Network Working Group                                         K. Nichols
Request for Comments: 3086                                 Packet Design
Category: Informational                                     B. Carpenter
                                                              April 2001
Network Working Group                                         K. Nichols
Request for Comments: 3086                                 Packet Design
Category: Informational                                     B. Carpenter
                                                              April 2001

Definition of Differentiated Services Per Domain Behaviors and Rules for their Specification


Status of this Memo


This memo provides information for the Internet community. It does not specify an Internet standard of any kind. Distribution of this memo is unlimited.


Copyright Notice


Copyright (C) The Internet Society (2001). All Rights Reserved.




The differentiated services framework enables quality-of-service provisioning within a network domain by applying rules at the edges to create traffic aggregates and coupling each of these with a specific forwarding path treatment in the domain through use of a codepoint in the IP header. The diffserv WG has defined the general architecture for differentiated services and has focused on the forwarding path behavior required in routers, known as "per-hop forwarding behaviors" (or PHBs). The WG has also discussed functionality required at diffserv (DS) domain edges to select (classifiers) and condition (e.g., policing and shaping) traffic according to the rules. Short-term changes in the QoS goals for a DS domain are implemented by changing only the configuration of these edge behaviors without necessarily reconfiguring the behavior of interior network nodes.


The next step is to formulate examples of how forwarding path components (PHBs, classifiers, and traffic conditioners) can be used to compose traffic aggregates whose packets experience specific forwarding characteristics as they transit a differentiated services domain. The WG has decided to use the term per-domain behavior, or PDB, to describe the behavior experienced by a particular set of packets as they cross a DS domain. A PDB is characterized by specific metrics that quantify the treatment a set of packets with a particular DSCP (or set of DSCPs) will receive as it crosses a DS domain. A PDB specifies a forwarding path treatment for a traffic aggregate and, due to the role that particular choices of edge and


PHB configuration play in its resulting attributes, it is where the forwarding path and the control plane interact. The measurable parameters of a PDB should be suitable for use in Service Level Specifications at the network edge.


This document defines and discusses Per-Domain Behaviors in detail and lays out the format and required content for contributions to the Diffserv WG on PDBs and the procedure that will be applied for individual PDB specifications to advance as WG products. This format is specified to expedite working group review of PDB submissions.


Table of Contents


    1. Introduction ................................................ 2
    2. Definitions ................................................. 4
    3. The Value of Defining Edge-to-Edge Behavior ................. 5
    4. Understanding PDBs .......................................... 7
    5. Format for Specification of Diffserv Per-Domain Behaviors ...13
    6. On PDB Attributes ...........................................16
    7. A Reference Per-Domain Behavior .............................19
    8. Guidelines for Advancing PDB Specifications .................21
    9. Security Considerations .....................................22
   10. Acknowledgements ............................................22
       References ..................................................22
       Authors' Addresses ..........................................23
       Full Copyright Statement ....................................24
    1. Introduction ................................................ 2
    2. Definitions ................................................. 4
    3. The Value of Defining Edge-to-Edge Behavior ................. 5
    4. Understanding PDBs .......................................... 7
    5. Format for Specification of Diffserv Per-Domain Behaviors ...13
    6. On PDB Attributes ...........................................16
    7. A Reference Per-Domain Behavior .............................19
    8. Guidelines for Advancing PDB Specifications .................21
    9. Security Considerations .....................................22
   10. Acknowledgements ............................................22
       References ..................................................22
       Authors' Addresses ..........................................23
       Full Copyright Statement ....................................24

1 Introduction


Differentiated Services allows an approach to IP Quality of Service that is modular, incrementally deployable, and scalable while introducing minimal per-node complexity [RFC2475]. From the end user's point of view, QoS should be supported end-to-end between any pair of hosts. However, this goal is not immediately attainable. It will require interdomain QoS support, and many untaken steps remain on the road to achieving this. One essential step, the evolution of the business models for interdomain QoS, will necessarily develop outside of the IETF. A goal of the diffserv WG is to provide the firm technical foundation that allows these business models to develop. The first major step will be to support edge-to-edge or intradomain QoS between the ingress and egress of a single network, i.e., a DS Domain in the terminology of RFC 2474. The intention is that this edge-to-edge QoS should be composable, in a purely technical sense, to a quantifiable QoS across a DS Region composed of multiple DS domains.

区分服务允许采用模块化、增量部署和可扩展的IP服务质量方法,同时引入最小的每节点复杂性[RFC2475]。从最终用户的角度来看,任何一对主机之间都应该支持端到端的QoS。然而,这一目标并非马上就能实现。这将需要域间QoS支持,实现这一目标的道路上还有许多未完成的步骤。一个重要的步骤,域间QoS业务模型的演变,必然会在IETF之外发展。DiffServ WG的目标是提供允许这些业务模型开发的坚实的技术基础。第一个主要步骤将是支持单个网络(即RFC 2474术语中的DS域)的入口和出口之间的边到边或域内QoS。其目的是,在纯技术意义上,这种边缘到边缘的QoS应可组合为跨由多个DS域组成的DS区域的可量化QoS。

The Diffserv WG has finished the first phase of standardizing the behaviors required in the forwarding path of all network nodes, the per-hop forwarding behaviors or PHBs. The PHBs defined in RFCs 2474, 2597 and 2598 give a rich toolbox for differential packet handling by individual boxes. The general architectural model for diffserv has been documented in RFC 2475. An informal router model [MODEL] describes a model of traffic conditioning and other forwarding behaviors. However, technical issues remain in moving "beyond the box" to intradomain QoS models.

Diffserv WG已经完成了标准化所有网络节点的转发路径所需行为的第一阶段,即每跳转发行为或PHB。RFCs 2474、2597和2598中定义的PHB提供了一个丰富的工具箱,用于通过各个盒子进行差异数据包处理。区分服务的通用体系结构模型已记录在RFC 2475中。非正式路由器模型[model]描述了流量调节和其他转发行为的模型。然而,将“开箱即用”转移到域内QoS模型仍然存在技术问题。

The ultimate goal of creating scalable end-to-end QoS in the Internet requires that we can identify and quantify behavior for a group of packets that is preserved when they are aggregated with other packets as they traverse the Internet. The step of specifying forwarding path attributes on a per-domain basis for a set of packets distinguished only by the mark in the DS field of individual packets is critical in the evolution of Diffserv QoS and should provide the technical input that will aid in the construction of business models. This document defines and specifies the term "Per-Domain Behavior" or PDB to describe QoS attributes across a DS domain.

在Internet中创建可扩展的端到端QoS的最终目标要求我们能够识别和量化一组数据包的行为,这些数据包在通过Internet时与其他数据包聚合时会被保留。在每个域的基础上为一组数据包指定转发路径属性的步骤仅通过单个数据包的DS字段中的标记来区分,这一步骤对于Diffserv QoS的发展至关重要,并应提供有助于构建业务模型的技术输入。本文档定义并指定术语“每域行为”或PDB,以描述DS域中的QoS属性。

Diffserv classification and traffic conditioning are applied to packets arriving at the boundary of a DS domain to impose restrictions on the composition of the resultant traffic aggregates, as distinguished by the DSCP marking , inside the domain. The classifiers and traffic conditioners are set to reflect the policy and traffic goals for that domain and may be specified in a TCA (Traffic Conditioning Agreement). Once packets have crossed the DS boundary, adherence to diffserv principles makes it possible to group packets solely according to the behavior they receive at each hop (as selected by the DSCP). This approach has well-known scaling advantages, both in the forwarding path and in the control plane. Less well recognized is that these scaling properties only result if the per-hop behavior definition gives rise to a particular type of invariance under aggregation. Since the per-hop behavior must be equivalent for every node in the domain, while the set of packets marked for that PHB may be different at every node, PHBs should be defined such that their characteristics do not depend on the traffic volume of the associated BA on a router's ingress link nor on a particular path through the DS domain taken by the packets. Specifically, different streams of traffic that belong to the same traffic aggregate merge and split as they traverse the network. If the properties of a PDB using a particular PHB hold regardless of how the temporal characteristics of the marked traffic aggregate change as it traverses the domain, then that PDB scales. (Clearly this assumes that numerical parameters such as bandwidth allocated to the particular PDB may be different at different points in the network, and may be adjusted dynamically as traffic volume varies.) If there


are limits to where the properties hold, that translates to a limit on the size or topology of a DS domain that can use that PDB. Although useful single-link DS domains might exist, PDBs that are invariant with network size or that have simple relationships with network size and whose properties can be recovered by reapplying rules (that is, forming another diffserv boundary or edge to re-enforce the rules for the traffic aggregate) are needed for building scalable end-to-end quality of service.


There is a clear distinction between the definition of a Per-Domain Behavior in a DS domain and a service that might be specified in a Service Level Agreement. The PDB definition is a technical building block that permits the coupling of classifiers, traffic conditioners, specific PHBs, and particular configurations with a resulting set of specific observable attributes which may be characterized in a variety of ways. These definitions are intended to be useful tools in configuring DS domains, but the PDB (or PDBs) used by a provider is not expected to be visible to customers any more than the specific PHBs employed in the provider's network would be. Network providers are expected to select their own measures to make customer-visible in contracts and these may be stated quite differently from the technical attributes specified in a PDB definition, though the configuration of a PDB might be taken from a Service Level Specification (SLS). Similarly, specific PDBs are intended as tools for ISPs to construct differentiated services offerings; each may choose different sets of tools, or even develop their own, in order to achieve particular externally observable metrics. Nevertheless, the measurable parameters of a PDB are expected to be among the parameters cited directly or indirectly in the Service Level Specification component of a corresponding SLA.


This document defines Differentiated Services Per-Domain Behaviors and specifies the format that must be used for submissions of particular PDBs to the Diffserv WG.

本文档定义了每个域的区分服务行为,并指定了向Diffserv WG提交特定PDB时必须使用的格式。

2 Definitions


The following definitions are stated in RFCs 2474 and 2475 and are repeated here for easy reference:

RFCs 2474和2475中规定了以下定义,为便于参考,此处重复了这些定义:

" Behavior Aggregate: a collection of packets with the same codepoint crossing a link in a particular direction.


" Differentiated Services Domain: a contiguous portion of the Internet over which a consistent set of differentiated services policies are administered in a coordinated fashion. A differentiated services domain can represent different


administrative domains or autonomous systems, different trust regions, different network technologies (e.g., cell/frame), hosts and routers, etc. Also DS domain.


" Differentiated Services Boundary: the edge of a DS domain, where classifiers and traffic conditioners are likely to be deployed. A differentiated services boundary can be further sub-divided into ingress and egress nodes, where the ingress/egress nodes are the downstream/upstream nodes of a boundary link in a given traffic direction. A differentiated services boundary typically is found at the ingress to the first-hop differentiated services-compliant router (or network node) that a host's packets traverse, or at the egress of the last-hop differentiated services-compliant router or network node that packets traverse before arriving at a host. This is sometimes referred to as the boundary at a leaf router. A differentiated services boundary may be co-located with a host, subject to local policy. Also DS boundary.


To these we add:


" Traffic Aggregate: a collection of packets with a codepoint that maps to the same PHB, usually in a DS domain or some subset of a DS domain. A traffic aggregate marked for the foo PHB is referred to as the "foo traffic aggregate" or "foo aggregate" interchangeably. This generalizes the concept of Behavior Aggregate from a link to a network.

“流量聚合:具有映射到同一PHB的代码点的数据包的集合,通常位于DS域或DS域的某个子集中。标记为foo PHB的流量聚合被互换地称为“foo流量聚合”或“foo聚合”。这概括了从链接到网络的行为聚合的概念。

" Per-Domain Behavior: the expected treatment that an identifiable or target group of packets will receive from "edge-to-edge" of a DS domain. (Also PDB.) A particular PHB (or, if applicable, list of PHBs) and traffic conditioning requirements are associated with each PDB.


" A Service Level Specification (SLS) is a set of parameters and their values which together define the service offered to a traffic stream by a DS domain. It is expected to include specific values or bounds for PDB parameters.


3 The Value of Defining Edge-to-Edge Behavior


As defined in section 2, a PDB describes the edge-to-edge behavior across a DS domain's "cloud." Specification of the transit expectations of packets matching a target for a particular diffserv behavior across a DS domain will both assist in the deployment of single-domain QoS and will help enable the composition of end-to-end, cross-domain services. Networks of DS domains can be connected to create end-to-end services by building on the PDB characteristics without regard to the particular PHBs used. This level of


abstraction makes it easier to compose cross-domain services as well as making it possible to hide details of a network's internals while exposing information sufficient to enable QoS.


Today's Internet is composed of multiple independently administered domains or Autonomous Systems (ASs), represented by the "clouds" in figure 1. To deploy ubiquitous end-to-end quality of service in the Internet, business models must evolve that include issues of charging and reporting that are not in scope for the IETF. In the meantime, there are many possible uses of quality of service within an AS and the IETF can address the technical issues in creating an intradomain QoS within a Differentiated Services framework. In fact, this approach is quite amenable to incremental deployment strategies.


Where DS domains are independently administered, the evolution of the necessary business agreements and future signaling arrangements will take some time, thus, early deployments will be within a single administrative domain. Putting aside the business issues, the same technical issues that arise in interconnecting DS domains with homogeneous administration will arise in interconnecting the autonomous systems (ASs) of the Internet.


                 |                AS2                   |
                 |                                      |
    -------      |     ------------     ------------    |
    | AS1 |------|-----X           |    |          |    |
    -------      |     |           |    Y          |    |        -------
                 |     |           |   /|          X----|--------| AS3 |
                 |     |           |  / |          |    |        -------
                 |     |           | /  ------------    |
                 |     |           Y      |             |
                 |     |           | \  ------------    |
    -------      |     |           |  \ |          |    |
    | AS4 |------|-----X           |   \|          |    |
    -------      |     |           |    Y          X----|------
                 |     |           |    |          |    |
                 |     ------------     ------------    |
                 |                                      |
                 |                                      |
                 |                AS2                   |
                 |                                      |
    -------      |     ------------     ------------    |
    | AS1 |------|-----X           |    |          |    |
    -------      |     |           |    Y          |    |        -------
                 |     |           |   /|          X----|--------| AS3 |
                 |     |           |  / |          |    |        -------
                 |     |           | /  ------------    |
                 |     |           Y      |             |
                 |     |           | \  ------------    |
    -------      |     |           |  \ |          |    |
    | AS4 |------|-----X           |   \|          |    |
    -------      |     |           |    Y          X----|------
                 |     |           |    |          |    |
                 |     ------------     ------------    |
                 |                                      |
                 |                                      |

Figure 1: Interconnection of ASs and DS Domains


A single AS (e.g., AS2 in figure 1) may be composed of subnetworks and, as the definition allows, these can be separate DS domains. An AS might have multiple DS domains for a number of reasons, most notable being to follow topological and/or technological boundaries


and to separate the allocation of resources. If we confine ourselves to the DS boundaries between these "interior" DS domains, we avoid the non-technical problems of setting up a service and can address the issues of creating characterizable PDBs.


The incentive structure for differentiated services is based on upstream domains ensuring their traffic conforms to the Traffic Conditioning Agreements (TCAs) with downstream domains and downstream domains enforcing that TCA, thus metrics associated with PDBs can be sensibly computed. The letters "X" and "Y" in figure 1 represent the DS boundary routers containing traffic conditioners that ensure and enforce conformance (e.g., shapers and policers). Although policers and shapers are expected at the DS boundaries of ASs (the "X" boxes), they might appear anywhere, or nowhere, inside the AS. Specifically, the boxes at the DS boundaries internal to the AS (the "Y" boxes) may or may not condition traffic. Technical guidelines for the placement and configuration of DS boundaries should derive from the attributes of a particular PDB under aggregation and multiple hops.


This definition of PDB continues the separation of forwarding path and control plane described in RFC 2474. The forwarding path characteristics are addressed by considering how the behavior at every hop of a packet's path is affected by the merging and branching of traffic aggregates through multiple hops. Per-hop behaviors in nodes are configured infrequently, representing a change in network infrastructure. More frequent quality-of-service changes come from employing control plane functions in the configuration of the DS boundaries. A PDB provides a link between the DS domain level at which control is exercised to form traffic aggregates with quality-of-service goals across the domain and the per-hop and per-link treatments packets receive that results in meeting the quality-of-service goals.

PDB的定义继续了RFC 2474中描述的转发路径和控制平面的分离。转发路径特性是通过考虑数据包路径的每一跳的行为如何受到通过多跳的流量聚合的合并和分支的影响来解决的。节点中的每跳行为很少配置,这表示网络基础设施发生了变化。更频繁的服务质量变化来自于在DS边界的配置中采用控制平面功能。PDB提供DS域级别之间的链路,在该级别执行控制以形成具有跨域服务质量目标的流量聚合,以及接收的每跳和每链路处理数据包,从而实现服务质量目标。

4 Understanding PDBs


4.1 Defining PDBs
4.1 定义PDB

RFCs 2474 and 2475 define a Differentiated Services Behavior Aggregate as "a collection of packets with the same DS codepoint crossing a link in a particular direction" and further state that packets with the same DSCP get the same per-hop forwarding treatment (or PHB) everywhere inside a single DS domain. Note that even if multiple DSCPs map to the same PHB, this must hold for each DSCP individually. In section 2 of this document, we introduced a more general definition of a traffic aggregate in the diffserv sense so that we might easily refer to the packets which are mapped to the same PHB everywhere within a DS domain. Section 2 also presented a short definition of PDBs which we expand upon in this section:

RFCs 2474和2475将区分服务行为聚合定义为“具有在特定方向上穿过链路的相同DS码点的数据包集合”,并进一步声明具有相同DSCP的数据包在单个DS域内的任何地方都获得相同的每跳转发处理(或PHB)。请注意,即使多个DSCP映射到同一PHB,每个DSCP也必须单独保持此状态。在本文档的第2节中,我们介绍了diffserv意义上的流量聚合的更一般定义,以便我们可以轻松地引用映射到DS域中任何地方的相同PHB的数据包。第2节还介绍了PDB的简短定义,我们在本节中对此进行了扩展:

Per-Domain Behavior: the expected treatment that an identifiable or target group of packets will receive from "edge to edge" of a DS domain. A particular PHB (or, if applicable, list of PHBs) and traffic conditioning requirements are associated with each PDB.


Each PDB has measurable, quantifiable, attributes that can be used to describe what happens to its packets as they enter and cross the DS domain. These derive from the characteristics of the traffic aggregate that results from application of classification and traffic conditioning during the entry of packets into the DS domain and the forwarding treatment (PHB) the packets get inside the domain, but can also depend on the entering traffic loads and the domain's topology. PDB attributes may be absolute or statistical and they may be parameterized by network properties. For example, a loss attribute might be expressed as "no more than 0.1% of packets will be dropped when measured over any time period larger than T", a delay attribute might be expressed as "50% of delivered packets will see less than a delay of d milliseconds, 30% will see a delay less than 2d ms, 20% will see a delay of less than 3d ms." A wide range of metrics is possible. In general they will be expressed as bounds or percentiles rather than as absolute values.

每个PDB都具有可测量、可量化的属性,这些属性可用于描述其数据包在进入和穿越DS域时发生的情况。这些来源于流量聚合的特征,该特征源于数据包进入DS域期间应用分类和流量调节以及数据包进入域内的转发处理(PHB),但也取决于进入的流量负载和域的拓扑结构。PDB属性可以是绝对属性或统计属性,它们可以由网络属性参数化。例如,丢失属性可能表示为“在大于T的任何时间段内测量时,丢弃的数据包不超过0.1%”,延迟属性可能表示为“50%的已交付数据包的延迟小于d毫秒,30%的延迟小于2dms,20%的延迟小于3d ms。”一系列广泛的指标是可能的。通常,它们将表示为边界或百分位数,而不是绝对值。

A PDB is applied to a target group of packets arriving at the edge of the DS domain. The target group is distinguished from all arriving packets by use of packet classifiers [RFC2475] (where the classifier may be "null"). The action of the PDB on the target group has two parts. The first part is the the use of traffic conditioning to create a traffic aggregate. During traffic conditioning, conformant packets are marked with a DSCP for the PHB associated with the PDB (see figure 2). The second part is the treatment experienced by packets from the same traffic aggregate transiting the interior of a DS domain, between and inside of DS domain boundaries. The following subsections further discuss these two effects on the target group that arrives at the DS domain boundary.


           -----------   ------------   --------------------   foo
arriving _|classifiers|_|target group|_|traffic conditioning|_ traffic
packets   |           | |of packets  | |& marking (for foo) |  aggregate
           -----------   ------------   --------------------
           -----------   ------------   --------------------   foo
arriving _|classifiers|_|target group|_|traffic conditioning|_ traffic
packets   |           | |of packets  | |& marking (for foo) |  aggregate
           -----------   ------------   --------------------

Figure 2: Relationship of the traffic aggregate associated with a PDB to arriving packets


4.1.1 Crossing the DS edge: the effects of traffic conditioning on the target group

4.1.1 穿越DS边缘:交通条件对目标人群的影响

This effect is quantified by the relationship of the emerging traffic aggregate to the entering target group. That relationship can depend on the arriving traffic pattern as well as the configuration of the traffic conditioners. For example, if the EF PHB [RFC2598] and a strict policer of rate R are associated with the foo PDB, then the first part of characterizing the foo PDB is to write the relationship between the arriving target packets and the departing foo traffic aggregate. In this case, "the rate of the emerging foo traffic aggregate is less than or equal to the smaller of R and the arrival rate of the target group of packets" and additional temporal characteristics of the packets (e.g., burst) may be specified as desired. Thus, there is a "loss rate" on the arriving target group that results from sending too much traffic or the traffic with the wrong temporal characteristics. This loss rate should be entirely preventable (or controllable) by the upstream sender conforming to the traffic conditioning associated with the PDB specification.

这种影响通过新兴交通总量与进入目标群体的关系进行量化。这种关系可能取决于到达的交通模式以及交通调节器的配置。例如,如果EF PHB[RFC2598]和速率为R的严格policr与foo PDB相关联,则表征foo PDB的第一部分是写入到达的目标分组和离开的foo业务聚合之间的关系。在这种情况下,“新兴foo业务聚合的速率小于或等于R和目标分组组的到达速率中的较小者”,并且可以根据需要指定分组的附加时间特性(例如,突发)。因此,在到达的目标组上存在“丢失率”,这是由于发送过多的通信量或具有错误时间特征的通信量造成的。该损失率应由符合PDB规范相关流量调节的上游发送方完全可预防(或控制)。

The issue of "who is in control" of the loss (or demotion) rate helps to clearly delineate this component of PDB performance from that associated with transiting the domain. The latter is completely under control of the operator of the DS domain and the former is used to ensure that the entering traffic aggregate conforms to the traffic profile to which the operator has provisioned the network. Further, the effects of traffic conditioning on the target group can usually be expressed more simply than the effects of transiting the DS domain on the traffic aggregate's traffic profile.


A PDB may also apply traffic conditioning at DS domain egress. The effect of this conditioning on the overall PDB attributes would be treated similarly to the ingress characteristics (the authors may develop more text on this in the future, but it does not materially affect the ideas presented in this document.)


4.1.2 Crossing the DS domain: transit effects
4.1.2 穿越DS域:过境效应

The second component of PDB performance is the metrics that characterize the transit of a packet of the PDB's traffic aggregate between any two edges of the DS domain boundary shown in figure 3. Note that the DS domain boundary runs through the DS boundary routers since the traffic aggregate is generally formed in the boundary router before the packets are queued and scheduled for output. (In most cases, this distinction is expected to be important.)


DSCPs should not change in the interior of a DS domain as there is no traffic conditioning being applied. If it is necessary to reapply the kind of traffic conditioning that could result in remarking, there should be a DS domain boundary at that point, though such an "interior" boundary can have "lighter weight" rules in its TCA. Thus, when measuring attributes between locations as indicated in figure 3, the DSCP at the egress side can be assumed to have held throughout the domain.


                               |           |
                          -----X           |
                               |           |
                               |   DS      |
                               |   domain  X----
                               |           |
                          -----X           |
                               |           |
                               |           |
                          -----X           |
                               |           |
                               |   DS      |
                               |   domain  X----
                               |           |
                          -----X           |
                               |           |

Figure 3: Range of applicability of attributes of a traffic aggregate associated with a PDB (is between the points marked "X")


Though a DS domain may be as small as a single node, more complex topologies are expected to be the norm, thus the PDB definition must hold as its traffic aggregate is split and merged on the interior links of a DS domain. Packet flow in a network is not part of the PDB definition; the application of traffic conditioning as packets enter the DS domain and the consistent PHB through the DS domain must suffice. A PDB's definition does not have to hold for arbitrary topologies of networks, but the limits on the range of applicability for a specific PDB must be clearly specified.


In general, a PDB operates between N ingress points and M egress points at the DS domain boundary. Even in the degenerate case where N=M=1, PDB attributes are more complex than the definition of PHB attributes since the concatenation of the behavior of intermediate nodes affects the former. A complex case with N and M both greater than one involves splits and merges in the traffic path and is non-trivial to analyze. Analytic, simulation, and experimental work will all be necessary to understand even the simplest PDBs.


4.2 Constructing PDBs
4.2 构建PDB

A DS domain is configured to meet the network operator's traffic engineering goals for the domain independently of the performance goals for a particular flow of a traffic aggregate. Once the


interior routers are configured for the number of distinct traffic aggregates that the network will handle, each PDB's allocation at the edge comes from meeting the desired performance goals for the PDB's traffic aggregate subject to that configuration of packet schedulers and bandwidth capacity. The configuration of traffic conditioners at the edge may be altered by provisioning or admission control but the decision about which PDB to use and how to apply classification and traffic conditioning comes from matching performance to goals.


For example, consider the DS domain of figure 3. A PDB with an explicit bound on loss must apply traffic conditioning at the boundary to ensure that on the average no more packets are admitted than can emerge. Though, queueing internal to the network may result in a difference between input and output traffic over some timescales, the averaging timescale should not exceed what might be expected for reasonably sized buffering inside the network. Thus if bursts are allowed to arrive into the interior of the network, there must be enough capacity to ensure that losses don't exceed the bound. Note that explicit bounds on the loss level can be particularly difficult as the exact way in which packets merge inside the network affects the burstiness of the PDB's traffic aggregate and hence, loss.


PHBs give explicit expressions of the treatment a traffic aggregate can expect at each hop. For a PDB, this behavior must apply to merging and diverging traffic aggregates, thus characterizing a PDB requires understanding what happens to a PHB under aggregation. That is, PHBs recursively applied must result in a known behavior. As an example, since maximum burst sizes grow with the number of microflows or traffic aggregate streams merged, a PDB specification must address this. A clear advantage of constructing behaviors that aggregate is the ease of concatenating PDBs so that the associated traffic aggregate has known attributes that span interior DS domains and, eventually, farther. For example, in figure 1 assume that we have configured the foo PDB on the interior DS domains of AS2. Then traffic aggregates associated with the foo PDB in each interior DS domain of AS2 can be merged at the shaded interior boundary routers. If the same (or fewer) traffic conditioners as applied at the entrance to AS2 are applied at these interior boundaries, the attributes of the foo PDB should continue to be used to quantify the expected behavior. Explicit expressions of what happens to the behavior under aggregation, possibly parameterized by node in-degrees or network diameters, are necessary to determine what to do at the internal aggregation points. One approach might be to completely reapply the traffic conditioning at these points; another might employ some limited rate-based remarking only.

PHB给出了流量聚合在每个跃点可以期望的处理的显式表达式。对于PDB,此行为必须适用于合并和分流流量聚合,因此描述PDB的特征需要了解聚合下PHB的情况。也就是说,递归应用PHB必须导致已知的行为。例如,由于最大突发大小随着合并的微流或流量聚合流的数量而增长,因此PDB规范必须解决这一问题。构建聚合行为的一个明显优势是易于连接PDB,从而使关联的流量聚合具有跨内部DS域的已知属性,并最终具有更远的属性。例如,在图1中,假设我们已经在AS2的内部DS域上配置了foo PDB。然后,与AS2的每个内部DS域中的foo PDB相关联的流量聚合可以在阴影内部边界路由器处合并。如果在这些内部边界处应用了与AS2入口处相同(或更少)的交通调节器,则应继续使用foo PDB的属性来量化预期行为。聚合下行为的显式表达式(可能由节点以度或网络直径为单位进行参数化)对于确定在内部聚合点执行的操作是必需的。一种方法可能是在这些点上完全重新应用交通调节;另一种可能只使用一些有限的基于比率的评论。

Multiple PDBs may use the same PHB. The specification of a PDB can contain a list of PHBs and their required configuration, all of which would result in the same PDB. In operation, it is expected that a single domain will use a single PHB to implement a particular PDB, though different domains may select different PHBs. Recall that in the diffserv definition [RFC2474], a single PHB might be selected within a domain by a list of DSCPs. Multiple PDBs might use the same PHB in which case the transit performance of traffic aggregates of these PDBs will, of necessity, be the same. Yet, the particular characteristics that the PDB designer wishes to claim as attributes may vary, so two PDBs that use the same PHB might not be specified with the same list of attributes.


The specification of the transit expectations of PDBs across domains both assists in the deployment of QoS within a DS domain and helps enable the composition of end-to-end, cross-domain services to proceed by making it possible to hide details of a domain's internals while exposing characteristics necessary for QoS.


4.3 PDBs using PHB Groups
4.3 使用PHB组的PDB

The use of PHB groups to construct PDBs can be done in several ways. A single PHB member of a PHB group might be used to construct a single PDB. For example, a PDB could be defined using just one of the Class Selector Compliant PHBs [RFC2474]. The traffic conditioning for that PDB and the required configuration of the particular PHB would be defined in such a way that there was no dependence or relationship with the manner in which other PHBs of the group are used or, indeed, whether they are used in that DS domain. In this case, the reasonable approach would be to specify this PDB alone in a document which expressly called out the conditions and configuration of the Class Selector PHB required.


A single PDB can be constructed using more than one PHB from the same PHB group. For example, the traffic conditioner described in RFC 2698 might be used to mark a particular entering traffic aggregate for one of the three AF1x PHBs [RFC2597] while the transit performance of the resultant PDB is specified, statistically, across all the packets marked with one of those PHBs.

可以使用来自同一PHB组的多个PHB构建单个PDB。例如,RFC 2698中描述的业务调节器可用于标记三个AF1x phb[RFC2597]中的一个的特定进入业务聚合,同时在统计上,在标记有这些phb中的一个的所有分组上指定所得PDB的传输性能。

A set of related PDBs might be defined using a PHB group. In this case, the related PDBs should be defined in the same document. This is appropriate when the traffic conditioners that create the traffic aggregates associated with each PDB have some relationships and interdependencies such that the traffic aggregates for these PDBs should be described and characterized together. The transit attributes will depend on the PHB associated with the PDB and will not be the same for all PHBs in the group, though there may be some


parameterized interrelationship between the attributes of each of these PDBs. In this case, each PDB should have a clearly separate description of its transit attributes (delineated in a separate subsection) within the document. For example, the traffic conditioner described in RFC 2698 might be used to mark arriving packets for three different AF1x PHBs, each of which is to be treated as a separate traffic aggregate in terms of transit properties. Then a single document could be used to define and quantify the relationship between the arriving packets and the emerging traffic aggregates as they relate to one another. The transit characteristics of packets of each separate AF1x traffic aggregate should be described separately within the document.

每个PDB属性之间的参数化相互关系。在这种情况下,每个PDB应在文件中清楚地单独描述其运输属性(在单独的小节中描述)。例如,RFC 2698中描述的业务调节器可用于为三个不同的AF1x phb标记到达的分组,每个AF1x phb在传输属性方面被视为单独的业务聚合。然后,可以使用单个文档定义和量化到达的数据包和新兴流量集合之间的关系,因为它们彼此相关。每个单独的AF1x流量聚合的数据包的传输特性应在文件中单独描述。

Another way in which a PHB group might be used to create one PDB per PHB might have decoupled traffic conditioners, but some relationship between the PHBs of the group. For example, a set of PDBs might be defined using Class Selector Compliant PHBs [RFC2474] in such a way that the traffic conditioners that create the traffic aggregates are not related, but the transit performance of each traffic aggregate has some parametric relationship to the other. If it makes sense to specify them in the same document, then the author(s) should do so.


4.4 Forwarding path vs. control plane
4.4 转发路径与控制平面

A PDB's associated PHB, classifiers, and traffic conditioners are all in the packet forwarding path and operate at line rates. PHBs, classifiers, and traffic conditioners are configured in response to control plane activity which takes place across a range of time scales, but, even at the shortest time scale, control plane actions are not expected to happen per-packet. Classifiers and traffic conditioners at the DS domain boundary are used to enforce who gets to use the PDB and how the PDB should behave temporally. Reconfiguration of PHBs might occur monthly, quarterly, or only when the network is upgraded. Classifiers and traffic conditioners might be reconfigured at a few regular intervals during the day or might happen in response to signalling decisions thousands of times a day. Much of the control plane work is still evolving and is outside the charter of the Diffserv WG. We note that this is quite appropriate since the manner in which the configuration is done and the time scale at which it is done should not affect the PDB attributes.


5 Format for Specification of Diffserv Per-Domain Behaviors


PDBs arise from a particular relationship between edge and interior (which may be parameterized). The quantifiable characteristics of a PDB must be independent of whether the network edge is configured statically or dynamically. The particular configuration of traffic


conditioners at the DS domain edge is critical to how a PDB performs, but the act(s) of configuring the edge is a control plane action which can be separated from the specification of the PDB.


The following sections must be present in any specification of a Differentiated Services PDB. Of necessity, their length and content will vary greatly.


5.1 Applicability Statement
5.1 适用性声明

All PDB specs must have an applicability statement that outlines the intended use of this PDB and the limits to its use.


5.2 Technical specification
5.2 技术规格

This section specifies the rules or guidelines to create this PDB, each distinguished with "may", "must" and "should." The technical specification must list the classification and traffic conditioning required (if any) and the PHB (or PHBs) to be used with any additional requirements on their configuration beyond that contained in RFCs. Classification can reflect the results of an admission control process. Traffic conditioning may include marking, traffic shaping, and policing. A Service Provisioning Policy might be used to describe the technical specification of a particular PDB.


5.3 Attributes
5.3 属性

A PDB's attributes tell how it behaves under ideal conditions if configured in a specified manner (where the specification may be parameterized). These might include drop rate, throughput, delay bounds measured over some time period. They may be bounds, statistical bounds, or percentiles (e.g., "90% of all packets measured over intervals of at least 5 minutes will cross the DS domain in less than 5 milliseconds"). A wide variety of characteristics may be used but they must be explicit, quantifiable, and defensible. Where particular statistics are used, the document must be precise about how they are to be measured and about how the characteristics were derived.


Advice to a network operator would be to use these as guidelines in creating a service specification rather than use them directly. For example, a "loss-free" PDB would probably not be sold as such, but rather as a service with a very small packet loss probability.


5.4 Parameters
5.4 参数

The definition and characteristics of a PDB may be parameterized by network-specific features; for example, maximum number of hops, minimum bandwidth, total number of entry/exit points of the PDB to/from the diffserv network, maximum transit delay of network elements, minimum buffer size available for the PDB at a network node, etc.


5.5 Assumptions
5.5 假设

In most cases, PDBs will be specified assuming lossless links, no link failures, and relatively stable routing. This is reasonable since otherwise it would be very difficult to quantify behavior and this is the operating conditions for which most operators strive. However, these assumptions must be clearly stated. Since PDBs with specific bandwidth parameters require that bandwidth to be available, the assumptions to be stated may include standby capacity. Some PDBs may be specifically targeted for cases where these assumptions do not hold, e.g., for high loss rate links, and such targeting must also be made explicit. If additional restrictions, especially specific traffic engineering measures, are required, these must be stated.


Further, if any assumptions are made about the allocation of resources within a diffserv network in the creation of the PDB, these must be made explicit.


5.6 Example Uses
5.6 示例使用

A PDB specification must give example uses to motivate the understanding of ways in which a diffserv network could make use of the PDB although these are not expected to be detailed. For example, "A bulk handling PDB may be used for all packets which should not take any resources from the network unless they would otherwise go unused. This might be useful for Netnews traffic or for traffic rejected from some other PDB by traffic policers."


5.7 Environmental Concerns (media, topology, etc.)
5.7 环境问题(介质、拓扑等)

Note that it is not necessary for a provider to expose which PDB (if a commonly defined one) is being used nor is it necessary for a provider to specify a service by the PDB's attributes. For example, a service provider might use a PDB with a "no queueing loss" characteristic in order to specify a "very low loss" service.


This section is to inject realism into the characteristics described above. Detail the assumptions made there and what constraints that puts on topology or type of physical media or allocation.


5.8 Security Considerations for each PDB
5.8 每个PDB的安全注意事项

This section should include any security considerations that are specific to the PDB. Is it subject to any unusual theft-of-service or denial-of-service attacks? Are any unusual security precautions needed?


It is not necessary to repeat the general security discussions in [RFC2474] and [RFC2475], but a reference should be included. Also refer to any special security considerations for the PHB or PHBs used.


6 On PDB Attributes


As discussed in section 4, measurable, quantifiable attributes associated with each PDB can be used to describe what will happen to packets using that PDB as they cross the domain. In its role as a building block for the construction of interdomain quality-of-service, a PDB specification should provide the answer to the question: Under what conditions can we join the output of this domain to another under the same traffic conditioning and expectations? Although there are many ways in which traffic might be distributed, creating quantifiable, realizable PDBs that can be concatenated into multi-domain services limits the realistic scenarios. A PDB's attributes with a clear statement of the conditions under which the attributes hold is critical to the composition of multi-domain services.


There is a clear correlation between the strictness of the traffic conditioning and the quality of the PDB's attributes. As indicated earlier, numerical bounds are likely to be statistical or expressed as a percentile. Parameters expressed as strict bounds will require very precise mathematical analysis, while those expressed statistically can to some extent rely on experiment. Section 7 gives the example of a PDB without strict traffic conditioning and concurrent work on a PDB with strict traffic conditioning and attributes is also in front of the WG [VW]. This section gives some general considerations for characterizing PDB attributes.


There are two ways to characterize PDBs with respect to time. First are properties over "long" time periods, or average behaviors. A PDB specification should report these as the rates or throughput seen over some specified time period. In addition, there are properties of "short" time behavior, usually expressed as the allowable burstiness in a traffic aggregate. The short time behavior is important in understanding buffering requirements (and associated loss characteristics) and for metering and conditioning considerations at DS boundaries. For short-time behavior, we are


interested primarily in two things: 1) how many back-to-back packets of the PDB's traffic aggregate will we see at any point (this would be metered as a burst) and 2) how large a burst of packets of this PDB's traffic aggregate can appear in a queue at once (gives queue overflow and loss). If other PDBs are using the same PHB within the domain, that must be taken into account.


6.1 Considerations in specifying long-term or average PDB attributes
6.1 指定长期或平均PDB属性时的注意事项

To characterize the average or long-term behavior for the foo PDB we must explore a number of questions, for instance: Can the DS domain handle the average foo traffic flow? Is that answer topology dependent or are there some specific assumptions on routing which must hold for the foo PDB to preserve its "adequately provisioned" capability? In other words, if the topology of D changes suddenly, will the foo PDB's attributes change? Will its loss rate dramatically increase?

为了描述foo PDB的平均或长期行为,我们必须探索一些问题,例如:DS域能否处理平均的foo流量?这是否取决于拓扑结构,或者是否存在一些特定的路由假设,这些假设必须适用于foo PDB以保持其“充分配置”的功能?换句话说,如果D的拓扑突然改变,foo PDB的属性会改变吗?它的损失率会急剧增加吗?

Let domain D in figure 4 be an ISP ringing the U.S. with links of bandwidth B and with N tails to various metropolitan areas. Inside D, if the link between the node connected to A and the node connected to Z goes down, all the foo traffic aggregate between the two nodes must transit the entire ring: Would the bounded behavior of the foo PDB change? If this outage results in some node of the ring now having a larger arrival rate to one of its links than the capacity of the link for foo's traffic aggregate, clearly the loss rate would change dramatically. In this case, topological assumptions were made about the path of the traffic from A to Z that affected the characteristics of the foo PDB. If these topological assumptions no longer hold, the loss rate of packets of the foo traffic aggregate transiting the domain could change; for example, a characteristic such as "loss rate no greater than 1% over any interval larger than 10 minutes." A PDB specification should spell out the assumptions made on preserving the attributes.

让图4中的域D是一个ISP,它通过带宽为B的链路和N个尾端连接到不同的大都市区,向美国发出响铃。在D内部,如果连接到A的节点和连接到Z的节点之间的链路断开,则两个节点之间的所有foo流量聚合必须通过整个环:foo PDB的有界行为会改变吗?如果此中断导致环的某个节点现在对其一条链路的到达率大于foo流量聚合的链路容量,则显然丢失率将发生显著变化。在这种情况下,对影响foo PDB特性的从A到Z的流量路径进行了拓扑假设。如果这些拓扑假设不再成立,通过域的foo流量聚合的数据包丢失率可能会改变;例如,“任何大于10分钟的时间间隔内,损失率不超过1%”等特征。PDB规范应详细说明保留属性的假设。

                  ____X________X_________X___________          /
                 /                                   \    L   |
         A<---->X                                     X<----->|  E
                |                                     |       |
                |               D                     |        \
         Z<---->X                                     |
                |                                     |
                         X                 X
                  ____X________X_________X___________          /
                 /                                   \    L   |
         A<---->X                                     X<----->|  E
                |                                     |       |
                |               D                     |        \
         Z<---->X                                     |
                |                                     |
                         X                 X

Figure 4: ISP and DS domain D connected in a ring and connected to DS domain E


6.2 Considerations in specifying short-term or bursty PDB attributes
6.2 指定短期或突发PDB属性时的注意事项

Next, consider the short-time behavior of the traffic aggregate associated with a PDB, specifically whether permitting the maximum bursts to add in the same manner as the average rates will lead to properties that aggregate or under what conditions this will lead to properties that aggregate. In our example, if domain D allows each of the uplinks to burst p packets into the foo traffic aggregate, the bursts could accumulate as they transit the ring. Packets headed for link L can come from both directions of the ring and back-to-back packets from foo's traffic aggregate can arrive at the same time. If the bandwidth of link L is the same as the links of the ring, this probably does not present a buffering problem. If there are two input links that can send packets to queue for L, at worst, two packets can arrive simultaneously for L. If the bandwidth of link L equals or exceeds twice B, the packets won't accumulate. Further, if p is limited to one, and the bandwidth of L exceeds the rate of arrival (over the longer term) of foo packets (required for bounding the loss) then the queue of foo packets for link L will empty before new packets arrive. If the bandwidth of L is equal to B, one foo packet must queue while the other is transmitted. This would result in N x p back-to- back packets of this traffic aggregate arriving over L during the same time scale as the bursts of p were permitted on the uplinks. Thus, configuring the PDB so that link L can handle the sum of the rates that ingress to the foo PDB doesn't guarantee that L can handle the sum of the N bursts into the foo PDB.

接下来,考虑与PDB相关联的流量聚集的短时行为,具体地,是否允许最大突发以与平均速率将导致聚集的属性相同的方式添加,或者在什么条件下,这将导致聚集的属性。在我们的示例中,如果域D允许每条上行链路将p个数据包突发到foo流量聚合中,则突发可能会在传输环时累积。指向链路L的数据包可以来自环的两个方向,来自foo的流量聚合的背靠背数据包可以同时到达。如果链路L的带宽与环的链路相同,则可能不会出现缓冲问题。如果有两个输入链路可以发送数据包到L的队列,最坏情况下,两个数据包可以同时到达L。如果链路L的带宽等于或超过B的两倍,数据包将不会累积。此外,如果p被限制为1,并且L的带宽超过foo分组(限制丢失所需的)的到达速率(长期),则链路L的foo分组队列将在新分组到达之前清空。如果L的带宽等于B,则一个foo数据包必须排队,而另一个则被传输。这将导致该业务聚合的N x p背对背数据包在上行链路上允许的p突发相同的时间尺度内通过L到达。因此,将PDB配置为链路L能够处理进入foo PDB的速率总和并不保证L能够处理进入foo PDB的N个突发的总和。

If the bandwidth of L is less than B, then the link must buffer Nxpx(B-L)/B foo packets to avoid loss. If the PDB is getting less than the full bandwidth L, this number is larger. For probabilistic bounds, a smaller buffer might do if the probability of exceeding it can be bounded.

如果L的带宽小于B,则链路必须缓冲Nxpx(B-L)/B foo数据包以避免丢失。如果PDB小于全带宽L,则该数字更大。对于概率边界,如果超过它的概率是有界的,则较小的缓冲区可能会这样做。

More generally, for router indegree of d, bursts of foo packets might arrive on each input. Then, in the absence of any additional traffic conditioning, it is possible that dxpx(# of uplinks) back-to-back foo packets can be sent across link L to domain E. Thus the DS domain E must permit these much larger bursts into the foo PDB than domain D permits on the N uplinks or else the foo traffic aggregate must be made to conform to the TCA for entering E (e.g., by shaping).

更一般地说,对于d级别的路由器,foo数据包的突发可能会到达每个输入端。然后,在没有任何附加流量调节的情况下,dxpx(上行链路的#)可能背对背的foo数据包可以通过链路L发送到域E。因此,DS域E必须允许这些比域D在N上行链路上允许的更大的突发进入foo PDB,否则必须使foo流量聚合符合TCA以进入E(例如,通过整形)。

What conditions should be imposed on a PDB and on the associated PHB in order to ensure PDBs can be concatenated, as across the interior DS domains of figure 1? Traffic conditioning for constructing a PDB that has certain attributes across a DS domain should apply independently of the origin of the packets. With reference to the


example we've been exploring, the TCA for the PDB's traffic aggregate entering link L into domain E should not depend on the number of uplinks into domain D.


6.3 Remarks
6.3 评论

This section has been provided as motivational food for thought for PDB specifiers. It is by no means an exhaustive catalog of possible PDB attributes or what kind of analysis must be done. We expect this to be an interesting and evolutionary part of the work of understanding and deploying differentiated services in the Internet. There is a potential for much interesting research work. However, in submitting a PDB specification to the Diffserv WG, a PDB must also meet the test of being useful and relevant by a deployment experience, described in section 8.


7 A Reference Per-Domain Behavior


The intent of this section is to define as a reference a Best Effort PDB, a PDB that has little in the way of rules or expectations.


7.1 Best Effort PDB
7.1 尽力而为的PDB
7.1.1 Applicability
7.1.1 适用性

A Best Effort (BE) PDB is for sending "normal internet traffic" across a diffserv network. That is, the definition and use of this PDB is to preserve, to a reasonable extent, the pre-diffserv delivery expectation for packets in a diffserv network that do not require any special differentiation. Although the PDB itself does not include bounds on availability, latency, and packet loss, this does not preclude Service Providers from engineering their networks so as to result in commercially viable bounds on services that utilize the BE PDB. This would be analogous to the Service Level Guarantees that are provided in today's single-service Internet.

最大努力(BE)PDB用于通过diffserv网络发送“正常互联网流量”。也就是说,该PDB的定义和使用是为了在合理的程度上保留区分服务网络中不需要任何特殊区分的分组的区分服务前交付期望。尽管PDB本身不包括可用性、延迟和数据包丢失的界限,但这并不妨碍服务提供商对其网络进行工程设计,从而对利用BE PDB的服务产生商业上可行的界限。这类似于当今单一服务互联网中提供的服务级别保证。

In the present single-service commercial Internet, Service Level Guarantees for availability, latency, and packet delivery can be found on the web sites of ISPs [WCG, PSI, UU]. For example, a typical North American round-trip latency bound is 85 milliseconds, with each service provider's site information specifying the method of measurement of the bounds and the terms associated with these bounds contractually.


7.1.2 TCS and PHB configurations
7.1.2 TCS和PHB配置

There are no restrictions governing rate and bursts of packets beyond the limits imposed by the ingress link. The network edge ensures that packets using the PDB are marked for the Default PHB (as defined in [RFC2474]), but no other traffic conditioning is required. Interior network nodes apply the Default PHB on these packets.


7.1.3 Attributes of this PDB
7.1.3 此PDB的属性

"As much as possible as soon as possible".


Packets of this PDB will not be completely starved and when resources are available (i.e., not required by packets from any other traffic aggregate), network elements should be configured to permit packets of this PDB to consume them.


Network operators may bound the delay and loss rate for services constructed from this PDB given knowledge about their network, but such attributes are not part of the definition.


7.1.4 Parameters
7.1.4 参数



7.1.5 Assumptions
7.1.5 假设

A properly functioning network, i.e., packets may be delivered from any ingress to any egress.


7.1.6 Example uses
7.1.6 示例使用

1. For the normal Internet traffic connection of an organization.

1. 用于组织的正常Internet流量连接。

2. For the "non-critical" Internet traffic of an organization.

2. 用于组织的“非关键”互联网流量。

3. For standard domestic consumer connections

3. 用于标准家用用户连接

7.1.7 Environmental Concerns
7.1.7 环境问题

There are no environmental concerns specific to this PDB.


7.1.8 Security Considerations for BE PDB
7.1.8 BE PDB的安全注意事项

There are no specific security exposures for this PDB. See the general security considerations in [RFC2474] and [RFC2475].


8 Guidelines for writing PDB specifications


G1. Following the format given in this document, write a draft and submit it as an Internet Draft. The document should have "diffserv" as some part of the name. Either as an appendix to the draft, or in a separate document, provide details of deployment experience with measured results on a network of non-trivial size carrying realistic traffic and/or convincing simulation results (simulation of a range of modern traffic patterns and network topologies as applicable). The document should be brought to the attention of the diffserv WG mailing list, if active.

G1。按照本文件中给出的格式,写一份草稿并作为互联网草稿提交。文档名称中应包含“diffserv”。作为草案的附录,或在单独的文件中,提供部署经验的详细信息,以及在具有真实流量和/或令人信服的模拟结果(适用时模拟一系列现代流量模式和网络拓扑)的非小规模网络上的测量结果。如果该文档处于活动状态,则应提请diffserv WG邮件列表注意。

G2. Initial discussion should focus primarily on the merits of the PDB, though comments and questions on the claimed attributes are reasonable. This is in line with the Differentiated Services goal to put relevance before academic interest in the specification of PDBs. Academically interesting PDBs are encouraged, but would be more appropriate for technical publications and conferences, not for submission to the IETF. (An "academically interesting" PDB might become a PDB of interest for deployment over time.)


The implementation of the following guidelines varies, depending on whether there is an active diffserv working group or not.


Active Diffserv Working Group path:


G3. Once consensus has been reached on a version of a draft that it is a useful PDB and that the characteristics "appear" to be correct (i.e., not egregiously wrong) that version of the draft goes to a review panel the WG co-chairs set up to audit and report on the characteristics. The review panel will be given a deadline for the review. The exact timing of the deadline will be set on a case-by-case basis by the co-chairs to reflect the complexity of the task and other constraints (IETF meetings, major holidays) but is expected to be in the 4-8 week range. During that time, the panel may correspond with the authors directly (cc'ing the WG co-chairs) to get clarifications. This process should result in a revised draft and/or a report to the WG from the panel that either endorses or disputes the claimed characteristics.


G4. If/when endorsed by the panel, that draft goes to WG last call. If not endorsed, the author(s) can give an itemized response to the panel's report and ask for a WG Last Call.


G5. If/when passes Last Call, goes to ADs for publication as a WG Informational RFC in our "PDB series".


If no active Diffserv Working Group exists:


G3. Following discussion on relevant mailing lists, the authors should revise the Internet Draft and contact the IESG for "Expert Review" as defined in section 2 of RFC 2434 [RFC2434].

G3。在讨论相关邮件列表后,作者应修改互联网草案,并联系IESG进行RFC 2434[RFC2434]第2节中定义的“专家评审”。

G4. Subsequent to the review, the IESG may recommend publication of the Draft as an RFC, request revisions, or decline to publish as an Informational RFC in the "PDB series".


9 Security Considerations


The general security considerations of [RFC2474] and [RFC2475] apply to all PDBs. Individual PDB definitions may require additional security considerations.


10 Acknowledgements


The ideas in this document have been heavily influenced by the Diffserv WG and, in particular, by discussions with Van Jacobson, Dave Clark, Lixia Zhang, Geoff Huston, Scott Bradner, Randy Bush, Frank Kastenholz, Aaron Falk, and a host of other people who should be acknowledged for their useful input but not be held accountable for our mangling of it. Grenville Armitage coined "per domain behavior (PDB)" though some have suggested similar terms prior to that. Dan Grossman, Bob Enger, Jung-Bong Suk, and John Dullaert reviewed the document and commented so as to improve its form.

本文件中的想法受到Diffserv工作组的重大影响,特别是与Van Jacobson、Dave Clark、Lixia Zhang、Geoff Huston、Scott Bradner、Randy Bush、Frank Kastenholz、Aaron Falk、,还有许多其他的人,他们的有用的意见应该得到承认,但不应该为我们的错误负责。格伦维尔·阿米蒂奇(Grenville Armitage)创造了“每域行为(per domain behavior,PDB)”,尽管在此之前有人提出了类似的术语。Dan Grossman、Bob Enger、Jung Bong Suk和John Dullaert审查了该文件并发表了评论,以改进其形式。



[RFC2474] Nichols, K., Blake, S. Baker, F. and D. Black, "Definition of the Differentiated Services Field (DS Field) in the IPv4 and IPv6 Headers", RFC 2474, December 1998.

[RFC2474]Nichols,K.,Blake,S.Baker,F.和D.Black,“IPv4和IPv6标头中区分服务字段(DS字段)的定义”,RFC 2474,1998年12月。

[RFC2475] Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z. and W. Weiss, "An Architecture for Differentiated Services", December 1998.


[RFC2597] Heinanen, J., Baker, F., Weiss, W. and J. Wroclawski, "Assured Forwarding PHB Group", RFC 2597, June 1999.

[RFC2597]Heinanen,J.,Baker,F.,Weiss,W.和J.Wroclawski,“保付PHB集团”,RFC 25971999年6月。

[RFC2598] Jacobson, V., Nichols, K. and K. Poduri, "An Expedited Forwarding PHB", RFC 2598, June 1999.

[RFC2598]Jacobson,V.,Nichols,K.和K.Poduri,“快速转发PHB”,RFC 25981999年6月。

[RFC2698] Heinanen, J. and R. Geurin, "A Two Rate Three Color Marker", RFC 2698, June 1999.

[RFC2698]Heinanen,J.和R.Geurin,“双速率三色标记”,RFC 26981999年6月。

[MODEL] Bernet, Y., Blake, S., Grossman, D. and A. Smith, "An Informal Management Model for Diffserv Routers", Work in Progress.


[MIB] Baker, F., Chan, K. and A. Smith, "Management Information Base for the Differentiated Services Architecture", Work in Progress.


[VW] Jacobson, V., Nichols, K. and K. Poduri, "The 'Virtual Wire' Per-Domain Behavior", Work in Progress.


   [WCG]     Worldcom, "Internet Service Level Guarantee",
   [WCG]     Worldcom, "Internet Service Level Guarantee",
   [PSI]     PSINet, "Service Level Agreements",
   [PSI]     PSINet, "Service Level Agreements",
   [UU]      UUNET USA Web site, "Service Level Agreements",
   [UU]      UUNET USA Web site, "Service Level Agreements",

[RFC2434] Alvestrand, H. and T. Narten, "Guidelines for IANA Considerations", BCP 26, RFC 2434, October 1998.

[RFC2434]Alvestrand,H.和T.Narten,“IANA考虑的指南”,BCP 26,RFC 2434,1998年10月。

Authors' Addresses


Kathleen Nichols Packet Design, LLC 2465 Latham Street, Third Floor Mountain View, CA 94040 USA

Kathleen Nichols Packet Design,LLC美国加利福尼亚州山景城莱瑟姆街2465号三楼,邮编94040


Brian Carpenter IBM c/o iCAIR Suite 150 1890 Maple Avenue Evanston, IL 60201 USA

Brian Carpenter IBM c/o iCAIR套房150 1890美国伊利诺伊州埃文斯顿枫叶大道1890号,邮编60201


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