One document matched: draft-ietf-conex-concepts-uses-03.xml
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<rfc category="info" docName="draft-ietf-conex-concepts-uses-03"
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<front>
<title abbrev="ConEx Concepts & Use Cases">ConEx Concepts and Use
Cases</title>
<!--
<author fullname="Toby Moncaster" initials="T." surname="Moncaster">
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<author fullname="Alissa Cooper" initials="A." role="editor"
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<date day="22" month="October" year="2011" />
<area>Transport Area</area>
<workgroup>ConEx</workgroup>
<keyword>Internet-Draft</keyword>
<abstract>
<t>This document provides the entry point to the set of documentation
about the Congestion Exposure (ConEx) protocol. It explains the
motivation for including a ConEx field at the IP layer: to expose
information about congestion to network nodes. Although such information
may have a number of uses, this document focuses on how the information
communicated in the ConEx field can serve as the basis for significantly
more efficient and effective traffic management than what exists on the
Internet today.</t>
</abstract>
</front>
<middle>
<!-- ====================================================================== -->
<section anchor="conex-uses-intro" title="Introduction">
<t>The power of Internet technology comes from multiplexing shared
capacity with packets rather than circuits. Network operators aim to
provide sufficient shared capacity, but when too much packet load meets
too little shared capacity, congestion results. Congestion appears as
either increased delay, dropped packets or packets explicitly marked
with Explicit Congestion Notification (ECN) markings <xref
target="RFC3168"></xref>. As described in <xref
target="conex-uses_Fig_ConEx_Placement"></xref>, congestion control
currently relies on the transport receiver detecting these 'Congestion
Signals' and informing the transport sender in 'Congestion Feedback
Signals.' The sender is then expected to reduce its rate in
response.</t>
<t>This document provides the entry point to the set of documentation
about the Congestion Exposure (ConEx) protocol. It focuses on the
motivation for including a ConEx field at the IP layer. (A companion
document, <xref target="ConEx-Abstract-Mech"></xref>, focuses on the
mechanics of the protocol.) Briefly, the idea is for the sender to
continually signal expected congestion in the headers of any data it
sends. To a first approximation, the sender does this by relaying the
'Congestion Feedback Signals' back into the IP layer. They then travel
unchanged across the network to the receiver (shown as
'IP-Layer-ConEx-Signals' in <xref
target="conex-uses_Fig_ConEx_Placement"></xref>). This enables IP layer
devices on the path to see information about the whole path
congestion.</t>
<figure anchor="conex-uses_Fig_ConEx_Placement"
title="The ConEx Protocol in the Internet Architecture">
<!--0 1 2 3 4 5 6 7
123456789012345678901234567890123456789012345678901234567890123456789012 -->
<artwork><![CDATA[
,---------. ,---------.
|Transport| |Transport|
| Sender | . |Receiver |
| | /|___________________________________________| |
| ,-<---------------Congestion-Feedback-Signals--<--------. |
| | |/ | | |
| | |\ Transport Layer Feedback Flow | | |
| | | \ ___________________________________________| | |
| | | \| | | |
| | | ' ,-----------. . | | |
| | |_____________| |_______________|\ | | |
| | | IP Layer | | Data Flow \ | | |
| | | |(Congested)| \ | | |
| | | | Network |--Congestion-Signals--->-' |
| | | | Device | \| |
| | | | | /| |
| `----------->--(new)-IP-Layer-ConEx-Signals-------->| |
| | | | / | |
| |_____________| |_______________ / | |
| | | | |/ | |
`---------' `-----------' ' `---------'
]]></artwork>
</figure>
<t>One of the key benefits of exposing this congestion information at
the IP layer is that it makes the information available to network
operators for use as input into their traffic management procedures. As
shown in <xref target="conex-uses_Fig_ConEx_Placement"></xref>, a
ConEx-enabled sender signals whole path congestion, which is
(approximately) the congestion one round trip time earlier as reported
by the receiver to the sender. The ConEx signal is a mark in the IP
header that is easy for any IP device to read. Therefore a node
performing traffic management can count congestion as easily as it might
count data volume today by simply counting the volume of packets with
ConEx markings.</t>
<t>ConEx-based traffic management can make highly efficient use of
capacity. In times of no congestion, all traffic management restraints
can be removed, leaving the network's full capacity available to all its
users. If some users on the network cause disproportionate congestion,
the traffic management function can learn about this and directly limit
those users' traffic in order to protect the service of other users
sharing the same capacity. ConEx-based traffic management thus presents
a step change in terms of the options available to operators for
managing traffic on their networks.</t>
<t>The remainder of this document explains the concepts behind ConEx and
how exposing congestion can significantly improve Internet traffic
management, among other benefits. <xref target="concepts"></xref>
introduces a number of concepts that are fundamental to understanding
how ConEx-based traffic management works. <xref
target="traffic-management"></xref> shows how ConEx can be used for
traffic management, discusses additional benefits from such usage, and
compares ConEx-based traffic management to existing traffic management
approaches. <xref target="other-use-cases"></xref> discusses other
related use cases. <xref target="deployments"></xref> briefly discusses
deployment arrangements. The final sections are standard RFC back
matter.</t>
</section>
<!-- ====================================================================== -->
<section anchor="concepts" title="Concepts">
<t>ConEx relies on a precise definition of congestion and a number of
newer concepts that are introduced and defined in this section.</t>
<section anchor="congestion" title="Congestion">
<t>Despite its central role in network control and management,
congestion is a remarkably difficult concept to define. Experts in
different disciplines and with different perspectives define
congestion in a variety of ways <xref target="Bauer09"></xref>.</t>
<t>The definition used for the purposes of ConEx is expressed as the
probability of packet loss (or the probability of packet marking if
ECN is in use). This definition focuses on how congestion is measured,
rather than describing congestion as a condition or state.</t>
</section>
<section anchor="congestion-volume" title="Congestion-Volume">
<t>The metric that ConEx exposes is congestion-volume: the volume of
bytes dropped or ECN-marked in a given period of time. Counting
congestion-volume allows each user to be held responsible for his or
her contribution to causing congestion. Congestion-volume is a
property of traffic, whereas congestion is a property of a link or a
path.</t>
<t>To understand congestion-volume, consider a simple example. Imagine
Alice sends 1GB while the loss-probability is a constant 0.2%. Her
contribution to congestion -- her congestion-volume -- is 1GB x 0.2% =
2MB. If she then sends 3GB while the loss-probability is 0.1%, this
adds 3MB to her congestion-volume. Her total contribution to
congestion is then 2MB+3MB = 5MB.</t>
<t>Fortunately, measuring Alice's congestion-volume on a real network
does not require the kind of arithmetic shown above because
congestion-volume can be directly measured by counting the total
volume of Alice's traffic that gets discarded or ECN-marked. (A queue
with a percentage loss involves multiplication inherently.)</t>
</section>
<section anchor="upstream-downstream-congestion"
title="Rest-of-Path Congestion">
<t>At a particular measurement point within a network, "rest-of-path
congestion" (also known as "downstream congestion") measures the level
of congestion that a traffic flow is expected to experience between
the measurement point and its final destination. "Upstream congestion"
measures the level of congestion experienced up to the measurement
point.</t>
<t>Measurement points that only observe ECN marks are capable of
measuring upstream congestion, whereas measurement points that observe
ConEx marks in addition to ECN marks can use both kinds of marks to
calculate rest-of-path congestion. When ECN signals are monitored in
the middle of a network, they indicate the level of congestion
experienced so far on the path (upstream congestion). In contrast, the
ConEx signals inserted into IP headers as shown in <xref
target="conex-uses_Fig_ConEx_Placement"></xref> indicate the level of
congestion along a whole path from source to destination. Therefore if
a measurement point detects both of these signals, it can subtract the
level of ECN (upstream congestion) from the level of ConEx (whole
path) to derive a measure of the congestion that packets are likely to
experience between the monitoring point and their destination
(rest-of-path congestion).</t>
<t><xref target="ConEx-Abstract-Mech"></xref> has further discussion
of the constraints around the network's ability to measure
rest-of-path congestion.</t>
</section>
<section title="Definitions">
<t><list style="hanging">
<t hangText="Congestion:">In general, congestion occurs when any
user's traffic suffers loss, ECN marking, or increased delay as a
result of one or more network resources becoming overloaded. For
the purposes of ConEx, congestion is measured using the concrete
signals provided by loss and ECN markings (delay is not
considered). Congestion is measured as the probability of loss or
the probability of ECN marking, usually expressed as a
dimensionless percentage.</t>
<t hangText="Congestion-volume:">For any granularity of traffic
(packet, flow, aggregate, link, etc.), the volume of bytes dropped
or ECN-marked in a given period of time. Conceptually, data volume
multiplied by the congestion each packet of the volume
experienced. Usually expressed in bytes (or MB or GB).</t>
<t
hangText="Rest-of-path congestion (or downstream congestion):">The
level of congestion a flow of traffic is expected to experience on
the remainder of its path. In other words, at a measurement point
in the network the rest-of-path congestion is the level of
congestion the traffic flow has yet to experience as it travels
from that point to the receiver.</t>
<t hangText="Upstream congestion:">The accumulated level of
congestion experienced by a traffic flow thus far, relative to a
point along its path. In other words, at a measurement point in
the network the upstream congestion is the accumulated level of
congestion the traffic flow has experienced as it travels from the
sender to that point. At the receiver this is equivalent to the
end-to-end congestion level that (usually) is reported back to the
sender.</t>
<t hangText="Network provider (or operator):">Operator of a
residential, commercial, enterprise, campus or other network.</t>
<t hangText="User:">The contractual entity that represents an
individual, household, business, or institution that uses the
service of a network provider. There is no implication that the
contract has to be commercial; for instance, the users of a
university or enterprise network service could be students or
employees who do not pay for access but may be required to comply
with some form of contract or acceptable use policy. There is also
no implication that every user is an end user. Where two networks
form a customer-provider relationship, the term user applies to
the customer network.</t>
</list></t>
<t><xref target="ConEx-Abstract-Mech"></xref> gives further
definitions for aspects of ConEx related to protocol mechanisms.</t>
</section>
</section>
<!-- ====================================================================== -->
<section anchor="traffic-management"
title="Core Use Case: Informing Traffic Management">
<t>This section explains how ConEx could be used as the basis for
traffic management, highlights additional benefits derived from having
ConEx-aware nodes on the network, and compares ConEx-based traffic
management to existing approaches.</t>
<section anchor="using-conex" title="Use Case Description">
<t>One of the key benefits that ConEx can deliver is in helping
network operators to improve how they manage traffic on their
networks. Consider the common case of a commercial broadband network
where a relatively small number of users place disproportionate demand
on network resources, at times resulting in congestion. The network
operator seeks a way to manage traffic such that the traffic that
contributes more to congestion bears more of the brunt of the
management.</t>
<t>Assuming ConEx signals are visible at the IP layer, the operator
can accomplish this by placing a congestion policer at an enforcement
point within the network and configuring it with a traffic management
policy that monitors each user's contribution to congestion. As
described in <xref target="ConEx-Abstract-Mech"></xref> and elaborated
in <xref target="CongPol"></xref>, a congestion policer can be
implemented in a similar way to a bit-rate policer, except that it
monitors and polices congestion-volume rather than bit-rate. When
implemented as a token bucket, the tokens provide users with the right
to cause bits of congestion-volume, rather than to send bits of data
volume. The fill rate represents each user's congestion-volume
quota.</t>
<t>The congestion policer monitors the ConEx signals of the traffic
entering the network. As long as the network remains uncongested and
users stay within their quotas, no action is taken. When the network
becomes congested and a user exhausts his quota, some action is taken
against the traffic that breached the quota in accordance with the
operator's traffic management policy. For example, the traffic may be
dropped, delayed, or marked with a lower QoS class. In this way,
traffic is managed according to its contribution to congestion -- not
some application- or flow-specific policy -- and is not managed at all
during times of no congestion.</t>
<t>As an example of how a network operator might employ a ConEx-based
traffic management system, consider a typical DSL network architecture
(as elaborated in <xref target="TR-059"></xref> and <xref
target="TR-101"></xref>). Traffic is routed from regional and global
IP networks to an operator-controlled IP node, the Broadband Remote
Access Server (BRAS). From the BRAS, traffic is delivered to access
nodes. The BRAS carries enhanced functionality including IP QoS and
traffic management capabilities.</t>
<t>Based on typical network designs and current traffic patterns, the
BRAS is located at a point in the network where congestion may be most
likely to occur. As a consequence, the BRAS is a logical choice of
location for deploying traffic management functionality. By deploying
a congestion policer at the BRAS location, the operator can measure
the congestion-volume created by users within the access nodes. The
policer would be provisioned with a traffic management policy, perhaps
directing the BRAS to drop packets from users that exceed their
congestion-volume quotas during times of congestion. Those users would
be expected to react in the typical way to drops, backing off
(assuming use of standard TCP), and thereby lowering their
congestion-volumes back within the quota limits.</t>
</section>
<section anchor="additional-benefits" title="Additional Benefits">
<t>The ConEx-based approach to traffic management has a number of
benefits in addition to efficient management of traffic. It provides
incentives for users to make use of scavenger transport protocols,
such as <xref target="LEDBAT"></xref>, that provide ways for
bulk-transfer applications to rapidly yield when interactive
applications require capacity. With a congestion policer in place as
described in <xref target="using-conex"></xref>, users of these
protocols will be less likely to run afoul of the operator's traffic
management policy than those whose bulk-transfer applications generate
the same volume of traffic without being sensitive to congestion.</t>
<t>ConEx-based traffic management also makes it possible for a user to
control the relative performance among its own traffic flows. If a
user wants some flows to have more bandwidth than others, it can allow
the higher bandwidth traffic to generate more congestion signals,
leaving less congestion "budget" for the user to "spend" on other
traffic. This approach is most relevant if congestion is signalled by
ECN, because no impairment due to loss is involved and delay can
remain low.</t>
</section>
<section anchor="comparison" title="Comparison with Existing Approaches">
<t>A variety of approaches already exist for network operators to
manage congestion, traffic, and the disproportionate usage of scarce
capacity by a small number of users. Common approaches can be
categorized as rate-based, volume-based, or application-based.</t>
<t>Rate-based approaches constrain the traffic rate per user or per
network. A user's peak and average (or "committed") rate may be
limited. These approaches have the potential to either over- or
under-constrain the network, suppressing rates even when the network
is uncongested or not suppressing them enough during heavy usage
periods.</t>
<t>Round-robin scheduling and fair queuing were developed to address
these problems. They equalize relative rates between active users (or
flows) at a known bottleneck. The bit-rate allocated to any one user
depends on the number of active users at each instant. The drawback of these approaches is that they favor heavy users over light users over time, because they do not have any memory of usage. Heavy users will be active at every instant
whereas light users will only occupy their share of the link
occassionally, but bit-rate is shared instant by instant.</t>
<t>Volume-based approaches measure the overall volume of traffic a
user sends (and/or receives) over time. Users may be subject to an
absolute volume cap (for example, 10GB per month) or the "heaviest"
users may be sanctioned in some other manner. Many providers use
monthly volume limits and count volume regardless of whether the
network is congested or not, creating the potential for over- or
under-constraining problems, as with the original rate-based
approaches.</t>
<t>ConEx-based approaches, by comparison, only react during times of
congestion and in proportion to each user's congestion contribution,
making more efficient use of capacity and more proportionate
management decisions.</t>
<t>Unlike ConEx-based approaches, neither rate-based nor volume-based
approaches provide incentives for applications to use scavenger
transports. They may even penalize users of applications that employ
scavenger services for the large amount of volume they send, rather
than rewarding them for carefully avoiding congestion while sending
it. While the volume-based approach described in Comcast's
Protocol-Agnostic Congestion Management System <xref
target="RFC6057"></xref> aims to overcome the over/under-constraining
problem by only measuring volume and triggering traffic management
action during periods of high utilization, it still does not provide
incentives to use scavenger transports because congestion-causing
volume cannot be distinguished from volume overall. ConEx provides
this ability.</t>
<t>Application-based approaches use deep packet inspection or other
techniques to determine what application a given traffic flow is
associated with. Operators may then use this information to rate-limit
or otherwise sanction certain applications, in some cases only during
peak hours. These approaches suffer from being at odds with IPSec and
some application-layer encryption, and they may raise additional
policy concerns. In contrast, ConEx offers an application-agnostic
metric to serve as the basis for traffic management decisions.</t>
<t>The existing types of approaches share a further limitation that
ConEx can help to overcome: performance uncertainty. Flat-rate pricing
plans are popular because users appreciate the certainty of having
their monthly bill amount remain the same for each billing period,
allowing them to plan their costs accordingly. But while flat-rate
pricing avoids billing uncertainty, it creates performance
uncertainty: users cannot know whether the performance of their
connections is being altered or degraded based on how the network
operator is attempting to manage congestion. By exposing congestion
information at the IP layer, ConEx instead provides a metric that can
serve as an open, transparent basis for traffic management policies
that both providers and their customers can measure and verify.</t>
</section>
</section>
<section anchor="other-use-cases" title="Other Use Cases">
<t>ConEx information can be put to a number of uses other than informing
traffic management. These include:</t>
<t><list style="hanging">
<t hangText="Informing inter-operator contracts:">ConEx information
is made visible to every IP node, including border nodes between
networks. Network operators can use this information to measure how
much traffic from each network contributes to congestion in the
other. As such, congestion-volume could be included as a metric in
inter-operator contracts, just as volume or bit-rate are included
today.</t>
<t hangText="Enabling more efficient capacity provisioning:">Operators currently provision capacity based on observations of a number of network characteristics, including averaged utilization and congestion. Without ConEx, a user may have little incentive to back off during times of congestion, even if the reduction in performance resulting from backing off certain applications (bulk transfer, for example) would go largely unnoticed by the user. Using ConEx to ration congestion-volume directly creates incentives where appropriate for users and applications to switch to scavenger transports, resulting in traffic demand that more accurately reflects the actual capacity needed for the mix of applications on the network to perform well. This enables capacity to be provisioned more efficiently because traffic more closely tracks users' real capacity needs.</t>
<!--{Why Bob changed the previous text:
Capacity provisioning based on congestion measured locally at each link can be done today without ConEx
standardisation. However the congestion metric isn't meaningful unless it's the metric used for rationing.} -->
</list></t>
</section>
<!-- ====================================================================== -->
<section anchor="deployments" title="Deployment Arrangements">
<t>ConEx is designed so that it can be incrementally deployed in the
Internet and still be valuable for early adopters. As long as some
senders are ConEx-enabled, a network on the path can unilaterally use
ConEx-aware policy devices for traffic management; no changes to network
forwarding elements are needed and ConEx still works if there are other
networks on the path that are unaware of ConEx marks.</t>
<t>The above two steps seem to represent a stand-off where neither step
is useful until the other has made the first move: i) some sending hosts
must be modifed to give information to the network and ii) a network
must deploy policy devices to monitor this information and act on it.
Nonetheless, the developer of a scavenger transport protocol like LEDBAT
does have a strong incentive to tell the network how little congestion
it is causing despite sending large volumes of data. In this case the
developer makes the first move expecting it will prompt at least some
networks to move in response—so that they use the ConEx
information to reward users of the scavenger protocol.</t>
<t>On the host side, we have already shown (Figure <xref
target="conex-uses_Fig_ConEx_Placement"></xref>) how the sender
piggy-backs ConEx signals on normal data packets to re-insert feedback
about packet drops (and/or ECN) back into the IP layer. In the case of
TCP, <xref target="I-D.conex-tcp-mods"></xref> specifies the required
sender modifications. ConEx works with any TCP receiver as long as it
uses SACK, which most do. There is a receiver optimisation <xref
target="I-D.conex-accurate-ecn"></xref> that improves ConEx precision
when using ECN, but ConEx can still use ECN without it.</t>
<t>On the network side the operator solely needs to place ConEx
congestion policers at each ingress to its network, in a similar
arrangement to the edge-policed architecture of Diffserv <xref
target="RFC2475"></xref>.</t>
<t>A sender can choose whether to send ConEx or Not-ConEx packets. ConEx
packets bring information to the policer about congestion expected on
the rest of the path beyond the policer. Not-ConEx packets bring no such
information. Therefore the network will tend to rate-limit not-ConEx
packets conservatively in order to manage the unknown risk of
congestion. In contrast, a network doesn't normally need to rate-limit
ConEx-enabled packets unless they reveal a persistently high
contribution to congestion. This natural tendency for networks to favour
senders that provide ConEx information reinforces ConEx deployment.</t>
<t>The above gives only the most salient aspects of ConEx deployment.
For further detail, <xref target="ConEx-Abstract-Mech"></xref> describes
the incremental deployment features of the ConEx protocol and the
components that need to be deployed for ConEx to work. Then <xref
target="I-D.conex-init-deploy"></xref> gives concrete examples of
feasible initial deployment scenarios.</t>
</section>
<!-- ====================================================================== -->
<section title="Security Considerations">
<t>This document does not specify a mechanism, it merely
motivates congestion exposure at the IP layer. Therefore security
considerations are described in the companion document that gives an
abstract description of the ConEx protocol and the components that would
use it <xref target="ConEx-Abstract-Mech"></xref>.</t>
</section>
<!-- ====================================================================== -->
<section title="IANA Considerations">
<t>This document does not require actions by IANA.</t>
</section>
<!-- ====================================================================== -->
<section title="Acknowledgments">
<t>Bob Briscoe was partly funded by Trilogy, a research project
(ICT-216372) supported by the European Community under its Seventh
Framework Programme. The views expressed here are those of the author
only.</t>
<t>The authors would like to thank the many people that have commented
on this document: Bernard Aboba, Mikael Abrahamsson, João Taveira
Araújo, Marcelo Bagnulo Braun, Steve Bauer, Caitlin Bestler,
Steven Blake, Louise Burness, Ken Carlberg, Nandita Dukkipati, Dave
McDysan, Wes Eddy, Matthew Ford, Ingemar Johansson, Georgios
Karagiannis, Mirja Kuehlewind, Dirk Kutscher, Zhu Lei, Kevin Mason, Matt
Mathis, Michael Menth, Chris Morrow, Tim Shepard, Hannes Tschofenig and
Stuart Venters. Please accept our apologies if your name has been missed
off this list.</t>
<section title="Contributors">
<t>Philip Eardley and Andrea Soppera made helpful text contributions
to this document.</t>
<t>The following co-edited this document through most of its life:</t>
<figure>
<artwork><![CDATA[
Toby Moncaster
Computer Laboratory
William Gates Building
JJ Thomson Avenue
Cambridge, CB3 0FD
UK
EMail: toby.moncaster@cl.cam.ac.uk
John Leslie
JLC.net
10 Souhegan Street
Milford, NH 03055
US
EMail: john@jlc.net
]]></artwork>
</figure>
</section>
</section>
<!-- ====================================================================== -->
</middle>
<back>
<references title="Informative References">
<?rfc include='reference.RFC.2475.xml'?>
<?rfc include='reference.RFC.3168.xml'?>
<?rfc include='reference.RFC.6057.xml'?>
<reference anchor="LEDBAT">
<front>
<title>Low Extra Delay Background Transport (LEDBAT)</title>
<author fullname="Stanislav Shalunov" initials="S"
surname="Shalunov">
<organization></organization>
</author>
<author fullname="Greg Hazel" initials="G" surname="Hazel">
<organization></organization>
</author>
<author fullname="Janardhan Iyengar" initials="J" surname="Iyengar">
<organization></organization>
</author>
<author fullname="Mirja Kuehlewind" initials="M"
surname="Kuehlewind">
<organization></organization>
</author>
<date day="31" month="May" year="2011" />
<abstract>
<t>LEDBAT is an experimental delay-based congestion control
algorithm that attempts to utilize the available bandwidth on an
end-to-end path while limiting the consequent increase in queueing
delay on the path. LEDBAT uses changes in one-way delay
measurements to limit congestion that the flow itself induces in
the network. LEDBAT is designed for use by background
bulk-transfer applications; it is designed to be no more
aggressive than TCP congestion control and to yield in the
presence of any competing TCP flows, thus limiting interference
with the network performance of the competing flows.</t>
</abstract>
</front>
<seriesInfo name="Internet-Draft"
value="draft-ietf-ledbat-congestion-08" />
<format target="http://www.ietf.org/internet-drafts/draft-ietf-ledbat-congestion-08.txt"
type="TXT" />
</reference>
<!--
<reference anchor="Savage">
<front>
<title>TCP Congestion Control with a Misbehaving Receiver</title>
<author fullname="S. Savage" initials="S." surname="Savage">
<organization></organization>
</author>
<author fullname="D. Wetherall" initials="D." surname="Wetherall">
<organization></organization>
</author>
<author fullname="T. Anderson" initials="T." surname="Anderson">
<organization></organization>
</author>
<date year="1999" />
</front>
<seriesInfo name="ACM SIGCOMM Computer Communication Review" value="" />
<format target="http://www.cs.ucsd.edu/~savage/papers/CCR99.pdf"
type="PDF" />
</reference>
-->
<!--
<reference anchor="KGao">
<front>
<title>Incrementally Deployable Prevention to TCP Attack with
Misbehaving Receivers</title>
<author fullname="Kun Gar" initials="K." surname="Gao">
<organization>Computer Science Department, Carnegie Mellon
University</organization>
</author>
<author fullname="Chengwen Chris Wang" initials="C. C."
surname="Wang">
<organization>Computer Science Department, Carnegie Mellon
University</organization>
</author>
<date day="14" month="December" year="2004" />
</front>
<format target="http://www.cs.cmu.edu/~kgao/course/15744/network.pdf"
type="PDF" />
</reference>
-->
<reference anchor="CongPol">
<front>
<title>Policing Freedom to Use the Internet Resource Pool</title>
<author fullname="Bob Briscoe" initials="B" surname="Briscoe">
<organization>BT & UCL</organization>
</author>
<author fullname="Arnaud Jacquet" initials="A" surname="Jacquet">
<organization>BT</organization>
</author>
<author fullname="Toby Moncaster" initials="T" surname="Moncaster">
<organization>BT</organization>
</author>
<date day="4" month="December" year="2008" />
</front>
<seriesInfo name="RE-Arch 2008 hosted at the 2008 CoNEXT conference"
value="" />
<format target="http://portal.acm.org/ft_gateway.cfm?id=1544083&type=pdf&coll=GUIDE&dl=GUIDE&CFID=94433196&CFTOKEN=11585540"
type="PDF" />
</reference>
<reference anchor="ConEx-Abstract-Mech">
<front>
<title>Congestion Exposure (ConEx) Concepts and Abstract
Mechanism</title>
<author fullname="Matt Mathis" initials="M" surname="Mathis">
<organization>Google</organization>
</author>
<author fullname="Bob Briscoe" initials="B" surname="Briscoe">
<organization>BT</organization>
</author>
<date day="11" month="July" year="2011" />
</front>
<seriesInfo name="Internet-Draft"
value="draft-ietf-conex-abstract-mech-02" />
<format target="http://www.ietf.org/internet-drafts/draft-ietf-conex-abstract-mech-00.txt"
type="TXT" />
</reference>
<reference anchor="I-D.conex-tcp-mods">
<front>
<title>TCP modifications for Congestion Exposure</title>
<author fullname="Mirja Kuehlewind" initials="M"
surname="Kuehlewind">
<organization></organization>
</author>
<author fullname="Richard Scheffenegger" initials="R"
surname="Scheffenegger">
<organization></organization>
</author>
<date day="4" month="July" year="2011" />
<abstract>
<t>Congestion Exposure (ConEx) is a mechanism by which senders
inform the network about the congestion encountered by previous
packets on the same flow. This document describes the necessary
modifications to use ConEx with the Transmission Control Protocol
(TCP).</t>
</abstract>
</front>
<seriesInfo name="Internet-Draft"
value="draft-kuehlewind-conex-tcp-modifications-00" />
<format target="http://www.ietf.org/internet-drafts/draft-kuehlewind-conex-tcp-modifications-00.txt"
type="TXT" />
</reference>
<reference anchor="I-D.conex-accurate-ecn">
<front>
<title>Accurate ECN Feedback in TCP</title>
<author fullname="Mirja Kuehlewind" initials="M"
surname="Kuehlewind">
<organization></organization>
</author>
<author fullname="Richard Scheffenegger" initials="R"
surname="Scheffenegger">
<organization></organization>
</author>
<date day="4" month="July" year="2011" />
<abstract>
<t>Explicit Congestion Notification (ECN) is an IP/TCP mechanism
where network nodes can mark IP packets instead of dropping them
to indicate congestion to the end-points. An ECN-capable receiver
will feedback this information to the sender. ECN is specified for
TCP in such a way that only one feedback signal can be transmitted
per Round-Trip Time (RTT). Recently new TCP mechanisms like ConEx
or DCTCP need more accurate feedback information in the case where
more than one marking is received in one RTT.</t>
</abstract>
</front>
<seriesInfo name="Internet-Draft"
value="draft-kuehlewind-conex-accurate-ecn-00" />
<format target="http://www.ietf.org/internet-drafts/draft-kuehlewind-conex-accurate-ecn-00.txt"
type="TXT" />
</reference>
<reference anchor="I-D.conex-init-deploy">
<front>
<title>Initial Congestion Exposure (ConEx) Deployment
Examples</title>
<author fullname="Bob Briscoe" initials="B" surname="Briscoe">
<organization>BT</organization>
</author>
<date day="24" month="October" year="2011" />
</front>
<seriesInfo name="Internet-Draft"
value="draft-briscoe-conex-initial-deploy-00" />
<format target="http://www.ietf.org/internet-drafts/draft-briscoe-conex-initial-deploy-00.txt"
type="TXT" />
</reference>
<reference anchor="Bauer09">
<front>
<title>The Evolution of Internet Congestion</title>
<author fullname="Steven Bauer" initials="S" surname="Bauer">
<organization>MIT</organization>
</author>
<author fullname="David Clark" initials="D" surname="Clark">
<organization>MIT</organization>
</author>
<author fullname="William Lehr" initials="W" surname="Lehr">
<organization>MIT</organization>
</author>
<date year="2009" />
</front>
<format target="http://mitas.csail.mit.edu/papers/Bauer_Clark_Lehr_2009.pdf"
type="PDF" />
</reference>
<reference anchor="TR-059">
<front>
<title>DSL Forum Technical Report TR-059: Requirements for the
Support of QoS-Enabled IP Services</title>
<author fullname="Tom Anschutz" initials="T." role="editor"
surname="Anschutz">
<organization>BellSouth Telecommunications</organization>
</author>
<date month="September" year="2003" />
</front>
<format target="http://www.broadband-forum.org/technical/download/TR-059.pdf"
type="PDF" />
</reference>
<reference anchor="TR-101">
<front>
<title>DSL Forum Technical Report TR-101: Migration to
Ethernet-Based DSL Aggregation</title>
<author fullname="Amit Cohen" initials="A." role="editor"
surname="Cohen">
<organization>ECI Telecom</organization>
</author>
<author fullname="Ed Shrum" initials="E." role="editor"
surname="Schrum">
<organization>BellSouth Telecommunications</organization>
</author>
<date month="April" year="2006" />
</front>
<format target="http://www.broadband-forum.org/technical/download/TR-101.pdf"
type="PDF" />
</reference>
</references>
<!-- ====================================================================== -->
<section title="Changes from previous drafts (to be removed by the RFC Editor)">
<t><list style="hanging">
<t
hangText="From draft-ietf-conex-concepts-uses-02 to -03:">Reorganization
and re-write of most sections.</t>
<t hangText="From draft-ietf-conex-concepts-uses-01 to -02:">New
Abstract & Introduction. Concepts and Misconceptions sections
added around definitions. Minor clarifications to Existing Traffic
Management and Use-Cases sections, with Other use Cases Added.
Deployment Arrangements Section added.</t>
<t hangText="From draft-ietf-conex-concepts-uses-00 to -01:"></t>
<t>Added section on timescales: Section 6</t>
<t>Revised introduction to clarify congestion definitions</t>
<t>Changed source for congestion definition in <xref
target="concepts"></xref></t>
<t>Other minor changes</t>
<t
hangText="From draft-moncaster-conex-concepts-uses-02 to draft-ietf-conex-concepts-uses-00 (per decisions of working group):"></t>
<t>Removed section on DDoS mitigation use case.</t>
<t>Removed appendix on ConEx Architectural Elements. PLEASE NOTE:
Alignment of terminology with the Abstract Mechanism draft has been
deferred to the next version.</t>
<t
hangText="From draft-moncaster-conex-concepts-uses-01 to draft-moncaster-conex-concepts-uses-02:"></t>
<t>Updated document to take account of the new Abstract Mechanism
draft <xref target="ConEx-Abstract-Mech"></xref>.</t>
<t>Updated the definitions section.</t>
<t>Removed sections on Requirements and Mechanism.</t>
<t>Moved section on ConEx Architectural Elements to appendix.</t>
<t>Minor changes throughout.</t>
<t
hangText="From draft-moncaster-conex-concepts-uses-00 to draft-moncaster-conex-concepts-uses-01:"></t>
<t>Changed end of Abstract to better reflect new title</t>
<t>Created new section describing the architectural elements of
ConEx. Added Edge Monitors and Border Monitors (other elements are
Ingress, Egress and Border Policers).</t>
<t>Extensive re-write of use cases partly in response to suggestions
from Dirk Kutscher</t>
<t>Improved layout of <xref target="concepts"></xref> and added
definitions of Whole Path Congestion, ConEx-Enabled and ECN-Enabled.
Re-wrote definition of Congestion Volume. Renamed Ingress and Egress
Router to Ingress and Egress Node as these nodes may not actually be
routers.</t>
<t>Improved document structure. Merged sections on Exposing
Congestion and ECN.</t>
<t>Added new section on ConEx requirements with a ConEx Issues
subsection. Text for these came from the start of the old ConEx Use
Cases section</t>
<t>Added a sub-section on Partial vs Full Deployment (Section
5.5)</t>
<t>Added a discussion on ConEx as a Business Secret</t>
<t
hangText="From draft-conex-mechanism-00 to draft-moncaster-conex-concepts-uses-00:"></t>
<t>Changed filename to draft-moncaster-conex-concepts-uses.</t>
<t>Changed title to ConEx Concepts and Use Cases.</t>
<t>Chose uniform capitalization of ConEx.</t>
<t>Moved definition of Congestion Volume to list of definitions.</t>
<t>Clarified mechanism section. Changed section title.</t>
<t>Modified text relating to conex-aware policing and policers
(which are NOT defined terms).</t>
<t>Re-worded bullet on distinguishing ConEx and non-ConEx traffic in
use cases section.</t>
</list></t>
</section>
</back>
</rfc>
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