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rfc:rfc6057

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.

Bastian, et al. Informational [Page 1] RFC 6057 An ISP Congestion Management System December 2010

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

Bastian, et al. Informational [Page 2] RFC 6057 An ISP Congestion Management System December 2010

 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,

Bastian, et al. Informational [Page 3] RFC 6057 An ISP Congestion Management System December 2010

 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].

Bastian, et al. Informational [Page 4] RFC 6057 An ISP Congestion Management System December 2010

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".

Bastian, et al. Informational [Page 5] RFC 6057 An ISP Congestion Management System December 2010

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.

Bastian, et al. Informational [Page 6] RFC 6057 An ISP Congestion Management System December 2010

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

Bastian, et al. Informational [Page 7] RFC 6057 An ISP Congestion Management System December 2010

 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.

Bastian, et al. Informational [Page 8] RFC 6057 An ISP Congestion Management System December 2010

    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

Bastian, et al. Informational [Page 9] RFC 6057 An ISP Congestion Management System December 2010

 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

Bastian, et al. Informational [Page 10] RFC 6057 An ISP Congestion Management System December 2010

 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:

Bastian, et al. Informational [Page 11] RFC 6057 An ISP Congestion Management System December 2010

 Figure 1: Simplified Network Diagram Showing High-Level Comcast
 Network and Servers Relevant to Congestion Management
  1. ————————

/ \

                          | 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
     |             |                  |                       |
     \/            \/                 \/                      \/

Bastian, et al. Informational [Page 12] RFC 6057 An ISP Congestion Management System December 2010

 +---------+   +---------+       +---------+             +---------+
 | 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:

Bastian, et al. Informational [Page 13] RFC 6057 An ISP Congestion Management System December 2010

 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

Bastian, et al. Informational [Page 14] RFC 6057 An ISP Congestion Management System December 2010

 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

Bastian, et al. Informational [Page 15] RFC 6057 An ISP Congestion Management System December 2010

 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

Bastian, et al. Informational [Page 16] RFC 6057 An ISP Congestion Management System December 2010

 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.

Bastian, et al. Informational [Page 17] RFC 6057 An ISP Congestion Management System December 2010

 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-------------+

Bastian, et al. Informational [Page 18] RFC 6057 An ISP Congestion Management System December 2010

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

Bastian, et al. Informational [Page 19] RFC 6057 An ISP Congestion Management System December 2010

 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

Bastian, et al. Informational [Page 20] RFC 6057 An ISP Congestion Management System December 2010

 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.

Bastian, et al. Informational [Page 21] RFC 6057 An ISP Congestion Management System December 2010

 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

Bastian, et al. Informational [Page 22] RFC 6057 An ISP Congestion Management System December 2010

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.

Bastian, et al. Informational [Page 23] RFC 6057 An ISP Congestion Management System December 2010

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

Bastian, et al. Informational [Page 24] RFC 6057 An ISP Congestion Management System December 2010

 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:
  1. Kris Bransom
  1. Bob Briscoe
  1. Lars Eggert
  1. Ari Keranen
  1. Tero Kivinen
  1. Matt Mathis
  1. Stanislav Shalunov

Bastian, et al. Informational [Page 25] RFC 6057 An ISP Congestion Management System December 2010

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>.

Bastian, et al. Informational [Page 26] RFC 6057 An ISP Congestion Management System December 2010

 [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>.

Bastian, et al. Informational [Page 27] RFC 6057 An ISP Congestion Management System December 2010

 [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.

Bastian, et al. Informational [Page 28] RFC 6057 An ISP Congestion Management System December 2010

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

Bastian, et al. Informational [Page 29]

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