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Versions: 00 01 02                                                      
Internet Engineering Task Force                                 J. Arkko
Internet-Draft                                                  Ericsson
Intended status: Informational                              May 15, 2017
Expires: November 16, 2017

         Low Latency Applications and the Internet Architecture


   Some recent Internet technology developments relate to improvements
   in communications latency.  For instance, improvements in radio
   communications or the recent work in IETF transport, security, and
   web protocols.  There are also potential applications where latency
   is potentially in a more significant role than it has traditionally
   been in Internet communications.  Modern networking systems offer
   many tools for building low-latency networks, from highly optimised
   individual protocol components to software controlled, virtualised
   and tailored network functions.  This memo views the developments
   from a system viewpoint, and considers the potential future stresses
   that the strive for low-latency support for applications may bring.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
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   This Internet-Draft will expire on November 16, 2017.

Copyright Notice

   Copyright (c) 2017 IETF Trust and the persons identified as the
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   This document is subject to BCP 78 and the IETF Trust's Legal
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   (http://trustee.ietf.org/license-info) in effect on the date of

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   publication of this document.  Please review these documents
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Applications with Special Focus on Low Latency  . . . . . . .   3
   3.  Role of Low-Latency vs. Other Communications  . . . . . . . .   4
   4.  Selected Improvements to Communications Latency . . . . . . .   4
   5.  Architectural Considerations  . . . . . . . . . . . . . . . .   5
     5.1.  Background  . . . . . . . . . . . . . . . . . . . . . . .   5
     5.2.  Implications  . . . . . . . . . . . . . . . . . . . . . .   6
     5.3.  Recommendations for Further Work  . . . . . . . . . . . .   8
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   8
   7.  Informative References  . . . . . . . . . . . . . . . . . . .   9
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  11

1.  Introduction

   Some recent Internet technology developments relate to improvements
   in communications latency.  For instance, improvements in radio
   communications or the recent work in IETF transport, security, and
   web protocols.

   There are also potential applications where latency is potentially in
   a more significant role than it has traditionally been in Internet

   New applications or technologies does not necessarily imply that
   latency should be the main driving concern, or that any further
   efforts beyond those already ongoing are needed.  Indeed, modern
   networking systems offer many tools for building low-latency
   networks, across the stack.  At the IETF, for instance, there has
   been a recent increase in work related to transport, security, and
   web application protocols, in part to make significant improvements
   in latency and connection set-up times.  Similar efforts in other
   parts of the stack exist in 3GPP, IEEE, and other standards

   Despite a large number of specific developments, it may be
   interesting to view the developments from a system viewpoint, and to
   consider the potential future stresses that the strive for low-
   latency support for applications may bring.

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   The rest of this memo is organised as follows.  Section 2 discusses
   potential applications for low-latency communications.  Section 4
   reviews some of the recent work across the stack, relating to latency
   improvements.  Finally, Section 5 discusses some of the implications
   (and non-implications) from an architectural perspective.

2.  Applications with Special Focus on Low Latency

   Most Internet applications enjoy significant benefits from low-
   latency communications.

   There are also potential applications where latency is potentially in
   an even more significant role.  For instance, embedding
   communications technology in automation or traffic systems, or
   consumer applications such as augmented or virtual reality where
   advance buffering may not be feasible.

   Many of the Internet-of-Things and critical services use cases in 5G,
   for instance, have been listed as requiring low latency and high
   reliability for communications [ER2015] [HU2015] [NGMN2015] [NO2015]
   [QU2016] [IMT2020].

   Some example use cases include optimisation of utility services such
   as electricity networks, connected automation systems in factories,
   remote control of machinery such as mining equipment, or embedded
   technology in road or railway traffic.

   The different applications vary in terms of their needs.  Some may be
   very focused on high-speed local area communication, others need to
   connect at optimal speed over a wide-area network, and yet others
   need to find the right ways to provide global services without
   incurring unreasonable delays.

   Note that when we say "low-latency capabilities", there is no intent
   to imply any specific implementation of those capabilities.  In
   particular, we look at the low-latency requirements from a broader
   perspective than Quality-of-Service guarantees or separating traffic
   onto different classes.  Indeed, while today's virtualisation and
   software-driven technologies give us more tools to deal with those
   kinds of arrangements as well, past experience on deploying Quality-
   of-Service mechanisms in the Internet should give us pause [CC2015].

   It is not the purpose of this memo to analyse the application
   requirements for low-latency applications much further; for our
   purposes it suffices to note that there are applications that are
   enabled by low-latency capabilities of the underlying network

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3.  Role of Low-Latency vs. Other Communications

   There are some limited applications that rely solely on local
   communication.  One example of such an application is vehicles
   communicating braking status to nearby ones.  However, many
   applications will include also wide-area communication.  If the
   factory automation machines are not talking other than with
   themselves, at least their control systems are doing so in order to
   ensure parts orders, monitoring and maintenance by equipment
   manufacturers, and so on.  This does not imply that these perhaps
   critical applications are openly accessible from the Internet, but
   many of them are likely to communicate outside their immediate

   Many applications also rely on wide-area connectivity for software

   As a result, this document recommends that when building
   architectures for low-latency applications it is important to take
   into account that these applications can also benefit from
   communications elsewhere.

4.  Selected Improvements to Communications Latency

   It should be noted that latency is a very broad topic in
   communications protocol design, almost as broad as "security", or
   even "correctness".

   Implementation techniques to satisfy these requirements vary, some
   applications can be built with sufficient fast local networking
   capabilities, others may require, for instance, building world-wide,
   distributed content delivery mechanisms.

   Modern networking systems offer many tools for building low-latency
   networks, across the stack. from highly optimised individual protocol
   components [I-D.ietf-tls-tls13] [I-D.ietf-quic-transport] [RFC7540]
   to software controlled, virtualised and tailored network functions
   [NFV2012] [I-D.ietf-sfc-nsh] [OF2008].  Data- and software-driven
   network managment and orchestration tools enable networks to be built
   to serve particular needs.

   Across the stack there are also many other tools, as well as tools
   being in development, e.g., a new transport design [L4S] at the IETF.

   On the lower layers, improvements in radio communications are being
   made.  For instance, the IEEE 802.1 Time-Sensitive Networking Task
   Group [TSN8021] has worked to define precise time synchronization
   mechanisms for a local area network, and scheduling mechanisms to

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   enable different classes of traffic to use the same network while
   minimising jitter and latency.  At the IETF, the DETNET working group
   is taking these capabilities and applying them for layer 3 networking

   The 3GPP 5G requirements for next-generation access technology are
   stringent, and are leading to the optimization of the radio
   interfaces.  The requirements specify a one-way latency limit of
   0.5ms for ultra-reliable low-latency communications [TS38913].

5.  Architectural Considerations

   Despite a large number of specific developments, it may be
   interesting to view the developments from a system viewpoint, and to
   consider the potential future stresses that the strive for low-
   latency support for applications may bring.

5.1.  Background

   To begin with, it may be useful to observe that the requirements and
   developments outlined above do not necessarily imply that any
   specific new technology is needed or that the nature of
   communications in the Internet would somehow fundamentally change.
   And certainly not that latency should be the only or primary concern
   in technology development.

   With the drive for a new class of applications, there is often an
   expectation that this means significant changes.  However, all
   changes need to stand on their own, be justifiable and deployable on
   a global network.  For instance, the discussion around the
   introduction of the newest 4K or 8K high-definition video streaming
   applications is reminiscent of the discussions about the introduction
   of VoIP applications in the Internet.  At the time, there was some
   expectation that special arrangements and Quality-of-Service
   mechanisms might be needed to support this new traffic class.  This
   turned out to be not true, at least not in general networks.

   Experience tells us, for instance, that deploying Quality-of-Service
   mechanisms in the Internet is hard, not so much because of the
   technology itself, but due to lack of forces that would be able to
   drive the necessary business changes in the ecosystem for the
   technology to be feasibly deployable [CC2015].  As claffy and Clark

      "Although the Internet has a standards body (the IETF) to resolve
      technical issues, it lacks any similar forum to discuss business
      issues such as how to allocate revenues among competing ISPs
      offering enhanced services.  In the U.S., ISPs feared such

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      discussions would risk anti-trust scrutiny.  Thus, lacking a way
      to negotiate the business implications of QoS, it was considered a
      cost rather than a potential source of revenue.  Yet, the
      relentless growth of a diversity of applications with widely
      varying performance requirements continued on the public Internet,
      with ISPs using relatively primitive, and not always completely
      benign, mechanisms for handling them."

   These difficulties should not be read as prohibiting all changes.  Of
   course, change can also seem unlikely even in cases where it becomes
   absolutely necessary or the forces necessary to make a change have
   actually built up.  As a result, statements regarding change in the
   Internet should be carefully evaluated on their merits from both
   technical and ecosystem perspective.

   Secondly, we often consider characteristics from a too narrow
   viewpoint.  In the case of latency, it is easy to focus on a
   particular protocol or link, whereas from the user perspective
   latency is a property of the system, not a property of an individual

   For instance, improvements on the performance of one link on a
   communications path can be insignificant, if the other parts make up
   a significant fraction of the system-level latency.  That may seem
   obvious, but many applications are highly dependent on communications
   between a number of different parties which may reside in different
   places.  For instance, a third party may perform authentication for a
   cloud-based service that also interacts with user's devices and a
   number of different sensors and actuators.

   We cannot change the speed of light, and a single exchange with
   another part of the world may result in a 100ms delay, or about 200
   times longer than the expected 5G radio link delay for critical
   applications.  It is clear that designing applications from a system
   perspective is very important.

5.2.  Implications

   As noted above, low-latency applications need to pay particular
   attention to the placement of services in the global network.
   Operations that are on the critical path for the low-latency aspects
   of an application are unlikely to work well if those communications
   need to traverse half of the Internet.

   Many widely used services are already distributed and replicated
   throughout the world, to minimise communications latency.  But many
   other services are not distributed in this manner.  For low-latency
   applications such distribution becomes necessary.  Hosting a global

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   service in one location is not feasible due to latency, even when
   from a scale perspective a single server might otherwise suffice for
   the service.

   Content-Delivery Networks (CDNs) and similar arrangements are likely
   to flourish because of this.  In the most extreme cases, edge
   computing services are needed.

   How the communications are routed also matters.  For instance,
   architectures based on tunneling to a central point may incur extra
   delay.  One way to address this pressure is to use SDN- and
   virtualisation-based networks that can be provisioned in the desired
   manner, so that, for instance, instances of tunnel servers can be
   placed in the topologically optimal place for a particular

   Recent developments in multipath transport protocols [RFC6824] also
   provide application- and service-level control of some of the
   networking behaviour.  There is tension between application control
   (often by content providers) and network control (often by network

   One special case where that tension has appeared in the past is
   whether there should be ways to provide information from applications
   to networks on how packets should be treated.  This was extensively
   discussed during the discussion stemming from implications of
   increased use of encryption in the Internet, and how that affects
   operators [I-D.nrooney-marnew-report].

   Another case where there is tension is between mechanisms designed
   for a single link or network vs. end-to-end mechanisms.  Many of the
   stated requirements for low-latency applications are explicitly about
   end-to-end characteristics and capabilities.  Yet, the two mechanisms
   are very different, and most of the deployment difficulties reported
   in [CC2015] relate to end-to-end mechanisms.

   Finally, in the search for even faster connection setup times one
   obvious technique is cross-layer optimisation.  We have seen some of
   this in the IETF in the rethinking of the layers for transport,
   transport layer security, and application framework protocols.

   But while cross-layer optimisation can bring benefits, it also has
   downsides.  In particular, it connects different parts of the stack
   in additional ways.  This can lead to difficulties in further
   evolution of the technology, if done wrong.

      In the case of the IETF transport protocol evolution, significant
      improvements were made to ensure better evolvability of the

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      protocols than what we've experienced with TCP, starting from an
      ability to implement the new protocols in applications rather than
      in the kernel.

   The effects of badly designed cross-layer optimisation are a
   particular form of Internet ossification.  The general networking
   trend, however, is for greater flexibility and programmability.
   Arguably, the ease at which networks can evolve is probably even more
   important than their specific characteristics.

5.3.  Recommendations for Further Work

   Low-latency applications continue to be a hot topic in networking.
   The following topics in particular deserve further work from an
   architectural point of view:

   o  Application architectures for globally connected but low-latency

   o  What are the issues with inter-domain Quality-of-Service
      mechanisms?  Are there approaches that would offer progress on
      this field?

   o  Network architectures that employ tunneling, and mitigations
      against the delay impacts of tunnels (such as tunnel server
      placement or "local breakout" techniques).

   o  The emergence of cross-layer optimisations and how that affects
      the Internet architecture and its future evolution.

   o  Inter-organisatorial matters, e.g., to what extent different
      standards organisations need to talk about low latency effects and
      ongoing work, to promote system-level understanding?

   Overall, this memo stresses the importance of the system-level
   understanding of Internet applications and their latency issues.
   Efforts to address specific sub-issues are unlikely to be fruitful
   without a holistic plan.

6.  Acknowledgements

   The author would like to thank Brian Trammell, Mirja Kuehlewind,
   Linda Dunbar, Goran Rune, Ari Keranen, Jeff Tantsura, Stephen
   Farrell, and many others for interesting discussions in this problem

   The author would also like to acknowledge the important contribution
   that [I-D.dunbar-e2e-latency-arch-view-and-gaps] made in this topic.

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7.  Informative References

   [CC2015]   claffy, kc. and D. Clark, "Adding Enhanced Services to the
              Internet: Lessons from History", September 2015

   [DETNET]   "Deterministic Networking (DETNET) Working Group", March
              2016 (https://tools.ietf.org/wg/detnet/charters).

   [ER2015]   Yilmaz, O., "5G Radio Access for Ultra-Reliable and Low-
              Latency Communications", Ericsson Research Blog, May 2015

   [HU2015]   "5G Vision: 100 Billion connections, 1 ms Latency, and 10
              Gbps Throughput", Huawei 2015

              Dunbar, L., "Architectural View of E2E Latency and Gaps",
              draft-dunbar-e2e-latency-arch-view-and-gaps-01 (work in
              progress), March 2017.

              Iyengar, J. and M. Thomson, "QUIC: A UDP-Based Multiplexed
              and Secure Transport", draft-ietf-quic-transport-02 (work
              in progress), March 2017.

              Quinn, P. and U. Elzur, "Network Service Header", draft-
              ietf-sfc-nsh-12 (work in progress), February 2017.

              Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", draft-ietf-tls-tls13-20 (work in progress),
              April 2017.

              Rooney, N., "IAB Workshop on Managing Radio Networks in an
              Encrypted World (MaRNEW) Report", draft-nrooney-marnew-
              report-02 (work in progress), August 2016.

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   [IMT2020]  "Framework and overall objectives of the future
              development of IMT for 2020 and beyond", ITU
              Recommendation M.2083-0, September 2015

   [L4S]      "Low Latency Low Loss Scalable throughput (L4S) Birds-of-
              Feather Session", July 2016

   [NFV2012]  "Network Functions Virtualisation - Introductory White
              Paper", ETSI,
              http://portal.etsi.org/NFV/NFV_White_Paper.pdf, October

              "5G White Paper", NGMN Alliance, February 2015

   [NO2015]   Doppler, K., "5G the next major wireless standard", DREAMS
              Seminar, January 2015

   [OF2008]   McKeown, N., Anderson, T., Balakrishnan, H., Parulkar, G.,
              Peterson, L., Rexford, J., Shenker, S., and J. Turner,
              "OpenFlow: Enabling Innovation in Campus Networks", ACM
              SIGCOMM Computer Communication Review, Volume 38, Issue 2,
              pp. 69-74 2008.

   [QU2016]   "Leading the world to 5G", Qualcomm, February 2016

   [RFC6824]  Ford, A., Raiciu, C., Handley, M., and O. Bonaventure,
              "TCP Extensions for Multipath Operation with Multiple
              Addresses", RFC 6824, DOI 10.17487/RFC6824, January 2013,

   [RFC7540]  Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext
              Transfer Protocol Version 2 (HTTP/2)", RFC 7540,
              DOI 10.17487/RFC7540, May 2015,

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   [TS38913]  "3rd Generation Partnership Project; Technical
              Specification Group Radio Access Network; Study on
              Scenarios and Requirements for Next Generation Access
              Technologies; (Release 14)", 3GPP Technical Report TR
              38.913 V14.2.0, March 2017

   [TSN8021]  "Time-Sensitive Networking Task Group", IEEE

Author's Address

   Jari Arkko
   Kauniainen  02700

   Email: jari.arkko@piuha.net

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