One document matched: draft-finn-detnet-problem-statement-02.xml
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<front>
<title>Deterministic Networking Problem Statement</title>
<author initials="N" surname="Finn" fullname="Norm Finn" >
<organization abbrev="Cisco">
Cisco Systems
</organization>
<address>
<postal>
<street>510 McCarthy Blvd</street>
<street>SJ-24</street>
<city>Milpitas</city>
<code>95035</code>
<region>California</region>
<country>USA</country>
</postal>
<phone> +1 408 526 4495</phone>
<email>nfinn@cisco.com</email>
</address>
</author>
<author initials="P" surname="Thubert" fullname="Pascal Thubert">
<organization abbrev="Cisco">
Cisco Systems
</organization>
<address>
<postal>
<street>Village d'Entreprises Green Side</street>
<street>400, Avenue de Roumanille</street>
<street>Batiment T3</street>
<city>Biot - Sophia Antipolis</city>
<code>06410</code>
<country>FRANCE</country>
</postal>
<phone>+33 4 97 23 26 34</phone>
<email>pthubert@cisco.com</email>
</address>
</author>
<date/>
<area>Internet</area>
<workgroup>detnet</workgroup>
<abstract>
<t>
This paper documents the needs in various
industries to establish multi-hop paths
for characterized flows with deterministic properties .
</t>
</abstract>
</front>
<middle>
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<section anchor='introduction' title="Introduction">
<t>
Operational Technology (OT) refers to industrial networks that are typically
used for monitoring systems and supporting control loops, as well as movement
detection systems for use in process control (i.e., process manufacturing) and
factory automation (i.e., discrete manufacturing). Due to its different goals,
OT has evolved in parallel but in a manner that is radically different from
IT/ICT, focusing on highly secure, reliable and deterministic networks, with
limited scalability over a bounded area.
</t> <t>
The convergence of IT and OT technologies, also called the Industrial Internet,
represents a major evolution for both sides. The work has already started;
in particular, the industrial automation space has been developing a number
of Ethernet-based replacements for existing digital control systems, often
not packet-based (fieldbus technologies).
</t> <t>
These replacements are meant to provide similar behavior as the incumbent
protocols, and their common focus is to transport a fully characterized
flow over a well-controlled environment (i.e., a factory floor), with a
bounded latency, extraordinarily low frame loss, and a very narrow jitter.
Examples of such protocols include PROFINET, ODVA Ethernet/IP, and EtherCAT.
</t><t>
In parallel, the need for determinism in professional and home audio/video
markets drove the formation of the Audio/Video Bridging (AVB) standards effort
of IEEE 802.1. With the explosion of demand for connectivity and multimedia in
transportation in general, the Ethernet AVB technology has become one of the
hottest topics, in particular in the automotive connectivity. It is finding
application in all elements of the vehicle from head units, to rear seat
entertainment modules, to amplifiers and camera modules. While aimed at less
critical applications than some industrial networks, AVB networks share the
requirement for extremely low packet loss rates and guaranteed finite latency
and jitter.
</t><t>
Other instances of in-vehicle deterministic networks have arisen as well for
control networks in cars, trains and buses, as well as avionics, with, for
instance, the mission-critical "Avionics Full-Duplex Switched Ethernet" (AFDX)
that was designed as part of the ARINC 664 standards. Existing automotive
control networks such as the LIN, CAN and FlexRay standards were not designed
to cover these increasing demands in terms of bandwidth and scalability that we
see with various kinds of Driver Assistance Systems (DAS) and new multiplexing
technologies based on Ethernet are now getting traction.
</t><t>
Examples of industries where strong needs for deterministic networks are now
emerging include
<xref target="I-D.korhonen-detnet-telreq">radio access networks</xref>,
<xref target="I-D.wetterwald-detnet-utilities-reqs">the smartgrid</xref>, and
<xref target="I-D.gunther-detnet-proaudio-req">ProAudio networks</xref>.
</t><t>
The generalization of the needs for more deterministic networks have led to the
IEEE 802.1 AVB Task Group becoming the
<xref target="IEEE802.1TSNTG">Time-Sensitive Networking (TSN)
Task Group (TG)</xref>, with a much-expanded constituency from the industrial and
vehicular markets. Along with this expansion, the networks in consideration are
becoming larger and structured, requiring deterministic forwarding beyond the
LAN boundaries. For instance, Industrial Automation segregates the network along
the broad lines of the Purdue Enterprise Reference Architecture (PERA), using
different technologies at each level, and public infrastructures such as
Electricity Automation require deterministic properties over the Wide Area. The
realization is now coming that the convergence of IT and OT networks requires
Layer-3, as well as Layer-2, capabilities.
</t><t>
In order to serve this extended requirement, the IETF and the IEEE must
collaborate and define an abstract model that can be applicable both at Layer-2
and Layer-3, and along segments of different technologies. With this new work,
a path may span, for instance, across a (limited) number of 802.1 bridges and
then a (limited) number of IP routers. In that example, the IEEE802.1 bridges
may be operating at Layer-2 over Ethernet whereas the IP routers may be
<xref target="TiSCH">6TiSCH</xref>
nodes operating at Layer-2 and/or Layer-3 over the IEEE802.15.4 MAC.
</t> <t>
The proposed model should enable a fully scheduled operation orchestrated by
a central controller, as well as a more distributed operation with probably
lesser capabilities. In any fashion, the model should not compromise the ability
of a network to keep carrying the sorts of traffic that is already carried
today in conjunction with new, more deterministic flows.
</t><t>
Once the abstract model is agreed upon, the IETF will need to specify the
signaling elements to be used to establish a path and the tagging elements to be
used identify the flows that are to be forwarded along that path. The IETF will
also need to specify the necessary protocols, or protocol additions, based
on relevant IETF technologies such as <xref target="PCE">PCE</xref>,
<xref target="TEAS">TEAS</xref>, <xref target="CCAMP">CCAMP</xref> and
<xref target="MPLS">MPLS</xref>, to implement the selected model.
As a result of this work, it will be possible to establish
a multi-hop path over the IP network, for a particular flow with precise
timing and throughput requirements, and carry this particular flow along the
multi-hop path with such characteristics as low latency and ultra-low jitter,
duplication and elimination of packets over non-congruent paths for a higher
delivery ratio, and/or zero congestion loss. Depending on the network
capabilities and on the current state, requests to establish a path by an
end-node or a network management entity may be granted or rejected, and an
existing path may be moved or removed.
</t>
</section>
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<section title="Terminology">
<t>The key words "MUST", "MUST NOT", "REQUIRED", "SHALL",
"SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",
and "OPTIONAL" in this document are to be interpreted as
described in <xref target="RFC2119"/>.</t>
</section>
<section title="On Deterministic Networking">
<t>
The Internet is not the only digital network that has grown dramatically over
the last 30-40 years. Video and audio entertainment, and control systems for
machinery, manufacturing processes, and vehicles are also ubiquitous, and are
now based almost entirely on digital technologies. Over the past 10 years,
engineers in these fields have come to realize that significant advantages in
both cost and in the ability to accelerate growth can be obtained by basing all
of these disparate digital technologies on packet networks.
</t><t>
The goals of Deterministic Networking are to enable the migration of
applications that use special-purpose fieldbus technologies (HDMI, CANbus,
ProfiBus, etc... even RS-232!) to packet technologies in general, and the
Internet Protocol in particular, and to support both these new applications,
and existing packet network applications, over the same physical network.
</t><t>
Considerable experience (<xref target="ODVA"/>,<xref target="AVnu"/>,
<xref target="Profinet"/>,<xref target="HSR-PRP"/>, etc...)
has shown that these applications need a some or all of a suite of features that
includes:
<list style="numbers"> <t>
Time synchronization of all host and network nodes (routers and/or bridges),
accurate to something between 10 nanoseconds and 10 microseconds, depending on
the application.
</t> <t>
Support for critical packet flows that:
<list style="symbols"> <t>
Can be unicast or multicast;
</t> <t>
Need absolute guarantees of minimum and maximum latency end-to-end across
the network;
</t> <t>
Need a packet loss ratio in the range of 1.0e-9 to 1.0e-12, or better;
</t> <t>
Can, in total, absorb more than half of the network's available bandwidth
(that is, over-provisioning is ruled out as a solution);
</t> <t>
Cannot suffer throttling, congestion feedback, or any other network-imposed
transmission delay, although the flows can be meaningfully characterized
either by a fixed, repeating transmission schedule, or by a maximum
bandwidth and packet size.
</t> </list>
</t> <t>
Multiple methods to schedule, shape, limit, and otherwise control the
transmission of critical packets at each hop through the network data
plane.
</t> <t>
Robust defenses against misbehaving hosts, routers, or bridges, both in the
data and control planes.
</t> <t>
One or more methods to reserve resources in bridges and routers to carry
these flows.
</t> </list>
</t>
<t>
Time synchronization techniques need not be addressed by an IETF Working Group;
there are a number of standards available for this purpose, including IEEE 1588,
IEEE 802.1AS, and more.
</t> <t>
The multicast, latency, loss ratio, and non-throttling needs are made necessary
by the algorithms employed by the applications.
They are not simply the transliteration of fieldbus needs to a packet-based
fieldbus simulation, but reflect fundamental mathematics of the control of a
physical system.
</t> <t>
When forwarding latency- and loss-sensitive packets across a network,
interactions among different critical flows introduce fundamental uncertainties
in delivery schedules. The details of the queuing, shaping, and scheduling
algorithms employed by each bridge or router to control the output sequence
on a given port affect the detailed makeup of the output stream, e.g. how
finely a given flow's packets are mixed among those of other flows.
</t> <t>
This, in turn, has a strong effect on the buffer requirements, and hence the
latency guarantees deliverable, by the next bridge or router along the path.
For this reason, the IEEE 802.1 Time-Sensitive Networking Task Group has defined
a set of queuing, shaping, and scheduling algorithms
(see <xref target="Shaping"/>) that enable each bridge or router to
compute the exact number of buffers to be allocated for each flow or class of
flows. The present authors assume that these techniques will be used by the
DetNet Working Group.
</t> <t>
Robustness is a common need for networking protocols, but plays a more important
part in real-time control networks, where expensive equipment, and even lives,
can be lost due to misbehaving equipment.
</t> <t>
Reserving resources before packet transmission is the one fundamental shift in
the behavior of network applications that is impossible to avoid.
In the first place, a network cannot deliver finite latency and practically zero
packet loss to an arbitrarily high offered load. Secondly, achieving
practically zero packet loss for unthrottled (though bandwidth limited) flows
means that bridges and routers have to dedicate buffer resources to specific
flows or to classes of flows. The requirements of each reservation have to be
translated into the parameters that control each host's, bridge's, and router's
queuing, shaping, and scheduling functions and delivered to the hosts, bridges,
and routers.
</t>
</section>
<section anchor="rel" title="Related IETF work">
<section anchor="del" title='Deterministic PHB'>
<t>
<xref target="I-D.svshah-tsvwg-deterministic-forwarding"/>
defines a Differentiated Services Per-Hop-Behavior
(PHB) Group called Deterministic Forwarding (DF). The document
describes the purpose and semantics of this PHB. It also describes
creation and forwarding treatment of the service class. The document
also describes how the code-point can be mapped into one of the
aggregated Diffserv service classes <xref target="RFC5127"/>.
</t>
</section>
<section anchor="sixt" title='6TiSCH'>
<t>
Industrial process control already leverages deterministic
wireless Low power and Lossy Networks (LLNs) to interconnect critical
resource-constrained devices and form wireless mesh networks, with
standards such as <xref target="ISA100.11a"/> and <xref target="WirelessHART"/>.
</t> <t>
These standards rely on variations of the <xref target="IEEE802154"/>
<xref target="RFC7554">timeSlotted Channel Hopping (TSCH)
</xref> Medium Access Control (MAC), and a form of centralized Path
Computation Element (PCE), to deliver deterministic capabilities.
</t> <t>
The TSCH MAC benefits include high reliability against interference, low
power consumption on characterized flows, and Traffic Engineering
capabilities. Typical applications are open and closed control loops,
as well as supervisory control flows and management.
</t> <t>
The 6TiSCH Working Group focuses only on the TSCH mode of the IEEE802.15.4e
standard. The WG currently defines a framework for managing the TSCH schedule.
Future work will standardize deterministic operations over so-called tracks
as described in <xref target="I-D.ietf-6tisch-architecture"/>.
Tracks are an instance of a deterministic path, and the DetNet work
is a prerequisite to specify track operations and serve process control
applications. The dependencies that 6TiSCH has on PCE and DetNet work
are further discussed in <xref target='I-D.thubert-6tisch-4detnet'/>.
</t><t>
<xref target="RFC5673"/> and
<xref target="I-D.ietf-roll-rpl-industrial-applicability"/> section 2.1.3
and next discuss application-layer paradigms, such as Source-sink (SS)
that is a Multipeer to Multipeer (MP2MP) model that is primarily used for
alarms and alerts, Publish-subscribe (PS, or pub/sub) that is typically
used for sensor data, as well as Peer-to-peer (P2P) and Peer-to-multipeer
(P2MP) communications. Additional considerations on Duocast and its N-cast
generalization are also provided for improved reliability.
</t> <t>
</t>
</section>
</section>
<section anchor="RelatedIEEE" title="Related work in other standards organizations">
<section anchor="BridgedSolutions" title="Bridged solutions">
<t>
Completed and ongoing work in other standards bodies have, to date, produced
viable solutions, suitable for carrying IP traffic for a subset of the
applications of interest to DetNet, but only over bridged
networks, not through routers. Among these are:
<list style="symbols">
<t>
<xref target="IEEE802.1BA-2011">IEEE 802 Audio-Video Bridging</xref>.
</t><t>
<xref target="IEEE802.1TSNTG">IEEE 802 Time-Sensitive Networking (TSN)
Task Group (TG)</xref>
</t><t>
<xref target="HSR-PRP">ISO/IEC HSR and PRP</xref>.
</t>
</list>
</t>
</section>
<section anchor="Shaping" title="Queuing and shaping">
<t>
A number of standards are completed or in progress in the IEEE 802.1 (bridging)
and IEEE 802.3 (Ethernet) Working Groups related to the queuing and transmission
of Ethernet frames. Most of these standards could be applied to
non-Ethernet or non-802 media with equal facility, and so will likely be
of use to DetNet. See <xref target="I-D.finn-detnet-architecture">the DetNet
architecture draft</xref> for a detailed list.
</t>
</section>
</section>
<section anchor="ps" title="Problem Statement">
<section anchor="arch" title="DetNet architecture">
<t>
An architecture that defines the space in which the various parts of
the DetNet solution operate is required. A start has been made
with <xref target="I-D.finn-detnet-architecture"/>.
</t>
</section>
<section anchor="flow" title="Flow Characterization">
<t>
Deterministic forwarding can only apply on flows with well-defined
characteristics such as periodicity and burstiness. Before a path can be
established to serve them, the expression of those characteristics, and how
the network can serve them, for instance in shaping and forwarding
operations, must be specified.
</t>
</section>
<section anchor="pce" title="Centralized Path Computation and Installation">
<t>
A centralized routing model, such as provided with a PCE, enables global and
per-flow optimizations. The model is attractive but a number of issues are
left to be solved.
In particular:
<list style="symbols"> <t>whether and how the path computation can
be installed by 1) an end device or 2) a Network Management entity,
</t><t>
and how
the path is set up, either by installing state at each hop with a direct
interaction between the forwarding device and the PCE, or along a path by
injecting a source-routed request at one end of the path.
</t> </list>
</t>
</section>
<section anchor="dc" title="Distributed Path Setup">
<t> Whether a distributed alternative without a PCE can be valuable should
be studied as well. Such an alternative could for instance inherit from the
<xref target="RFC5127">Resource ReSerVation Protocol</xref> (RSVP) flows.
</t>
</section>
<section anchor="DupFormat" title="Duplicated data format">
<t>
In some cases the duplication and elimination of packets over
non-congruent paths is required to achieve a sufficiently high
delivery ratio to meet application needs. In these cases, a
small number of packet formats and supporting protocols are
required (preferably, just one) to serialize the packets of
a DetNet stream at one point in the network,
replicate them at one or more points in the network, and
discard duplicates at one or more other points in the network,
including perhaps the destination host. Using an existing
solution would be preferable to inventing a new one.
</t>
</section>
</section>
<section title="Security Considerations">
<t>
Security in the context of Deterministic Networking has an added
dimension; the time of delivery of a packet can be just as important
as the contents of the packet, itself. A man-in-the-middle attack,
for example, can impose, and then systematically adjust, additional
delays into a link, and thus disrupt or subvert a real-time
application without having to crack any encryption methods employed.
See <xref target="RFC7384"/> for an
exploration of this issue in a related context.
</t>
<t>Security must cover:
<list style="symbols"> <t>
the protection of the signaling protocol
</t><t>
the authentication and authorization of the controlling nodes
</t><t>
the identification and shaping of the flows
</t> </list>
</t>
</section>
<section title="IANA Considerations">
<t>This document does not require an action from IANA.
</t>
</section>
<section title="Acknowledgements">
<t>The authors wish to thank Jouni Korhonen, Erik Nordmark, George Swallow,
Rudy Klecka, Anca Zamfir, David Black, Thomas Watteyne, Shitanshu Shah,
Craig Gunther, Rodney Cummings, Wilfried Steiner, Marcel Kiessling, Karl Weber,
Ethan Grossman and Pat Thaler,
for their various contribution with this work.</t>
</section>
</middle>
<back>
<references title='Normative References'>
<?rfc include="reference.RFC.2119"?>
<?rfc include='reference.I-D.thubert-6tisch-4detnet'?>
<?rfc include='reference.I-D.korhonen-detnet-telreq'?>
<?rfc include='reference.I-D.wetterwald-detnet-utilities-reqs'?>
<?rfc include='reference.I-D.gunther-detnet-proaudio-req'?>
</references>
<references title='Informative References'>
<?rfc include='reference.I-D.svshah-tsvwg-deterministic-forwarding'?>
<?rfc include='reference.I-D.ietf-roll-rpl-industrial-applicability'?>
<?rfc include='reference.I-D.ietf-6tisch-architecture'?>
<?rfc include='reference.I-D.finn-detnet-architecture'?>
<?rfc include='reference.RFC.2205'?>
<?rfc include='reference.RFC.5127'?>
<?rfc include='reference.RFC.5673'?>
<?rfc include='reference.RFC.7384'?>
<?rfc include='reference.RFC.7554'?> <!-- 6TiSCH TSCH -->
<reference anchor="IEEE802.1Qav"
target="http://standards.ieee.org/getieee802/download/802.1Qav-2009.pdf">
<front>
<title>Forwarding and Queuing (IEEE 802.1Qav-2009)</title>
<author>
<organization>IEEE</organization>
</author>
<date year="2009" />
</front>
</reference>
<reference anchor="IEEE802.1Qat-2010"
target="http://standards.ieee.org/getieee802/download/802.1Qat-2010.pdf">
<front>
<title>Stream Reservation Protocol (IEEE 802.1Qat-2010)</title>
<author>
<organization>IEEE</organization>
</author>
<date year="2010" />
</front>
</reference>
<reference anchor="IEEE802.1AS-2011"
target="http://standards.ieee.org/getieee802/download/802.1AS-2011.pdf">
<front>
<title>Timing and Synchronizations (IEEE 802.1AS-2011)</title>
<author>
<organization>IEEE</organization>
</author>
<date year="2011" />
</front>
</reference>
<reference anchor="IEEE802.1BA-2011"
target="http://standards.ieee.org/getieee802/download/802.1BA-2011.pdf">
<front>
<title>AVB Systems (IEEE 802.1BA-2011)</title>
<author>
<organization>IEEE</organization>
</author>
<date year="2011" />
</front>
</reference>
<reference anchor="IEEE802.1Q-2011"
target="http://standards.ieee.org/getieee802/download/802.1Q-2011.pdf">
<front>
<title>MAC Bridges and VLANs (IEEE 802.1Q-2011</title>
<author>
<organization>IEEE</organization>
</author>
<date year="2011" />
</front>
</reference>
<reference anchor="ISA100.11a"
target=" http://www.isa100wci.org/en-US/Documents/PDF/3405-ISA100-WirelessSystems-Future-broch-WEB-ETSI.aspx">
<front>
<title>ISA100.11a, Wireless Systems for Automation, also IEC 62734</title>
<author>
<organization>ISA/IEC</organization>
</author>
<date year="2011" />
</front>
</reference>
<reference anchor="IEEE802.1TSNTG" target="http://www.ieee802.org/1/pages/avbridges.html">
<front>
<title>IEEE 802.1 Time-Sensitive Networks Task Group</title>
<author>
<organization>IEEE Standards Association</organization>
</author>
<date year="2013" />
</front>
</reference>
<reference anchor="IEEE802154e">
<front>
<title>IEEE std. 802.15.4e, Part. 15.4: Low-Rate Wireless Personal Area Networks (LR-WPANs) Amendment 1: MAC sublayer</title>
<author>
<organization>IEEE standard for Information Technology</organization>
</author>
<date month="April" year="2012"/>
</front>
</reference>
<reference anchor="IEEE802154">
<front>
<title>IEEE std. 802.15.4, Part. 15.4: Wireless Medium Access Control
(MAC) and Physical Layer (PHY) Specifications for Low-Rate Wireless
Personal Area Networks</title>
<author>
<organization>IEEE standard for Information Technology</organization>
</author>
<date/>
</front>
</reference>
<reference anchor="WirelessHART">
<front>
<title>Industrial Communication Networks - Wireless Communication
Network and Communication Profiles - WirelessHART - IEC 62591</title>
<author>
<organization>www.hartcomm.org</organization>
</author>
<date year="2010" />
</front>
</reference>
<reference anchor="HART">
<front>
<title>Highway Addressable Remote Transducer, a group of
specifications for industrial process and control devices
administered by the HART Foundation</title>
<author>
<organization>www.hartcomm.org</organization>
</author>
<date></date>
</front>
</reference>
<reference anchor="ODVA">
<front>
<title>The organization that supports network technologies built on
the Common Industrial Protocol (CIP) including EtherNet/IP.</title>
<author>
<organization>http://www.odva.org/</organization>
</author>
<date></date>
</front>
</reference>
<reference anchor="AVnu">
<front>
<title>The AVnu Alliance tests and certifies devices for
interoperability, providing a simple and reliable networking
solution for AV network implementation based on the IEEE Audio
Video Bridging (AVB) and Time-Sensitive Networking (TSN)
standards.</title>
<author>
<organization>http://www.avnu.org/</organization>
</author>
<date></date>
</front>
</reference>
<reference anchor="Profinet" target="http://us.profinet.com/technology/profinet/">
<front>
<title>PROFINET is a standard for industrial networking in
automation. </title>
<author>
<organization>http://us.profinet.com/technology/profinet/</organization>
</author>
<date></date>
</front>
</reference>
<reference anchor="HSR-PRP">
<front>
<title>High availability seamless redundancy (HSR) is a further
development of the PRP approach, although HSR functions primarily
as a protocol for creating media redundancy while PRP, as described
in the previous section, creates network redundancy.
PRP and HSR are both described in the IEC 62439 3 standard.</title>
<author>
<organization>IEC</organization>
</author>
<date></date>
</front>
</reference>
<reference anchor="TEAS" target="https://datatracker.ietf.org/doc/charter-ietf-teas/">
<front>
<title>Traffic Engineering Architecture and Signaling</title>
<author>
<organization>IETF</organization>
</author>
<date></date>
</front>
</reference>
<reference anchor="PCE" target="https://datatracker.ietf.org/doc/charter-ietf-pce/">
<front>
<title>Path Computation Element</title>
<author>
<organization>IETF</organization>
</author>
<date></date>
</front>
</reference>
<reference anchor="CCAMP" target="https://datatracker.ietf.org/doc/charter-ietf-ccamp/">
<front>
<title>Common Control and Measurement Plane</title>
<author>
<organization>IETF</organization>
</author>
<date></date>
</front>
</reference>
<reference anchor="MPLS" target="https://datatracker.ietf.org/doc/charter-ietf-mpls/">
<front>
<title>Multiprotocol Label Switching</title>
<author>
<organization>IETF</organization>
</author>
<date></date>
</front>
</reference>
<reference anchor="TiSCH" target="https://datatracker.ietf.org/doc/charter-ietf-6tisch/">
<front>
<title>IPv6 over the TSCH mode over 802.15.4</title>
<author>
<organization>IETF</organization>
</author>
<date></date>
</front>
</reference>
</references>
</back>
</rfc>
| PAFTECH AB 2003-2026 | 2026-04-22 22:46:25 |