Network Working Group E. Crawley
Request for Comments: 2386 Argon Networks
Category: Informational R. Nair
Arrowpoint
B. Rajagopalan
NEC USA
H. Sandick
Bay Networks
August 1998
Network Working Group E. Crawley
Request for Comments: 2386 Argon Networks
Category: Informational R. Nair
Arrowpoint
B. Rajagopalan
NEC USA
H. Sandick
Bay Networks
August 1998
A Framework for QoS-based Routing in the Internet
一种基于QoS的Internet路由框架
Status of this Memo
本备忘录的状况
This memo provides information for the Internet community. It does not specify an Internet standard of any kind. Distribution of this memo is unlimited.
本备忘录为互联网社区提供信息。它没有规定任何类型的互联网标准。本备忘录的分发不受限制。
Copyright Notice
版权公告
Copyright (C) The Internet Society (1998). All Rights Reserved.
版权所有（C）互联网协会（1998年）。版权所有。
ABSTRACT
摘要
QoS-based routing has been recognized as a missing piece in the evolution of QoS-based service offerings in the Internet. This document describes some of the QoS-based routing issues and requirements, and proposes a framework for QoS-based routing in the Internet. This framework is based on extending the current Internet routing model of intra and interdomain routing to support QoS.
基于QoS的路由已经被认为是Internet上基于QoS的服务发展过程中缺失的一部分。本文档描述了一些基于QoS的路由问题和需求，并提出了Internet中基于QoS的路由框架。该框架基于扩展现有的域内和域间路由模型来支持QoS。
This document proposes a framework for QoS-based routing, with the objective of fostering the development of an Internet-wide solution while encouraging innovations in solving the many problems that arise. QoS-based routing has many complex facets and it is recommended that the following two-pronged approach be employed towards its development:
本文件提出了一个基于QoS的路由框架，旨在促进互联网范围解决方案的开发，同时鼓励在解决出现的许多问题方面进行创新。基于QoS的路由有许多复杂的方面，建议采用以下双管齐下的方法进行开发：
1. Encourage the growth and evolution of novel intradomain QoS-based routing architectures. This is to allow the development of independent, innovative solutions that address the many QoS-based routing issues. Such solutions may be deployed in autonomous systems (ASs), large and small, based on their specific needs.
1. 鼓励新的基于域内QoS的路由架构的增长和发展。这是为了开发独立、创新的解决方案，解决许多基于QoS的路由问题。此类解决方案可根据其具体需求部署在大型和小型自治系统（ASs）中。
2. Encourage simple, consistent and stable interactions between ASs implementing routing solutions developed as above.
2. 鼓励ASs之间进行简单、一致和稳定的交互，实现上述开发的路由解决方案。
This approach follows the traditional separation between intra and interdomain routing. It allows solutions like QOSPF [GKOP98, ZSSC97], Integrated PNNI [IPNNI] or other schemes to be deployed for intradomain routing without any restriction, other than their ability to interact with a common, and perhaps simple, interdomain routing protocol. The need to develop a single, all encompassing solution to the complex problem of QoS-based routing is therefore obviated. As a practical matter, there are many different views on how QoS-based routing should be done. Much overall progress can be made if an opportunity exists for various ideas to be developed and deployed concurrently, while some consensus on the interdomain routing architecture is being developed. Finally, this routing model is perhaps the most practical from an evolution point of view. It is superfluous to say that the eventual success of a QoS-based Internet routing architecture would depend on the ease of evolution.
这种方法遵循域内和域间路由之间的传统分离。它允许像QOSPF[GKOP98，ZSSC97]、集成PNNI[IPNNI]或其他方案这样的解决方案被部署用于域内路由，而不受任何限制，除了它们能够与通用的、也许是简单的域间路由协议交互之外。因此，无需为基于QoS的路由的复杂问题开发单一、全面的解决方案。作为一个实际问题，对于如何进行基于QoS的路由有许多不同的观点。如果有机会同时开发和部署各种想法，同时就域间路由架构达成一些共识，则可以取得很大的总体进展。最后，从进化的角度来看，这种路由模型可能是最实用的。毫无疑问，基于QoS的Internet路由体系结构的最终成功取决于演化的容易程度。
The aim of this document is to describe the QoS-based routing issues, identify basic requirements on intra and interdomain routing, and describe an extension of the current interdomain routing model to support QoS. It is not an objective of this document to specify the details of intradomain QoS-based routing architectures. This is left up to the various intradomain routing efforts that might follow. Nor is it an objective to specify the details of the interface between reservation protocols such as RSVP and QoS-based routing. The specific interface functionality needed, however, would be clear from the intra and interdomain routing solutions devised. In the intradomain area, the goal is to develop the basic routing requirements while allowing maximum freedom for the development of solutions. In the interdomain area, the objectives are to identify the QoS-based routing functions, and facilitate the development or enhancement of a routing protocol that allows relatively simple interaction between domains.
本文档的目的是描述基于QoS的路由问题，确定域内和域间路由的基本要求，并描述当前域间路由模型的扩展以支持QoS。本文档的目的不是详细说明域内基于QoS的路由体系结构。这取决于随后可能进行的各种域内路由工作。指定诸如RSVP和基于QoS的路由等保留协议之间的接口细节也不是目标。然而，从设计的域内和域间路由解决方案中可以清楚地看到所需的特定接口功能。在域内领域，目标是开发基本路由需求，同时允许最大限度地自由开发解决方案。在域间领域，目标是确定基于QoS的路由功能，并促进允许域间相对简单交互的路由协议的开发或增强。
In the next section, a glossary of relevant terminology is given. In Section 3, the objectives of QoS-based routing are described and the issues that must be dealt with by QoS-based Internet routing efforts are outlined. In Section 4, some requirements on intradomain routing are defined. These requirements are purposely broad, putting few constraints on solution approaches. The interdomain routing model and issues are described in Section 5 and QoS-based multicast routing is discussed in Section 6. The interaction between QoS-based routing and resource reservation protocols is briefly considered in Section 7. Security considerations are listed in Section 8 and related work is described in Section 9. Finally, summary and conclusions are presented in Section 10.
在下一节中，将给出相关术语的词汇表。在第3节中，描述了基于QoS的路由的目标，并概述了基于QoS的Internet路由必须解决的问题。在第4节中，定义了域内路由的一些要求。这些需求是有目的地广泛的，对解决方案方法几乎没有限制。第5节描述了域间路由模型和问题，第6节讨论了基于QoS的多播路由。第7节简要讨论了基于QoS的路由协议和资源预留协议之间的相互作用。第8节列出了安全注意事项，第9节描述了相关工作。最后，第10节给出了总结和结论。
The following glossary lists the terminology used in this document and an explanation of what is meant. Some of these terms may have different connotations, but when used in this document, their meaning is as given.
以下术语表列出了本文件中使用的术语，并解释了其含义。其中一些术语可能有不同的含义，但在本文件中使用时，其含义与给定的相同。
Alternate Path Routing : A routing technique where multiple paths, rather than just the shortest path, between a source and a destination are utilized to route traffic. One of the objectives of alternate path routing is to distribute load among multiple paths in the network.
备用路径路由：一种路由技术，利用源和目标之间的多条路径（而不仅仅是最短路径）来路由流量。备用路径路由的目标之一是在网络中的多条路径之间分配负载。
Autonomous System (AS): A routing domain which has a common administrative authority and consistent internal routing policy. An AS may employ multiple intradomain routing protocols internally and interfaces to other ASs via a common interdomain routing protocol.
自治系统（AS）：具有共同管理权限和一致内部路由策略的路由域。AS可在内部采用多个域内路由协议，并通过公共域间路由协议与其他ASs接口。
Source: A host or router that can be identified by a unique unicast IP address.
来源：可通过唯一单播IP地址识别的主机或路由器。
Unicast destination: A host or router that can be identified by a unique unicast IP address.
单播目的地：可由唯一单播IP地址标识的主机或路由器。
Multicast destination: A multicast IP address indicating all hosts and routers that are members of the corresponding group.
多播目的地：多播IP地址，指示作为相应组成员的所有主机和路由器。
IP flow (or simply "flow"): An IP packet stream from a source to a destination (unicast or multicast) with an associated Quality of Service (QoS) (see below) and higher level demultiplexing information. The associated QoS could be "best-effort".
IP流（或简称“流”）：从源到目的地（单播或多播）的IP数据包流，具有相关的服务质量（QoS）（见下文）和更高级别的解复用信息。相关的QoS可以是“尽力而为”。
Quality-of-Service (QoS): A set of service requirements to be met by the network while transporting a flow.
服务质量（QoS）：网络在传输流时要满足的一组服务要求。
Service class: The definitions of the semantics and parameters of a specific type of QoS.
服务类：特定类型的QoS的语义和参数的定义。
Integrated services: The Integrated Services model for the Internet defined in RFC 1633 allows for integration of QoS services with the best effort services of the Internet. The Integrated Services (IntServ) working group in the IETF has defined two service classes, Controlled Load Service [W97] and Guaranteed Service [SPG97].
综合服务：RFC1633中定义的互联网综合服务模型允许将QoS服务与互联网的尽力而为服务进行集成。IETF中的综合服务（IntServ）工作组定义了两个服务类，受控负载服务[W97]和保证服务[SPG97]。
RSVP: The ReSerVation Protocol [BZBH97]. A QoS signaling protocol for the Internet.
RSVP：预约协议[BZBH97]。因特网的QoS信令协议。
Path: A unicast or multicast path.
路径：单播或多播路径。
Unicast path: A sequence of links from an IP source to a unicast IP destination, determined by the routing scheme for forwarding packets.
单播路径：从IP源到单播IP目的地的链路序列，由转发数据包的路由方案确定。
Multicast path (or Multicast Tree): A subtree of the network topology in which all the leaves and zero or more interior nodes are members of the same multicast group. A multicast path may be per-source, in which case the subtree is rooted at the source.
多播路径（或多播树）：网络拓扑的子树，其中所有叶子和零个或多个内部节点都是同一多播组的成员。多播路径可以是每个源，在这种情况下，子树的根位于源。
Flow set-up: The act of establishing state in routers along a path to satisfy the QoS requirement of a flow.
流设置：在路由器中沿路径建立状态以满足流的QoS要求的行为。
Crankback: A technique where a flow setup is recursively backtracked along the partial flow path up to the first node that can determine an alternative path to the destination.
回溯：一种技术，其中流设置沿着部分流路径递归回溯到第一个节点，该节点可以确定到目的地的替代路径。
QoS-based routing: A routing mechanism under which paths for flows are determined based on some knowledge of resource availability in the network as well as the QoS requirement of flows.
基于QoS的路由：一种路由机制，根据网络中资源可用性的一些知识以及流的QoS要求来确定流的路径。
Route pinning: A mechanism to keep a flow path fixed for a duration of time.
路由钉扎：一种在一段时间内保持流路径固定的机制。
Flow Admission Control (FAC): A process by which it is determined whether a link or a node has sufficient resources to satisfy the QoS required for a flow. FAC is typically applied by each node in the path of a flow during flow set-up to check local resource availability.
流量接纳控制（FAC）：确定链路或节点是否有足够的资源来满足流量所需的QoS的过程。FAC通常在流设置期间由流路径中的每个节点应用，以检查本地资源可用性。
Higher-level admission control: A process by which it is determined whether or not a flow set-up should proceed, based on estimates and policy requirements of the overall resource usage by the flow. Higher-level admission control may result in the failure of a flow set-up even when FAC at each node along the flow path indicates resource availability.
更高级别的许可控制：根据流对总体资源使用情况的估计和政策要求，确定是否应进行流设置的过程。即使流路径上每个节点的FAC指示资源可用性，更高级别的准入控制也可能导致流设置失败。
Routing deployed in today's Internet is focused on connectivity and typically supports only one type of datagram service called "best effort" [WC96]. Current Internet routing protocols, e.g. OSPF, RIP, use "shortest path routing", i.e. routing that is optimized for a single arbitrary metric, administrative weight or hop count. These routing protocols are also "opportunistic," using the current shortest path or route to a destination. Alternate paths with acceptable but non-optimal cost can not be used to route traffic (shortest path routing protocols do allow a router to alternate among
当今互联网上部署的路由主要关注连接性，通常只支持一种称为“尽力而为”的数据报服务[WC96]。当前的Internet路由协议，例如OSPF、RIP，使用“最短路径路由”，即针对单个任意度量、管理权重或跳数进行优化的路由。这些路由协议也是“机会主义的”，使用当前最短路径或到目的地的路由。具有可接受但非最优成本的备用路径不能用于路由流量（最短路径路由协议允许路由器在不同路径之间进行备用）
several equal cost paths to a destination).
到目的地的多条等成本路径）。
QoS-based routing must extend the current routing paradigm in three basic ways. First, to support traffic using integrated-services class of services, multiple paths between node pairs will have to be calculated. Some of these new classes of service will require the distribution of additional routing metrics, e.g. delay, and available bandwidth. If any of these metrics change frequently, routing updates can become more frequent thereby consuming network bandwidth and router CPU cycles.
基于QoS的路由必须以三种基本方式扩展当前的路由范式。首先，为了支持使用集成服务类服务的流量，必须计算节点对之间的多条路径。其中一些新的服务类别将需要分发额外的路由度量，例如延迟和可用带宽。如果这些指标中的任何一个频繁更改，路由更新可能会变得更频繁，从而消耗网络带宽和路由器CPU周期。
Second, today's opportunistic routing will shift traffic from one path to another as soon as a "better" path is found. The traffic will be shifted even if the existing path can meet the service requirements of the existing traffic. If routing calculation is tied to frequently changing consumable resources (e.g. available bandwidth) this change will happen more often and can introduce routing oscillations as traffic shifts back and forth between alternate paths. Furthermore, frequently changing routes can increase the variation in the delay and jitter experienced by the end users.
第二，今天的机会主义路由一旦找到“更好”的路径，就会将流量从一条路径转移到另一条路径。即使现有路径能够满足现有交通的服务要求，交通也会发生转移。如果路由计算与频繁变化的消耗性资源（例如可用带宽）相关联，则这种变化将更频繁地发生，并且当流量在备用路径之间来回移动时，会引入路由振荡。此外，频繁改变路由会增加最终用户所经历的延迟和抖动的变化。
Third, as mentioned earlier, today's optimal path routing algorithms do not support alternate routing. If the best existing path cannot admit a new flow, the associated traffic cannot be forwarded even if an adequate alternate path exists.
第三，正如前面提到的，今天的最优路径路由算法不支持备用路由。如果最佳现有路径不能接纳新的流，则即使存在足够的备用路径，也无法转发相关的流量。
It is important to understand the difference between QoS-based routing and resource reservation. While resource reservation protocols such as RSVP [BZBH97] provide a method for requesting and reserving network resources, they do not provide a mechanism for determining a network path that has adequate resources to accommodate the requested QoS. Conversely, QoS-based routing allows the determination of a path that has a good chance of accommodating the requested QoS, but it does not include a mechanism to reserve the required resources.
理解基于QoS的路由和资源预留之间的区别很重要。虽然诸如RSVP[BZBH97]之类的资源预留协议提供了请求和预留网络资源的方法，但它们不提供用于确定具有足够资源以适应所请求的QoS的网络路径的机制。相反，基于QoS的路由允许确定有很好机会容纳请求的QoS的路径，但它不包括保留所需资源的机制。
Consequently, QoS-based routing is usually used in conjunction with some form of resource reservation or resource allocation mechanism. Simple forms of QoS-based routing have been used in the past for Type of Service (TOS) routing [M98]. In the case of OSPF, a different shortest-path tree can be computed for each of the 8 TOS values in the IP header [ISI81]. Such mechanisms can be used to select specially provisioned paths but do not completely assure that resources are not overbooked along the path. As long as strict resource management and control are not needed, mechanisms such as TOS-based routing are useful for separating whole classes of traffic
因此，基于QoS的路由通常与某种形式的资源预留或资源分配机制结合使用。过去，基于QoS的路由的简单形式已用于服务类型（TOS）路由[M98]。在OSPF的情况下，可以为IP报头中的8个TOS值中的每一个计算不同的最短路径树[ISI81]。此类机制可用于选择特别配置的路径，但不能完全确保路径上的资源不会超售。只要不需要严格的资源管理和控制，基于TOS的路由等机制就有助于分离整个流量类别
over multiple routes. Such mechanisms might work well with the emerging Differential Services efforts [BBCD98].
在多条路线上。这种机制可能与新兴的差异化服务工作配合得很好[BBCD98]。
Combining a resource reservation protocol with QoS-based routing allows fine control over the route and resources at the cost of additional state and setup time. For example, a protocol such as RSVP may be used to trigger QoS-based routing calculations to meet the needs of a specific flow.
将资源预留协议与基于QoS的路由相结合，可以以额外的状态和设置时间为代价对路由和资源进行精细控制。例如，诸如RSVP的协议可用于触发基于QoS的路由计算以满足特定流的需要。
Under QoS-based routing, paths for flows would be determined based on some knowledge of resource availability in the network, as well as the QoS requirement of flows. The main objectives of QoS-based routing are:
在基于QoS的路由下，流的路径将基于网络中资源可用性的一些知识以及流的QoS需求来确定。基于QoS的路由的主要目标是：
1. Dynamic determination of feasible paths: QoS-based routing can determine a path, from among possibly many choices, that has a good chance of accommodating the QoS of the given flow. Feasible path selection may be subject to policy constraints, such as path cost, provider selection, etc.
1. 可行路径的动态确定：基于QoS的路由可以从可能的许多选择中确定一条路径，该路径很有可能适应给定流的QoS。可行的路径选择可能受到策略约束，例如路径成本、提供商选择等。
2. Optimization of resource usage: A network state-dependent QoS-based routing scheme can aid in the efficient utilization of network resources by improving the total network throughput. Such a routing scheme can be the basis for efficient network engineering.
2. 资源使用优化：基于网络状态相关QoS的路由方案可以通过提高网络总吞吐量来帮助有效利用网络资源。这种路由方案可以作为高效网络工程的基础。
3. Graceful performance degradation: State-dependent routing can compensate for transient inadequacies in network engineering (e.g., during focused overload conditions), giving better throughput and a more graceful performance degradation as compared to a state-insensitive routing scheme [A84].
3. 优雅的性能下降：与状态不敏感的路由方案相比，状态相关的路由可以弥补网络工程中的暂时不足（例如，在集中过载条件下），提供更好的吞吐量和更优雅的性能下降[A84]。
QoS-based routing in the Internet, however, raises many issues:
然而，Internet中基于QoS的路由产生了许多问题：
- How do routers determine the QoS capability of each outgoing link and reserve link resources? Note that some of these links may be virtual, over ATM networks and others may be broadcast multi-access links.
- 路由器如何确定每个传出链路和保留链路资源的QoS能力？请注意，其中一些链路可能是虚拟的，通过ATM网络，而其他链路可能是广播多址链路。
- What is the granularity of routing decision (i.e., destination-based, source and destination-based, or flow-based)?
- 路由决策的粒度是多少（即基于目的地、基于源和目的地或基于流）？
- What routing metrics are used and how are QoS-accommodating paths computed for unicast flows?
- 使用什么路由度量以及如何为单播流计算QoS适应路径？
- How are QoS-accommodating paths computed for multicast flows with different reservation styles and receiver heterogeneity?
- 如何为具有不同保留样式和接收器异构性的多播流计算QoS适应路径？
- What are the performance objectives while computing QoS-based paths?
- 计算基于QoS的路径时，性能目标是什么？
- What are the administrative control issues?
- 什么是行政控制问题？
- What factors affect the routing overheads?, and
- 哪些因素会影响路由开销？以及
- How is scalability achieved?
- 如何实现可伸缩性？
Some of these issues are discussed briefly next. Interdomain routing is discussed in Section 5.
下面将简要讨论其中一些问题。域间路由在第5节中讨论。
To determine whether the QoS requirements of a flow can be accommodated on a link, a router must be able to determine the QoS available on the link. It is still an open issue as to how the QoS availability is determined for broadcast multiple access links (e.g., Ethernet). A related problem is the reservation of resources over such links. Solutions to these problems are just emerging [GPSS98].
为了确定链路上是否可以满足流的QoS要求，路由器必须能够确定链路上可用的QoS。如何确定广播多址链路（如以太网）的QoS可用性仍然是一个悬而未决的问题。一个相关的问题是通过这种链接保留资源。这些问题的解决方案刚刚出现[GPSS98]。
Similar problems arise when a router is connected to a large non-broadcast multiple access network, such as ATM. In this case, if the destination of a flow is outside the ATM network, the router may have multiple egress choices. Furthermore, the QoS availability on the ATM paths to each egress point may be different. The issues then are,
当路由器连接到大型非广播多址网络（如ATM）时，也会出现类似的问题。在这种情况下，如果流的目的地在ATM网络之外，则路由器可能具有多个出口选择。此外，到每个出口点的ATM路径上的QoS可用性可能不同。那么问题是,，
o how does a router determine all the egress choices across the ATM network? o how does it determine what QoS is available over the path to each egress point?, and o what QoS value does the router advertise for the ATM link.
o 路由器如何确定ATM网络中的所有出口选择？o它如何确定到每个出口点的路径上有什么QoS可用？o路由器为ATM链路公布什么QoS值。
Typically, IP routing over ATM (e.g., NHRP) allows the selection of a single egress point in the ATM network, and the procedure does not incorporate any knowledge of the QoS required over the path. An approach like I-PNNI [IPNNI] would be helpful here, although it introduces some complexity.
通常，ATM上的IP路由（例如，NHRP）允许在ATM网络中选择单个出口点，并且该过程不包含路径上所需的QoS的任何知识。像I-PNNI[IPNNI]这样的方法在这里会有所帮助，尽管它会带来一些复杂性。
An additional problem with resource reservation is how to determine what resources have already been allocated to a multicast flow. The availability of this information during path computation improves the chances of finding a path to add a new receiver to a multicast flow. QOSPF [ZSSC97] handles this problem by letting routers broadcast reserved resource information to other routers in their area.
资源保留的另一个问题是如何确定已分配给多播流的资源。路径计算期间此信息的可用性提高了找到路径以向多播流添加新接收器的机会。QOSPF[ZSSC97]通过允许路由器向其所在区域的其他路由器广播保留的资源信息来处理此问题。
Alternate path routing [ZES97] deals with this issue by using probe messages to find a path with sufficient resources. Path QoS Computation (PQC) method, proposed in [GOA97], propagates bandwidth allocation information in RSVP PATH messages. A router receiving the PATH message gets an indication of the resource allocation only on those links in the path to itself from the source. Allocation for the same flow on other remote branches of the multicast tree is not available. Thus, the PQC method may not be sufficient to find feasible QoS-accommodating paths to all receivers.
备用路径路由[ZES97]通过使用探测消息查找具有足够资源的路径来解决此问题。[GOA97]中提出的路径QoS计算（PQC）方法在RSVP路径消息中传播带宽分配信息。接收路径消息的路由器仅在从源到自身的路径中的那些链路上获得资源分配指示。无法在多播树的其他远程分支上分配相同的流。因此，PQC方法可能不足以找到到所有接收机的可行QoS适应路径。
Routing in the Internet is currently based only on the destination address of a packet. Many multicast routing protocols require routing based on the source AND destination of a packet. The Integrated Services architecture and RSVP allow QoS determination for an individual flow between a source and a destination. This set of routing granularities presents a problem for QoS routing solutions.
Internet中的路由目前仅基于数据包的目标地址。许多多播路由协议要求基于数据包的源和目的地进行路由。集成服务体系结构和RSVP允许对源和目标之间的单个流进行QoS确定。这组路由粒度为QoS路由解决方案提出了一个问题。
If routing based only on destination address is considered, then an intermediate router will route all flows between different sources and a given destination along the same path. This is acceptable if the path has adequate capacity but a problem arises if there are multiple flows to a destination that exceed the capacity of the link.
如果只考虑基于目标地址的路由，则中间路由器将沿同一路径在不同源和给定目标之间路由所有流。如果路径有足够的容量，这是可以接受的，但是如果有多个流到一个目的地，超过了链路的容量，就会出现问题。
One version of QOSPF [ZSSC97] determines QoS routes based on source and destination address. This implies that all traffic between a given source and destination, regardless of the flow, will travel down the same route. Again, the route must have capacity for all the QoS traffic for the source/destination pair. The amount of routing state also increases since the routing tables must include source/destination pairs instead of just the destination.
QOSPF[ZSSC97]的一个版本根据源地址和目标地址确定QoS路由。这意味着，给定来源和目的地之间的所有流量，无论流量如何，都将沿同一路线行驶。同样，路由必须具有源/目的地对的所有QoS流量的容量。由于路由表必须包括源/目标对，而不仅仅是目标，因此路由状态的数量也会增加。
The best granularity is found when routing is based on individual flows but this incurs a tremendous cost in terms of the routing state. Each QoS flow can be routed separately between any source and destination. PQC [GOA97] and alternate path routing [ZES97], are examples of solutions which operate at the flow level.
当路由基于单个流时，可以找到最佳粒度，但这会导致路由状态方面的巨大成本。每个QoS流可以在任何源和目标之间单独路由。PQC[GOA97]和备用路径路由[ZES97]是在流量级别运行的解决方案的示例。
Both source/destination and flow-based routing may be susceptible to packet looping under hop-by-hop forwarding. Suppose a node along a flow or source/destination-based path loses the state information for the flow. Also suppose that the flow-based route is different from the regular destination-based route. The potential then exists for a routing loop to form when the node forwards a packet belonging to the flow using its destination-based routing table to a node that occurs
源/目的地和基于流的路由都可能容易受到逐跳转发下的包循环的影响。假设沿流或基于源/目标的路径的节点丢失流的状态信息。还假设基于流的路由不同于基于常规目的地的路由。然后，当节点使用其基于目的地的路由表将属于流的数据包转发给发生故障的节点时，存在形成路由循环的可能性
earlier on the flow-based path. This is because the latter node may use its flow-based routing table to forward the packet again to the former and this can go on indefinitely.
前面介绍了基于流的路径。这是因为后一个节点可以使用其基于流的路由表将数据包再次转发给前一个节点，并且这种情况可以无限期地继续下去。
There are some considerations in defining suitable link and node metrics [WC96]. First, the metrics must represent the basic network properties of interest. Such metrics include residual bandwidth, delay and jitter. Since the flow QoS requirements have to be mapped onto path metrics, the metrics define the types of QoS guarantees the network can support. Alternatively, QoS-based routing cannot support QoS requirements that cannot be meaningfully mapped onto a reasonable combination of path metrics. Second, path computation based on a metric or a combination of metrics must not be too complex as to render them impractical. In this regard, it is worthwhile to note that path computation based on certain combinations of metrics (e.g., delay and jitter) is theoretically hard. Thus, the allowable combinations of metrics must be determined while taking into account the complexity of computing paths based on these metrics and the QoS needs of flows. A common strategy to allow flexible combinations of metrics while at the same time reduce the path computation complexity is to utilize "sequential filtering". Under this approach, a combination of metrics is ordered in some fashion, reflecting the importance of different metrics (e.g., cost followed by delay, etc.). Paths based on the primary metric are computed first (using a simple algorithm, e.g., shortest path) and a subset of them are eliminated based on the secondary metric and so forth until a single path is found. This is an approximation technique and it trades off global optimality for path computation simplicity (The filtering technique may be simpler, depending on the set of metrics used. For example, with bandwidth and cost as metrics, it is possible to first eliminate the set of links that do not have the requested bandwidth and then compute the least cost path using the remaining links.)
在定义合适的链路和节点度量时，需要考虑一些因素[WC96]。首先，度量必须表示感兴趣的基本网络属性。这些指标包括剩余带宽、延迟和抖动。由于流QoS需求必须映射到路径度量上，因此这些度量定义了网络可以支持的QoS保证的类型。或者，基于QoS的路由无法支持无法有意义地映射到路径度量的合理组合上的QoS需求。其次，基于度量或度量组合的路径计算不能太复杂，以致于无法实现。在这方面，值得注意的是，基于特定度量组合（例如，延迟和抖动）的路径计算在理论上是困难的。因此，必须确定允许的度量组合，同时考虑基于这些度量的计算路径的复杂性和流的QoS需求。允许灵活组合度量，同时降低路径计算复杂性的常用策略是利用“顺序过滤”。在这种方法下，度量的组合以某种方式排序，反映不同度量的重要性（例如，成本之后是延迟等）。首先计算基于主要度量的路径（使用简单的算法，例如最短路径），然后基于次要度量消除其中的子集，依此类推，直到找到单个路径。这是一种近似技术，它用路径计算的简单性来权衡全局最优性（过滤技术可能更简单，具体取决于所使用的指标集。例如，以带宽和成本为指标，可以首先消除不具有请求带宽的链路集，然后使用剩余链路计算最小成本路径。）
Now, once suitable link and node metrics are defined, a uniform representation of them is required across independent domains - employing possibly different routing schemes - in order to derive path metrics consistently (path metrics are obtained by the composition of link and node metrics). Encoding of the maximum, minimum, range, and granularity of the metrics are needed. Also, the definitions of comparison and accumulation operators are required. In addition, suitable triggers must be defined for indicating a significant change from a minor change. The former will cause a routing update to be generated. The stability of the QoS routes would
现在，一旦定义了合适的链路和节点度量，就需要跨独立域对它们进行统一表示（可能采用不同的路由方案），以便一致地导出路径度量（路径度量通过链路和节点度量的组合获得）。需要对度量的最大、最小、范围和粒度进行编码。此外，还需要比较运算符和累加运算符的定义。此外，必须定义适当的触发器，以指示微小变化的重大变化。前者将导致生成路由更新。QoS路由的稳定性将受到影响
depend on the ability to control the generation of updates. With interdomain routing, it is essential to obtain a fairly stable view of the interconnection among the ASs.
取决于控制更新生成的能力。对于域间路由，必须获得ASs之间互连的相当稳定的视图。
A hierarchy can be defined among various classes of service based on the degree to which traffic from one class can potentially degrade service of traffic from lower classes that traverse the same link. In this hierarchy, guaranteed constant bit rate traffic is at the top and "best-effort" datagram traffic at the bottom. Classes providing service higher in the hierarchy impact classes providing service in lower levels. The same situation is not true in the other direction. For example, a datagram flow cannot affect a real-time service. Thus, it may be necessary to distribute and update different metrics for each type of service in the worst case. But, several advantages result by identifying a single default metric. For example, one could derive a single metric combining the availability of datagram and real-time service over a common substrate.
可以根据来自一个类别的流量可能降低来自穿越同一链路的较低类别的流量的服务的程度，在各种服务类别之间定义层次结构。在这个层次结构中，保证恒定比特率的流量位于顶部，“尽力而为”的数据报流量位于底部。在层次结构中提供较高服务的类会影响在较低级别提供服务的类。从另一个角度看，情况并非如此。例如，数据报流不能影响实时服务。因此，在最坏的情况下，可能需要为每种类型的服务分发和更新不同的度量。但是，识别一个单一的默认指标会带来一些好处。例如，可以导出一个单一的度量，该度量结合了数据报的可用性和公共基础上的实时服务。
A delay-sensitive metric is probably the most obvious type of metric suitable for datagram flows. However, it requires careful analysis to avoid instabilities and to reduce storage and bandwidth requirements. For example, a recursive filtering technique based on a simple and efficient weighted averaging algorithm [NC94] could be used. This filter is used to stabilize the metric. While it is adequate for smoothing most loading patterns, it will not distinguish between patterns consisting of regular bursts of traffic and random loading. Among other stabilizing tools, is a minimum time between updates that can help filter out high-frequency oscillations.
延迟敏感度量可能是适合数据报流的最明显的度量类型。但是，它需要仔细分析，以避免不稳定，并减少存储和带宽需求。例如，可以使用基于简单有效的加权平均算法[NC94]的递归滤波技术。此过滤器用于稳定度量。虽然它足以平滑大多数加载模式，但它不会区分由规则流量突发和随机加载组成的模式。在其他稳定工具中，最短的更新间隔时间有助于滤除高频振荡。
In real-time quality-of-service, delay variation is generally more critical than delay as long as the delay is not too high. Clearly, voice-based applications cannot tolerate more than a certain level of delay. The condition of varying delays may be expected to a greater degree in a shared medium environment with datagrams, than in a network implemented over a switched substrate. Routing a real-time flow therefore reduces to an exercise in allocating the required network resources while minimizing fragmentation of bandwidth. The resulting situation is a bandwidth-limited minimum hop path from a source to the destination. In other words, the router performs an ordered search through paths of increasing hop count until it finds one that meets all the bandwidth needs of the flow. To reduce contention and the probability of false probes (due to inaccuracy in
在实时服务质量中，只要延迟不太高，延迟变化通常比延迟更为关键。显然，基于语音的应用程序不能容忍超过一定程度的延迟。与在交换基板上实现的网络相比，在具有数据报的共享介质环境中，可以更大程度地预期不同延迟的情况。因此，路由实时流将减少为分配所需网络资源的练习，同时最小化带宽碎片。由此产生的情况是从源到目的地的带宽受限的最小跳数路径。换句话说，路由器通过增加跳数的路径执行有序搜索，直到找到满足流所有带宽需求的路径。减少争用和错误探测的概率（由于
route tables), the router could select a path randomly from a "window" of paths which meet the needs of the flow and satisfy one of three additional criteria: best-fit, first-fit or worst-fit. Note that there is a similarity between the allocation of bandwidth and the allocation of memory in a multiprocessing system. First-fit seems to be appropriate for a system with a high real-time flow arrival rates; and worst-fit is ideal for real-time flows with high holding times. This rather nonintuitive result was shown in [NC94].
路由表），路由器可以从满足流量需求的路径“窗口”中随机选择一条路径，并满足三个附加标准之一：最佳拟合、首次拟合或最差拟合。注意，在多处理系统中，带宽分配和内存分配是相似的。首次拟合似乎适用于具有高实时流量到达率的系统；最差拟合是具有高保持时间的实时流的理想选择。这一相当非直观的结果如[NC94]所示。
Path computation by itself is merely a search technique, e.g., Shortest Path First (SPF) is a search technique based on dynamic programming. The usefulness of the paths computed depends to a large extent on the metrics used in evaluating the cost of a path with respect to a flow.
路径计算本身只是一种搜索技术，例如，最短路径优先（SPF）是一种基于动态规划的搜索技术。计算出的路径的有用性在很大程度上取决于用于评估路径相对于流的成本的度量。
Each link considered by the path computation engine must be evaluated against the requirements of the flow, i.e., the cost of providing the services required by the flow must be estimated with respect to the capabilities of the link. This requires a uniform method of combining features such as delay, bandwidth, priority and other service features. Furthermore, the costs must reflect the lost opportunity of using each link after routing the flow.
路径计算引擎考虑的每个链路必须根据流的要求进行评估，即，必须根据链路的能力估计提供流所需服务的成本。这需要一种统一的方法来组合延迟、带宽、优先级和其他服务特性等特性。此外，成本必须反映在路由流之后使用每个链路所失去的机会。
One common objective during path computation is to improve the total network throughput. In this regard, merely routing a flow on any path that accommodates its QoS requirement is not a good strategy. In fact, this corresponds to uncontrolled alternate routing [SD95] and may adversely impact performance at higher traffic loads. It is therefore necessary to consider the total resource allocation for a flow along a path, in relation to available resources, to determine whether or not the flow should be routed on the path. Such a mechanism is referred to in this document as "higher level admission control". The goal of this is to ensure that the "cost" incurred by the network in routing a flow with a given QoS is never more than the revenue gained. The routing cost in this regard may be the lost revenue in potentially blocking other flows that contend for the same resources. The formulation of the higher level admission control strategy, with suitable administrative hooks and with fairness to all flows desiring entry to the network, is an issue. The fairness problem arises because flows with smaller reservations tend to be more successfully routed than flows with large reservations, for a given engineered capacity. To guarantee a certain level of
路径计算的一个共同目标是提高网络总吞吐量。在这方面，仅仅在满足其QoS需求的任何路径上路由流不是一个好的策略。事实上，这与不受控制的备用路由[SD95]相对应，并可能对较高流量负载下的性能产生不利影响。因此，需要考虑与可用资源相关的路径上的流的总资源分配，以确定流是否应该在路径上路由。这种机制在本文件中称为“更高级别的准入控制”。这样做的目的是确保网络在路由具有给定QoS的流时产生的“成本”永远不会超过获得的收入。在这方面，路由成本可能是由于可能阻塞争夺相同资源的其他流而损失的收入。制定更高级别的准入控制策略是一个问题，该策略具有适当的管理挂钩，并且对希望进入网络的所有流公平。公平性问题的产生是因为对于给定的工程容量，具有较小保留的流往往比具有较大保留的流更成功地路由。保证一定程度的
acceptance rate for "larger" flows, without over-engineering the network, requires a fair higher level admission control mechanism. The application of higher level admission control to multicast routing is discussed later.
对于“较大”流的接受率，在不过度设计网络的情况下，需要公平的更高级别的接纳控制机制。随后讨论了高层接纳控制在组播路由中的应用。
There are several administrative control issues. First, within an AS employing state-dependent routing, administrative control of routing behavior may be necessary. One example discussed earlier was higher level admission control. Some others are described in this section. Second, the control of interdomain routing based on policy is an issue. The discussion of interdomain routing is defered to Section 5.
有几个行政控制问题。首先，在采用依赖于状态的路由的AS中，可能需要对路由行为进行管理控制。前面讨论的一个例子是更高级别的准入控制。本节将介绍其他一些。其次，基于策略的域间路由控制是一个问题。域间路由的讨论推迟到第5节。
Two areas that need administrative control, in addition to appropriate routing mechanisms, are handling flow priority with preemption, and resource allocation for multiple service classes.
除了适当的路由机制之外，还需要管理控制的两个领域是使用抢占处理流优先级，以及为多个服务类分配资源。
If there are critical flows that must be accorded higher priority than other types of flows, a mechanism must be implemented in the network to recognize flow priorities. There are two aspects to prioritizing flows. First, there must be a policy to decide how different users are allowed to set priorities for flows they originate. The network must be able to verify that a given flow is allowed to claim a priority level signaled for it. Second, the routing scheme must ensure that a path with the requested QoS will be found for a flow with a probability that increases with the priority of the flow. In other words, for a given network load, a high priority flow should be more likely to get a certain QoS from the network than a lower priority flow requesting the same QoS. Routing procedures for flow prioritization can be complex. Identification and evaluation of different procedures are areas that require investigation.
如果存在必须给予比其他类型流更高优先级的关键流，则必须在网络中实施一种机制来识别流优先级。确定流程优先级有两个方面。首先，必须有一个政策来决定如何允许不同的用户为他们发起的流设置优先级。网络必须能够验证是否允许给定的流声明为其发出信号的优先级。其次，路由方案必须确保为具有随流优先级增加的概率的流找到具有请求的QoS的路径。换句话说，对于给定的网络负载，与请求相同QoS的低优先级流相比，高优先级流更有可能从网络获得特定QoS。流优先级的路由过程可能很复杂。不同程序的识别和评估是需要调查的领域。
If there are multiple service classes, it is necessary to engineer a network to carry the forecasted traffic demands of each class. To do this, router and link resources may be logically partitioned among various service classes. It is desirable to have dynamic partitioning whereby unused resources in various partitions are dynamically shifted to other partitions on demand [ACFH92]. Dynamic sharing, however, must be done in a controlled fashion in order to prevent traffic under some service class from taking up more resources than
如果存在多个服务类别，则需要设计一个网络来承载每个类别的预测流量需求。为此，路由器和链路资源可以在各种服务类之间进行逻辑分区。希望具有动态分区，从而根据需要动态地将不同分区中未使用的资源转移到其他分区[ACFH92]。然而，动态共享必须以受控的方式进行，以防止某些服务类别下的通信占用的资源多于
what was engineered for it for prolonged periods of time. The design of such a resource sharing scheme, and its incorporation into the QoS-based routing scheme are significant issues.
为它设计的是长时间的。设计这样一个资源共享方案，并将其纳入基于QoS的路由方案是一个重要的问题。
QoS-based multicast routing is an important problem, especially if the notion of higher level admission control is included. The dynamism in the receiver set allowed by IP multicast, and receiver heterogeneity add to the problem. With straightforward implementation of distributed heuristic algorithms for multicast path computation [W88, C91], the difficulty is essentially one of scalability. To accommodate QoS, multicast path computation at a router must have knowledge of not only the id of subnets where group members are present, but also the identity of branches in the existing tree. In other words, routers must keep flow-specific state information. Also, computing optimal shared trees based on the shared reservation style [BZBH97], may require new algorithms. Multicast routing is discussed in some detail in Section 6.
基于QoS的多播路由是一个重要的问题，特别是如果包含更高级别的接纳控制的概念。IP多播所允许的接收器集的动态性和接收器异构性增加了问题。对于多播路径计算的分布式启发式算法的直接实现[W88，C91]，困难主要在于可伸缩性。为了适应QoS，路由器上的多播路径计算不仅必须知道组成员所在子网的id，还必须知道现有树中分支的标识。换句话说，路由器必须保持特定于流的状态信息。此外，基于共享保留样式[BZBH97]计算最优共享树可能需要新算法。第6节详细讨论了多播路由。
The overheads incurred by a routing scheme depend on the type of the routing scheme, as well as the implementation. There are three types of overheads to be considered: computation, storage and communication. It is necessary to understand the implications of choosing a routing mechanism in terms of these overheads.
路由方案产生的开销取决于路由方案的类型以及实现。需要考虑三种类型的开销：计算、存储和通信。有必要了解根据这些开销选择路由机制的含义。
For example, considering link state routing, the choice of the update propagation mechanism is important since network state is dynamic and changes relatively frequently. Specifically, a flooding mechanism would result in many unnecessary message transmissions and processing. Alternative techniques, such as tree-based forwarding [R96], have to be considered. A related issue is the quantization of state information to prevent frequent updating of dynamic state. While coarse quantization reduces updating overheads, it may affect the performance of the routing scheme. The tradeoff has to be carefully evaluated. QoS-based routing incurs certain overheads during flow establishment, for example, computing a source route. Whether this overhead is disproportionate compared to the length of the sessions is an issue. In general, techniques for the minimization of routing-related overheads during flow establishment must be investigated. Approaches that are useful include pre-computation of routes, caching recently used routes, and TOS routing based on hints in packets (e.g., the TOS field).
例如，考虑到链路状态路由，更新传播机制的选择很重要，因为网络状态是动态的，并且变化相对频繁。具体而言，泛洪机制将导致许多不必要的消息传输和处理。必须考虑替代技术，例如基于树的转发[R96]。一个相关的问题是状态信息的量化，以防止动态状态的频繁更新。虽然粗量化减少了更新开销，但它可能会影响路由方案的性能。必须仔细评估权衡。基于QoS的路由在流建立期间会产生某些开销，例如，计算源路由。与会话长度相比，这种开销是否不成比例是一个问题。一般来说，必须研究在流量建立过程中最小化路由相关开销的技术。有用的方法包括路由的预计算、缓存最近使用的路由以及基于数据包中的提示的TOS路由（例如，TOS字段）。
QoS-based routing should be scalable, and hierarchical aggregation is a common technique for scaling (e.g., [PNNI96]). But this introduces problems with regard to the accuracy of the aggregated state information [L95]. Also, the aggregation of paths under multiple constraints is difficult. One of the difficulties is the risk of accepting a flow based on inaccurate information, but not being able to support the QoS requirements of flow because the capabilities of the actual paths that are aggregated are not known during route computation. Performance impacts of aggregating path metric information must therefore be understood. A way to compensate for inaccuracies is to use crankback, i.e., dynamic search for alternate paths as a flow is being routed. But crankback increases the time to set up a flow, and may adversely affect the performance of the routing scheme under some circumstances. Thus, crankback must be used judiciously, if at all, along with a higher level admission control mechanism.
基于QoS的路由应该是可伸缩的，分层聚合是一种常用的伸缩技术（例如[PNNI96]）。但这就带来了有关聚合状态信息准确性的问题[L95]。此外，在多个约束条件下聚合路径也很困难。其中一个困难是接受基于不准确信息的流的风险，但不能支持流的QoS要求，因为在路由计算期间，聚合的实际路径的能力是未知的。因此，必须了解聚合路径度量信息对性能的影响。补偿不准确的一种方法是使用回退，即在流路由时动态搜索备用路径。但是回退会增加建立流的时间，并且在某些情况下可能会对路由方案的性能产生不利影响。因此，必须明智地使用回退（如果有的话）以及更高级别的准入控制机制。
At the intradomain level, the objective is to allow as much latitude as possible in addressing the QoS-based routing issues. Indeed, there are many ideas about how QoS-based routing services can be provisioned within ASs. These range from on-demand path computation based on current state information, to statically provisioned paths supporting a few service classes.
在域内级别，目标是在解决基于QoS的路由问题时，允许尽可能多的自由度。事实上，关于如何在ASs中提供基于QoS的路由服务，有很多想法。这些想法从基于当前状态信息的按需路径计算，到支持少数服务类的静态提供路径。
Another aspect that might invite differing solutions is performance optimization. Based on the technique used for this, intradomain routing could be very sophisticated or rather simple. Finally, the service classes supported, as well as the specific QoS engineered for a service class, could differ from AS to AS. For instance, some ASs may not support guaranteed service, while others may. Also, some ASs supporting the service may be engineered for a better delay bound than others. Thus, it requires considerable thought to determine the high level requirements for intradomain routing that both supports the overall view of QoS-based routing in the Internet and allows maximum autonomy in developing solutions.
另一个可能需要不同解决方案的方面是性能优化。基于用于此的技术，域内路由可能非常复杂或相当简单。最后，支持的服务类以及为服务类设计的特定QoS可能与as有所不同。例如，一些ASs可能不支持保证服务，而其他ASs可能不支持保证服务。此外，一些支持服务的ASs可能比其他ASs具有更好的延迟限制。因此，确定域内路由的高层次要求需要大量的思考，这既支持Internet中基于QoS的路由的总体视图，又允许在开发解决方案时实现最大的自主权。
Our view is that certain minimum requirements must be satisfied by intradomain routing in order to be qualified as "QoS-based" routing. These are:
我们的观点是，域内路由必须满足某些最低要求，才能被认定为“基于QoS的”路由。这些是：
- The routing scheme must route a flow along a path that can accommodate its QoS requirements, or indicate that the flow cannot be admitted with the QoS currently being requested.
- 路由方案必须沿着能够满足其QoS要求的路径路由流，或者指示在当前请求QoS的情况下不能接纳流。
- The routing scheme must indicate disruptions to the current route of a flow due to topological changes.
- 路由方案必须指示由于拓扑更改而对流的当前路由造成的中断。
- The routing scheme must accommodate best-effort flows without any resource reservation requirements. That is, present best effort applications and protocol stacks need not have to change to run in a domain employing QoS-based routing.
- 路由方案必须适应最大努力流，而不需要任何资源预留要求。也就是说，现有的尽力而为的应用程序和协议栈无需更改，即可在采用基于QoS的路由的域中运行。
- The routing scheme may optionally support QoS-based multicasting with receiver heterogeneity and shared reservation styles.
- 路由方案可以可选地支持具有接收器异质性和共享预约样式的基于QoS的多播。
In addition, the following capabilities are also recommended:
此外，还建议使用以下功能：
- Capabilities to optimize resource usage.
- 优化资源使用的功能。
- Implementation of higher level admission control procedures to limit the overall resource utilization by individual flows.
- 实施更高级别的准入控制程序，以限制单个流程的总体资源利用率。
Further requirements along these lines may be specified. The requirements should capture the consensus view of QoS-based routing, but should not preclude particular approaches (e.g., TOS-based routing) from being implemented. Thus, the intradomain requirements are expected to be rather broad.
可能会规定这些方面的进一步要求。这些要求应捕获基于QoS的路由的共识视图，但不应排除实施特定方法（例如，基于TOS的路由）。因此，域内需求预计将相当广泛。
The fundamental requirement on interdomain QoS-based routing is scalability. This implies that interdomain routing cannot be based on highly dynamic network state information. Rather, such routing must be aided by sound network engineering and relatively sparse information exchange between independent routing domains. This approach has the advantage that it can be realized by straightforward extensions of the present Internet interdomain routing model. A number of issues, however, need to be addressed to achieve this, as discussed below.
基于域间QoS的路由的基本要求是可伸缩性。这意味着域间路由不能基于高度动态的网络状态信息。相反，这种路由必须借助于健全的网络工程和独立路由域之间相对稀疏的信息交换。这种方法的优点是可以通过直接扩展现有的Internet域间路由模型来实现。然而，如下文所述，要实现这一目标，需要解决一些问题。
The interdomain QoS-based routing model is depicted below:
基于域间QoS的路由模型描述如下：
AS1 AS2 AS3
___________ _____________ ____________
| | | | | |
| B------B B----B |
| | | | | |
-----B----- B------------- --B---------
\ / /
\ / /
____B_____B____ _________B______
| | | |
| B-------B |
| | | |
| B-------B |
--------------- ----------------
AS4 AS5
AS1 AS2 AS3
___________ _____________ ____________
| | | | | |
| B------B B----B |
| | | | | |
-----B----- B------------- --B---------
\ / /
\ / /
____B_____B____ _________B______
| | | |
| B-------B |
| | | |
| B-------B |
--------------- ----------------
AS4 AS5
Here, ASs exchange standardized routing information via border nodes B. Under this model, each AS can itself consist of a set of interconnected ASs, with standardized routing interaction. Thus, the interdomain routing model is hierarchical. Also, each lowest level AS employs an intradomain QoS-based routing scheme (proprietary or standardized by intradomain routing efforts such as QOSPF). Given this structure, some questions that arise are:
在此，ASs通过边界节点B交换标准化路由信息。在此模型下，每个AS本身可以由一组互连的ASs组成，具有标准化路由交互。因此，域间路由模型是分层的。此外，每个最低级别AS采用基于域内QoS的路由方案（专有或由域内路由工作（如QOSPF）标准化）。鉴于这种结构，出现的一些问题是：
- What information is exchanged between ASs?
- 驴和驴之间交换什么信息？
- What routing capabilities does the information exchange lead to? (E.g., source routing, on-demand path computation, etc.)
- 信息交换带来了哪些路由功能？（例如，源路由、按需路径计算等）
- How is the external routing information represented within an AS?
- AS中的外部路由信息是如何表示的？
- How are interdomain paths computed?
- 如何计算域间路径？
- What sort of policy controls may be exerted on interdomain path computation and flow routing?, and
- 可以对域间路径计算和流路由施加何种策略控制
- How is interdomain QoS-based multicast routing accomplished?
- 基于域间QoS的多播路由是如何实现的？
At a high level, the answers to these questions depend on the routing paradigm. Specifically, considering link state routing, the information exchanged between domains would consist of an abstract representation of the domains in the form of logical nodes and links, along with metrics that quantify their properties and resource availability. The hierarchical structure of the ASs may be handled
在高层次上，这些问题的答案取决于路由范式。具体地说，考虑到链路状态路由，域之间交换的信息将包括逻辑节点和链路形式的域的抽象表示，以及量化其属性和资源可用性的度量。可以处理ASs的层次结构
by a hierarchical link state representation, with appropriate metric aggregation.
通过具有适当度量聚合的分层链路状态表示。
Link state routing may not necessarily be advantageous for interdomain routing for the following reasons:
由于以下原因，链路状态路由不一定对域间路由有利：
- One advantage of intradomain link state routing is that it would allow fairly detailed link state information be used to compute paths on demand for flows requiring QoS. The state and metric aggregation used in interdomain routing, on the other hand, erodes this property to a great degree.
- 域内链路状态路由的一个优点是，它允许相当详细的链路状态信息用于根据需要计算需要QoS的流的路径。另一方面，域间路由中使用的状态和度量聚合在很大程度上削弱了这一特性。
- The usefulness of keeping track of the abstract topology and metrics of a remote domain, or the interconnection between remote domains is not obvious. This is especially the case when the remote topology and metric encoding are lossy.
- 跟踪远程域的抽象拓扑和度量，或者远程域之间的互连的有用性并不明显。当远程拓扑和度量编码有损时尤其如此。
- ASs may not want to advertise any details of their internal topology or resource availability.
- ASs可能不想公布其内部拓扑或资源可用性的任何详细信息。
- Scalability in interdomain routing can be achieved only if information exchange between domains is relatively infrequent. Thus, it seems practical to limit information flow between domains as much as possible.
- 只有当域之间的信息交换相对较少时，域间路由的可伸缩性才能实现。因此，尽可能限制域之间的信息流似乎是可行的。
Compact information flow allows the implementation QoS-enhanced versions of existing interdomain protocols such as BGP-4. We look at the interdomain routing issues in this context.
紧凑的信息流允许实现现有域间协议（如BGP-4）的QoS增强版本。在此背景下，我们研究域间路由问题。
The information flow between routing domains must enable certain basic functions:
路由域之间的信息流必须启用某些基本功能：
1. Determination of reachability to various destinations
1. 确定到达不同目的地的可达性
2. Loop-free flow routes
2. 环路自由流动路线
3. Address aggregation whenever possible
3. 尽可能地进行地址聚合
4. Determination of the QoS that will be supported on the path to a destination. The QoS information should be relatively static, determined from the engineered topology and capacity of an AS rather than ephemeral fluctuations in traffic load through the AS. Ideally, the QoS supported in a transit AS should be allowed to vary significantly only under exceptional circumstances, such as failures or focused overload.
4. 确定目标路径上支持的QoS。QoS信息应该是相对静态的，根据AS的工程拓扑和容量确定，而不是通过AS的流量负载的短暂波动。理想情况下，只有在异常情况下（如故障或集中过载），传输中支持的QoS才应允许显著变化。
5. Determination, optionally, of multiple paths for a given destination, based on service classes.
5. 根据服务类确定给定目的地的多条路径（可选）。
6. Expression of routing policies, including monetary cost, as a function of flow parameters, usage and administrative factors.
6. 路由策略的表达，包括货币成本，作为流量参数、使用和管理因素的函数。
Items 1-3 are already part of existing interdomain routing. Item 5 is also a straightfoward extension of the current model. The main problem areas are therefore items 4 and 6.
项目1-3已经是现有域间路由的一部分。第5项也是当前模型的直接扩展。因此，主要问题领域是第4项和第6项。
The QoS of an end-to-end path is obtained by composing the QoS available in each transit AS. Thus, border routers must first determine what the locally available QoS is in order to advertise routes to both internal and external destinations. The determination of local "AS metrics" (corresponding to link metrics in the intradomain case) should not be subject to too much dynamism. Thus, the issue is how to define such metrics and what triggers an occasional change that results in re-advertisements of routes.
端到端路径的QoS是通过将每次传输中可用的QoS组合为来获得的。因此，边界路由器必须首先确定本地可用的QoS是什么，以便向内部和外部目的地通告路由。本地“AS度量”（对应于域内情况下的链接度量）的确定不应受到太多的影响。因此，问题在于如何定义此类指标，以及是什么触发了偶尔的改变，从而导致重新发布路线。
The approach suggested in this document is not to compute paths based on residual or instantaneous values of AS metics (which can be dynamic), but utilize only the QoS capabilities engineered for aggregate transit flows. Such engineering may be based on the knowledge of traffic to be expected from each neighboring ASs and the corresponding QOS needs. This information may be obtained based on contracts agreed upon prior to the provisioning of services. The AS metric then corresponds to the QoS capabilities of the "virtual path" engineered through the AS (for transit traffic) and a different metric may be used for different neighbors. This is illustrated in the following figure.
本文件中建议的方法不是基于AS metics的剩余值或瞬时值（可以是动态的）来计算路径，而是仅利用为聚合公交流设计的QoS能力。这种工程可以基于每个相邻的ASs预期的业务量的知识和相应的QOS需求。该信息可根据提供服务前商定的合同获得。AS度量随后对应于通过AS（用于中转业务）设计的“虚拟路径”的QoS能力，并且不同的度量可用于不同的邻居。下图对此进行了说明。
AS1 AS2 AS3
___________ _____________ ____________
| | | | | |
| B------B1 B2----B |
| | | | | |
-----B----- B3------------ --B---------
\ /
\ /
____B_____B____
| |
| |
| |
| |
---------------
AS4
AS1 AS2 AS3
___________ _____________ ____________
| | | | | |
| B------B1 B2----B |
| | | | | |
-----B----- B3------------ --B---------
\ /
\ /
____B_____B____
| |
| |
| |
| |
---------------
AS4
Here, B1 may utilize an AS metric specific for AS1 when computing path metrics to be advertised to AS1. This metric is based on the resources engineered in AS2 for transit traffic from AS1. Similarly, B3 may utilize a different metric when computing path metrics to be advertised to AS4. Now, it is assumed that as long as traffic flow into AS2 from AS1 or AS4 does not exceed the engineered values, these path metrics would hold. Excess traffic due to transient fluctuations, however, may be handled as best effort or marked with a discard bit.
这里，B1在计算要通告给AS1的路径度量时，可以利用特定于AS1的AS度量。该指标基于AS2中针对AS1的过境交通设计的资源。类似地，B3在计算要向AS4通告的路径度量时可以利用不同的度量。现在，假设只要从AS1或AS4流入AS2的流量不超过工程值，这些路径度量将保持不变。然而，由于瞬时波动而产生的过量流量可以作为尽力而为的方式处理，或者用丢弃位标记。
Thus, this model is different from the intradomain model, where end nodes pick a path dynamically based on the QoS needs of the flow to be routed. Here, paths within ASs are engineered based on presumed, measured or declared traffic and QoS requirements. Under this model, an AS can contract for routes via multiple transit ASs with different QoS requirements. For instance, AS4 above can use both AS1 and AS2 as transits for same or different destinations. Also, a QoS contract between one AS and another may generate another contract between the second and a third AS and so forth.
因此，该模型不同于域内模型，在域内模型中，终端节点根据要路由的流的QoS需求动态地选择路径。在这里，ASs内的路径是基于假定、测量或声明的流量和QoS需求设计的。在该模型下，AS可以通过具有不同QoS要求的多个公交ASs来合约路由。例如，上面的AS4可以使用AS1和AS2作为相同或不同目的地的中转。此外，一个AS和另一个AS之间的QoS契约可以在第二个AS和第三个AS之间生成另一个契约，以此类推。
An issue is what triggers the recomputation of path metrics within an AS. Failures or other events that prevent engineered resource allocation should certainly trigger recomputation. Recomputation should not be triggered in response to arrival of flows within the engineered limit.
一个问题是什么触发AS中路径度量的重新计算。阻止工程资源分配的故障或其他事件肯定会触发重新计算。当流量到达工程限制范围内时，不应触发重新计算。
Path computation for an external destination at a border node is based on reachability, path metrics and local policies of selection. If there are multiple selection criteria (e.g., delay, bandwidth, cost, etc.), mutiple alternaives may have to be maintained as well as propagated by border nodes. Selection of a path from among many alternatives would depend on the QoS requests of flows, as well as policies. Path computation may also utilze any heuristics for optimizing resource usage.
边界节点处外部目的地的路径计算基于可达性、路径度量和本地选择策略。如果存在多个选择标准（例如，延迟、带宽、成本等），则可能需要维护多个备选方案，并通过边界节点进行传播。从许多备选方案中选择路径将取决于流的QoS请求以及策略。路径计算还可以使用任何启发式方法来优化资源使用。
An important issue in interdomain routing is the amount of flow state to be processed by transit ASs. Reducing the flow state by aggregation techniques must therefore be seriously considered. Flow aggregation means that transit traffic through an AS is classified into a few aggregated streams rather than being routed at the individual flow level. For example, an entry border router may classify various transit flows entering an AS into a few coarse categories, based on the egress node and QoS requirements of the flows. Then, the aggregated stream for a given traffic class may be
域间路由中的一个重要问题是transit ASs要处理的流状态量。因此，必须认真考虑通过聚合技术减少流状态。流量聚合是指通过AS的中转流量被划分为几个聚合流，而不是在单个流量级别进行路由。例如，入口边界路由器可以基于流的出口节点和QoS要求，将进入AS的各种传输流分类为几个粗略类别。然后，给定业务类别的聚合流可以是
routed as a single flow inside the AS to the exit border router. This router may then present individual flows to different neighboring ASs and the process repeats at each entry border router. Under this scenario, it is essential that entry border routers keep track of the resource requirements for each transit flow and apply admission control to determine whether the aggregate requirement from any neighbor exceeds the engineered limit. If so, some policy must be invoked to deal with the excess traffic. Otherwise, it may be assumed that aggregated flows are routed over paths that have adequate resources to guarantee QoS for the member flows. Finally, it is possible that entry border routers at a transit AS may prefer not to aggregate flows if finer grain routing within the AS may be more efficient (e.g., to aid load balancing within the AS).
在as内部作为单个流路由到出口边界路由器。然后，该路由器可以向不同的相邻ASs呈现单独的流，并且该过程在每个入口边界路由器处重复。在这种情况下，入口边界路由器必须跟踪每个交通流的资源需求，并应用准入控制来确定来自任何邻居的总需求是否超过工程限制。如果是这样，则必须调用一些策略来处理多余的流量。否则，可以假设聚合流路由到具有足够资源以保证成员流的QoS的路径上。最后，如果AS内的细粒度路由可能更有效（例如，帮助AS内的负载平衡），则过境AS处的入口边界路由器可能不希望聚合流。
It is hoped that the integrated services Internet architecture would allow providers to charge for IP flows based on their QoS requirements. A QoS-based routing architecture can aid in distributing information on expected costs of routing flows to various destinations via different domains. Clearly, from a provider's point of view, there is a cost incurred in guaranteeing QoS to flows. This cost could be a function of several parameters, some related to flow parameters, others based on policy. From a user's point of view, the consequence of requesting a particular QoS for a flow is the cost incurred, and hence the selection of providers may be based on cost. A routing scheme can aid a provider in distributing the costs in routing to various destinations, as a function of several parameters, to other providers or to end users. In the interdomain routing model described earlier, the costs to a destination will change as routing updates are passed through a transit domain. One of the goals of the routing scheme should be to maintain a uniform semantics for cost values (or functions) as they are handled by intermediate domains. As an example, consider the cost function generated by border node B1 in domain A and passed to node B2 in domain B below. The routing update may be injected into domain B by B2 and finally passed to B4 in domain C by router B3. Domain B may interpret the cost value received from domain A in any way it wants, for instance, adding a locally significant component to it. But when this cost value is passed to domain C, the meaning of it must be what domain A intended, plus the incremental cost of transiting domain B, but not what domain B uses internally.
希望综合服务互联网体系结构将允许提供商根据其QoS要求对IP流收费。基于QoS的路由体系结构可以帮助将关于路由流的预期成本的信息通过不同的域分发到不同的目的地。显然，从提供者的角度来看，保证流的QoS是有成本的。该成本可能是多个参数的函数，一些与流量参数相关，另一些基于策略。从用户的角度来看，请求流的特定QoS的结果是产生的成本，因此提供者的选择可以基于成本。路由方案可以帮助提供商将路由成本分配到各个目的地，作为多个参数的函数，分配给其他提供商或最终用户。在前面描述的域间路由模型中，随着路由更新通过传输域，目的地的成本将发生变化。路由方案的目标之一应该是维护成本值（或函数）的统一语义，因为它们由中间域处理。作为一个例子，考虑域A中的边界节点B1生成的成本函数，并将其传递到下面的域B中的节点B2。路由更新可由B2注入域B，并最终由路由器B3传递到域C中的B4。域B可以以其想要的任何方式解释从域A收到的成本值，例如，向其添加本地重要组件。但是当这个成本值传递给域C时，它的含义必须是域A想要的，加上转移域B的增量成本，而不是域B内部使用的成本。
Domain A Domain B Domain C
____________ ___________ ____________
| | | | | |
| B1------B2 B3---B4 |
| | | | | |
------------ ----------- ------------
Domain A Domain B Domain C
____________ ___________ ____________
| | | | | |
| B1------B2 B3---B4 |
| | | | | |
------------ ----------- ------------
A problem with charging for a flow is the determination of the cost when the QoS promised for the flow was not actually delivered. Clearly, when a flow is routed via multiple domains, it must be determined whether each domain delivers the QoS it declares possible for traffic through it.
流收费的一个问题是，当为流承诺的QoS没有实际交付时，如何确定成本。显然，当一个流通过多个域路由时，必须确定每个域是否为通过它的流量提供它声明的可能的QoS。
The goals of QoS-based multicast routing are as follows:
基于QoS的多播路由的目标如下：
- Scalability to large groups with dynamic membership
- 可扩展到具有动态成员资格的大型组
- Robustness in the presence of topological changes
- 拓扑变化下的鲁棒性
- Support for receiver-initiated, heterogeneous reservations
- 支持接收方发起的异构预订
- Support for shared reservation styles, and
- 支持共享预订样式，以及
- Support for "global" admission control, i.e., administrative control of resource consumption by the multicast flow.
- 支持“全局”许可控制，即多播流对资源消耗的管理控制。
The RSVP multicast flow model is as follows. The sender of a multicast flow advertises the traffic characteristics periodically to the receivers. On receipt of an advertisement, a receiver may generate a message to reserve resources along the flow path from the sender. Receiver reservations may be heterogeneous. Other multicast models may be considered.
RSVP多播流模型如下所示。多播流的发送方周期性地向接收方播发业务特性。在接收到广告时，接收器可以生成消息以沿来自发送者的流路径保留资源。接收方保留可能是异构的。可以考虑其他多播模型。
The multicast routing scheme attempts to determine a path from the sender to each receiver that can accommodate the requested reservation. The routing scheme may attempt to maximize network resource utilization by minimizing the total bandwidth allocated to the multicast flow, or by optimizing some other measure.
多播路由方案尝试确定从发送方到每个接收方的路径，该路径可以容纳请求的保留。路由方案可以尝试通过最小化分配给多播流的总带宽或通过优化某些其他度量来最大化网络资源利用率。
When addressing scalability, two aspects must be considered:
在解决可伸缩性问题时，必须考虑两个方面：
1. The overheads associated with receiver discovery. This overhead is incurred when determining the multicast tree for forwarding best-effort sender traffic characterization to receivers.
1. 与接收器发现相关的开销。当确定多播树以将尽力而为的发送方流量特征转发给接收方时，会产生此开销。
2. The overheads associated with QoS-based multicast path computation. This overhead is incurred when flow-specific state information has to be collected by a router to determine QoS-accommodating paths to a receiver.
2. 与基于QoS的多播路径计算相关的开销。当路由器必须收集特定于流的状态信息以确定到接收器的QoS适应路径时，就会产生这种开销。
Depending on the multicast routing scheme, one or both of these aspects become important. For instance, under the present RSVP model, reservations are established on the same path over which sender traffic characterizations are sent, and hence there is no path computation overhead. On the other hand, under the proposed QOSPF model [ZSSC97] of multicast source routing, receiver discovery overheads are incurred by MOSPF [M94] receiver location broadcasts, and additional path computation overheads are incurred due to the need to keep track of existing flow paths. Scaling of QoS-based multicast depends on both these scaling issues. However, scalable best-effort multicasting is really not in the domain of QoS-based routing work (solutions for this are being devised by the IDMR WG [BCF94, DEFV94]). QoS-based multicast routing may build on these solutions to achieve overall scalability.
根据多播路由方案，这些方面中的一个或两个变得很重要。例如，在目前的RSVP模型下，保留建立在发送发送方流量特征的同一路径上，因此没有路径计算开销。另一方面，在提出的多播源路由的QOSPF模型[ZSSC97]下，MOSPF[M94]接收机位置广播会产生接收机发现开销，并且由于需要跟踪现有流路径，会产生额外的路径计算开销。基于QoS的多播的扩展取决于这两个扩展问题。然而，可扩展的尽力而为多播实际上并不属于基于QoS的路由工作领域（IDMR WG[BCF94，DEFV94]正在设计解决方案）。基于QoS的多播路由可以基于这些解决方案来实现总体可伸缩性。
There are several options for QoS-based multicast routing. Multicast source routing is one under which multicast trees are computed by the first-hop router from the source, based on sender traffic advertisements. The advantage of this is that it blends nicely with the present RSVP signaling model. Also, this scheme works well when receiver reservations are homogeneous and the same as the maximum reservation derived from sender advertisement. The disadvantages of this scheme are the extra effort needed to accommodate heterogeneous reservations and the difficulties in optimizing resource allocation based on shared reservations.
基于QoS的多播路由有几种选择。多播源路由是由第一跳路由器根据发送方流量广告从源计算多播树的路由。这样做的优点是，它与当前的RSVP信令模型很好地融合在一起。此外，当接收者保留是同质的并且与从发送者广告中得到的最大保留相同时，该方案工作良好。该方案的缺点是需要额外的努力来适应异构保留，并且难以基于共享保留优化资源分配。
In these regards, a receiver-oriented multicast routing model seems to have some advantage over multicast source routing. Under this model:
在这些方面，面向接收者的多播路由模型似乎比多播源路由具有一些优势。在这种模式下：
1. Sender traffic advertisements are multicast over a best-effort tree which can be different from the QoS-accommodating tree for sender data.
1. 发送方流量广告是在最大努力树上的多播，该树可能不同于发送方数据的QoS适应树。
2. Receiver discovery overheads are minimized by utilizing a scalable scheme (e.g., PIM, CBT), to multicast sender traffic characterization.
2. 通过利用可伸缩方案（例如，PIM、CBT）对多播发送方流量特征进行描述，将接收方发现开销降至最低。
3. Each receiver-side router independently computes a QoS-accommodating path from the source, based on the receiver reservation. This path can be computed based on unicast routing information only, or with additional multicast flow-specific state information. In any case, multicast path computation is
3. 每个接收器侧路由器基于接收器预留独立地计算来自源的QoS适应路径。此路径可以仅基于单播路由信息计算，或者使用附加的多播流特定状态信息计算。在任何情况下，都需要进行多播路径计算
broken up into multiple, concurrent nunicast path computations.
分解为多个并发nunicast路径计算。
4. Routers processing unicast reserve messages from receivers aggregate resource reservations from multiple receivers.
4. 处理来自接收器的单播保留消息的路由器聚合来自多个接收器的资源保留。
Flow-specific state information may be limited in Step 3 to achieve scalability [RN98]. In general, limiting flow-specific information in making multicast routing decisions is important in any routing model. The advantages of this model are the ease with which heterogeneous reservations can be accommodated, and the ability to handle shared reservations. The disadvantages are the incompatibility with the present RSVP signaling model, and the need to rely on reverse paths when link state routing is not used. Both multicast source routing and the receiver-oriented routing model described above utilize per-source trees to route multicast flows. Another possibility is the utilization of shared, per-group trees for routing flows. The computation and usage of such trees require further work.
在步骤3中，可以限制特定于流的状态信息，以实现可伸缩性[RN98]。一般来说，在任何路由模型中，在做出多播路由决策时限制特定于流的信息都很重要。该模型的优点是易于容纳异构预订，并且能够处理共享预订。缺点是与现有的RSVP信令模型不兼容，并且在不使用链路状态路由时需要依赖反向路径。上述多播源路由和面向接收器的路由模型都利用每源树来路由多播流。另一种可能性是利用共享的每组树来路由流。这些树的计算和使用需要进一步的工作。
Finally, scalability at the interdomain level may be achieved if QoS-based multicast paths are computed independently in each domain. This principle is illustrated by the QOSPF multicast source routing scheme which allows independent path computation in different OSPF areas. It is easy to incorporate this idea in the receiver-oriented model also. An evaluation of multicast routing strategies must take into account the relative advantages and disadvantages of various approaches, in terms of scalability features and functionality supported.
最后，如果在每个域中独立地计算基于QoS的多播路径，则可以实现域间级别的可伸缩性。QOSPF多播源路由方案说明了这一原理，该方案允许在不同的OSPF区域进行独立的路径计算。在面向接收者的模型中也很容易融入这一思想。对多播路由策略的评估必须考虑到各种方法在可伸缩性特征和支持的功能方面的相对优势和劣势。
Higher level admission control, as defined for unicast, prevents excessive resource consumption by flows when traffic load is high. Such an admission control strategy must be applied to multicast flows when the flow path computation is receiver-oriented or sender-oriented. In essence, a router computing a path for a receiver must determine whether the incremental resource allocation for the receiver is excessive under some administratively determined admission control policy. Other admission control criteria, based on the total resource consumption of a tree may be defined.
为单播定义的更高级别的接纳控制可防止流量负载较高时流过度消耗资源。当流路径计算是面向接收方的或面向发送方的时，这种接纳控制策略必须应用于多播流。本质上，计算接收器路径的路由器必须确定在某些管理确定的许可控制策略下，接收器的增量资源分配是否过多。可以定义基于树的总资源消耗的其他接纳控制标准。
There must clearly be a well-defined interface between routing and resource reservation protocols. The nature of this interface, and the interaction between routing and resource reservation has to be determined carefully to avoid incompatibilities. The importance of this can be readily illustrated in the case of RSVP.
路由协议和资源预留协议之间必须有明确定义的接口。必须仔细确定此接口的性质以及路由和资源保留之间的交互，以避免不兼容。在RSVP的情况下，可以很容易地说明这一点的重要性。
RSVP has been designed to operate independent of the underlying routing scheme. Under this model, RSVP PATH messages establish the reverse path for RESV messages. In essence, this model is not compatible with QoS-based routing schemes that compute paths after receiver reservations are received. While this incompatibility can be resolved in a simple manner for unicast flows, multicast with heterogeneous receiver requirements is a more difficult case. For this, reconciliation between RSVP and QoS-based routing models is necessary. Such a reconciliation, however, may require some changes to the RSVP model depending on the QoS-based routing model [ZES97, ZSSC97, GOA97]. On the other hand, QoS-based routing schemes may be designed with RSVP compatibility as a necessary goal. How this affects scalability and other performance measures must be considered.
RSVP设计为独立于底层路由方案运行。在此模型下，RSVP PATH消息为RESV消息建立反向路径。本质上，该模型与基于QoS的路由方案不兼容，这些方案在接收到接收机预留后计算路径。虽然这种不兼容性可以通过单播流的简单方式解决，但具有异构接收器需求的多播是一种更困难的情况。为此，需要协调RSVP和基于QoS的路由模型。然而，根据基于QoS的路由模型[ZES97、ZSSC97、GOA97]，这种协调可能需要对RSVP模型进行一些更改。另一方面，基于QoS的路由方案可以设计为以RSVP兼容性为必要目标。必须考虑这对可伸缩性和其他性能度量的影响。
Security issues that arise with routing in general are about maintaining the integrity of the routing protocol in the presence of unintentional or malicious introduction of information that may lead to protocol failure [P88]. QoS-based routing requires additional security measures both to validate QoS requests for flows and to prevent resource-depletion type of threats that can arise when flows are allowed to make arbitratry resource requests along various paths in the network. Excessive resource consumption by an errant flow results in denial of resources to legitimate flows. While these situations may be prevented by setting up proper policy constraints, charging models and policing at various points in the network, the formalization of such protection requires work [BCCH94].
路由产生的安全问题通常是在存在可能导致协议失败的无意或恶意引入信息的情况下保持路由协议的完整性[P88]。基于QoS的路由需要额外的安全措施，以验证流的QoS请求，并防止在允许流沿网络中的各种路径发出仲裁资源请求时可能出现的资源耗尽类型的威胁。错误流过度消耗资源会导致拒绝向合法流提供资源。虽然可以通过在网络中的各个点设置适当的政策约束、收费模式和监管来防止这些情况，但这种保护的形式化需要努力[BCCH94]。
"Adaptive" routing, based on network state, has a long history, especially in circuit-switched networks. Such routing has also been implemented in early datagram and virtual circuit packet networks. More recently, this type of routing has been the subject of study in the context of ATM networks, where the traffic characteristics and topology are substantially different from those of circuit-switched networks [MMR96]. It is instructive to review the adaptive routing methodologies, both to understand the problems encountered and possible solutions.
基于网络状态的“自适应”路由由来已久，尤其是在电路交换网络中。这种路由也在早期的数据报和虚拟电路分组网络中实现。最近，这种类型的路由已经成为ATM网络的研究主题，ATM网络的流量特性和拓扑结构与电路交换网络的流量特性和拓扑结构有很大不同[MMR96]。回顾自适应路由方法对于理解遇到的问题和可能的解决方案都很有指导意义。
Fundamentally, there are two aspects to adaptive, network state-dependent routing:
基本上，自适应、网络状态相关的路由有两个方面：
1. Measuring and gathering network state information, and 2. Computing routes based on the available information.
1. 测量和收集网络状态信息。根据可用信息计算路线。
Depending on how these two steps are implemented, a variety of routing techniques are possible. These differ in the following respects:
根据这两个步骤的实现方式，可以使用多种路由技术。它们在以下方面有所不同：
- what state information is used - whether local or global state is used - what triggers the propagation of state information - whether routes are computed in a distributed or centralized manner - whether routes are computed on-demand, pre-computed, or in a hybrid manner - what optimization criteria, if any, are used in computing routes - whether source routing or hop by hop routing is used, and - how alternate route choices are explored
- 使用的状态信息是什么-使用的是局部还是全局状态-触发状态信息传播的因素是什么-路由是以分布式或集中式方式计算的-路由是按需计算的、预先计算的还是以混合方式计算的-优化标准是什么，如果有的话，用于计算路由-是否使用源路由或逐跳路由，以及-如何探索备用路由选择
It should be noted that most of the adaptive routing work has focused on unicast routing. Multicast routing is one of the areas that would be prominent with Internet QoS-based routing. We treat this separately, and the following review considers only unicast routing. This review is not exhaustive, but gives a brief overview of some of the approaches.
应该注意的是，大多数自适应路由工作都集中在单播路由上。组播路由是基于Internet QoS路由的一个突出领域。我们将单独处理这个问题，下面的综述只考虑单播路由。本综述并非详尽无遗，但简要概述了一些方法。
The most common optimization criteria used in adaptive routing is throughput maximization or delay minimization. A general formulation of the optimization problem is the one in which the network revenue is maximized, given that there is a cost associated with routing a flow over a given path [MMR96, K88]. In general, global optimization solutions are difficult to implement, and they rely on a number of assumptions on the characteristics of the traffic being routed [MMR96]. Thus, the practical approach has been to treat the routing of each flow (VC, circuit or packet stream to a given destination) independently of the routing of other flows. Many such routing schemes have been implemented.
自适应路由中最常用的优化标准是吞吐量最大化或延迟最小化。优化问题的一般公式是网络收益最大化的公式，假设存在与在给定路径上路由流相关的成本[MMR96，K88]。一般来说，全局优化解决方案很难实现，它们依赖于对路由流量特征的大量假设[MMR96]。因此，实际方法是独立于其他流的路由来处理每个流（VC、电路或分组流到给定目的地）的路由。许多这样的路由方案已经实现。
Many adaptive routing concepts have been proposed for circuit-switched networks. An example of a simple adaptive routing scheme is sequential alternate routing [T88]. This is a hop-by-hop destination-based routing scheme where only local state information is utilized. Under this scheme, a routing table is computed for each node, which lists multiple output link choices for each destination. When a call set-up request is received by a node, it tries each output link choice in sequence, until it finds one that can accommodate the call. Resources are reserved on this link, and the call set-up is forwarded to the next node. The set-up either reaches the destination, or is blocked at some node. In the latter case, the
许多自适应路由概念已经被提出用于电路交换网络。简单自适应路由方案的一个例子是顺序交替路由[T88]。这是一种基于逐跳目的地的路由方案，其中仅使用本地状态信息。在该方案下，为每个节点计算一个路由表，其中列出了每个目的地的多个输出链路选择。当节点接收到呼叫设置请求时，它会按顺序尝试每个输出链路选择，直到找到一个可以容纳呼叫的输出链路。资源在此链路上保留，呼叫设置被转发到下一个节点。设置要么到达目的地，要么在某个节点被阻止。在后一种情况下
set-up can be cranked back to the previous node or a failure declared. Crankback allows the previous node to try an alternate path. The routing table under this scheme can be computed in a centralized or distributed manner, based only on the topology of the network. For instance, a k-shortest-path algorithm can be used to determine k alternate paths from a node with distinct initial links [T88]. Some mechanism must be implemented during path computation or call set-up to prevent looping.
可以将设置返回到上一个节点或声明故障。回退允许上一个节点尝试另一个路径。该方案下的路由表可以通过集中式或分布式的方式计算，只需根据网络的拓扑结构即可。例如，可以使用k-最短路径算法来确定来自具有不同初始链路的节点的k条备用路径[T88]。在路径计算或调用设置期间必须实现一些机制以防止循环。
Performance studies of this scheme illustrate some of the pitfalls of alternate routing in general, and crankback in particular [A84, M86, YS87]. Specifically, alternate routing improves the throughput when traffic load is relatively light, but adversely affects the performance when traffic load is heavy. Crankback could further degrade the performance under these conditions. In general, uncontrolled alternate routing (with or without crankback) can be harmful in a heavily utilized network, since circuits tend to be routed along longer paths thereby utilizing more capacity. This is an obvious, but important result that applies to QoS-based Internet routing also.
该方案的性能研究说明了备用路由的一些缺陷，特别是回退[A84，M86，YS87]。具体地说，备用路由在流量负载相对较轻时提高吞吐量，但在流量负载较重时对性能产生不利影响。在这些条件下，拖转可能会进一步降低性能。一般来说，在使用率较高的网络中，不受控制的备用路由（带或不带回退）可能是有害的，因为电路往往沿着较长的路径路由，从而利用更多的容量。这是一个明显但重要的结果，同样适用于基于QoS的Internet路由。
The problem with alternate routing is that both direct routed (i.e., over shortest paths) and alternate routed calls compete for the same resource. At higher loads, allocating these resources to alternate routed calls result in the displacement of direct routed calls and hence the alternate routing of these calls. Therefore, many approaches have been proposed to limit the flow of alternate routed calls under high traffic loads. These schemes are designed for the fully-connected logical topology of long distance telephone networks (i.e., there is a logical link between every pair of nodes). In this topology, direct routed calls always traverse a 1-hop path to the destination and alternate routed calls traverse at most a 2-hop path.
备用路由的问题是，直接路由（即通过最短路径）和备用路由呼叫都会争夺相同的资源。在负载较高时，将这些资源分配给备用路由呼叫会导致直接路由呼叫的置换，从而导致这些呼叫的备用路由。因此，已经提出了许多方法来限制高流量负载下的备用路由呼叫流。这些方案设计用于长途电话网络的全连接逻辑拓扑（即，每对节点之间都有逻辑链路）。在这种拓扑中，直接路由呼叫总是通过一个1跳路径到达目的地，而备用路由呼叫最多通过一个2跳路径。
"Trunk reservation" is a scheme whereby on each link a certain bandwidth is reserved for direct routed calls [MS91]. Alternate routed calls are allowed on a trunk as long as the remaining trunk bandwidth is greater than the reserved capacity. Thus, alternate routed calls cannot totally displace direct routed calls on a trunk. This strategy has been shown to be very effective in preventing the adverse effects of alternate routing.
“中继保留”是一种在每条链路上为直接路由呼叫保留一定带宽的方案[MS91]。只要剩余的中继带宽大于保留容量，就允许在中继上进行备用路由呼叫。因此，备用路由呼叫不能完全取代主干上的直接路由呼叫。该策略已被证明在防止备用路由的不利影响方面非常有效。
"Dynamic alternate routing" (DAR) is a strategy whereby alternate routing is controlled by limiting the number of choices, in addition to trunk reservation [MS91]. Under DAR, the source first attempts to use the direct link to the destination. When blocked, the source attempts to alternate route the call via a pre-selected neighbor. If the call is still blocked, a different neighbor is selected for alternate routing to this destination in the future. The present call
“动态备用路由”（DAR）是一种策略，除了中继保留外，还通过限制选择数量来控制备用路由[MS91]。在DAR下，源首先尝试使用到目标的直接链接。当阻塞时，源尝试通过预先选择的邻居交替路由呼叫。如果呼叫仍被阻止，则会选择另一个邻居作为将来到该目的地的备用路由。目前的呼吁
is dropped. DAR thus requires only local state information. Also, it "learns" of good alternate paths by random sampling and sticks to them as long as possible.
被丢弃了。因此，DAR只需要本地州信息。此外，它通过随机抽样“学习”良好的交替路径，并尽可能长时间地坚持下去。
More recent circuit-switched routing schemes utilize global state to select routes for calls. An example is AT&T's Real-Time Network Routing (RTNR) scheme [ACFH92]. Unlike schemes like DAR, RTNR handles multiple classes of service, including voice and data at fixed rates. RTNR utilizes a sophisticated per-class trunk reservation mechanism with dynamic bandwidth sharing between classes. Also, when alternate routing a call, RTNR utilizes the loading on all trunks in the network to select a path. Because of the fully-connected topology, disseminating status information is simple under RTNR; each node simply exchanges status information directly with all others.
最近的电路交换路由方案利用全局状态为呼叫选择路由。AT&T的实时网络路由（RTNR）方案[ACFH92]就是一个例子。与DAR等方案不同，RTNR处理多类服务，包括固定速率的语音和数据。RTNR利用复杂的每类中继保留机制，在类之间动态共享带宽。此外，在交替路由呼叫时，RTNR利用网络中所有中继上的负载来选择路径。由于完全连接的拓扑结构，在RTNR下传播状态信息很简单；每个节点只需直接与所有其他节点交换状态信息。
From the point of view of designing QoS-based Internet routing schemes, there is much to be learned from circuit-switched routing. For example, alternate routing and its control, and dynamic resource sharing among different classes of traffic. It is, however, not simple to apply some of the results to a general topology network with heterogeneous multirate traffic. Work in the area of ATM network routing described next illustrates this.
从设计基于QoS的Internet路由方案的角度来看，电路交换路由有很多值得学习的地方。例如，备用路由及其控制，以及不同类别流量之间的动态资源共享。然而，将一些结果应用于具有异构多速率流量的一般拓扑网络并不简单。下面介绍的ATM网络路由领域的工作说明了这一点。
The VC routing problem in ATM networks presents issues similar to that encountered in circuit-switched networks. Not surprisingly, some extensions of circuit-switched routing have been proposed. The goal of these routing schemes is to achieve higher throughput as compared to traditional shortest-path routing. The flows considered usually have a single QoS requirement, i.e., bandwidth.
ATM网络中的VC路由问题与电路交换网络中遇到的问题类似。毫不奇怪，有人提出了电路交换路由的一些扩展。这些路由方案的目标是实现比传统最短路径路由更高的吞吐量。所考虑的流通常具有单个QoS需求，即带宽。
The first idea is to extend alternate routing with trunk reservation to general topologies [SD95]. Under this scheme, a distance vector routing protocol is used to build routing tables at each node with multiple choices of increasing hop count to each destination. A VC set-up is first routed along the primary ("direct") path. If sufficient resources are not available along this path, alternate paths are tried in the order of increasing hop count. A flag in the VC set-up message indicates primary or alternate routing, and bandwidth on links along an alternate path is allocated subject to trunk reservation. The trunk reservation values are determined based on some assumptions on traffic characteristics. Because the scheme works only for a single data rate, the practical utility of it is limited.
第一个想法是将具有中继保留的备用路由扩展到一般拓扑[SD95]。在该方案下，使用距离向量路由协议在每个节点上建立路由表，并有多个增加到每个目的地的跳数的选择。VC设置首先沿主（“直接”）路径路由。如果此路径上没有足够的资源可用，将按照增加跃点计数的顺序尝试备用路径。VC设置消息中的标志表示主路由或备用路由，备用路径上链路上的带宽根据中继保留进行分配。中继保留值是根据对交通特性的一些假设确定的。由于该方案仅适用于单一数据速率，因此其实用性受到限制。
The next idea is to import the notion of controlled alternate routing into traditional link state QoS-based routing [GKR96]. To do this,
下一个想法是将受控备用路由的概念引入传统的基于链路状态QoS的路由[GKR96]。为此,，
first each VC is associated with a maximum permissible routing cost. This cost can be set based on expected revenues in carrying the VC or simply based on the length of the shortest path to the destination. Each link is associated with a metric that increases exponentially with its utilization. A switch computing a path for a VC simply determines a least-cost feasible path based on the link metric and the VC's QoS requirement. The VC is admitted if the cost of the path is less than or equal to the maximum permissible routing cost. This routing scheme thus limits the extent of "detour" a VC experiences, thus preventing excessive resource consumption. This is a practical scheme and the basic idea can be extended to hierarchical routing. But the performance of this scheme has not been analyzed thoroughly. A similar notion of admission control based on the connection route was also incorporated in a routing scheme presented in [ACG92].
首先，每个VC与最大允许路由成本相关联。该成本可根据VC的预期收入设定，或仅根据到达目的地的最短路径长度设定。每个链接都与一个随着其利用率呈指数增长的度量相关联。计算VC路径的交换机仅根据链路度量和VC的QoS要求确定成本最低的可行路径。如果路径成本小于或等于最大允许路由成本，则允许VC。因此，该路由方案限制了VC经历的“迂回”程度，从而防止过度的资源消耗。这是一个实用的方案，其基本思想可以推广到分层路由。但是该方案的性能还没有得到充分的分析。[ACG92]中提出的一种路由方案中也包含了基于连接路由的类似接纳控制概念。
Considering the ATM Forum PNNI protocol [PNNI96], a partial list of its stated characteristics are as follows:
考虑到ATM论坛PNNI协议[PNNI96]，其所述特征的部分列表如下：
o Scales to very large networks o Supports hierarchical routing o Supports QoS o Uses source routed connection setup o Supports multiple metrics and attributes o Provides dynamic routing
o 可扩展到非常大的网络o支持分层路由o支持QoS o使用源路由连接设置o支持多个指标和属性o提供动态路由
The PNNI specification is sub-divided into two protocols: a signaling and a routing protocol. The PNNI signaling protocol is used to establish point-to-point and point to multipoint connections and supports source routing, crankback and alternate routing. PNNI source routing allows loop free paths. Also, it allows each implementation to use its own path computation algorithm. Furthermore, source routing is expected to support incremental deployment of future enhancements such as policy routing.
PNNI规范分为两个协议：信令协议和路由协议。PNNI信令协议用于建立点对点和点对多点连接，并支持源路由、回退和备用路由。PNNI源路由允许无循环路径。此外，它允许每个实现使用自己的路径计算算法。此外，源路由预计将支持未来增强功能（如策略路由）的增量部署。
The PNNI routing protocol is a dynamic, hierarchical link state protocol that propagates topology information by flooding it through the network. The topology information is the set of resources (e.g., nodes, links and addresses) which define the network. Resources are qualified by defined sets of metrics and attributes (delay, available bandwidth, jitter, etc.) which are grouped by supported traffic class. Since some of the metrics used will change frequently, e.g., available bandwidth, threshold algorithms are used to determine if the change in a metric or attribute is significant enough to require propagation of updated information. Other features include, auto configuration of the routing hierarchy, connection admission control (as part of path calculation) and aggregation and summarization of topology and reachability information.
PNNI路由协议是一种动态的、分层的链路状态协议，它通过在网络中传播拓扑信息来传播拓扑信息。拓扑信息是定义网络的一组资源（例如节点、链路和地址）。资源由定义的度量集和属性（延迟、可用带宽、抖动等）限定，这些度量集和属性按支持的流量类别分组。由于所使用的一些度量将频繁更改，例如可用带宽，因此使用阈值算法来确定度量或属性中的更改是否显著到需要传播更新的信息。其他功能包括路由层次结构的自动配置、连接允许控制（作为路径计算的一部分）以及拓扑和可达性信息的聚合和汇总。
Despite its functionality, the PNNI routing protocol does not address the issues of multicast routing, policy routing and control of alternate routing. A problem in general with link state QoS-based routing is that of efficient broadcasting of state information. While flooding is a reasonable choice with static link metrics it may impact the performance adversely with dynamic metrics.
尽管PNNI路由协议具有功能，但它不能解决多播路由、策略路由和备用路由控制问题。基于链路状态QoS路由的一个普遍问题是状态信息的有效广播。虽然洪泛是静态链路度量的合理选择，但它可能会对动态度量的性能产生不利影响。
Finally, Integrated PNNI [I-PNNI] has been designed from the start to take advantage of the QoS Routing capabilities that are available in PNNI and integrate them with routing for layer 3. This would provide an integrated layer 2 and layer 3 routing protocol for networks that include PNNI in the ATM core. The I-PNNI specification has been under development in the ATM Forum and, at this time, has not yet incorporated QoS routing mechanisms for layer 3.
最后，集成PNNI[I-PNNI]从一开始就被设计为利用PNNI中可用的QoS路由功能，并将其与第3层的路由集成。这将为ATM核心中包含PNNI的网络提供一个集成的第2层和第3层路由协议。I-PNNI规范已经在ATM论坛上开发，目前还没有为第3层引入QoS路由机制。
Early attempts at adaptive routing in packet networks had the objective of delay minimization by dynamically adapting to network congestion. Alternate routing based on k-shortest path tables, with route selection based on some local measure (e.g., shortest output queue) has been described [R76, YS81]. The original ARPAnet routing scheme was a distance vector protocol with delay-based cost metric [MW77]. Such a scheme was shown to be prone to route oscillations [B82]. For this and other reasons, a link state delay-based routing scheme was later developed for the ARPAnet [MRR80]. This scheme demonstrated a number of techniques such as triggered updates, flooding, etc., which are being used in OSPF and PNNI routing today. Although none of these schemes can be called QoS-based routing schemes, they had features that are relevant to QoS-based routing.
分组网络中自适应路由的早期尝试的目标是通过动态地适应网络拥塞来最小化延迟。已经描述了基于k-最短路径表的备用路由，以及基于某些局部度量（例如，最短输出队列）的路由选择[R76，YS81]。最初的ARPAnet路由方案是一种基于延迟的成本度量的距离向量协议[MW77]。这种方案被证明容易出现路由振荡[B82]。出于这个和其他原因，后来为ARPAnet[MRR80]开发了一种基于链路状态延迟的路由方案。该方案展示了许多技术，如触发更新、泛洪等，这些技术目前正在OSPF和PNNI路由中使用。虽然这些方案都不能称为基于QoS的路由方案，但它们具有与基于QoS的路由相关的特性。
IBM's System Network Architecture (SNA) introduced the concept of Class of Service (COS)-based routing [A79, GM79]. There were several classes of service: interactive, batch, and network control. In addition, users could define other classes. When starting a data session an application or device would request a COS. Routing would then map the COS into a statically configured route which marked a path across the physical network. Since SNA is connection oriented, a session was set up along this path and the application's or device's data would traverse this path for the life of the session. Initially, the service delivered to a session was based on the network engineering and current state of network congestion. Later, transmission priority was added to subarea SNA. Transmission priority allowed more important traffic (e.g. interactive) to proceed before less time-critical traffic (e.g. batch) and improved link and network utilization. Transmission priority of a session was based on its COS.
IBM的系统网络体系结构（SNA）引入了基于服务类（COS）的路由的概念[A79，GM79]。有几类服务：交互式、批处理和网络控制。此外，用户还可以定义其他类。启动数据会话时，应用程序或设备将请求COS。然后，路由将COS映射到静态配置的路由中，该路由标记了物理网络中的路径。由于SNA是面向连接的，因此会话是沿着此路径建立的，并且应用程序或设备的数据将在会话的生命周期内遍历此路径。最初，提供给会话的服务基于网络工程和当前网络拥塞状态。后来，传输优先级被添加到分区SNA中。传输优先级允许更重要的流量（如交互）在时间要求较低的流量（如批量）之前进行，并提高链路和网络利用率。会话的传输优先级基于其COS。
SNA later evolved to support multiple or alternate paths between nodes. But, although assisted by network design tools, the network administrator still had to statically configure routes. IBM later introduced SNA's Advanced Peer to Peer Networking (APPN) [B85]. APPN added new features to SNA including dynamic routing based on a link state database. An application would use COS to indicate it traffic requirements and APPN would calculate a path capable of meeting these requirements. Each COS was mapped to a table of acceptable metrics and parameters that qualified the nodes and links contained in the APPN topology Database. Metrics and parameters used as part of the APPN route calculation include, but are not limited to: delay, cost per minute, node congestion and security. The dynamic nature of APPN allowed it to route around failures and reduce network configuration.
SNA后来发展为支持节点之间的多条或备用路径。但是，尽管有网络设计工具的帮助，网络管理员仍然必须静态地配置路由。IBM后来推出了SNA的高级对等网络（APPN）[B85]。APPN为SNA增加了新功能，包括基于链路状态数据库的动态路由。应用程序将使用COS指示it流量需求，APPN将计算能够满足这些需求的路径。每个COS都映射到一个可接受的度量和参数表，该表限定了APPN拓扑数据库中包含的节点和链接。APPN路由计算中使用的度量和参数包括但不限于：延迟、每分钟成本、节点拥塞和安全性。APPN的动态特性允许它绕过故障并减少网络配置。
The service delivered by APPN was still based on the network engineering, transmission priority and network congestion. IBM later introduced an extension to APPN, High Performance Routing (HPR)[IBM97]. HPR uses a congestion avoidance algorithm called adaptive rate based (ARB) congestion control. Using predictive feedback methods, the ARB algorithm prevents congestion and improves network utilization. Most recently, an extension to the COS table has been defined so that HPR routing could recognize and take advantage of ATM QoS capabilities.
APPN提供的服务仍然基于网络工程、传输优先级和网络拥塞。IBM后来引入了APPN的一个扩展，即高性能路由（HPR）[IBM97]。HPR使用一种称为自适应速率（ARB）拥塞控制的拥塞避免算法。使用预测反馈方法，ARB算法可以防止拥塞并提高网络利用率。最近，定义了COS表的扩展，以便HPR路由能够识别和利用ATM QoS功能。
Considering IP routing, both IDRP [R92] and OSPF support type of service (TOS)-based routing. While the IP header has a TOS field, there is no standardized way of utilizing it for TOS specification and routing. It seems possible to make use of the IP TOS feature, along with TOS-based routing and proper network engineering, to do QoS-based routing. The emerging differentiated services model is generating renewed interest in TOS support. Among the newer schemes, Source Demand Routing (SDR) [ELRV96] allows on-demand path computation by routers and the implementation of strict and loose source routing. The Nimrod architecture [CCM96] has a number of concepts built in to handle scalability and specialized path computation. Recently, some work has been done on QoS-based routing schemes for the integrated services Internet. For example, in [M98], heuristic schemes for efficient routing of flows with bandwidth and/or delay constraints is described and evaluated.
考虑到IP路由，IDRP[R92]和OSPF都支持基于服务类型（TOS）的路由。虽然IP报头有一个TOS字段，但没有标准化的方法将其用于TOS规范和路由。似乎可以利用IP TOS特性，以及基于TOS的路由和适当的网络工程来进行基于QoS的路由。新兴的差异化服务模式正在重新引起人们对TOS支持的兴趣。在较新的方案中，源请求路由（SDR）[ELRV96]允许路由器按需计算路径，并实现严格和松散的源路由。Nimrod架构[CCM96]内置了许多概念，用于处理可伸缩性和专用路径计算。近年来，基于QoS的综合业务Internet路由方案研究取得了一些成果。例如，在[M98]中，描述并评估了具有带宽和/或延迟约束的流的有效路由的启发式方案。
In this document, a framework for QoS-based Internet routing was defined. This framework adopts the traditional separation between intra and interdomain routing. This approach is especially meaningful in the case of QoS-based routing, since there are many views on how QoS-based routing should be accomplished and many different needs. The objective of this document was to encourage the development of
本文定义了一个基于QoS的Internet路由框架。该框架采用了传统的域内和域间路由分离。这种方法在基于QoS的路由的情况下尤其有意义，因为对于如何实现基于QoS的路由有许多观点，并且有许多不同的需求。本文件的目的是鼓励发展
different solution approaches for intradomain routing, subject to some broad requirements, while consensus on interdomain routing is achieved. To this end, the QoS-based routing issues were described, and some broad intradomain routing requirements and an interdomain routing model were defined. In addition, QoS-based multicast routing was discussed and a detailed review of related work was presented.
域内路由的不同解决方案取决于一些广泛的需求，而域间路由则达成了共识。为此，描述了基于QoS的路由问题，定义了一些广泛的域内路由需求和域间路由模型。此外，还讨论了基于QoS的组播路由，并对相关工作进行了详细的回顾。
The deployment of QoS-based routing across multiple administrative domains requires both the development of intradomain routing schemes and a standard way for them to interact via a well-defined interdomain routing mechanism. This document, while outlining the issues that must be addressed, did not engage in the specification of the actual features of the interdomain routing scheme. This would be the next step in the evolution of wide-area, multidomain QoS-based routing.
跨多个管理域部署基于QoS的路由既需要开发域内路由方案，也需要为它们提供一种通过定义良好的域间路由机制进行交互的标准方式。本文件虽然概述了必须解决的问题，但并未详细说明域间路由方案的实际特点。这将是广域、多域QoS路由演进的下一步。
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AUTHORS' ADDRESSES
作者地址
Bala Rajagopalan NEC USA, C&C Research Labs 4 Independence Way Princeton, NJ 08540 U.S.A
Bala Rajagopalan NEC USA，美国新泽西州普林斯顿市独立大道4号C&C研究实验室，邮编：08540
Phone: +1-609-951-2969
EMail: braja@ccrl.nj.nec.com
Phone: +1-609-951-2969
EMail: braja@ccrl.nj.nec.com
Raj Nair Arrowpoint 235 Littleton Rd. Westford, MA 01886 U.S.A
美国马萨诸塞州韦斯特福德利特尔顿路235号拉吉·奈尔箭头点01886
Phone: +1-508-692-5875, x29
EMail: nair@arrowpoint.com
Phone: +1-508-692-5875, x29
EMail: nair@arrowpoint.com
Hal Sandick Bay Networks, Inc. 1009 Slater Rd., Suite 220 Durham, NC 27703 U.S.A
美国北卡罗来纳州达勒姆市斯莱特路1009号220室Hal Sandick Bay Networks，Inc.27703
Phone: +1-919-941-1739
EMail: Hsandick@baynetworks.com
Phone: +1-919-941-1739
EMail: Hsandick@baynetworks.com
Eric S. Crawley Argon Networks, Inc. 25 Porter Rd. Littelton, MA 01460 U.S.A
美国马萨诸塞州利特尔顿波特路25号Eric S.Crawley Argon Networks，Inc.01460
Phone: +1-508-486-0665
EMail: esc@argon.com
Phone: +1-508-486-0665
EMail: esc@argon.com
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