One document matched: draft-tschofenig-conex-ps-00.txt
CONEX H. Tschofenig
Internet-Draft Nokia Siemens Networks
Intended status: Informational A. Cooper
Expires: April 22, 2010 Center for Democracy &
Technology
October 19, 2009
Congestion Exposure Problem Statement
draft-tschofenig-conex-ps-00.txt
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Abstract
The availability of broadband connections together with flat-rate
pricing has made new types of peer-to-peer applications possible.
From an Internet evolution and end user value point of view this is
very exciting. As a consequence, an increase of user-to-user traffic
was observable all around the world over the last few years. With
the usage of p2p systems the observation can be made that a certain
group of users, called high-consuming users, decided to use their
flat-rate contract excessively. This in turn seems to have caused
network operators to take actions.
This document illustrates a couple of techniques used by operators
today to deal with excessive bandwidth usage. More information can
improve the decision making process.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. State-of-the-Art Building Blocks . . . . . . . . . . . . . . . 5
2.1. Means of Identifying the Causes of Congestion . . . . . . 5
2.2. Potential Actions Operators might take in Response . . . . 6
3. New Activities . . . . . . . . . . . . . . . . . . . . . . . . 8
4. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
5. Security Considerations . . . . . . . . . . . . . . . . . . . 10
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 12
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
8.1. Normative References . . . . . . . . . . . . . . . . . . . 13
8.2. 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
In 2006 K. Cho et al. [traffic] published a paper about the growth of
residential user-to-user traffic in Japan that indicates '... a small
number of users dictate the overall behavior; 4 % of high-consuming
users account for 75 % of the inbound volume, and the fiber users
account for 86 % of the inbound volume.'. The same paper also
indicates a substantial increase in traffic growth, namely 37 % per
year according, and not just a different distribution of traffic
among the users. At that time 63 % of the residential traffic volume
is contributed by user-to-user traffic.
These numbers itself do not represent a problem as by themself and do
not necessarily lead to congestion. However, some operators very
likely had different expectations about the growth rates and traffic
consumption of individual users and statistics (used for their
pricing models) did not work out too well for them. The profit
margins for Internet access are quite slim due to fierce competition.
This puts a lot of pressure on operators to deal with these high-
consuming users who cost them a lot of money. Finally, some
broadband networks may not have the ideal characteristics (such as
the topology for routing traffic) for user-to-user traffic (e.g.,
Cable Networks).
Congestion is often mentioned in this context and as stated in RFC
5594 [RFC5594] "... congestion can be viewed merely as a
manifestation of cost. An ISP that invests in capacity could be
considered to be paying to relieve congestion. Or, if subscribers
are charged for congesting the network, then cost and congestion
could be viewed as one and the same. The distinction between them
may thus be artificial.".
To summarize in a simplistic way, those who produce a lot of traffic
cost a lot.
Operators are now facing a range of options, see sections below, that
can be taken and there is a tradeoff between what is allowed (legally
and from a public relation point of view) and what is useful from a
performance point of view. The latter aspect can be seen from the
point of view of a device performance (as many of the mechanisms
actually slow down the forwarding performance quite a bit) and
consequently a cost challenge.
The existence of flat rate pricing contributes to some of the
problems since the bandwidth usage in total needs to be covered by
the money obtained from broadband customers but the usage of
individual users is not reflected in the amount. As such, users that
rarely utilize the network pay the same amount as someone who uses
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P2p filesharing excessively.
However, from a psychological point of view humans tend to strive to
avoid uncertainty and hence offerings that reduced uncertainty. For
a user there are essentially two aspects to worry about
o Uncertainty in the bill: unpredicable costs that make planning
difficult.
o Uncertainty in the performance: performance degradation as part of
the actions being taken
True flat rate pricing avoids uncertainty in the bill.
Unfortunately, most of the solutions described below lead to some
uncertainty and thereby increase unhappyness of customers.
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2. State-of-the-Art Building Blocks
2.1. Means of Identifying the Causes of Congestion
RFC 2975 [RFC2975] describes accounting as "The collection of
resource consumption data for the purposes of capacity and trend
analysis, cost allocation, auditing, and billing.".
Over the years the number of information elements that can be sent
from an accounting client to an accounting server using standardized
protocols, such as RADIUS (see [RFC2866] and [RFC2865]) and Diameter
[RFC3588], has increased. The fact that standardized protocols have
been available allowed different AAA networks to be interconnected
and their usage can be found 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.
It has to be noted that RADIUS and Diameter are not the only
protocols that can be used to collect usage information and to
trigger certain actions, even they are fairly popular. Other
approaches, as documented in [I-D.livingood-woundy-congestion-mgmt],
lead to similar results.
Deep packet inspection refers to inspecting traffic that passes
through the operators networks up to the application layer.
Depending on the configuration of the device traffic shaping, packet
dropping/blocking and other usages might be applied. For example,
content sharing p2p applications maintain many simultaneous TCP
connections with other nodes for the purpose of simultaneous
downloads. An operator may, for example, limit the number of
connection setups from a single subscriber. Certain end user
contracts may also allow operators to ban servers from residential
access.
Determining the type of application that a subscriber is running was
seen as necessary to throttle only certain applications, instead of
impacting the full range of traffic a subscriber is using. A side-
effect is the additional investment for the device and operational
costs. The process of inspecting traffic is performance intensive
and continous software updates are necessary to ensure that the
detection engine recognizes the latest protocol variants.
Additionally, the attempt to selectively deal with applications (even
though these applications might be the reason for the high traffic
volume) has not been received well by the users.
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2.2. Potential Actions Operators might take in Response
What actions are taken based on the collected information and in what
time frame is largely left to the choice of those who run the
infrastructure. In the context of this discussion the collected
information may be used to charge the user per volume, per time and
in various different combinations. Additionally, the RADIUS and
Diameter allow the server side with a server-initiated message (see
Change of Authorization in [RFC3576], and the functionality provided
in the Diameter Base specification [RFC3588]) to push decisions to
the AAA clients, typically edge nodes, acting as enforcement nodes.
These decisions include actions like shaping or packet marking.
Shaping: End user contracts often offer a combination of 'flat-rate'
scheme whereby a fixed price tariff is used up to a certain usage
volume (typically quite high for regular usage). Subsequently, if
the consumption goes beyond a certain threshold then the entire
traffic is given lower priority and potentially shaped.
In many countries operators have to offer a clear description
of the service they offer and since the term 'flat-rate' is
already associated with a certain meaning the term 'Unlimited
Data Rate' is often used for this type of service. Contracts
typically contain statements that allow certain actions to be
taken. An example of such a fair use statement can be found in
Appendix A.
Note that traffic shaping is often only applied to high-consuming
users (since they are known based on the accounting procedures) or
the effect becomes only visible during peak hours when the network
fills up.
Class-Based Assignment: In this technique users are classified into
a set of classes depending on their past behavior. Subsequently,
the traffic is treated according to the associated class. It is
ensured that the traffic of lightweight users, users that really
rarely use their Internet connection, cannot be pushed away by
heavy users. This mechanism again requires some form of DiffServ
marking to be in place.
Charging for Excessive Traffic: As a possible action a user might
get charged differently for traffic that exeeds a certain
threshold compared to the traffic that falls within the agreed
limits.
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Discontinuing Contracts: In some rare cases ISP also decided to cut
connectivity under certain condition. In fact this might be
justified in certain cases. For example, in case of new botnets
malware distribution when the operator recognizes an infected
machine and hotlines the entire traffic of that particular machine
to a separate network and, like in WLAN hotspots, HTTP traffic is
intercepted to display further information. In some cases the
same technique has been applied with excessive usage of P2P
traffic, either intentionally or due to a false alarm caused by a
statistical traffic analysis technique.
In France the HADOPI law adopted in parliament that allowed an
'independent authority' to punish copyright violators with a
temporary suspension of their Internet access has raised
discussions within Europe about the fundamental right to
'communicate and express' and its applicability to the Internet
access. Although this discussion is still ongoing the French
Supreme Court had striked down portions of the law arguing that
any restriction of such a right can only be decided by a judge.
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3. New Activities
In response to the P2P infrastructure workshop in 2008 (with a
summary documented [RFC5594]) two working groups and one research
group has been created that focus on a certain area of the
application space:
LEDBAT (Low Extra Delay Background Transport) [ledbat] is designed
to allow to keep the latency across the 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 application, to operate without destroying the
user experience in interactive applications.
LEDBAT is a promising approach when applied widely in P2P clients.
This solution has been focused 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. For legal content
ALTO mechanisms with the ability for ISPs to deploy proxies appear
to be a viable solution. However, a lot of the content being
distributed in P2P filesharing networks today is not legal and
caching such content by operators could turn out problematic for
them.
Peer to Peer Research Group [p2prg] aims to provide a discussion
forum for resarchers related to all sorts of challenges of P2P
systems in general, such as P2P streaming, interconnecting
distinct P2P application overlays, security and privacy, etc.
[I-D.irtf-p2prg-mythbustering] provides a number of literature
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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4. Summary
Heavy users are a reality. Operators that would like to counteract
the impact of heavy users 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 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).
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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5. Security Considerations
This document highlights approaches for dealing with heavy network
usage and all of them raise security and privacy concerns. This
document does, however, not introduce new mechanism and hence the
reader is referred to the description of the respective mechanism.
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6. IANA Considerations
This document does not require actions by IANA.
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7. Acknowledgments
The authors would like to thank Alan DeKok, Jens-Peter Haack, Jouni
Korhonen, Tommy Lindgren, Lars Eggert, for their time to discuss the
topic. Additionally, we would like to thank Marcin Matuszewski for
his help with the P2P infrastructure workshop paper (as it was used
as a starting point).
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8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
8.2. 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-00
(work in progress), August 2009.
[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-01 (work
in progress), September 2009.
[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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[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.
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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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