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Versions: (draft-mathis-conex-abstract-mech)
00 01 02 03 04 05 06 07 08 09 10 11
12 13 RFC 7713
Congestion Exposure (ConEx) Working M. Mathis
Group Google, Inc
Internet-Draft B. Briscoe
Intended status: Informational BT
Expires: September 8, 2011 March 7, 2011
Congestion Exposure (ConEx) Concepts and Abstract Mechanism
draft-ietf-conex-abstract-mech-00
Abstract
This document describes an abstract mechanism by which senders inform
the network about the congestion encountered by packets earlier in
the same flow. Today, the network may signal congestion to the
receiver by ECN markings or by dropping packets, and the receiver may
pass this information back to the sender in transport-layer feedback.
The mechanism to be developed by the ConEx WG will enable the sender
to also relay this congestion information back into the network in-
band at the IP layer, such that the total level of congestion is
visible to all IP devices along the path, from where it could, for
example, be provided as input to traffic management.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 8, 2011.
Copyright Notice
Copyright (c) 2011 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
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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. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
2. Requirements for the ConEx Signal . . . . . . . . . . . . . . 4
3. Representing Congestion Exposure . . . . . . . . . . . . . . . 6
3.1. Strawman Encoding . . . . . . . . . . . . . . . . . . . . 7
3.2. ECN Based Encoding . . . . . . . . . . . . . . . . . . . . 7
3.2.1. ECN Changes . . . . . . . . . . . . . . . . . . . . . 8
3.3. Abstract Encoding . . . . . . . . . . . . . . . . . . . . 8
3.3.1. Independent Bits . . . . . . . . . . . . . . . . . . . 9
3.3.2. Codepoint Encoding . . . . . . . . . . . . . . . . . . 9
4. Congestion Exposure Components . . . . . . . . . . . . . . . . 9
4.1. Modified Senders . . . . . . . . . . . . . . . . . . . . . 9
4.2. Receivers (Optionally Modified) . . . . . . . . . . . . . 10
4.3. Audit . . . . . . . . . . . . . . . . . . . . . . . . . . 10
4.4. Policy Devices . . . . . . . . . . . . . . . . . . . . . . 11
4.4.1. Congestion Policers . . . . . . . . . . . . . . . . . 11
4.4.2. Other Policy Devices . . . . . . . . . . . . . . . . . 11
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
6. Security Considerations . . . . . . . . . . . . . . . . . . . 12
7. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 12
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12
9. Comments Solicited . . . . . . . . . . . . . . . . . . . . . . 12
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
10.1. Normative References . . . . . . . . . . . . . . . . . . . 12
10.2. Informative References . . . . . . . . . . . . . . . . . . 12
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1. Introduction
One of the required functions of a transport protocol is controlling
congestion in the network. There are three techniques in use today
for the network to signal congestion to a transport:
o The most common congestion signal is packet loss. When congested,
the network simply discards some packets either as part of an
explicit control function [RFC2309] or as the consequence of a
queue overflow or other resource starvation. The transport
receiver detects that some data is missing and signals such
through transport acknowledgments to the transport sender (e.g.
TCP SACK options). The sender performs the appropriate congestion
control rate reduction (e.g. [RFC5681] for TCP) and, if it is a
reliable transport, it retransmits the missing data.
o If the transport supports explicit congestion notification (ECN)
[RFC3168] or pre-congestion notification (PCN) [RFC5670] , the
transport sender indicates this by setting an ECN-capable
transport (ECT) codepoint in every packet. Network devices can
then explicitly signal congestion to the receiver by setting ECN
bits in the IP header of such packets. The transport receiver
communicates these ECN signals back to the sender, which then
performs the appropriate congestion control rate reduction.
o Some experimental transport protocols and TCP variants [Vegas]
sense queuing delays in the network and reduce their rate before
the network has to signal congestion using loss or ECN. A purely
delay-sensing transport will tend to be pushed out by other
competing transports that do not back off until they have driven
the queue into loss. Therefore, modern delay-sensing algorithms
use delay in some combination with loss to signal congestion (e.g.
LEDBAT [I-D.ietf-ledbat-congestion], Compound
[I-D.sridharan-tcpm-ctcp]). In the rest of this document, we will
confine the discussion to concrete signals of congestion such as
loss and ECN. We will not discuss delay-sensing further, because
it can only avoid these more concrete signals of congestion in
some circumstances.
In all cases the congestion signals follow the route indicated in
Figure 1. A congested network device sends a signal in the data
stream on the forward path to the transport receiver, the receiver
passes it back to the sender through transport level feedback, and
the sender makes some congestion control adjustment.
This document proposes to extend the capabilities of the Internet
protocol suite with the addition of a ConEx Signal that, to a first
approximation, relays the congestion information from the transport
sender back through the internetwork layer. That signal is shown in
Figure 1. It would be visible to all internetwork layer devices
along the forward (data) path and is intended to support a number of
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new policy-controlled mechanisms that might be used to manage
traffic.
123456789012345678901234567890123456789012345678901234567890123456789
+---------+ +---------+
| |<==Feedback Path==============================<| |
| |<--Transport Layer returned Congestion Signal-<| |
| | | |
|Transport| |Transport|
| Sender |>---------(new)-IP layer ConEx Signal--------->| Receiver|
| | (Carried in Data Packet Headers) | |
| | +-----------+ | |
| |>=Data=Path=>|(Congested)|>=====Data=Path=====>| |
| | | Network |>-Congestion-Signal->| |
| | | Device | | |
+---------+ +-----------+ +---------+
Not shown are policy devices along the data path that observe the
ConEx Signal, and use the information to monitor or manage traffic.
These are discussed in Section 4.4.
Figure 1
1.1. 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 RFC 2119 [RFC2119].
ConEx signals in IP packet headers from the sender to the network
{ToDo: These are placeholders for whatever words we decide to use}:
Not-ConEx: The transport is not ConEx-capable
ConEx-Capable: The transport is ConEx-Capable. This is the opposite
of Not-ConEx and implies one of the following signals
Re-Echo-Loss: (aka Purple) The transport has experienced a loss
Re-Echo-ECN: (aka Black) The transport has experienced an ECN
mark
Credit: (aka Green) The transport is building up credit to allow
for any future delay in expected ConEx signals
ConEx-Not-Marked: The transport is ConEx-capable but is signaling
none of Re-Echo-Loss, Re-Echo-ECN or Credit
ConEx-Marked: At least one of Re-Echo-Loss, Re-Echo-ECN or
Credit.
2. Requirements for the ConEx Signal
Ideally, all the following requirements would be met by a Congestion
Exposure Signal. However it is already known that some compromises
will be necessary, therefore all the requirements are expressed with
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the keyword 'SHOULD' rather than 'MUST'. The only mandatory
requirement is that a concrete protocol description MUST give sound
reasoning if it chooses not to meet any of these requirements:
a. The ConEx Signal SHOULD be visible to internetwork layer devices
along the entire path from the transport sender to the transport
receiver. Equivalently, it SHOULD be present in the IPv4 or IPv6
header, and in the outermost IP header if using IP in IP
tunneling. The ConEx Signal SHOULD be immutable once set by the
transport sender. A corollary of these requirements is that
existing (legacy) networking gear SHOULD pass the Congestion
Exposure Signal silently without modification.
b. The ConEx Signal SHOULD be useful under only partial deployment.
A minimal deployment SHOULD only require changes to transport
senders. Furthermore, partial deployment SHOULD create
incentives for additional deployment, both in terms of enabling
ConEx on more devices and adding richer features to existing
devices. Nonetheless, ConEx deployment need never be universal,
and it is anticipated that some hosts and some transports may
never support the ConEx Protocol and some networks may never use
the ConEx Signals.
c. The ConEx Signal SHOULD be accurate. In potentially hostile
environments such as the public Internet, it SHOULD be possible
for techniques to be deployed to audit the Congestion Exposure
Signal by comparing it to the actual congestion signals on the
forward data path. The auditing mechanism must have a capability
for providing sufficient disincentives against misreported
congestion, such as by throttling traffic that reports less
congestion than it is actually experiencing.
d. The ConEx Signal SHOULD be timely. There will be a delay between
the time when an auditing device sees an actual congestion signal
and when it sees the subsequent Congestion Exposure Signal from
the sender. The minimum delay will be one round trip, but it may
be much longer depending on the transport's choice of feedback
delay (consider RTCP [RFC3550] for example). It is not practical
to expect auditing devices in the network to make allowance for
such feedback delays. Instead, the sender SHOULD be able to send
ConEx signals in advance, as 'credit' for any audit device to
hold as a balance against the risk of congestion during the
feedback delay. This design choice simplifies auditing devices
and correctly makes the transport responsible for both minimizing
feedback delay and minimizing sharp increases in packets in
flight that would risk causing excessive congestion to others.
This issue is discussed in more detail in Section 4.3.
It is important to note that the auditing requirement implies a
number of additional constraints: The basic auditing technique is to
count both actual congestion signals and ConEx Signals someplace
along the data path:
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o For congestion signaled by ECN, auditing is most accurate when
located near the transport receiver. Within any flow or aggregate
of flows, the total volume of ECN marked data seen near the
receiver should always be equal to or less than the volume of data
tagged with ConEx Signals.
o For congestion signaled by loss, totally accurate auditing is not
believed to be possible in the general case, because it involves a
network node detecting the absence of some packets, when it cannot
necessarily see the transport protocol sequence numbers and when
the missing packets might simply be taking a different route. But
there are common cases where sufficient audit accuracy should be
possible:
* For non-IPsec traffic conforming to standard TCP sequence
numbering on a single path, an auditor could detect losses by
observing both the original transmission and the retransmission
after the loss. Such auditing would be most accurate near the
sender.
* For networks designed so that losses predominantly occur under
the management of one IP-aware node on the path, the auditor
could be located at this bottleneck. It could simply compare
ConEx Signals with actual local losses. This is a good model
for most consumer access networks and audit accuracy could well
be sufficient even if losses occasionally occurred at other
nodes in the network, such as border gateways (see Section 4.3
for details).
Given that loss-based and ECN-based ConEx might sometimes be best
audited at different locations, having distinct encodings would widen
the design space for the auditing function.
3. Representing Congestion Exposure
Most protocol specifications start with a description of packet
formats and codepoints with their associated meanings. This document
does not: It is already known that choosing the encoding for the
ConEx Signal is likely to entail some engineering compromises that
have the potential to reduce the protocol's usefulness in some
settings. Rather than making these engineering choices prematurely,
this document side steps the encoding problem by describing an
abstract representation of ConEx Signals. All of the elements of the
protocol can be defined in terms of this abstract representation.
Most important, the preliminary use cases for the protocol are
described in terms of the abstract representation in companion
documents [I-D.conex-concepts-uses].
Once we have some example use cases we can evaluate different
encoding schemes. Since these schemes are likely to include some
conflated code points, some information will be lost resulting in
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weakening or disabling some of the algorithms and eliminating some
use cases.
The goal of this approach is to be as complete as possible for
discovering the potential usage and capabilities of the ConEx
protocol, so we have some hope of making optimal design decisions
when choosing the encoding.
3.1. Strawman Encoding
As an aid to the reader, it might be helpful to describe a naive
strawman encoding of the ConEx protocol described solely in terms of
TCP: set the Reserved bit in the IPv4 header (bit 48 counting from
zero [RFC0791]--aka the "evil bit" [RFC3514]) on all retransmissions
or once per ECN signaled window reduction. Clearly network devices
along the forward path can see this bit and act on it. For example
they can count marked and unmarked packets to estimate the congestion
levels along the path.
However, the IESG has chartered the ConEx working group to establish
that there is sufficient demand for an IPv6 ConEx protocol before
using the last available bit in the IPv4 header. Furthermore this
encoding, by itself, does not sufficiently support partial deployment
or strong auditing and might motivate users and/or applications to
misrepresent the congestion that they are causing.
Nonetheless, this strawman encoding does present a clear mental model
of how the ConEx protocol might function under various uses.
3.2. ECN Based Encoding
Ideally ConEx and ECN are orthogonal signals and SHOULD be entirely
independent. However, given the limited number of header bit and/or
code points, these signals may have to share code points, at least
partially.
The re-ECN specification [I-D.briscoe-tsvwg-re-ecn-tcp] presents an
implementation of ConEx that is tightly integrated with the encoding
of ECN in the IP header. The central theme of this work is an audit
mechanism that can provide sufficient disincentives against
misrepresenting congestion [I-D.briscoe-tsvwg-re-ecn-motiv], which is
analyzed extensively in Briscoe's PhD dissertation [Refb-dis].
Re-ECN is a good example of one chosen set of compromises attempting
to meet the requirements of Section 2. However, the present document
takes a step back, aiming to state the ideal requirements in order to
allow the Internet community to assess whether other compromises are
possible.
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In particular, different incremental deployment choices may be
desirable to meet the partial deployment requirement of Section 2.
Re-ECN requires the receiver to be at least ECN-capable as well as
requiring an update to the sender. Although ConEx will inherently
require change at the sender, it would be preferable if it could
work, even partially, with any receiver.
The chosen ConEx protocol certainly must not require ECN to be
deployed in any network. In this respect re-ECN is already a good
example--it acts perfectly well as a loss-based ConEx protocol it the
loss-based audit techniques in Section 4.3 are used. However, it
would still be desirable to avoid the dependence on an ECN receiver.
For a tutorial background on Re-Feedback techniques, see [Re-fb,
FairerFaster].
3.2.1. ECN Changes
Although the re-ECN protocol requires no changes to the network side
of the ECN protocol, it is important to note that it does propose
some relatively minor modifications to the host-to-host aspects of
the ECN protocol specified in RFC 3168. They include: redefining the
ECT(1) code point (the change is consistent with RFC3168 but requires
deprecating the experimental ECN nonce [RFC3540]); modifications to
the ECN negotiations carried on the SYN and SYN-ACK; and using a
different state machine to carry ECN signals in the transport
acknowledgments from the Receiver to the Sender. This last change
permits the transport protocol to carry multiple congestion signals
per round trip, and greatly simplifies accurate auditing.
All of these adjustments to RFC 3168 may also be needed in a future
standardized ConEx protocol. There will need to be very careful
consideration of any proposed changes to ECN or other existing
protocols, because any such changes increase the cost of deployment.
3.3. Abstract Encoding
The ConEx protocol could take one of two different encodings:
independently settable bits or an enumerated set of mutually
exclusive codepoints.
In both cases, the amount of congestion is signaled by the volume of
marked data--just as the volume of lost data or ECN marked data
signals the amount of congestion experienced. Thus the size of each
packet carrying a ConEx Signal is significant.
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3.3.1. Independent Bits
This encoding involves flag bits, each of which the sender can set
independently to indicate to the network one of the following four
signals:
ConEx (Not-ConEx) The transport is (or is not) using ConEx with this
packet (the protocol MUST be arranged so that legacy transport
senders implicitly send Not-ConEx)
Re-Echo-Loss (Not-Re-Echo-Loss) The transport has (or has not)
experienced a loss
Re-Echo-ECN (Not-Re-Echo-ECN) The transport has (or has not)
experienced ECN signaled congestion
Credit (Not-Credit) The transport is (or is not) building up
congestion credit (see Section 4.3 on audit devices)
3.3.2. Codepoint Encoding
This encoding involves signaling one of the following five
codepoints:
ENUM {Not-ConEx, ConEx, Re-Echo-Loss, Re-Echo-ECN, Credit}
Each named codepoint has the same meaning as in the encoding using
independent bits (Section 3.3.1). The use of any one codepoint
implies the negative of all the others, except the last three
codepoints (Re-Echo-Loss, Re-Echo-ECN and Credit) obviously also
imply ConEx is supported.
Inherently, the semantics of most of the enumerated codepoints are
mutually exclusive. 'Credit' is the only one that might need to be
used in combination with either Re-Echo-Loss or Re-Echo-ECN, but even
that requirement is questionable. It must not be forgotten that the
enumerated encoding loses the flexibility to signal these two
combinations, whereas the encoding with four independent bits is not
so limited. Alternatively two extra codepoints could be assigned to
these two combinations of semantics.
4. Congestion Exposure Components
{ToDo: Picture of the components, similar to that in the last
slideset about conex-concepts-uses?}
4.1. Modified Senders
The sending transport needs to be modified to send Congestion
Exposure Signals in response to congestion feedback signals.
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4.2. Receivers (Optionally Modified)
The receiving transport may already feedback sufficiently useful
signals to the sender so that it does not need to be altered.
However, a TCP receiver feeds back ECN congestion signals no more
than once within a round trip. The sender may require more precise
feedback from the receiver otherwise it will appear to be
understating its ConEx Signals (see Section 3.2.1).
Ideally, ConEx should be added to a transport like TCP without
mandatory modifications to the receiver. But an optional
modification to the receiver could be recommended for precision.
This was the approach taken when adding re-ECN to TCP
[I-D.briscoe-tsvwg-re-ecn-tcp].
4.3. Audit
To audit ConEx Signals against actual losses an auditor could use one
of the following techniques:
TCP-specific approach: The auditor could monitor TCP flows or
aggregates of flows, only holding state on a flow if it first
sends a Credit or a Re-Echo-Loss marking. The auditor could
detect retransmissions by monitoring sequence numbers. It would
assure that (volume of retransmitted data) <= (volume of data
marked Re-Echo-Loss). Traffic would only be auditable in this way
if it conformed to the standard TCP protocol and the IP payload
was not encrypted (e.g. with IPsec).
Predominant bottleneck approach: Unlike the above TCP-specific
solution, this technique would work for IP packets carrying any
transport layer protocol, and whether encrypted or not. But it
only works well for networks designed so that losses predominantly
occur under the management of one IP-aware node on the path. The
auditor could then be located at this bottleneck. It could simply
compare ConEx Signals with actual local losses. Most consumer
access networks are design to this model, e.g. the radio network
controller (RNC) in a cellular network or the broadband remote
access server (BRAS) in a digital subscriber line (DSL) network.
The accuracy of an auditor at one predominant bottleneck might
still be sufficient, even if losses occasionally occurred at other
nodes in the network (e.g. border gateways). Although the auditor
at the predominant bottleneck would not always be able to detect
losses at other nodes, transports would not know where losses were
occurring either. Therefore any transport would not know which
losses it could cheat on without getting caught, and which ones it
couldn't.
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To audit ConEx Signals against actual ECN markings or losses, the
auditor could work as follows: monitor flows or aggregates of flows,
only holding state on a flow if it first sends a Credit or either Re-
Echo marking. Count the number of bytes marked with Credit or Re-
Echo-ECN. Separately count the number of bytes marked with ECN. Use
Credits to assure that #ECN<=#Re-Echo-ECN+#Credit, even though the
Re-Echo-ECN markings are delayed by at least one RTT.
4.4. Policy Devices
Policy devices are characterised by a need to be configured with a
policy related to the users or neighboring networks being served. In
contrast, the auditing devices referred to in the previous section
primarily enforce compliance with the ConEx protocol and do not need
to be configured with any client-specific policy.
4.4.1. Congestion Policers
Note that a congestion policer can be implemented in a very similar
way to a bit-rate policer, but its effect is focused solely on
traffic causing congestion downstream, not on all traffic just in
case it causes congestion.
It monitors all ConEx traffic entering a network, or some
identifiable subset. Using ConEx signals, it measures the amount of
congestion being caused by this traffic. If this exceeds a policy-
configured 'congestion-bit-rate' the congestion policer will limit
all the monitored ConEx traffic. A congestion policer can be
implemented by a simple token bucket. But unlike a bit-rate policer,
it only removes tokens when forwarding packets that a ConEx marked.
See [CongPol] for details.
4.4.2. Other Policy Devices
Other policy devices that use ConEx signaling might traffic traffic
based on ConEx Signals in much the same way as the monitoring element
of a Congestion Policer. But the resulting action could be
different. It might re-route traffic or downgrade the class of
service.
It might do nothing directly to the traffic, but instead report
measurements of ConEx Signals to systems designed to control
congestion indirectly. For instance the measurements might be used
to trigger penalty clauses in contracts, to levy charges between
networks based on congestion or simply to notify customers who cause
excessive congestion.
an auditing device only needs to enforce protocol compliance, it does
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not need to reflect any policy.
5. IANA Considerations
This memo includes no request to IANA.
Note to RFC Editor: this section may be removed on publication as an
RFC.
6. Security Considerations
Significant parts of this whole document are about the auditability
of ConEx Signals, in particular Section 4.3.
7. Conclusions
{ToDo:}
8. Acknowledgements
This document was improved by review comments from Toby Moncaster.
9. Comments Solicited
Comments and questions are encouraged and very welcome. They can be
addressed to the IETF Congestion Exposure (ConEx) working group
mailing list <conex@ietf.org>, and/or to the authors.
10. References
10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in
RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119,
March 1997.
10.2. Informative References
[CongPol] Jacquet, A., Briscoe, B., and T.
Moncaster, "Policing Freedom to Use
the Internet Resource Pool", Proc
ACM Workshop on Re-Architecting the
Internet (ReArch'08) ,
December 2008, <http://
bobbriscoe.net/projects/
refb/#polfree>.
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[FairerFaster] Briscoe, B., "A Fairer, Faster
Internet Protocol", IEEE
Spectrum Dec 2008:38--43,
December 2008, <http://
bobbriscoe.net/projects/
refb/#fairfastip>.
[I-D.briscoe-tsvwg-re-ecn-motiv] Briscoe, B., Jacquet, A.,
Moncaster, T., and A. Smith, "Re-
ECN: A Framework for adding
Congestion Accountability to
TCP/IP", draft-briscoe-tsvwg-re-
ecn-tcp-motivation-01 (work in
progress), September 2009.
[I-D.briscoe-tsvwg-re-ecn-tcp] Briscoe, B., Jacquet, A.,
Moncaster, T., and A. Smith, "Re-
ECN: Adding Accountability for
Causing Congestion to TCP/IP",
draft-briscoe-tsvwg-re-ecn-tcp-09
(work in progress), October 2010.
[I-D.conex-concepts-uses] Briscoe, B., Woundy, R., Moncaster,
T., and J. Leslie, "ConEx Concepts
and Use Cases", draft-moncaster-
conex-concepts-uses-01 (work in
progress), July 2010.
[I-D.ietf-ledbat-congestion] Shalunov, S., Hazel, G., and J.
Iyengar, "Low Extra Delay
Background Transport (LEDBAT)",
draft-ietf-ledbat-congestion-03
(work in progress), October 2010.
[I-D.sridharan-tcpm-ctcp] Sridharan, M., Tan, K., Bansal, D.,
and D. Thaler, "Compound TCP: A New
TCP Congestion Control for High-
Speed and Long Distance Networks",
draft-sridharan-tcpm-ctcp-02 (work
in progress), November 2008.
[RFC0791] Postel, J., "Internet Protocol",
STD 5, RFC 791, September 1981.
[RFC2309] Braden, B., Clark, D., Crowcroft,
J., Davie, B., Deering, S., Estrin,
D., Floyd, S., Jacobson, V.,
Minshall, G., Partridge, C.,
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Peterson, L., Ramakrishnan, K.,
Shenker, S., Wroclawski, J., and L.
Zhang, "Recommendations on Queue
Management and Congestion Avoidance
in the Internet", RFC 2309,
April 1998.
[RFC3168] Ramakrishnan, K., Floyd, S., and D.
Black, "The Addition of Explicit
Congestion Notification (ECN) to
IP", RFC 3168, September 2001.
[RFC3514] Bellovin, S., "The Security Flag in
the IPv4 Header", RFC 3514, April 1
2003.
[RFC3540] Spring, N., Wetherall, D., and D.
Ely, "Robust Explicit Congestion
Notification (ECN) Signaling with
Nonces", RFC 3540, June 2003.
[RFC3550] Schulzrinne, H., Casner, S.,
Frederick, R., and V. Jacobson,
"RTP: A Transport Protocol for
Real-Time Applications", STD 64,
RFC 3550, July 2003.
[RFC5670] Eardley, P., "Metering and Marking
Behaviour of PCN-Nodes", RFC 5670,
November 2009.
[RFC5681] Allman, M., Paxson, V., and E.
Blanton, "TCP Congestion Control",
RFC 5681, September 2009.
[Re-fb] Briscoe, B., Jacquet, A., Di
Cairano-Gilfedder, C., Salvatori,
A., Soppera, A., and M. Koyabe,
"Policing Congestion Response in an
Internetwork Using Re-Feedback",
ACM SIGCOMM CCR 35(4)277--288,
August 2005, <http://www.acm.org/
sigs/sigcomm/sigcomm2005/
techprog.html#session8>.
[Refb-dis] Briscoe, B., "Re-feedback: Freedom
with Accountability for Causing
Congestion in a Connectionless
Mathis & Briscoe Expires September 8, 2011 [Page 14]
Internet-Draft ConEx Concepts and Abstract Mechanism March 2011
Internetwork", UCL PhD
Dissertation , 2009, <http://
bobbriscoe.net/projects/
refb/#refb-dis>.
[Vegas] Brakmo, L. and L. Peterson, "TCP
Vegas: End-to-End Congestion
Avoidance on a Global Internet",
IEEE Journal on Selected Areas in
Communications 13(8)1465--80,
October 1995, <http://
ieeexplore.ieee.org/iel1/49/9740/
00464716.pdf?arnumber=464716>.
Authors' Addresses
Matt Mathis
Google, Inc
1600 Amphitheater Parkway
Mountain View, California 93117
USA
EMail: mattmathis at google.com
Bob Briscoe
BT
B54/77, Adastral Park
Martlesham Heath
Ipswich IP5 3RE
UK
Phone: +44 1473 645196
EMail: bob.briscoe@bt.com
URI: http://bobbriscoe.net/
Mathis & Briscoe Expires September 8, 2011 [Page 15]
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