of the video and audio, delay and jitter has to be guaranteed to avoid
possible interruption which is the killer of all online media on demand service. Now with
4K and 8K video in the near future, the delay guarantee become one of the most challenging
issue than ever before. 4K/8K UHD video service requires 6Gbps-100Gbps for uncompressed
video and compressed video starting from 60Mbps. The delay requirement is 100ms while some
specific interactive applications may require 10ms delay [UHD-video]. </t>
</section>
</section>
<section title="Use Case Common Elements">
<t>Looking at the use cases collectively, the following common desires for the DetNet-based
networks of the future emerge: </t>
<t>
<list style="symbols">
<t>Open standards-based network (replace various proprietary networks, reduce cost, create
multi-vendor market)</t>
<t>Centrally administered (though such administration may be distributed for scale and
resiliency)</t>
<t>Integrates L2 (bridged) and L3 (routed) environments (independent of the Link layer,
e.g. can be used with Ethernet, 6TiSCH, etc.)</t>
<t>Carries both deterministic and best-effort traffic (guaranteed end-to-end delivery of
deterministic flows, deterministic flows isolated from each other and from best-effort
traffic congestion, unused deterministic BW available to best-effort traffic)</t>
<t>Ability to add or remove systems from the network with minimal, bounded service
interruption (applications include replacement of failed devices as well as plug and
play)</t>
<t>Uses standardized data flow information models capable of expressing deterministic
properties (models express device capabilities, flow properties. Protocols for pushing
models from controller to devices, devices to controller)</t>
<t>Scalable size (long distances (many km) and short distances (within a single machine),
many hops (radio repeaters, microwave links, fiber links...) and short hops (single
machine))</t>
<t>Scalable timing parameters and accuracy (bounded latency, guaranteed worst case
maximum, minimum. Low latency, e.g. control loops may be less than 1ms, but larger for
wide area networks)</t>
<t>High availability (99.9999 percent up time requested, but may be up to twelve 9s)</t>
<t>Reliability, redundancy (lives at stake)</t>
<t>Security (from failures, attackers, misbehaving devices - sensitive to both packet
content and arrival time) </t>
</list>
</t>
</section>
<section title="Acknowledgments">
<t> This document has benefited from reviews, suggestions, comments and proposed text provided
by the following members, listed in alphabetical order: Jing Huang, Junru Lin, Lehong Niu
and Oilver Huang. </t>
</section>
</middle>
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<back>
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<reference anchor="TS36211">
<front>
<title>Evolved Universal Terrestrial Radio Access (E-UTRA); Physical channels and
modulation</title>
<author>
<organization>3GPP</organization>
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<date day="15" month="March" year="2013"/>
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<title>Evolved Universal Terrestrial Radio Access (E-UTRA); Requirements for support of
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<author>
<organization>3GPP</organization>
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<date day="3" month="April" year="2015"/>
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<reference anchor="TS36300">
<front>
<title>Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal
Terrestrial Radio Access Network (E-UTRAN); Overall description; Stage 2</title>
<author>
<organization>3GPP</organization>
</author>
<date day="19" month="September" year="2013"/>
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<seriesInfo name="3GPP TS" value="36.300 10.11.0"/>
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<reference anchor="Fronthaul"
target="http://www.ieee1904.org/3/meeting_archive/2015/02/tf3_1502_che
n_1a.pdf">
<front>
<title>Ethernet Fronthaul Considerations</title>
<author initials="D. T." surname="Chen" fullname="David T. Chen">
<organization>Nokia</organization>
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<organization>Nokia</organization>
</author>
<date day="5" month="February" year="2015"/>
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<seriesInfo name="IEEE" value="1904.3"/>
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<reference anchor="IEEE19043" target="http://www.ieee1904.org/3/tf3_home.shtml">
<front>
<title>IEEE 1904.3 TF</title>
<author>
<organization>IEEE Standards Association</organization>
</author>
<date year="2015"/>
</front>
<seriesInfo name="IEEE" value="1904.3"/>
</reference>
<reference anchor="NGMN"
target="https://www.ngmn.org/uploads/media/NGMN_5G_White_Paper_V1_0.pdf">
<front>
<title>5G White Paper</title>
<author>
<organization>NGMN Alliance</organization>
</author>
<date day="17" month="February" year="2015"/>
</front>
<seriesInfo name="NGMN 5G White Paper" value="v1.0"/>
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<reference anchor="IEEE8021CM"
target="http://www.ieee802.org/1/files/public/docs2015/new-P802-1CM-dr
aft-PAR-0515-v02.pdf">
<front>
<title>Time-Sensitive Networking for Fronthaul</title>
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<reference anchor="METIS"
target="https://www.metis2020.com/wp-content/uploads/deliverables/METIS_D1.1_v1.pdf">
<front>
<title>Scenarios, requirements and KPIs for 5G mobile and wireless system</title>
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<organization>METIS</organization>
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<reference anchor="net5G" target="http://www.ericsson.com/res/docs/whitepapers/wp-5g.pdf">
<front>
<title>5G Radio Access, Challenges for 2020 and Beyond</title>
<author>
<organization>Ericsson</organization>
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<reference anchor="CoMP"
target="https://www.ngmn.org/uploads/media/NGMN_RANEV_D3_CoMP_Evaluation_and_Enhancement_v2.0.pdf">
<front>
<title>RAN EVOLUTION PROJECT COMP EVALUATION AND ENHANCEMENT</title>
<author>
<organization>NGMN Alliance</organization>
</author>
<date month="March" year="2015"/>
</front>
<seriesInfo name="NGMN Alliance" value="NGMN_RANEV_D3_CoMP_Evaluation_and_Enhancement_v2.0"/>
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</reference>
<reference anchor="LTE-Latency"
target="http://opensignal.com/blog/2014/03/10/lte-latency-how-does-it-compare-to-other-technologies">
<front>
<title>LTE Latency: How does it compare to other technologies</title>
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</reference>
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<front>
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<organization>OpenSignal</organization>
</author>
<date month="November" year="2012"/>
</front>
</reference>
<reference anchor="UHD-video"
target="http://www.aist-victories.org/jp/7th_sympo_ws/PetrHolub_presentation.pdf">
<front>
<title>Ultra-High Definition Videos and Their Applications over the Network</title>
<author initials="P" surname="Holub">
<organization>The 7th International Symposium on VICTORIES Project</organization>
</author>
<date month="October" year="2014"/>
</front>
<seriesInfo name="The 7th International Symposium on VICTORIES Project"
value="PetrHolub_presentation"/>
<format type="PDF"
target="http://www.aist-victories.org/jp/7th_sympo_ws/PetrHolub_presentation.pdf"/>
</reference>
<reference anchor="bacnetip">
<front>
<title>Annex J to ANSI/ASHRAE 135-1995 - BACnet/IP</title>
<author>
<organization abbrev="ASHRAE"> ASHRAE </organization>
</author>
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</front>
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<front>
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ASHRAE
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<date month="September" year="2006"/>
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<reference anchor="knx">
<front>
<title>ISO/IEC 14543-3 - KNX</title>
<author>
<organization abbrev="KNX"> KNX Association </organization>
</author>
<date month="November" year="2006"/>
</front>
</reference>
<reference anchor="lontalk">
<front>
<title>LonTalk(R) Protocol Specification Version 3.0</title>
<author>
<organization abbrev="ECHELON"> ECHELON </organization>
</author>
<date year="1994"/>
</front>
</reference>
<reference anchor="modbus">
<front>
<title>MODBUS APPLICATION PROTOCOL SPECIFICATION V1.1b</title>
<author>
<organization abbrev="Modbus"> Modbus Organization </organization>
</author>
<date month="December" year="2006"/>
</front>
</reference>
<reference anchor="profibus">
<front>
<title>IEC 61158 Type 3 - Profibus DP</title>
<author>
<organization abbrev="IEC"> IEC </organization>
</author>
<date month="January" year="2001"/>
</front>
</reference>
<reference anchor="flnet">
<front>
<title>JEMA 1479 - English Edition</title>
<author>
<organization abbrev="JEMA"> Japan Electrical Manufacturers' Association </organization>
</author>
<date month="September" year="2012"/>
</front>
</reference>
<reference anchor="IETFDetNet" target="https://datatracker.ietf.org/wg/detnet/charter/">
<front>
<title>Charter for IETF DetNet Working Group</title>
<author>
<organization>IETF</organization>
</author>
<date year="2015"/>
</front>
</reference>
<reference anchor="IEEE8021TSN" target="http://www.ieee802.org/1/pages/tsn.html">
<front>
<title>The charter of the TG is to provide the specifications that will allow
time-synchronized low latency streaming services through 802 networks. </title>
<author>
<organization>IEEE 802.1</organization>
</author>
<date year="2016"/>
</front>
</reference>
</references>
<!-- Change Log
v00 2015-10-14 EAG Initial version
v01 2015-10-15 EAG Integrate comments from Lou 15Oct15
v02 2015-10-18 EAG Integrate BAS draft 7. Add para to abstract per Lou.
v03 2015-11-09 EAG Remove 6TiSCH text with IPR per Pascal.
Add Intro and Commonalities sections.
-->
</back>
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