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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>
<address>
<postal>
<street>1275 Market Street</street>
<city>San Francisco</city>
<region>CA</region>
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<email>ethan.grossman@dolby.com</email>
<uri>http://www.dolby.com</uri>
</address>
</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>
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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>
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<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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<author fullname="Subir Das" initials="S" surname="Das">
<organization>Applied Communication Sciences</organization>
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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>
<address>
<postal>
<street/>
<city/>
<code/>
<region/>
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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>
</postal>
<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>
</address>
</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">
<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>
<section title="Utility Telecom Use Cases">
<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>
<section title="Building Automation Systems">
<section title="Use Case Description">
<t> A Building Automation System (BAS) manages equipment and sensors in a building
for improving residents' comfort, reducing energy consumption, and responding to
failures and emergencies. For example, the BAS measures the temperature of a
room using sensors and then controls the HVAC (heating, ventilating, and air
conditioning) to maintain a set temperature and minimize energy consumption. </t>
<t> A BAS primarily performs the following functions: <list style="symbols">
<t> Periodically measures states of devices, for example humidity and
illuminance of rooms, open/close state of doors, FAN speed, etc. </t>
<t> Stores the measured data. </t>
<t> Provides the measured data to BAS systems and operators. </t>
<t> Generates alarms for abnormal state of devices. </t>
<t>Controls devices (e.g. turn off room lights at 10:00 PM).</t>
</list>
</t>
</section>
<section title="Building Automation Systems Today">
<section title="BAS Architecture">
<t> A typical BAS architecture of today is shown in <xref target="localbas"/>. </t>
<figure title="BAS architecture" anchor="localbas">
<artwork align="center"><![CDATA[
+----------------------------+
| |
| 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> There are typically two layers of network in a BAS. The upper one is called
the Management Network and the lower one is called the Field Network. In
management networks an IP-based communication protocol is used, while in
field networks non-IP based communication protocols ("field protocols") are
mainly used. Field networks have specific timing requirements, whereas
management networks can be best-effort. </t>
<t> A Human Machine Interface (HMI) is typically a desktop PC used by operators
to monitor and display device states, send device control commands to Local
Controllers (LCs), and configure building schedules (for example "turn off
all room lights in the building at 10:00 PM"). </t>
<t> A Building Management Server (BMS) performs the following operations. <list
style="symbols">
<t> Collect and store device states from LCs at regular intervals. </t>
<t> Send control values to LCs according to a building schedule. </t>
<t> Send an alarm signal to operators if it detects abnormal devices
states.</t>
</list>
</t>
<t> The BMS and HMI communicate with LCs via IP-based "management protocols"
(see standards <xref target="bacnetip"/>, <xref target="knx"/>). </t>
<t> A LC is typically a Programmable Logic Controller (PLC) which is connected
to several tens or hundreds of devices using "field protocols". An LC
performs the following kinds of operations: <list style="symbols">
<t> Measure device states and provide the information to BMS or HMI.</t>
<t> Send control values to devices, unilaterally or as part of a
feedback control loop.</t>
</list>
</t>
<t> There are many field protocols used today; some are standards-based and
others are proprietary (see standards <xref target="lontalk"/>, <xref
target="modbus"/>, <xref target="profibus"/> and <xref target="flnet"
/>). The result is that BASs have multiple MAC/PHY modules and interfaces.
This makes BASs more expensive, slower to develop, and can result in "vendor
lock-in" with multiple types of management applications. </t>
</section>
<section title="BAS Deployment Model">
<t> An example BAS for medium or large buildings is shown in <xref
target="deploy-localbas"/>. The physical layout spans multiple floors,
and there is 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="BAS Deployment model for Medium/Large Buildings"
anchor="deploy-localbas">
<artwork align="center"><![CDATA[
+--------------------------------------------------+
| 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 connected to the monitoring room via the Management network, and
the management functions are performed within the building. In most cases,
fast Ethernet (e.g. 100BASE-T) is used for the management network. Since the
management network is non-realtime, use of Ethernet without quality of
service is sufficient for today's deployment.</t>
<t> In the field network a variety of physical interfaces such as RS232C and
RS485 are used, which have specific timing requirements. Thus if a field
network is to be replaced with an Ethernet or wireless network, such
networks must support time-critical deterministic flows. </t>
<t> In <xref target="deploy-remotebas"/>, another deployment model is presented
in which the management system is hosted remotely. This is becoming popular
for small office and residential buildings in which a standalone monitoring
system is not cost-effective. </t>
<figure title="Deployment model for Small Buildings" anchor="deploy-remotebas">
<artwork align="center"><![CDATA[
+---------------+
| Remote Center |
| |
| BMS HMI |
+------------------------------------+ | | | |
| Floor 2 | | +---+---+ |
| +----LC~~~~+~~~~~+ Field Network| | | |
| | | | | | Router |
| | Dev Dev | +-------|-------+
| | | |
|--- | ------------------------------| |
| | Floor 1 | |
| +----LC~~~~+~~~~~+ | |
| | | | | |
| | Dev Dev | |
| | | |
| | Management Network | WAN |
| +------------------------Router-------------+
| |
+------------------------------------+
]]></artwork>
</figure>
<t> Some interoperability is possible today in the Management Network, but not
in today's field networks due to their non-IP-based design. </t>
</section>
<section title="Use Cases for Field Networks">
<t> Below are use cases for Environmental Monitoring, Fire Detection, and
Feedback Control, and their implications for field network performance. </t>
<section title="Environmental Monitoring">
<t> The BMS polls each LC at a maximum measurement interval of 100ms (for
example to draw a historical chart of 1 second granularity with a 10x
sampling interval) and then performs the operations as specified by the
operator. Each LC needs to measure each of its several hundred sensors
once per measurement interval. Latency is not critical in this scenario
as long as all sensor values are completed in the measurement interval.
Availability is expected to be 99.999 %.</t>
</section>
<section title="Fire Detection">
<t> On detection of a fire, the BMS must stop the HVAC, close the fire
shutters, turn on the fire sprinklers, send an alarm, etc. There are
typically ~10s of sensors per LC that BMS needs to manage. In this
scenario the measurement interval is 10-50ms, the communication delay is
10ms, and the availability must be 99.9999 %. </t>
</section>
<section title="Feedback Control">
<t> BAS systems utilize feedback control in various ways; the most
time-critial is control of DC motors, which require a short feedback
interval (1-5ms) with low communication delay (10ms) and jitter (1ms).
The feedback interval depends on the characteristics of the device and a
target quality of control value. There are typically ~10s of such
devices per LC. </t>
<t> Communication delay is expected to be less than 10 ms, jitter less than
1 sec while the availability must be 99.9999% .</t>
</section>
</section>
<section title="Security Considerations">
<t> When BAS field networks were developed it was assumed that the field
networks would always be physically isolated from external networks and
therefore security was not a concern. In today's world many BASs are managed
remotely and are thus connected to shared IP networks and so security is
definitely a concern, yet security features are not available in the
majority of BAS field network deployments .</t>
<t> The management network, being an IP-based network, has the protocols
available to enable network security, but in practice many BAS systems do
not implement even the available security features such as device
authentication or encryption for data in transit.</t>
</section>
</section>
<section title="BAS Future">
<t> In the future we expect more fine-grained environmental monitoring and lower
energy consumption, which will require more sensors and devices, thus requiring
larger and more complex building networks. </t>
<t> We expect building networks to be connected to or converged with other networks
(Enterprise network, Home network, and Internet). </t>
<t> Therefore better facilities for network management, control, reliability and
security are critical in order to improve resident and operator convenience and
comfort. For example the ability to monitor and control building devices via the
internet would enable (for example) control of room lights or HVAC from a
resident's desktop PC or phone application. </t>
</section>
<section title="BAS Asks">
<t> The community would like to see an interoperable protocol specification that can
satisfy the timing, security, availability and QoS constraints described above,
such that the resulting converged network can replace the disparate field
networks. Ideally this connectivity could extend to the open Internet.</t>
<t> This would imply an architecture that can guarantee <list style="symbols">
<t> Low communication delays (from <10ms to 100ms in a network of several
hundred devices)</t>
<t> Low jitter (< 1 ms)</t>
<t> Tight feedback intervals (1ms - 10ms)</t>
<t> High network availability (up to 99.9999% ) </t>
<t> Availability of network data in disaster scenario </t>
<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>
</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>
<section title="Cellular Radio Use Cases">
<section title="Use Case Description">
<t> This use case describes the application of deterministic networking in the
context of cellular telecom transport networks. Important elements include time
synchronization, clock distribution, and ways of establishing time-sensitive
streams for both Layer-2 and Layer-3 user plane traffic. </t>
<section title="Network Architecture">
<t>
<xref target="cr_arch"/> illustrates a typical 3GPP-defined cellular network
architecture, which includes "Fronthaul" and "Midhaul" network segments. The
"Fronthaul" is the network connecting base stations (baseband processing
units) to the remote radio heads (antennas). The "Midhaul" is the network
inter-connecting base stations (or small cell sites). </t>
<figure title="Generic 3GPP-based Cellular Network Architecture"
anchor="cr_arch">
<artwork><![CDATA[
Y (remote radio heads (antennas))
\
Y__ \.--. .--. +------+
\_( `. +---+ _(Back`. | 3GPP |
Y------( Front )----|eNB|----( Haul )----| core |
( ` .Haul ) +---+ ( ` . ) ) | netw |
/`--(___.-' \ `--(___.-' +------+
Y_/ / \.--. \
Y_/ _( Mid`. \
( Haul ) \
( ` . ) ) \
`--(___.-'\_____+---+ (small cell sites)
\ |SCe|__Y
+---+ +---+
Y__|eNB|__Y
+---+
Y_/ \_Y ("local" radios)
]]></artwork>
</figure>
<t> The available processing time for Fronthaul networking overhead is limited
to the available time after the baseband processing of the radio frame has
completed. For example in Long Term Evolution (LTE) radio, processing of a
radio frame is allocated 3ms, but typically the processing completes much
earlier (<400us) allowing the remaining time to be used by the Fronthaul
network. This ultimately determines the distance the remote radio heads can
be located from the base stations (200us equals roughly 40 km of optical
fiber-based transport, thus round trip time is 2*200us = 400us). </t>
<t>The remainder of the "maximum delay budget" is consumed by all nodes and
buffering between the remote radio head and the baseband processing, plus
the distance-incurred delay. </t>
<t> The baseband processing time and the available "delay budget" for the
fronthaul is likely to change in the forthcoming "5G" due to reduced radio
round trip times and other architectural and service requirements <xref
target="NGMN"/>. </t>
</section>
<section title="Time Synchronization Requirements" anchor="cr_sync">
<t> Fronthaul time synchronization requirements are given by <xref
target="TS25104"/>, <xref target="TS36104"/>, <xref target="TS36211"/>,
and <xref target="TS36133"/>. These can be summarized for the current 3GPP
LTE-based networks as: <list style="hanging">
<t hangText="Delay Accuracy:">
<vspace blankLines="0"/> +-8ns (i.e. +-1/32 Tc, where Tc is the UMTS
Chip time of 1/3.84 MHz) resulting in a round trip accuracy of
+-16ns. The value is this low to meet the 3GPP Timing Alignment
Error (TAE) measurement requirements. </t>
<t hangText="Packet Delay Variation:">
<vspace blankLines="0"/> Packet Delay Variation (PDV aka Jitter aka
Timing Alignment Error) is problematic to Fronthaul networks and
must be minimized. If the transport network cannot guarantee low
enough PDV then additional buffering has to be introduced at the
edges of the network to buffer out the jitter. Buffering is not
desirable as it reduces the total available delay budget. </t>
<t>
<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>
<t hangText="Transport link contribution to radio frequency error:">
<vspace blankLines="0"/>+-2 PPB. This value is considered to be
"available" for the Fronthaul link out of the total 50 PPB budget
reserved for the radio interface. Note: the reason that the
transport link contributes to radio frequency error is as follows.
The current way of doing Fronthaul is from the radio unit to remote
radio head directly. The remote radio head is essentially a passive
device (without buffering etc.) The transport drives the antenna
directly by feeding it with samples and everything the transport
adds will be introduced to radio as-is. So if the transport causes
additional frequence error that shows immediately on the radio as
well.</t>
</list>
</t>
<t> The above listed time synchronization requirements are difficult to meet
with point-to-point connected networks, and more difficult when the network
includes multiple hops. It is expected that networks must include buffering
at the ends of the connections as imposed by the jitter requirements, 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 makes it easier to meet the end-to-end requirements. </t>
<t> In order to meet the timing requirements both senders and receivers must
remain time synchronized, demanding very accurate clock distribution, for
example support for IEEE 1588 transparent clocks in every intermediate node. </t>
<t> In cellular networks from the LTE radio era onward, phase synchronization is
needed in addition to frequency synchronization (<xref target="TS36300"/>,
<xref target="TS23401"/>). </t>
</section>
<section title="Time-Sensitive Stream Requirements">
<t>In addition to the time synchronization requirements listed in Section <xref
target="cr_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 imply a packet error rate (PER) of 2.4*10^-9
(assuming ~300 bytes packets). Retransmitting lost packets and/or using
forward error correction (FEC) to circumvent bit errors is practically
impossible due to the additional delay incurred. Using redundant streams for
better guarantees for delivery is also practically impossible in many cases
due to high bandwidth requirements of Fronthaul networks. For instance,
current uncompressed CPRI bandwidth expansion ratio is roughly 20:1 compared
to the IP layer user payload it carries. Protection switching is also a
candidate but current technologies for the path switch are too slow. We do
not currently know of a better solution for this issue.</t>
<t> Fronthaul links are assumed to be symmetric, and all Fronthaul streams (i.e.
those carrying radio data) have equal priority and cannot delay or pre-empt
each other. This implies that the network must guarantee that each
time-sensitive flow meets their schedule. </t>
</section>
<section title="Security Considerations">
<t> Establishing time-sensitive streams in the network entails reserving
networking resources for long periods of time. It is important that these
reservation requests be authenticated to prevent malicious reservation
attempts from hostile nodes (or accidental misconfiguration). This is
particularly important in the case where the reservation requests span
administrative domains. Furthermore, the reservation information itself
should be digitally signed to reduce the risk of a legitimate node pushing a
stale or hostile configuration into another networking node. </t>
</section>
</section>
<section title="Cellular Radio Networks Today">
<t> Today's Fronthaul networks typically consist of:</t>
<t>
<list style="symbols">
<t> Dedicated point-to-point fiber connection is common </t>
<t> Proprietary protocols and framings </t>
<t> Custom equipment and no real networking</t>
</list>
</t>
<t> Today's Midhaul and Backhaul networks typically consist of:</t>
<t>
<list style="symbols">
<t> Mostly normal IP networks, MPLS-TP, etc.</t>
<t> Clock distribution and sync using 1588 and SyncE</t>
</list>
</t>
<t> Telecommunication networks in the cellular domain are already heading towards
transport networks where precise time synchronization support is one of the
basic building blocks. While the transport networks themselves have practically
transitioned to all-IP packet based networks to meet the bandwidth and cost
requirements, highly accurate clock distribution has become a challenge. </t>
<t>Transport networks in the cellular domain are typically based on Time Division
Multiplexing (TDM-based) and provide frequency synchronization capabilities as a
part of the transport media. Alternatively other technologies such as Global
Positioning System (GPS) or Synchronous Ethernet (SyncE) are used <xref
target="SyncE"/>. </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"/>. </t>
</section>
<section title="Cellular Radio Networks Future">
<t> We would like to see the following in future Cellular Radio networks:</t>
<t>
<list style="symbols">
<t> Unified standards-based transport protocols and standard networking
equipment that can make use of underlying deterministic link-layer
services </t>
<t> Unified and standards-based network management systems and protocols in
all parts of the network (including Fronthaul)</t>
</list>
</t>
<t> 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, on the
order of sub +-20 ns packet delay variation (PDV) and frequency accuracy of
+0.002 PPM <xref target="Fronthaul"/>. </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 are not limited to) solutions directly over Ethernet,
over IP, and MPLS/PseudoWire transport. </t>
<t> Even the current time-sensitive networking features may not be sufficient for
Fronthaul traffic. Therefore, having specific profiles that take the
requirements of Fronthaul into account is desirable <xref target="IEEE8021CM"/>. </t>
<t>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> 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. </t>
<t> Furthermore, not all "user plane" traffic will be IP. Therefore, the same
solution also must 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 targets solutions for time-sensitive (IP/transport)
streams with deterministic properties over Ethernet-based switched networks. </t>
</section>
<section title="Cellular Radio Networks Asks">
<t> A standard for data plane transport specification which is:</t>
<t>
<list style="symbols">
<t> Unified among all *hauls </t>
<t> Deployed in a highly deterministic network environment </t>
</list>
</t>
<t> A standard for data flow information models that are:</t>
<t>
<list style="symbols">
<t> Aware of the time sensitivity and constraints of the target networking
environment </t>
<t> Aware of underlying deterministic networking services (e.g. on the
Ethernet layer) </t>
</list>
</t>
<t> Mapping the Fronthaul requirements to IETF DetNet <xref
target="I-D.finn-detnet-architecture"/> Section 3 "Providing the DetNet
Quality of Service", the relevant features are: <list style="symbols">
<t> Zero congestion loss.</t>
<t> Pinned-down paths.</t>
</list>
</t>
</section>
</section>
<section title="Industrial M2M">
<section title="Use Case Description">
<t> Industrial Automation in general refers to automation of manufacturing, quality
control and material processing. In this "machine to machine" (M2M) use case we
consider machine units in a plant floor which periodically exchange data with
upstream or downstream machine modules and/or a supervisory controller within a
local area network. </t>
<t> The actors of M2M communication are Programmable Logic Controllers (PLCs).
Communication between PLCs and between PLCs and the supervisory PLC (S-PLC) is
achieved via critical control/data streams <xref target="fig_indm2m"/>. </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> This use case focuses on PLC-related communications; communication to
Manufacturing-Execution-Systems (MESs) are not addressed. </t>
<t> This use case covers only critical control/data streams; non-critical traffic
between industrial automation applications (such as communication of state,
configuration, set-up, and database communication) are adequately served by
currently available prioritizing techniques. Such traffic can use up to 80% of
the total bandwidth required. There is also a subset of non-time-critical
traffic that must be reliable even though it is not time sensitive. </t>
<t> In this use case the primary need for deterministic networking is to provide
end-to-end delivery of M2M messages within specific timing constraints, for
example in closed loop automation control. Today this level of determinism is
provided by proprietary networking technologies. In addition, standard
networking technologies are used to connect the local network to remote
industrial automation sites, e.g. over an enterprise or metro network which also
carries other types of traffic. Therefore, flows that should be forwarded with
deterministic guarantees need to be sustained regardless of the amount of other
flows in those networks.</t>
</section>
<section title="Industrial M2M Communication Today">
<t>Today, proprietary networks fulfill the needed timing and availability for M2M
networks.</t>
<t> The network topologies used today by industrial automation are similar to those
used by telecom networks: Daisy Chain, Ring, Hub and Spoke, and Comb (a subset
of Daisy Chain). </t>
<t> PLC-related control/data streams are transmitted periodically and carry either a
pre-configured payload or a payload configured during runtime.</t>
<t> Some industrial applications require time synchronization at the end nodes. For
such time-coordinated PLCs, accuracy of 1 microsecond is required. Even in the
case of "non-time-coordinated" PLCs time sync may be needed e.g. for
timestamping of sensor data.</t>
<t> Industrial network scenarios require advanced security solutions. Many of the
current industrial production networks are physically separated. Preventing
critical flows from be leaked outside a domain is handled today by filtering
policies that are typically enforced in firewalls. </t>
<section anchor="sec_m2mtr" title="Transport Parameters">
<t> The Cycle Time defines the frequency of message(s) between industrial
actors. The Cycle Time is application dependent, in the range of 1ms - 100ms
for critical control/data streams.</t>
<t> Because industrial applications assume deterministic transport for critical
Control-Data-Stream parameters (instead of defining latency and delay
variation parameters) it is sufficient to fulfill the upper bound of latency
(maximum latency). The underlying networking infrastructure 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> The 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. Usually no more than 20% of available bandwidth
is used for critical control/data streams. In today's networks 1Gbps links
are commonly used.</t>
<t> Most PLC control loops are rather tolerant of packet loss, however critical
control/data streams accept no more than 1 packet loss per consecutive
communication cycle (i.e. if a packet gets lost in cycle "n", then the next
cycle ("n+1") must be lossless). After two or more consecutive packet losses
the network may be considered to be "down" by the Application.</t>
<t> As network downtime may impact the whole production system the required
network availability is rather high (99,999%).</t>
<t> Based on the above parameters we expect that some form of redundancy will be
required for M2M communications, however any individual solution depends on
several parameters including cycle time, delivery time, etc. </t>
</section>
<section anchor="sec_m2mfm" title="Stream Creation and Destruction">
<t> In an industrial environment, critical control/data streams are created
rather infrequently, on the order of ~10 times per day / week / month. Most
of these critical control/data streams get created at machine startup,
however flexibility is also needed during runtime, for example when adding
or removing a machine. Going forward as production systems become more
flexible, we expect a significant increase in the rate at which streams are
created, changed and destroyed. </t>
</section>
</section>
<section title="Industrial M2M Future">
<t>We would like to see the various proprietary networks replaced with a converged
IP-standards-based network with deterministic properties that can satisfy the
timing, security and reliability constraints described above.</t>
</section>
<section title="Industrial M2M Asks">
<t>
<list style="symbols">
<t> Converged IP-based network </t>
<t> Deterministic behavior (bounded latency and jitter )</t>
<t> High availability (presumably through redundancy) (99.999 %)</t>
<t> Low message delivery time (100us - 50ms) </t>
<t> Low packet loss (burstless, 0.1-1 %)</t>
<t> Precise time synchronization accuracy (1us) </t>
<t> Security (e.g. prevent critical flows from being leaked between
physically separated networks) </t>
</list>
</t>
</section>
</section>
<section title="Other Use Cases">
<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">
<section title="Pro Audio">
<t> This section was derived from draft-gunther-detnet-proaudio-req-01. </t>
<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 title="Utility Telecom">
<t> This section was derived from draft-wetterwald-detnet-utilities-reqs-02. </t>
<t>Faramarz Maghsoodlou, Ph. D. IoT Connected Industries and Energy Practice Cisco </t>
<t>Pascal Thubert, CTAO Cisco</t>
</section>
<section title="Building Automation Systems">
<t> This section was derived from draft-bas-usecase-detnet-00. </t>
</section>
<section title="Wireless for Industrial">
<t> This section was derived from draft-thubert-6tisch-4detnet-01. </t>
<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 title="Cellular Radio">
<t> This section was derived from draft-korhonen-detnet-telreq-00. </t>
</section>
<section title="Industrial M2M">
<t>The authors would like to thank Feng Chen and Marcel Kiessling for their comments
and suggestions.</t>
</section>
<section title="Other">
<t> This section was derived from draft-zha-detnet-use-case-00. </t>
<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>
</section>
</middle>
<!-- *****BACK MATTER ***** -->
<back>
<!-- References (all are considered informative for a use case draft) -->
<references title="Informative References">
<!--?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.2119.xml"?-->
&RFC2119; <reference anchor="ISO7240-16"
target="http://www.iso.org/iso/catalogue_detail.htm?csnumber=42978">
<front>
<title>ISO 7240-16:2007 Fire detection and alarm systems -- Part 16: Sound
system control and indicating equipment</title>
<author>
<organization>ISO</organization>
</author>
<date year="2007"/>
</front>
</reference>
<reference anchor="CONTENT_PROTECTION"
target="http://grouper.ieee.org/groups/1722/contributions/2012/avtp_dolsen_1722a_content_protection.pdf">
<front>
<title>1722a Content Protection</title>
<author initials="D" surname="Olsen">
<organization>Harman</organization>
</author>
<date year="2012"/>
</front>
</reference>
<reference anchor="ESPN_DC2"
target="http://sportsvideo.org/main/blog/2014/06/espns-dc2-scales-avb-large">
<front>
<title>ESPN's DC2 Scales AVB Large</title>
<author initials="D" surname="Daley">
<organization>Sports Video Group</organization>
</author>
<date year="2014"/>
</front>
</reference>
<reference anchor="SRP_LATENCY"
target="http://www.ieee802.org/1/files/public/docs2014/cc-cgunther-acceptable-latency-0314-v01.pdf">
<front>
<title>Specifying SRP Latency</title>
<author initials="C" surname="Gunther">
<organization>Harman International</organization>
</author>
<date year="2014"/>
</front>
</reference>
<reference anchor="STUDIO_IP"
target="http://www.ieee802.org/1/files/public/docs2047/avb-mace-ip-networked-studio-infrastructure-0107.pdf">
<front>
<title>IP Networked Studio Infrastructure for Synchronized & Real-Time
Multimedia Transmissions</title>
<author initials="G" surname="Mace">
<organization>CR / CP&M Lab (Rennes / France)</organization>
</author>
<date year="2007"/>
</front>
</reference>
<reference anchor="DCI" target="http://www.dcimovies.com/">
<front>
<title>DCI Specification, Version 1.2</title>
<author>
<organization>Digital Cinema Initiatives, LLC</organization>
</author>
<date year="2012"/>
</front>
</reference>
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<?rfc include="reference.RFC.7554"?>
<?rfc include='reference.I-D.ietf-6tisch-terminology'?>
<?rfc include='reference.I-D.ietf-6tisch-architecture'?>
<?rfc include='reference.I-D.ietf-6tisch-6top-interface'?>
<?rfc include='reference.I-D.ietf-6tisch-coap'?>
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<?rfc include="reference.RFC.2460"?>
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<?rfc include="reference.RFC.2474"?>
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<?rfc include="reference.RFC.3209"?>
<!-- RSVP TE -->
<?rfc include="reference.RFC.4291"?>
<!-- IP Version 6 Addressing Architecture -->
<?rfc include="reference.RFC.3444"?>
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<?rfc include="reference.RFC.3972"?>
<!-- Cryptographically Generated Addresses -->
<?rfc include="reference.RFC.4919"?>
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<?rfc include="reference.RFC.4903"?>
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<?rfc include="reference.RFC.6282"?>
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<?rfc include="reference.RFC.6550"?>
<!-- RPL: IPv6 Routing Protocol for Low-Power and Lossy Networks -->
<?rfc include="reference.RFC.6551"?>
<!-- RPL: IPv6 Routing Protocol for Low-Power and Lossy Networks -->
<?rfc include="reference.RFC.6775"?>
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<?rfc include='reference.I-D.ietf-ipv6-multilink-subnets'?>
<?rfc include='reference.I-D.ietf-roll-rpl-industrial-applicability'?>
<?rfc include='reference.I-D.thubert-6lowpan-backbone-router'?>
<?rfc include='reference.I-D.svshah-tsvwg-deterministic-forwarding'?>
<?rfc include='reference.I-D.wang-6tisch-6top-sublayer'?>
<reference anchor="IEEE802154">
<front>
<title>IEEE std. 802.15.4, Part. 15.4: Wireless Medium Access Control (MAC) and
Physical Layer (PHY) Specifications for Low-Rate Wireless Personal Area
Networks </title>
<author>
<organization>IEEE standard for Information Technology</organization>
</author>
<date/>
</front>
</reference>
<reference anchor="IEEE802154e">
<front>
<title>IEEE standard for Information Technology, IEEE std. 802.15.4, Part. 15.4:
Wireless Medium Access Control (MAC) and Physical Layer (PHY) Specifications
for Low-Rate Wireless Personal Area Networks, June 2011 as amended by IEEE
std. 802.15.4e, Part. 15.4: Low-Rate Wireless Personal Area Networks
(LR-WPANs) Amendment 1: MAC sublayer </title>
<author>
<organization>IEEE standard for Information Technology</organization>
</author>
<date month="April" year="2012"/>
</front>
</reference>
<reference anchor="IEEE802.1TSNTG"
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<front>
<title>IEEE 802.1 Time-Sensitive Networks Task Group</title>
<author>
<organization>IEEE Standards Association</organization>
</author>
<date day="08" month="March" year="2013"/>
</front>
</reference>
<reference anchor="WirelessHART">
<front>
<title>Industrial Communication Networks - Wireless Communication Network and
Communication Profiles - WirelessHART - IEC 62591</title>
<author>
<organization>www.hartcomm.org</organization>
</author>
<date year="2010"/>
</front>
</reference>
<reference anchor="HART">
<front>
<title>Highway Addressable remote Transducer, a group of specifications for
industrial process and control devices administered by the HART
Foundation</title>
<author>
<organization>www.hartcomm.org</organization>
</author>
<date/>
</front>
</reference>
<reference anchor="ISA100.11a"
target="http://www.isa.org/Community/SP100WirelessSystemsforAutomation">
<front>
<title>Wireless Systems for Industrial Automation: Process Control and Related
Applications - ISA100.11a-2011 - IEC 62734</title>
<author>
<organization>ISA/ANSI</organization>
</author>
<date year="2011"/>
</front>
</reference>
<reference anchor="ISA100" target="https://www.isa.org/isa100/">
<front>
<title>ISA100, Wireless Systems for Automation</title>
<author>
<organization>ISA/ANSI</organization>
</author>
<date/>
</front>
</reference>
<reference anchor="TEAS" target="https://datatracker.ietf.org/doc/charter-ietf-teas/">
<front>
<title>Traffic Engineering Architecture and Signaling</title>
<author>
<organization>IETF</organization>
</author>
<date/>
</front>
</reference>
<reference anchor="PCE" target="https://datatracker.ietf.org/doc/charter-ietf-pce/">
<front>
<title>Path Computation Element</title>
<author>
<organization>IETF</organization>
</author>
<date/>
</front>
</reference>
<reference anchor="CCAMP" target="https://datatracker.ietf.org/doc/charter-ietf-ccamp/">
<front>
<title>Common Control and Measurement Plane</title>
<author>
<organization>IETF</organization>
</author>
<date/>
</front>
</reference>
<reference anchor="DICE" target="https://datatracker.ietf.org/doc/charter-ietf-dice/">
<front>
<title>DTLS In Constrained Environments</title>
<author>
<organization>IETF</organization>
</author>
<date/>
</front>
</reference>
<reference anchor="ACE" target="https://datatracker.ietf.org/doc/charter-ietf-ace/">
<front>
<title>Authentication and Authorization for Constrained Environments</title>
<author>
<organization>IETF</organization>
</author>
<date/>
</front>
</reference>
<?rfc include='reference.I-D.finn-detnet-problem-statement'?>
<reference anchor="IEC61850-90-12">
<front>
<title>IEC 61850-90-12 TR: Communication networks and systems for power utility
automation - Part 90-12: Wide area network engineering guidelines</title>
<author initials="IEC" surname="TC57 WG10">
<organization abbrev="IEC">International Electrotechnical
Commission</organization>
</author>
<date year="2015"/>
</front>
</reference>
<reference anchor="IEC62439-3:2012">
<front>
<title>IEC 62439-3: Industrial communication networks - High availability
automation networks - Part 3: Parallel Redundancy Protocol (PRP) and
High-availability Seamless Redundancy (HSR)</title>
<author initials="IEC" surname="TC65">
<organization abbrev="IEC">International Electrotechnical
Commission</organization>
</author>
<date year="2012"/>
</front>
</reference>
<?rfc include='reference.I-D.ietf-tictoc-1588overmpls'?>
<?rfc include='reference.I-D.kh-spring-ip-ran-use-case'?>
<?rfc include='reference.I-D.mirsky-mpls-residence-time'?>
<?rfc include="reference.RFC.3031"?>
<?rfc include="reference.RFC.3985"?>
<?rfc include="reference.RFC.5087"?>
<?rfc include="reference.RFC.5086"?>
<?rfc include="reference.RFC.4553"?>
<?rfc include="reference.RFC.3393"?>
<reference anchor="CPRI"
target="http://www.cpri.info/downloads/CPRI_v_6_1_2014-07-01.pdf">
<front>
<title>Common Public Radio Interface (CPRI); Interface Specification</title>
<author>
<organization>CPRI Cooperation</organization>
</author>
<date day="1" month="July" year="2014"/>
</front>
<seriesInfo name="CPRI Specification" value="V6.1"/>
</reference>
<reference anchor="TSNTG" target="http://www.IEEE802.org/1/pages/avbridges.html">
<front>
<title>IEEE 802.1 Time-Sensitive Networks Task Group</title>
<author>
<organization>IEEE Standards Association</organization>
</author>
<date year="2013"/>
</front>
</reference>
<reference anchor="IEEE8021AS"
target="http://standards.ieee.org/getIEEE802/download/802.1AS-2011.pdf">
<front>
<title>Timing and Synchronizations (IEEE 802.1AS-2011)</title>
<author>
<organization>IEEE</organization>
</author>
<date year="2011"/>
</front>
<seriesInfo name="IEEE" value="802.1AS-2001"/>
</reference>
<reference anchor="IEEE1722"
target="http://standards.ieee.org/findstds/standard/1722-2011.html">
<front>
<title>1722-2011 - IEEE Standard for Layer 2 Transport Protocol for Time
Sensitive Applications in a Bridged Local Area Network</title>
<author>
<organization>IEEE</organization>
</author>
<date year="2011"/>
</front>
<seriesInfo name="IEEE Std" value="1722-2011"/>
</reference>
<reference anchor="IEEE1588"
target="http://standards.ieee.org/findstds/standard/1588-2008.html">
<front>
<title>IEEE Standard for a Precision Clock Synchronization Protocol for
Networked Measurement and Control Systems</title>
<author>
<organization>IEEE</organization>
</author>
<date year="2008"/>
</front>
<seriesInfo name="IEEE Std" value="1588-2008"/>
</reference>
<reference anchor="SyncE" target="http://www.itu.int/rec/T-REC-G.8261">
<front>
<title>G.8261 : Timing and synchronization aspects in packet networks</title>
<author>
<organization>ITU-T</organization>
</author>
<date month="August" year="2013"/>
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<seriesInfo name="Recommendation" value="G.8261"/>
<format type="HTML" target="http://www.itu.int/rec/T-REC-G.8261"/>
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<reference anchor="MEF"
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<front>
<title>Mobile Backhaul Phase 2 Amendment 1 -- Small Cells</title>
<author>
<organization>MEF</organization>
</author>
<date month="July" year="2014"/>
</front>
<seriesInfo name="MEF" value="22.1.1"/>
<format type="PDF"
target="http://www.mef.net/Assets/Technical_Specifications/PDF/MEF_22.1.1.pdf"/>
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<reference anchor="TS23401">
<front>
<title>General Packet Radio Service (GPRS) enhancements for Evolved Universal
Terrestrial Radio Access Network (E-UTRAN) access</title>
<author>
<organization>3GPP</organization>
</author>
<date day="07" month="March" year="2013"/>
</front>
<seriesInfo name="3GPP TS" value="23.401 10.10.0"/>
<format type="HTML" target="http://www.3gpp.org/ftp/Specs/html-info/23401.htm"/>
</reference>
<reference anchor="TS25104">
<front>
<title>Base Station (BS) radio transmission and reception (FDD)</title>
<author>
<organization>3GPP</organization>
</author>
<date day="23" month="March" year="2007"/>
</front>
<seriesInfo name="3GPP TS" value="25.104 3.14.0"/>
<format type="HTML" target="http://www.3gpp.org/ftp/Specs/html-info/25104.htm"/>
</reference>
<reference anchor="TS36104">
<front>
<title>Evolved Universal Terrestrial Radio Access (E-UTRA); Base Station (BS)
radio transmission and reception</title>
<author>
<organization>3GPP</organization>
</author>
<date day="07" month="July" year="2013"/>
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<seriesInfo name="3GPP TS" value="36.104 10.11.0"/>
<format type="HTML" target="http://www.3gpp.org/ftp/Specs/html-info/36104.htm"/>
</reference>
<reference anchor="TS36211">
<front>
<title>Evolved Universal Terrestrial Radio Access (E-UTRA); Physical channels
and modulation</title>
<author>
<organization>3GPP</organization>
</author>
<date day="15" month="March" year="2013"/>
</front>
<seriesInfo name="3GPP TS" value="36.211 10.7.0"/>
<format type="HTML" target="http://www.3gpp.org/ftp/Specs/html-info/36211.htm"/>
</reference>
<reference anchor="TS36133">
<front>
<title>Evolved Universal Terrestrial Radio Access (E-UTRA); Requirements for
support of radio resource management</title>
<author>
<organization>3GPP</organization>
</author>
<date day="3" month="April" year="2015"/>
</front>
<seriesInfo name="3GPP TS" value="36.133 12.7.0"/>
<format type="HTML" target="http://www.3gpp.org/ftp/Specs/html-info/36133.htm"/>
</reference>
<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"/>
<format type="HTML" target="http://www.3gpp.org/ftp/Specs/html-info/36300.htm"/>
</reference>
<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>
</author>
<author initials="T." surname="Mustala" fullname="Tero Mustala">
<organization>Nokia</organization>
</author>
<date day="5" month="February" year="2015"/>
</front>
<seriesInfo name="IEEE" value="1904.3"/>
<format type="PDF"
target="http://www.ieee1904.org/3/meeting_archive/2015/02/tf3_1502_chen_1a.pdf"
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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>
<author initials="J. F." surname="Farkas" fullname="Janos Farkas">
<organization>Ericsson</organization>
</author>
<date day="16" month="April" year="2015"/>
</front>
<seriesInfo name="Unapproved PAR, PAR for a New IEEE Standard; IEEE"
value="P802.1CM"/>
<format type="PDF"
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</reference>
<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>
<author>
<organization>METIS</organization>
</author>
<date month="April" year="2013"/>
</front>
<seriesInfo name="ICT-317669-METIS/D1.1" value="ICT-317669-METIS/D1.1"/>
<format type="PDF"
target="https://www.metis2020.com/wp-content/uploads/deliverables/METIS_D1.1_v1.pdf"
/>
</reference>
<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>
</author>
<date month="June" year="2013"/>
</front>
<seriesInfo name="Ericsson white paper" value="wp-5g"/>
<format type="PDF" target="http://www.ericsson.com/res/docs/whitepapers/wp-5g.pdf"/>
</reference>
<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"/>
<format type="PDF"
target="https://www.ngmn.org/uploads/media/NGMN_RANEV_D3_CoMP_Evaluation_and_Enhancement_v2.0.pdf"
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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>
<author initials="S" surname="Johnston">
<organization>OpenSignal</organization>
</author>
<date month="March" year="2014"/>
</front>
</reference>
<reference anchor="EA12">
<front>
<title>Industrial Internet: Pushing the Boundaries of Minds and Machines</title>
<author initials="P. C." surname="Evans">
<organization>OpenSignal</organization>
</author>
<author initials="M" surname="Annunziata">
<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"/>
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value="PetrHolub_presentation"/>
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</reference>
<reference anchor="bacnetip">
<front>
<title>Annex J to ANSI/ASHRAE 135-1995 - BACnet/IP</title>
<author>
<organization abbrev="ASHRAE"> ASHRAE </organization>
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<date month="January" year="1999"/>
</front>
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<reference anchor="knx">
<front>
<title>ISO/IEC 14543-3 - KNX</title>
<author>
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<date month="November" year="2006"/>
</front>
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<reference anchor="lontalk">
<front>
<title>LonTalk(R) Protocol Specification Version 3.0</title>
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<organization abbrev="ECHELON"> ECHELON </organization>
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<date year="1994"/>
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<reference anchor="modbus">
<front>
<title>MODBUS APPLICATION PROTOCOL SPECIFICATION V1.1b</title>
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<organization abbrev="Modbus"> Modbus Organization </organization>
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<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
v01 2016-02-09 EAG Add Industrial M2M section from Varga et al.
v02 2016-02-10 EAG Edit M2M section.
v03 2016-02-16 EAG Edit BAS and Cellular Radio sections.
-->
</back>
</rfc>
| PAFTECH AB 2003-2026 | 2026-04-23 09:25:10 |