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
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
康卡斯特的协议无关拥塞管理系统
Abstract
摘要
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.
本文件描述了美国大型有线宽带互联网服务提供商（ISP）Comcast Cable的拥塞管理系统。Comcast于2008年12月31日完成了该拥塞管理系统的部署。
Status of This Memo
关于下段备忘
This document is not an Internet Standards Track specification; it is published for informational purposes.
本文件不是互联网标准跟踪规范；它是为了提供信息而发布的。
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.
本文件是互联网工程任务组（IETF）的产品。它代表了IETF社区的共识。它已经接受了公众审查，并已被互联网工程指导小组（IESG）批准出版。并非IESG批准的所有文件都适用于任何级别的互联网标准；见RFC 5741第2节。
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.
有关本文件当前状态、任何勘误表以及如何提供反馈的信息，请访问http://www.rfc-editor.org/info/rfc6057.
Copyright Notice
版权公告
Copyright (c) 2010 IETF Trust and the persons identified as the document authors. All rights reserved.
版权所有（c）2010 IETF信托基金和确定为文件作者的人员。版权所有。
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.
本文件受BCP 78和IETF信托有关IETF文件的法律规定的约束(http://trustee.ietf.org/license-info)自本文件出版之日起生效。请仔细阅读这些文件，因为它们描述了您对本文件的权利和限制。从本文件中提取的代码组件必须包括信托法律条款第4.e节中所述的简化BSD许可证文本，并提供简化BSD许可证中所述的无担保。
Table of Contents
目录
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 ....................................................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
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.
Comcast Cable是一家大型宽带互联网服务提供商（ISP），总部位于美国，通过电缆调制解调器技术为其大多数客户提供服务。2008年下半年，康卡斯特在其整个网络上部署了一个新的拥塞管理系统，并于2008年12月31日完成。这一新系统是针对互联网社区的不满以及美国联邦通信委员会（FCC）对Comcast旧系统的投诉而开发的，该系统针对特定的对等（P2P）应用。这种新的拥塞管理系统与协议无关，这意味着它不会检查或影响特定的用户应用程序或网络协议，这被认为是在可能发生拥塞的有限时间内管理网络资源的更公平的系统。
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
读者需要注意的是，任何IP网络都可能发生拥塞，当拥塞发生时，数据包可能会被延迟或丢弃。正如Bob Briscoe在IETF邮件列表中指出的，一些数据包丢失是正常的和/或可以容忍的，注意到“但是一个往返时间（RTT）为80毫秒的TCP流可以达到50 Mbps，丢失率为0.0013%（约74000个数据包中有1个），因此没有必要尝试实现比这低得多的丢失率。事实上，如果
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.
在其他地方，流量不会受到限制，TCP将驱动系统，直到达到这样的损失水平。相反，如果客户下载五个单独的10 Mbps TCP流，并且仍然使用80 ms RTT，TCP将导致高达1/3000的损失，即0.03%，任何较低的损失率都无法提高性能“。因此，应用程序和协议的设计是为了应对任何IP网络都可能发生拥塞的现实，我们将在本文档后面详细解释其机制。
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.
本文档的目的是描述这个大规模拥塞管理系统的示例是如何工作的。这部分是为了回答其他ISP以及解决方案开发人员提出的问题，他们对学习和/或在其他网络中部署类似系统感兴趣。此外，希望这样一份文件有助于为IETF中的新工作提供信息，以期在未来可能有更好的系统和协议。最后，作者希望以透明和公开的方式记录该系统，这样就可以毫无疑问地了解该系统的功能。
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.
几位文件评审员和其他IETF参与者指出，尽管我们提到的功能元素特定于基于数据电缆服务接口规范（DOCSIS）的网络实现，但这种类型的拥塞管理系统通常可以应用于几乎任何类型的网络。因此，读者必须注意这一点，并考虑到这种协议无关的拥塞管理系统肯定可以适用于各种各样的网络类型和实现。
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.
本节定义了本文件中使用的关键术语。以下一些术语指康卡斯特网络的要素。因此，在查看其中一些术语时，参考图1（参见第7节）可能会有所帮助。
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,
位于客户场所的用于访问康卡斯特高速互联网（HSI）网络的设备。在某些情况下，电缆调制解调器归客户所有，而在其他情况下，则归电缆运营商所有。该设备有一个接口（即插入电缆的地方），用于将电缆公司提供的同轴电缆连接到调制解调器，以及一个或多个接口，用于将调制解调器连接到客户的PC或家庭网关设备（例如，家庭网关、，
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.
路由器、防火墙、接入点等）。在某些情况下，电缆调制解调器功能，即访问互联网的能力，被集成到家庭网关设备或嵌入式多媒体终端适配器（eMTA）中。连接后，电缆调制解调器将客户连接到HSI网络，最终连接到更广泛的互联网。
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.
位于有线电视运营商本地网络（通常位于“前端”，第3.10节）中的一块硬件，用作特定地理区域内有线电视调制解调器的互联网网关。一种简单的方法是将CMT视为路由器，在所谓的“最后一英里”网络中，一端的接口通向互联网，另一端的接口连接到光节点，然后连接到客户。
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].
也称为“端口”。端口是设备上的物理接口，用于连接电缆，以便与其他设备连接以传输信息/数据。物理端口的一个示例是CMTS端口。CMT同时具有上游和下游网络接口以服务于本地接入网络，这些接口被称为上游或下游端口。一个港口通常服务于数百户人家的社区。随着时间的推移，CMTS端口往往为越来越少的家庭提供服务，因为网络是为了容量增长而分割的。在DOCSIS版本3之前，单个CMTS物理端口用于向给定邻域的下游或上游发送或接收数据。使用DOCSIS版本3和通道绑定功能，可以组合多个CMT物理端口来创建虚拟端口。[RFC3083]第2.6节也简要定义了CMT。
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].
一种组合多个下游和/或上游渠道的技术，分别提高客户的下载和/或上传速度。来自混合光纤同轴电缆（HFC）网络（第3.11节）的多个信道可以绑定到单个虚拟端口（称为绑定组）中，该虚拟端口充当大型单个信道或端口，为客户提供更高的速度。信道连接是电缆数据服务接口规范（DOCSIS）第3版的一项功能，如[DOCSIS_MULPI]所述。
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.
电缆运营商使用的一种电缆，用于将用户端设备（CPE）连接到HFC网络，如电视、电缆调制解调器（包括EMTA）和机顶盒。该电缆可在家庭内使用，也可在“最后一英里”网络中连接到家庭或客户场所。有许多等级的同轴电缆用于不同的用途。不同类型的同轴电缆用于网络上的不同用途。
A service/product offered by Comcast for delivering Internet service over a broadband connection.
康卡斯特提供的通过宽带连接提供互联网服务的服务/产品。
Any device that resides at the customer's residence, connected to the Comcast network, whether controlled by Comcast or not.
驻留在客户住所、连接到康卡斯特网络的任何设备，无论是否由康卡斯特控制。
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.
由CableLabs开发的参考标准，规定需要如何构建电缆网络上的组件，以实现HFC网络上的HSI服务，如[DOCSIS_CM2CPE]、[DOCSIS_PHY]、[DOCSIS_MULPI]、[DOCSIS_SEC]和[DOCSIS_OSSI]中所述。这些标准定义了电缆调制解调器和CMT的规范，使得任何DOCSIS认证的电缆调制解调器都可以在任何DOCSIS认证的CMT上工作，而不依赖于选定的供应商。有线调制解调器和CMTS的互操作性允许客户从零售店购买经DOCSIS认证的调制解调器，并在有线网络家庭中使用。所有与DOCSIS相关的标准均可在CableLabs网站上获得，网址为http://www.cablelabs.com.
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.
信号传播方向的描述，在这种情况下，从网络到用户。下游流量发生在用户从Internet下载内容时，例如观看基于web的视频、阅读网页或下载软件更新。
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".
负责接收电视信号并通过HFC网络分配给终端客户的电缆设施。该设施通常还容纳一个或多个CMT。这有时也称为“枢纽”。
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].
主要由电缆公司使用的网络架构，由光纤和同轴电缆组成，目前向客户提供语音、视频和互联网服务，如[DOCSIS_MULPI]第1.2节所定义。
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].
基于有线调制解调器监控和/或记录用户上下游互联网使用数据的标准化技术。数据从CMT收集并发送到服务器进行进一步处理。有关更多信息，请访问http://www.ipdr.org，以及[IPDR_标准]和[DOCSIS_IPDR]。
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.
HFC网络的一个组件，通常位于客户的本地区，用于将通过光纤电缆发送的光信号转换为可通过同轴电缆发送到客户电缆调制解调器的电信号，反之亦然。光纤电缆通过分配集线器将光纤节点连接到CMT，同轴电缆将光纤节点连接到客户的电缆调制解调器。
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.
与客户购买的服务级别相关的峰值速度。例如，具有105 Mbps下游和10 Mbps上游速度层的客户将被称为配备了105 Mbps下游带宽和10 Mbps上游带宽。在行业术语中，这通常被称为105/10服务。
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.
所提供的带宽是客户调制解调器配置（以及网络设计）以定期提供的速度（与“提交的信息速率”或保证速率不同）。互联网速度通常是一种尽力而为的服务，它取决于许多变量，其中许多变量不受互联网服务提供商（ISP）的控制。通常，速度通常不会超过客户提供的速度。然而，Comcast发明了一种称为“PowerBoost”[PowerBoost_Specification]的技术，例如，通过利用当时网络中可能存在的过剩容量，用户在通过互联网传输大型文件时，可以体验到超过其配置速度的短暂提升。
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.
一组管理网络资源的技术，以确保特定数据流的性能水平，如[RFC1633]和[RFC2475]中所述。向网络提供QoS的一种方法是按类别或流量区分流量类型，并为每种类型分配优先级。当网络变得拥挤时，被标记为具有更高优先级的数据分组将具有更高的被服务的可能性。
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.
信号传播方向的描述，在这种情况下是从用户到网络。上游流量发生在用户向网络上传内容时，例如发送电子邮件、将文件发送到另一台计算机或将照片上载到数字照片网站。
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.
Comcast于2008年3月开始开发新的拥塞管理系统的工程项目，同一个月Comcast在美国宾夕法尼亚州费城主办了IETF第71次会议。2008年5月28日，Comcast参加了由麻省理工学院（MIT）主办的IETF点对点基础设施研讨会[RFC5594]在美国马萨诸塞州剑桥市。
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.
为了参加本次研讨会，要求感兴趣的与会者向技术审查小组提交一份论文，康卡斯特于2008年5月9日在[Comcast_P2PI_论文]中提交了该论文。康卡斯特随后出席并参加了这次宝贵的研讨会。研讨会期间，Comcast概述了新拥塞管理系统[Comcast_P2PI_PRES]的高级设计，并征求与会者和互联网社区其他成员的意见和其他反馈（演示文稿也发布到IETF的P2PI邮件列表中）。2008年5月研讨会上概述的拥堵管理系统后来在试验市场上进行了测试，本质上是康卡斯特在2008年晚些时候部署的。
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
2008年8月，美国联邦通信委员会发布了一份关于康卡斯特如何管理高速互联网（“HSI”）网络拥塞的文件[FCC_备忘录_意见]，康卡斯特随后向FCC[FCC_Net_Mgmt_Response]和公众披露了其计划在2008年底之前实施的拥塞管理系统的其他技术细节[FCC_拥塞_管理_Ltr]，包括本新协议中涉及的阈值
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.
系统虽然对该系统在康卡斯特网络中的部署方式的描述必然特定于该网络的各种技术和设计，但类似的系统几乎可以部署在任何大型ISP网络或其他IP网络上。
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.
康卡斯特的HSI网络有许多用户共享的元素。这意味着康卡斯特的HSI客户与其邻居共享上游和下游带宽。虽然可用带宽很大，但需求也很大。因此，当一个社区中相对较少的客户对网络资源的需求不成比例时，这可能会导致拥塞，从而降低其邻居的互联网体验。康卡斯特新的拥塞管理系统的目标是使我们网络资源的所有用户都能够访问该带宽的“公平份额”，以确保康卡斯特所有HSI客户的高质量在线体验。
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.
重要的是，新方法与协议无关；也就是说，它不会通过关注对网络资源造成不成比例负担的特定协议或任何其他协议的使用来管理拥塞。相反，新方法侧重于管理那些在网络拥塞威胁降低用户宽带体验时使用最多带宽的个人的流量，这些人在这些时间点对此类拥塞的贡献不成比例。
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:
关于这些实践的具体细节，包括相关阈值信息、使用的设备类型和其他细节，将在本文件后面进行详细讨论。然而，在一开始，我们对这些实践如何工作给出了一个非常高层次的、简化的概述。尽管下文提供了所有详细信息，但该方法的基本原理可以简单总结：
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.
1. 康卡斯特网络中安装的软件持续检查康卡斯特HSI网络各个部分的总流量使用数据。如果康卡斯特HSI网络特定部分的整体上游或下游使用率达到预定水平，软件将进入第二步。
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.
2. 在第二步，软件检查受影响网段中订户的带宽使用数据，以确定哪些订户正在使用不成比例的带宽份额。
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.
如果软件确定某个或多个特定订阅者在最近几分钟内是高流量网络流量的来源，则来自该订阅者或这些订阅者的流量将被临时分配为较低优先级状态。
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.
3. 在用户的通信量被分配较低优先级状态期间，只要网段没有实际拥塞，他们的数据包就不会被延迟或丢弃。然而，如果网段变得拥挤，其数据包可能会间歇性延迟或丢弃。
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.
4. 一旦用户的带宽使用率在特定时间间隔内下降到设定阈值以下，用户的通信量将恢复到正常优先级状态。
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.
康卡斯特在几个月的时间里做出了相当大的努力，为这种拥堵管理方法制定了我们的计划，对其进行了调整，并进行了实际试验。在宾夕法尼亚州的昌伯斯堡进行了市场试验；弗吉尼亚州沃伦顿；佛罗里达州湖城；佛罗里达州东橙；2008年6月至9月，科罗拉多州斯普林斯市。这使我们能够验证通用方法的效用，并收集大量试验数据，以测试多种变体和替代配方。
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.
许多人质疑，如果ISP增加了足够的容量，拥塞是否会存在。容量和拥挤之间肯定有关系。但在网络中通常会出现两种类型的拥塞。
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.
第一种一般类型的拥堵是经常发生的，是交通量逐渐增加到一定程度的结果，典型的使用高峰会定期导致拥堵。Comcast和许多ISP一样，有一套容量管理流程，根据特定的使用趋势自动触发容量增加；这一过程旨在在经常发生拥塞之前为网络带来额外的容量。因此，容量会在需要时和出现明显效果之前添加。这一过程已经到位，因为容量的增加不是瞬时的，在许多情况下需要大量的体力劳动。
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
第二种常见的拥塞类型是不可预测的拥塞，其发生的原因非常广泛。一个例子可能是由于当前的事件，其中用户可能都在同一时间匆忙访问特定内容，而服务于该内容的系统
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.
内容可能跟不上需求。另一个例子可能是由于局部灾难，其中一些网络路径已被破坏或以其他方式受损，并且许多用户正试图以显著高于正常水平的通信量彼此通信。
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.
因此，在这两种情况下，即使不断升级和不断投资于额外容量，事实仍然是网络容量不是无限的。因此，如果没有目前尚不存在的基于高级协议的解决方案，拥塞管理系统可以帮助管理拥塞对用户的影响，改善他们的互联网体验。
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.
需要注意的是，下面的实施细节和系统的总体设计与当前互联网上存在的流量模式相匹配，作者相信在不久的将来会存在这种模式。虽然作者希望使系统具有高度适应性和良好的长期网络投资，但此类流量模式的重大变化可能需要改变系统的配置，或者在极端情况下，需要完全不同类型的系统。
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.
为了准确了解这些新的拥塞管理实践是如何工作的，全面了解康卡斯特HSI网络的设计是很有帮助的。康卡斯特的HSI网络通常被称为混合光纤同轴网络，同轴电缆将每个用户的电缆调制解调器连接到一个光节点，光纤电缆通过分配集线器将光节点连接到电缆调制解调器终端系统（CMTS），该系统也称为“数据节点”。然后，CMTS连接到更高级别的路由器，路由器又连接到康卡斯特的互联网主干设施。今天，康卡斯特在我们的网络中部署了3200多个CMT，为1500多万HSI用户提供服务。
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
每个CMT都有多个“端口”，用于处理进出CMT的流量。特别是，部署在Comcast HSI网络上的每个电缆调制解调器都通过CMT上的端口连接到CMT。这些端口可以是“下游”端口或“上游”端口，具体取决于它们是向电缆调制解调器（下游）发送信息，还是从连接到端口的电缆调制解调器（上游）接收信息。（注意，此处使用的术语“端口”通常考虑CMT上的单个信道，但这些语句将适用于虚拟信道，也称为“绑定”
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.
在DOCSIS 3.0环境中），即使没有通道绑定，通常也会将多个通道配置为从每个物理端口出来。换句话说，通常会有多个通道到每个物理端口的映射。
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.
目前，平均约275个电缆调制解调器共享同一下游端口，约100个电缆调制解调器共享同一上游端口；然而，这是不断变化的（根据当前的DOCSIS技术，这两个数字通常随着时间的推移而变小）。这两种类型的端口都可能出现拥塞，这可能会降低我们用户的宽带体验，并且与以前的拥塞管理实践不同，在这种新的拥塞管理系统中，上游和下游流量都受到管理。
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).
根据网络设计和观察到的流量模式，最有可能发生拥塞的地方是这些CMTS端口。因此，拥塞管理系统测量CMTS端口的流量状况，并对这些端口上的流量（而不是网络中其他较远的部分）应用任何策略操作。
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.
为了实施康卡斯特新的协议无关拥塞管理实践，康卡斯特购买了新的硬件和软件，部署在康卡斯特网络更上游的区域网络路由器（“RNR”）附近。这种新的硬件包括互联网协议详细记录（“IPDR”）服务器、拥塞管理服务器和PacketCable多媒体（“PCMM”）服务器。有关这些设备的详细信息，请参见下文第7.4节。然而，这里需要注意的是，即使这些服务器的物理位置位于RNR，这些服务器也与多个CMT上的多个端口通信，并单独管理这些端口，以实现本文档中描述的实践。也就是说，一个CMTS端口上的带宽使用将不会影响本文描述的拥塞管理实践是否应用于不同CMTS端口上的订户。
Figure 1 provides a simplified graphical depiction of the network architecture just described:
图1提供了刚才描述的网络体系结构的简化图形描述：
Figure 1: Simplified Network Diagram Showing High-Level Comcast
图1：显示高级Comcast的简化网络图
Network and Servers Relevant to Congestion Management
与拥塞管理相关的网络和服务器
-------------------------
/ \
| 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
| | | |
\/ \/ \/ \/
-------------------------
/ \
| 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 =
+=======+ +=======+ +=======+ +=======+ +=======+ +=======+
+---------+ +---------+ +---------+ +---------+
| 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. +
================================================================
================================================================
+ 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
图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.
每个Comcast HSI用户的电缆调制解调器都有一个“引导文件”，它本质上是一个配置文件，包含有关用户服务的某些信息，以确保服务正常运行。（注意：引导文件中不包含任何个人信息；它只包含订阅者购买的服务的信息。）例如，引导文件包含特定调制解调器基于层可以实现的最大速度（我们在本文档中称为“配置带宽”）的信息（个人/住宅、商业等）客户已购买。引导文件通常会根据网络变化和其他更新情况不时重置，这通常通过网络发送的命令完成，而订阅者不会注意到。为了准备过渡到新的拥塞管理系统，Comcast向我们的HSI发送了新的引导文件客户的电缆调制解调器为进出电缆调制解调器的互联网流量创建了两个服务质量（QoS）级别：（1）“优先尽力而为”（PBE）流量；（2）“尽力而为”（BE）与以前对电缆调制解调器引导文件的更改一样，用新引导文件替换旧引导文件不需要康卡斯特客户的积极参与。
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:
此后，所有进出康卡斯特HSI网络上电缆调制解调器的通信量被指定为PBE或BE。PBE是来自或前往特定电缆调制解调器的所有Internet流量的默认状态。仅当满足以下两个条件时，才为特定电缆调制解调器指定通信量：
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 首先，在特定时间段内测量的CMT特定上游或下游端口的使用水平必须接近拥塞可能降低用户体验的点。我们将其称为“接近拥塞状态”，并根据我们进行的技术试验（在我们的全面部署中进一步验证），确定了特定CMTS端口何时进入该状态的阈值，下文将对此进行更详细的描述。
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.
o 第二，特定订户必须对特定端口上的带宽使用做出更大、更高的贡献，相对于他们购买的服务层，这是在特定时间段内测量的。我们将其称为“扩展高消耗状态”，并且根据我们进行的技术试验（在我们的全面部署中进一步验证），我们已经为特定用户进入该状态确定了一个阈值，下面将对此进行更详细的描述。
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.
当且仅当两个条件都满足时，用户的上游或下游流量（取决于处于接近拥塞状态的端口类型）被指定为BE。然后，在实际发生拥塞的情况下，由拥塞引起的任何延迟将在影响PBE流量之前影响BE流量。
We now explain the foregoing in greater detail in the following sections.
现在，我们将在以下章节中更详细地解释上述内容。
7.1. Thresholds for Determining When a CMTS Port Is in a Near Congestion State
7.1. 用于确定CMTS端口何时处于接近拥塞状态的阈值
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.
要使CMTS端口进入接近拥塞状态，进出该CMTS端口的流量必须在特定时间段（“端口利用持续时间”）内超过指定水平（“端口利用阈值”）。CMTS端口上的端口利用率阈值以特定端口在相关时间段内的总聚合上游或下游带宽的百分比来度量。CMT上的端口使用持续时间以分钟为单位。
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
在经过大量的实验室测试、模拟、技术试验、供应商评估、客户反馈和第三方咨询分析后，已初步确定了作为该拥塞管理技术一部分使用的每个阈值的值。正如调整特定的反垃圾邮件或其他网络管理实践以解决出现的新问题一样，随着康卡斯特收集更多数据并执行新技术的广泛使用而产生的额外分析，这些值几乎肯定会随着时间的推移而改变。而且,
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.
对于任何大型网络或软件系统，可能会出现软件错误和/或意外错误，需要软件补丁或其他纠正措施。与往常一样，康卡斯特在这些问题上的决定是由市场需求驱动的，即我们向HSI用户提供尽可能最好的体验。
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.
根据上述经验，我们确定上游港口利用率阈值的起点应为70%，下游港口利用率阈值应为80%。对于端口利用持续时间，我们确定起始点应为大约15分钟（尽管Comcast网络上部署的一些较新CMT中的一些技术限制可能会使该时间段略有变化）。因此，在任何15分钟的时间段内，如果平均使用了超过70%的端口上游带宽容量或超过80%的端口下游带宽容量，则确定该端口处于接近拥塞状态。
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.
根据迄今为止进行的试验和运营经验，我们HSI网络上的典型CMTS端口仅在一天中相对较小的时间处于接近拥塞状态（如果有的话），尽管无法预测特定端口在特定日期最繁忙的时间。此外，试验数据和运营经验表明，即使某个特定端口处于接近拥塞状态，网络在端口使用期间实际变得拥塞的实例也很少，并且，如下文所述，其数据包可能在这些拥挤时段内间歇性延迟或丢弃的受管用户几乎感觉不到（如果有的话）影响。
7.2. Thresholds for Determining When a User Is in an Extended High Consumption State and for Release from That Classification
7.2. 用于确定用户何时处于扩展高消耗状态以及从该分类中释放的阈值
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
一旦某个特定的CMTS端口处于接近拥塞状态，软件将检查是否有任何电缆调制解调器过度消耗带宽。（注意：虽然每个电缆调制解调器通常分配给特定的家庭，但软件并不也不能实际识别单个用户或共享电缆调制解调器的用户数量，或分析特定用户的流量。）在本文档中，我们使用“电缆调制解调器”、“用户”和“订户”可互换地指订户帐户或用户帐户，而非个人帐户。对于要进入扩展高消耗状态的用户，他或她必须在特定的时间长度（“用户消耗持续时间”）内消耗大于其所提供的上游或下游带宽的某个百分比（“用户消耗阈值”）。用户消耗阈值被测量为用户对其总供应的上游或下游带宽的特定百分比的消耗。那个
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.
带宽是特定调制解调器根据客户购买的层（个人/住宅、商业等）可以达到的最大速度。例如，如果用户购买的服务的下行速度为50 Mbps，上行速度为10 Mbps，则他或她提供的下行速度为50 Mbps，而提供的上行速度为10 Mbps。还需要注意的是，由于用户消耗阈值是特定用户帐户的已配置带宽的百分比，而不是静态值，因此速度更高层的用户具有相应更高的用户消耗阈值。最后，用户消费持续时间以分钟为单位。
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.
经过实验室测试、模拟、技术试验、客户反馈、供应商评估和独立的第三方咨询分析，我们确定用户消费阈值的适当起点为订户提供的上游或下游带宽的70%，用户消费持续时间的适当起点是15分钟（这在我们的全面部署中得到了进一步验证）。也就是说，当订户在特定的15分钟周期内平均使用他或她的供应的上游或下游带宽的70%或更多时，该用户随后处于扩展的高消耗状态。因此，这是基于消耗的阈值，而不是基于峰值速度的阈值。因此，扩展的高消耗状态与用户是否在短时间内爆发一次或多次超过此70%阈值无关。相反，它是基于消耗的，这意味着必须在至少整个用户消耗持续时间内超过某个比特率。
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.
用户消费阈值已设置得足够高，因此仅将HSI连接用于IP语音（VoIP）、游戏、网络冲浪或大多数流式视频不能导致我们的标准级别HSI服务的订户超过用户消费阈值。例如，虽然康卡斯特的一个普通HSI服务层目前的下行带宽为22 Mbps，但Hulu的流媒体视频（甚至一些高清视频）使用低于2.5 Mbps，Vonage或Skype VoIP呼叫使用低于131 kbps，流媒体音乐使用低于128 kbps（在本例中，22 Mbps的70%为15.4 Mbps）。如上所述，这些值可能会根据需要进行更改，就像调整特定的反垃圾邮件或其他网络管理实践以解决出现的新问题，或者如果出现意外的软件错误或其他问题一样。
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
根据从测试新拥堵管理实践的试验市场收集的数据（在我们的全面部署中进一步验证），平均不到三分之一的用户在任何一天将其流量优先级状态更改为BE状态。例如，在科罗拉多州的科罗拉多斯普林斯
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.
最大的测试市场，在2008年8月的任何一天，在测试的6016个总用户中，平均有22个用户的流量优先级状态在一天中的某个时间被更改。
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.
当用户的带宽消耗在大约15分钟的时间内下降到他或她供应的上游或下游带宽的50%以下时，用户的通信量从BE状态释放。这些发布标准旨在最小化（并有望防止）用户QoS振荡，即特定用户可以在BE和PBE之间重复循环的情况。因此，如果没有这个较低的发布标准，我们担心某些用户会在BE和PBE状态之间长时间振荡，对系统和其他用户没有明显的好处，并且会给系统带来不必要的信令负担。NetForecast，Inc.是一家独立咨询公司，负责就康卡斯特的试验和相关拥塞管理工作提供分析和建议。该公司建议采用这种方法，这种方法在我们的试验、实验室测试和随后的国家部署中效果良好。
Simply put, there are four steps for determining whether the traffic associated with a particular cable modem is designated as PBE or BE:
简言之，有四个步骤可确定与特定电缆调制解调器相关的通信量是否指定为PBE或BE：
1. Determine if the CMTS port is in a Near Congestion State.
1. 确定CMTS端口是否处于接近拥塞状态。
2. If yes, determine whether any users are in an Extended High Consumption State.
2. 如果是，确定是否有任何用户处于扩展高消耗状态。
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.
3. 如果是，将这些用户的流量更改为来自PBE。如果第一步或第二步的答案是否定的，则不采取任何行动。
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.
4. 如果用户的流量已被指定为BE，请在下一个间隔检查用户消耗量。如果用户消费下降到预定阈值以下，则将用户的流量重新分配为PBE。如果没有，请在下一个间隔重新检查。
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.
如果CMT定期进入接近拥塞状态，并且随后确实发生了拥塞，但是没有用户符合要分类为扩展高消耗状态的标准，则这可能表明观察到的拥塞是定期发生的，而不是不可预测的拥塞。因此，这可能是一个额外的数据点，有利于考虑是否以及何时增加容量。
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):
图2以图形方式描述了该拥塞管理过程的工作原理，使用了上游港口利用率可能达到接近拥塞状态的情况示例（相同的图表，在适当的位置具有不同的值，也可用于描述下游港口的管理过程）：
Figure 2: Upstream Congestion Management Decision Flowchart
图2：上游拥塞管理决策流程图
/\
+------------+ / \ +---------+ +---------+
| 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-------------+
/\
+------------+ / \ +---------+ +---------+
| 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:
上图2的关键点：
Question #1: Is the CMTS Upstream Port Utilization at an average of OVER 70% for OVER 15 minutes?
问题#1：CMTS上游端口利用率是否在15分钟内平均超过70%？
Result #1: CMTS marked in a Near Congestion State, indicating congestion *may* occur soon.
结果#1:CMT标记为接近拥塞状态，表明拥塞*可能*很快发生。
Action #1: Search most recent analysis timeframe (approx. 15 mins.) of IPDR usage data.
行动#1：搜索IPDR使用数据的最新分析时间范围（约15分钟）。
Question #2: Are any users consuming an average of OVER 70% of provisioned upstream bandwidth for OVER 15 minutes?
问题#2：是否有用户在15分钟内平均消耗超过70%的已配置上行带宽？
Result #2: No action taken.
结果#2：未采取任何行动。
Result #3: Change user's upstream traffic from Priority Best Effort (PBE) to Best Effort (BE).
结果#3：将用户的上游流量从优先级最大努力（PBE）更改为最大努力（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?
问题#3：在15分钟的时间内，尽力而为（BE）的用户平均消耗的上行带宽是否少于所配置带宽的50%？
Result #4: Change user's upstream traffic back to Priority Best Effort (PBE) from Best Effort (BE).
结果#4：将用户的上游流量从最大努力（BE）更改回优先级最大努力（PBE）。
Figure 2
图2
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.
当CMTS端口处于接近拥塞状态且连接到该端口的电缆调制解调器处于扩展高消耗状态时，该电缆调制解调器的通信量被指定为BE。取决于CMTS端口上的利用率水平，该指定可能会或可能不会导致用户的通信被延迟，或者在极端情况下，在PBE通信被丢弃之前丢弃。这是因为CMT处理流量的方式。具体来说，CMTS端口具有通常称为“调度器”的功能，该功能将来自或前往该特定端口的所有数据包放入队列中，然后依次处理这些数据包。调度器可以在任何给定时刻处理一定数量的数据包；对于每个时隙，PBE流量被赋予对可用容量的优先访问权，BE流量在可用空间的基础上进行处理。
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
一个粗略的类比是，公共汽车以难以置信的速度空置和充满。当空车到达象征性的“公共汽车站”——在本例中，每两毫秒一次——它们装满的数据包与在公共汽车上等待“座位”的数据包一样多
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.
公共汽车容量的限制。在非拥堵期间，公交车通常会有几个空座位，但在拥堵期间，公交车会加满乘客，乘客将不得不等待下一辆公交车。正是在拥塞期间，数据包才会受到影响。如果没有拥塞，来自处于BE状态的用户的数据包在到达公交车站时应该不会有什么问题。另一方面，如果在特定实例中存在拥塞，则总线可能在任何BE分组可以到达之前被处于PBE状态的分组填满。在这种情况下，BE数据包将不得不等待下一条没有被PBE数据包填充的总线。实际上，这一切都以两毫秒的增量发生，因此即使数据包错过了50条“总线”，延迟也只有十分之一秒左右。
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.
在实际网络拥塞期间，当来自BE流量的数据包可能间歇性延迟时，其流量延迟的用户可能会经历各种影响，这取决于他或她正在使用的应用程序。通常，在实际拥塞期间流量处于BE状态的用户可能会发现网页加载缓慢，点对点上传需要更长的时间才能完成，或者VoIP呼叫听起来不稳定。当然，在没有任何拥堵管理的情况下，同样的事情也可能发生在拥堵港口的客户身上；这里的不同之处在于，任何此类延迟的影响都会转移到那些给网络带来最大负担的人身上，而不是在该端口的用户之间随机分布，而不考虑他们的消费水平。事实上，我们的研究得出结论，当启用此拥塞管理系统时，PBE用户的体验会得到改善。这一结论基于网络测量，如延迟。
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
NetForecast探讨了流量处于BE状态的用户最坏情况下的潜在风险：在理论情况下，PBE流量在很长一段时间内占用了100%的CMTS带宽，可能出现“带宽不足”。理论上，这种情况可能意味着指定流量的给定用户在一段时间内无法实现上传或下载（如上所述，两者都是单独管理的）。然而，当这些管理技术首先在公司试验台上进行测试，然后在我们在五个市场上进行的真实世界试验（在我们的全面部署中进一步验证）中进行测试时，这种理论条件并未出现。此外，我们在生产网络中全面部署该系统的经验表明，这些管理实践对现实世界的影响非常小。此外，康卡斯特在任何一个试验市场都没有收到任何客户投诉，可以追溯到该拥堵管理系统，尽管已广泛宣传了这些试验。在我们随后的国家报告中
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.
部署到我们的生产网络中，我们仍然没有找到具体的投诉，可以追溯到这种拥塞管理系统的影响。
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.
康卡斯特将继续监控这些新的拥塞管理技术对用户流量的影响，并将做出必要的调整，以确保所有康卡斯特HSI客户都有高质量的互联网体验。
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.
上述功能是使用三个不同供应商提供的三种不同类型的应用服务器执行的。如上所述，这些服务器安装在康卡斯特区域网络路由器附近。这些服务器的确切位置与本文档无关，因为这些信息不会改变服务器管理单个CMTS端口的事实。
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.
第一个应用服务器是IPDR服务器，它从CMT收集相关的电缆调制解调器卷使用信息，例如订户在特定时间段内使用多少聚合上游或下游字节。IPDR已被许多行业组织和倡议采纳为标准，如CableLabs、电信行业解决方案联盟（ATIS）、国际电信联盟（ITU）和第三代合作伙伴计划（3GPP）等。部署的IPDR软件是由主动宽带网络开发的，在图3中被称为统计数据收集服务器。
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.
第二个应用服务器是拥塞管理服务器，它使用简单网络管理协议（SNMP）[RFC3410]测量CMTS端口利用率，并检测端口何时处于接近拥塞状态。发生这种情况时，拥塞管理服务器随后查询相关IPDR数据，以获得满足上述标准的电缆调制解调器列表，以确定其处于扩展高消耗状态。部署的拥塞管理服务器软件由Sandvine开发。
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.
如果一个或多个用户满足要管理的标准，则拥塞管理服务器通知第三个应用服务器PCMM应用服务器，哪些用户处于扩展高消耗状态，哪些流量应被视为正常。PCMM服务器负责向给定CMT发送信号，以设置具有BE QoS的特定电缆调制解调器的通信量，并负责跟踪和管理此类CMT动作的状态。如果没有用户满足要管理的标准，则没有用户将管理其流量。部署的PCMM软件由Camiant开发，在图3中被称为QoS服务器。
Figure 3 graphically depicts the high-level management flows among the congestion management components on Comcast's network, as described above:
图3以图形方式描述了康卡斯特网络拥塞管理组件之间的高级管理流程，如上所述：
Figure 3: Simplified Diagram Showing High-Level Management Flows Relevant to the System
图3：显示与系统相关的高级管理流程的简化图
+---------------+ +---------------+
| 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
+---------------+ +---------------+
| 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
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.
Comcast于2008年3月开始设计和开发这种新的协议无关拥塞管理系统。康卡斯特与IETF和互联网社区的其他人以及独立顾问分享了设计，并将我们收到的反馈纳入最终设计。经过实验室测试，该系统于2008年6月至9月在康卡斯特的生产网络中进行了测试。康卡斯特的生产网络过渡到这种新的协议无关拥塞管理系统始于2008年10月，并于2008年12月31日完成。
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.
如本文所述，新方法不通过集中管理特定协议的使用来管理拥塞。这种方法也不使用TCP“重置数据包”[RFC3360]。相反，系统的行为使得在CMTS端口处于接近拥塞状态期间，系统（1）识别该端口上在前15分钟内消耗了不成比例的带宽的订户（2）将这些订阅服务器的流量的优先级状态降低为状态，直到这些订阅服务器满足释放标准。在实际拥塞期间，系统在BE流量之前处理PBE流量。康卡斯特的试验和随后在全国的部署表明，这一新的拥塞管理系统确保了康卡斯特所有HSI客户的优质在线体验。
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.
开发该系统是为了应对几乎任何IP网络上可能出现的某种“正常”拥塞。然而，还应注意，在现有网络使用模型无法或无法准确预测的“异常网络使用”事件的情况下，这种系统也可能证明特别有用。一些网络运营商将这些异常事件称为利用率的“激增”，类似于许多人可能熟悉的电网需求的突然激增。
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.
例如，在一场严重的全球大流行的情况下，人们可能会预期大量人口可能需要通过互联网连接远程工作。在这种情况下，可能会出现前所未有的利用率。在这种情况下，拥有一个灵活的拥塞管理系统可能会有所帮助，该系统可以适应这种情况，并在额外容量上线或临时情况持续时帮助分配网络资源。
The main limitations of the system include:
该系统的主要限制包括：
o The system is not an end-to-end congestion management system, nor does it enable one.
o 该系统不是一个端到端的拥塞管理系统，也没有启用。
o The system does not signal the presence of congestion to user applications or to all devices on the network path.
o 系统不会向用户应用程序或网络路径上的所有设备发出拥塞信号。
o The system does not explicitly enable additional user and/or application responses to congestion.
o 系统不会显式启用其他用户和/或应用程序对拥塞的响应。
o The system does not enable distributed denial-of-service (DDoS) mitigation or other capabilities.
o 系统不支持分布式拒绝服务（DDoS）缓解或其他功能。
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.
IETF有几个新的工作组致力于解决拥塞及其影响、避免拥塞、管理拥塞和传输拥塞信息等问题。这包括拥塞暴露（CONEX）工作组、应用层传输优化（ALTO）工作组和低额外延迟后台传输（LEDBAT）工作组。如果这些工作组中的一个或多个成功地完成了有用的工作，则此处记录的系统的设计或配置可能需要更改。例如，该拥塞管理系统目前没有一种方法来考虑不同的数据传输类别，例如LEDBAT可能指定的数据传输类别，与现有传输协议相比，该类别可能更好地产生其他流量。此外，CONEX可以指定用于该系统或其他系统的方法，以向网络的其他部分和/或特定网络流的任一端的主机发送拥塞状态或预期拥塞的信号。此外，可以想象，当前或未来IETF工作的结果可以完全消除对此类拥塞管理系统的需求。
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.
ISP必须确保对拥塞管理服务器和QoS服务器的安全访问，以及对CMTSs的QoS信令，以便未经授权的用户和/或主机不能对网络中的QoS设置进行未经授权的更改。
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
保护对统计数据收集服务器的访问也很重要，因为该服务器包含最终用户个人认为私有的基于IPDR的字节传输数据。此外，该数据被视为ISP专有的聚合流量数据
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.
原因还应保护对统计数据收集服务器的访问，以便不能向系统提供虚假的使用统计数据。请务必注意，IPDR数据包含在给定时间间隔内通过电缆调制解调器MAC地址发送和接收的字节数。此数据不包含诸如该数据的源和/或目标Internet地址之类的内容，也不包含所使用的协议、所使用的端口等。
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.
作者希望感谢帮助开发和/或审查本文件的许多人的辛勤工作，以及在如此短的时间内帮助部署该系统的人。
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:
作者还希望感谢以下人员对本文件进行详细审查和/或提供有助于改进和发展本文件的意见和反馈：
- Kris Bransom
- 克里斯·布兰森
- Bob Briscoe
- 鲍勃·布里斯科
- Lars Eggert
- 拉尔斯·艾格特
- Ari Keranen
- 阿里凯拉宁
- Tero Kivinen
- 泰罗基文
- Matt Mathis
- 马特·马蒂斯
- Stanislav Shalunov
- 斯坦尼斯拉夫·沙卢诺夫
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[COMCAST_P2PI_论文]Livingood，J.和R.Woundy，“COMCAST的IETF P2P基础设施研讨会立场论文”，FCC文件COMCAST网络管理会议，2008年5月<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>.
[COMCAST_P2PI_PRES]Livingood，J.和R.Woundy，“COMCAST于2008年5月28日举办的IETF P2P基础设施研讨会”，FCC文件COMCAST网络管理会议，2008年5月<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_CM2CPE]CableLabs，“电缆数据服务接口规范-DOCSIS 3.0-电缆调制解调器至客户场所设备接口规范”，DOCSIS 3.0 CM-SP-CMCIv3-I01-0803202，2008年3月<http://www.cablelabs.com/cablemodem/specifications/ 技术规格30.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_IPDR]Yassini，R.，“有线数据服务接口规范-DOCSIS 2.0-运营支持系统接口规范”，DOCSIS 2.0 CM-SP-OSSIv2.0-C01-0811042008年11月<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_MULPI]CableLabs，“有线数据服务接口规范-DOCSIS 3.0-MAC和上层协议接口规范”，DOCSIS 3.0 CM-SP-MULPIv3.0-I11-0910022009年10月，<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_OSSI]CableLabs，“有线数据服务接口规范-DOCSIS 3.0-运营支持系统接口规范”，DOCSIS 3.0 CM-SP-OSSIv3.0-I10-091002，2009年10月<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_PHY]CableLabs，“电缆数据服务接口规范-DOCSIS 3.0-物理层规范”，DOCSIS 3.0 CM-SP-PHYv3.0-I08-0901212009年1月<http://www.cablelabs.com/cablemodem/ 规格/规格30.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>.
[DOCSIS_SEC]CableLabs，“有线数据服务接口规范-DOCSIS 3.0-安全规范”，DOCSIS 3.0 CM-SP-SECv3.0-I11-0910022008年3月，<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_consucch_Mgmt_Ltr]Zachem，K.，“致FCC的关于康卡斯特新拥塞管理系统成功部署的通知函”，FCC备案康卡斯特网络管理程序，2009年1月<http://fjallfoss.fcc.gov/ecfs/document/ 视图？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备忘录意见]Martin，K.，Copps，M.，Adelstein，J.，Tate，D.，和R.McDowell，“FCC关于合理网络管理的备忘录和意见”，文件号EB-08-IH-1518 WC卷宗号07-52，2008年8月<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>.
[FCC_Net_Mgmt_Response]Zachem，K.，“致FCC关于康卡斯特网络管理实践的信函”，FCC提交康卡斯特网络管理程序，2008年9月，<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>.
[IPDR_标准]Cotton，S.，Cockrell，B.，Walls，P.，和T.Givoly，“基于IP的服务的网络数据管理-使用（NDM-U）。服务规范-电缆实验室DOCSIS 2.0 SAMIS”，IPDR服务规范NDM-U，2004年11月<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>.
[PowerBoost_规范]康卡斯特电缆通信管理有限责任公司，“康卡斯特PowerBoost规范”，康卡斯特网站，2010年6月<http://customer.comcast.com/Pages/ FAQListViewer.aspx？主题=互联网和文件夹=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.
[RFC1633]Braden，B.，Clark，D.，和S.Shenker，“互联网体系结构中的综合服务：概述”，RFC163331994年6月。
[RFC2475] Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z., and W. Weiss, "An Architecture for Differentiated Services", RFC 2475, December 1998.
[RFC2475]Blake，S.，Black，D.，Carlson，M.，Davies，E.，Wang，Z.，和W.Weiss，“差异化服务架构”，RFC 24751998年12月。
[RFC3083] Woundy, R., "Baseline Privacy Interface Management Information Base for DOCSIS Compliant Cable Modems and Cable Modem Termination Systems", RFC 3083, March 2001.
[RFC3083]Woundy，R.，“符合DOCSIS标准的电缆调制解调器和电缆调制解调器终端系统的基线隐私接口管理信息库”，RFC 3083，2001年3月。
[RFC3360] Floyd, S., "Inappropriate TCP Resets Considered Harmful", BCP 60, RFC 3360, August 2002.
[RFC3360]Floyd，S.，“不适当的TCP重置被认为是有害的”，BCP 60，RFC 3360，2002年8月。
[RFC3410] Case, J., Mundy, R., Partain, D., and B. Stewart, "Introduction and Applicability Statements for Internet-Standard Management Framework", RFC 3410, December 2002.
[RFC3410]Case，J.，Mundy，R.，Partain，D.，和B.Stewart，“互联网标准管理框架的介绍和适用性声明”，RFC 34102002年12月。
[RFC5594] Peterson, J. and A. Cooper, "Report from the IETF Workshop on Peer-to-Peer (P2P) Infrastructure, May 28, 2008", RFC 5594, July 2009.
[RFC5594]Peterson，J.和A.Cooper，“IETF对等（P2P）基础设施研讨会报告，2008年5月28日”，RFC 55942009年7月。
Authors' Addresses
作者地址
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
Chris Bastian Comcast有线通信一号Comcast中心宾夕法尼亚州费城肯尼迪大道1701号19103美国电子邮件：Chris_bastian@cable.comcast.comURI: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
Tom Klieber Comcast有线通信1306 Goshen Parkway West Chester，宾夕法尼亚州19380美国电子邮件：Tom_klieber@cable.comcast.comURI: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
Jason Livingood Comcast有线通信一号Comcast中心宾夕法尼亚州费城肯尼迪大道1701号，邮编：19103美国电子邮件：Jason_livingood@cable.comcast.comURI: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
Jim Mills Comcast有线通信一号Comcast中心1800主教门大道新泽西州劳雷尔山08054美国电子邮件：Jim_mills@cable.comcast.comURI: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
Richard Woundy Comcast有线通信公司马萨诸塞州切姆斯福德工业大道27号01824美国电子邮件：Richard_woundy@cable.comcast.comURI:http://www.comcast.com