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Versions: 00 01

INTAREA Working Group                                          S. Bryant
Internet-Draft                                               U. Chunduri
Intended status: Informational                                 T. Eckert
Expires: January 14, 2021                                       A. Clemm
                                             Futurewei Technologies Inc.
                                                           July 13, 2020


                   Forwarding Layer Problem Statement
                   draft-bryant-arch-fwd-layer-ps-01

Abstract

   This document considers the problems that need to addressed in IP in
   order to address the use cases and new network services described in
   draft-bryant-arch-fwd-layer-uc-00.

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 https://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 January 14, 2021.

Copyright Notice

   Copyright (c) 2020 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
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
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   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.



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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Forwarding Layer  . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Underlying New Requirements . . . . . . . . . . . . . . . . .   4
     3.1.  Better than Best Effort . . . . . . . . . . . . . . . . .   4
     3.2.  Efficient Packet Design . . . . . . . . . . . . . . . . .   5
     3.3.  Forwarding Identifiers  . . . . . . . . . . . . . . . . .   6
     3.4.  Operational visibility  . . . . . . . . . . . . . . . . .   6
     3.5.  Holistic Solution . . . . . . . . . . . . . . . . . . . .   7
   4.  Existing Protocol, Layering Challenges and Gaps . . . . . . .   7
     4.1.  Challenges with IPv6  . . . . . . . . . . . . . . . . . .   8
       4.1.1.  The End-to-End Model  . . . . . . . . . . . . . . . .   8
       4.1.2.  Fixed Address Length  . . . . . . . . . . . . . . . .  11
     4.2.  Better Than Best Effort E2E Network Services  . . . . . .  13
     4.3.  Adaptive Bit-rate Video streaming . . . . . . . . . . . .  14
     4.4.  Limited Domain Opportunities  . . . . . . . . . . . . . .  15
     4.5.  DetNet and Higher Precision Networking Service  . . . . .  15
     4.6.  Forwarding Plane vs. Control Plane  . . . . . . . . . . .  16
     4.7.  User-Network/Network-User Interface Signaling . . . . . .  17
   5.  Candidate Solution Directions . . . . . . . . . . . . . . . .  18
     5.1.  Variable Length Addresses . . . . . . . . . . . . . . . .  18
     5.2.  Address Semantics . . . . . . . . . . . . . . . . . . . .  19
     5.3.  Multiple Instructions . . . . . . . . . . . . . . . . . .  19
     5.4.  Node and Path Specific Processing Instructions  . . . . .  19
     5.5.  Integrated Assurance and Verification . . . . . . . . . .  20
     5.6.  For Consideration in a Future Version . . . . . . . . . .  20
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  20
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  21
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  21
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  21
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  21
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  26

1.  Introduction

   There is an emerging set of new requirements that exceed the network
   and transport services of the current Internet, which only delivers
   "best effort" service.  While many controlled or private networks
   include further services, such as other DiffServ QoS in addition to
   best effort and traffic engineering with bandwidth guarantees, the
   solutions used today only support walled gardens and are thus not
   available to application service providers and consumers across the
   Internet.

   The uses cases and service needs that are foreseen as necessary for
   deployment in the medium future are described in [I-D.bryant-arch-
   fwd-layer-uc].



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   The purpose of this document is to examine the shortcomings that the
   existing network and transport layer protocols a well as their
   associated control plane need to overcome to meet these needs.

   The IETF is the body responsible for the long term evolution of the
   IP protocol suit, but is missing a work track to discuss the long-
   term Internet network architecture evolution.  In particular it lacks
   a programme for the long term evolution of IP itself.

   Approximately 30 years ago, the IETF started a process to
   revolutionize the IPv4 [RFC0791] Internet Protocol.  In this process,
   researchers, industry, and service providers got together, and
   brought up a number of new proposals, and worked toward a successor
   to IPv4, which became IPv6 [RFC2460] and later [RFC8200].

   30 years later, there is heavy resistance to anything more than minor
   incremental evolutions to IPv6.  There are a number of reasons for
   this ranging from opinions that all future IP needs can be met
   through minor incremental evolutions to fears that major proposals
   for innovation at the IP would be an unwelcome disrupter to the
   current business of the vendors or the service providers.

   The authors take no position on the scale of the problem or the
   difficulties of deploying any solutions at scale in the Internet.
   What we seek to do is to establish the scope and nature of the
   problem.  A decision on which aspects of the problem are economically
   tractable is out of scope of this text, but technologies to support
   monetization are not.

   As a problem statement, this documents goal is to not propose or
   promote specific solutions to the problems raised.  Instead it uses
   references to not Internet adopted, but proposed or existing
   solutions only as example evidence that the described problem can
   actually be solved.

   Because the document does not propose specific solutions, it also
   does not attempt to structure the problem description in a way that
   would identify sub-set of problems to be resolved by specific
   solution components.

   The purpose of this text is thus to stimulate discussion on the
   emerging needs of the forwarding layer and to start the process of
   determining how they are best satisfied within the IETF protocol
   suite.







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2.  Forwarding Layer

   The term "forwarding layer" is used in this work because none of the
   standard terms encompass the parts of the network stack that need
   attention to address the needs of the applications that are foreseen.

   It is possible that development work will need to reach down to layer
   2.5 in order to ensure that packets are handled correctly down to the
   physical layer.  The MAC layer is quite sophisticated and includes
   its own switching function so we need to be sure that the good work
   done in the network layer is not undone lower down the stack.
   Equally it is possible that development work will need to reach into
   the transport layer to address new approaches to congestion, and to
   ensure that the network layer understands the requirements placed on
   it by the application.  An open mind is needed on the boundaries of
   the layers as they exist today when analyzing the consequential
   network changes needed to support the evolving application space.

   In the network layer itself, this document is only concerned with the
   forwarding component, not path selection or the other components of
   routing.

   Thus, we use the term forwarding layer to describe the scope of the
   stack that this document addresses.

3.  Underlying New Requirements

3.1.  Better than Best Effort

   The current Internet is essentially of best-effort system, but future
   applications require high-precision KPIs on throughput, latency and
   packet loss for industrial manufacturing, control, automation, and
   machine-to-machine communications.

   The emerging use cases for networks require deployment of
   capabilities that are beyond best effort.  Best effort networks can
   do remarkably well by simply throwing bandwidth at the problem and
   lightly loading the network.  For the case where a greater capability
   is needed the IETF has invested effort in deterministic networking
   (DN) [RFC8655].  Whilst DN is an improvement over best effort it is
   still fundamentally a best effort service with enhancement to
   improved the probability of a packet not being delayed or lost due to
   congestion.  It is an after the fact enhancement to the method of
   operation of what is a largely unmodified data plane.  I the case of
   MPLS [I-D.ietf-detnet-mpls] there is some assistance from the PREOF
   function, but IP runs the standard data plane and relies entirely on
   special case packet selection queue management.  It is thus an after-




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   the-fact enhancement to a minimally changed data plane restricted to
   a single network domain.

   With upcoming Cellular technologies (5G/B5G) there is a need for
   Service Providers to expand the type of customers for metropolitan
   size networks to address their better than best-effort traffic needs.

   DetNet has been proposed to support this, however:

   o  Only some aspects of DetNet currently only run on top of current
      IP/IPv6.

   o  DetNet service is constrained: It only supports constant bit rate
      (CBR), reserved bandwidth.  It does not support flexible
      bandwidth.  The notion of contracts in a future development of the
      forwarding layer will support more flexible managed bandwidth and
      managed latency contracts for traffic.

3.2.  Efficient Packet Design

   The ratio of useful data in the payload to overhead has a direct
   financial impact on communication links; these links are of finite
   capacity and hence have a finite cost-per-unit-data that can be
   calculated.  The capacity used to transport information as compared
   to the overhead which is unavailable for use by a customer, but
   required to transmit is often expresses as a good-put efficiency and
   can be related to cost to transmit payload data.

   o  There is a need to support large number of low power user
      equipment (UE) devices (low-power IoTs) connecting through various
      radio networks (LTE/5G/B5G) where spectral efficiency is needed.
      This needs to be achieved without header compression techniques
      like as [RFC6282] since, compression can result in additional
      processing and energy consumption overhead.

   o  The handling network protocol headers, requires that portions of
      each packet be held in memory or buffer structures; the more
      levels of information which need to be held for processing by
      network nodes, the more memory space will be required, and this
      directly effects the cost of operation and cost of manufacture/
      provision of such equipment.

   On the other hand, in various non-constrained environments where
   various network layer functionalities are desired, there are
   different set of requirements.  For example:






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   o  Segment Routing over IPv6 (SRv6) parameter encoding
      [I-D.ietf-spring-srv6-network-programming] in the SRv6 SID
      [RFC8754] is limited by the prefix portion of the IPv6 address.

   o  In Identifier Locator Addressing (ILA), the identifier (ID)
      portion of the address length is limited because of 128 bits
      limit.

3.3.  Forwarding Identifiers

   Developments in IPv6 [I-D.ietf-spring-srv6-network-programming]
   formalize a trend that has been happening for a long time: the
   morphing of network layer addresses into forwarding identifiers (FI).
   However, constraining FIs to a fixed size ill serves the development
   of the forwarding layer.  There are clear cases as illustrated above
   where it would be useful to have shorter network layer addresses.
   Equally we can see that there will be future cases where 128 bits may
   be insufficient to specify a forwarding operation.  The requirement
   is thus to formally introduce the concept of forwarding identifiers
   in place of network layer addresses, and use a forwarding identifier
   construct that supports multiple semantics and multiple, possibly
   fully variable, lengths.

   There is further discussion on this point in Section 4.1.2.

3.4.  Operational visibility

   Network operators require facilities that let them better understand
   and fine tune detailed network behavior.  These features are hard to
   retrofit with current IP/IPv6.

   The rise of machine learning has led to the expectation of being able
   to better optimize networks This in turn leads to the increase of
   network telemetry as a source of data to base these systems on.  In-
   Situ OAM (IOAM) [I-D.ietf-ippm-ioam-data] represents one of the
   latest developments in that space, allowing the data plane to piggy-
   back telemetry data onto individual packets in order to diagnose and
   fine-tune service levels such as latency or jitter.  However, there
   are several issues with this approach:

   o  MTU issues limit amount of data that can be obtained.  With IOAM
      packet size increases with number of data items and number of
      hops.

   o  The data that can be obtained is very limited.

   o  The OAM data volume can easily exceeds that of production traffic
      which is wasteful



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   o  There is no ability to aggregate OAM data, or make context
      dependent OAM collection.

   o  Integration with other solutions such as DetNet is unclear.

   While useful, IOAM exposes the limits of what add-on solutions can
   provide.  Solutions that provide visibility at the level of flows or
   that provide automatic verification of Service Level Objectives are
   missing entirely.

3.5.  Holistic Solution

   It needs to be recognized that it will not be sufficient for
   solutions to support new services and capabilities one at a time and
   independently from one another.  For example, better-than-best-
   effort, operational visibility, and efficient packet design should go
   together, without leading to additional integration problems ore
   requiring users to make a choice.

   A piecemeal approach, in which solutions for any one particular
   problem are developed and emerge one at a time, results in a
   fragmented solution which gets progressively more difficult to
   integrate with components previously designed.  Thus it is better if
   solutions are holistic and be able to support new services and
   capabilities in integrated fashion and simultaneously with each
   other.

   We therefore need to identify an elegant approach that is simple and
   naturally extensible to address problems that we do not yet conceive
   as requiring addressing.

   Any such solution needs to be intrinsically secure and yet be able to
   support security without privacy and privacy without security.

4.  Existing Protocol, Layering Challenges and Gaps

   Despite IPv4 still having a large user base, and having a number of
   useful properties the IETF has abandoned future development of IPv4
   as a way to force the deployment of IPv6.  For example, in terms of
   traffic steering the segment routing could have usefully been applied
   to IPv4 to support network operators that wished to retain IPv4 as
   their preferred internal protocol.

   Given the gaps in each of the existing network layer protocols the
   IETF may wish to look at the design of a protocol that both fills the
   gaps and unifies its three existing network layer protocols: IPv4,
   IPv6 and MPLS.




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   Additionally there is a clear need for a more sophisticated approach
   to indicating the required quality of service that a packet, or flow,
   needs in an IP network.

4.1.  Challenges with IPv6

4.1.1.  The End-to-End Model

   IPv6 and specifically [RFC8200] was designed to fit within an
   Internet architecture centered around the end-to-end model with
   "Internet Paths" potentially passing through one or more networks
   without any relationship to the endpoints of a communication such as
   most so-called transit-AS.  As history already from IPv4 had shown,
   anything more than the most simple per-hop processing options can
   cause interoperability issues.  In result, [RFC8200] has drastically
   limited such per-hop processing options.

   Two core restrictions of RFC8200 are the following:

   o  Restrictions on extension headers (EH): EHs must never be deleted
      or changed in size by any node on the path the packet takes.
      Intermediate nodes are only expected to examine these headers (if
      they are configured to do so).  Implementations cannot expect
      intermediate nodes to examine, or act on, except for hop-by-hop
      header (section 4.8 of [RFC8200]).

   At the time of writing this is an area of considerable active
   discussion in the IETF 6MAN and SPRING working groups.  The issues
   that arise from allowing unrestricted insertion, deletion or
   modification of EHs are for example:

   o  Breakage of path MTU discovery

   o  Impact on the Authentication Header protocol

   o  Inability to return ICMP error messages to the correct node.

   See Section 4.1.1.1 for further discussion.

   o  No new hop-by-hop headers (HBH) in IPV6: No new EHs that require
      hop-by-hop behavior should be defined (section 4 of [RFC8200]) -
      the only EH that has hop-by-hop behavior is the Hop-by-Hop Options
      header.  The only alternative available to the designer is instead
      to use destination headers (section 6.8 of [RFC8200]).







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4.1.1.1.  IPv6 For Controlled Networks

   While [RFC8200] is a conservative set of requirements to enable
   proliferation of the target use case of "Internet Paths", the same
   set of requirements limit the flexibility of IPv6 unnecessarily when
   it is used in controlled networks where the constraints and
   interoperability issues for "Internet Paths" do not equally apply,
   for example the deployment scenarios described in Sections "Embedded
   Service" and "Embedded Global Service" of [I-D.bryant-arch-fwd-layer-
   uc].

   One typical type of controlled networks are service providers (SP)
   where SRv6 is used as the architecture within the SP network.

   o  IPv6 extension headers can not be added on a midpoint.  Any
      addition/change requires an encapsulation where another IPv6
      header with optional SRH extension header is prepended to the
      carried IPv6 packet.  This is expensive in terms of packet MTU,
      and in terms of packet buffer requirements at the ends of the
      provider path which can be an economic issue in cost sensitive
      network segments.

   o  The requirement to encapsulate instead of being allowed to add an
      EH along the path stems from the desire to isolate any header
      changes from Path MTU Discovery (PMTUD).  This is a necessary
      complexity when traversing uncontrolled hops across the Internet,
      but it is unnecessary overhead when only passing through
      controlled hops.  In MPLS and SR-MPLS, the MPLS header size is not
      included in the MTU available to the MPLS payload, instead the
      network is managed such that the maximum MPLS header size plus the
      available payload MTU is always smaller that the encapsulating L2
      frame MTU.  In IPv6 instead, the encapsulating and decapsulating
      would logically have to perform signaling for PMTUD
      (unnecessarily).

   o  Because of the authorization header (AH) [RFC4302] and OAM
      concerns, [RFC8200] likewise prohibits removing extension headers
      or fields thereof on hops along the path, requiring for example
      more complex packet parsers.  In SR-MPLS it is possible to simply
      remove the top SID on a node that has processed it, in SRv6 it is
      instead necessary to look up an offset field in the SRH and, read
      the appropriate SID (which may be deep in the packet), and then
      increment the offset field.

   o  Even though the number of identifiers required within a controlled
      network is often less than 16 bit, and almost always 32 bits,
      carrying the overhead of 128 bits per SID in SRv6 can be seen as a
      significant unnecessary overhead, and workarounds such a proposed



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      micro programs [I-D.bonica-6man-comp-rtg-hdr],
      [I-D.bonica-spring-srv6-plus],
      [I-D.filsfils-spring-net-pgm-extension-srv6-usid] require complex
      forwarding plane processing and SRv6 programmability in the lower
      64 bit is not required in the majority of use-cases for SIDs on
      midpoints.

   For use-cases like this, it would be a lot easier to innovate IPv6 by
   clone & modify: E.g.: defining (say) IPv7 to be similar to IPv6, but
   without the constraints that are not useful for the controlled
   network use-case.  A better alternative would be to create different
   profiles of IPv6 with [RFC8200] being one.  However, there is, as
   yet, no concept of "profiles" in IPv6.

   The issue of IP protocol operation in limited domains is discussed in
   [I-D.carpenter-limited-domains].

   Some possible solutions are described in
   [I-D.herbert-6man-eh-attrib].  This will be considered further in a
   future version of this text.

4.1.1.2.  IPv6 for Edge-Compute

   Today, the majority of end-to-end connections already do not pass via
   the traditional "Internet-Path" but instead toward a server in data
   center co-located with the access service provider Edge-2-Edge-EP
   [DOT].  In this case, there is no transit service provider, but there
   is a well-established commercial relationship between either end of
   the communications and the access service provider.

   Today, the majority of traffic consists of video-streaming/TV
   services, but in the future, Edge-Compute will enable ever more
   applications to operate in such a controlled environment.

   The difference between the aforementioned use-case of IPv6 within an
   service provider, and this use-case is that enhanced services in this
   would naturally operate end-to-end between a Data Center application
   server and the subscriber endpoints.

   In the case of SRv6, it is not necessary to incur the overhead of an
   IPv6 in IPv6 encapsulation, the SRH can be inserted by the endpoint
   and removed by the endpoint on the other side.  Nevertheless, the
   [RFC8200] limitations of not being able to add/remove or freely
   change the content of the SRH payload or any other EH on a midpoint
   router still exists.  This seriously limits the usage and evolution
   of IPv6 to the edge-to-edge model.





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4.1.1.3.  Hop-by-Hop Extension Header processing

   Hop-by-hop IPv6 extension headers caused interoperability and
   performance issues and as a result caused resistance to further
   leverage and extend them except for SRv6-SRH RPL-SRH [RFC6554].  In
   the authors opinions, this regression on hop-by-hop extension headers
   is because of a combination of insufficient specifications and
   resulting implementation issues.  Both could be solved in future work
   with new hop-by-hop processing specifications.

   For example, router alert (RA) was (and still maybe) implemented in
   routers so that all router alert packets are punted from the fast-
   path to the slow-path even when the "value" field identifies a
   protocol that the router can not process.  As a result, protocols
   that rely on RA such as RSVP [RFC2205] or even more so Pragmatic
   General Multicast (PGM) [RFC3208] where filtered in networks because
   they caused high control plane load on routers that did not support
   either protocols but still unnecessarily punted their packets with
   RA.

   There are no normative statements about the need that fast-path
   forwarding planes "MUST" be able to ignore unsupported/not-enabled EH
   features at a speed such that such a packet can be forward at the
   same speed as the same packet without the EH.  For example, for RA,
   there is only a "SHOULD" requirement to do this in [RFC6398], a BCP
   published a decade after IPv6 router alert [RFC2711].  With such a
   gap in time between the specification and the BCP, it is impossible
   to rely on the existing RA and expect safe deployment across the
   Internet without still running into performance issues.

4.1.1.4.  Segment Routing Header Constraints

   The same design paradigm could have been used for the Segment Routing
   Header (SRH) [RFC8754], but there is no distinction possible for IPv6
   instances running in such a controlled network or running as an
   Internetwork instance to form the Internet.  This is particularly
   unfortunate as we are evolving to a model where, as noted earlier in
   this document, in most cases the packet will only travel through two
   well-known networks: the hosts network and the service provider
   network hosting the server to which the client is interacting.

4.1.2.  Fixed Address Length

   When IPv6 was designed, the key focus was on solving the problem of
   growth of the Internet and resulting growth of global Internet
   address space.  Variable length and a heterogeneous address approach
   were proposed [RFC1347] however, these were rejected partially for




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   political reasons and partially out of a concern over the difficulty
   of parsing the packet and doing a fast address lookup.

   There was seemingly no focus on better supporting the now millions of
   often network-layer isolated TCP/IP networks in industrial, defense,
   research, embedded, industrial or other commercial environments.

   One key problems with with 128 bit addresses is the overhead on low-
   speed radio/IoT-wire networks.  This is especially the case when
   using source-routing, where multiple of these addresses have to be
   included in the header.  Current solutions are only able to resolve
   these issues with CPU expensive IETF standardized header compression
   techniques [RFC2507], [RFC3095], [RFC5795].  Even though these
   approaches are feasible in many of todays IoT networks, there is a
   strong desire to reduce power consumption in such devices.  This is
   particularly the case where they are powered by a single-for-life-
   battery, or are self-powering through automatic replenished energy
   sources.  As a result of this CPU performance in future IoT network
   should not be expected to increase but whenever feasible is more
   likely to decrease.

   Another, often overlooked, problem of the 128 bit IPv6 addresses is
   that global address prefix allocation is a a big up-front burden on
   many IoT networks, but also isolated networks (industrial, defense,
   research, industrial).  Often, this leads to the use of Unique Local
   Addresses (ULA) [RFC4193], which have the risk of conflicts when
   those previously isolated networks need to interconnect with other
   networks.

   A further insight into the issues of IPv6 address lengths of 128 bits
   can be seen in the tussle over how to compress the address lengths in
   Segment Routing and network programming (in no particular order):

   [I-D.bonica-6man-comp-rtg-hdr], [I-D.bonica-6man-crh-helper-opt],
   [I-D.bonica-spring-sr-mapped-six],
   [I-D.cheng-spring-shorter-srv6-sid-requirement],
   [I-D.decraene-spring-srv6-vlsid],
   [I-D.filsfilscheng-spring-srv6-srh-comp-sl-enc],
   [I-D.lc-6man-generalized-srh], [I-D.li-spring-compressed-srv6-np],
   [I-D.mirsky-spring-unified-id-network-programming],
   [I-D.steinberg-6man-crh-vs-sr-mpls], [I-D.templin-6man-crh-variable].

   The root cause of this debate is the inflexibility of IPv6 in terms
   of its address length and semantics.

   While solutions to these problems may look easier enough, it should
   be noted that in the time when IPv6 was designed, variable length
   addresses in the fastest forwarding planes were not seen as feasible,



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   and there was also a lack of experience with the impact of
   interconnecting heterogeneous address spaces other than as ships-in-
   the-night parallel operation of protocols.  A lot of that experience
   came later through 14++ IPv4/IPv6 transition solutions designed in
   the past 20 years and respective work on address discovery in IETF
   frameworks such as SIP/STUN/ICE.

   Another issue with the fixed length homogeneous address approach is
   the constraints this places on the current practice of overloading
   addresses with other functionality for example
   [I-D.ietf-spring-srv6-network-programming].

   Since the original decision to only support fixed length packet
   addresses was taken there has been a significant improvement in the
   packet lookup capability of hardware.  This is has been driven by the
   need to perform complex ACL lookup for security reasons and the
   interest in flow based techniques such as OpenFlow.  It is thus worth
   revisiting the decision to only allow a single fixed address length
   and format.

4.2.  Better Than Best Effort E2E Network Services

   Some of the fastest growing network segments where new services are
   being introduced in an End-2-End manner belong to deployment models
   as described in [I-D.bryant-arch-fwd-layer-uc].  The requirements
   here for service delivery involves stringent E2E latency with no
   retransmission and no packet loss.  Not all scenarios need "lower"
   latency but bounded to a particular value/range.  Example use cases
   involving an user equipment (UE) consuming service from the provider
   cloud network or another UE (e.g.  Vehicular device, IIoT) in the
   same network.  Here the service endpoints could be connected over
   wire or wireless (LTE/NR) and the service termination happens in the
   provider network either close to the access network or provider core
   network.  The existing network layer and best-effort model simply
   cannot guarantee needed service level objectives in these scenarios.

   Some specific needs and requirements from cellular fixed transport
   networks are:

   o  Need for determinism on E2E throughput and latency.  The current
      TCP/IP is hence not-suitable for Mission-critical and real-time
      E2E applications.

   o  Need for E2E QoS for ultra-reliable-low-latency communications
      (uRLLC).

   o  Efficient use of protocols in the network by minimizing tunnels
      over tunnels and duplicate header fields.



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   o  Efficient deployment of network slicing

4.3.  Adaptive Bit-rate Video streaming

   Even without going to future application requirements as described
   elsewhere in this document, even the majority of existing Internet
   traffic is lacking competitively usable and standardized service to
   support quality of service.

   The majority of traffic today is Adaptive Bit-rate (ABR) based audio/
   video streaming.  The primary benefit of this approach is that it can
   adjust itself to much lower bandwidth than the bandwidth to offer the
   ideal/target experience quality to the user.  It therefore enabled
   Over The Top (OTT) services to offer streaming media.  Nevertheless,
   ABR itself does not provide any actual quality guarantees.

   Service providers that use ABR streaming to their subscribers do
   therefore combine ABR with IP developments, some non-published, which
   are often out-of-band bandwidth reservation schemes.  These allow ABR
   video streams to have their ideal/target experience bandwidth within
   the SP's network and only need to degrade if there was bandwidth
   contention in the subscribers (home) network.

   If a subscriber, or a content provider which is not the access
   service provider wanted to get the same type of bandwidth guarantees
   for other content across the access providers network, they could do
   so with existing IETF standards via RSVP [RFC2205] which is widely
   implemented, or NSIS [RFC4080], which was to the knowledge of the
   authors never implemented in widely used router products (because it
   does not offer sufficient benefits over RSVP).  In either case, the
   per-flow control-plane based signaling architecture including the
   aforementioned router-alert issues make these protocols a difficult,
   likely not future-proof solution.

   Even more fundamentally, ABR has shown that media streaming can
   easily support elastic adjustment between a range of bandwidth limits
   in which the quality is between acceptable and ideal, but there is as
   of today no standardized mechanisms by which to express relative
   bandwidth allocations when streams compete against each other that
   goes beyond the very loosely defined "internet fairness".  For
   example, more intelligent congestion management could defend
   bandwidth the more the bandwidth approaches the minimum acceptable
   bandwidth, or admission control of bandwidth could be elastic.  Some
   work in these direction exists in [RFC8698] with its ability for
   weighted congestion control or
   [I-D.ietf-tsvwg-intserv-multiple-tspec] for (limited) elastic
   admission control management.




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4.4.  Limited Domain Opportunities

   Strictly of course this refers to the opportunities that the
   acceptance of limited domains [I-D.carpenter-limited-domains]
   provides to the network operator in terms of the flexibility to
   enhance packet delivery in cases of high value traffic.

   The removal of the constraint of a globally uniform protocol, such as
   unenhanced IPv6 would allow a best in class, domain specific
   forwarding layer to be deployed without the constant of the
   requirement that the protocol needed to serve all purposed, for all
   applications in all parts of the global network.

   These opportunities are are further enhanced by noting that the
   delivery protocol to the application server, which as noted elsewhere
   in this text is moving closer to the edge, does not need to be the
   same as the host to application protocol since this is increasingly
   being opaquely tunneled over the delivery protocol.  Furthermore, any
   distributed set of application servers maybe in their own domain, and
   this is not constrained to the same protocol that is used between the
   client and the server.

   Clearly their are costs and complexities associated with moving from
   a globally heterogeneous protocol to a domain specific protocol, but
   the deciding factors are whether the application is deliverable over
   a globally general purpose forwarding layer, and whether there
   application and delivery system are economically attractive.

4.5.  DetNet and Higher Precision Networking Service

   Time Critical (TC), Ultra-Reliable, Low Latency (URLLC), Internet-of-
   Things is another important use case scenario-set that highlights
   requirements that are difficult to satisfy with existing Internet
   connectivity paths where a part of that path includes a radio access
   link.  These kind of close-loop control systems borne over
   heterogeneous communications networks have very precision and bounded
   latency requirements for the E2E network connecting the sensor and
   actuator.

   Deterministic networking within the IETF is focused on only one
   dimension of the URLLC problem.

   DetNet is also far from attempting to identify currently if/how the
   services it plans to introduce could be made to operate over the
   Internet in general, instead, it focuses mostly on the shorter term
   goal to enable them in controlled networks within a limited domains.





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   Currently, the requirements for a DetNet forwarding plane have been
   reasonably mapped out for an MPLS based forwarding layer.
   Nevertheless, in addressing these needs within an IP network
   [I-D.ietf-detnet-ip] the solution has of necessity been limited to
   the capabilities of the IP as it exists today.  It has not, for
   example, been possible to add the packet replication elimination and
   reordering function (PREOF)which allows multiple concurrent packet
   delivery attempts in an MPLS network [I-D.ietf-detnet-mpls].  The
   DETNET body of requirements needs to be revisited in the light of any
   development to network forwarding capabilities.

4.6.  Forwarding Plane vs. Control Plane

   High-end hardware with accelerated forwarding plane devices, can
   support a significant number of forwarding states including
   destination entries (IP destination/mask, MPLS label, SR SID) as well
   as 2, 3 or 5 tuple IP/IPv6 "flow" entries.  Nevertheless, the control
   plane that builds and changes these entries often limits their
   usability because the control plane does not even scale to the number
   of hardware accelerated forwarding entries possible, or because the
   supported rate of changes is slow.

   The root of this problem is that with the increase of speed and scale
   of hardware accelerated forwarding hardware, control plane had
   challenges to keep up in performance.  The performance of
   appropriately priced control plane CPUs (relative to the cost of the
   forwarding plane) has not grown at the same speed as that of hardware
   accelerated forwarding plane chips.

   One of the directions to overcome these challenges is invisible
   outside these forwarder devices and it is to optimize the control-
   plane to forwarding plane interactions, such as programming the
   building of forwarding state directly on the accelerated forwarding
   infrastructure (e.g.  NPU), but using otherwise existing control
   plane protocols.

   A more fundamental approach is to redesign control plane protocols
   such that they are lighter weight in their signaling and state
   machinery, and can therefore be completely implemented in the
   hardware accelerated forwarding plane.  Effectively turning a control
   plane protocol into an advanced forwarding plane protocol function.

   This approach is logically most easily applicable to on-path per-flow
   signaling mechanisms such as RSVP or RSVP-TE, both of which are quite
   complex with their signaling messaging and state keeping and
   therefore directly infeasible to become hardware accelerated
   forwarding implementations.  An example approach to provide similar
   functionality to RSVP with signaling light-weight enough to allow



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   hardware accelerated implementation are the in-band signaling
   mechanisms (e.g. for TCP or UDP) described in [DIP1]
   [I-D.han-tsvwg-ip-transport-qos] [I-D.han-tsvwg-enhanced-diffserv].

   Signaling that is feasible to become part of a complete in-
   forwarding-plane signaling solution is not limited to in-band on-path
   flow signaling, but would likely also be applied to other signaling
   options.  Of the aforementioned existing signaling protocols, IGPs
   are likely the ones whose signaling could most easily be processed in
   an NPU compute elements except that the SPF calculation itself
   introduces a complexity that would make this very complex.  One
   example of a solution that solves this problem by signaling the
   actual per-hop adjacencies in IGP and therefore eases NPU
   implementation can be found in
   [I-D.chunduri-isis-preferred-path-routing].

   In summary: The scope of what should be considered forwarding plane
   today is defined by decade historic architectures, but should for the
   future be scoped by the realities of the new, different "layers" of
   hardware and their capabilities.  Hence also the use of the term
   forwarding plane, because it can span not only across classical
   bridging (L2), label/tag/SIG switching (L2.5), network/internetwork
   (L3) and transport (L4) layers, but also across the classical "data
   plane" and "control plane" components of each such layer.

4.7.  User-Network/Network-User Interface Signaling

   Some of the deployment models as described in [I-D.bryant-arch-fwd-
   layer-uc], needs specific signaling mechanism from user/applications.
   These are needed for E2E service offering for better than best effort
   Section 4.2 or high-precision networking Section 4.5.  These may
   involve new transport mechanisms at hosts, middle-boxes and routers
   to meet the E2E service requirements in these limited domain
   deployments.

   Here one of the functional requirements is to signal the service
   level objectives (SLOs) dynamically for a particular service from the
   network.  This signaling includes the service description, the
   service negotiation with the network, the service setup or
   modification, or the need to execute some functions at network device
   and send the results back to the sender.  However, the current IP was
   not designed for this.  For example, the result of SLO negotiation at
   any hop needs to be updated in the IP packet at the router and
   returned back to the sender (originating host or gateway device for a
   Service Provider).

   There are some attempts to achieve the above as described in
   [I-D.han-tsvwg-ip-transport-qos], which describes general in-band



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   signaling for QoS control with IPv6 protocol and
   [I-D.han-tsvwg-enhanced-diffserv], which proposes a backward
   compatible class-based queuing and scheduling schema for hybrid
   service to support guaranteed service from the network (e.g. for
   latency and bandwidth).

   In summary, it is difficult to do better than best effort or High
   Precision Services described in Section Section 4.5, in closed
   domains with current IP given the best effort congestion control
   (TCP/QUIC) and explicit congestion notification (ECN) framework.  A
   comprehensive mechanism needs to be explored as the limitations in
   silicon technologies or deployment models 30 years ago are not
   relevant with respect to security, scalability, packet size change,
   MSS or FCS recalculation, etc.

5.  Candidate Solution Directions

   This section is an incomplete list of solution considerations, but is
   not prescriptive about any specific approach or technical solution,
   and is provided to stimulate thought on the subject.

5.1.  Variable Length Addresses

   When private networks are set up, they only need to use an address
   length that allows the construction of networks sufficiently large to
   meet the expected service requirements.  If a future network layer
   protocol could support address length of e.g.: 16, 24, 32, 48, 64 and
   128 bits (or maybe more), it would be easy for such networks to pick
   a right size.  This would allow them to have as efficient packets
   without compression as possible, and it would also avoid for them to
   have to think about allocation procedures for "global" addresses.

   Whenever networks with a smaller address size would later on have to
   interconnect to other networks, the shorter length address would have
   to be interpreted as the suffix of a sufficiently larger address
   space through which those connecting networks could achieve unique,
   non-overlapping addresses.  At the border between these networks,
   high speed forwarding planes could easily perform per-packet
   stateless prefix addition/deletion transformations of addresses in
   the packet header when the interconnection should be free of further
   policy.  When such an interconnection is desired to employ specific
   traffic control policies, mapping of addresses in a stateful manner
   is a convenient way to enforce and support such policies through the
   forwarding plane.







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5.2.  Address Semantics

   Classically IP unicast addresses identify an interface.  There is the
   special case of a loop-back address, but this is normally modeled as
   an internal interface.  Addresses are often silently mapped to
   include other semantics and this is most developed in the IP network
   programming concept [I-D.ietf-spring-srv6-network-programming].

   MPLS is more general.  It defines the concept of a Forwarding
   Equivalence Class in which a Label which can be visualized as an
   offset into a specific table with up to 2^20 entries, with the table
   containing the instruction to be executed.  Thus a single identifier
   is able to specify: forward towards an egress, forward along a
   specific path, decapsulate and sent to an interface, decapsulate and
   forward via an IP lookup in a label specific address table etc.

   The semantics of the MPLS label and the size of the label are such
   that it is not possible to include any instruction parameters in the
   label and very inefficient to include those parameters in one or more
   further labels.  The only example of doing this is the Entropy Label
   indicator [RFC6790] which uses two Label Stack Entries (LSEs).  Any
   future development along these lines will need at least three LSEs.

   Whilst an IPv6 is larger there is still limited space to add
   parameters within the address.  In the current work on this the size
   is limited to 16 bits, and there is a fundamental limit of 64 bits.

   It is clear that move is towards a multiplicity of semantic for the
   network layer address, and indeed a formal recognition that the
   address is in reality an instruction with a specific scope.

5.3.  Multiple Instructions

   What we have learned from MPLS and then from SRv6 is that it is often
   desirable for a node (be that the originating host or a router) to
   impose on a packet a set of instructions to be executed in sequence
   by one or more entities in the network.  An development of IP or any
   successor needs to recognize this and provide a simple and efficient
   way to incorporate a list (or stack) of instructions within the
   packet header.

5.4.  Node and Path Specific Processing Instructions

   There is an established need to do node specific instructions as is
   indicated by the design of MPLS and Segment Routing (SR).  Any
   development of the forwarding system needs to retain this feature and
   ideally develop a method that is simultaneously both general and
   efficient.



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   References to efficiency include efficiency in packet size and
   efficiency decoding and and executing the instruction.  The
   efficiency of encoding is not simply a matter of on the wire
   bandwidth, but is also a matter of the size of the forwarder packet
   header cache.  This cache has to operate at wire speed can be an
   expensive silicon element.

   There is also a need to do path specific operations as are done in
   RSVP-TE.  However RSVP has a significant path set-up and path
   maintenance cost.  Clearly a per path instruction can be specified as
   a set of N per node instructions where N is the number of hops along
   the path, for example by using SR, but that is not an efficient
   encoding where N is large.  It is thus a useful optimization to
   include the ability to include per path instructions, and this is the
   subject of further study.

5.5.  Integrated Assurance and Verification

   Being best effort in nature, assurance for services provided using IP
   is left to add-on solutions built after the fact.  How to perform
   tasks such as verifying of service levels is left as an exercise for
   network providers, often approached using statistical approaches that
   are themselves "best effort" in nature.  This will be no longer
   sufficient for mission-critical services such as tele-driving or
   tele-operations that demand guarantees, where failure to meet those
   guarantees may expose providers and users exposed to liability
   demands and call the feasibility of applications relying on those
   services into question.

   Moving forward, network protocols suitable to deliver high-precision
   services for mission critical applications need to address assurance
   as an intrinsic property, not left to afterthoughts.

5.6.  For Consideration in a Future Version

   A future version of this document will consider E2E communication
   beyond-best-effort, high precision services, high precision
   telemetry, E2E Volumetric data transfer and high precision congestion
   control beyond that provided by the diffserv QoS bits.

6.  IANA Considerations

   This document does not request any allocations from IANA.








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7.  Security Considerations

   Security is likely to be more significant with the applications being
   considered in this work.  With interest in tightly controlled access
   and latency, and contractual terms of business it is going to be
   necessary to have provable right of access to network resources.
   However heavyweight security is a contra-requirement to the light-
   weight process needed for power efficiency, fast forwarding and low
   latency.  Addressing this will require new insights into network
   security.

   Further information on the issue of providing security in latency
   sensitive environments can be found in [I-D.ietf-detnet-security]
   which are a sub-set of the considerations applicable to the new use
   cases considered in this text.

8.  References

8.1.  Normative References

   [RFC0791]  Postel, J., "Internet Protocol", STD 5, RFC 791,
              DOI 10.17487/RFC0791, September 1981,
              <https://www.rfc-editor.org/info/rfc791>.

   [RFC8200]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", STD 86, RFC 8200,
              DOI 10.17487/RFC8200, July 2017,
              <https://www.rfc-editor.org/info/rfc8200>.

8.2.  Informative References

   [DIP1]     ETSI, "Recommendation for New Transport Technologies, GR
              NGP 010", September 2018,
              <https://www.etsi.org/deliver/etsi_gr/
              NGP/001_099/010/01.01.01_60/gr_NGP010v010101p.pdf>.

   [DOT]      Huston, G., "The Death of Transit and Beyond", n.d.,
              <https://hknog.net/wp-content/uploads/2018/03/01_GeoffHust
              on_TheDeath_of_Transit_and_Beyond.pdf>.

   [I-D.bonica-6man-comp-rtg-hdr]
              Bonica, R., Kamite, Y., Niwa, T., Alston, A., and L.
              Jalil, "The IPv6 Compact Routing Header (CRH)", draft-
              bonica-6man-comp-rtg-hdr-22 (work in progress), May 2020.







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   [I-D.bonica-6man-crh-helper-opt]
              Li, X., Bao, C., Ruan, E., and R. Bonica, "Compressed
              Routing Header (CRH) Helper Option", draft-bonica-6man-
              crh-helper-opt-01 (work in progress), May 2020.

   [I-D.bonica-spring-sr-mapped-six]
              Bonica, R., Hegde, S., Kamite, Y., Alston, A., Henriques,
              D., Jalil, L., Halpern, J., Linkova, J., and G. Chen,
              "Segment Routing Mapped To IPv6 (SRm6)", draft-bonica-
              spring-sr-mapped-six-01 (work in progress), April 2020.

   [I-D.bonica-spring-srv6-plus]
              Bonica, R., Hegde, S., Kamite, Y., Alston, A., Henriques,
              D., Jalil, L., Halpern, J., Linkova, J., and G. Chen,
              "Segment Routing Mapped To IPv6 (SRm6)", draft-bonica-
              spring-srv6-plus-06 (work in progress), October 2019.

   [I-D.carpenter-limited-domains]
              Carpenter, B. and B. Liu, "Limited Domains and Internet
              Protocols", draft-carpenter-limited-domains-13 (work in
              progress), February 2020.

   [I-D.cheng-spring-shorter-srv6-sid-requirement]
              Cheng, W., Xie, C., Pang, R., Li, Z., Chen, R., Lijun, L.,
              Duan, X., and G. Mirsky, "Shorter SRv6 SID Requirements",
              draft-cheng-spring-shorter-srv6-sid-requirement-01 (work
              in progress), March 2020.

   [I-D.chunduri-isis-preferred-path-routing]
              Chunduri, U., Li, R., White, R., Tantsura, J., Contreras,
              L., and Y. Qu, "Preferred Path Routing (PPR) in IS-IS",
              draft-chunduri-isis-preferred-path-routing-00 (work in
              progress), June 2018.

   [I-D.decraene-spring-srv6-vlsid]
              Decraene, B., Raszuk, R., Li, Z., and C. Li, "SRv6 vSID:
              Network Programming extension for variable length SIDs",
              draft-decraene-spring-srv6-vlsid-03 (work in progress),
              March 2020.

   [I-D.filsfils-spring-net-pgm-extension-srv6-usid]
              Filsfils, C., Camarillo, P., Cai, D., Voyer, D., Meilik,
              I., Patel, K., Henderickx, W., Jonnalagadda, P., Melman,
              D., Liu, Y., and J. Guichard, "Network Programming
              extension: SRv6 uSID instruction", draft-filsfils-spring-
              net-pgm-extension-srv6-usid-07 (work in progress), May
              2020.




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   [I-D.filsfilscheng-spring-srv6-srh-comp-sl-enc]
              Cheng, W., Filsfils, C., Li, Z., Cai, D., Voyer, D., Clad,
              F., Shay, S., Guichard, J., and L. Aihua, "Compressed SRv6
              Segment List Encoding in SRH", draft-filsfilscheng-spring-
              srv6-srh-comp-sl-enc-01 (work in progress), May 2020.

   [I-D.han-tsvwg-enhanced-diffserv]
              Han, L., Qu, Y., and R. Li, "Enhanced DiffServ by In-band
              Signaling", draft-han-tsvwg-enhanced-diffserv-00 (work in
              progress), November 2019.

   [I-D.han-tsvwg-ip-transport-qos]
              Han, L., Qu, Y., Dong, L., Li, R., Nadeau, T., Smith, K.,
              and J. Tantsura, "Resource Reservation Protocol for IP
              Transport QoS", draft-han-tsvwg-ip-transport-qos-03 (work
              in progress), October 2019.

   [I-D.herbert-6man-eh-attrib]
              Herbert, T., "Attribution Option for Extension Header
              Insertion", draft-herbert-6man-eh-attrib-01 (work in
              progress), July 2020.

   [I-D.ietf-detnet-ip]
              Varga, B., Farkas, J., Berger, L., Fedyk, D., and S.
              Bryant, "DetNet Data Plane: IP", draft-ietf-detnet-ip-07
              (work in progress), July 2020.

   [I-D.ietf-detnet-mpls]
              Varga, B., Farkas, J., Berger, L., Malis, A., Bryant, S.,
              and J. Korhonen, "DetNet Data Plane: MPLS", draft-ietf-
              detnet-mpls-09 (work in progress), July 2020.

   [I-D.ietf-detnet-security]
              Mizrahi, T. and E. Grossman, "Deterministic Networking
              (DetNet) Security Considerations", draft-ietf-detnet-
              security-10 (work in progress), May 2020.

   [I-D.ietf-ippm-ioam-data]
              Brockners, F., Bhandari, S., Pignataro, C., Gredler, H.,
              Leddy, J., Youell, S., Mizrahi, T., Mozes, D., Lapukhov,
              P., remy@barefootnetworks.com, r., daniel.bernier@bell.ca,
              d., and J. Lemon, "Data Fields for In-situ OAM", draft-
              ietf-ippm-ioam-data-09 (work in progress), March 2020.








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   [I-D.ietf-spring-srv6-network-programming]
              Filsfils, C., Camarillo, P., Leddy, J., Voyer, D.,
              Matsushima, S., and Z. Li, "SRv6 Network Programming",
              draft-ietf-spring-srv6-network-programming-16 (work in
              progress), June 2020.

   [I-D.ietf-tsvwg-intserv-multiple-tspec]
              Polk, J. and S. Dhesikan, "Integrated Services (IntServ)
              Extension to Allow Signaling of Multiple Traffic
              Specifications and Multiple Flow Specifications in
              RSVPv1", draft-ietf-tsvwg-intserv-multiple-tspec-02 (work
              in progress), February 2013.

   [I-D.lc-6man-generalized-srh]
              Li, Z., Li, C., Cheng, W., Xie, C., Cong, L., Tian, H.,
              and F. Zhao, "Generalized Segment Routing Header", draft-
              lc-6man-generalized-srh-00 (work in progress), February
              2020.

   [I-D.li-spring-compressed-srv6-np]
              Li, Z., Li, C., Xie, C., LEE, K., Tian, H., Zhao, F.,
              Guichard, J., Cong, L., and S. Peng, "Compressed SRv6
              Network Programming", draft-li-spring-compressed-
              srv6-np-02 (work in progress), February 2020.

   [I-D.mirsky-spring-unified-id-network-programming]
              Cheng, W., Mirsky, G., Aihua, L., and S. Peng, "SRv6
              network programming using Unified Identifier", draft-
              mirsky-spring-unified-id-network-programming-00 (work in
              progress), March 2020.

   [I-D.steinberg-6man-crh-vs-sr-mpls]
              Steinberg, D., Henderickx, W., Li, Z., Cheng, W., and D.
              Voyer, "SR-MPLS over IPv6 satisfies CRH requirements",
              draft-steinberg-6man-crh-vs-sr-mpls-00 (work in progress),
              June 2020.

   [I-D.templin-6man-crh-variable]
              Templin, F., "IPv6 Compressed Routing Header with Variable
              Length Addresses", draft-templin-6man-crh-variable-00
              (work in progress), May 2020.

   [RFC1347]  Callon, R., "TCP and UDP with Bigger Addresses (TUBA), A
              Simple Proposal for Internet Addressing and Routing",
              RFC 1347, DOI 10.17487/RFC1347, June 1992,
              <https://www.rfc-editor.org/info/rfc1347>.





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   [RFC2205]  Braden, R., Ed., Zhang, L., Berson, S., Herzog, S., and S.
              Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1
              Functional Specification", RFC 2205, DOI 10.17487/RFC2205,
              September 1997, <https://www.rfc-editor.org/info/rfc2205>.

   [RFC2460]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460,
              December 1998, <https://www.rfc-editor.org/info/rfc2460>.

   [RFC2507]  Degermark, M., Nordgren, B., and S. Pink, "IP Header
              Compression", RFC 2507, DOI 10.17487/RFC2507, February
              1999, <https://www.rfc-editor.org/info/rfc2507>.

   [RFC2711]  Partridge, C. and A. Jackson, "IPv6 Router Alert Option",
              RFC 2711, DOI 10.17487/RFC2711, October 1999,
              <https://www.rfc-editor.org/info/rfc2711>.

   [RFC3095]  Bormann, C., Burmeister, C., Degermark, M., Fukushima, H.,
              Hannu, H., Jonsson, L-E., Hakenberg, R., Koren, T., Le,
              K., Liu, Z., Martensson, A., Miyazaki, A., Svanbro, K.,
              Wiebke, T., Yoshimura, T., and H. Zheng, "RObust Header
              Compression (ROHC): Framework and four profiles: RTP, UDP,
              ESP, and uncompressed", RFC 3095, DOI 10.17487/RFC3095,
              July 2001, <https://www.rfc-editor.org/info/rfc3095>.

   [RFC3208]  Speakman, T., Crowcroft, J., Gemmell, J., Farinacci, D.,
              Lin, S., Leshchiner, D., Luby, M., Montgomery, T., Rizzo,
              L., Tweedly, A., Bhaskar, N., Edmonstone, R.,
              Sumanasekera, R., and L. Vicisano, "PGM Reliable Transport
              Protocol Specification", RFC 3208, DOI 10.17487/RFC3208,
              December 2001, <https://www.rfc-editor.org/info/rfc3208>.

   [RFC4080]  Hancock, R., Karagiannis, G., Loughney, J., and S. Van den
              Bosch, "Next Steps in Signaling (NSIS): Framework",
              RFC 4080, DOI 10.17487/RFC4080, June 2005,
              <https://www.rfc-editor.org/info/rfc4080>.

   [RFC4193]  Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
              Addresses", RFC 4193, DOI 10.17487/RFC4193, October 2005,
              <https://www.rfc-editor.org/info/rfc4193>.

   [RFC4302]  Kent, S., "IP Authentication Header", RFC 4302,
              DOI 10.17487/RFC4302, December 2005,
              <https://www.rfc-editor.org/info/rfc4302>.







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   [RFC5795]  Sandlund, K., Pelletier, G., and L-E. Jonsson, "The RObust
              Header Compression (ROHC) Framework", RFC 5795,
              DOI 10.17487/RFC5795, March 2010,
              <https://www.rfc-editor.org/info/rfc5795>.

   [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,
              <https://www.rfc-editor.org/info/rfc6282>.

   [RFC6398]  Le Faucheur, F., Ed., "IP Router Alert Considerations and
              Usage", BCP 168, RFC 6398, DOI 10.17487/RFC6398, October
              2011, <https://www.rfc-editor.org/info/rfc6398>.

   [RFC6554]  Hui, J., Vasseur, JP., Culler, D., and V. Manral, "An IPv6
              Routing Header for Source Routes with the Routing Protocol
              for Low-Power and Lossy Networks (RPL)", RFC 6554,
              DOI 10.17487/RFC6554, March 2012,
              <https://www.rfc-editor.org/info/rfc6554>.

   [RFC6790]  Kompella, K., Drake, J., Amante, S., Henderickx, W., and
              L. Yong, "The Use of Entropy Labels in MPLS Forwarding",
              RFC 6790, DOI 10.17487/RFC6790, November 2012,
              <https://www.rfc-editor.org/info/rfc6790>.

   [RFC8655]  Finn, N., Thubert, P., Varga, B., and J. Farkas,
              "Deterministic Networking Architecture", RFC 8655,
              DOI 10.17487/RFC8655, October 2019,
              <https://www.rfc-editor.org/info/rfc8655>.

   [RFC8698]  Zhu, X., Pan, R., Ramalho, M., and S. Mena, "Network-
              Assisted Dynamic Adaptation (NADA): A Unified Congestion
              Control Scheme for Real-Time Media", RFC 8698,
              DOI 10.17487/RFC8698, February 2020,
              <https://www.rfc-editor.org/info/rfc8698>.

   [RFC8754]  Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J.,
              Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header
              (SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020,
              <https://www.rfc-editor.org/info/rfc8754>.

Authors' Addresses

   Stewart Bryant
   Futurewei Technologies Inc.

   Email: sb@stewartbryant.com




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   Uma Chunduri
   Futurewei Technologies Inc.

   Email: uma.chunduri@futurewei.com


   Toerless Eckert
   Futurewei Technologies Inc.

   Email: tte@cs.fau.de


   Alexander Clemm
   Futurewei Technologies Inc.

   Email: ludwig@clemm.org



































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