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<front>
<title abbrev="DetNet Use Cases"> Deterministic Networking Use Cases</title>
<author fullname="Ethan Grossman" initials="E.A.G." role="editor" surname="Grossman">
<organization abbrev="DOLBY">Dolby Laboratories, Inc.</organization>
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<author fullname="Craig Gunther" initials="C.A.G." surname="Gunther">
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<email>craig.gunther@harman.com</email>
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<author fullname="Jean Raymond" initials="J" surname="Raymond">
<organization abbrev="HYDRO-QUEBEC"> Hydro-Quebec </organization>
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<email>raymond.jean@hydro.qc.ca</email>
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<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 fullname="Yu Kaneko" initials="Y" surname="Kaneko">
<organization>Toshiba</organization>
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<author fullname="Subir Das" initials="S" surname="Das">
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<author fullname="Yiyong Zha" initials="Y.Z." surname="Zha">
<organization abbrev="HUAWEI">Huawei Technologies</organization>
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<author fullname="Balázs Varga" initials="B." surname="Varga">
<organization>Ericsson</organization>
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<author initials="X." surname="Vilajosana" fullname="Xavier Vilajosana">
<organization>Worldsensing</organization>
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<author initials="T." surname="Mahmoodi" fullname="Toktam Mahmoodi">
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<author initials="S." surname="Spirou" fullname="Spiros Spirou">
<organization>Intracom Telecom</organization>
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<email>spis@intracom-telecom.com </email>
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<author initials="P." surname="Vizarreta" fullname="Petra Vizarreta">
<organization>Technical University of Munich, TUM</organization>
<address>
<postal>
<street>Maxvorstadt, ArcisstraBe 21</street>
<city>Munich</city>
<region>Germany</region>
<code>80333</code>
<country>Germany</country>
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<email>petra.vizarreta@lkn.ei.tum.de</email>
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</author>
<date month="October" 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 and Video">
<section title="Use Case Description">
<t>The professional audio and video industry ("ProAV") includes: <list
style="symbols">
<t> Music and film content creation </t>
<t> Broadcast </t>
<t> Cinema </t>
<t> Live sound </t>
<t> Public address, media and emergency systems at large venues (airports,
stadiums, churches, theme parks).</t>
</list>
</t>
<t> These industries have already transitioned audio and video signals from analog
to digital. However, the digital 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 transitioning to packet-based infrastructure to reduce
cost, increase routing flexibility, and integrate with existing IT
infrastructure. </t>
<t>Today ProAV applications have no way to establish deterministic streams from a
standards-based Layer 3 (IP) interface, which is a fundamental limitation to the
use cases described here. Today deterministic streams can be created within
standards-based layer 2 LANs (e.g. using IEEE 802.1 AVB) however these are not
routable via IP and thus are not effective for distribution over wider areas
(for example broadcast events that span wide geographical areas).</t>
<t>It would be highly desirable if such streams could be routed over the open
Internet, however solutions with more limited scope (e.g. enterprise networks)
would still provide a substantial improvement. </t>
<t>The following sections describe specific ProAV use cases.</t>
<section title="Uninterrupted Stream Playback">
<t>Transmitting audio and video streams for live playback is unlike common file
transfer because uninterrupted stream playback in the presence of network
errors 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. Buffering can be used to provide enough delay to allow
time for one or more retries, however this is not an effective solution in
applications where large delays (latencies) are not acceptable (as discussed
below).</t>
<t>Streams with guaranteed bandwidth can eliminate congestion on the network as
a cause of transmission errors that would lead to playback interruption. Use
of redundant paths can further mitigate transmission errors to provide
greater stream reliability.</t>
</section>
<section title="Synchronized Stream Playback">
<t>Latency in this context is the time between when a signal is initially sent
over a stream and when it is received. A common example in ProAV is
time-synchronizing audio and video when they take separate paths through the
playback system. In this case the latency of both the audio and video
streams must be bounded and consistent if the sound is to remain matched to
the movement in the video. 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) delay (buffer) 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>
<section title="Sound Reinforcement">
<t>Consider the latency (delay) from when a person speaks into a microphone to
when their voice emerges from the speaker. If this delay is longer than
about 10-15 milliseconds it is noticeable and can make a sound reinforcement
system unusable (see slide 6 of [SRP_LATENCY]). (If you have ever tried to
speak in the presence of a delayed echo of your voice you may know this
experience).</t>
<t>Note that the 15ms latency bound includes all parts of the signal path, not
just the network, so the network latency must be significantly less than
15ms.</t>
<t>In some cases local performers must perform in synchrony with a remote
broadcast. In such cases the latencies of the broadcast stream and the local
performer must be adjusted to match each other, with a worst case of one
video frame (33ms for NTSC video). </t>
<t>In cases where audio phase is a consideration, for example beam-forming using
multiple speakers, latency requirements can be in the 10 microsecond range
(1 audio sample at 96kHz).</t>
</section>
<section title="Deterministic Time to Establish Streaming">
<t>Note: It is still under WG discussion whether this topic (stream startup
time) is within scope of DetNet. </t>
<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 (video stream) to another (see <xref target="STUDIO_IP"
/> and <xref target="ESPN_DC2"/>).</t>
</section>
<section title="Secure Transmission">
<section title="Safety">
<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). </t>
</section>
</section>
</section>
<section title="Pro Audio Today">
<t>Some proprietary systems have been created which enable deterministic streams at
Layer 3 however they are "engineered networks" which require careful
configuration to operate, often require that the system be over-provisioned, 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>
</section>
<section title="Pro Audio Future">
<section title="Layer 3 Interconnecting Layer 2 Islands">
<t>It would be valuable to enable IP to connect multiple Layer 2 LANs. </t>
<t>As an example, 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
<xref target="ESPN_DC2"/> ).</t>
<t>In designing DC2 they replaced as much point-to-point technology as they
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. However to interconnect these
layer 2 LAN islands together they ended up using dedicated paths in a custom
SDN (Software Defined Networking) router because there is no standards-based
routing solution available.</t>
</section>
<section title="High Reliability Stream Paths">
<t>On-air and other live media streams are often 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="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="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 reserve large quantities of bandwidth and then never un-reserve it even
though they are not using it, and soon the network will have no bandwidth
left").</t>
</section>
<section title="Traffic Segregation">
<t>Note: It is still under WG discussion whether this topic will be addressed by
DetNet.</t>
<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 title="Latency Optimization by a Central Controller">
<t>A central network 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 <xref target="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 <xref target="SRP_LATENCY"/>.</t>
</section>
<section title="Reduced Device Cost Due To Reduced Buffer Memory">
<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 title="Pro Audio Asks">
<t>
<list style="symbols">
<t>Layer 3 routing on top of AVB (and/or other high QoS networks)</t>
<t>Content delivery with bounded, lowest possible latency</t>
<t>IntServ and DiffServ integration with AVB (where practical)</t>
<t>Single network for A/V and IT traffic</t>
<t>Standards-based, interoperable, multi-vendor</t>
<t>IT department friendly</t>
<t>Enterprise-wide networks (e.g. size of San Francisco but not the whole
Internet (yet...)) </t>
</list>
</t>
</section>
</section>
<section title="Electrical Utilities">
<section title="Use Case Description">
<t> Many systems that an electrical utility deploys today rely on high availability
and deterministic behavior of the underlying networks. Here we present use cases
in Transmission, Generation and Distribution, including key timing and
reliability metrics. We also discuss security issues and industry trends which
affect the architecture of next generation utility networks</t>
<section title="Transmission Use Cases">
<section title="Protection">
<t> Protection means not only the protection of human operators but also the
protection of the electrical equipment and the preservation of the
stability and frequency of the grid. If a fault occurs in the
transmission or distribution of electricity then severe damage can occur
to human operators, electrical equipment and the grid itself, leading to
blackouts. </t>
<t> Communication links in conjunction with protection relays are used to
selectively isolate faults on high voltage lines, transformers, reactors
and other important electrical equipment. The role of the teleprotection
system is to selectively disconnect a faulty part by transferring
command signals within the shortest possible time.</t>
<section title="Key Criteria">
<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>
</t>
<t>Additional elements of the the teleprotection system that impact its
performance include:</t>
<t>
<list style="symbols">
<t> Network bandwidth</t>
<t> Failure recovery capacity (aka resiliency)</t>
</list>
</t>
</section>
<section title="Fault Detection and Clearance Timing">
<t> 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. </t>
<t>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="Symmetric Channel Delay">
<t>Note: It is currently under WG discussion whether symmetric path
delays are to be guaranteed by DetNet.</t>
<t> Teleprotection channels which are differential must be synchronous,
which means that any delays on the transmit and receive paths must
match each other. Teleprotection systems ideally support zero
asymmetric delay; typical legacy relays can tolerate delay
discrepancies of up to 750us.</t>
<t> Some tools available for lowering delay variation below this
threshold are: </t>
<t>
<list style="symbols">
<t>For legacy systems using Time Division Multiplexing (TDM),
jitter buffers 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. </t>
<t>For jitter-prone IP packet networks, traffic management tools
can ensure that the teleprotection signals receive the
highest transmission priority to minimize jitter. </t>
<t>Standard packet-based synchronization technologies, such as
1588-2008 Precision Time Protocol (PTP) and Synchronous
Ethernet (Sync-E), can help keep networks stable by
maintaining a highly accurate clock source on the various
network devices.</t>
</list>
</t>
</section>
<section title="Teleprotection Network Requirements (IEC 61850)">
<t>The following table captures the main network metrics as based on the
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 title="Inter-Trip Protection scheme">
<t>"Inter-tripping" is the signal-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. </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. At both end of the
lines the current is measured by the differential relays, and 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. 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 metrics">
<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. The network metrics are similar (but not
identical to) 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 MU 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>
<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 MU. The CT/VT in the substation send the sampled
value (analog voltage or current) to the MU over hard wire. The MU 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 the MU through a serial port or IEEE 1588 protocol
via a 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>
<c>Consecutive Packet Loss</c>
<c>At least 1 packet per application cycle must be received.</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. <xref target="table11"/> summarizes 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="Generation Use Case">
<t> Energy generation systems are complex infrastructures that require control
of both the generated power and the generation infrastructure.</t>
<section title="Control of the Generated Power">
<t> The electrical power generation frequency must be maintained within a
very narrow band. Deviations from the acceptable frequency range are
detected and the required signals are sent to the power plants for
frequency regulation. </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. </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 title="Control of the Generation Infrastructure">
<t> The control of the generation infrastructure combines requirements from
industrial automation systems and energy generation systems. In this
section we present the use case of the control of the generation
infrastructure of a wind turbine.</t>
<figure title="Wind Turbine Control Network" anchor="fig-windturbine">
<artwork align="center"><![CDATA[
|
|
| +-----------------+
| | +----+ |
| | |WTRM| WGEN |
WROT x==|===| | |
| | +----+ WCNV|
| |WNAC |
| +---+---WYAW---+--+
| | |
| | | +----+
|WTRF | |WMET|
| | | |
Wind Turbine | +--+-+
Controller | |
WTUR | | |
WREP | | |
WSLG | | |
WALG | WTOW | |
]]></artwork>
</figure>
<t>
<xref target="fig-windturbine"/> presents the subsystems that operate a
wind turbine. These subsystems include </t>
<t>
<list style="symbols">
<t>WROT (Rotor Control)</t>
<t>WNAC (Nacelle Control) (nacelle: housing containing the
generator)</t>
<t>WTRM (Transmission Control)</t>
<t>WGEN (Generator)</t>
<t>WYAW (Yaw Controller) (of the tower head)</t>
<t>WCNV (In-Turbine Power Converter)</t>
<t>WMET (External Meteorological Station providing real time
information to the controllers of the tower)</t>
</list>
</t>
<t> Traffic characteristics relevant for the network planning and
dimensioning process in a wind turbine scenario are listed below. The
values in this section are based mainly on the relevant references <xref
target="Ahm14"/> and <xref target="Spe09"/>. Each logical node
(<xref target="fig-windturbine"/>) is a part of the metering network
and produces analog measurements and status information which must
comply with their respective data rate constraints.</t>
<texttable align="center" style="full" suppress-title="false"
title="Wind Turbine Data Rate Constraints" anchor="tab_winturb1">
<preamble/>
<ttcol align="center">Subsystem</ttcol>
<ttcol align="center">Sensor Count</ttcol>
<ttcol align="center">Analog Sample Count</ttcol>
<ttcol align="center">Data Rate (bytes/sec)</ttcol>
<ttcol align="center">Status Sample Count</ttcol>
<ttcol align="center">Data rate (bytes/sec)</ttcol>
<c>WROT</c>
<c>14</c>
<c>9</c>
<c>642</c>
<c>5</c>
<c>10</c>
<c>WTRM</c>
<c>18</c>
<c>10</c>
<c>2828</c>
<c>8</c>
<c>16</c>
<c>WGEN</c>
<c>14</c>
<c>12</c>
<c>73764</c>
<c>2</c>
<c>4</c>
<c>WCNV</c>
<c>14</c>
<c>12</c>
<c>74060</c>
<c>2</c>
<c>4</c>
<c>WTRF</c>
<c>12</c>
<c>5</c>
<c>73740</c>
<c>2</c>
<c>4</c>
<c>WNAC</c>
<c>12</c>
<c>9</c>
<c>112</c>
<c>3</c>
<c>6</c>
<c>WYAW</c>
<c>7</c>
<c>8</c>
<c>220</c>
<c>4</c>
<c>8</c>
<c>WTOW</c>
<c>4</c>
<c>1</c>
<c>8</c>
<c>3</c>
<c>6</c>
<c>WMET</c>
<c>7</c>
<c>7</c>
<c>228</c>
<c>-</c>
<c>-</c>
<postamble/>
</texttable>
<t> Quality of Service (QoS) constraints for different services are
presented in <xref target="tab_winturb2"/>. These constraints are
defined by IEEE 1646 standard <xref target="IEEE1646"/> and IEC 61400
standard <xref target="IEC61400"/>. </t>
<texttable align="center" style="full" suppress-title="false"
title="Wind Turbine Reliability and Latency Constraints"
anchor="tab_winturb2">
<preamble/>
<ttcol align="center">Service</ttcol>
<ttcol align="center">Latency</ttcol>
<ttcol align="center">Reliability</ttcol>
<ttcol align="center">Packet Loss Rate</ttcol>
<c>Analogue measure</c>
<c>16 ms</c>
<c>99.99%</c>
<c>< 10-6</c>
<c>Status information</c>
<c>16 ms</c>
<c>99.99%</c>
<c>< 10-6</c>
<c>Protection traffic</c>
<c>4 ms</c>
<c>100.00%</c>
<c>< 10-9</c>
<c>Reporting and logging</c>
<c>1 s</c>
<c>99.99%</c>
<c>< 10-6</c>
<c>Video surveillance</c>
<c>1 s</c>
<c>99.00%</c>
<c>No specific requirement</c>
<c>Internet connection</c>
<c>60 min</c>
<c>99.00%</c>
<c>No specific requirement</c>
<c>Control traffic</c>
<c>16 ms</c>
<c>100.00%</c>
<c>< 10-9</c>
<c>Data polling</c>
<c>16 ms</c>
<c>99.99%</c>
<c>< 10-6</c>
<postamble/>
</texttable>
<section title="Intra-Domain Network Considerations">
<t> A wind turbine is composed of a large set of subsystems including
sensors and actuators which require time-critical operation. The
reliability and latency constraints of these different subsystems is
shown in <xref target="tab_winturb2"/>. These subsystems are
connected to an intra-domain network which is used to monitor and
control the operation of the turbine and connect it to the SCADA
subsystems. The different components are interconnected using fiber
optics, industrial buses, industrial Ethernet, EtherCat, or a
combination of them. Industrial signaling and control protocols such
as Modbus, Profibus, Profinet and EtherCat are used directly on top
of the Layer 2 transport or encapsulated over TCP/IP. </t>
<t> The Data collected from the sensors and condition monitoring systems
is multiplexed onto fiber cables for transmission to the base of the
tower, and to remote control centers. The turbine controller
continuously monitors the condition of the wind turbine and collects
statistics on its operation. This controller also manages a large
number of switches, hydraulic pumps, valves, and motors within the
wind turbine.</t>
<t>There is usually a controller both at the bottom of the tower and in
the nacelle. The communication between these two controllers usually
takes place using fiber optics instead of copper links. Sometimes, a
third controller is installed in the hub of the rotor and manages
the pitch of the blades. That unit usually communicates with the
nacelle unit using serial communications.</t>
</section>
<section title="Inter-Domain network considerations">
<t> A remote control center belonging to a grid operator regulates the
power output, enables remote actuation, and monitors the health of
one or more wind parks in tandem. It connects to the local control
center in a wind park over the Internet (<xref
target="fig-windturbine-internet"/>) via firewalls at both ends.
The AS path between the local control center and the Wind Park
typically involves several ISPs at different tiers. For example, a
remote control center in Denmark can regulate a wind park in Greece
over the normal public AS path between the two locations. </t>
<t> The remote control center is part of the SCADA system, setting the
desired power output to the wind park and reading back the result
once the new power output level has been set. Traffic between the
remote control center and the wind park typically consists of
protocols like IEC 60870-5-104 <xref target="IEC-60870-5-104"/>, OPC
XML-DA <xref target="OPCXML"/>, Modbus <xref target="MODBUS"/>, and
SNMP <xref target="RFC3411"/>. Currently, traffic flows between the
wind farm and the remote control center are best effort. QoS
requirements are not strict, so no SLAs or service provisioning
mechanisms (e.g., VPN) are employed. In case of events like
equipment failure, tolerance for alarm delay is on the order of
minutes, due to redundant systems already in place.</t>
<figure title="Wind Turbine Control via Internet"
anchor="fig-windturbine-internet">
<artwork align="center"><![CDATA[
+--------------+
| |
| |
| Wind Park #1 +----+
| | | XXXXXX
| | | X XXXXXXXX +----------------+
+--------------+ | XXXX X XXXXX | |
+---+ XXX | Remote Control |
XXX Internet +----+ Center |
+----+X XXX | |
+--------------+ | XXXXXXX XX | |
| | | XX XXXXXXX +----------------+
| | | XXXXX
| Wind Park #2 +----+
| |
| |
+--------------+
]]></artwork>
</figure>
<t> We expect future use cases which require bounded latency, bounded
jitter and extraordinary low packet loss for inter-domain traffic
flows due to the softwarization and virtualization of core wind farm
equipment (e.g. switches, firewalls and SCADA server components).
These factors will create opportunities for service providers to
install new services and dynamically manage them from remote
locations. For example, to enable fail-over of a local SCADA server,
a SCADA server in another wind farm site (under the administrative
control of the same operator) could be utilized temporarily (<xref
target="fig-windturbine-operatorwan"/>). In that case local
traffic would be forwarded to the remote SCADA server and existing
intra-domain QoS and timing parameters would have to be met for
inter-domain traffic flows. </t>
<figure title="Wind Turbine Control via Operator Administered WAN"
anchor="fig-windturbine-operatorwan">
<artwork align="center"><![CDATA[
+--------------+
| |
| |
| Wind Park #1 +----+
| | | XXXXXX
| | | X XXXXXXXX +----------------+
+--------------+ | XXXX XXXXX | |
+---+ Operator XXX | Remote Control |
XXX Administered +----+ Center |
+----+X WAN XXX | |
+--------------+ | XXXXXXX XX | |
| | | XX XXXXXXX +----------------+
| | | XXXXX
| Wind Park #2 +----+
| |
| |
+--------------+
]]></artwork>
</figure>
</section>
</section>
</section>
<section title="Distribution use case">
<section title="Fault Location Isolation and Service Restoration (FLISR)">
<t> 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. This will likely be the
first widespread application of distributed intelligence in the grid. </t>
<t> Static power switch status (open/closed) in the network dictates the
power flow to secondary substations. Reconfiguring the network in the
event of a fault is typically done manually on site to
energize/de-energize alternate paths. Automating the operation of
substation switchgear allows the flow of power to be altered
automatically under fault conditions.</t>
<t> FLISR can be managed centrally from a Distribution Management System
(DMS) or executed locally through distributed control via intelligent
switches and fault sensors. </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>
<section title="Electrical Utilities Today">
<t> Many utilities still rely on complex environments formed of multiple
application-specific proprietary networks, including TDM networks. </t>
<t> In this kind of environment there is no mixing of OT and IT applications on the
same network, and information is siloed between operational areas. </t>
<t> Specific calibration of the full chain is required, which is costly. </t>
<t> This kind of environment prevents utility operations from realizing the
operational efficiency benefits, visibility, and functional integration of
operational information across grid applications and data networks. </t>
<t> In addition, there are many security-related issues as discussed in the
following section.</t>
<section title="Security Current Practices and Limitations">
<t>Grid monitoring and control devices are already targets for cyber attacks,
and legacy telecommunications protocols have many intrinsic network-related
vulnerabilities. For example, 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>
</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>
<section title="Electrical Utilities Future">
<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>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 and device management across disparate networks and devices, as
it has been already demonstrated in many mission-critical and highly secure
networks. </t>
<t> IPv6 is seen as a future telecommunications technology for the Smart Grid; the
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. </t>
<t> We expect cloud-based SCADA systems to control and monitor the critical and
non-critical subsystems of generation systems, for example wind farms.</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 title="Telecommunications Trends">
<t>These general telecommunications topics are in addition to the use cases that
have been addressed so far. These include both current and future
telecommunications related topics 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>
<section title="Specific Network topologies of Smart Grid Applications">
<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 system 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, with individual runs as
long as 280 km.</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. </t>
<t> Some companies plan to transition to the Precision Time Protocol (PTP,
<xref target="IEEE1588"/>), distributing the synchronization signal
over the IP/MPLS network. PTP 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). </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,
however 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 delay asymmetry in the paths taken by event
messages. Asymmetry is not detectable by PTP, however, if such
delays are known a priori, PTP can correct for asymmetry. </t>
</list>
</t>
<t>IEC 61850 will recommend the use of the IEEE PTP 1588 Utility Profile (as
defined in <xref target="IEC62439-3:2012"/> Annex B) which offers the
support of redundant attachment of clocks to Parallel Redundancy Protcol
(PRP) and High-availability Seamless Redundancy (HSR) networks.</t>
</section>
</section>
<section title="Security Trends in Utility Networks" toc="default">
<t> Although advanced telecommunications networks can assist in transforming the
energy industry by 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. </t>
<t> "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 is 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>
<list style="symbols">
<t>IP enables a rich set of features and capabilities to enhance the
security posture </t>
<t>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>
</list>
</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 title="Electrical Utilities Asks">
<t>
<list style="symbols">
<t>Mixed L2 and L3 topologies</t>
<t>Deterministic behavior</t>
<t>Bounded latency and jitter</t>
<t>Tight feedback intervals</t>
<t>High availability, low recovery time</t>
<t>Redundancy, low packet loss</t>
<t>Precise timing</t>
<t>Centralized computing of deterministic paths</t>
<t>Distributed configuration may also be useful</t>
</list>
</t>
</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">
<section title="Use Case Description">
<t> Wireless networks are useful for industrial applications, for example when
portable, fast-moving or rotating objects are involved, and for the
resource-constrained devices found in the Internet of Things (IoT).</t>
<t> Such network-connected sensors, actuators, control loops (etc.) typically
require that the underlying network support real-time quality of service (QoS),
as well as specific classes of other network properties such as reliability,
redundancy, and security.</t>
<t> These networks may also contain very large numbers of devices, for example for
factories, "big data" acquisition, and the IoT. Given the large numbers of
devices installed, and the potential pervasiveness of the IoT, this is a huge
and very cost-sensitive market. For example, a 1% cost reduction in some areas
could save $100B</t>
<section title="Network Convergence using 6TiSCH">
<t> Some wireless network technologies support real-time QoS, and are thus
useful for these kinds of networks, but others do not. For example WiFi is
pervasive but does not provide guaranteed timing or delivery of packets, and
thus is not useful in this context. </t>
<t> In this use case we focus on one specific wireless network technology which
does provide the required deterministic QoS, which is "IPv6 over the TSCH
mode of IEEE 802.15.4e" (6TiSCH, where TSCH stands for "Time-Slotted Channel
Hopping", see <xref target="I-D.ietf-6tisch-architecture"/>, <xref
target="IEEE802154"/>, <xref target="IEEE802154e"/>, and <xref
target="RFC7554"/>). </t>
<t> There are other deterministic wireless busses and networks available today,
however they are imcompatible with each other, and incompatible with IP
traffic (for example <xref target="ISA100"/>, <xref target="WirelessHART"
/>). </t>
<t> Thus the primary goal of this use case is to apply 6TiSH as a converged IP-
and standards-based wireless network for industrial applications, i.e. to
replace multiple proprietary and/or incompatible wireless networking and
wireless network management standards.</t>
</section>
<section title="Common Protocol Development for 6TiSCH">
<t> Today there are a number of protocols required by 6TiSCH which are still in
development, and a second intent of this use case is to highlight the ways
in which these "missing" protocols share goals in common with DetNet. Thus
it is possible that some of the protocol technology developed for DetNet
will also be applicable to 6TiSCH. </t>
<t> These protocol goals are identified here, along with their relationship to
DetNet. It is likely that ultimately the resulting protocols will not be
identical, but will share design principles which contribute to the
eficiency of enabling both DetNet and 6TiSCH.</t>
<t> One such commonality is that although at a different time scale, in both TSN
<xref target="IEEE802.1TSNTG"/> and TSCH a packet crosses the network
from node to node follows a precise schedule, as a train that leaves
intermediate stations at precise times along its path. This kind of
operation reduces collisions, saves energy, and enables engineering the
network for deterministic properties. </t>
<t> Another commonality is remote monitoring and scheduling management of a TSCH
network by a Path Computation Element (PCE) and Network Management Entity
(NME). The PCE/NME manage timeslots and device resources in a manner that
minimizes the interaction with and the load placed on resource-constrained
devices. For example, a tiny IoT device may have just enough buffers to
store one or a few IPv6 packets, and will have limited bandwidth between
peers such that it can maintain only a small amount of peer information, and
will not be able to store many packets waiting to be forwarded. It is
advantageous then for it to only be required to carry out the specific
behavior assigned to it by the PCE/NME (as opposed to maintaining its own IP
stack, for example). </t>
<t>Note: Current WG discussion indicates that some peer-to-peer communication
must be assumed, i.e. the PCE may communicate only indirectly with any given
device, enabling hierarchical configuration of the system.</t>
<t> 6TiSCH depends on <xref target="PCE"/> and <xref
target="I-D.finn-detnet-architecture"/>. </t>
<t> 6TiSCH also depends on the fact that DetNet will maintain consistency with
<xref target="IEEE802.1TSNTG"/>.</t>
</section>
</section>
<section title="Wireless Industrial Today">
<t> Today industrial wireless is accomplished using multiple deterministic wireless
networks which are incompatible with each other and with IP traffic. </t>
<t> 6TiSCH is not yet fully specified, so it cannot be used in today's
applications.</t>
</section>
<section title="Wireless Industrial Future">
<section title="Unified Wireless Network and Management">
<t> We expect DetNet and 6TiSCH together to enable converged transport of
deterministic and best-effort traffic flows between real-time industrial
devices and wide area networks via IP routing. A high level view of a basic
such network is shown in <xref target="wi_fig1"/>.</t>
<t>
<figure anchor="wi_fig1" title="Basic 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>
<xref target="wi_fig2"/> shows a backbone router federating multiple
synchronized 6TiSCH subnets into a single subnet connected to the external
network. </t>
<t>
<figure anchor="wi_fig2" title="Extended 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> The backbone router must ensure end-to-end deterministic behavior between
the LLN and the backbone. We would like to see this accomplished in
conformance with the work done in <xref
target="I-D.finn-detnet-architecture"/> with respect to Layer-3 aspects
of deterministic networks that span multiple Layer-2 domains. </t>
<t> The PCE must compute a deterministic path end-to-end across the TSCH network
and IEEE802.1 TSN Ethernet backbone, and DetNet protocols are expected to
enable end-to-end deterministic forwarding. </t>
<t>
<figure anchor="wi_fig3" title="6TiSCH Network with PRE">
<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>
<section title="PCE and 6TiSCH ARQ Retries">
<t>Note: The possible use of ARQ techniques in DetNet is currently
considered a possible design alternative.</t>
<t> 6TiSCH uses the IEEE802.15.4 Automatic Repeat-reQuest (ARQ) mechanism to
provide higher reliability of packet delivery. ARQ is related to packet
replication and elimination because there are two independent paths for
packets to arrive at the destination, and if an expected packed does not
arrive on one path then it checks for the packet on the second path. </t>
<t> Although to date this mechanism is only used by wireless networks, this
may be a technique that would be appropriate for DetNet and so aspects
of the enabling protocol could be co-developed. </t>
<t> For example, in <xref target="wi_fig3"/>, 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> In ARQ 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 arrives within the allocated 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). </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>
</section>
<section title="Schedule Management by a PCE">
<t> A common feature of 6TiSCH and DetNet is the action of a PCE to configure
paths through the network. Specifically, what is needed is a protocol and
data model that the PCE will use to get/set the relevant configuration
from/to the devices, as well as perform operations on the devices. We expect
that this protocol will be developed by DetNet with consideration for its
reuse by 6TiSCH. The remainder of this section provides a bit more context
from the 6TiSCH side.</t>
<section title="PCE Commands and 6TiSCH CoAP Requests">
<t> The 6TiSCH device does not expect to place the request for bandwidth
between itself and another device in the network. Rather, an operation
control system invoked through a human interface specifies the required
traffic specification and the end nodes (in terms of latency and
reliability). Based on this information, the PCE must compute a path
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 recognizing that a
certain packet belongs to a certain path, 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 paths. 6TiSCH expects that the programing of the
schedule will be done over COAP as discussed in <xref
target="I-D.ietf-6tisch-coap"/>. </t>
<t> 6TiSCH expects that the PCE commands will 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. Related information about 6TiSCH can be
found at <xref target="I-D.ietf-6tisch-6top-interface"/> and <xref
target="RFC6550">RPL</xref>. </t>
<t> A protocol may be used to update the state in the devices during
runtime, for example if it appears that a path through the network has
ceased to perform as expected, but in 6TiSCH that flow was not designed
and no protocol was selected. We would like to see DetNet define the
appropriate end-to-end protocols to be used in that case. The
implication is that these state updates take place once the system is
configured and running, i.e. they are not limited to the initial
communication of the configuration of the system. </t>
<t> A "slotFrame" is the base object that a PCE would manipulate to program
a schedule into an LLN node (<xref target="I-D.ietf-6tisch-architecture"
/>). </t>
<t> We would like to see the PCE read energy data from devices, and compute
paths that will implement policies on how energy in devices is consumed,
for instance to ensure that the spent energy does not exceeded the
available energy over a period of time. Note: this statement implies
that an extensible protocol for communicating device info to the PCE and
enabling the PCE to act on it will be part of the DetNet architecture,
however for subnets with specific protocols (e.g. CoAP) a gateway may be
required.</t>
<t> 6TiSCH devices can discover their neighbors over the radio using a
mechanism such as beacons, but even though the neighbor information is
available in the 6TiSCH interface data model, 6TiSCH does not describe a
protocol to proactively push the neighborhood information to a PCE. We
would like to see DetNet define such a protocol; one possible design
alternative is that it could operate over CoAP, alternatively it could
be converted to/from CoAP by a gateway. We would like to see such a
protocol carry multiple metrics, for example similar to those used for
RPL operations <xref target="RFC6551"/></t>
</section>
<section title="6TiSCH IP Interface">
<t> "6top" (<xref target="I-D.wang-6tisch-6top-sublayer"/>) 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 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> An IP packet that is sent along a 6TiSCH path 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 title="6TiSCH Security Considerations">
<t> On top of the classical requirements for protection of control signaling, it
must be noted that 6TiSCH networks operate on limited resources that can be
depleted rapidly in a DoS attack on the system, for instance by placing a
rogue device in the network, or by obtaining management control and setting
up unexpected additional paths. </t>
</section>
</section>
<section title="Wireless Industrial Asks">
<t>6TiSCH depends on DetNet to define:</t>
<t>
<list style="symbols">
<t> Configuration (state) and operations for deterministic paths </t>
<t> End-to-end protocols for deterministic forwarding (tagging, IP)</t>
<t> Protocol for packet replication and elimination</t>
</list>
</t>
</section>
</section>
<section title="Cellular Radio">
<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>
<t> In <xref target="cr_arch"/> "eNB" ("E-UTRAN Node B") is the hardware that is
connected to the mobile phone network which communicates directly with
mobile handsets (<xref target="TS36300"/>).</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>
</section>
<section title="Delay Constraints">
<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 uses most of it,
allowing only a small fraction to be used by the Fronthaul network (e.g. up
to 250us one-way delay, though the existing spec (<xref target="NGMN-fronth"
/>) supports delay only up to 100us). This ultimately determines the
distance the remote radio heads can be located from the base stations (e.g.,
100us equals roughly 20 km of optical fiber-based transport). Allocation
options of the available time budget between processing and transport are
under heavy discussions in the mobile industry. </t>
<t> For packet-based transport the allocated transport time (e.g. CPRI would
allow for 100us delay <xref target="CPRI"/>) is consumed by all nodes and
buffering between the remote radio head and the baseband processing unit,
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>
<t>
<xref target="METIS"/> documents the fundamental challenges as well as
overall technical goals of the future 5G mobile and wireless system as the
starting point. These future systems should support much higher data volumes
and rates and significantly lower end-to-end latency for 100x more connected
devices (at similar cost and energy consumption levels as today's
system).</t>
<t> For Midhaul connections, delay constraints are driven by Inter-Site radio
functions like Coordinated Multipoint Processing (CoMP, see <xref
target="CoMP"/>). CoMP reception and transmission is a framework in
which 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-UE
(User Equipment) transmission to a multi-cell-to-multi-UEs transmission by
base station cooperation. </t>
<t> CoMP has delay-sensitive performance parameters, which are "midhaul latency"
and "CSI (Channel State Information) reporting and accuracy". The essential
feature of CoMP is signaling between eNBs, so Midhaul latency is the
dominating limitation of CoMP performance. Generally, CoMP can benefit from
coordinated scheduling (either distributed or centralized) of different
cells if the signaling delay between eNBs is within 1-10ms. This delay
requirement is both rigid and absolute because any uncertainty in delay will
degrade the performance significantly. </t>
<t> Inter-site CoMP is one of the key requirements for 5G and is also a
near-term goal for the current 4.5G network architecture.</t>
</section>
<section title="Time Synchronization Constraints" 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. Note: performance guarantees
of low nanosecond values such as these are considered to be below
the DetNet layer - it is assumed that the underlying implementation,
e.g. the hardware, will provide sufficient support (e.g. buffering)
to enable this level of accuracy. These values are maintained in the
use case to give an indication of the overall application.</t>
<t hangText="Timing Alignment Error:">
<vspace blankLines="0"/> Timing Alignment Error (TAE) is problematic
to Fronthaul networks and must be minimized. If the transport
network cannot guarantee low enough TAE 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. Packet Delay Variation (PDV) requirements can be
derived from TAE for packet based Fronthaul networks.</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 frequency error that shows immediately on the radio as
well. Note: performance guarantees of low nanosecond values such as
these are considered to be below the DetNet layer - it is assumed
that the underlying implementation, e.g. the hardware, will provide
sufficient support to enable this level of performance. These values
are maintained in the use case to give an indication of the overall
application.</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="Transport Loss Constraints">
<t>Fronthaul and Midhaul networks assume almost error-free transport. Errors can
result in a reset of the radio interfaces, which can cause reduced
throughput or broken radio connectivity for mobile customers. </t>
<t> For packetized Fronthaul and Midhaul connections packet loss may be caused
by BER, congestion, or network failure scenarios. Current tools for
elminating packet loss for Fronthaul and Midhaul networks have serious
challenges, for example 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 and Midhaul networks. Protection
switching is also a candidate but current technologies for the path switch
are too slow to avoid reset of mobile interfaces. </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>
<t>Note: This is considered important for the security policy of the network,
but does not affect the core DetNet architecture and design.</t>
</section>
</section>
<section title="Cellular Radio Networks Today">
<section title="Fronthaul">
<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> Current solutions for Fronthaul are direct optical cables or
Wavelength-Division Multiplexing (WDM) connections.</t>
</section>
<section title="Midhaul and Backhaul">
<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 Mid- and Backhaul 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> In the past, Mid- and Backhaul connections were typically based on Time
Division Multiplexing (TDM-based) and provided frequency synchronization
capabilities as a part of the transport media. Alternatively other
technologies such as Global Positioning System (GPS) or Synchronous Ethernet
(SyncE) 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 (RANs)
<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"
/> and <xref target="I-D.ietf-mpls-residence-time"/>, these solution are not
necessarily sufficient for the forthcoming RAN architectures nor do they
guarantee the more stringent time-synchronization requirements such as <xref
target="CPRI"/>. </t>
<t>There are also existing solutions for TDM over IP such as <xref
target="RFC5087"/> and <xref target="RFC4553"/>, as well as TDM over
Ethernet transports such as <xref target="RFC5086"/>. </t>
</section>
</section>
<section title="Cellular Radio Networks Future">
<t> Future Cellular Radio Networks will be based on a mix of different xHaul
networks (xHaul = front-, mid- and backhaul), and future transport networks
should be able to support all of them simultaneously. It is already envisioned
today that:</t>
<t>
<list style="symbols">
<t> Not all "cellular radio network" traffic will be IP, for example some
will remain at Layer 2 (e.g. Ethernet based). DetNet solutions must
address all traffic types (Layer 2, Layer 3) with the same tools and
allow their transport simultaneously. </t>
<t> All form of xHaul networks will need some form of DetNet solutions. For
example with the advent of 5G some Backhaul traffic will also have
DetNet requirements (e.g. traffic belonging to time-critical 5G
applications).</t>
</list>
</t>
<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. Time and
synchronization support are already topical for Backhaul and Midhaul packet
networks <xref target="MEF"/> and are becoming a real issue for Fronthaul
networks also. Specifically in 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 using 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> Interesting and important 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. <xref target="IEEE8021AS"/> specifies a Layer 2 time
synchronizing service, and other specifications such as IEEE 1722 <xref
target="IEEE1722"/> specify Ethernet-based Layer-2 transport for
time-sensitive streams. </t>
<t> New promising work seeks to enable the transport of time-sensitive fronthaul
streams in Ethernet bridged networks <xref target="IEEE8021CM"/>. Analogous to
IEEE 1722 there is an ongoing standardization effort to define the Layer-2
transport encapsulation format for transporting radio over Ethernet (RoE) in the
IEEE 1904.3 Task Force <xref target="IEEE19043"/>. </t>
<t> All-IP RANs and xHhaul 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. </t>
<t>While there are existing technologies to establish circuits through the routed
and switched networks (especially in MPLS/PWE space), there is still no way to
signal the time synchronization and time-sensitive stream
requirements/reservations for Layer-3 flows in a way that addresses the entire
transport stack, including the Ethernet layers that need to be configured.</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 a
different layer, for example Ethernet frames. </t>
<t>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 xHauls (meaning that different flows with diverse
DetNet requirements can coexist in the same network and traverse the
same nodes without interfering with each other) </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>
</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 a converged IP-standards-based network with deterministic
properties that can satisfy the timing, security and reliability constraints
described above. Today's proprietary networks could then be interfaced to such a
network via gateways or, in the case of new installations, devices could be
connected directly to the converged network.</t>
<t>For this use case we expect time synchronization accuracy on the order of
1us.</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> Security (e.g. prevent critical flows from being leaked between
physically separated networks) </t>
</list>
</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="Use Cases Explicitly Out of Scope for DetNet">
<t>This section contains use case text that has been determined to be outside of the
scope of the present DetNet work. </t>
<section title="DetNet Scope Limitations">
<t>The scope of DetNet is deliberately limited to specific use cases that are
consistent with the WG charter, subject to the interpretation of the WG. At the
time the DetNet Use Cases were solicited and provided by the authors the scope
of DetNet was not clearly defined, and as that clarity has emerged, certain of
the use cases have been determined to be outside the scope of the present DetNet
work. Such text has been moved into this section to clarify that these use cases
will not be supported by the DetNet work. </t>
<t>The text in this section was moved here based on the following "exclusion"
principles. Or, as an alternative to moving all such text to this section, some
draft text has been modified in situ to reflect these same principles.</t>
<t>The following principles have been established to clarify the scope of the
present DetNet work.</t>
<t>
<list style="symbols">
<t>The scope of network addressed by DetNet is limited to networks that can
be centrally controlled, i.e. an "enterprise" aka "corporate" network.
This explicitly excludes "the open Internet".</t>
<t>Maintaining synchronized time across a DetNet network is crucial to its
operation, however DetNet assumes that time is to be maintained using
other means, for example (but not limited to) Precision Time Protocol
(<xref target="IEEE1588"/>). A use case may state the accuracy and
reliability that it expects from the DetNet network as part of a whole
system, however it is understood that such timing properties are not
guaranteed by DetNet itself. It is currently an open question as to
whether DetNet protocols will include a way for an application to
communicate such timing expectations to the network, and if so whether
they would be expected to materially affect the performance they would
receive from the network as a result.</t>
</list>
</t>
</section>
<section title="Internet-based Applications">
<section title="Use Case Description">
<t> There are many applications that communicate across the open Internet that
could benefit from guaranteed delivery and bounded latency. The following
are some representative examples.</t>
<section title="Media Content Delivery">
<t> Media content delivery continues to be an important use of the Internet,
yet users often experience poor quality audio and video due to the delay
and jitter inherent in today's Internet. </t>
</section>
<section title="Online Gaming">
<t> Online gaming is a significant part of the gaming market, however
latency can degrade the end user experience. For example "First Person
Shooter" (FPS) games are highly delay-sensitive. </t>
</section>
<section title="Virtual Reality">
<t>Virtual reality (VR) has many commercial applications including real
estate presentations, remote medical procedures, and so on. Low latency
is critical to interacting with the virtual world because perceptual
delays can cause motion sickness. </t>
</section>
</section>
<section title="Internet-Based Applications Today">
<t> Internet service today is by definition "best effort", with no guarantees on
delivery or bandwidth. </t>
</section>
<section title="Internet-Based Applications Future">
<t> We imagine an Internet from which we will be able to play a video without
glitches and play games without lag.</t>
<t> For online gaming, the maximum round-trip delay can be 100ms and stricter
for FPS gaming which can be 10-50ms. Transport delay is the dominate part
with a 5-20ms budget. </t>
<t> For VR, 1-10ms maximum delay is needed and total network budget is 1-5ms if
doing remote VR.</t>
<t> Flow identification can be used for gaming and VR, i.e. it can recognize a
critical flow and provide appropriate latency bounds. </t>
</section>
<section title="Internet-Based Applications Asks">
<t>
<list style="symbols">
<t> Unified control and management protocols to handle time-critical
data flow </t>
<t> Application-aware flow filtering mechanism to recognize the timing
critical flow without doing 5-tuple matching </t>
<t> Unified control plane to provide low latency service on Layer-3
without changing the data plane </t>
<t> OAM system and protocols which can help to provide E2E-delay
sensitive service provisioning </t>
</list>
</t>
</section>
</section>
<section title="Pro Audio and Video - Digital Rights Management (DRM)">
<t>This section was moved here because this is considered a Link layer topic, not
direct responsibility of DetNet.</t>
<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 <xref target="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="Pro Audio and Video - Link Aggregation">
<t>Note: The term "Link Aggregation" is used here as defined by the text in the
following paragraph, i.e. not following a more common Network Industry
definition. Current WG consensus is that this item won't be directly supported
by the DetNet architecture, for example because it implies guarantee of in-order
delivery of packets which conflicts with the core goal of achieving the lowest
possible latency.</t>
<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. </t>
</section>
</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="Internet Applications and CoMP">
<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 title="Electrical Utilities">
<t> The wind power generation use case has been extracted from the study of Wind
Farms conducted within the 5GPPP Virtuwind Project. The project is funded by the
European Union's Horizon 2020 research and innovation programme under grant
agreement No 671648 (VirtuWind). </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>
<!-- 6TiSCH -->
<?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'?>
<!-- others -->
<!-- rfc include="reference.RFC.2119"?-->
<!-- MUST HAVE -->
<?rfc include="reference.RFC.2460"?>
<!-- Internet Protocol, Version 6 (IPv6) Specification -->
<?rfc include="reference.RFC.2474"?>
<!-- Differentiated Services Field -->
<?rfc include="reference.RFC.3209"?>
<!-- RSVP TE -->
<?rfc include="reference.RFC.4291"?>
<!-- IP Version 6 Addressing Architecture -->
<?rfc include="reference.RFC.3444"?>
<!-- On the Difference between Information Models and Data Models -->
<?rfc include="reference.RFC.3972"?>
<!-- Cryptographically Generated Addresses -->
<?rfc include="reference.RFC.4919"?>
<!-- IPv6 over Low-Power Wireless Personal Area Networks -->
<?rfc include="reference.RFC.4903"?>
<!-- IPv6 Multi-Link Subnet Issues -->
<?rfc include="reference.RFC.6282"?>
<!-- Compression Format for IPv6 Datagrams over IEEE 802.15.4-Based Networks -->
<?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"?>
<!-- neighbor Discovery Optimization for IPv6 over Low-Power Wireless Personal Area Networks -->
<!-- others -->
<?rfc include='reference.I-D.finn-detnet-architecture'?>
<?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"
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 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>
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<!-- 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.
v04 2016-02-22 EAG Other Use Cases section: remove V2V and Industrial Automation, refactor remainder into Internet-based and CoMP sections.
v05 2016-02-22 EAG Edit Industrial Wireless section.
v06 2016-03-04 EAG Edit Electrical Utilities section. Address "replace" vs "interwork" in M2M Future.
v07 2016-03-04 EAG Edit Pro Audio section.
v08 2016-03-07 EAG Incorporate Cellular Radio review items per Varga/Korhonen, including subsuming CoMP section as subtopic of this chapter.
v09 2016-03-21 EAG Fix various typos and minor updates.
v10 2016-07-04 EAG Clarify scope questions raised at IETF95 based on conclusions drawn from DetNet list discussions.
v11 2016-09-25 XVG Merge wind farm example into utility network use case. EAG Minor edits and formatting.
-->
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| PAFTECH AB 2003-2026 | 2026-04-23 09:24:54 |