| Rfc | 6057 |
|---|
| Title | Comcast's Protocol-Agnostic Congestion Management System |
|---|
| Author | C.
Bastian, T. Klieber, J. Livingood, J. Mills, R. Woundy |
|---|
| Date | December
2010 |
|---|
| Format: | TXT, HTML |
|---|
| Status: | HISTORIC |
|---|
|
Internet Engineering Task Force (IETF) C. Bastian
Request for Comments: 6057 T. Klieber
Category: Informational J. Livingood
ISSN: 2070-1721 J. Mills
R. Woundy
Comcast
December 2010
Comcast's Protocol-Agnostic Congestion Management System
Abstract
This document describes the congestion management system of Comcast
Cable, a large cable broadband Internet Service Provider (ISP) in the
U.S. Comcast completed deployment of this congestion management
system on December 31, 2008.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Not all documents
approved by the IESG are a candidate for any level of Internet
Standard; see Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc6057.
Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction ....................................................2
2. Applicability to Other Types of Networks ........................3
3. Key Terminology .................................................3
4. Historical Overview .............................................7
5. Summary .........................................................8
6. Relationship between Managing Congestion and Adding Capacity ....9
7. Implementation and Configuration ...............................10
7.1. Thresholds for Determining When a CMTS Port Is in a Near
Congestion State ..........................................14
7.2. Thresholds for Determining When a User Is in an
Extended High Consumption State and for Release from
That Classification .......................................15
7.3. Effect of BE Quality of Service on Users'
Broadband Experience ......................................19
7.4. Equipment/Software Used and Location ......................21
8. Conclusion .....................................................23
9. Exceptional Network Utilization Considerations .................23
10. Limitations of This Congestion Management System ..............24
11. Low Extra Delay Background Transport and Other Possibilities ..24
12. Security Considerations .......................................24
13. Acknowledgements ..............................................25
14. Informative References ........................................26
1. Introduction
Comcast Cable is a large broadband Internet Service Provider (ISP),
based in the U.S., serving the majority of its customers via cable
modem technology. During the late part of 2008, and completing on
December 31, 2008, Comcast deployed a new congestion management
system across its entire network. This new system was developed in
response to dissatisfaction in the Internet community as well as
complaints to the U.S. Federal Communications Commission (FCC)
regarding Comcast's old system, which targeted specific peer-to-peer
(P2P) applications. This new congestion management system is
protocol-agnostic, meaning that it does not examine or impact
specific user applications or network protocols, which is perceived
as a more fair system for managing network resources at limited times
when congestion may occur.
It is important for readers to note that congestion can occur in any
IP network, and, when it does, packets can be delayed or dropped. As
Bob Briscoe has pointed out on an IETF mailing list, some amount of
packet loss can be normal and/or tolerable, noting "But a single TCP
flow with a round trip time (RTT) of 80 ms can attain 50 Mbps with a
loss fraction of 0.0013% (1 in ~74,000 packets) so there's no need to
try to achieve loss figures much lower than this. And indeed, if
flows aren't bottlenecked elsewhere, TCP will drive the system until
it gets such loss levels. If, instead, a customer is downloading
five separate 10 Mbps TCP flows still with an 80-ms RTT, TCP will
drive losses up to 1 in ~3,000, or 0.03%, and any lower loss rates
won't be able to improve performance". As a result, applications and
protocols have been designed to deal with the reality that congestion
can occur in any IP network, the mechanics of which we explain in
detail later in this document.
The purpose of this document is to describe how this example of a
large-scale congestion management system functions. This is
partially in response to questions from other ISPs as well as
solution developers, who are interested in learning from and/or
deploying similar systems in other networks. In addition, it is
hoped that such a document may help inform new work in the IETF, in
the hope that better systems and protocols may be possible in the
future. Lastly, the authors wish to transparently and openly
document this system, so that there could be no doubt about how the
system functioned.
2. Applicability to Other Types of Networks
Several document reviewers and other IETF participants have pointed
out that, though we refer to functional elements that are specific to
a Data Over Cable Service Interface Specification (DOCSIS)-based
network implementation, this type of congestion management system
could be generally applied to nearly any type of network. Thus, it
is important for readers to take note of this and take into
consideration that this sort of protocol-agnostic congestion
management system could certainly fit in a wide variety of network
types and implementations.
3. Key Terminology
This section defines the key terms used in this document. Some terms
below refer to elements of the Comcast network. As a result, it may
be helpful to refer to Figure 1 (see Section 7) when reviewing some
of these terms.
3.1. Cable Modem
A device located at the customer premise used to access the Comcast
High Speed Internet (HSI) network. In some cases, the cable modem is
owned by the customer, and in other cases it is owned by the cable
operator. This device has an interface (i.e., someplace to plug in a
cable) for connecting the coaxial cable provided by the cable company
to the modem, as well as one or more interfaces for connecting the
modem to a customer's PC or home gateway device (e.g., home gateway,
router, firewall, access point, etc.). In some cases, the cable
modem function, i.e., the ability to access the Internet, is
integrated into a home gateway device or Embedded Multimedia Terminal
Adapter (eMTA). Once connected, the cable modem links the customer
to the HSI network and ultimately the broader Internet.
3.2. Cable Modem Termination System (CMTS)
A piece of hardware located in a cable operator's local network
(generally in a "headend", Section 3.10) that acts as the gateway to
the Internet for cable modems in a particular geographic area. A
simple way to think of the CMTS is as a router with interfaces on one
side leading to the Internet and interfaces on the other connecting
to Optical Nodes and then customers, in a so-called "last mile"
network.
3.3. Cable Modem Termination System (CMTS) Port
Also referred to simply as a "port". A port is a physical interface
on a device used to connect cables in order to connect with other
devices for transferring information/data. An example of a physical
port is a CMTS port. A CMTS has both upstream and downstream network
interfaces to serve the local access network, which are referred to
as upstream or downstream ports. A port generally serves a
neighborhood of hundreds of homes. Over time, CMTS ports tend to
serve fewer and fewer homes, as the network is segmented for capacity
growth purposes. Prior to DOCSIS version 3, a single CMTS physical
port was used for either transmitting or receiving data downstream or
upstream to a given neighborhood. With DOCSIS version 3, and the
channel bonding feature, multiple CMTS physical ports can be combined
to create a virtual port. A CMTS is also briefly defined in
Section 2.6 of [RFC3083].
3.4. Channel Bonding
A technique for combining multiple downstream and/or upstream
channels to increase customers' download and/or upload speeds,
respectively. Multiple channels from the Hybrid Fiber Coax (HFC)
network (Section 3.11) can be bonded into a single virtual port
(called a bonded group), which acts as a large single channel or port
to provide increased speeds for customers. Channel bonding is a
feature of Data Over Cable Service Interface Specification (DOCSIS)
version 3, as described in [DOCSIS_MULPI].
3.5. Coaxial Cable (Coax)
A type of cable used by a cable operator to connect customer premise
equipment (CPE) -- such as TVs, cable modems (including eMTAs), and
Set Top Boxes -- to the HFC network. This cable may be used within
the home as well as in segments of the "last mile" network running to
a home or customer premise location. There are many grades of
coaxial cable that are used for different purposes. Different types
of coaxial cable are used for different purposes on the network.
3.6. Comcast High Speed Internet (HSI)
A service/product offered by Comcast for delivering Internet service
over a broadband connection.
3.7. Customer Premise Equipment (CPE)
Any device that resides at the customer's residence, connected to the
Comcast network, whether controlled by Comcast or not.
3.8. Data Over Cable Service Interface Specification (DOCSIS)
A reference standard developed by CableLabs that specifies how
components on cable networks need to be built to enable HSI service
over an HFC network, as noted in [DOCSIS_CM2CPE], [DOCSIS_PHY],
[DOCSIS_MULPI], [DOCSIS_SEC], and [DOCSIS_OSSI]. These standards
define the specifications for the cable modem and the CMTS such that
any DOCSIS-certified cable modem will work on any DOCSIS-certified
CMTS, independent of the selected vendor. The interoperability of
cable modems and CMTSs allows customers to purchase a DOCSIS-
certified modem from a retail outlet and use it on their cable-
networked home. All DOCSIS-related standards are available to the
public at the CableLabs website, at http://www.cablelabs.com.
3.9. Downstream
Description of the direction in which a signal travels, in this case
from the network to a user. Downstream traffic occurs when users are
downloading something from the Internet, such as watching a web-based
video, reading web pages, or downloading software updates.
3.10. Headend
A cable facility responsible for receiving TV signals for
distribution over the HFC network to the end customers. This
facility typically also houses one or more CMTSs. This is sometimes
also called a "hub".
3.11. Hybrid Fiber Coax (HFC)
A network architecture used primarily by cable companies, comprised
of fiber-optic and coaxial cables that currently deliver Voice,
Video, and Internet services to customers, as defined in Section 1.2
of [DOCSIS_MULPI].
3.12. Internet Protocol Detail Record (IPDR)
Standardized technology for monitoring and/or recording subscribers'
upstream and downstream Internet usage data based on their cable
modem. The data is collected from the CMTS and sent to a server for
further processing. Additional information is available at
http://www.ipdr.org, as well as [IPDR_Standard] and [DOCSIS_IPDR].
3.13. Optical Node
A component of the HFC network generally located in customers' local
neighborhoods that is used to convert the optical signals sent over
fiber-optic cables to electrical signals that can be sent over
coaxial cable to customers' cable modems, or vice versa. A fiber-
optic cable connects the Optical Node, through distribution hubs, to
the CMTS, and coaxial cable connects the Optical Node to customers'
cable modems.
3.14. Provisioned Bandwidth
The peak speed associated with a tier of service purchased by a
customer. For example, a customer with a 105 Mbps downstream and
10 Mbps upstream speed tier would be said to be provisioned with
105 Mbps of downstream bandwidth and 10 Mbps of upstream bandwidth.
This is often referred to as 105/10 service in industry parlance.
The Provisioned Bandwidth is the speed that a customer's modem is
configured (and the network is engineered) to deliver on a regular
basis (which is not the same as a "Committed Information Rate" or a
guaranteed rate). Internet speeds are generally a best effort
service that are dependent on a number of variables, many of which
are outside the control of an Internet Service Provider (ISP). In
general, speeds do not typically exceed a customer's provisioned
speed. Comcast, however, invented a technology called "PowerBoost"
[PowerBoost_Specification] that, for example, enables users to
experience brief boosts above their provisioned speeds while they
transfer large files over the Internet, by utilizing excess capacity
that may be available in the network at that time.
3.15. Quality of Service (QoS)
A set of techniques to manage network resources to ensure a level of
performance to specific data flows, as described in [RFC1633] and
[RFC2475]. One method for providing QoS to a network is by
differentiating the type of traffic by class or flow and assigning
priorities to each type. When the network becomes congested, the
data packets that are marked as having higher priority will have
higher likelihood of being serviced.
3.16. Upstream
Description of the direction in which a signal travels, in this case
from the user to the network. Upstream traffic occurs when users are
uploading something to the network, such as sending email, sending
files to another computer, or uploading photos to a digital photo
website.
4. Historical Overview
Comcast began the engineering project to develop a new congestion
management system in March 2008, the same month that Comcast hosted
the 71st meeting of the IETF in Philadelphia, PA, USA. On May 28,
2008, Comcast participated in an IETF Peer-to-Peer Infrastructure
Workshop [RFC5594], hosted by the Massachusetts Institute of
Technology (MIT) in Cambridge, MA, USA.
In order to participate in this workshop, interested attendees were
asked to submit a paper to a technical review team, which Comcast did
on May 9, 2008, in [COMCAST_P2PI_PAPER]. Comcast subsequently
attended and participated in this valuable workshop. During the
workshop, Comcast outlined the high-level design for a new congestion
management system [COMCAST_P2PI_PRES] and solicited comments and
other feedback from attendees and other members of the Internet
community (presentations were also posted to the IETF's P2Pi mailing
list). The congestion management system outlined in that May 2008
workshop was later tested in trial markets and is in essence what was
then deployed by Comcast later in 2008.
Following an August 2008 FCC document [FCC_Memo_Opinion] regarding
how Comcast managed congestion on its High-Speed Internet ("HSI")
network, Comcast disclosed to the FCC [FCC_Net_Mgmt_Response] and the
public additional technical details of the congestion management
system that it intended to and did implement by the end of 2008
[FCC_Congest_Mgmt_Ltr], including the thresholds involved in this new
system. While the description of how this system is deployed in the
Comcast network is necessarily specific to the various technologies
and designs specific to that network, a similar system could be
deployed on virtually any large-scale ISP network or other IP
network.
5. Summary
Comcast's HSI network has elements that are shared across many
subscribers. This means that Comcast's HSI customers share upstream
and downstream bandwidth with their neighbors. Although the
available bandwidth is substantial, so, too, is the demand. Thus,
when a relatively small number of customers in a neighborhood place
disproportionate demands on network resources, this can cause
congestion that degrades their neighbors' Internet experience. The
goal of Comcast's new congestion management system is to enable all
users of our network resources to access a "fair share" of that
bandwidth, in the interest of ensuring a high-quality online
experience for all of Comcast's HSI customers.
Importantly, the new approach is protocol-agnostic; that is, it does
not manage congestion by focusing on the use of the specific
protocols that place a disproportionate burden on network resources,
or any other protocols. Rather, the new approach focuses on managing
the traffic of those individuals who are using the most bandwidth at
times when network congestion threatens to degrade subscribers'
broadband experience and who are contributing disproportionately to
such congestion at those points in time.
Specific details about these practices, including relevant threshold
information, the type of equipment used, and other particulars, are
discussed at some length later in this document. At the outset,
however, we present a very high-level, simplified overview of how
these practices work. Despite all the detail provided further below,
the fundamentals of this approach can be summarized succinctly:
1. Software installed in the Comcast network continuously examines
aggregate traffic usage data for individual segments of Comcast's
HSI network. If overall upstream or downstream usage on a
particular segment of Comcast's HSI network reaches a
pre-determined level, the software moves on to step two.
2. At step two, the software examines bandwidth usage data for
subscribers in the affected network segment to determine which
subscribers are using a disproportionate share of the bandwidth.
If the software determines that a particular subscriber or
subscribers have been the source of high volumes of network
traffic during a recent period of minutes, traffic originating
from that subscriber or those subscribers temporarily will be
assigned a lower priority status.
3. During the time that a subscriber's traffic is assigned the lower
priority status, their packets will not be delayed or dropped so
long as the network segment is not actually congested. If,
however, the network segment becomes congested, their packets
could be intermittently delayed or dropped.
4. The subscriber's traffic returns to normal priority status once
his or her bandwidth usage drops below a set threshold over a
particular time interval.
Comcast undertook considerable effort, over the course of many
months, to formulate our plans for this congestion management
approach, adjusting them, and subjecting them to real-world trials.
Market trials were conducted in Chambersburg, PA; Warrenton, VA; Lake
City, FL; East Orange, FL; and Colorado Springs, CO, between June and
September 2008. This enabled us to validate the utility of the
general approach and collect substantial trial data to test multiple
variations and alternative formulations.
6. Relationship between Managing Congestion and Adding Capacity
Many people have questioned whether congestion should ever exist at
all, if an ISP was adding sufficient capacity. There is certainly a
relationship between capacity and congestion. But there are two
types of congestion that generally present themselves in a network.
The first general type of congestion is regularly occurring and is
the result of gradually increasing traffic levels up to a point where
typical usage peaks cause congestion on a regular basis. Comcast,
like many ISPs, has a set capacity management process by which
capacity additions are automatically triggered based on certain usage
trends; this process is geared towards bringing additional capacity
to the network prior to the onset of regularly occurring congestion.
As such, capacity is added when needed and before it presents
noticeable effects. This process is in place since capacity
additions are not instantaneous and in many cases require significant
physical work.
The second general type of congestion is unpredictable congestion,
which can occur for a wide range of reasons. One example may be due
to current events, where users may be all rushing to access specific
content at the exact same time, and where the systems serving that
content may not be able to keep up with demand. Another example may
be due to a localized disaster, where some network paths have been
destroyed or otherwise impaired, and where many users are attempting
to communicate with one another at traffic levels significantly above
normal.
Thus, in both cases, even with continuous upgrades and constant
investment in additional capacity, the fact remains that network
capacity is not unlimited. A congestion management system, absent
superior protocol-based solutions that do not currently exist, can
therefore help manage the effects of congestion on users, improving
their Internet experience.
7. Implementation and Configuration
It is important to note that the implementation details below and the
overall design of the system are matched to traffic patterns that
exist on the Internet today and that the authors believe will exist
in the near future. While the authors desired to make the system
highly adaptable and a good long-term network investment, significant
changes in such traffic patterns may necessitate a change in the
configuration of the system or, in extreme cases, a different type of
system altogether.
To understand exactly how these new congestion management practices
work, it is helpful to have a general understanding of how Comcast's
HSI network is designed. Comcast's HSI network is what is commonly
referred to as a hybrid fiber-coax network, with coaxial cable
connecting each subscriber's cable modem to an Optical Node, and
fiber-optic cables connecting the Optical Node, through distribution
hubs, to the Cable Modem Termination System (CMTS), which is also
known as a "data node". The CMTSs are then connected to higher-level
routers, which in turn are connected to Comcast's Internet backbone
facilities. Today, Comcast has over 3,200 CMTSs deployed throughout
our network, serving over 15 million HSI subscribers.
Each CMTS has multiple "ports" that handle traffic coming into and
leaving the CMTS. In particular, each cable modem deployed on the
Comcast HSI network is connected to the CMTS through the ports on the
CMTS. These ports can be either "downstream" ports or "upstream"
ports, depending on whether they send information to cable modems
(downstream) or receive information from cable modems (upstream)
attached to the port. (Note that the term "port" as used here
generally contemplates single channels on a CMTS, but these
statements will apply to virtual channels, also known as "bonded
groups", in a DOCSIS 3.0 environment.) Even without channel bonding,
multiple channels are usually configured to come out of each physical
port. Said another way, there is generally a mapping of multiple
channels to each physical port.
Currently, on average, approximately 275 cable modems share the same
downstream port, and about 100 cable modems share the same upstream
port; however, this is constantly changing (both numbers generally
become smaller over time, based on current DOCSIS technology). Both
types of ports can experience congestion that could degrade the
broadband experience of our subscribers and, unlike with the previous
congestion management practices, both upstream and downstream traffic
are subject to management in this new congestion management system.
Based upon the design of the network and traffic patterns observed,
the most likely place for congestion to occur is on these CMTS ports.
As a result, the congestion management system measures the traffic
conditions of CMTS ports, and applies any policy actions to traffic
on those ports (rather than some other, more distant segment of the
network).
To implement Comcast's new protocol-agnostic congestion management
practices, Comcast purchased new hardware and software that were
deployed near the Regional Network Routers ("RNRs") that are further
upstream in Comcast's network. This new hardware consists of
Internet Protocol Detail Record ("IPDR") servers, Congestion
Management servers, and PacketCable Multimedia ("PCMM") servers.
Further details about each of these pieces of equipment can be found
below, in Section 7.4. It is important to note here, however, that
even though the physical location of these servers is at the RNR, the
servers communicate with -- and manage individually -- multiple ports
on multiple CMTSs to effectuate the practices described in this
document. That is to say, bandwidth usage on one CMTS port will have
no effect on whether the congestion management practices described
herein are applied to a subscriber on a different CMTS port.
Figure 1 provides a simplified graphical depiction of the network
architecture just described:
Figure 1: Simplified Network Diagram Showing High-Level Comcast
Network and Servers Relevant to Congestion Management
-------------------------
/ \
| Comcast Internet Backbone |
\ -----
+------------+ --------------------/ \
| Congestion | / \
| Management |<+++GigE++++ +---->| Internet |
| Server | + | | Backbone |
+------------+ + | \ Router /
+ Fiber \ /
+------------+ + | -----
| QoS | + |
| Server |<+++GigE++++ \/
| | + -----
+------------+ + / \
+ / \
+------------+ + | Regional |
| Statistics | +++++++>| Network |
| Collection |<+++GigE++++ | Router |
| Server | \ /
+------------+ +---Fiber------>\ /<------Fiber----+
| ----- |
\/ \/
----- -----
/ \ / \
/ Local \ / Local \
| Market | | Market |
\ Router / \ Router /
+--------->\ /<------------+ \ /
| ----- | ------
| /\ | /\
Fiber | Fiber |
| Fiber | Fiber
| | | |
\/ \/ \/ \/
/------\ /------\ /------\ /------\
| CMTS | | CMTS | | CMTS | | CMTS |
\------/ \------/ \------/ \------/
/\ /\ /\ /\
| | | |
Fiber Fiber Fiber Fiber
| | | |
\/ \/ \/ \/
+---------+ +---------+ +---------+ +---------+
| Optical | | Optical | | Optical | | Optical |
| Node | | Node | | Node | | Node |
+---------+ +---------+ +---------+ +---------+
/\ /\ /\ /\ /\ /\
|| || ||______ || _____|| ||
Coax Coax |__Coax| Coax |Coax__| Coax
|| || || || || ||
\/ \/ \/ \/ \/ \/
+=======+ +=======+ +=======+ +=======+ +=======+ +=======+
= Cable = = Cable = = Cable = = Cable = = Cable = = Cable =
= Modem = = Modem = = Modem = = Modem = = Modem = = Modem =
+=======+ +=======+ +=======+ +=======+ +=======+ +=======+
================================================================
+ Note: This diagram is a simplification of the actual network +
+ and servers, which in actuality includes significant +
+ redundancy and other details too complex to represent here. +
================================================================
Figure 1
Each Comcast HSI subscriber's cable modem has a "bootfile", which is
essentially a configuration file that contains certain pieces of
information about the subscriber's service to ensure that the service
functions properly. (Note: No personal information is included in
the bootfile; it only includes information about the service that the
subscriber has purchased.) For example, the bootfile contains
information about the maximum speed (what we refer to in this
document as the "provisioned bandwidth") that a particular modem can
achieve based on the tier (personal/residential, commercial, etc.)
the customer has purchased. Bootfiles are generally reset from time
to time to account for changes in the network and other updates, and
this is usually done through a command sent from the network and
without the subscriber noticing. In preparation for the transition
to this new congestion management system, Comcast sent new bootfiles
to our HSI customers' cable modems that created two Quality of
Service (QoS) levels for Internet traffic going to and from the cable
modem: (1) "Priority Best Effort" ("PBE") traffic; and (2) "Best
Effort" ("BE") traffic. As with previous changes to cable modem
bootfiles, the replacement of the old bootfile with the new bootfile
requires no active participation by Comcast customers.
Thereafter, all traffic going to or coming from cable modems on the
Comcast HSI network is designated as either PBE or BE. PBE is the
default status for all Internet traffic coming from or going to a
particular cable modem. Traffic is designated BE for a particular
cable modem only when both of two conditions are met:
o First, the usage level of a particular upstream or downstream port
of a CMTS, as measured over a particular period of time, must be
nearing the point where congestion could degrade users'
experience. We refer to this as the "Near Congestion State" and,
based on the technical trials we have conducted (further validated
in our full deployment), we have established a threshold,
described in more detail below, for when a particular CMTS port
enters that state.
o Second, a particular subscriber must be making an extended, high
contribution to the bandwidth usage on the particular port,
relative to the service tier they purchased, as measured over a
particular period of time. We refer to this as the "Extended High
Consumption State" and, based on the technical trials we have
conducted (further validated in our full deployment), we have
established a threshold, described in more detail below, for when
a particular user enters that state.
When, and only when, both conditions are met, a user's upstream or
downstream traffic (depending on which type of port is in the Near
Congestion State) is designated as BE. Then, to the extent that
actual congestion occurs, any delay resulting from the congestion
will affect BE traffic before it affects PBE traffic.
We now explain the foregoing in greater detail in the following
sections.
7.1. Thresholds for Determining When a CMTS Port Is in a Near
Congestion State
For a CMTS port to enter the Near Congestion State, traffic flowing
to or from that CMTS port must exceed a specified level (the "Port
Utilization Threshold") for a specific period of time (the "Port
Utilization Duration"). The Port Utilization Threshold on a CMTS
port is measured as a percentage of the total aggregate upstream or
downstream bandwidth for the particular port during the relevant
timeframe. The Port Utilization Duration on the CMTS is measured in
minutes.
Values for each of the thresholds that are used as part of this
congestion management technique have been tentatively established
after an extensive process of lab tests, simulations, technical
trials, vendor evaluations, customer feedback, and a third-party
consulting analysis. In the same way that specific anti-spam or
other network management practices are adjusted to address new issues
that arise, it is a near certainty that these values will change over
time, as Comcast gathers more data and performs additional analysis
resulting from wide-scale use of the new technique. Moreover, as
with any large network or software system, software bugs and/or
unexpected errors may arise, requiring software patches or other
corrective actions. As always, Comcast's decisions on these matters
are driven by the marketplace imperative that we deliver the best
possible experience to our HSI subscribers.
Given our experience as described above, we determined that a
starting point for the upstream Port Utilization Threshold should be
70 percent and the downstream Port Utilization Threshold should be
80 percent. For the Port Utilization Duration, we determined that
the starting point should be approximately 15 minutes (although some
technical limitations in some newer CMTSs deployed on Comcast's
network may make this time period vary slightly). Thus, over any
15-minute period, if an average of more than 70 percent of a port's
upstream bandwidth capacity or more than 80 percent of a port's
downstream bandwidth capacity is utilized, that port is determined to
be in a Near Congestion State.
Based on the trials conducted and operational experience to date, a
typical CMTS port on our HSI network is in a Near Congestion State
only for relatively small portions of the day, if at all, though
there is no way to forecast what will be the busiest time on a
particular port on a particular day. Moreover, the trial data and
operational experience indicate that, even when a particular port is
in a Near Congestion State, the instances where the network actually
becomes congested during the Port Utilization Duration are few, and
managed users whose packets may be intermittently delayed or dropped
during those congested periods perceive little, if any, effect, as
discussed below.
7.2. Thresholds for Determining When a User Is in an Extended High
Consumption State and for Release from That Classification
Once a particular CMTS port is in a Near Congestion State, the
software examines whether any cable modems are consuming bandwidth
disproportionately. (Note: Although each cable modem is typically
assigned to a particular household, the software does not and cannot
actually identify individual users or the number of users sharing a
cable modem, or analyze particular users' traffic.) For purposes of
this document, we use "cable modem", "user", and "subscriber"
interchangeably to mean a subscriber account or user account and not
an individual person. For a user to enter an Extended High
Consumption State, he or she must consume greater than a certain
percentage of his or her provisioned upstream or downstream bandwidth
(the "User Consumption Threshold") for a specific length of time (the
"User Consumption Duration"). The User Consumption Threshold is
measured as a user's consumption of a particular percentage of his or
her total provisioned upstream or downstream bandwidth. That
bandwidth is the maximum speed that a particular modem can achieve
based on the tier (personal/residential, commercial, etc.) the
customer has purchased. For example, if a user buys a service with
speeds of 50 Mbps downstream and 10 Mbps upstream, then his or her
provisioned downstream speed is 50 Mbps and provisioned upstream
speed is 10 Mbps. It is also important to note that because the User
Consumption Threshold is a percentage of provisioned bandwidth for a
particular user account, and not a static value, users of higher-
speed tiers have correspondingly higher User Consumption Thresholds.
Lastly, the User Consumption Duration is measured in minutes.
Following lab tests, simulations, technical trials, customer
feedback, vendor evaluations, and an independent third-party
consulting analysis, we have determined that the appropriate starting
point for the User Consumption Threshold is 70 percent of a
subscriber's provisioned upstream or downstream bandwidth, and that
the appropriate starting point for the User Consumption Duration is
15 minutes (this has been further validated in our full deployment).
That is, when a subscriber uses an average of 70 percent or more of
his or her provisioned upstream or downstream bandwidth over a
particular 15-minute period, that user is then in an Extended High
Consumption State. Therefore, this is a consumption-based threshold
and not a peak-speed-based threshold. Thus, the Extended High
Consumption State is not tied to whether a user has bursted once or
more above this 70% threshold for a brief moment. Instead, it is
consumption-based, meaning that a certain bitrate must be exceeded
over at least the entire User Consumption Duration.
The User Consumption Thresholds have been set sufficiently high that
using the HSI connection for Voice over IP (VoIP), gaming, web
surfing, or most streaming video cannot alone cause subscribers to
our standard-level HSI service to exceed the User Consumption
Threshold. For example, while one of Comcast's common HSI service
tiers has a provisioned downstream bandwidth of 22 Mbps today,
streaming video (even some HD video) from Hulu uses less than
2.5 Mbps, a Vonage or Skype VoIP call uses less than 131 kbps, and
streaming music uses less than 128 kbps (in this example, 70 percent
of 22 Mbps is 15.4 Mbps). As noted above, these values are subject
to change as necessary in the same way that specific anti-spam or
other network management practices are adjusted to address new issues
that arise, or should unexpected software bugs or other problems
arise.
Based on data collected from the trial markets where the new
congestion management practices were tested (further validated in our
full deployment), on average less than one-third of one percent of
subscribers have had their traffic priority status changed to the BE
state on any given day. For example, in Colorado Springs, CO, the
largest test market, on any given day in August 2008, an average of
22 users out of 6,016 total subscribers in the trial had their
traffic priority status changed to BE at some point during the day.
A user's traffic is released from a BE state when the user's
bandwidth consumption drops below 50 percent of his or her
provisioned upstream or downstream bandwidth for a period of
approximately 15 minutes. These release criteria are intended to
minimize (and hopefully prevent) user QoS oscillation, i.e., a
situation in which a particular user could cycle repeatedly between
BE and PBE. Thus, without this lower release criteria, we were
concerned that certain users would oscillate between BE and PBE
states for an extended period, without clear benefit to the system
and other users, and would place an unnecessary signaling burden on
the system. NetForecast, Inc., an independent consultant retained to
provide analysis and recommendations regarding Comcast's trials and
related congestion management work, suggested this approach, which
has worked well in our trials, lab testing, and subsequent national
deployment.
Simply put, there are four steps for determining whether the traffic
associated with a particular cable modem is designated as PBE or BE:
1. Determine if the CMTS port is in a Near Congestion State.
2. If yes, determine whether any users are in an Extended High
Consumption State.
3. If yes, change those users' traffic to BE from PBE. If the answer
at either step one or step two is no, no action is taken.
4. If a user's traffic has been designated BE, check user consumption
at the next interval. If user consumption has declined below the
predetermined threshold, reassign the user's traffic as PBE. If
not, recheck at the next interval.
In cases where a CMTS regularly enters a Near Congestion State, and
where congestion subsequently does occur, but where no users match
the criteria to be classified in an Extended High Consumption State,
this may indicate the congestion observed is regularly occurring,
rather than unpredictable congestion. As such, this may be an
additional data point in favor of considering whether and when to add
capacity.
Figure 2 graphically depicts how this congestion management process
works, using an example of a situation where upstream port
utilization may be reaching a Near Congestion State (the same
diagram, with different values in the appropriate places, could be
used to depict the management process for downstream ports, as well):
Figure 2: Upstream Congestion Management Decision Flowchart
/\
+------------+ / \ +---------+ +---------+
| Start | / \ | | / /
| Congestion | / \ | | / /
| Management +-->+ Question +--YES-->| Result |--THEN-->/ Action /
| Process | \ #1 / | #1 | / #1 /
| | \ / | | / /
+------------+ \ / +---------+ +---------+
\/ |
| THEN
NO |
| \/
\/ /\
+---------+ / \
| | / \
| | / \
| Result |<-------------NO------------+ Question +
| #2 | \ #2 /
| | \ /
+---------+ \ /
\/
|
YES
|
/\ \/
+---------+ / \ +---------+
| | / \ | |
| | / \ THEN, AT | |
| Result |<--YES--+ Question + <---NEXT ANALYSIS------+ Result |
| #4 | \ #3 / POINT /\ | #3 |
| | \ / | | |
+---------+ \ / | +---------+
\/ |
| |
+------------NO-------------+
KEY TO FIGURE 2 ABOVE:
Question #1: Is the CMTS Upstream Port Utilization at an average
of OVER 70% for OVER 15 minutes?
Result #1: CMTS marked in a Near Congestion State, indicating
congestion *may* occur soon.
Action #1: Search most recent analysis timeframe (approx. 15 mins.)
of IPDR usage data.
Question #2: Are any users consuming an average of OVER 70% of
provisioned upstream bandwidth for OVER 15 minutes?
Result #2: No action taken.
Result #3: Change user's upstream traffic from Priority Best Effort
(PBE) to Best Effort (BE).
Question #3: Is the user in Best Effort (BE) consuming an average
of LESS THAN 50% of provisioned upstream bandwidth
over a period of 15 minutes?
Result #4: Change user's upstream traffic back to Priority Best
Effort (PBE) from Best Effort (BE).
Figure 2
7.3. Effect of BE Quality of Service on Users' Broadband Experience
When a CMTS port is in a Near Congestion State and a cable modem
connected to that port is in an Extended High Consumption State, that
cable modem's traffic is designated as BE. Depending upon the level
of utilization on the CMTS port, this designation may or may not
result in the user's traffic being delayed or, in extreme cases,
dropped before PBE traffic is dropped. This is because of the way
that the CMTS handles traffic. Specifically, CMTS ports have what is
commonly called a "scheduler" that puts all the packets coming from
or going to cable modems on that particular port in a queue and then
handles them in turn. A certain number of packets can be processed
by the scheduler in any given moment; for each time slot, PBE traffic
is given priority access to the available capacity, and BE traffic is
processed on a space-available basis.
A rough analogy would be to busses that empty and fill up at
incredibly fast speeds. As empty busses arrive at the figurative
"bus stop" -- every two milliseconds in this case -- they fill up
with as many packets as are waiting for "seats" on the bus, to the
limits of the bus' capacity. During non-congested periods, the bus
will usually have several empty seats, but during congested periods,
the bus will fill up and packets will have to wait for the next bus.
It is during the congested periods that BE packets will be affected.
If there is no congestion, packets from a user in a BE state should
have little trouble getting on the bus when they arrive at the bus
stop. If, on the other hand, there is congestion in a particular
instance, the bus may become filled by packets in a PBE state before
any BE packets can get on. In that situation, the BE packets would
have to wait for the next bus that is not filled by PBE packets. In
reality, this all takes place in two-millisecond increments, so even
if the packets miss 50 "busses", the delay will only be about one-
tenth of a second.
During times of actual network congestion, when packets from BE
traffic might be intermittently delayed, there is a variety of
effects that could be experienced by a user whose traffic is delayed,
depending upon what applications he or she is using. Typically, a
user whose traffic is in a BE state during actual congestion may find
that a webpage loads sluggishly, a peer-to-peer upload takes somewhat
longer to complete, or a VoIP call sounds choppy. Of course, the
same thing could happen to the customers on a port that is congested
in the absence of any congestion management; the difference here is
that the effects of any such delays are shifted toward those who have
been placing the greatest burden on the network, instead of being
distributed randomly among the users of that port without regard to
their consumption levels. As a matter of fact, our studies concluded
that the experience of the PBE subscribers improves when this
congestion management system is enabled. This conclusion is based on
network measurements, such as latency.
NetForecast explored the potential risk of a worst-case scenario for
users whose traffic is in a BE state: the possibility of "bandwidth
starvation" in the theoretical case where 100 percent of the CMTS
bandwidth is taken up by PBE traffic for an extended period of time.
In theory, such a condition could mean that a given user whose
traffic is designated BE would be unable to effectuate an upload or
download (as noted above, both are managed separately) for some
period of time. However, when these management techniques were
tested, first in company testbeds and then in our real-world trials
conducted in the five markets (further validated in our full
deployment), such a theoretical condition did not occur. In
addition, our experience with the system as fully deployed in our
production network demonstrates that these management practices have
very modest real-world impacts. In addition, Comcast did not receive
a single customer complaint, in any of the trial markets, that could
be traced to this congestion management system, despite having
broadly publicized these trials. In our subsequent national
deployment into our production network, we still have yet to find a
specific complaint that can be traced back to the effect of this
congestion management system.
Comcast continues to monitor how user traffic is affected by these
new congestion management techniques and will make the adjustments
necessary to ensure that all Comcast HSI customers have a high-
quality Internet experience.
7.4. Equipment/Software Used and Location
The above-mentioned functions are carried out using three different
types of application servers, supplied by three different vendors.
As mentioned above, these servers are installed near Comcast's
regional network routers. The exact locations of these servers are
not particularly relevant to this document, as this information does
not change the fact that the servers manage individual CMTS ports.
The first application server is an IPDR server, which collects
relevant cable modem volume usage information from the CMTS, such as
how many aggregate upstream or downstream bytes a subscriber uses
over a particular period of time. IPDR has been adopted as a
standard by many industry organizations and initiatives, such as
CableLabs, the Alliance for Telecommunications Industry Solutions
(ATIS), the International Telecommunication Union (ITU), and the
Third Generation Partnership Project (3GPP), among others. The IPDR
software deployed was developed by Active Broadband Networks, and is
noted as the Statistics Collection Server in Figure 3.
The second application server is the Congestion Management server,
which uses the Simple Network Management Protocol (SNMP) [RFC3410] to
measure CMTS port utilization and detect when a port is in a Near
Congestion State. When this happens, the Congestion Management
server then queries the relevant IPDR data for a list of cable modems
meeting the criteria set forth above for being in an Extended High
Consumption State. The Congestion Management server software
deployed was developed by Sandvine.
If one or more users meet the criteria to be managed, then the
Congestion Management server notifies a third application server, the
PCMM application server, as to which users have been in an Extended
High Consumption State and whose traffic should be treated as BE.
The PCMM servers are responsible for signaling a given CMTS to set
the traffic for specific cable modems with a BE QoS, and for tracking
and managing the state of such CMTS actions. If no users meet the
criteria to be managed, no users will have their traffic managed.
The PCMM software deployed was developed by Camiant, and is noted as
the QoS Server in Figure 3.
Figure 3 graphically depicts the high-level management flows among
the congestion management components on Comcast's network, as
described above:
Figure 3: Simplified Diagram Showing High-Level Management Flows
Relevant to the System
+---------------+ +---------------+
| Congestion | Instruct QoS Server | QoS |
| Management |******to Change QoS for****>| Server |
| Server | a Device | |
+----+---+------+ +-------+-------+
/\ /\ *
| | Relay Selected *
X +---Statistics: Bytes---+ QoS Action:
| Up/Down by Device | Change from PBE
X +-------+-------+ to BE, or from
| | Statistics | BE to PBE
X | Collection | *
Periodic SNMP | Server | *
Requests to +---------------+ *
Check CMTS Port /\ *
Utilization | *
Levels Statistics Sent *
| Periodically From CMTS *
X | *
| +-----------+-----------+ *
+-X-X-X-X-X-X->| CMTS in Headend |<********
+-----------------------+
H /\ /\ H
H Internet Traffic H
H to/from User H
H \/ \/ H
/+---------------------+\
/ | User's +---------+ |\
/ | Home | Cable | | \
| | Modem | |
============ | +---------+ |
= Notes: = +----------------------+
= ========================================================
= 1 - Statistics Collection Servers use IP Detail Records (IPDR). =
= 2 - QoS Servers use PacketCable Multimedia (PCMM) =
= to set QoS gates on the CMTS. =
= 3 - This figure is a simplification of the actual network and =
= servers, which included redundancies and other complexities =
= not necessary to depict the functional design. =
===================================================================
Figure 3
8. Conclusion
Comcast started design and development of this new protocol-agnostic
congestion management system in March 2008. Comcast shared the
design with the IETF and others in the Internet community, as well as
with an independent consultant, incorporating feedback we received
into the final design. Following lab testing, the system was tested
in Comcast's production network in trial markets between June and
September 2008. Comcast's production network transition to this new
protocol-agnostic congestion management system began in October 2008
and was completed on December 31, 2008.
As described herein, the new approach does not manage congestion by
focusing on managing the use of specific protocols. Nor does this
approach use TCP "reset packets" [RFC3360]. Rather, the system acts
such that during periods when a CMTS port is in a Near Congestion
State, the system (1) identifies the subscribers on that port who
have consumed a disproportionate amount of bandwidth over the
preceding 15 minutes and (2) lowers the priority status of those
subscribers' traffic to BE status until those subscribers meet the
release criteria. During periods of actual congestion, the system
handles PBE traffic before BE traffic. Comcast's trials and
subsequent national deployment indicate that this new congestion
management system ensures a quality online experience for all of
Comcast's HSI customers.
9. Exceptional Network Utilization Considerations
This system was developed to cope with somewhat "normal" occurrences
of congestion that could occur on virtually any IP network. It
should also be noted, however, that such a system could also prove
particularly useful in the case of "exceptional network utilization"
events that existing network usage models do not or cannot accurately
predict. Some network operators refer to these exceptional events as
"surges" in utilization, similar to sudden surges in demand in
electrical power grids, with which many people may be familiar.
For example, in the case of a severe global pandemic, it may be
expected that large swaths of the population may need to work
remotely, via their Internet connection. In such a case, a largely
unprecedented level of utilization may occur. In such cases, it may
be helpful to have a flexible congestion management system that could
adapt to this situation and help allocate network resources while
additional capacity is being brought online or while a temporary
condition persists.
10. Limitations of This Congestion Management System
The main limitations of the system include:
o The system is not an end-to-end congestion management system, nor
does it enable one.
o The system does not signal the presence of congestion to user
applications or to all devices on the network path.
o The system does not explicitly enable additional user and/or
application responses to congestion.
o The system does not enable distributed denial-of-service (DDoS)
mitigation or other capabilities.
11. Low Extra Delay Background Transport and Other Possibilities
There are several new IETF working group efforts that are focused on
the question of congestion and its effects, avoiding congestion,
managing congestion, and communicating congestion information. This
includes the Congestion Exposure (CONEX) working group, the
Application Layer Transport Optimization (ALTO) working group, and
the Low Extra Delay Background Transport (LEDBAT) working group.
Should one or more of these working groups be successful in producing
useful work, it is possible that the design or configuration of the
system documented here may need to change. For example, this
congestion management system does not currently have a way to take
into account differing classes of data transfer, such as a class of
data transfer that LEDBAT may specify, which may better yield to
other traffic than existing transport protocols. In addition, CONEX
may specify methods for this or other systems to signal congestion
state or expected congestion to other parts of the network, and/or to
hosts on either end of a particular network flow. Furthermore, it is
conceivable that the result of current or future IETF work could
obviate the need for such a congestion management system entirely.
12. Security Considerations
It is important that an ISP secure access to the Congestion
Management servers and the QoS Servers, as well as QoS signaling to
the CMTSs, so that unauthorized users and/or hosts cannot make
unauthorized changes to QoS settings in the network.
It is also important to secure access to the Statistics Collection
Server since this contains IPDR-based byte transfer data that is
considered private by end users on an individual basis. In addition,
this data is considered ISP-proprietary traffic data on an aggregate
basis. Access to the Statistics Collection Server should also be
secured so that false usage statistics cannot be fed into the system.
It is important to note that IPDR data contains a count of bytes sent
and bytes received, by cable modem MAC address, over a given interval
of time. This data does not contain things such as the source and/or
destination Internet address of that data, nor does it contain the
protocols used, ports used, etc.
13. Acknowledgements
The authors wish to acknowledge the hard work of the many people who
helped to develop and/or review this document, as well as the people
who helped deploy the system in such a short period of time.
The authors also wish to acknowledge the following individuals for
performing a detailed review of this document and/or providing
comments and feedback that helped to improve and evolve this
document:
- Kris Bransom
- Bob Briscoe
- Lars Eggert
- Ari Keranen
- Tero Kivinen
- Matt Mathis
- Stanislav Shalunov
14. Informative References
[COMCAST_P2PI_PAPER]
Livingood, J. and R. Woundy, "Comcast's IETF P2P
Infrastructure Workshop Position Paper", FCC
Filings Comcast Network Management Proceedings, May 2008,
<http://trac.tools.ietf.org/area/rai/trac/raw-attachment/
wiki/PeerToPeerInfrastructure/
16%20ietf-p2pi-comcast-20080509.pdf>.
[COMCAST_P2PI_PRES]
Livingood, J. and R. Woundy, "Comcast's IETF P2P
Infrastructure Workshop Presentation on May 28, 2008",
FCC Filings Comcast Network Management Proceedings,
May 2008,
<http://trac.tools.ietf.org/area/rai/trac/raw-attachment/
wiki/PeerToPeerInfrastructure/02-Comcast-IETF-P2Pi.pdf>.
[DOCSIS_CM2CPE]
CableLabs, "Data-Over-Cable Service Interface
Specifications - DOCSIS 3.0 - Cable Modem to Customer
Premise Equipment Interface Specification", DOCSIS
3.0 CM-SP-CMCIv3-I01-080320, March 2008,
<http://www.cablelabs.com/cablemodem/specifications/
specifications30.html>.
[DOCSIS_IPDR]
Yassini, R., "Data-Over-Cable Service Interface
Specifications - DOCSIS 2.0 - Operations Support System
Interface Specification", DOCSIS 2.0 CM-SP-OSSIv2.0-C01-
081104, November 2008, <http://www.cablelabs.com/
cablemodem/specifications/specifications30.html>.
[DOCSIS_MULPI]
CableLabs, "Data-Over-Cable Service Interface
Specifications - DOCSIS 3.0 - MAC and Upper Layer
Protocols Interface Specification", DOCSIS 3.0 CM-SP-
MULPIv3.0-I11-091002, October 2009, <http://
www.cablelabs.com/cablemodem/specifications/
specifications30.html>.
[DOCSIS_OSSI]
CableLabs, "Data-Over-Cable Service Interface
Specifications - DOCSIS 3.0 - Operations Support System
Interface Specification", DOCSIS 3.0 CM-SP-OSSIv3.0-I10-
091002, October 2009, <http://www.cablelabs.com/
cablemodem/specifications/specifications30.html>.
[DOCSIS_PHY]
CableLabs, "Data-Over-Cable Service Interface
Specifications - DOCSIS 3.0 - Physical Layer
Specification", DOCSIS 3.0 CM-SP-PHYv3.0-I08-090121,
January 2009, <http://www.cablelabs.com/cablemodem/
specifications/specifications30.html>.
[DOCSIS_SEC]
CableLabs, "Data-Over-Cable Service Interface
Specifications - DOCSIS 3.0 - Security Specification",
DOCSIS 3.0 CM-SP-SECv3.0-I11-091002, March 2008, <http://
www.cablelabs.com/cablemodem/specifications/
specifications30.html>.
[FCC_Congest_Mgmt_Ltr]
Zachem, K., "Letter to the FCC Advising of Successful
Deployment of Comcast's New Congestion Management
System", FCC Filings Comcast Network Management
Proceedings, January 2009,
<http://fjallfoss.fcc.gov/ecfs/document/
view?id=6520192582>.
[FCC_Memo_Opinion]
Martin, K., Copps, M., Adelstein, J., Tate, D., and R.
McDowell, "FCC Memorandum and Opinion Regarding
Reasonable Network Management", File No. EB-08-IH-1518 WC
Docket No. 07-52, August 2008,
<http://hraunfoss.fcc.gov/
edocs_public/attachmatch/FCC-08-183A1.pdf>.
[FCC_Net_Mgmt_Response]
Zachem, K., "Letter to the FCC Regarding Comcast's
Network Management Practices", FCC Filings Comcast
Network Management Proceedings, September 2008, <http://
fjallfoss.fcc.gov/ecfs/document/view?id=6520169715>.
[IPDR_Standard]
Cotton, S., Cockrell, B., Walls, P., and T. Givoly,
"Network Data Management - Usage (NDM-U) For IP-Based
Services. Service Specification - Cable Labs DOCSIS 2.0
SAMIS", IPDR Service Specifications NDM-U, November 2004,
<http://www.ipdr.org/public/Service_Specifications/3.X/
DOCSIS(R)3.5-A.0.pdf>.
[PowerBoost_Specification]
Comcast Cable Communications Management LLC, "Comcast
PowerBoost Specification", Website Comcast.com,
June 2010, <http://customer.comcast.com/Pages/
FAQListViewer.aspx?topic=Internet&
folder=8b2fc392-4cde-4750-ba34-051cd5feacf0>.
[RFC1633] Braden, B., Clark, D., and S. Shenker, "Integrated
Services in the Internet Architecture: an Overview",
RFC 1633, June 1994.
[RFC2475] Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z.,
and W. Weiss, "An Architecture for Differentiated
Services", RFC 2475, December 1998.
[RFC3083] Woundy, R., "Baseline Privacy Interface Management
Information Base for DOCSIS Compliant Cable Modems and
Cable Modem Termination Systems", RFC 3083, March 2001.
[RFC3360] Floyd, S., "Inappropriate TCP Resets Considered Harmful",
BCP 60, RFC 3360, August 2002.
[RFC3410] Case, J., Mundy, R., Partain, D., and B. Stewart,
"Introduction and Applicability Statements for Internet-
Standard Management Framework", RFC 3410, December 2002.
[RFC5594] Peterson, J. and A. Cooper, "Report from the IETF
Workshop on Peer-to-Peer (P2P) Infrastructure, May 28,
2008", RFC 5594, July 2009.
Authors' Addresses
Chris Bastian
Comcast Cable Communications
One Comcast Center
1701 John F. Kennedy Boulevard
Philadelphia, PA 19103
US
EMail: chris_bastian@cable.comcast.com
URI: http://www.comcast.com
Tom Klieber
Comcast Cable Communications
1306 Goshen Parkway
West Chester, PA 19380
US
EMail: tom_klieber@cable.comcast.com
URI: http://www.comcast.com
Jason Livingood
Comcast Cable Communications
One Comcast Center
1701 John F. Kennedy Boulevard
Philadelphia, PA 19103
US
EMail: jason_livingood@cable.comcast.com
URI: http://www.comcast.com
Jim Mills
Comcast Cable Communications
One Comcast Center
1800 Bishops Gate Drive
Mount Laurel, NJ 08054
US
EMail: jim_mills@cable.comcast.com
URI: http://www.comcast.com
Richard Woundy
Comcast Cable Communications
27 Industrial Avenue
Chelmsford, MA 01824
US
EMail: richard_woundy@cable.comcast.com
URI: http://www.comcast.com