Internet DRAFT - draft-briscoe-tsvwg-aqm-tcpm-rmcat-l4s-problem
draft-briscoe-tsvwg-aqm-tcpm-rmcat-l4s-problem
Transport Services (tsv) B. Briscoe, Ed.
Internet-Draft Simula Research Lab
Intended status: Informational K. De Schepper
Expires: December 5, 2016 Nokia Bell Labs
M. Bagnulo Braun
Universidad Carlos III de Madrid
June 3, 2016
Low Latency, Low Loss, Scalable Throughput (L4S) Internet Service:
Problem Statement
draft-briscoe-tsvwg-aqm-tcpm-rmcat-l4s-problem-00
Abstract
This document motivates a new service that the Internet could provide
to eventually replace best efforts for all traffic: Low Latency, Low
Loss, Scalable throughput (L4S). It is becoming common for all (or
most) applications being run by a user at any one time to require low
latency, but the only solution the IETF can offer for ultra-low
queuing latency is Diffserv, which only offers low latency for some
packets at the expense of others. Diffserv has also proved hard to
deploy widely end-to-end.
In contrast, a zero-config incrementally deployable solution has been
demonstrated that keeps average queuing delay under a millisecond for
_all_ applications even under very heavy load; and it keeps
congestion loss to zero. At the same time it solves the long-running
problem with the scalability of TCP throughput. Even with a high
capacity broadband access, the resulting performance under load is
remarkably and consistently improved for applications such as
interactive video, conversational video, voice, Web, gaming, instant
messaging, remote desktop and cloud-based apps. This document
explains the underlying problems that have been preventing the
Internet from enjoying such performance improvements. It then
outlines the parts necessary for a solution and the steps that will
be needed to standardize them.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Briscoe, et al. Expires December 5, 2016 [Page 1]
Internet-Draft L4S Problem Statement June 2016
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 December 5, 2016.
Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. The Application Performance Problem . . . . . . . . . . . 3
1.2. The Technology Problem . . . . . . . . . . . . . . . . . 3
1.3. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5
1.4. The Standardization Problem . . . . . . . . . . . . . . . 5
2. Rationale . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.1. Why These Primary Components? . . . . . . . . . . . . . . 7
2.2. Why Not Alternative Approaches? . . . . . . . . . . . . . 7
3. Opportunities . . . . . . . . . . . . . . . . . . . . . . . . 8
3.1. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . 9
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
5. Security Considerations . . . . . . . . . . . . . . . . . . . 10
5.1. Traffic (Non-)Policing . . . . . . . . . . . . . . . . . 10
5.2. 'Latency Friendliness' . . . . . . . . . . . . . . . . . 11
5.3. ECN Integrity . . . . . . . . . . . . . . . . . . . . . . 11
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 11
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
7.1. Normative References . . . . . . . . . . . . . . . . . . 11
7.2. Informative References . . . . . . . . . . . . . . . . . 12
Appendix A. The "TCP Prague Requirements" . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16
Briscoe, et al. Expires December 5, 2016 [Page 2]
Internet-Draft L4S Problem Statement June 2016
1. Introduction
1.1. The Application Performance Problem
It is increasingly common for _all_ of a user's applications at any
one time to require low delay: interactive Web, Web services, voice,
conversational video, interactive video, instant messaging, online
gaming, remote desktop and cloud-based applications. In the last
decade or so, much has been done to reduce propagation delay by
placing caches or servers closer to users. However, queuing remains
a major, albeit intermittent, component of latency. Low loss is also
important because, for interactive applications, losses translate
into delays.
It has been demonstrated that, once access network bit rate reaches
levels now common in the developed world, increasing capacity offers
diminishing returns if latency (delay) is not addressed.
Differentiated services (Diffserv) offers Expedited Forwarding
[RFC3246] for some packets at the expense of others, but this is not
applicable when all (or most) of a user's applications require low
latency.
Therefore, the goal is an Internet service with ultra-Low queueing
Latency, ultra-Low Loss and Scalable throughput (L4S) - for all
traffic. Having motivated the goal of 'L4S for all', this document
enumerates the problems that have to be overcome to reach it.
It must be said that queuing delay only degrades performance
infrequently [Hohlfeld14]. It only occurs when a large enough
capacity-seeking (e.g. TCP) flow is running alongside the user's
traffic in the bottleneck link, which is typically in the access
network. Or when the low latency application is itself a large
capacity-seeking flow (e.g. interactive video). At these times, the
performance improvement must be so remarkable that network operators
will be motivated to deploy it.
1.2. The Technology Problem
Active Queue Management (AQM) is part of the solution to queuing
under load. AQM improves performance for all traffic, but there is a
limit to how much queuing delay can be reduced by solely changing the
network; without addressing the root of the problem.
The root of the problem is the presence of standard TCP congestion
control (Reno [RFC5681]) or compatible variants (e.g. TCP Cubic
[I-D.ietf-tcpm-cubic]). We shall call this family of congestion
controls 'Classic' TCP. It has been demonstrated that if the sending
host replaces Classic TCP with a 'Scalable' alternative, when a
Briscoe, et al. Expires December 5, 2016 [Page 3]
Internet-Draft L4S Problem Statement June 2016
suitable AQM is deployed in the network the performance under load of
all the above interactive applications can be stunningly improved -
even in comparison to a state-of-the-art AQM such as
fq_CoDel [I-D.ietf-aqm-fq-codel] or PIE [I-D.ietf-aqm-pie].
It has been convincingly demonstrated [DCttH15] that it is possible
to deploy such an L4S service alongside the existing best efforts
service so that all of a user's applications can shift to it when
their stack is updated. Access networks are typically designed with
one link as the bottleneck for each site (which might be a home,
small enterprise or mobile device), so deployment at a single node
should give nearly all the benefit. Although the main incremental
deployment problem has been solved, and the remaining work seems
straightforward, there may need to be changes in approach during the
process of engineering a complete solution.
There are three main parts to the L4S approach (illustrated in Fig
{ToDo: ASCII art of slide 9 from
https://riteproject.files.wordpress.com/2015/10/1604-l4s-bar-
bof.pdf}):
1. The L4S service needs to be isolated from the queuing latency of
the Classic service. However, the two must be able to freely
share a common pool of capacity. There is no way to predict how
many flows at any one time might use each service and capacity in
access networks is too scarce to partition into two. The Dual
Queue Coupled AQM is an example of such a 'semi-permeable'
membrane [I-D.briscoe-aqm-dualq-coupled]. Per-flow queuing such
as in [I-D.ietf-aqm-fq-codel] could be used, but it is rather
overkill, which brings disadvantages (see Section 2.2).
2. An identifier is needed to so that L4S and Classic packets can be
classified into their separate treatments.
[I-D.briscoe-tsvwg-ecn-l4s-id] considers various alternative
identifiers, and concludes that all alternatives involve
compromises, but the ECT(1) codepoint of the ECN field is a
workable solution.
3. Scalable congestion controls already exist. They solve the
scaling problem with TCP first pointed out in [RFC3649]. The one
used most widely (in controlled environments) is Data Centre TCP
(DCTCP [I-D.ietf-tcpm-dctcp]), which has been implemented and
deployed in Windows Server Editions (since 2012), in Linux and in
FreeBSD. Although DCTCP as-is 'works' well over the public
Internet, most implementations lack certain safety features that
will be necessary once it is used outside controlled environments
like data centres (see later). A similar scalable congestion
Briscoe, et al. Expires December 5, 2016 [Page 4]
Internet-Draft L4S Problem Statement June 2016
control will also need to be transplanted into protocols other
than TCP (SCTP, RTP/RTCP, RMCAT, etc.)
1.3. Terminology
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 [RFC2119]. In this
document, these words will appear with that interpretation only when
in ALL CAPS. Lower case uses of these words are not to be
interpreted as carrying RFC-2119 significance.
Classic service: The 'Classic' service is intended for all the
behaviours that currently co-exist with TCP Reno (e.g. TCP Cubic,
Compound, SCTP, etc).
Low-Latency, Low-Loss and Scalable (L4S) service: The 'L4S' service
is intended for traffic from scalable TCP algorithms such as Data
Centre TCP. But it is also more general--it will allow a set of
congestion controls with similar scaling properties to DCTCP (e.g.
Relentless [Mathis09]) to evolve.
Both Classic and L4S services can cope with a proportion of
unresponsive or less-responsive traffic as well (e.g. DNS, VoIP,
etc).
Scalable Congestion Control: A congestion control where flow rate is
inversely proportional to the level of congestion signals. Then,
as flow rate scales, the number of congestion signals per round
trip remains invariant, maintaining the same degree of control.
With Classic congestion controls such as TCP Reno and Cubic, as
capacity increases enable higher flow rates, the number of round
trips between signals becomes very large, so control of queuing
and/or utilization becomes very slack.
Classic ECN: The original Explicit Congestion Notification (ECN)
protocol [RFC3168].
1.4. The Standardization Problem
1. The first step will be to articulate the structure and
interworking requirements of the set of parts that would satisfy
the overall application performance requirements.
Then specific interworking aspects of the following three components
parts will need to be defined:
Briscoe, et al. Expires December 5, 2016 [Page 5]
Internet-Draft L4S Problem Statement June 2016
1. The L4S service needs to be isolated from the queuing latency of
the Classic service. However, the two must be able to freely
share a common pool of capacity. There is no way to predict how
many flows at any one time might use each service and capacity in
access networks is too scarce to partition into two. The Dual
Queue Coupled AQM is an example of such a 'semi-permeable'
membrane [I-D.briscoe-aqm-dualq-coupled]. Per-flow queuing such
as in [I-D.ietf-aqm-fq-codel] could be used, but it has
disadvantages, not least that thousands of queues are not needed
if two are sufficient.
2. Identifier
A. [I-D.briscoe-tsvwg-ecn-l4s-id] recommends ECT(1) is used as
the identifier to classify L4S and Classic packets into their
separate treatments, as required by [RFC4774]. The draft
also points out that the experimental assignment of this
codepoint as an ECN nonce [RFC3540] will need to be made
obsolete (it was never deployed, and it offers no security
benefit now that deployment is optional).
B. An essential aspect of a scalable congestion control is the
use of Explicit Congestion Notification (ECN [RFC3168]).
'Classic' ECN requires an ECN signal to be treated the same
as a drop, both when it is generated in the network and when
it is responded to by hosts. A separate queue for L4S allows
the network to support two separate meanings for ECN. And
break from this 'same as drop' constraint is an essential
feature of a scalable congestion control as well.
3. Scalable congestion controls
A. Data Centre TCP is being documented in the TCPM WG as an
informational record of the protocol currently in use
[I-D.ietf-tcpm-dctcp]. It will be necessary to define a
number of safety features for a variant usable on the public
Internet. A draft list of these, known as the TCP Prague
requirements, has been drawn up (see Appendix A).
B. Transport protocols other than TCP use various congestion
controls designed to be friendly with Classic TCP. It will
be necessary to implement scalable variants of each of these
transport behaviours before they can use the L4S service, by
sending packets with the ECT(1) identifier. The following
standards track RFCs currently define these protocols: ECN in
TCP [RFC3168], in SCTP [RFC4960], in RTP [RFC6679], and in
DCCP [RFC4340].
Briscoe, et al. Expires December 5, 2016 [Page 6]
Internet-Draft L4S Problem Statement June 2016
C. For the case of TCP, the feedback protocol for ECN is too
tightly coupled to Classic ECN to be usable for a scalable
TCP. Therefore, the implementation of TCP receivers will
have to be upgraded [RFC7560]. Work to standardize more
accurate ECN feedback for TCP (AccECN
[I-D.ietf-tcpm-accurate-ecn]) is already in progress.
2. Rationale
2.1. Why These Primary Components?
{ToDo: /Why/ the various elements are necessary:}
ECN rather than drop
Packet identifier (pretty obvious why)
Scalable congestion notification (host behaviour)
Semi-permeable membrane (network behaviour)
{We will probably move some of the text in the bullets under "The
Technology Problem" to here, e.g. why you need capacity shared across
the semi-permeable membrane.}
2.2. Why Not Alternative Approaches?
All the following approaches address some part of the same problem
space as L4S. In each case, it is shown that L4S complements them or
improves on them, rather than being a mutually exclusive alternative:
Diffserv: Diffserv addresses the problem of bandwidth apportionment
for important traffic as well as queuing latency for delay-
sensitive traffic. L4S solely addresses the problem of queuing
latency. Diffserv will still be necessary where important traffic
requires priority (e.g. for commercial reasons, or for protection
of critical infrastructure traffic). Nonetheless, if there are
Diffserv classes for important traffic, the L4S approach can
provide low latency for _all_ traffic within each Diffserv class
(including the case where there is only one Diffserv class).
Also, as already explained, Diffserv only works for a small subset
of the traffic on a link. It is not applicable when all the
applications in use at one time at a single site (home, small
business or mobile device) require low latency. Also, because L4S
is for all traffic, it needs none of the management baggage
(traffic policing, traffic contracts) associated with favouring
Briscoe, et al. Expires December 5, 2016 [Page 7]
Internet-Draft L4S Problem Statement June 2016
some packets over others. This baggage has held Diffserv back
from widespread end-to-end deployment.
State-of-the-art AQMs: AQMs such as PIE and fq_CoDel give a
significant reduction in queuing delay relative to no AQM at all.
The L4S work is intended to complement these AQMs, and we
definitely do not want to distract from the need to deploy them as
widely as possible. Nonetheless, without addressing the large
saw-toothing rate variations of Classic congestion controls, they
cannot reduce queuing delay too far without significantly reducing
link utilization. The L4S approach resolves this tension by
ensuring hosts can minimize the sawtoothing.
Per-flow queuing: Similarly per-flow queuing is not incompatible
with the L4S approach. However, one queue for every flow can be
thought of as overkill compared to the minimum of two queues for
all traffic needed for the L4S approach. The overkill of per-flow
queuing has side-effects:
A. fq makes high performance networking equipment costly
(processing and memory) - in contrast dual queue code can be
very simple;
B. fq requires packet inspection into the end-to-end transport
layer, which doesn't sit well alongside encryption for privacy
- in contrast a dual queue, which only operates at the IP
layer;
C. fq has to take control of the decisions over which flows are
scheduled when - in contrast, in the L4S approach the sender
still controls the relative rate of each flow dependent on the
needs of each application.
Alternative Back-off ECN (ABE): Yet again, L4S is not an alternative
to ABE but a complement. ABE alters the host behaviour in
response to ECN marking to utilize a link better and give ECN
flows a faster throughput, but it assumes the network still treats
ECN and drop the same. Therefore ABE exploits any lower queuing
delay that AQMs can provide. But as explained above, AQMs still
cannot reduce queuing delay too far without losing link
utilization (for other non-ABE flows).
3. Opportunities
A transport layer that solves the current latency issues will provide
new service, product and application opportunities.
Briscoe, et al. Expires December 5, 2016 [Page 8]
Internet-Draft L4S Problem Statement June 2016
If applications can rely on minimal queues in the network, they can
focus on reducing their own latency by only minimizing the
application send queue. Following existing applications will
immediately experience a better quality of experience in the best
effort class:
Gaming
VoIP
Video conferencing
Web browsing
(Adaptive) Video Streaming
The lower transport layer latency will also allow more interactive
application functions offloading to the cloud. If last-minute
interactions need to be done locally, more data must be send over the
link. When all interactive processing can be done in the cloud, only
the info to be rendered to the end user can be sent. It will allow
applications such as:
Cloud based interactive video
Cloud based virtual and augmented reality
Also lower network layers can finally be further optimized for low
latency and stable throughput. Today it is not cost efficient, as
the largest part of the traffic (classic best effort) needs to allow
"big" queues anyway (up to several 100s of milliseconds) to make
classic congestion control work correctly. While technology is known
and feasible to support low latency with reliable throughput (even
mobile), it is today not considered as economically relevant, as best
effort can absorb any burst, delay or throughput variations without
end-users experiencing any difference from the normal tay-to-day
operation due to congestion control limitations.
3.1. Use Cases
{ToDo: Just bullets below - text to be added by those interested in
various use-cases}
Different types of access network: DSL, cable, mobile
The challenges and opportunities with radio links: cellular, Wifi
Briscoe, et al. Expires December 5, 2016 [Page 9]
Internet-Draft L4S Problem Statement June 2016
Private networks of heterogeneous data centres (DC interconnect,
multi-tenant cloud, etc)
Different types of transport/app: elastic (TCP/SCTP); real-time (RTP,
RMCAT); query (DNS/LDAP).
Avoiding reliance on middleboxes to enable encryption/privacy
(because the L4S approach does not look deeper than IP in the
network).
4. IANA Considerations
This specification contains no IANA considerations.
5. Security Considerations
5.1. Traffic (Non-)Policing
Because the L4S service can serve all traffic that is using the
capacity of a link, it should not be necessary to police access to
the L4S service. In contrast, Diffserv has to use traffic policers
to limit how much traffic can access each service, otherwise it
doesn't work, In turn, traffic policers require traffic contracts
between users and networks and between networks. Because L4S will
lack all this management complexity, it is more likely to work end-
to-end.
During early deployment (and perhaps always), some networks will not
offer the L4S service. These networks do not need to police or re-
mark L4S traffic - they just forward it unchanged as best efforts
traffic, as they would already forward traffic with ECT(1) today. At
a bottleneck, such networks will introduce some queuing and dropping.
When the scalable congestion controll detects a drop it has to
respond as if it is a Classic congestion control, and there will then
be no interworking problems.
Certain network operators might choose to restict access to the L4S
class, perhaps only to customers who have paid a premium. In the
packet classifer, they could identify such customers using some other
field (e.g. source address range), and just ignoring the L4S
identifier for non-paying customers. This will ensure that the L4S
identifier survives end-to-end even though the service does not have
to be supported at every hop. Such arrangements would only require
simple registered/not-registered packet classification, rather than
the complex application-specific traffic contracts of Diffserv.
Briscoe, et al. Expires December 5, 2016 [Page 10]
Internet-Draft L4S Problem Statement June 2016
5.2. 'Latency Friendliness'
The L4S service does rely on self-constraint - not in terms of
limiting capacity usage, but in terms of limiting burstiness. It is
believed that standardisation of dynamic behaviour (cf. TCP slow-
start) and self-interest will be sufficient to prevent transports
from sending excessive bursts of L4S traffic, given the application's
own latency will suffer most from such behaviour.
Whether burst policing becomes necessary remains to be seen. Without
it, there will be potential for attacks on the low latency of the L4S
service. However it may only be necessary to apply such policing
reactively, e.g. punitively targeted at any deployments of new bursty
malware.
5.3. ECN Integrity
{ToDo: Paraphrase discussion from ecn-l4s-id}
6. Acknowledgements
7. References
7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition
of Explicit Congestion Notification (ECN) to IP",
RFC 3168, DOI 10.17487/RFC3168, September 2001,
<http://www.rfc-editor.org/info/rfc3168>.
[RFC4774] Floyd, S., "Specifying Alternate Semantics for the
Explicit Congestion Notification (ECN) Field", BCP 124,
RFC 4774, DOI 10.17487/RFC4774, November 2006,
<http://www.rfc-editor.org/info/rfc4774>.
[RFC6679] Westerlund, M., Johansson, I., Perkins, C., O'Hanlon, P.,
and K. Carlberg, "Explicit Congestion Notification (ECN)
for RTP over UDP", RFC 6679, DOI 10.17487/RFC6679, August
2012, <http://www.rfc-editor.org/info/rfc6679>.
Briscoe, et al. Expires December 5, 2016 [Page 11]
Internet-Draft L4S Problem Statement June 2016
7.2. Informative References
[DCttH15] De Schepper, K., Bondarenko, O., Briscoe, B., and I.
Tsang, "'Data Centre to the Home': Ultra-Low Latency for
All", 2015, <http://www.bobbriscoe.net/projects/latency/
dctth_preprint.pdf>.
(Under submission)
[Hohlfeld14]
Hohlfeld , O., Pujol, E., Ciucu, F., Feldmann, A., and P.
Barford, "A QoE Perspective on Sizing Network Buffers",
Proc. ACM Internet Measurement Conf (IMC'14) hmm, November
2014.
[I-D.briscoe-aqm-dualq-coupled]
Schepper, K., Briscoe, B., Bondarenko, O., and I. Tsang,
"DualQ Coupled AQM for Low Latency, Low Loss and Scalable
Throughput", draft-briscoe-aqm-dualq-coupled-01 (work in
progress), March 2016.
[I-D.briscoe-tsvwg-ecn-l4s-id]
Schepper, K., Briscoe, B., and I. Tsang, "Identifying
Modified Explicit Congestion Notification (ECN) Semantics
for Ultra-Low Queuing Delay", draft-briscoe-tsvwg-ecn-l4s-
id-01 (work in progress), March 2016.
[I-D.ietf-aqm-fq-codel]
Hoeiland-Joergensen, T., McKenney, P.,
dave.taht@gmail.com, d., Gettys, J., and E. Dumazet, "The
FlowQueue-CoDel Packet Scheduler and Active Queue
Management Algorithm", draft-ietf-aqm-fq-codel-06 (work in
progress), March 2016.
[I-D.ietf-aqm-pie]
Pan, R., Natarajan, P., and F. Baker, "PIE: A Lightweight
Control Scheme To Address the Bufferbloat Problem", draft-
ietf-aqm-pie-07 (work in progress), April 2016.
[I-D.ietf-tcpm-accurate-ecn]
Briscoe, B., KĂźhlewind, M., and R.
Scheffenegger, "More Accurate ECN Feedback in TCP", draft-
ietf-tcpm-accurate-ecn-00 (work in progress), December
2015.
Briscoe, et al. Expires December 5, 2016 [Page 12]
Internet-Draft L4S Problem Statement June 2016
[I-D.ietf-tcpm-cubic]
Rhee, I., Xu, L., Ha, S., Zimmermann, A., Eggert, L., and
R. Scheffenegger, "CUBIC for Fast Long-Distance Networks",
draft-ietf-tcpm-cubic-01 (work in progress), January 2016.
[I-D.ietf-tcpm-dctcp]
Bensley, S., Eggert, L., Thaler, D., Balasubramanian, P.,
and G. Judd, "Datacenter TCP (DCTCP): TCP Congestion
Control for Datacenters", draft-ietf-tcpm-dctcp-01 (work
in progress), November 2015.
[I-D.moncaster-tcpm-rcv-cheat]
Moncaster, T., Briscoe, B., and A. Jacquet, "A TCP Test to
Allow Senders to Identify Receiver Non-Compliance", draft-
moncaster-tcpm-rcv-cheat-03 (work in progress), July 2014.
[I-D.stewart-tsvwg-sctpecn]
Stewart, R., Tuexen, M., and X. Dong, "ECN for Stream
Control Transmission Protocol (SCTP)", draft-stewart-
tsvwg-sctpecn-05 (work in progress), January 2014.
[Mathis09]
Mathis, M., "Relentless Congestion Control", PFLDNeT'09 ,
May 2009, <http://www.hpcc.jp/pfldnet2009/
Program_files/1569198525.pdf>.
[RFC3246] Davie, B., Charny, A., Bennet, J., Benson, K., Le Boudec,
J., Courtney, W., Davari, S., Firoiu, V., and D.
Stiliadis, "An Expedited Forwarding PHB (Per-Hop
Behavior)", RFC 3246, DOI 10.17487/RFC3246, March 2002,
<http://www.rfc-editor.org/info/rfc3246>.
[RFC3540] Spring, N., Wetherall, D., and D. Ely, "Robust Explicit
Congestion Notification (ECN) Signaling with Nonces",
RFC 3540, DOI 10.17487/RFC3540, June 2003,
<http://www.rfc-editor.org/info/rfc3540>.
[RFC3649] Floyd, S., "HighSpeed TCP for Large Congestion Windows",
RFC 3649, DOI 10.17487/RFC3649, December 2003,
<http://www.rfc-editor.org/info/rfc3649>.
[RFC4340] Kohler, E., Handley, M., and S. Floyd, "Datagram
Congestion Control Protocol (DCCP)", RFC 4340,
DOI 10.17487/RFC4340, March 2006,
<http://www.rfc-editor.org/info/rfc4340>.
Briscoe, et al. Expires December 5, 2016 [Page 13]
Internet-Draft L4S Problem Statement June 2016
[RFC4960] Stewart, R., Ed., "Stream Control Transmission Protocol",
RFC 4960, DOI 10.17487/RFC4960, September 2007,
<http://www.rfc-editor.org/info/rfc4960>.
[RFC5681] Allman, M., Paxson, V., and E. Blanton, "TCP Congestion
Control", RFC 5681, DOI 10.17487/RFC5681, September 2009,
<http://www.rfc-editor.org/info/rfc5681>.
[RFC7560] Kuehlewind, M., Ed., Scheffenegger, R., and B. Briscoe,
"Problem Statement and Requirements for Increased Accuracy
in Explicit Congestion Notification (ECN) Feedback",
RFC 7560, DOI 10.17487/RFC7560, August 2015,
<http://www.rfc-editor.org/info/rfc7560>.
[RFC7713] Mathis, M. and B. Briscoe, "Congestion Exposure (ConEx)
Concepts, Abstract Mechanism, and Requirements", RFC 7713,
DOI 10.17487/RFC7713, December 2015,
<http://www.rfc-editor.org/info/rfc7713>.
Appendix A. The "TCP Prague Requirements"
This list of requirements was produced at an ad hoc meeting during
IETF-94 in Prague. The list prioritised features that would need to
be added to DCTCP to make it safe for use on the public Internet
alongside existing non-DCTCP traffic. It also includes features to
improve the performance of DCTCP in the wider range of conditions
found on the public Internet.
The table is too wide for the ASCII draft format, so it been split
into two, with a common column of row index numbers on the left.
Briscoe, et al. Expires December 5, 2016 [Page 14]
Internet-Draft L4S Problem Statement June 2016
+-----+---------------------------+---------------------------------+
| # | Requirement | Reference |
+-----+---------------------------+---------------------------------+
| 0 | ARCHITECTURE | |
| 1 | L4S IDENTIFIER | [I-D.briscoe-tsvwg-ecn-l4s-id] |
| 2 | DUAL QUEUE AQM | [I-D.briscoe-aqm-dualq-coupled] |
| | SCALABLE TRANSPORT SAFETY | |
| | ADDITIONS | |
| 3-1 | Fall back to Reno/Cubic | [I-D.ietf-tcpm-dctcp] |
| | on loss | |
| 3-2 | TCP ECN Feedback | [I-D.ietf-tcpm-accurate-ecn] |
| 3-4 | Scaling TCP's Congestion | |
| | Window for Small Round | |
| | Trip Times | |
| 3-5 | Reduce RTT-dependence | |
| 3-6 | Smooth ECN feedback over | |
| | own RTT | |
| 3-7 | Fall back to Reno/Cubic | |
| | if classic ECN bottleneck | |
| | detected | |
| | SCALABLE TRANSPORT | |
| | PERFORMANCE ENHANCEMENTS | |
| 3-8 | Faster-than-additive | |
| | increase | |
| 3-9 | Less drastic exit from | |
| | slow-start | |
+-----+---------------------------+---------------------------------+
Briscoe, et al. Expires December 5, 2016 [Page 15]
Internet-Draft L4S Problem Statement June 2016
+-----+--------+-----+-------+-----------+--------+--------+--------+
| # | WG | TCP | DCTCP | DCTCP-bis | TCP | SCTP | RMCAT |
| | | | | | Prague | Prague | Prague |
+-----+--------+-----+-------+-----------+--------+--------+--------+
| 0 | tsvwg? | Y | Y | Y | Y | Y | Y |
| 1 | tsvwg? | | | Y | Y | Y | Y |
| 2 | aqm? | n/a | n/a | n/a | n/a | n/a | n/a |
| | | | | | | | |
| 3-1 | tcpm | | Y | Y | Y | Y | Y |
| 3-2 | tcpm | Y | Y | Y | Y | n/a | n/a |
| 3-4 | tcpm | Y | Y | Y | Y | Y | ? |
| 3-5 | tcpm/ | | | Y | Y | Y | ? |
| | iccrg? | | | | | | |
| 3-6 | tcpm/ | | ? | Y | Y | Y | ? |
| | iccrg? | | | | | | |
| 3-7 | tcpm/ | | | | Y | Y | ? |
| | iccrg? | | | | | | |
| | | | | | | | |
| 3-8 | tcpm/ | | | Y | Y | Y | ? |
| | iccrg? | | | | | | |
| 3-9 | tcpm/ | | | Y | Y | Y | ? |
| | iccrg? | | | | | | |
+-----+--------+-----+-------+-----------+--------+--------+--------+
Authors' Addresses
Bob Briscoe (editor)
Simula Research Lab
Email: ietf@bobbriscoe.net
URI: http://bobbriscoe.net/
Koen De Schepper
Nokia Bell Labs
Antwerp
Belgium
Email: koen.de_schepper@nokia.com
URI: https://www.bell-labs.com/usr/koen.de_schepper
Briscoe, et al. Expires December 5, 2016 [Page 16]
Internet-Draft L4S Problem Statement June 2016
Marcelo Bagnulo
Universidad Carlos III de Madrid
Av. Universidad 30
Leganes, Madrid 28911
Spain
Phone: 34 91 6249500
Email: marcelo@it.uc3m.es
URI: http://www.it.uc3m.es
Briscoe, et al. Expires December 5, 2016 [Page 17]
