Internet Engineering Task Force E. Grossman, Ed.
Internet-Draft DOLBY
Intended status: Informational C. Gunther
Expires: August 26, 2016 HARMAN
P. Thubert
P. Wetterwald
CISCO
J. Raymond
HYDRO-QUEBEC
J. Korhonen
BROADCOM
Y. Kaneko
Toshiba
S. Das
Applied Communication Sciences
Y. Zha
HUAWEI
B. Varga
J. Farkas
Ericsson
F. Goetz
J. Schmitt
Siemens
February 23, 2016
Deterministic Networking Use Cases
draft-ietf-detnet-use-cases-05
Abstract
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.
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.
For each case, this document will identify the application, identify
representative solutions used today, and what new uses an IETF DetNet
solution may enable.
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Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on August 26, 2016.
Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 5
2. Pro Audio Use Cases . . . . . . . . . . . . . . . . . . . . . 5
2.1. Introduction . . . . . . . . . . . . . . . . . . . . . . 5
2.2. Fundamental Stream Requirements . . . . . . . . . . . . . 6
2.2.1. Guaranteed Bandwidth . . . . . . . . . . . . . . . . 6
2.2.2. Bounded and Consistent Latency . . . . . . . . . . . 7
2.2.2.1. Optimizations . . . . . . . . . . . . . . . . . . 8
2.3. Additional Stream Requirements . . . . . . . . . . . . . 9
2.3.1. Deterministic Time to Establish Streaming . . . . . . 9
2.3.2. Use of Unused Reservations by Best-Effort Traffic . . 9
2.3.3. Layer 3 Interconnecting Layer 2 Islands . . . . . . . 10
2.3.4. Secure Transmission . . . . . . . . . . . . . . . . . 10
2.3.5. Redundant Paths . . . . . . . . . . . . . . . . . . . 10
2.3.6. Link Aggregation . . . . . . . . . . . . . . . . . . 10
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2.3.7. Traffic Segregation . . . . . . . . . . . . . . . . . 11
2.3.7.1. Packet Forwarding Rules, VLANs and Subnets . . . 11
2.3.7.2. Multicast Addressing (IPv4 and IPv6) . . . . . . 11
2.4. Integration of Reserved Streams into IT Networks . . . . 12
2.5. Security Considerations . . . . . . . . . . . . . . . . . 12
2.5.1. Denial of Service . . . . . . . . . . . . . . . . . . 12
2.5.2. Control Protocols . . . . . . . . . . . . . . . . . . 12
2.6. A State-of-the-Art Broadcast Installation Hits Technology
Limits . . . . . . . . . . . . . . . . . . . . . . . . . 13
3. Utility Telecom Use Cases . . . . . . . . . . . . . . . . . . 13
3.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 13
3.2. Telecommunications Trends and General telecommunications
Requirements . . . . . . . . . . . . . . . . . . . . . . 14
3.2.1. General Telecommunications Requirements . . . . . . . 14
3.2.1.1. Migration to Packet-Switched Network . . . . . . 15
3.2.2. Applications, Use cases and traffic patterns . . . . 16
3.2.2.1. Transmission use cases . . . . . . . . . . . . . 16
3.2.2.2. Distribution use case . . . . . . . . . . . . . . 26
3.2.2.3. Generation use case . . . . . . . . . . . . . . . 29
3.2.3. Specific Network topologies of Smart Grid
Applications . . . . . . . . . . . . . . . . . . . . 30
3.2.4. Precision Time Protocol . . . . . . . . . . . . . . . 31
3.3. IANA Considerations . . . . . . . . . . . . . . . . . . . 32
3.4. Security Considerations . . . . . . . . . . . . . . . . . 32
3.4.1. Current Practices and Their Limitations . . . . . . . 32
3.4.2. Security Trends in Utility Networks . . . . . . . . . 34
4. Building Automation Systems . . . . . . . . . . . . . . . . . 35
4.1. Use Case Description . . . . . . . . . . . . . . . . . . 35
4.2. Building Automation Systems Today . . . . . . . . . . . . 36
4.2.1. BAS Architecture . . . . . . . . . . . . . . . . . . 36
4.2.2. BAS Deployment Model . . . . . . . . . . . . . . . . 37
4.2.3. Use Cases for Field Networks . . . . . . . . . . . . 39
4.2.3.1. Environmental Monitoring . . . . . . . . . . . . 39
4.2.3.2. Fire Detection . . . . . . . . . . . . . . . . . 39
4.2.3.3. Feedback Control . . . . . . . . . . . . . . . . 40
4.2.4. Security Considerations . . . . . . . . . . . . . . . 40
4.3. BAS Future . . . . . . . . . . . . . . . . . . . . . . . 40
4.4. BAS Asks . . . . . . . . . . . . . . . . . . . . . . . . 41
5. Wireless for Industrial . . . . . . . . . . . . . . . . . . . 41
5.1. Use Case Description . . . . . . . . . . . . . . . . . . 41
5.1.1. Network Convergence using 6TiSCH . . . . . . . . . . 42
5.1.2. Common Protocol Development for 6TiSCH . . . . . . . 42
5.2. Wireless Industrial Today . . . . . . . . . . . . . . . . 43
5.3. Wireless Industrial Future . . . . . . . . . . . . . . . 43
5.3.1. Unified Wireless Network and Management . . . . . . . 43
5.3.1.1. PCE and 6TiSCH ARQ Retries . . . . . . . . . . . 45
5.3.2. Schedule Management by a PCE . . . . . . . . . . . . 46
5.3.2.1. PCE Commands and 6TiSCH CoAP Requests . . . . . . 46
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5.3.2.2. 6TiSCH IP Interface . . . . . . . . . . . . . . . 47
5.3.3. 6TiSCH Security Considerations . . . . . . . . . . . 47
5.4. Wireless Industrial Asks . . . . . . . . . . . . . . . . 48
6. Cellular Radio Use Cases . . . . . . . . . . . . . . . . . . 48
6.1. Use Case Description . . . . . . . . . . . . . . . . . . 48
6.1.1. Network Architecture . . . . . . . . . . . . . . . . 48
6.1.2. Time Synchronization Requirements . . . . . . . . . . 49
6.1.3. Time-Sensitive Stream Requirements . . . . . . . . . 51
6.1.4. Security Considerations . . . . . . . . . . . . . . . 51
6.2. Cellular Radio Networks Today . . . . . . . . . . . . . . 52
6.3. Cellular Radio Networks Future . . . . . . . . . . . . . 52
6.4. Cellular Radio Networks Asks . . . . . . . . . . . . . . 54
7. Cellular Coordinated Multipoint Processing (CoMP) . . . . . . 54
7.1. Use Case Description . . . . . . . . . . . . . . . . . . 54
7.1.1. CoMP Architecture . . . . . . . . . . . . . . . . . . 55
7.1.2. Delay Sensitivity in CoMP . . . . . . . . . . . . . . 56
7.2. CoMP Today . . . . . . . . . . . . . . . . . . . . . . . 56
7.3. CoMP Future . . . . . . . . . . . . . . . . . . . . . . . 56
7.3.1. Mobile Industry Overall Goals . . . . . . . . . . . . 56
7.3.2. CoMP Infrastructure Goals . . . . . . . . . . . . . . 57
7.4. CoMP Asks . . . . . . . . . . . . . . . . . . . . . . . . 57
8. Industrial M2M . . . . . . . . . . . . . . . . . . . . . . . 58
8.1. Use Case Description . . . . . . . . . . . . . . . . . . 58
8.2. Industrial M2M Communication Today . . . . . . . . . . . 59
8.2.1. Transport Parameters . . . . . . . . . . . . . . . . 59
8.2.2. Stream Creation and Destruction . . . . . . . . . . . 60
8.3. Industrial M2M Future . . . . . . . . . . . . . . . . . . 60
8.4. Industrial M2M Asks . . . . . . . . . . . . . . . . . . . 61
9. Internet-based Applications . . . . . . . . . . . . . . . . . 61
9.1. Use Case Description . . . . . . . . . . . . . . . . . . 61
9.1.1. Media Content Delivery . . . . . . . . . . . . . . . 61
9.1.2. Online Gaming . . . . . . . . . . . . . . . . . . . . 61
9.1.3. Virtual Reality . . . . . . . . . . . . . . . . . . . 61
9.2. Internet-Based Applications Today . . . . . . . . . . . . 62
9.3. Internet-Based Applications Future . . . . . . . . . . . 62
9.4. Internet-Based Applications Asks . . . . . . . . . . . . 62
10. Use Case Common Elements . . . . . . . . . . . . . . . . . . 62
11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 63
11.1. Pro Audio . . . . . . . . . . . . . . . . . . . . . . . 63
11.2. Utility Telecom . . . . . . . . . . . . . . . . . . . . 64
11.3. Building Automation Systems . . . . . . . . . . . . . . 64
11.4. Wireless for Industrial . . . . . . . . . . . . . . . . 64
11.5. Cellular Radio . . . . . . . . . . . . . . . . . . . . . 64
11.6. Industrial M2M . . . . . . . . . . . . . . . . . . . . . 64
11.7. Internet Applications and CoMP . . . . . . . . . . . . . 64
12. Informative References . . . . . . . . . . . . . . . . . . . 65
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 73
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1. Introduction
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?)
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.
We present for each use case the answers to the following questions:
o What is the use case?
o How is it addressed today?
o How would you like it to be addressed in the future?
o What do you want the IETF to deliver?
The level of detail in each use case should be sufficient to express
the relevant elements of the use case, but not more.
At the end we consider the use cases collectively, and examine the
most significant goals they have in common.
2. Pro Audio Use Cases
2.1. Introduction
The professional audio and video industry includes music and film
content creation, broadcast, cinema, and live exposition as well as
public address, media and emergency systems at large venues
(airports, stadiums, churches, theme parks). These industries have
already gone through the transition of audio and video signals from
analog to digital, however the interconnect systems remain primarily
point-to-point with a single (or small number of) signals per link,
interconnected with purpose-built hardware.
These industries are now attempting to transition to packet based
infrastructure for distributing audio and video in order to reduce
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cost, increase routing flexibility, and integrate with existing IT
infrastructure.
However, there are several requirements for making a network the
primary infrastructure for audio and video which are not met by
todays networks and these are our concern in this draft.
The principal requirement is that pro audio and video applications
become able to establish streams that provide guaranteed (bounded)
bandwidth and latency from the Layer 3 (IP) interface. Such streams
can be created today within standards-based layer 2 islands however
these are not sufficient to enable effective distribution over wider
areas (for example broadcast events that span wide geographical
areas).
Some proprietary systems have been created which enable deterministic
streams at layer 3 however they are engineered networks in that they
require careful configuration to operate, often require that the
system be over designed, and it is implied that all devices on the
network voluntarily play by the rules of that network. To enable
these industries to successfully transition to an interoperable
multi-vendor packet-based infrastructure requires effective open
standards, and we believe that establishing relevant IETF standards
is a crucial factor.
It would be highly desirable if such streams could be routed over the
open Internet, however even intermediate solutions with more limited
scope (such as enterprise networks) can provide a substantial
improvement over todays networks, and a solution that only provides
for the enterprise network scenario is an acceptable first step.
We also present more fine grained requirements of the audio and video
industries such as safety and security, redundant paths, devices with
limited computing resources on the network, and that reserved stream
bandwidth is available for use by other best-effort traffic when that
stream is not currently in use.
2.2. Fundamental Stream Requirements
The fundamental stream properties are guaranteed bandwidth and
deterministic latency as described in this section. Additional
stream requirements are described in a subsequent section.
2.2.1. Guaranteed Bandwidth
Transmitting audio and video streams is unlike common file transfer
activities because guaranteed delivery cannot be achieved by re-
trying the transmission; by the time the missing or corrupt packet
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has been identified it is too late to execute a re-try operation and
stream playback is interrupted, which is unacceptable in for example
a live concert. In some contexts large amounts of buffering can be
used to provide enough delay to allow time for one or more retries,
however this is not an effective solution when live interaction is
involved, and is not considered an acceptable general solution for
pro audio and video. (Have you ever tried speaking into a microphone
through a sound system that has an echo coming back at you? It makes
it almost impossible to speak clearly).
Providing a way to reserve a specific amount of bandwidth for a given
stream is a key requirement.
2.2.2. Bounded and Consistent Latency
Latency in this context means the amount of time that passes between
when a signal is sent over a stream and when it is received, for
example the amount of time delay between when you speak into a
microphone and when your voice emerges from the speaker. Any delay
longer than about 10-15 milliseconds is noticeable by most live
performers, and greater latency makes the system unusable because it
prevents them from playing in time with the other players (see slide
6 of [SRP_LATENCY]).
The 15ms latency bound is made even more challenging because it is
often the case in network based music production with live electric
instruments that multiple stages of signal processing are used,
connected in series (i.e. from one to the other for example from
guitar through a series of digital effects processors) in which case
the latencies add, so the latencies of each individual stage must all
together remain less than 15ms.
In some situations it is acceptable at the local location for content
from the live remote site to be delayed to allow for a statistically
acceptable amount of latency in order to reduce jitter. However,
once the content begins playing in the local location any audio
artifacts caused by the local network are unacceptable, especially in
those situations where a live local performer is mixed into the feed
from the remote location.
In addition to being bounded to within some predictable and
acceptable amount of time (which may be 15 milliseconds or more or
less depending on the application) the latency also has to be
consistent. For example when playing a film consisting of a video
stream and audio stream over a network, those two streams must be
synchronized so that the voice and the picture match up. A common
tolerance for audio/video sync is one NTSC video frame (about 33ms)
and to maintain the audience perception of correct lip sync the
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latency needs to be consistent within some reasonable tolerance, for
example 10%.
A common architecture for synchronizing multiple streams that have
different paths through the network (and thus potentially different
latencies) is to enable measurement of the latency of each path, and
have the data sinks (for example speakers) buffer (delay) all packets
on all but the slowest path. Each packet of each stream is assigned
a presentation time which is based on the longest required delay.
This implies that all sinks must maintain a common time reference of
sufficient accuracy, which can be achieved by any of various
techniques.
This type of architecture is commonly implemented using a central
controller that determines path delays and arbitrates buffering
delays.
2.2.2.1. Optimizations
The controller might also perform optimizations based on the
individual path delays, for example sinks that are closer to the
source can inform the controller that they can accept greater latency
since they will be buffering packets to match presentation times of
farther away sinks. The controller might then move a stream
reservation on a short path to a longer path in order to free up
bandwidth for other critical streams on that short path. See slides
3-5 of [SRP_LATENCY].
Additional optimization can be achieved in cases where sinks have
differing latency requirements, for example in a live outdoor concert
the speaker sinks have stricter latency requirements than the
recording hardware sinks. See slide 7 of [SRP_LATENCY].
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
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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.
2.3. Additional Stream Requirements
The requirements in this section are more specific yet are common to
multiple audio and video industry applications.
2.3.1. Deterministic Time to Establish Streaming
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].
Similar requirements apply when the system is restarted after a power
cycle, cable re-connection, or system reconfiguration.
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).
Video systems introduce related requirements, for example when
transitioning from one camera feed to another. Such systems
currently use purpose-built hardware to switch feeds smoothly,
however there is a current initiative in the broadcast industry to
switch to a packet-based infrastructure (see [STUDIO_IP] and the ESPN
DC2 use case described below).
2.3.2. Use of Unused Reservations by Best-Effort Traffic
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.
This also addresses a concern of IT network administrators that are
considering adding reserved bandwidth traffic to their networks that
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users will just reserve a ton of bandwidth and then never un-reserve
it even though they are not using it, and soon they will have no
bandwidth left.
2.3.3. Layer 3 Interconnecting Layer 2 Islands
As an intermediate step (short of providing guaranteed bandwidth
across the open internet) it would be valuable to provide a way to
connect multiple Layer 2 networks. For example layer 2 techniques
could be used to create a LAN for a single broadcast studio, and
several such studios could be interconnected via layer 3 links.
2.3.4. Secure Transmission
Digital Rights Management (DRM) is very important to the audio and
video industries. Any time protected content is introduced into a
network there are DRM concerns that must be maintained (see
[CONTENT_PROTECTION]). Many aspects of DRM are outside the scope of
network technology, however there are cases when a secure link
supporting authentication and encryption is required by content
owners to carry their audio or video content when it is outside their
own secure environment (for example see [DCI]).
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.
2.3.5. Redundant Paths
On-air and other live media streams must be backed up with redundant
links that seamlessly act to deliver the content when the primary
link fails for any reason. In point-to-point systems this is
provided by an additional point-to-point link; the analogous
requirement in a packet-based system is to provide an alternate path
through the network such that no individual link can bring down the
system.
2.3.6. Link Aggregation
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
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network controller (or equivalent) must be able to determine the
maximum latency of any path through the aggregate link (see Bounded
and Consistent Latency section above).
2.3.7. Traffic Segregation
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.
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.
There are many techniques that can be used to support this
requirement including (but not limited to) the following examples.
2.3.7.1. Packet Forwarding Rules, VLANs and Subnets
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.
2.3.7.2. Multicast Addressing (IPv4 and IPv6)
Multicast addressing is commonly used to keep bandwidth utilization
of shared links to a minimum.
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.
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.
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2.4. Integration of Reserved Streams into IT Networks
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.
2.5. Security Considerations
Many industries that are moving from the point-to-point world to the
digital network world have little understanding of the pitfalls that
they can create for themselves with improperly implemented network
infrastructure. DetNet should consider ways to provide security
against DoS attacks in solutions directed at these markets. Some
considerations are given here as examples of ways that we can help
new users avoid common pitfalls.
2.5.1. Denial of Service
One security pitfall that this author is aware of involves the use of
technology that allows a presenter to throw the content from their
tablet or smart phone onto the A/V system that is then viewed by all
those in attendance. The facility introducing this technology was
quite excited to allow such modern flexibility to those who came to
speak. One thing they hadn't realized was that since no security was
put in place around this technology it left a hole in the system that
allowed other attendees to "throw" their own content onto the A/V
system.
2.5.2. Control Protocols
Professional audio systems can include amplifiers that are capable of
generating hundreds or thousands of watts of audio power which if
used incorrectly can cause hearing damage to those in the vicinity.
Apart from the usual care required by the systems operators to
prevent such incidents, the network traffic that controls these
devices must be secured (as with any sensitive application traffic).
In addition, it would be desirable if the configuration protocols
that are used to create the network paths used by the professional
audio traffic could be designed to protect devices that are not meant
to receive high-amplitude content from having such potentially
damaging signals routed to them.
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2.6. A State-of-the-Art Broadcast Installation Hits Technology Limits
ESPN recently constructed a state-of-the-art 194,000 sq ft, $125
million broadcast studio called DC2. The DC2 network is capable of
handling 46 Tbps of throughput with 60,000 simultaneous signals.
Inside the facility are 1,100 miles of fiber feeding four audio
control rooms. (See details at [ESPN_DC2] ).
In designing DC2 they replaced as much point-to-point technology as
they possibly could with packet-based technology. They constructed
seven individual studios using layer 2 LANS (using IEEE 802.1 AVB)
that were entirely effective at routing audio within the LANs, and
they were very happy with the results, however to interconnect these
layer 2 LAN islands together they ended up using dedicated links
because there is no standards-based routing solution available.
This is the kind of motivation we have to develop these standards
because customers are ready and able to use them.
3. Utility Telecom Use Cases
3.1. Overview
[I-D.finn-detnet-problem-statement] defines the characteristics of a
deterministic flow as a data communication flow with a bounded
latency, extraordinarily low frame loss, and a very narrow jitter.
This document intends to define the utility requirements for
deterministic networking.
Utility Telecom Networks
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.
Many utilities still rely on complex environments formed of multiple
application-specific, proprietary networks. Information is siloed
between operational areas. This prevents utility operations from
realizing the operational efficiency benefits, visibility, and
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functional integration of operational information across grid
applications and data networks. The key to modernizing grid
telecommunications is to provide a common, adaptable, multi-service
network infrastructure for the entire utility organization. Such a
network serves as the platform for current capabilities while
enabling future expansion of the network to accommodate new
applications and services.
To meet this diverse set of requirements, both today and in the
future, the next generation utility telecommunnications network will
be based on open-standards-based IP architecture. An end-to-end IP
architecture takes advantage of nearly three decades of IP technology
development, facilitating interoperability across disparate networks
and devices, as it has been already demonstrated in many mission-
critical and highly secure networks.
IEC (International Electrotechnical Commission) and different
National Committees have mandated a specific adhoc group (AHG8) to
define the migration strategy to IPv6 for all the IEC TC57 power
automation standards. IPv6 is seen as the obvious future
telecommunications technology for the Smart Grid. The Adhoc Group
has disclosed, to the IEC coordination group, their conclusions at
the end of 2014.
It is imperative that utilities participate in standards development
bodies to influence the development of future solutions and to
benefit from shared experiences of other utilities and vendors.
3.2. Telecommunications Trends and General telecommunications
Requirements
These general telecommunications requirements are over and above the
specific requirements of the use cases that have been addressed so
far. These include both current and future telecommunications
related requirements that should be factored into the network
architecture and design.
3.2.1. General Telecommunications Requirements
o IP Connectivity everywhere
o Monitoring services everywhere and from different remote centers
o Move services to a virtual data center
o Unify access to applications / information from the corporate
network
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o Unify services
o Unified Communications Solutions
o Mix of fiber and microwave technologies - obsolescence of SONET/
SDH or TDM
o Standardize grid telecommunications protocol to opened standard to
ensure interoperability
o Reliable Telecommunications for Transmission and Distribution
Substations
o IEEE 1588 time synchronization Client / Server Capabilities
o Integration of Multicast Design
o QoS Requirements Mapping
o Enable Future Network Expansion
o Substation Network Resilience
o Fast Convergence Design
o Scalable Headend Design
o Define Service Level Agreements (SLA) and Enable SLA Monitoring
o Integration of 3G/4G Technologies and future technologies
o Ethernet Connectivity for Station Bus Architecture
o Ethernet Connectivity for Process Bus Architecture
o Protection, teleprotection and PMU (Phaser Measurement Unit) on IP
3.2.1.1. Migration to Packet-Switched Network
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:
o Grid monitoring, control, and protection data
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o Non-control grid data (e.g. asset data for condition-based
monitoring)
o Physical safety and security data (e.g. voice and video)
o Remote worker access to corporate applications (voice, maps,
schematics, etc.)
o Field area network backhaul for smart metering, and distribution
grid management
o Enterprise traffic (email, collaboration tools, business
applications)
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.
3.2.2. Applications, Use cases and traffic patterns
Among the numerous applications and use cases that a utility deploys
today, many rely on high availability and deterministic behaviour of
the telecommunications networks. Protection use cases and generation
control are the most demanding and can't rely on a best effort
approach.
3.2.2.1. Transmission use cases
Protection means not only the protection of the human operator but
also the protection of the electric equipments and the preservation
of the stability and frequency of the grid. If a default occurs on
the transmission or the distribution of the electricity, important
damages could occured to the human operator but also to very costly
electrical equipments and perturb the grid leading to blackouts. The
time and reliability requirements are very strong to avoid dramatic
impacts to the electrical infrastructure.
3.2.2.1.1. Tele Protection
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:
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o 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.
o 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.
o 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.
Additional key elements that may impact Teleprotection performance
include bandwidth rate of the Teleprotection system and its
resiliency or failure recovery capacity. Transmission time,
bandwidth utilization and resiliency are directly linked to the
telecommunications equipments and the connections that are used to
transfer the commands between relays.
3.2.2.1.1.1. Latency Budget Consideration
Delay requirements for utility networks may vary depending upon a
number of parameters, such as the specific protection equipments
used. Most power line equipment can tolerate short circuits or
faults for up to approximately five power cycles before sustaining
irreversible damage or affecting other segments in the network. This
translates to total fault clearance time of 100ms. As a safety
precaution, however, actual operation time of protection systems is
limited to 70- 80 percent of this period, including fault recognition
time, command transmission time and line breaker switching time.
Some system components, such as large electromechanical switches,
require particularly long time to operate and take up the majority of
the total clearance time, leaving only a 10ms window for the
telecommunications part of the protection scheme, independent of the
distance to travel. Given the sensitivity of the issue, new networks
impose requirements that are even more stringent: IEC standard 61850
limits the transfer time for protection messages to 1/4 - 1/2 cycle
or 4 - 8ms (for 60Hz lines) for the most critical messages.
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3.2.2.1.1.2. Asymetric delay
In addition to minimal transmission delay, a differential protection
telecommunications channel must be synchronous, i.e., experiencing
symmetrical channel delay in transmit and receive paths. This
requires special attention in jitter-prone packet networks. While
optimally Teleprotection systems should support zero asymmetric
delay, typical legacy relays can tolerate discrepancies of up to
750us.
The main tools available for lowering delay variation below this
threshold are:
o A jitter buffer at the multiplexers on each end of the line can be
used to offset delay variation by queuing sent and received
packets. The length of the queues must balance the need to
regulate the rate of transmission with the need to limit overall
delay, as larger buffers result in increased latency. This is the
old TDM traditional way to fulfill this requirement.
o Traffic management tools ensure that the Teleprotection signals
receive the highest transmission priority and minimize the number
of jitter addition during the path. This is one way to meet the
requirement in IP networks.
o Standard Packet-Based synchronization technologies, such as
1588-2008 Precision Time Protocol (PTP) and Synchronous Ethernet
(Sync-E), can help maintain stable networks by keeping a highly
accurate clock source on the different network devices involved.
3.2.2.1.1.2.1. Other traffic characteristics
o Redundancy: The existence in a system of more than one means of
accomplishing a given function.
o Recovery time : The duration of time within which a business
process must be restored after any type of disruption in order to
avoid unacceptable consequences associated with a break in
business continuity.
o performance management : In networking, a management function
defined for controlling and analyzing different parameters/metrics
such as the throughput, error rate.
o packet loss : One or more packets of data travelling across
network fail to reach their destination.
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3.2.2.1.1.2.2. Teleprotection network requirements
The following table captures the main network requirements (this is
based on IEC 61850 standard)
+-----------------------------+-------------------------------------+
| Teleprotection Requirement | Attribute |
+-----------------------------+-------------------------------------+
| One way maximum delay | 4-10 ms |
| Asymetric delay required | Yes |
| Maximum jitter | less than 250 us (750 us for legacy |
| | IED) |
| Topology | Point to point, point to Multi- |
| | point |
| Availability | 99.9999 |
| precise timing required | Yes |
| Recovery time on node | less than 50ms - hitless |
| failure | |
| performance management | Yes, Mandatory |
| Redundancy | Yes |
| Packet loss | 0.1% to 1% |
+-----------------------------+-------------------------------------+
Table 1: Teleprotection network requirements
3.2.2.1.2. Inter-Trip Protection scheme
Inter-tripping is the controlled tripping of a circuit breaker to
complete the isolation of a circuit or piece of apparatus in concert
with the tripping of other circuit breakers. The main use of such
schemes is to ensure that protection at both ends of a faulted
circuit will operate to isolate the equipment concerned. Inter-
tripping schemes use signaling to convey a trip command to remote
circuit breakers to isolate circuits.
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+--------------------------------+----------------------------------+
| Inter-Trip protection | Attribute |
| Requirement | |
+--------------------------------+----------------------------------+
| One way maximum delay | 5 ms |
| Asymetric delay required | No |
| Maximum jitter | Not critical |
| Topology | Point to point, point to Multi- |
| | point |
| Bandwidth | 64 Kbps |
| Availability | 99.9999 |
| precise timing required | Yes |
| Recovery time on node failure | less than 50ms - hitless |
| performance management | Yes, Mandatory |
| Redundancy | Yes |
| Packet loss | 0.1% |
+--------------------------------+----------------------------------+
Table 2: Inter-Trip protection network requirements
3.2.2.1.3. Current Differential Protection Scheme
Current differential protection is commonly used for line protection,
and is typical for protecting parallel circuits. A main advantage
for differential protection is that, compared to overcurrent
protection, it allows only the faulted circuit to be de-energized in
case of a fault. At both end of the lines, the current is measured
by the differential relays, and based on Kirchhoff's law, both relays
will trip the circuit breaker if the current going into the line does
not equal the current going out of the line. This type of protection
scheme assumes some form of communications being present between the
relays at both end of the line, to allow both relays to compare
measured current values. A fault in line 1 will cause overcurrent to
be flowing in both lines, but because the current in line 2 is a
through following current, this current is measured equal at both
ends of the line, therefore the differential relays on line 2 will
not trip line 2. Line 1 will be tripped, as the relays will not
measure the same currents at both ends of the line. Line
differential protection schemes assume a very low telecommunications
delay between both relays, often as low as 5ms. Moreover, as those
systems are often not time-synchronized, they also assume symmetric
telecommunications paths with constant delay, which allows comparing
current measurement values taken at the exact same time.
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+----------------------------------+--------------------------------+
| Current Differential protection | Attribute |
| Requirement | |
+----------------------------------+--------------------------------+
| One way maximum delay | 5 ms |
| Asymetric delay Required | Yes |
| Maximum jitter | less than 250 us (750us for |
| | legacy IED) |
| Topology | Point to point, point to |
| | Multi-point |
| Bandwidth | 64 Kbps |
| Availability | 99.9999 |
| precise timing required | Yes |
| Recovery time on node failure | less than 50ms - hitless |
| performance management | Yes, Mandatory |
| Redundancy | Yes |
| Packet loss | 0.1% |
+----------------------------------+--------------------------------+
Table 3: Current Differential Protection requirements
3.2.2.1.4. Distance Protection Scheme
Distance (Impedance Relay) protection scheme is based on voltage and
current measurements. A fault on a circuit will generally create a
sag in the voltage level. If the ratio of voltage to current
measured at the protection relay terminals, which equates to an
impedance element, falls within a set threshold the circuit breaker
will operate. The operating characteristics of this protection are
based on the line characteristics. This means that when a fault
appears on the line, the impedance setting in the relay is compared
to the apparent impedance of the line from the relay terminals to the
fault. If the relay setting is determined to be below the apparent
impedance it is determined that the fault is within the zone of
protection. When the transmission line length is under a minimum
length, distance protection becomes more difficult to coordinate. In
these instances the best choice of protection is current differential
protection.
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+-------------------------------+-----------------------------------+
| Distance protection | Attribute |
| Requirement | |
+-------------------------------+-----------------------------------+
| One way maximum delay | 5 ms |
| Asymetric delay Required | No |
| Maximum jitter | Not critical |
| Topology | Point to point, point to Multi- |
| | point |
| Bandwidth | 64 Kbps |
| Availability | 99.9999 |
| precise timing required | Yes |
| Recovery time on node failure | less than 50ms - hitless |
| performance management | Yes, Mandatory |
| Redundancy | Yes |
| Packet loss | 0.1% |
+-------------------------------+-----------------------------------+
Table 4: Distance Protection requirements
3.2.2.1.5. Inter-Substation Protection Signaling
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.
The Current Transformer or Voltage Transformer (CT/VT) in one
substation sends the sampled analog voltage or current value to the
Merging Unit (MU) over hard wire. The merging unit sends the time-
synchronized 61850-9-2 sampled values to the slave IED. The slave
IED forwards the information to the Master IED in the other
substation. The master IED makes the determination (for example
based on sampled value differentials) to send a trip command to the
originating IED. Once the slave IED/Relay receives the GOOSE trip
for breaker tripping, it opens the breaker. It then sends a
confirmation message back to the master. All data exchanges between
IEDs are either through Sampled Value and/or GOOSE messages.
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+----------------------------------+--------------------------------+
| Inter-Substation protection | Attribute |
| Requirement | |
+----------------------------------+--------------------------------+
| One way maximum delay | 5 ms |
| Asymetric delay Required | No |
| Maximum jitter | Not critical |
| Topology | Point to point, point to |
| | Multi-point |
| Bandwidth | 64 Kbps |
| Availability | 99.9999 |
| precise timing required | Yes |
| Recovery time on node failure | less than 50ms - hitless |
| performance management | Yes, Mandatory |
| Redundancy | Yes |
| Packet loss | 1% |
+----------------------------------+--------------------------------+
Table 5: Inter-Substation Protection requirements
3.2.2.1.6. Intra-Substation Process Bus Communications
This use case describes the data flow from the CT/VT to the IEDs in
the substation via the merging unit (MU). The CT/VT in the
substation send the sampled value (analog voltage or current) to the
Merging Unit (MU) over hard wire. The merging unit sends the time-
synchronized 61850-9-2 sampled values to the IEDs in the substation
in GOOSE message format. The GPS Master Clock can send 1PPS or
IRIG-B format to MU through serial port, or IEEE 1588 protocol via
network. Process bus communication using 61850 simplifies
connectivity within the substation and removes the requirement for
multiple serial connections and removes the slow serial bus
architectures that are typically used. This also ensures increased
flexibility and increased speed with the use of multicast messaging
between multiple devices.
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+----------------------------------+--------------------------------+
| Intra-Substation protection | Attribute |
| Requirement | |
+----------------------------------+--------------------------------+
| One way maximum delay | 5 ms |
| Asymetric delay Required | No |
| Maximum jitter | Not critical |
| Topology | Point to point, point to |
| | Multi-point |
| Bandwidth | 64 Kbps |
| Availability | 99.9999 |
| precise timing required | Yes |
| Recovery time on Node failure | less than 50ms - hitless |
| performance management | Yes, Mandatory |
| Redundancy | Yes - No |
| Packet loss | 0.1% |
+----------------------------------+--------------------------------+
Table 6: Intra-Substation Protection requirements
3.2.2.1.7. Wide Area Monitoring and Control Systems
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:
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+----------------------+--------------------------------------------+
| WAMS Requirement | Attribute |
+----------------------+--------------------------------------------+
| One way maximum | 50 ms |
| delay | |
| Asymetric delay | No |
| Required | |
| Maximum jitter | Not critical |
| Topology | Point to point, point to Multi-point, |
| | Multi-point to Multi-point |
| Bandwidth | 100 Kbps |
| Availability | 99.9999 |
| precise timing | Yes |
| required | |
| Recovery time on | less than 50ms - hitless |
| Node failure | |
| performance | Yes, Mandatory |
| management | |
| Redundancy | Yes |
| Packet loss | 1% |
+----------------------+--------------------------------------------+
Table 7: WAMS Special Communication Requirements
3.2.2.1.8. IEC 61850 WAN engineering guidelines requirement
classification
The IEC (International Electrotechnical Commission) has recently
published a Technical Report which offers guidelines on how to define
and deploy Wide Area Networks for the interconnections of electric
substations, generation plants and SCADA operation centers. The IEC
61850-90-12 is providing a classification of WAN communication
requirements into 4 classes. You will find herafter the table
summarizing these requirements:
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+----------------+------------+------------+------------+-----------+
| WAN | Class WA | Class WB | Class WC | Class WD |
| Requirement | | | | |
+----------------+------------+------------+------------+-----------+
| Application | EHV (Extra | HV (High | MV (Medium | General |
| field | High | Voltage) | Voltage) | purpose |
| | Voltage) | | | |
| Latency | 5 ms | 10 ms | 100 ms | > 100 ms |
| Jitter | 10 us | 100 us | 1 ms | 10 ms |
| Latency | 100 us | 1 ms | 10 ms | 100 ms |
| Asymetry | | | | |
| Time Accuracy | 1 us | 10 us | 100 us | 10 to 100 |
| | | | | ms |
| Bit Error rate | 10-7 to | 10-5 to | 10-3 | |
| | 10-6 | 10-4 | | |
| Unavailability | 10-7 to | 10-5 to | 10-3 | |
| | 10-6 | 10-4 | | |
| Recovery delay | Zero | 50 ms | 5 s | 50 s |
| Cyber security | extremely | High | Medium | Medium |
| | high | | | |
+----------------+------------+------------+------------+-----------+
Table 8: 61850-90-12 Communication Requirements; Courtesy of IEC
3.2.2.2. Distribution use case
3.2.2.2.1. Fault Location Isolation and Service Restoration (FLISR)
As the name implies, Fault Location, Isolation, and Service
Restoration (FLISR) refers to the ability to automatically locate the
fault, isolate the fault, and restore service in the distribution
network. It is a self-healing feature whose purpose is to minimize
the impact of faults by serving portions of the loads on the affected
circuit by switching to other circuits. It reduces the number of
customers that experience a sustained power outage by reconfiguring
distribution circuits. This will likely be the first wide spread
application of distributed intelligence in the grid. Secondary
substations can be connected to multiple primary substations.
Normally, static power switch statuses (open/closed) in the network
dictate the power flow to secondary substations. Reconfiguring the
network in the event of a fault is typically done manually on site to
operate switchgear to energize/de-energize alternate paths.
Automating the operation of substation switchgear allows the utility
to have a more dynamic network where the flow of power can be altered
under fault conditions but also during times of peak load. It allows
the utility to shift peak loads around the network. Or, to be more
precise, alters the configuration of the network to move loads
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between different primary substations. The FLISR capability can be
enabled in two modes:
o Managed centrally from DMS (Distribution Management System), or
o Executed locally through distributed control via intelligent
switches and fault sensors.
There are 3 distinct sub-functions that are performed:
1. Fault Location Identification
This sub-function is initiated by SCADA inputs, such as lockouts,
fault indications/location, and, also, by input from the Outage
Management System (OMS), and in the future by inputs from fault-
predicting devices. It determines the specific protective device,
which has cleared the sustained fault, identifies the de-energized
sections, and estimates the probable location of the actual or the
expected fault. It distinguishes faults cleared by controllable
protective devices from those cleared by fuses, and identifies
momentary outages and inrush/cold load pick-up currents. This step
is also referred to as Fault Detection Classification and Location
(FDCL). This step helps to expedite the restoration of faulted
sections through fast fault location identification and improved
diagnostic information available for crew dispatch. Also provides
visualization of fault information to design and implement a
switching plan to isolate the fault.
2. Fault Type Determination
I. Indicates faults cleared by controllable protective devices by
distinguishing between:
a. Faults cleared by fuses
b. Momentary outages
c. Inrush/cold load current
II. Determines the faulted sections based on SCADA fault indications
and protection lockout signals
III. Increases the accuracy of the fault location estimation based
on SCADA fault current measurements and real-time fault analysis
3. Fault Isolation and Service Restoration
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Once the location and type of the fault has been pinpointed, the
systems will attempt to isolate the fault and restore the non-faulted
section of the network. This can have three modes of operation:
I. Closed-loop mode : This is initiated by the Fault location sub-
function. It generates a switching order (i.e., sequence of
switching) for the remotely controlled switching devices to isolate
the faulted section, and restore service to the non-faulted sections.
The switching order is automatically executed via SCADA.
II. Advisory mode : This is initiated by the Fault location sub-
function. It generates a switching order for remotely and manually
controlled switching devices to isolate the faulted section, and
restore service to the non-faulted sections. The switching order is
presented to operator for approval and execution.
III. Study mode : the operator initiates this function. It analyzes
a saved case modified by the operator, and generates a switching
order under the operating conditions specified by the operator.
With the increasing volume of data that are collected through fault
sensors, utilities will use Big Data query and analysis tools to
study outage information to anticipate and prevent outages by
detecting failure patterns and their correlation with asset age,
type, load profiles, time of day, weather conditions, and other
conditions to discover conditions that lead to faults and take the
necessary preventive and corrective measures.
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+----------------------+--------------------------------------------+
| FLISR Requirement | Attribute |
+----------------------+--------------------------------------------+
| One way maximum | 80 ms |
| delay | |
| Asymetric delay | No |
| Required | |
| Maximum jitter | 40 ms |
| Topology | Point to point, point to Multi-point, |
| | Multi-point to Multi-point |
| Bandwidth | 64 Kbps |
| Availability | 99.9999 |
| precise timing | Yes |
| required | |
| Recovery time on | Depends on customer impact |
| Node failure | |
| performance | Yes, Mandatory |
| management | |
| Redundancy | Yes |
| Packet loss | 0.1% |
+----------------------+--------------------------------------------+
Table 9: FLISR Communication Requirements
3.2.2.3. Generation use case
3.2.2.3.1. Frequency Control / Automatic Generation Control (AGC)
The system frequency should be maintained within a very narrow band.
Deviations from the acceptable frequency range are detected and
forwarded to the Load Frequency Control (LFC) system so that required
up or down generation increase / decrease pulses can be sent to the
power plants for frequency regulation. The trend in system frequency
is a measure of mismatch between demand and generation, and is a
necessary parameter for load control in interconnected systems.
Automatic generation control (AGC) is a system for adjusting the
power output of generators at different power plants, in response to
changes in the load. Since a power grid requires that generation and
load closely balance moment by moment, frequent adjustments to the
output of generators are necessary. The balance can be judged by
measuring the system frequency; if it is increasing, more power is
being generated than used, and all machines in the system are
accelerating. If the system frequency is decreasing, more demand is
on the system than the instantaneous generation can provide, and all
generators are slowing down.
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Where the grid has tie lines to adjacent control areas, automatic
generation control helps maintain the power interchanges over the tie
lines at the scheduled levels. The AGC takes into account various
parameters including the most economical units to adjust, the
coordination of thermal, hydroelectric, and other generation types,
and even constraints related to the stability of the system and
capacity of interconnections to other power grids.
For the purpose of AGC we use static frequency measurements and
averaging methods are used to get a more precise measure of system
frequency in steady-state conditions.
During disturbances, more real-time dynamic measurements of system
frequency are taken using PMUs, especially when different areas of
the system exhibit different frequencies. But that is outside the
scope of this use case.
+---------------------------------------------------+---------------+
| FCAG (Frequency Control Automatic Generation) | Attribute |
| Requirement | |
+---------------------------------------------------+---------------+
| One way maximum delay | 500 ms |
| Asymetric delay Required | No |
| Maximum jitter | Not critical |
| Topology | Point to |
| | point |
| Bandwidth | 20 Kbps |
| Availability | 99.999 |
| precise timing required | Yes |
| Recovery time on Node failure | N/A |
| performance management | Yes, |
| | Mandatory |
| Redundancy | Yes |
| Packet loss | 1% |
+---------------------------------------------------+---------------+
Table 10: FCAG Communication Requirements
3.2.3. Specific Network topologies of Smart Grid Applications
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.
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Going forward, one network will support operation and maintenance of
electrical networks (generation, transmission, and distribution),
voice and data services for ten of thousands of employees and for
exchange with neighboring interconnections, and administrative
services. To meet those requirements, utility may deploy several
physical networks leveraging different technologies across the
country: an optical network and a microwave network for instance.
Each protection and automatism system between two points has two
telecommunications circuits, one on each network. Path diversity
between two substations is key. Regardless of the event type
(hurricane, ice storm, etc.), one path shall stay available so the
SPS can still operate.
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.
Due to vast distances between transmission substations (for example
as far as 280km apart), the fiber signal can be amplified to reach a
distance of 280 km without attenuation.
3.2.4. Precision Time Protocol
Some utilities do not use GPS clocks in generation substations. One
of the main reasons is that some of the generation plants are 30 to
50 meters deep under ground and the GPS signal can be weak and
unreliable. Instead, atomic clocks are used. Clocks are
synchronized amongst each other. Rubidium clocks provide clock and
1ms timestamps for IRIG-B. Some companies plan to transition to the
Precision Time Protocol (IEEE 1588), distributing the synchronization
signal over the IP/MPLS network.
The Precision Time Protocol (PTP) is defined in IEEE standard 1588.
PTP is applicable to distributed systems consisting of one or more
nodes, communicating over a network. Nodes are modeled as containing
a real-time clock that may be used by applications within the node
for various purposes such as generating time-stamps for data or
ordering events managed by the node. The protocol provides a
mechanism for synchronizing the clocks of participating nodes to a
high degree of accuracy and precision.
PTP operates based on the following assumptions :
It is assumed that the network eliminates cyclic forwarding of PTP
messages within each communication path (e.g., by using a spanning
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tree protocol). PTP eliminates cyclic forwarding of PTP messages
between communication paths.
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.
PTP was designed assuming a multicast communication model. PTP
also supports a unicast communication model as long as the
behavior of the protocol is preserved.
Like all message-based time transfer protocols, PTP time accuracy
is degraded by asymmetry in the paths taken by event messages.
Asymmetry is not detectable by PTP, however, if known, PTP
corrects for asymmetry.
A time-stamp event is generated at the time of transmission and
reception of any event message. The time-stamp event occurs when the
message's timestamp point crosses the boundary between the node and
the network.
IEC 61850 will recommend the use of the IEEE PTP 1588 Utility Profile
(as defined in IEC 62439-3 Annex B) which offers the support of
redundant attachment of clocks to Paralell Redundancy Protcol (PRP)
and High-availability Seamless Redundancy (HSR) networks.
3.3. IANA Considerations
This memo includes no request to IANA.
3.4. Security Considerations
3.4.1. Current Practices and Their Limitations
Grid monitoring and control devices are already targets for cyber
attacks and legacy telecommunications protocols have many intrinsic
network related vulnerabilities. DNP3, Modbus, PROFIBUS/PROFINET,
and other protocols are designed around a common paradigm of request
and respond. Each protocol is designed for a master device such as
an HMI (Human Machine Interface) system to send commands to
subordinate slave devices to retrieve data (reading inputs) or
control (writing to outputs). Because many of these protocols lack
authentication, encryption, or other basic security measures, they
are prone to network-based attacks, allowing a malicious actor or
attacker to utilize the request-and-respond system as a mechanism for
command-and-control like functionality. Specific security concerns
common to most industrial control, including utility
telecommunication protocols include the following:
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o Network or transport errors (e.g. malformed packets or excessive
latency) can cause protocol failure.
o 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.
o Protocol commands may be available that are capable of restarting
communications and otherwise interrupting processes.
o Protocol commands may be available that are capable of clearing,
erasing, or resetting diagnostic information such as counters and
diagnostic registers.
o Protocol commands may be available that are capable of requesting
sensitive information about the controllers, their configurations,
or other need-to-know information.
o 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.
o Protocol commands may be available that are capable of
broadcasting messages to many devices at once (i.e. a potential
DoS).
o Protocol commands may be available to query the device network to
obtain defined points and their values (i.e. a configuration
scan).
o Protocol commands may be available that will list all available
function codes (i.e. a function scan).
o Bump in the wire (BITW) solutions : A hardware device is added to
provide IPSec services between two routers that are not capable of
IPSec functions. This special IPsec device will intercept then
intercept outgoing datagrams, add IPSec protection to them, and
strip it off incoming datagrams. BITW can all IPSec to legacy
hosts and can retrofit non-IPSec routers to provide security
benefits. The disadvantages are complexity and cost.
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
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could provide both control over a process and misrepresentation of
data back to operator consoles.
3.4.2. Security Trends in Utility Networks
Although advanced telecommunications networks can assist in
transforming the energy industry, playing a critical role in
maintaining high levels of reliability, performance, and
manageability, they also introduce the need for an integrated
security infrastructure. Many of the technologies being deployed to
support smart grid projects such as smart meters and sensors can
increase the vulnerability of the grid to attack. Top security
concerns for utilities migrating to an intelligent smart grid
telecommunications platform center on the following trends:
o Integration of distributed energy resources
o Proliferation of digital devices to enable management, automation,
protection, and control
o Regulatory mandates to comply with standards for critical
infrastructure protection
o Migration to new systems for outage management, distribution
automation, condition-based maintenance, load forecasting, and
smart metering
o Demand for new levels of customer service and energy management
This development of a diverse set of networks to support the
integration of microgrids, open-access energy competition, and the
use of network-controlled devices is driving the need for a converged
security infrastructure for all participants in the smart grid,
including utilities, energy service providers, large commercial and
industrial, as well as residential customers. Securing the assets of
electric power delivery systems, from the control center to the
substation, to the feeders and down to customer meters, requires an
end-to-end security infrastructure that protects the myriad of
telecommunications assets used to operate, monitor, and control power
flow and measurement. Cyber security refers to all the security
issues in automation and telecommunications that affect any functions
related to the operation of the electric power systems.
Specifically, it involves the concepts of:
o Integrity : data cannot be altered undetectably
o Authenticity : the telecommunications parties involved must be
validated as genuine
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o Authorization : only requests and commands from the authorized
users can be accepted by the system
o Confidentiality : data must not be accessible to any
unauthenticated users
When designing and deploying new smart grid devices and
telecommunications systems, it's imperative to understand the various
impacts of these new components under a variety of attack situations
on the power grid. Consequences of a cyber attack on the grid
telecommunications network can be catastrophic. This is why security
for smart grid is not just an ad hoc feature or product, it's a
complete framework integrating both physical and Cyber security
requirements and covering the entire smart grid networks from
generation to distribution. Security has therefore become one of the
main foundations of the utility telecom network architecture and must
be considered at every layer with a defense-in-depth approach.
Migrating to IP based protocols is key to address these challenges
for two reasons:
1. IP enables a rich set of features and capabilities to enhance the
security posture
2. IP is based on open standards, which allows interoperability
between different vendors and products, driving down the costs
associated with implementing security solutions in OT networks.
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.
4. Building Automation Systems
4.1. Use Case Description
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.
A BAS primarily performs the following functions:
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o Periodically measures states of devices, for example humidity and
illuminance of rooms, open/close state of doors, FAN speed, etc.
o Stores the measured data.
o Provides the measured data to BAS systems and operators.
o Generates alarms for abnormal state of devices.
o Controls devices (e.g. turn off room lights at 10:00 PM).
4.2. Building Automation Systems Today
4.2.1. BAS Architecture
A typical BAS architecture of today is shown in Figure 1.
+----------------------------+
| |
| BMS HMI |
| | | |
| +----------------------+ |
| | Management Network | |
| +----------------------+ |
| | | |
| LC LC |
| | | |
| +----------------------+ |
| | Field Network | |
| +----------------------+ |
| | | | | |
| Dev Dev Dev Dev |
| |
+----------------------------+
BMS := Building Management Server
HMI := Human Machine Interface
LC := Local Controller
Figure 1: BAS architecture
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.
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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").
A Building Management Server (BMS) performs the following operations.
o Collect and store device states from LCs at regular intervals.
o Send control values to LCs according to a building schedule.
o Send an alarm signal to operators if it detects abnormal devices
states.
The BMS and HMI communicate with LCs via IP-based "management
protocols" (see standards [bacnetip], [knx]).
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:
o Measure device states and provide the information to BMS or HMI.
o Send control values to devices, unilaterally or as part of a
feedback control loop.
There are many field protocols used today; some are standards-based
and others are proprietary (see standards [lontalk], [modbus],
[profibus] and [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.
4.2.2. BAS Deployment Model
An example BAS for medium or large buildings is shown in Figure 2.
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.
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+--------------------------------------------------+
| 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 | | | |
| +--------------------------------+-----+ |
| | |
+--------------------------------------------------+
Figure 2: BAS Deployment model for Medium/Large Buildings
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.
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.
In Figure 3, 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.
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+---------------+
| Remote Center |
| |
| BMS HMI |
+------------------------------------+ | | | |
| Floor 2 | | +---+---+ |
| +----LC~~~~+~~~~~+ Field Network| | | |
| | | | | | Router |
| | Dev Dev | +-------|-------+
| | | |
|--- | ------------------------------| |
| | Floor 1 | |
| +----LC~~~~+~~~~~+ | |
| | | | | |
| | Dev Dev | |
| | | |
| | Management Network | WAN |
| +------------------------Router-------------+
| |
+------------------------------------+
Figure 3: Deployment model for Small Buildings
Some interoperability is possible today in the Management Network,
but not in today's field networks due to their non-IP-based design.
4.2.3. Use Cases for Field Networks
Below are use cases for Environmental Monitoring, Fire Detection, and
Feedback Control, and their implications for field network
performance.
4.2.3.1. Environmental Monitoring
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 %.
4.2.3.2. Fire Detection
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
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scenario the measurement interval is 10-50ms, the communication delay
is 10ms, and the availability must be 99.9999 %.
4.2.3.3. Feedback Control
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.
Communication delay is expected to be less than 10 ms, jitter less
than 1 sec while the availability must be 99.9999% .
4.2.4. Security Considerations
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 .
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.
4.3. BAS Future
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.
We expect building networks to be connected to or converged with
other networks (Enterprise network, Home network, and Internet).
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.
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4.4. BAS Asks
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.
This would imply an architecture that can guarantee
o Low communication delays (from <10ms to 100ms in a network of
several hundred devices)
o Low jitter (< 1 ms)
o Tight feedback intervals (1ms - 10ms)
o High network availability (up to 99.9999% )
o Availability of network data in disaster scenario
o Authentication between management and field devices (both local
and remote)
o Integrity and data origin authentication of communication data
between field and management devices
o Confidentiality of data when communicated to a remote device
5. Wireless for Industrial
5.1. Use Case Description
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).
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.
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
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market. For example, a 1% cost reduction in some areas could save
$100B
5.1.1. Network Convergence using 6TiSCH
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.
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 [I-D.ietf-6tisch-architecture],
[IEEE802154], [IEEE802154e], and [RFC7554]).
There are other deterministic wireless busses and networks available
today, however they are imcompatible with each other, and
incompatible with IP traffic (for example [ISA100], [WirelessHART]).
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.
5.1.2. Common Protocol Development for 6TiSCH
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.
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.
One such commonality is that although at a different time scale, in
both TSN [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.
Another commonality is remote monitoring and scheduling management of
a TSCH network by a Path Computation Element (PCE) and Network
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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).
6TiSCH depends on [PCE] and [I-D.finn-detnet-architecture], and we
expect that DetNet will maintain consistency with [IEEE802.1TSNTG].
5.2. Wireless Industrial Today
Today industrial wireless is accomplished using multiple
deterministic wireless networks which are incompatible with each
other and with IP traffic.
6TiSCH is not yet fully specified, so it cannot be used in today's
applications.
5.3. Wireless Industrial Future
5.3.1. Unified Wireless Network and Management
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 Figure 4.
---+-------- ............ ------------
| External Network |
| +-----+
+-----+ | NME |
| | LLN Border | |
| | router +-----+
+-----+
o o o
o o o o
o o LLN o o o
o o o o
o
Figure 4: Basic 6TiSCH Network
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Figure 5 shows a backbone router federating multiple synchronized
6TiSCH subnets into a single subnet connected to the external
network.
---+-------- ............ ------------
| 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
Figure 5: Extended 6TiSCH Network
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
[I-D.finn-detnet-architecture] with respect to Layer-3 aspects of
deterministic networks that span multiple Layer-2 domains.
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.
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+-----+
| 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
Figure 6: 6TiSCH Network with PRE
5.3.1.1. PCE and 6TiSCH ARQ Retries
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.
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.
For example, in Figure 6, 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.
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.
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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).
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.
5.3.2. Schedule Management by a PCE
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.
5.3.2.1. PCE Commands and 6TiSCH CoAP Requests
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.
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
[I-D.ietf-6tisch-coap].
6TiSCH expects that the PCE commands will be issued directly as CoAP
requests or 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 DetNet
[I-D.finn-detnet-architecture] when the work is formalized. Related
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information about 6TiSCH can be found at
[I-D.ietf-6tisch-6top-interface] and RPL [RFC6550].
If it appears that a path through the network does not perform as
expected, a protocol may be used to update the state in the devices,
but in 6TiSCH that flow was not designed and no protocol was selected
and it is expected that DetNet will determine the appropriate end-to-
end protocols to be used in that case.
A "slotFrame" is the base object that the PCE needs to manipulate to
program a schedule into an LLN node ([I-D.ietf-6tisch-architecture]).
The PCE should be able to 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.
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. DetNet should define this protocol, and it and should
operate over CoAP. The protocol should be able to carry multiple
metrics, in particular the same metrics as used for RPL operations
[RFC6551]
5.3.2.2. 6TiSCH IP Interface
"6top" ([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
[I-D.ietf-6tisch-6top-interface] and [I-D.ietf-6tisch-coap].
An IP packet that is sent along a 6TiSCH path uses the Differentiated
Services Per-Hop-Behavior Group called Deterministic Forwarding, as
described in [I-D.svshah-tsvwg-deterministic-forwarding].
5.3.3. 6TiSCH Security Considerations
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.
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5.4. Wireless Industrial Asks
6TiSCH depends on DetNet to define:
o Configuration (state) and operations for deterministic paths
o End-to-end protocols for deterministic forwarding (tagging, IP)
o Protocol for packet replication and elimination
o Protocol for packet automatic retries (ARQ) (specific to wireless)
6. Cellular Radio Use Cases
6.1. Use Case Description
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.
6.1.1. Network Architecture
Figure 7 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).
In Figure 7 "eNB" ("E-UTRAN Node B") is the hardware that is
connected to the mobile phone network which communicates directly
with mobile handsets ([TS36300]).
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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)
Figure 7: Generic 3GPP-based Cellular Network Architecture
The available processing time for Fronthaul networking overhead is
limited to the available time after the baseband processing of the
radio frame has completed. For example in Long Term Evolution (LTE)
radio, processing of a radio frame is allocated 3ms, but typically
the processing completes much earlier (<400us) allowing the remaining
time to be used by the Fronthaul network. This ultimately determines
the distance the remote radio heads can be located from the base
stations (200us equals roughly 40 km of optical fiber-based
transport, thus round trip time is 2*200us = 400us).
The remainder of the "maximum delay budget" is consumed by all nodes
and buffering between the remote radio head and the baseband
processing, plus the distance-incurred delay.
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 [NGMN].
6.1.2. Time Synchronization Requirements
Fronthaul time synchronization requirements are given by [TS25104],
[TS36104], [TS36211], and [TS36133]. These can be summarized for the
current 3GPP LTE-based networks as:
Delay Accuracy:
+-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
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this low to meet the 3GPP Timing Alignment Error (TAE) measurement
requirements.
Packet Delay Variation:
Packet Delay Variation (PDV aka Jitter aka Timing Alignment Error)
is problematic to Fronthaul networks and must be minimized. If
the transport network cannot guarantee low enough PDV then
additional buffering has to be introduced at the edges of the
network to buffer out the jitter. Buffering is not desirable as
it reduces the total available delay budget.
* 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).
* For intra-band contiguous carrier aggregation, with or without
MIMO or TX diversity, TAE shall not exceed 130 ns (i.e. 1/2
Tc).
* For intra-band non-contiguous carrier aggregation, with or
without MIMO or TX diversity, TAE shall not exceed 260 ns (i.e.
one Tc).
* For inter-band carrier aggregation, with or without MIMO or TX
diversity, TAE shall not exceed 260 ns.
Transport link contribution to radio frequency error:
+-2 PPB. This value is considered to be "available" for the
Fronthaul link out of the total 50 PPB budget reserved for the
radio interface. Note: the reason that the transport link
contributes to radio frequency error is as follows. The current
way of doing Fronthaul is from the radio unit to remote radio head
directly. The remote radio head is essentially a passive device
(without buffering etc.) The transport drives the antenna
directly by feeding it with samples and everything the transport
adds will be introduced to radio as-is. So if the transport
causes additional frequence error that shows immediately on the
radio as well.
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,
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every measure to reduce jitter and delay on the path makes it easier
to meet the end-to-end requirements.
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.
In cellular networks from the LTE radio era onward, phase
synchronization is needed in addition to frequency synchronization
([TS36300], [TS23401]).
6.1.3. Time-Sensitive Stream Requirements
In addition to the time synchronization requirements listed in
Section Section 6.1.2 the Fronthaul networks assume practically
error-free transport. The maximum bit error rate (BER) has been
defined to be 10^-12. When packetized that would imply a packet
error rate (PER) of 2.4*10^-9 (assuming ~300 bytes packets).
Retransmitting lost packets and/or using forward error correction
(FEC) to circumvent bit errors is practically impossible due to the
additional delay incurred. Using redundant streams for better
guarantees for delivery is also practically impossible in many cases
due to high bandwidth requirements of Fronthaul networks. For
instance, current uncompressed CPRI bandwidth expansion ratio is
roughly 20:1 compared to the IP layer user payload it carries.
Protection switching is also a candidate but current technologies for
the path switch are too slow. We do not currently know of a better
solution for this issue.
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.
6.1.4. Security Considerations
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.
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6.2. Cellular Radio Networks Today
Today's Fronthaul networks typically consist of:
o Dedicated point-to-point fiber connection is common
o Proprietary protocols and framings
o Custom equipment and no real networking
Today's Midhaul and Backhaul networks typically consist of:
o Mostly normal IP networks, MPLS-TP, etc.
o Clock distribution and sync using 1588 and SyncE
Telecommunication networks in the cellular domain are already heading
towards transport networks where precise time synchronization support
is one of the basic building blocks. While the transport networks
themselves have practically transitioned to all-IP packet based
networks to meet the bandwidth and cost requirements, highly accurate
clock distribution has become a challenge.
Transport networks in the cellular domain are typically based on Time
Division Multiplexing (TDM-based) and provide frequency
synchronization capabilities as a part of the transport media.
Alternatively other technologies such as Global Positioning System
(GPS) or Synchronous Ethernet (SyncE) are used [SyncE].
Both Ethernet and IP/MPLS [RFC3031] (and PseudoWires (PWE) [RFC3985]
for legacy transport support) have become popular tools to build and
manage new all-IP Radio Access Networks (RAN)
[I-D.kh-spring-ip-ran-use-case]. Although various timing and
synchronization optimizations have already been proposed and
implemented including 1588 PTP enhancements
[I-D.ietf-tictoc-1588overmpls][I-D.mirsky-mpls-residence-time], these
solution are not necessarily sufficient for the forthcoming RAN
architectures or guarantee the higher time-synchronization
requirements [CPRI]. There are also existing solutions for the TDM
over IP [RFC5087] [RFC4553] or Ethernet transports [RFC5086].
6.3. Cellular Radio Networks Future
We would like to see the following in future Cellular Radio networks:
o Unified standards-based transport protocols and standard
networking equipment that can make use of underlying deterministic
link-layer services
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o Unified and standards-based network management systems and
protocols in all parts of the network (including Fronthaul)
New radio access network deployment models and architectures may
require time sensitive networking services with strict requirements
on other parts of the network that previously were not considered to
be packetized at all. The time and synchronization support are
already topical for Backhaul and Midhaul packet networks [MEF], and
becoming a real issue for Fronthaul networks. Specifically in the
Fronthaul networks the timing and synchronization requirements can be
extreme for packet based technologies, for example, on the order of
sub +-20 ns packet delay variation (PDV) and frequency accuracy of
+0.002 PPM [Fronthaul].
The actual transport protocols and/or solutions to establish required
transport "circuits" (pinned-down paths) for Fronthaul traffic are
still undefined. Those are likely to include (but are not limited
to) solutions directly over Ethernet, over IP, and MPLS/PseudoWire
transport.
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 [IEEE8021CM].
The really interesting and important existing work for time sensitive
networking has been done for Ethernet [TSNTG], which specifies the
use of IEEE 1588 time precision protocol (PTP) [IEEE1588] in the
context of IEEE 802.1D and IEEE 802.1Q. While IEEE 802.1AS
[IEEE8021AS] specifies a Layer-2 time synchronizing service other
specification, such as IEEE 1722 [IEEE1722] specify Ethernet-based
Layer-2 transport for time-sensitive streams. New promising work
seeks to enable the transport of time-sensitive fronthaul streams in
Ethernet bridged networks [IEEE8021CM]. Similarly to IEEE 1722 there
is an ongoing standardization effort to define Layer-2 transport
encapsulation format for transporting radio over Ethernet (RoE) in
IEEE 1904.3 Task Force [IEEE19043].
All-IP RANs and various "haul" networks would benefit from time
synchronization and time-sensitive transport services. Although
Ethernet appears to be the unifying technology for the transport
there is still a disconnect providing Layer-3 services. The protocol
stack typically has a number of layers below the Ethernet Layer-2
that shows up to the Layer-3 IP transport. It is not uncommon that
on top of the lowest layer (optical) transport there is the first
layer of Ethernet followed one or more layers of MPLS, PseudoWires
and/or other tunneling protocols finally carrying the Ethernet layer
visible to the user plane IP traffic. While there are existing
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technologies, especially in MPLS/PWE space, to establish circuits
through the routed and switched networks, there is a lack of
signaling the time synchronization and time-sensitive stream
requirements/reservations for Layer-3 flows in a way that the entire
transport stack is addressed and the Ethernet layers that needs to be
configured are addressed.
Furthermore, not all "user plane" traffic will be IP. Therefore, the
same solution also must address the use cases where the user plane
traffic is again another layer or Ethernet frames. There is existing
work describing the problem statement
[I-D.finn-detnet-problem-statement] and the architecture
[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.
6.4. Cellular Radio Networks Asks
A standard for data plane transport specification which is:
o Unified among all *hauls
o Deployed in a highly deterministic network environment
A standard for data flow information models that are:
o Aware of the time sensitivity and constraints of the target
networking environment
o Aware of underlying deterministic networking services (e.g. on the
Ethernet layer)
Mapping the Fronthaul requirements to IETF DetNet
[I-D.finn-detnet-architecture] Section 3 "Providing the DetNet
Quality of Service", the relevant features are:
o Zero congestion loss.
o Pinned-down paths.
7. Cellular Coordinated Multipoint Processing (CoMP)
7.1. Use Case Description
In cellular wireless communication systems, Inter-Site Coordinated
Multipoint Processing (CoMP, see [CoMP]) is a technique implemented
within a cell site which improves system efficiency and user quality
experience by significantly improving throughput in the cell-edge
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region (i.e. at the edges of that cell site's radio coverage area).
CoMP techniques depend on deterministic high-reliability
communication between cell sites, however such connections today are
IP-based which in current mobile networks can not meet the QoS
requirements, so CoMP is an emerging technology which can benefit
from DetNet.
Here we consider the JT (Joint Transmit) application for CoMP, which
provides the highest performance gain (compared to other
applications).
7.1.1. CoMP Architecture
+--------------------------+
| CoMP |
+--+--------------------+--+
| |
+----------+ +------------+
| Uplink | | Downlink |
+-----+----+ +--------+---+
| |
------------------- -----------------------
| | | | | |
+---------+ +----+ +-----+ +------------+ +-----+ +-----+
| Joint | | CS | | DPS | | Joint | | CS/ | | DPS |
|Reception| | | | | |Transmission| | CB | | |
+---------+ +----+ +-----+ +------------+ +-----+ +-----+
| |
|----------- |-------------
| | | |
+------------+ +---------+ +----------+ +------------+
| Joint | | Soft | | Coherent | | Non- |
|Equalization| |Combining| | JT | | Coherent JT|
+------------+ +---------+ +----------+ +------------+
Figure 8: Framework of CoMP Technology
As shown in Figure 8, 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.
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7.1.2. Delay Sensitivity in CoMP
In contrast to the single-cell scenario, CoMP has delay-sensitive
performance parameters, which are "backhaul latency" and "CSI
(Channel State Information) reporting and accuracy". The essential
feature of CoMP is signaling between eNBs, so the backhaul latency is
the dominating limitation of the CoMP performance. Generally, JT can
benefit from coordinated scheduling (either distributed or
centralized) of different cells if the signaling delay between eNBs
is within 4-10ms. This delay requirement is both rigid and absolute
because any uncertainty in delay will degrade the performance
significantly.
7.2. CoMP Today
Due to the strict sensitivity to latency and synchronization, CoMP
between eNB has not been deployed yet. This is because the current
interface path between eNBs cannot meet the delay bound because it is
usually IP-based and passing through multiple network hops (this
interface is called "X2" or "eX2" for "enhanced X2"). Today lack of
absolute delay guarantee on X2/eX2 traffic is the main obstacle to JT
and multi-eNB coordination.
There is still lack of Layer-3 (IP) transport protocol and signaling
that is capable of low latency services; current techniques such as
MPLS and PWE focus on establishing circuits using pre-routed paths
but there is no such signaling for reservation of time-sensitive
stream.
7.3. CoMP Future
7.3.1. Mobile Industry Overall Goals
[METIS] documents the fundamental challenges as well as overall
technical goals of the 5G mobile and wireless system as the starting
point. These future systems should support (at similar cost and
energy consumption levels as today's system):
o 1000 times higher mobile data volume per area
o 10 times to 100 times higher typical user data rate
o 10 times to 100 times higher number of connected devices
o 10 times longer battery life for low power devices
o 5 times reduced End-to-End (E2E) latency
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The current LTE networking system has E2E latency less than 20ms
[LTE-Latency] which leads to around 5ms E2E latency for 5G networks.
To fulfill these latency demands at similar cost will be challenging
because as the system also requires 100x bandwidth and 100x connected
devices, simply adding redundant bandwidth provisioning can no longer
be an efficient solution.
In addition to bandwidth provisioning, reserved critical flows should
not be affected by other flows no matter the pressure of the network.
Deterministic networking techniques in both layer-2 and layer-3 using
IETF protocol solutions can be promising to serve these scenarios.
7.3.2. CoMP Infrastructure Goals
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. Assuming
network architecture remains unchanged (i.e. no Fronthaul network and
data flow between eNB is via X2/eX2) we would like to see the
following in the near future:
o Unified protocols and delay-guaranteed forwarding network
equipment that is capable of delivering deterministic latency
services.
o Unified management and protocols which take delay and timing into
account.
o Unified deterministic latency data model and signaling for
resource reservation.
7.4. CoMP Asks
To fully utilize the power of CoMP, it requires:
o Very tight absolute delay bound (100-500us) within 7-10 hops.
o Standardized data plane with highly deterministic networking
capability.
o Standardized control plane to unify backhaul network elements with
time-sensitive stream reservation signaling.
In addition, a standardized deterministic latency data flow model
that includes:
o Network-aware constraints on the networking environment
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o Time-aware description of flow characteristics and network
resources, which may not need to be bandwidth based
o Application-aware description of deterministic latency services.
8. Industrial M2M
8.1. Use Case Description
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.
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
Figure 9.
S (Sensor)
\ +-----+
PLC__ \.--. .--. ---| MES |
\_( `. _( `./ +-----+
A------( Local )-------------( L2 )
( Net ) ( Net ) +-------+
/`--(___.-' `--(___.-' ----| S-PLC |
S_/ / PLC .--. / +-------+
A_/ \_( `.
(Actuator) ( Local )
( Net )
/`--(___.-'\
/ \ A
S A
Figure 9: Current Generic Industrial M2M Network Architecture
This use case focuses on PLC-related communications; communication to
Manufacturing-Execution-Systems (MESs) are not addressed.
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
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bandwidth required. There is also a subset of non-time-critical
traffic that must be reliable even though it is not time sensitive.
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.
8.2. Industrial M2M Communication Today
Today, proprietary networks fulfill the needed timing and
availability for M2M networks.
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).
PLC-related control/data streams are transmitted periodically and
carry either a pre-configured payload or a payload configured during
runtime.
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.
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.
8.2.1. Transport Parameters
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.
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
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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.
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.
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.
As network downtime may impact the whole production system the
required network availability is rather high (99,999%).
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.
8.2.2. Stream Creation and Destruction
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.
8.3. Industrial M2M Future
We would like to see the various proprietary networks replaced with a
converged IP-standards-based network with deterministic properties
that can satisfy the timing, security and reliability constraints
described above.
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8.4. Industrial M2M Asks
o Converged IP-based network
o Deterministic behavior (bounded latency and jitter )
o High availability (presumably through redundancy) (99.999 %)
o Low message delivery time (100us - 50ms)
o Low packet loss (burstless, 0.1-1 %)
o Precise time synchronization accuracy (1us)
o Security (e.g. prevent critical flows from being leaked between
physically separated networks)
9. Internet-based Applications
9.1. Use Case Description
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.
9.1.1. Media Content Delivery
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.
9.1.2. Online Gaming
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.
9.1.3. Virtual Reality
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.
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9.2. Internet-Based Applications Today
Internet service today is by definition "best effort", with no
guarantees on delivery or bandwidth.
9.3. Internet-Based Applications Future
We imagine an Internet from which we will be able to play a video
without glitches and play games without lag.
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.
For VR, 1-10ms maximum delay is needed and total network budget is
1-5ms if doing remote VR.
Flow identification can be used for gaming and VR, i.e. it can
recognize a critical flow and provide appropriate latency bounds.
9.4. Internet-Based Applications Asks
o Unified control and management protocols to handle time-critical
data flow
o Application-aware flow filtering mechanism to recognize the timing
critical flow without doing 5-tuple matching
o Unified control plane to provide low latency service on Layer-3
without changing the data plane
o OAM system and protocols which can help to provide E2E-delay
sensitive service provisioning
10. Use Case Common Elements
Looking at the use cases collectively, the following common desires
for the DetNet-based networks of the future emerge:
o Open standards-based network (replace various proprietary
networks, reduce cost, create multi-vendor market)
o Centrally administered (though such administration may be
distributed for scale and resiliency)
o Integrates L2 (bridged) and L3 (routed) environments (independent
of the Link layer, e.g. can be used with Ethernet, 6TiSCH, etc.)
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o 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)
o 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)
o 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)
o 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))
o 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)
o High availability (99.9999 percent up time requested, but may be
up to twelve 9s)
o Reliability, redundancy (lives at stake)
o Security (from failures, attackers, misbehaving devices -
sensitive to both packet content and arrival time)
11. Acknowledgments
11.1. Pro Audio
This section was derived from draft-gunther-detnet-proaudio-req-01.
The editors would like to acknowledge the help of the following
individuals and the companies they represent:
Jeff Koftinoff, Meyer Sound
Jouni Korhonen, Associate Technical Director, Broadcom
Pascal Thubert, CTAO, Cisco
Kieran Tyrrell, Sienda New Media Technologies GmbH
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11.2. Utility Telecom
This section was derived from draft-wetterwald-detnet-utilities-reqs-
02.
Faramarz Maghsoodlou, Ph. D. IoT Connected Industries and Energy
Practice Cisco
Pascal Thubert, CTAO Cisco
11.3. Building Automation Systems
This section was derived from draft-bas-usecase-detnet-00.
11.4. Wireless for Industrial
This section was derived from draft-thubert-6tisch-4detnet-01.
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.
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.
11.5. Cellular Radio
This section was derived from draft-korhonen-detnet-telreq-00.
11.6. Industrial M2M
The authors would like to thank Feng Chen and Marcel Kiessling for
their comments and suggestions.
11.7. Internet Applications and CoMP
This section was derived from draft-zha-detnet-use-case-00.
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.
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12. Informative References
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Environments", .
[bacnetip]
ASHRAE, "Annex J to ANSI/ASHRAE 135-1995 - BACnet/IP",
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.
[CoMP] NGMN Alliance, "RAN EVOLUTION PROJECT COMP EVALUATION AND
ENHANCEMENT", NGMN Alliance NGMN_RANEV_D3_CoMP_Evaluation_
and_Enhancement_v2.0, March 2015,
.
[CONTENT_PROTECTION]
Olsen, D., "1722a Content Protection", 2012,
.
[CPRI] CPRI Cooperation, "Common Public Radio Interface (CPRI);
Interface Specification", CPRI Specification V6.1, July
2014, .
[DCI] Digital Cinema Initiatives, LLC, "DCI Specification,
Version 1.2", 2012, .
[DICE] IETF, "DTLS In Constrained Environments",
.
[EA12] Evans, P. and M. Annunziata, "Industrial Internet: Pushing
the Boundaries of Minds and Machines", November 2012.
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Daley, D., "ESPN's DC2 Scales AVB Large", 2014,
.
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English Edition", September 2012.
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[Fronthaul]
Chen, D. and T. Mustala, "Ethernet Fronthaul
Considerations", IEEE 1904.3, February 2015,
.
[HART] www.hartcomm.org, "Highway Addressable remote Transducer,
a group of specifications for industrial process and
control devices administered by the HART Foundation".
[I-D.finn-detnet-architecture]
Finn, N., Thubert, P., and M. Teener, "Deterministic
Networking Architecture", draft-finn-detnet-
architecture-02 (work in progress), November 2015.
[I-D.finn-detnet-problem-statement]
Finn, N. and P. Thubert, "Deterministic Networking Problem
Statement", draft-finn-detnet-problem-statement-04 (work
in progress), October 2015.
[I-D.ietf-6tisch-6top-interface]
Wang, Q. and X. Vilajosana, "6TiSCH Operation Sublayer
(6top) Interface", draft-ietf-6tisch-6top-interface-04
(work in progress), July 2015.
[I-D.ietf-6tisch-architecture]
Thubert, P., "An Architecture for IPv6 over the TSCH mode
of IEEE 802.15.4", draft-ietf-6tisch-architecture-09 (work
in progress), November 2015.
[I-D.ietf-6tisch-coap]
Sudhaakar, R. and P. Zand, "6TiSCH Resource Management and
Interaction using CoAP", draft-ietf-6tisch-coap-03 (work
in progress), March 2015.
[I-D.ietf-6tisch-terminology]
Palattella, M., Thubert, P., Watteyne, T., and Q. Wang,
"Terminology in IPv6 over the TSCH mode of IEEE
802.15.4e", draft-ietf-6tisch-terminology-06 (work in
progress), November 2015.
[I-D.ietf-ipv6-multilink-subnets]
Thaler, D. and C. Huitema, "Multi-link Subnet Support in
IPv6", draft-ietf-ipv6-multilink-subnets-00 (work in
progress), July 2002.
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[I-D.ietf-roll-rpl-industrial-applicability]
Phinney, T., Thubert, P., and R. Assimiti, "RPL
applicability in industrial networks", draft-ietf-roll-
rpl-industrial-applicability-02 (work in progress),
October 2013.
[I-D.ietf-tictoc-1588overmpls]
Davari, S., Oren, A., Bhatia, M., Roberts, P., and L.
Montini, "Transporting Timing messages over MPLS
Networks", draft-ietf-tictoc-1588overmpls-07 (work in
progress), October 2015.
[I-D.kh-spring-ip-ran-use-case]
Khasnabish, B., hu, f., and L. Contreras, "Segment Routing
in IP RAN use case", draft-kh-spring-ip-ran-use-case-02
(work in progress), November 2014.
[I-D.mirsky-mpls-residence-time]
Mirsky, G., Ruffini, S., Gray, E., Drake, J., Bryant, S.,
and S. Vainshtein, "Residence Time Measurement in MPLS
network", draft-mirsky-mpls-residence-time-07 (work in
progress), July 2015.
[I-D.svshah-tsvwg-deterministic-forwarding]
Shah, S. and P. Thubert, "Deterministic Forwarding PHB",
draft-svshah-tsvwg-deterministic-forwarding-04 (work in
progress), August 2015.
[I-D.thubert-6lowpan-backbone-router]
Thubert, P., "6LoWPAN Backbone Router", draft-thubert-
6lowpan-backbone-router-03 (work in progress), February
2013.
[I-D.wang-6tisch-6top-sublayer]
Wang, Q. and X. Vilajosana, "6TiSCH Operation Sublayer
(6top)", draft-wang-6tisch-6top-sublayer-04 (work in
progress), November 2015.
[IEC61850-90-12]
TC57 WG10, IEC., "IEC 61850-90-12 TR: Communication
networks and systems for power utility automation - Part
90-12: Wide area network engineering guidelines", 2015.
[IEC62439-3:2012]
TC65, IEC., "IEC 62439-3: Industrial communication
networks - High availability automation networks - Part 3:
Parallel Redundancy Protocol (PRP) and High-availability
Seamless Redundancy (HSR)", 2012.
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[IEEE1588]
IEEE, "IEEE Standard for a Precision Clock Synchronization
Protocol for Networked Measurement and Control Systems",
IEEE Std 1588-2008, 2008,
.
[IEEE1722]
IEEE, "1722-2011 - IEEE Standard for Layer 2 Transport
Protocol for Time Sensitive Applications in a Bridged
Local Area Network", IEEE Std 1722-2011, 2011,
.
[IEEE19043]
IEEE Standards Association, "IEEE 1904.3 TF", IEEE 1904.3,
2015, .
[IEEE802.1TSNTG]
IEEE Standards Association, "IEEE 802.1 Time-Sensitive
Networks Task Group", March 2013,
.
[IEEE802154]
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".
[IEEE802154e]
IEEE standard for Information Technology, "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", April
2012.
[IEEE8021AS]
IEEE, "Timing and Synchronizations (IEEE 802.1AS-2011)",
IEEE 802.1AS-2001, 2011,
.
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[IEEE8021CM]
Farkas, J., "Time-Sensitive Networking for Fronthaul",
Unapproved PAR, PAR for a New IEEE Standard;
IEEE P802.1CM, April 2015,
.
[IEEE8021TSN]
IEEE 802.1, "The charter of the TG is to provide the
specifications that will allow time-synchronized low
latency streaming services through 802 networks.", 2016,
.
[IETFDetNet]
IETF, "Charter for IETF DetNet Working Group", 2015,
.
[ISA100] ISA/ANSI, "ISA100, Wireless Systems for Automation",
.
[ISA100.11a]
ISA/ANSI, "Wireless Systems for Industrial Automation:
Process Control and Related Applications - ISA100.11a-2011
- IEC 62734", 2011, .
[ISO7240-16]
ISO, "ISO 7240-16:2007 Fire detection and alarm systems --
Part 16: Sound system control and indicating equipment",
2007, .
[knx] KNX Association, "ISO/IEC 14543-3 - KNX", November 2006.
[lontalk] ECHELON, "LonTalk(R) Protocol Specification Version 3.0",
1994.
[LTE-Latency]
Johnston, S., "LTE Latency: How does it compare to other
technologies", March 2014,
.
[MEF] MEF, "Mobile Backhaul Phase 2 Amendment 1 -- Small Cells",
MEF 22.1.1, July 2014,
.
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[METIS] METIS, "Scenarios, requirements and KPIs for 5G mobile and
wireless system", ICT-317669-METIS/D1.1 ICT-
317669-METIS/D1.1, April 2013, .
[modbus] Modbus Organization, "MODBUS APPLICATION PROTOCOL
SPECIFICATION V1.1b", December 2006.
[net5G] Ericsson, "5G Radio Access, Challenges for 2020 and
Beyond", Ericsson white paper wp-5g, June 2013,
.
[NGMN] NGMN Alliance, "5G White Paper", NGMN 5G White Paper v1.0,
February 2015, .
[PCE] IETF, "Path Computation Element",
.
[profibus]
IEC, "IEC 61158 Type 3 - Profibus DP", January 2001.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
.
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460,
December 1998, .
[RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black,
"Definition of the Differentiated Services Field (DS
Field) in the IPv4 and IPv6 Headers", RFC 2474,
DOI 10.17487/RFC2474, December 1998,
.
[RFC3031] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
Label Switching Architecture", RFC 3031,
DOI 10.17487/RFC3031, January 2001,
.
[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001,
.
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[RFC3393] Demichelis, C. and P. Chimento, "IP Packet Delay Variation
Metric for IP Performance Metrics (IPPM)", RFC 3393,
DOI 10.17487/RFC3393, November 2002,
.
[RFC3444] Pras, A. and J. Schoenwaelder, "On the Difference between
Information Models and Data Models", RFC 3444,
DOI 10.17487/RFC3444, January 2003,
.
[RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)",
RFC 3972, DOI 10.17487/RFC3972, March 2005,
.
[RFC3985] Bryant, S., Ed. and P. Pate, Ed., "Pseudo Wire Emulation
Edge-to-Edge (PWE3) Architecture", RFC 3985,
DOI 10.17487/RFC3985, March 2005,
.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, DOI 10.17487/RFC4291, February
2006, .
[RFC4553] Vainshtein, A., Ed. and YJ. Stein, Ed., "Structure-
Agnostic Time Division Multiplexing (TDM) over Packet
(SAToP)", RFC 4553, DOI 10.17487/RFC4553, June 2006,
.
[RFC4903] Thaler, D., "Multi-Link Subnet Issues", RFC 4903,
DOI 10.17487/RFC4903, June 2007,
.
[RFC4919] Kushalnagar, N., Montenegro, G., and C. Schumacher, "IPv6
over Low-Power Wireless Personal Area Networks (6LoWPANs):
Overview, Assumptions, Problem Statement, and Goals",
RFC 4919, DOI 10.17487/RFC4919, August 2007,
.
[RFC5086] Vainshtein, A., Ed., Sasson, I., Metz, E., Frost, T., and
P. Pate, "Structure-Aware Time Division Multiplexed (TDM)
Circuit Emulation Service over Packet Switched Network
(CESoPSN)", RFC 5086, DOI 10.17487/RFC5086, December 2007,
.
[RFC5087] Stein, Y(J)., Shashoua, R., Insler, R., and M. Anavi,
"Time Division Multiplexing over IP (TDMoIP)", RFC 5087,
DOI 10.17487/RFC5087, December 2007,
.
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[RFC6282] Hui, J., Ed. and P. Thubert, "Compression Format for IPv6
Datagrams over IEEE 802.15.4-Based Networks", RFC 6282,
DOI 10.17487/RFC6282, September 2011,
.
[RFC6550] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J.,
Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur,
JP., and R. Alexander, "RPL: IPv6 Routing Protocol for
Low-Power and Lossy Networks", RFC 6550,
DOI 10.17487/RFC6550, March 2012,
.
[RFC6551] Vasseur, JP., Ed., Kim, M., Ed., Pister, K., Dejean, N.,
and D. Barthel, "Routing Metrics Used for Path Calculation
in Low-Power and Lossy Networks", RFC 6551,
DOI 10.17487/RFC6551, March 2012,
.
[RFC6775] Shelby, Z., Ed., Chakrabarti, S., Nordmark, E., and C.
Bormann, "Neighbor Discovery Optimization for IPv6 over
Low-Power Wireless Personal Area Networks (6LoWPANs)",
RFC 6775, DOI 10.17487/RFC6775, November 2012,
.
[RFC7554] Watteyne, T., Ed., Palattella, M., and L. Grieco, "Using
IEEE 802.15.4e Time-Slotted Channel Hopping (TSCH) in the
Internet of Things (IoT): Problem Statement", RFC 7554,
DOI 10.17487/RFC7554, May 2015,
.
[SRP_LATENCY]
Gunther, C., "Specifying SRP Latency", 2014,
.
[STUDIO_IP]
Mace, G., "IP Networked Studio Infrastructure for
Synchronized & Real-Time Multimedia Transmissions", 2007,
.
[SyncE] ITU-T, "G.8261 : Timing and synchronization aspects in
packet networks", Recommendation G.8261, August 2013,
.
[TEAS] IETF, "Traffic Engineering Architecture and Signaling",
.
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[TS23401] 3GPP, "General Packet Radio Service (GPRS) enhancements
for Evolved Universal Terrestrial Radio Access Network
(E-UTRAN) access", 3GPP TS 23.401 10.10.0, March 2013.
[TS25104] 3GPP, "Base Station (BS) radio transmission and reception
(FDD)", 3GPP TS 25.104 3.14.0, March 2007.
[TS36104] 3GPP, "Evolved Universal Terrestrial Radio Access
(E-UTRA); Base Station (BS) radio transmission and
reception", 3GPP TS 36.104 10.11.0, July 2013.
[TS36133] 3GPP, "Evolved Universal Terrestrial Radio Access
(E-UTRA); Requirements for support of radio resource
management", 3GPP TS 36.133 12.7.0, April 2015.
[TS36211] 3GPP, "Evolved Universal Terrestrial Radio Access
(E-UTRA); Physical channels and modulation", 3GPP
TS 36.211 10.7.0, March 2013.
[TS36300] 3GPP, "Evolved Universal Terrestrial Radio Access (E-UTRA)
and Evolved Universal Terrestrial Radio Access Network
(E-UTRAN); Overall description; Stage 2", 3GPP TS 36.300
10.11.0, September 2013.
[TSNTG] IEEE Standards Association, "IEEE 802.1 Time-Sensitive
Networks Task Group", 2013,
.
[UHD-video]
Holub, P., "Ultra-High Definition Videos and Their
Applications over the Network", The 7th International
Symposium on VICTORIES Project PetrHolub_presentation,
October 2014, .
[WirelessHART]
www.hartcomm.org, "Industrial Communication Networks -
Wireless Communication Network and Communication Profiles
- WirelessHART - IEC 62591", 2010.
Authors' Addresses
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Ethan Grossman (editor)
Dolby Laboratories, Inc.
1275 Market Street
San Francisco, CA 94103
USA
Phone: +1 415 645 4726
Email: ethan.grossman@dolby.com
URI: http://www.dolby.com
Craig Gunther
Harman International
10653 South River Front Parkway
South Jordan, UT 84095
USA
Phone: +1 801 568-7675
Email: craig.gunther@harman.com
URI: http://www.harman.com
Pascal Thubert
Cisco Systems, Inc
Building D
45 Allee des Ormes - BP1200
MOUGINS - Sophia Antipolis 06254
FRANCE
Phone: +33 497 23 26 34
Email: pthubert@cisco.com
Patrick Wetterwald
Cisco Systems
45 Allees des Ormes
Mougins 06250
FRANCE
Phone: +33 4 97 23 26 36
Email: pwetterw@cisco.com
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Jean Raymond
Hydro-Quebec
1500 University
Montreal H3A3S7
Canada
Phone: +1 514 840 3000
Email: raymond.jean@hydro.qc.ca
Jouni Korhonen
Broadcom Corporation
3151 Zanker Road
San Jose, CA 95134
USA
Email: jouni.nospam@gmail.com
Yu Kaneko
Toshiba
1 Komukai-Toshiba-cho, Saiwai-ku, Kasasaki-shi
Kanagawa, Japan
Email: yu1.kaneko@toshiba.co.jp
Subir Das
Applied Communication Sciences
150 Mount Airy Road, Basking Ridge
New Jersey, 07920, USA
Email: sdas@appcomsci.com
Yiyong Zha
Huawei Technologies
Email: zhayiyong@huawei.com
Balazs Varga
Ericsson
Konyves Kalman krt. 11/B
Budapest 1097
Hungary
Email: balazs.a.varga@ericsson.com
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Janos Farkas
Ericsson
Konyves Kalman krt. 11/B
Budapest 1097
Hungary
Email: janos.farkas@ericsson.com
Franz-Josef Goetz
Siemens
Gleiwitzerstr. 555
Nurnberg 90475
Germany
Email: franz-josef.goetz@siemens.com
Juergen Schmitt
Siemens
Gleiwitzerstr. 555
Nurnberg 90475
Germany
Email: juergen.jues.schmitt@siemens.com
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