CONEX H. Tschofenig
Internet-Draft Nokia Siemens Networks
Intended status: Informational A. Cooper
Expires: September 9, 2010 Center for Democracy &
Technology
March 8, 2010
Congestion Exposure Problem Statement
draft-tschofenig-conex-ps-02.txt
Abstract
The increasingly ubiquitous availability of broadband, together with
flat-rate pricing, have made for increasing congestion problems on
the network, which are often caused by a small number of users
consuming a large amount of bandwidth. In some cases, building out
more capacity to handle this new congestion may be infeasible or
unwarranted. As a result, network operators have sought other ways
to manage congestion both from their own users and from other
networks. These different types of solutions have different
strengths and weaknesses, but all of them are limited in a number of
key ways.
This document discusses the problems created for operators by high-
consuming users and describes the strengths and weaknesses of a
number of techniques operators are currently using to cope with high
bandwidth usage. The discussion of these solutions ultimately points
to a need for a new kind of congestion accounting.
Status of this Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Existing Approaches to Congestion Management . . . . . . . . . 5
2.1. Volume-Based Approaches . . . . . . . . . . . . . . . . . 5
2.2. Rate-Based Approaches . . . . . . . . . . . . . . . . . . 5
2.3. Congestion-Based Approaches . . . . . . . . . . . . . . . 5
2.4. Applications-Based Approaches . . . . . . . . . . . . . . 6
3. General Limitations of All Approaches . . . . . . . . . . . . 7
4. New Activities . . . . . . . . . . . . . . . . . . . . . . . . 8
5. Next Steps . . . . . . . . . . . . . . . . . . . . . . . . . . 9
6. Security Considerations . . . . . . . . . . . . . . . . . . . 10
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 12
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
9.1. Normative References . . . . . . . . . . . . . . . . . . . 13
9.2. Informative References . . . . . . . . . . . . . . . . . . 13
Appendix A. Example Policy Statement . . . . . . . . . . . . . . 15
A.1. Fair Usage Policy . . . . . . . . . . . . . . . . . . . . 15
A.1.1. What is the Fair Usage Policy? . . . . . . . . . . . . 15
A.1.2. How do I know I'm a very heavy user? . . . . . . . . . 15
A.1.3. I have Contract Option 3, does the Fair Usage
Policy apply to me? . . . . . . . . . . . . . . . . . 15
A.1.4. Peer to Peer (P2P) . . . . . . . . . . . . . . . . . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 17
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1. Introduction
With the growth of "always on" broadband connections, network
operators are increasingly facing congestion problems caused by a
small number of network users occupying a large proportion of network
capacity [broadband-traffic-report][traffic2]. This trend does not
necessarily present a problem on its face, as increased traffic
volumes do not automatically lead to congestion. However, in some
cases where operators were not expecting these changes in growth
rates and traffic consumption, their pricing models and congestion
management architectures have proved inadequate. This is true of
both congestion caused by an operator's own subscribers and
congestion caused by an interconnecting network.
In some cases, building out more capacity to handle this new
congestion may be infeasible or unwarranted. The cost of building
new capacity may be prohibitive, especially for network operators
that charge flat-rate feeds to subscribers and are thus unable to
charge heavier users more on the basis of their larger contribution
to the congestion problem. For an operator facing congestion caused
by other operators' networks, building out its own capacity is
unlikely to solve the congestion problem. Operators are thus facing
increased pressure to find effective solutions to dealing with high-
consuming users, other than building out new capacity.
There are many factors to consider for each kind of solution,
including how the solution performs, its cost, what its public
relations impact might be, and what legal framework exists to support
its use. The performance considerations must take into account the
balance between device performance and forwarding performance (since
many of the solution mechanisms slow down forwarding performance),
and this determination is intimiately related to measuring a
solution's overall cost.
The responses that operators have sought to manage congestion both
from their own users and from other networks are generally based on
one of four factors that the operator can observe for each subscriber
or hand-off point on the network: volume of bandwidth used, rates of
data transfer, congestion volume, and applications used. These
different types of solutions have different strengths and weaknesses,
but all of them are limited in a number of key ways. Section 2
discusses the specific strengths and weaknesses of each approach.
Section 3, discusses the limitations that are common to all of the
approaches.
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2. Existing Approaches to Congestion Management
2.1. Volume-Based Approaches
The volume of traffic sent or received by a particular user or
network is easy to measure. Operators have a number of different
standardized protocols available to them to conduct volume
accounting. Many information elements can be sent from an accounting
client to an accounting server using standardized protocols, such as
RADIUS (see [RFC2866] and [RFC2865]) and Diameter [RFC3588], to
effectuate volume-based accounting. The existence of standardized
protocols has allowed resource consumption measurement in roaming
cases due to the interconnected AAA systems. These protocols are now
used in almost every enterprise and operator network. The initial
accounting mechanisms envisioned a rather non-real time nature in
reporting resource consumption but with mechanisms like like Diameter
Credit Control [RFC4006] allowed real-time credit control checks,
allowing operators to make fine-grained congestion decisions based on
volume.
If the collected accounting information leads to billable events then
this typically leads to a quite effective countermeasure against
heavy usage. For example, data usage while roaming is often charged
per volume (or per time) and heavy usage leads to huge costs. So,
user's typically avoid heavy usage unless they are not aware of the
fact that they are roaming, which may happen.
In any case, the drawback of all of these approaches is that they
tend to be less user friendly nor do they reflect congestion in any
way.
2.2. Rate-Based Approaches
Volume-based protocols are blind to protocols like LEDBAT [ledbat]
that are specifically designed to be more sensitive to congestion
than the underlying transport. One way that operators have used
volume accounting is by including thresholds for baseline usage
volume in end user contracts and reducing priority (or charging fees)
when a user's consumption goes beyond the threshold. Under such a
scheme, users would not be incentivized to use applications that
support protocols like LEDBAT, because the volume accounting would
not take the congestion benefits of using a LEDBAT-style protocol
into consideration.
2.3. Congestion-Based Approaches
Initial attempts to capture congestion situations have simply focused
on the peak hours and aimed at rate limiting heavy users during that
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time. For example, users who have consumed a certain amount of
bandwidth during the last 24 hours got elected as those who get their
traffic shaped, in case the total amount of traffic reaches a
congestion situation in certain nodes within the operators network.
More sophisticated schemes were developed to measure the congestion
situation at different entities in the network and to take the
overall consumption of the user's traffic into account when picking
users for packet remarking that could lead, under congestion
situation, to packet dropping. The Comcast FairShare solution
[I-D.livingood-woundy-congestion-mgmt] belongs to the more
sophisticated schemes.
2.4. Applications-Based Approaches
The use of deep packet inspection (DPI) allows operators to observe
and analyze traffic at the application layer. This capability can be
used to determine the applications and/or application-layer protocols
that subscribers are using and respond on a per-application or per-
protocol basis. An example of an ISP's fair usage policy describing
how it manages specific protocols is included in Appendix A.
If an operator experiences much congestion based on the use of easily
identifiable applications protocols, or if the DPI capability can
also be used for other purposes, operators may find this approach
attractive. However, the applications-based approach has some
drawbacks. The process of inspecting traffic, particularly in real
time, can be highly performance-intensive. DPI equipment may also
require continous software updates to ensure that the detection
engine recognizes the latest protocol variants, and its use can
result in a cat-and-mouse game with applications developers
constantly seeking ways to work around the packet inspection engine.
Public policy concerns -- privacy, operator liability, user backlash,
and others -- are another drawback.
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3. General Limitations of All Approaches
All three of the approaches discussed above suffer from some general
limitations. First, they introduce performance uncertainty. Flat-
rate pricing plans are popular because operators know that users
appreciate the certainty of having their monthly bill amount remain
the same for each billing period, allowing users to plan their costs
accordingly. But while flat-rate pricing avoids billing uncertainty,
it creates performance uncertainty: users cannot be sure that the
performance of their connections is not being altered or degrated
based on how the network operator manages congestion.
Second, none of the approaches is able to make use of what may be the
most important factor in managing congestion: the amount that an
endpoint contributes to congestion on the network. This information
simply is not available to network nodes, and neither volume nor rate
nor application usage is an adequate proxy for congestion volume,
because none of these metrics measures a user or network's actual
contribution to congestion on the network. [This point needs a
little more discussion.]
Finally, none of these solutions accounts for inter-network
congestion. The currently available mechanisms for identifying and
mitigating congestion largely run wholly within an operator's network
and without a lot of information exchange about congestion
information to or from end hosts or other network operators.
Exposing this information may allow end devices to make more informed
decisions (although policy enforcement would still be required by the
operator). [This point needs to be filled in more.]
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4. New Activities
Following the IETF Workshop on Peer-to-Peer (P2P) Infrastructure in
2008 (see [RFC5594]), two working groups and one research group were
created that relate to the congestion issues created by peer-to-peer
application usage: :
LEDBAT (Low Extra Delay Background Transport) [ledbat] is designed
to keep the latency across a congested bottleneck low even as it
is saturated. This allows applications that send large amounts of
data, particularly upstream on home connections (such as peer-to-
peer applications) to operate without destroying the user
experience in interactive applications.
LEDBAT holds substantial promise should P2P clients adopt it
widely. This solution has been focused on P2P applications, and
its applicability to other applications, such as video using
H.264, is unclear.
ALTO (Application-Layer Traffic Optimization) [alto] aims to
design and specify mechanisms that will provide applications,
typically P2P applications, with information to perform better-
than-random initial peer selection to increase their performance
and at the same time to avoid excessive cross-domain traffic that
tends to be more expensive for the operator. ALTO services may
take different approaches at balancing factors such as maximum
bandwidth, minimum cross-domain traffic, or lowest cost to the
user, but in all cases the goal is to expose information that can
ameliorate the interactions between peer-to-peer usage and other
usages of shared networks.
Peer to Peer Research Group [p2prg] aims to provide a discussion
forum for resarchers related to all sorts of challenges presented
by P2P systems in general, such as P2P streaming, interconnecting
distinct P2P application overlays, security and privacy. Current
work on exposing myths about peer-to-peer filesharing
[I-D.irtf-p2prg-mythbustering] provides a number of references to
support some of the claimed benefits of ALTO solutions mechanisms,
such as the expected decrease in cross- domain traffic.
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5. Next Steps
Congestion is a reality. Operators that would like to counteract the
impact of congestion on their networks have a fair number of tools at
their disposal. These tools may allow operators to identify heavy
users, collect performance and usage indications, and choose from a
variety of mitigating steps depending on the operator's preferred
business practices. Subscriber-specific information, including
policies, resource consumption information, and details about the
current network attachment point, may be available in accounting
servers. Information about the network topology and the state of
particular topology elements may be available in the network
management infrastructure. Solution approaches similar to
[I-D.livingood-woundy-congestion-mgmt] have demonstrated one way of
taking congestion information into consideration.
The collection of congestion information poses the challenge of
deciding where in the network to put the metering agents to ensure
that enough information is collected at the right point in time.
Distributed collection and the correlation of the information across
different nodes is a complex task. An approach that collects this
congestion information along the path of the data packet (via inband
signaling) would simplify this task. Regardless of the technical
solution utilized for collecting information, certain users will
undoubtedly observe the effects of decisions that operators make
about how to handle congestion. Allowing users to understand these
decisions will be crucial and having a channel to send feedback to
the end device and/or subscriber would be a helpful step towards
increased transparency.
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6. Security Considerations
This document highlights approaches for dealing with high-consuming
network users and all of them raise security and privacy concerns.
It does not introduce new mechanisms. The security considerations
for the existing mechanisms mentioned apply.
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7. IANA Considerations
This document does not require actions by IANA.
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8. Acknowledgments
The authors would like to thank Alan DeKok, Jens-Peter Haack,
Alexander Bachmutsky, Jonne Soininen, Joachim Charzinski, Hannu
Flinck, Joachim Kross, Jouni Korhonen, Mayutan Arumaithurai, Richard
Woundy, Daniel Correa Lobato, Luca Caviglione, Tommy Lindgren, Lars
Eggert, and Jason Livingood for their time to discuss the topic.
Additionally, we would like to thank Marcin Matuszewski for his help
with the P2P infrastructure workshop paper (since it was used as a
starting point for the work on this memo).
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9. References
9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
9.2. Informative References
[I-D.irtf-p2prg-mythbustering]
Marocco, E., Fusco, A., Rimac, I., and V. Gurbani,
"Improving Peer Selection in Peer-to-peer Applications:
Myths vs. Reality", draft-irtf-p2prg-mythbustering-01
(work in progress), March 2010.
[I-D.livingood-woundy-congestion-mgmt]
Bastian, C., Klieber, T., Livingood, J., Mills, J., and R.
Woundy, "Comcast's Protocol-Agnostic Congestion Management
System", draft-livingood-woundy-congestion-mgmt-03 (work
in progress), February 2010.
[RFC2865] Rigney, C., Willens, S., Rubens, A., and W. Simpson,
"Remote Authentication Dial In User Service (RADIUS)",
RFC 2865, June 2000.
[RFC2866] Rigney, C., "RADIUS Accounting", RFC 2866, June 2000.
[RFC2975] Aboba, B., Arkko, J., and D. Harrington, "Introduction to
Accounting Management", RFC 2975, October 2000.
[RFC3576] Chiba, M., Dommety, G., Eklund, M., Mitton, D., and B.
Aboba, "Dynamic Authorization Extensions to Remote
Authentication Dial In User Service (RADIUS)", RFC 3576,
July 2003.
[RFC3588] Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J.
Arkko, "Diameter Base Protocol", RFC 3588, September 2003.
[RFC4006] Hakala, H., Mattila, L., Koskinen, J-P., Stura, M., and J.
Loughney, "Diameter Credit-Control Application", RFC 4006,
August 2005.
[RFC5594] Peterson, J. and A. Cooper, "Report from the IETF Workshop
on Peer-to-Peer (P2P) Infrastructure, May 28, 2008",
RFC 5594, July 2009.
[alto] "",
<http://www.ietf.org/dyn/wg/charter/alto-charter.html>.
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[broadband-traffic-report]
Cho, K., "Broadband Traffic Report", Internet
Infrastructure Review 4, 2009.
[ledbat] "",
<http://www.ietf.org/dyn/wg/charter/ledbat-charter.html>.
[p2prg] "", <http://www.irtf.org/charter?gtype=rg&group=p2prg>.
[traffic] Cho, K., Fukuda, K., Kato, H., and A. Kato, "The impact
and implications of the growth in residential user-to-user
traffic", SIGCOMM Comput. Commun. Rev. 36, 2006.
[traffic2]
Cho, K., Fukuda, K., Esaki, H., and A. Kato, "Observing
slow crustal movement in residential user traffic, in
International Conference On Emerging Networking
Experiments And Technologies, Proceedings of the 2008 ACM
CoNEXT Conference, Madrid, Spain, Article No. 12", ,
2008.
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Appendix A. Example Policy Statement
A.1. Fair Usage Policy
A.1.1. What is the Fair Usage Policy?
The Fair Usage Policy is designed to ensure that the service received
by the vast majority of our customers is not negatively impacted
because of extremely heavy usage by a very small minority of
customers. This is why ISP X continuously monitors network
performance and may restrict the speed available to very heavy users
during peak time. This applies to customers on all Options. Note if
you are a heavy user we will only restrict your speed, service will
not be stopped so ability to upload and download remains. No
restrictions will be imposed outside of the peak times. Only a very
small minority of customers will ever be affected by this (less than
1 %).
A.1.2. How do I know I'm a very heavy user?
There is no hard and fast usage limit that determines if you are a
heavy user as the parameters that determine heavy use vary with the
demands placed on the network at that given time. If you have a
query about fair usage related restrictions on your line please call
us.
A.1.3. I have Contract Option 3, does the Fair Usage Policy apply to
me?
Yes, the Fair Usage Policy applies to all customers on all Options,
including Option 3. Option 3 allows unlimited downloads and uploads
inclusive of the monthly rental price, so you will not be charged for
over-use, however this does not preclude ISP X from restricting your
speed at peak times if you are a heavy user. If you are an Option 3
heavy user this does not prevent you from continuing to use your
service, nor does it cost you any more but it ensures that you do not
negatively impact the majority of our customers who share the
available bandwidth with you.
A.1.4. Peer to Peer (P2P)
A.1.4.1. I'm noticing slower P2P speeds at peak times even though I'm
not a very heavy user, why is this?
P2P is the sharing and delivery of files amongst groups of people who
are logged on to a file sharing network. P2P consumes a significant
and highly disproportionate amount of bandwidth when in use even by
small numbers of users.
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This is why we have a peak time policy where we limit P2P speeds to
manage the amount of bandwidth that is used by this application in
particular.
Without these limits all our customers using their broadband service
at peak times would suffer, regardless of whether they are using P2P
or not. It's important to remember that P2P isn't a time-critical
application so if you do need to download large files we advise you
to do this at off-peak times when no restrictions are placed, not
only will you be able to download faster but your usage will not
negatively impact other users.
A.1.4.2. Does this mean I can't use Peer-to-Peer (P2P) applications?
No, we are not stopping you from using any P2P service, P2P will just
be slowed down at peak times. Again, P2P is not generally a time-
sensitive application.
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Authors' Addresses
Hannes Tschofenig
Nokia Siemens Networks
Linnoitustie 6
Espoo FIN-02600
Finland
Phone: +358 (50) 4871445
Email: Hannes.Tschofenig@gmx.net
URI: http://www.tschofenig.priv.at
Alissa Cooper
Center for Democracy & Technology
1634 I Street NW, Suite 1100
Washington, DC
USA
Email: acooper@cdt.org
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