Network Working Group D. Awduche
Request for Comments: 2702 J. Malcolm
Category: Informational J. Agogbua
M. O'Dell
J. McManus
UUNET (MCI Worldcom)
September 1999
Network Working Group D. Awduche
Request for Comments: 2702 J. Malcolm
Category: Informational J. Agogbua
M. O'Dell
J. McManus
UUNET (MCI Worldcom)
September 1999
Requirements for Traffic Engineering Over MPLS
MPLS上的流量工程要求
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 (1999). All Rights Reserved.
版权所有（C）互联网协会（1999年）。版权所有。
Abstract
摘要
This document presents a set of requirements for Traffic Engineering over Multiprotocol Label Switching (MPLS). It identifies the functional capabilities required to implement policies that facilitate efficient and reliable network operations in an MPLS domain. These capabilities can be used to optimize the utilization of network resources and to enhance traffic oriented performance characteristics.
本文档介绍了多协议标签交换（MPLS）上流量工程的一组要求。它确定了在MPLS域中实施促进高效可靠网络操作的策略所需的功能能力。这些功能可用于优化网络资源的利用率并增强面向流量的性能特性。
Table of Contents
目录
1.0 Introduction ............................................. 2
1.1 Terminology .............................................. 3
1.2 Document Organization .................................... 3
2.0 Traffic Engineering ...................................... 4
2.1 Traffic Engineering Performance Objectives ............... 4
2.2 Traffic and Resource Control ............................. 6
2.3 Limitations of Current IGP Control Mechanisms ............ 6
3.0 MPLS and Traffic Engineering ............................. 7
3.1 Induced MPLS Graph ....................................... 9
3.2 The Fundamental Problem of Traffic Engineering Over MPLS . 9
4.0 Augmented Capabilities for Traffic Engineering Over MPLS . 10
5.0 Traffic Trunk Attributes and Characteristics ........... 10
5.1 Bidirectional Traffic Trunks ............................. 11
5.2 Basic Operations on Traffic Trunks ....................... 12
5.3 Accounting and Performance Monitoring .................... 12
1.0 Introduction ............................................. 2
1.1 Terminology .............................................. 3
1.2 Document Organization .................................... 3
2.0 Traffic Engineering ...................................... 4
2.1 Traffic Engineering Performance Objectives ............... 4
2.2 Traffic and Resource Control ............................. 6
2.3 Limitations of Current IGP Control Mechanisms ............ 6
3.0 MPLS and Traffic Engineering ............................. 7
3.1 Induced MPLS Graph ....................................... 9
3.2 The Fundamental Problem of Traffic Engineering Over MPLS . 9
4.0 Augmented Capabilities for Traffic Engineering Over MPLS . 10
5.0 Traffic Trunk Attributes and Characteristics ........... 10
5.1 Bidirectional Traffic Trunks ............................. 11
5.2 Basic Operations on Traffic Trunks ....................... 12
5.3 Accounting and Performance Monitoring .................... 12
5.4 Basic Attributes of Traffic Trunks ....................... 13
5.5 Traffic Parameter Attributes ............................ 14
5.6 Generic Path Selection and Management Attributes ......... 14
5.6.1 Administratively Specified Explicit Paths ................ 15
5.6.2 Hierarchy of Preference Rules for Multi-paths ............ 15
5.6.3 Resource Class Affinity Attributes ....................... 16
5.6.4 Adaptivity Attribute ..................................... 17
5.6.5 Load Distribution Across Parallel Traffic Trunks ......... 18
5.7 Priority Attribute ....................................... 18
5.8 Preemption Attribute ..................................... 18
5.9 Resilience Attribute ..................................... 19
5.10 Policing Attribute ...................................... 20
6.0 Resource Attributes ...................................... 21
6.1 Maximum Allocation Multiplier ............................ 21
6.2 Resource Class Attribute ................................ 22
7.0 Constraint-Based Routing ................................ 22
7.1 Basic Features of Constraint-Based Routing ............... 23
7.2 Implementation Considerations ............................ 24
8.0 Conclusion ............................................. 25
9.0 Security Considerations .................................. 26
10.0 References ............................................. 26
11.0 Acknowledgments .......................................... 27
12.0 Authors' Addresses ....................................... 28
13.0 Full Copyright Statement ................................. 29
5.4 Basic Attributes of Traffic Trunks ....................... 13
5.5 Traffic Parameter Attributes ............................ 14
5.6 Generic Path Selection and Management Attributes ......... 14
5.6.1 Administratively Specified Explicit Paths ................ 15
5.6.2 Hierarchy of Preference Rules for Multi-paths ............ 15
5.6.3 Resource Class Affinity Attributes ....................... 16
5.6.4 Adaptivity Attribute ..................................... 17
5.6.5 Load Distribution Across Parallel Traffic Trunks ......... 18
5.7 Priority Attribute ....................................... 18
5.8 Preemption Attribute ..................................... 18
5.9 Resilience Attribute ..................................... 19
5.10 Policing Attribute ...................................... 20
6.0 Resource Attributes ...................................... 21
6.1 Maximum Allocation Multiplier ............................ 21
6.2 Resource Class Attribute ................................ 22
7.0 Constraint-Based Routing ................................ 22
7.1 Basic Features of Constraint-Based Routing ............... 23
7.2 Implementation Considerations ............................ 24
8.0 Conclusion ............................................. 25
9.0 Security Considerations .................................. 26
10.0 References ............................................. 26
11.0 Acknowledgments .......................................... 27
12.0 Authors' Addresses ....................................... 28
13.0 Full Copyright Statement ................................. 29
Multiprotocol Label Switching (MPLS) [1,2] integrates a label swapping framework with network layer routing. The basic idea involves assigning short fixed length labels to packets at the ingress to an MPLS cloud (based on the concept of forwarding equivalence classes [1,2]). Throughout the interior of the MPLS domain, the labels attached to packets are used to make forwarding decisions (usually without recourse to the original packet headers).
多协议标签交换（MPLS）[1,2]将标签交换框架与网络层路由集成在一起。其基本思想涉及为MPLS云入口的数据包分配短的固定长度标签（基于转发等价类的概念[1,2]）。在整个MPLS域内部，附加到数据包的标签用于做出转发决策（通常不依赖于原始数据包头）。
A set of powerful constructs to address many critical issues in the emerging differentiated services Internet can be devised from this relatively simple paradigm. One of the most significant initial applications of MPLS will be in Traffic Engineering. The importance of this application is already well-recognized (see [1,2,3]).
从这个相对简单的范例可以设计出一套强大的结构来解决新兴的差异化服务互联网中的许多关键问题。MPLS最重要的初始应用之一将是在流量工程中。该应用程序的重要性已经得到充分认识（见[1,2,3]）。
This manuscript is exclusively focused on the Traffic Engineering applications of MPLS. Specifically, the goal of this document is to highlight the issues and requirements for Traffic Engineering in a large Internet backbone. The expectation is that the MPLS specifications, or implementations derived therefrom, will address
本手稿专门关注MPLS的流量工程应用。具体而言，本文档的目标是强调大型Internet主干网中流量工程的问题和要求。人们期望MPLS规范或从中派生的实现能够解决这个问题
the realization of these objectives. A description of the basic capabilities and functionality required of an MPLS implementation to accommodate the requirements is also presented.
这些目标的实现。还描述了MPLS实现满足这些需求所需的基本能力和功能。
It should be noted that even though the focus is on Internet backbones, the capabilities described in this document are equally applicable to Traffic Engineering in enterprise networks. In general, the capabilities can be applied to any label switched network under a single technical administration in which at least two paths exist between two nodes.
应该注意的是，尽管重点是Internet主干网，但本文档中描述的功能同样适用于企业网络中的流量工程。通常，这些能力可以应用于在单个技术管理下的任何标签交换网络，其中两个节点之间存在至少两条路径。
Some recent manuscripts have focused on the considerations pertaining to Traffic Engineering and Traffic management under MPLS, most notably the works of Li and Rekhter [3], and others. In [3], an architecture is proposed which employs MPLS and RSVP to provide scalable differentiated services and Traffic Engineering in the Internet. The present manuscript complements the aforementioned and similar efforts. It reflects the authors' operational experience in managing a large Internet backbone.
最近的一些手稿侧重于与MPLS下的流量工程和流量管理相关的考虑因素，尤其是Li和Rekhter[3]等人的作品。在[3]中，提出了一种利用MPLS和RSVP在Internet上提供可扩展的区分服务和流量工程的体系结构。本手稿补充了上述和类似的努力。它反映了作者在管理大型互联网主干网方面的操作经验。
The reader is assumed to be familiar with the MPLS terminology as defined in [1].
假定读者熟悉[1]中定义的MPLS术语。
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [11].
本文件中的关键词“必须”、“不得”、“要求”、“应”、“不应”、“应”、“不应”、“建议”、“可”和“可选”应按照RFC 2119[11]中所述进行解释。
The remainder of this document is organized as follows: Section 2 discusses the basic functions of Traffic Engineering in the Internet. Section 3, provides an overview of the traffic Engineering potentials of MPLS. Sections 1 to 3 are essentially background material. Section 4 presents an overview of the fundamental requirements for Traffic Engineering over MPLS. Section 5 describes the desirable attributes and characteristics of traffic trunks which are pertinent to Traffic Engineering. Section 6 presents a set of attributes which can be associated with resources to constrain the routability of traffic trunks and LSPs through them. Section 7 advocates the introduction of a "constraint-based routing" framework in MPLS domains. Finally, Section 8 contains concluding remarks.
本文件的其余部分组织如下：第2节讨论了互联网流量工程的基本功能。第3节概述了MPLS的流量工程潜力。第1至3节基本上是背景材料。第4节概述了MPLS流量工程的基本要求。第5节描述了与交通工程相关的交通干线的理想属性和特征。第6节介绍了一组属性，这些属性可与资源关联，以约束通过它们的交通干线和LSP的可路由性。第7节主张在MPLS域中引入“基于约束的路由”框架。最后，第8节载有结论意见。
This section describes the basic functions of Traffic Engineering in an Autonomous System in the contemporary Internet. The limitations of current IGPs with respect to traffic and resource control are highlighted. This section serves as motivation for the requirements on MPLS.
本节描述了当代互联网中自治系统中流量工程的基本功能。强调了当前IGP在流量和资源控制方面的局限性。本节作为MPLS需求的动机。
Traffic Engineering (TE) is concerned with performance optimization of operational networks. In general, it encompasses the application of technology and scientific principles to the measurement, modeling, characterization, and control of Internet traffic, and the application of such knowledge and techniques to achieve specific performance objectives. The aspects of Traffic Engineering that are of interest concerning MPLS are measurement and control.
流量工程（TE）关注运营网络的性能优化。一般来说，它包括将技术和科学原理应用于互联网流量的测量、建模、表征和控制，以及应用这些知识和技术来实现特定的性能目标。与MPLS相关的流量工程方面是测量和控制。
A major goal of Internet Traffic Engineering is to facilitate efficient and reliable network operations while simultaneously optimizing network resource utilization and traffic performance. Traffic Engineering has become an indispensable function in many large Autonomous Systems because of the high cost of network assets and the commercial and competitive nature of the Internet. These factors emphasize the need for maximal operational efficiency.
Internet流量工程的一个主要目标是促进高效可靠的网络运行，同时优化网络资源利用率和流量性能。由于网络资产的高成本以及互联网的商业性和竞争性，流量工程已经成为许多大型自治系统中不可或缺的功能。这些因素强调了最大运营效率的需要。
The key performance objectives associated with traffic engineering can be classified as being either:
与交通工程相关的关键性能目标可分为：
1. traffic oriented or
1. 交通导向或
2. resource oriented.
2. 以资源为导向。
Traffic oriented performance objectives include the aspects that enhance the QoS of traffic streams. In a single class, best effort Internet service model, the key traffic oriented performance objectives include: minimization of packet loss, minimization of delay, maximization of throughput, and enforcement of service level agreements. Under a single class best effort Internet service model, minimization of packet loss is one of the most important traffic oriented performance objectives. Statistically bounded traffic oriented performance objectives (such as peak to peak packet delay variation, loss ratio, and maximum packet transfer delay) might become useful in the forthcoming differentiated services Internet.
面向流量的性能目标包括提高流量流的QoS的方面。在单一类别的尽力而为Internet服务模型中，面向流量的关键性能目标包括：数据包丢失最小化、延迟最小化、吞吐量最大化以及服务级别协议的实施。在单类尽力而为的Internet服务模型下，最小化数据包丢失是面向流量的最重要性能目标之一。统计上有界的面向流量的性能目标（例如峰-峰数据包延迟变化、丢失率和最大数据包传输延迟）可能在即将到来的区分服务互联网中变得有用。
Resource oriented performance objectives include the aspects pertaining to the optimization of resource utilization. Efficient management of network resources is the vehicle for the attainment of
以资源为导向的绩效目标包括与资源利用优化相关的方面。有效管理网络资源是实现
resource oriented performance objectives. In particular, it is generally desirable to ensure that subsets of network resources do not become over utilized and congested while other subsets along alternate feasible paths remain underutilized. Bandwidth is a crucial resource in contemporary networks. Therefore, a central function of Traffic Engineering is to efficiently manage bandwidth resources.
以资源为导向的绩效目标。特别地，通常希望确保网络资源的子集不会变得过度利用和拥挤，而沿备用可行路径的其他子集保持未充分利用。带宽是当代网络中的关键资源。因此，流量工程的中心功能是高效地管理带宽资源。
Minimizing congestion is a primary traffic and resource oriented performance objective. The interest here is on congestion problems that are prolonged rather than on transient congestion resulting from instantaneous bursts. Congestion typically manifests under two scenarios:
最小化拥塞是主要的流量和面向资源的性能目标。这里的兴趣在于长期的拥塞问题，而不是瞬时突发引起的瞬时拥塞。拥塞通常表现在两种情况下：
1. When network resources are insufficient or inadequate to accommodate offered load.
1. 当网络资源不足或不足以容纳提供的负载时。
2. When traffic streams are inefficiently mapped onto available resources; causing subsets of network resources to become over-utilized while others remain underutilized.
2. 当交通流无效地映射到可用资源时；导致网络资源的子集被过度利用，而其他资源仍然未被充分利用。
The first type of congestion problem can be addressed by either: (i) expansion of capacity, or (ii) application of classical congestion control techniques, or (iii) both. Classical congestion control techniques attempt to regulate the demand so that the traffic fits onto available resources. Classical techniques for congestion control include: rate limiting, window flow control, router queue management, schedule-based control, and others; (see [8] and the references therein).
第一类拥塞问题可以通过以下两种方式解决：（i）扩展容量，或（ii）应用经典拥塞控制技术，或（iii）两者兼而有之。经典的拥塞控制技术试图调节需求，使流量适应可用资源。拥塞控制的经典技术包括：速率限制、窗口流控制、路由器队列管理、基于调度的控制等；（见[8]及其参考文献）。
The second type of congestion problems, namely those resulting from inefficient resource allocation, can usually be addressed through Traffic Engineering.
第二类拥塞问题，即资源分配效率低下导致的拥塞问题，通常可以通过流量工程来解决。
In general, congestion resulting from inefficient resource allocation can be reduced by adopting load balancing policies. The objective of such strategies is to minimize maximum congestion or alternatively to minimize maximum resource utilization, through efficient resource allocation. When congestion is minimized through efficient resource allocation, packet loss decreases, transit delay decreases, and aggregate throughput increases. Thereby, the perception of network service quality experienced by end users becomes significantly enhanced.
通常，通过采用负载平衡策略，可以减少由于资源分配效率低下而导致的拥塞。这种策略的目标是通过有效的资源分配来最小化最大拥塞或最小化最大资源利用率。当通过有效的资源分配使拥塞最小化时，数据包丢失减少，传输延迟减少，总吞吐量增加。因此，终端用户体验到的网络服务质量感知显著增强。
Clearly, load balancing is an important network performance optimization policy. Nevertheless, the capabilities provided for Traffic Engineering should be flexible enough so that network administrators can implement other policies which take into account the prevailing cost structure and the utility or revenue model.
显然，负载平衡是一项重要的网络性能优化策略。尽管如此，为流量工程提供的功能应该足够灵活，以便网络管理员可以实施其他政策，这些政策考虑了当前的成本结构和效用或收入模型。
Performance optimization of operational networks is fundamentally a control problem. In the traffic engineering process model, the Traffic Engineer, or a suitable automaton, acts as the controller in an adaptive feedback control system. This system includes a set of interconnected network elements, a network performance monitoring system, and a set of network configuration management tools. The Traffic Engineer formulates a control policy, observes the state of the network through the monitoring system, characterizes the traffic, and applies control actions to drive the network to a desired state, in accordance with the control policy. This can be accomplished reactively by taking action in response to the current state of the network, or pro-actively by using forecasting techniques to anticipate future trends and applying action to obviate the predicted undesirable future states.
运营网络的性能优化从根本上说是一个控制问题。在交通工程过程模型中，交通工程师或合适的自动机充当自适应反馈控制系统中的控制器。该系统包括一组互连的网元、一个网络性能监控系统和一组网络配置管理工具。交通工程师制定控制策略，通过监控系统观察网络状态，描述交通特征，并根据控制策略应用控制措施，将网络驱动至所需状态。这可以通过响应网络的当前状态而采取行动，或者通过使用预测技术预测未来趋势并采取行动避免预测的不希望的未来状态而主动实现。
Ideally, control actions should involve:
理想情况下，控制措施应包括：
1. Modification of traffic management parameters,
1. 修改交通管理参数，
2. Modification of parameters associated with routing, and
2. 修改与布线相关的参数，以及
3. Modification of attributes and constraints associated with resources.
3. 修改与资源关联的属性和约束。
The level of manual intervention involved in the traffic engineering process should be minimized whenever possible. This can be accomplished by automating aspects of the control actions described above, in a distributed and scalable fashion.
交通工程过程中涉及的人工干预水平应尽可能降低。这可以通过以分布式和可伸缩的方式自动化上述控制操作的各个方面来实现。
This subsection reviews some of the well known limitations of current IGPs with regard to Traffic Engineering.
本小节回顾了当前IGP在交通工程方面的一些众所周知的局限性。
The control capabilities offered by existing Internet interior gateway protocols are not adequate for Traffic Engineering. This makes it difficult to actualize effective policies to address network performance problems. Indeed, IGPs based on shortest path algorithms contribute significantly to congestion problems in Autonomous Systems within the Internet. SPF algorithms generally optimize based on a simple additive metric. These protocols are topology driven, so bandwidth availability and traffic characteristics are not factors considered in routing decisions. Consequently, congestion frequently occurs when:
现有Internet内部网关协议提供的控制能力不足以进行流量工程。这使得很难实施有效的策略来解决网络性能问题。事实上，基于最短路径算法的IGP极大地加剧了互联网中自治系统的拥塞问题。SPF算法通常基于简单的加法度量进行优化。这些协议是拓扑驱动的，因此带宽可用性和流量特性不是路由决策中考虑的因素。因此，在以下情况下，交通拥堵频繁发生：
1. the shortest paths of multiple traffic streams converge on specific links or router interfaces, or
1. 多个业务流的最短路径汇聚在特定链路或路由器接口上，或
2. a given traffic stream is routed through a link or router interface which does not have enough bandwidth to accommodate it.
2. 给定的流量流通过链路或路由器接口进行路由，该链路或路由器接口没有足够的带宽容纳该流量流。
These scenarios manifest even when feasible alternate paths with excess capacity exist. It is this aspect of congestion problems (-- a symptom of suboptimal resource allocation) that Traffic Engineering aims to vigorously obviate. Equal cost path load sharing can be used to address the second cause for congestion listed above with some degree of success, however it is generally not helpful in alleviating congestion due to the first cause listed above and particularly not in large networks with dense topology.
即使存在容量过剩的可行替代路径，这些情况也会出现。交通工程的目标就是要大力消除拥堵问题的这一方面（这是资源分配不理想的症状）。等成本路径负载共享可用于解决上述拥塞的第二个原因，并取得一定程度的成功，但是，它通常无助于缓解上述第一个原因造成的拥塞，尤其是在拓扑密集的大型网络中。
A popular approach to circumvent the inadequacies of current IGPs is through the use of an overlay model, such as IP over ATM or IP over frame relay. The overlay model extends the design space by enabling arbitrary virtual topologies to be provisioned atop the network's physical topology. The virtual topology is constructed from virtual circuits which appear as physical links to the IGP routing protocols. The overlay model provides additional important services to support traffic and resource control, including: (1) constraint-based routing at the VC level, (2) support for administratively configurable explicit VC paths, (3) path compression, (4) call admission control functions, (5) traffic shaping and traffic policing functions, and (6) survivability of VCs. These capabilities enable the actualization of a variety of Traffic Engineering policies. For example, virtual circuits can easily be rerouted to move traffic from over-utilized resources onto relatively underutilized ones.
规避当前IGP不足之处的一种流行方法是通过使用覆盖模型，如IP over ATM或IP over frame relay。覆盖模型通过允许在网络的物理拓扑上提供任意虚拟拓扑来扩展设计空间。虚拟拓扑结构由虚拟电路构成，虚拟电路显示为IGP路由协议的物理链路。覆盖模型提供额外的重要服务来支持流量和资源控制，包括：（1）VC级别的基于约束的路由，（2）支持可管理配置的显式VC路径，（3）路径压缩，（4）呼叫接纳控制功能，（5）流量整形和流量管理功能，以及（6）风险投资的生存能力。这些功能可以实现各种流量工程策略。例如，虚拟电路可以很容易地重新路由，将通信量从过度利用的资源转移到相对未充分利用的资源。
For Traffic Engineering in large dense networks, it is desirable to equip MPLS with a level of functionality at least commensurate with current overlay models. Fortunately, this can be done in a fairly straight forward manner.
对于大型密集网络中的流量工程，需要为MPLS配备至少与当前覆盖模型相当的功能级别。幸运的是，这可以相当直接地完成。
This section provides an overview of the applicability of MPLS to Traffic Engineering. Subsequent sections discuss the set of capabilities required to meet the Traffic Engineering requirements.
本节概述了MPLS在流量工程中的适用性。后续章节将讨论满足流量工程需求所需的一组功能。
MPLS is strategically significant for Traffic Engineering because it can potentially provide most of the functionality available from the overlay model, in an integrated manner, and at a lower cost than the currently competing alternatives. Equally importantly, MPLS offers
MPLS对于流量工程具有重要的战略意义，因为它可以以集成的方式以比当前竞争对手更低的成本提供覆盖模型中可用的大部分功能。同样重要的是，MPLS提供
the possibility to automate aspects of the Traffic Engineering function. This last consideration requires further investigation and is beyond the scope of this manuscript.
实现交通工程功能各方面自动化的可能性。最后的考虑需要进一步调查，超出了本手稿的范围。
A note on terminology: The concept of MPLS traffic trunks is used extensively in the remainder of this document. According to Li and Rekhter [3], a traffic trunk is an aggregation of traffic flows of the same class which are placed inside a Label Switched Path. Essentially, a traffic trunk is an abstract representation of traffic to which specific characteristics can be associated. It is useful to view traffic trunks as objects that can be routed; that is, the path through which a traffic trunk traverses can be changed. In this respect, traffic trunks are similar to virtual circuits in ATM and Frame Relay networks. It is important, however, to emphasize that there is a fundamental distinction between a traffic trunk and the path, and indeed the LSP, through which it traverses. An LSP is a specification of the label switched path through which the traffic traverses. In practice, the terms LSP and traffic trunk are often used synonymously. Additional characteristics of traffic trunks as used in this manuscript are summarized in section 5.0.
术语说明：MPLS流量中继的概念在本文档的其余部分中广泛使用。根据Li和Rekhter[3]，交通干线是放置在标签交换路径内的同类交通流的集合。从本质上讲，交通干线是交通的抽象表示，具体特征可以与之关联。将交通干线视为可路由的对象很有用；也就是说，可以更改交通干线穿过的路径。在这方面，业务中继类似于ATM和帧中继网络中的虚拟电路。然而，重要的是要强调，交通干线和路径之间存在着根本的区别，事实上，它所通过的LSP也是如此。LSP是流量所通过的标签交换路径的规范。在实践中，术语LSP和交通干线通常是同义词。第5.0节总结了本手稿中使用的交通干线的其他特征。
The attractiveness of MPLS for Traffic Engineering can be attributed to the following factors: (1) explicit label switched paths which are not constrained by the destination based forwarding paradigm can be easily created through manual administrative action or through automated action by the underlying protocols, (2) LSPs can potentially be efficiently maintained, (3) traffic trunks can be instantiated and mapped onto LSPs, (4) a set of attributes can be associated with traffic trunks which modulate their behavioral characteristics, (5) a set of attributes can be associated with resources which constrain the placement of LSPs and traffic trunks across them, (6) MPLS allows for both traffic aggregation and disaggregation whereas classical destination only based IP forwarding permits only aggregation, (7) it is relatively easy to integrate a "constraint-based routing" framework with MPLS, (8) a good implementation of MPLS can offer significantly lower overhead than competing alternatives for Traffic Engineering.
MPLS对流量工程的吸引力可归因于以下因素：（1）不受基于目的地的转发范例约束的显式标签交换路径可以通过手动管理操作或底层协议的自动操作轻松创建，（2）LSP可能会得到有效维护，（3）交通干线可以实例化并映射到LSP上，（4）一组属性可以与交通干线相关联，这些交通干线可以调节它们的行为特征，（5）一组属性可以与资源相关联，这些资源限制LSP和交通干线在它们之间的位置，（6） MPLS允许流量聚合和分解，而传统的基于目的地的IP转发只允许聚合，（7）将“基于约束的路由”框架与MPLS集成相对容易，（8）MPLS的良好实现可以提供比流量工程竞争对手更低的开销。
Additionally, through explicit label switched paths, MPLS permits a quasi circuit switching capability to be superimposed on the current Internet routing model. Many of the existing proposals for Traffic Engineering over MPLS focus only on the potential to create explicit LSPs. Although this capability is fundamental for Traffic Engineering, it is not really sufficient. Additional augmentations are required to foster the actualization of policies leading to performance optimization of large operational networks. Some of the necessary augmentations are described in this manuscript.
此外，通过显式标签交换路径，MPLS允许在当前互联网路由模型上叠加准电路交换能力。MPLS流量工程的许多现有建议只关注创建显式LSP的潜力。虽然这种能力是交通工程的基础，但实际上还不够。需要进行额外的扩充，以促进政策的实施，从而实现大型运营网络的性能优化。本手稿中描述了一些必要的扩充。
This subsection introduces the concept of an "induced MPLS graph" which is central to Traffic Engineering in MPLS domains. An induced MPLS graph is analogous to a virtual topology in an overlay model. It is logically mapped onto the physical network through the selection of LSPs for traffic trunks.
本小节介绍了“诱导MPLS图”的概念，它是MPLS域中流量工程的核心。诱导MPLS图类似于覆盖模型中的虚拟拓扑。通过为交通干线选择LSP，将其逻辑映射到物理网络上。
An induced MPLS graph consists of a set of LSRs which comprise the nodes of the graph and a set of LSPs which provide logical point to point connectivity between the LSRs, and hence serve as the links of the induced graph. it may be possible to construct hierarchical induced MPLS graphs based on the concept of label stacks (see [1]).
诱导MPLS图由一组LSR组成，LSR包括图的节点和一组LSP，LSP提供LSR之间的逻辑点对点连接，因此用作诱导图的链路。可以基于标签堆栈的概念构造分层诱导MPLS图（参见[1]）。
Induced MPLS graphs are important because the basic problem of bandwidth management in an MPLS domain is the issue of how to efficiently map an induced MPLS graph onto the physical network topology. The induced MPLS graph abstraction is formalized below.
诱导MPLS图非常重要，因为MPLS域中带宽管理的基本问题是如何有效地将诱导MPLS图映射到物理网络拓扑上。诱导的MPLS图抽象形式化如下。
Let G = (V, E, c) be a capacitated graph depicting the physical
topology of the network. Here, V is the set of nodes in the network
and E is the set of links; that is, for v and w in V, the object
(v,w) is in E if v and w are directly connected under G. The
parameter "c" is a set of capacity and other constraints associated
with E and V. We will refer to G as the "base" network topology.
Let G = (V, E, c) be a capacitated graph depicting the physical
topology of the network. Here, V is the set of nodes in the network
and E is the set of links; that is, for v and w in V, the object
(v,w) is in E if v and w are directly connected under G. The
parameter "c" is a set of capacity and other constraints associated
with E and V. We will refer to G as the "base" network topology.
Let H = (U, F, d) be the induced MPLS graph, where U is a subset of
V representing the set of LSRs in the network, or more precisely the
set of LSRs that are the endpoints of at least one LSP. Here, F is
the set of LSPs, so that for x and y in U, the object (x, y) is in F
if there is an LSP with x and y as endpoints. The parameter "d" is
the set of demands and restrictions associated with F. Evidently, H
is a directed graph. It can be seen that H depends on the
transitivity characteristics of G.
Let H = (U, F, d) be the induced MPLS graph, where U is a subset of
V representing the set of LSRs in the network, or more precisely the
set of LSRs that are the endpoints of at least one LSP. Here, F is
the set of LSPs, so that for x and y in U, the object (x, y) is in F
if there is an LSP with x and y as endpoints. The parameter "d" is
the set of demands and restrictions associated with F. Evidently, H
is a directed graph. It can be seen that H depends on the
transitivity characteristics of G.
There are basically three fundamental problems that relate to Traffic Engineering over MPLS.
MPLS上的流量工程基本上有三个基本问题。
- The first problem concerns how to map packets onto forwarding equivalence classes.
- 第一个问题涉及如何将数据包映射到转发等价类。
- The second problem concerns how to map forwarding equivalence classes onto traffic trunks.
- 第二个问题涉及如何将转发等价类映射到交通干线。
- The third problem concerns how to map traffic trunks onto the physical network topology through label switched paths.
- 第三个问题涉及如何通过标签交换路径将流量中继映射到物理网络拓扑。
This document is not focusing on the first two problems listed. (even-though they are quite important). Instead, the remainder of this manuscript will focus on the capabilities that permit the third mapping function to be performed in a manner resulting in efficient and reliable network operations. This is really the problem of mapping an induced MPLS graph (H) onto the "base" network topology (G).
本文件不关注所列的前两个问题。（尽管它们非常重要）。取而代之的是，本手稿的其余部分将重点介绍允许以高效可靠的网络操作方式执行第三种映射功能的能力。这实际上是将诱导MPLS图（H）映射到“基本”网络拓扑（G）的问题。
The previous sections reviewed the basic functions of Traffic Engineering in the contemporary Internet. The applicability of MPLS to that activity was also discussed. The remaining sections of this manuscript describe the functional capabilities required to fully support Traffic Engineering over MPLS in large networks.
前几节回顾了流量工程在当代互联网中的基本功能。还讨论了MPLS对该活动的适用性。本手稿的其余部分描述了在大型网络中完全支持MPLS流量工程所需的功能能力。
The proposed capabilities consist of:
拟议的能力包括：
1. A set of attributes associated with traffic trunks which collectively specify their behavioral characteristics.
1. 与交通干线相关联的一组属性，共同指定其行为特征。
2. A set of attributes associated with resources which constrain the placement of traffic trunks through them. These can also be viewed as topology attribute constraints.
2. 与资源相关联的一组属性，用于约束通过资源的交通干线的位置。这些也可以被视为拓扑属性约束。
3. A "constraint-based routing" framework which is used to select paths for traffic trunks subject to constraints imposed by items 1) and 2) above. The constraint-based routing framework does not have to be part of MPLS. However, the two need to be tightly integrated together.
3. “基于约束的路由”框架，用于根据上述第1）项和第2）项施加的约束为交通干线选择路径。基于约束的路由框架不必是MPLS的一部分。然而，这两者需要紧密结合在一起。
The attributes associated with traffic trunks and resources, as well as parameters associated with routing, collectively represent the control variables which can be modified either through administrative action or through automated agents to drive the network to a desired state.
与流量中继线和资源相关的属性以及与路由相关的参数共同表示控制变量，这些控制变量可以通过管理操作或通过自动代理进行修改，以将网络驱动到所需状态。
In an operational network, it is highly desirable that these attributes can be dynamically modified online by an operator without adversely disrupting network operations.
在运营网络中，运营商可以在线动态修改这些属性，而不会对网络运营造成不利影响，这是非常理想的。
This section describes the desirable attributes which can be associated with traffic trunks to influence their behavioral characteristics.
本节描述了可与交通干线关联以影响其行为特征的理想属性。
First, the basic properties of traffic trunks (as used in this manuscript) are summarized below:
首先，交通干线（如本手稿所用）的基本特性总结如下：
- A traffic trunk is an *aggregate* of traffic flows belonging to the same class. In some contexts, it may be desirable to relax this definition and allow traffic trunks to include multi-class traffic aggregates.
- 交通干线是属于同一类别的交通流的*集合*。在某些情况下，可能需要放宽此定义，并允许交通干线包括多类交通总量。
- In a single class service model, such as the current Internet, a traffic trunk could encapsulate all of the traffic between an ingress LSR and an egress LSR, or subsets thereof.
- 在诸如当前因特网的单类服务模型中，业务中继可以封装入口LSR和出口LSR或其子集之间的所有业务。
- Traffic trunks are routable objects (similar to ATM VCs).
- 交通干线是可路由的对象（类似于ATM VCs）。
- A traffic trunk is distinct from the LSP through which it traverses. In operational contexts, a traffic trunk can be moved from one path onto another.
- 交通干线不同于它所经过的LSP。在操作环境中，交通干线可以从一条路径移动到另一条路径。
- A traffic trunk is unidirectional.
- 交通干线是单向的。
In practice, a traffic trunk can be characterized by its ingress and egress LSRs, the forwarding equivalence class which is mapped onto it, and a set of attributes which determine its behavioral characteristics.
在实践中，业务中继可以通过其入口和出口LSR、映射到其上的转发等价类以及确定其行为特征的一组属性来表征。
Two basic issues are of particular significance: (1) parameterization of traffic trunks and (2) path placement and maintenance rules for traffic trunks.
有两个基本问题特别重要：（1）交通干线的参数化；（2）交通干线的路径布置和维护规则。
Although traffic trunks are conceptually unidirectional, in many practical contexts, it is useful to simultaneously instantiate two traffic trunks with the same endpoints, but which carry packets in opposite directions. The two traffic trunks are logically coupled together. One trunk, called the forward trunk, carries traffic from an originating node to a destination node. The other trunk, called the backward trunk, carries traffic from the destination node to the originating node. We refer to the amalgamation of two such traffic trunks as one bidirectional traffic trunk (BTT) if the following two conditions hold:
尽管交通干线在概念上是单向的，但在许多实际环境中，同时实例化两个具有相同端点但携带相反方向数据包的交通干线是有用的。两条交通干线在逻辑上耦合在一起。一个称为前向中继的中继将流量从发起节点传送到目的节点。另一个中继称为后向中继，将通信量从目标节点传送到发起节点。如果满足以下两个条件，我们将两条此类交通干线合并为一条双向交通干线（BTT）：
- Both traffic trunks are instantiated through an atomic action at one LSR, called the originator node, or through an atomic action at a network management station.
- 两个流量中继都是通过一个LSR（称为发起者节点）上的原子操作实例化的，或者通过网络管理站上的原子操作实例化的。
- Neither of the composite traffic trunks can exist without the other. That is, both are instantiated and destroyed together.
- 两个复合交通干线中的任何一个都不可能没有另一个。也就是说，两者都被实例化并一起销毁。
The topological properties of BTTs should also be considered. A BTT can be topologically symmetric or topologically asymmetric. A BTT is said to be "topologically symmetric" if its constituent traffic trunks are routed through the same physical path, even though they operate in opposite directions. If, however, the component traffic trunks are routed through different physical paths, then the BTT is said to be "topologically asymmetric."
还应考虑BTT的拓扑特性。BTT可以是拓扑对称的，也可以是拓扑非对称的。如果BTT的组成业务干线通过相同的物理路径路由，则称BTT为“拓扑对称”，即使它们以相反的方向运行。但是，如果组件业务中继通过不同的物理路径路由，则BTT被称为“拓扑不对称”
It should be noted that bidirectional traffic trunks are merely an administrative convenience. In practice, most traffic engineering functions can be implemented using only unidirectional traffic trunks.
应该注意的是，双向交通干线仅仅是一种管理便利。实际上，大多数交通工程功能只能使用单向交通干线来实现。
The basic operations on traffic trunks significant to Traffic Engineering purposes are summarized below.
对交通工程目的具有重要意义的交通干线基本操作总结如下。
- Establish: To create an instance of a traffic trunk.
- 建立：创建交通干线的实例。
- Activate: To cause a traffic trunk to start passing traffic. The establishment and activation of a traffic trunk are logically separate events. They may, however, be implemented or invoked as one atomic action.
- 激活：使交通干线开始通过交通。交通干线的建立和激活在逻辑上是独立的事件。然而，它们可以作为一个原子操作来实现或调用。
- Deactivate: To cause a traffic trunk to stop passing traffic.
- 停用：使交通干线停止通行交通。
- Modify Attributes: To cause the attributes of a traffic trunk to be modified.
- 修改属性：使交通干线的属性被修改。
- Reroute: To cause a traffic trunk to change its route. This can be done through administrative action or automatically by the underlying protocols.
- 重新路由：使交通干线改变其路由。这可以通过管理操作完成，也可以通过底层协议自动完成。
- Destroy: To remove an instance of a traffic trunk from the network and reclaim all resources allocated to it. Such resources include label space and possibly available bandwidth.
- 销毁：从网络中删除流量中继实例并回收分配给它的所有资源。这些资源包括标签空间和可能的可用带宽。
The above are considered the basic operations on traffic trunks. Additional operations are also possible such as policing and traffic shaping.
以上是交通干线上的基本操作。此外，还可能开展其他行动，如警务和交通管制。
Accounting and performance monitoring capabilities are very important to the billing and traffic characterization functions. Performance statistics obtained from accounting and performance monitoring
计费和性能监控功能对于计费和流量特征化功能非常重要。从会计和绩效监控中获得的绩效统计数据
systems can be used for traffic characterization, performance optimization, and capacity planning within the Traffic Engineering realm..
系统可用于交通工程领域内的交通特征描述、性能优化和容量规划。。
The capability to obtain statistics at the traffic trunk level is so important that it should be considered an essential requirement for Traffic Engineering over MPLS.
在流量中继级别获取统计信息的能力非常重要，因此应将其视为MPLS流量工程的基本要求。
An attribute of a traffic trunk is a parameter assigned to it which influences its behavioral characteristics.
交通干线的属性是分配给它的参数，它影响其行为特征。
Attributes can be explicitly assigned to traffic trunks through administration action or they can be implicitly assigned by the underlying protocols when packets are classified and mapped into equivalence classes at the ingress to an MPLS domain. Regardless of how the attributes were originally assigned, for Traffic Engineering purposes, it should be possible to administratively modify such attributes.
属性可以通过管理操作显式分配给流量中继，或者当数据包被分类并映射到MPLS域入口的等价类时，它们可以由底层协议隐式分配。无论属性最初是如何分配的，出于流量工程的目的，应该可以通过管理方式修改这些属性。
The basic attributes of traffic trunks particularly significant for Traffic Engineering are itemized below.
对交通工程特别重要的交通干线的基本属性如下所示。
- Traffic parameter attributes
- 交通参数属性
- Generic Path selection and maintenance attributes
- 通用路径选择和维护属性
- Priority attribute
- 优先级属性
- Preemption attribute
- 抢占属性
- Resilience attribute
- 弹性属性
- Policing attribute
- 警务属性
The combination of traffic parameters and policing attributes is analogous to usage parameter control in ATM networks. Most of the attributes listed above have analogs in well established technologies. Consequently, it should be relatively straight forward to map the traffic trunk attributes onto many existing switching and routing architectures.
流量参数和警务属性的组合类似于ATM网络中的使用参数控制。上面列出的大多数属性都与成熟的技术类似。因此，将业务主干属性映射到许多现有的交换和路由架构上应该是相对简单的。
Priority and preemption can be regarded as relational attributes because they express certain binary relations between traffic trunks. Conceptually, these binary relations determine the manner in which traffic trunks interact with each other as they compete for network resources during path establishment and path maintenance.
优先级和抢占可以被视为关系属性，因为它们表示交通干线之间的某种二进制关系。从概念上讲，这些二元关系决定了在路径建立和路径维护期间，交通干线在竞争网络资源时相互作用的方式。
Traffic parameters can be used to capture the characteristics of the traffic streams (or more precisely the forwarding equivalence class) to be transported through the traffic trunk. Such characteristics may include peak rates, average rates, permissible burst size, etc. From a traffic engineering perspective, the traffic parameters are significant because they indicate the resource requirements of the traffic trunk. This is useful for resource allocation and congestion avoidance through anticipatory policies.
流量参数可用于捕获要通过流量中继传输的流量流（或更准确地说是转发等价类）的特征。此类特征可能包括峰值速率、平均速率、允许突发大小等。从交通工程的角度来看，交通参数非常重要，因为它们指示交通干线的资源需求。这有助于通过预期策略进行资源分配和避免拥塞。
For the purpose of bandwidth allocation, a single canonical value of bandwidth requirements can be computed from a traffic trunk's traffic parameters. Techniques for performing these computations are well known. One example of this is the theory of effective bandwidth.
为了进行带宽分配，可以从流量中继的流量参数计算带宽需求的单个标准值。执行这些计算的技术是众所周知的。有效带宽理论就是一个例子。
Generic path selection and management attributes define the rules for selecting the route taken by a traffic trunk as well as the rules for maintenance of paths that are already established.
通用路径选择和管理属性定义了用于选择交通干线所走路线的规则以及用于维护已建立路径的规则。
Paths can be computed automatically by the underlying routing protocols or they can be defined administratively by a network operator. If there are no resource requirements or restrictions associated with a traffic trunk, then a topology driven protocol can be used to select its path. However, if resource requirements or policy restrictions exist, then a constraint-based routing scheme should be used for path selection.
路径可以由底层路由协议自动计算，也可以由网络运营商管理性地定义。如果没有与流量中继相关的资源需求或限制，则可以使用拓扑驱动协议来选择其路径。但是，如果存在资源需求或策略限制，则应使用基于约束的路由方案进行路径选择。
In Section 7, a constraint-based routing framework which can automatically compute paths subject to a set of constraints is described. Issues pertaining to explicit paths instantiated through administrative action are discussed in Section 5.6.1 below.
在第7节中，描述了一个基于约束的路由框架，该框架可以自动计算受一组约束的路径。下面第5.6.1节讨论了与通过管理操作实例化的显式路径有关的问题。
Path management concerns all aspects pertaining to the maintenance of paths traversed by traffic trunks. In some operational contexts, it is desirable that an MPLS implementation can dynamically reconfigure itself, to adapt to some notion of change in "system state." Adaptivity and resilience are aspects of dynamic path management.
路径管理涉及与维护交通干线穿过的路径有关的所有方面。在某些操作环境中，MPLS实现可以动态地重新配置自身，以适应“系统状态”的某些变化。自适应性和弹性是动态路径管理的一个方面。
To guide the path selection and management process, a set of attributes are required. The basic attributes and behavioral characteristics associated with traffic trunk path selection and management are described in the remainder of this sub-section.
为了指导路径选择和管理过程，需要一组属性。与交通干线路径选择和管理相关的基本属性和行为特征将在本小节的其余部分中描述。
An administratively specified explicit path for a traffic trunk is one which is configured through operator action. An administratively specified path can be completely specified or partially specified. A path is completely specified if all of the required hops between the endpoints are indicated. A path is partially specified if only a subset of intermediate hops are indicated. In this case, the underlying protocols are required to complete the path. Due to operator errors, an administratively specified path can be inconsistent or illogical. The underlying protocols should be able to detect such inconsistencies and provide appropriate feedback.
交通干线的管理指定显式路径是通过操作员操作配置的路径。可以完全指定或部分指定管理指定的路径。如果指定了端点之间所有必需的跃点，则完全指定路径。如果仅指示中间跃点的子集，则部分指定路径。在这种情况下，需要底层协议来完成路径。由于操作员错误，管理指定的路径可能不一致或不合逻辑。底层协议应该能够检测到这种不一致，并提供适当的反馈。
A "path preference rule" attribute should be associated with administratively specified explicit paths. A path preference rule attribute is a binary variable which indicates whether the administratively configured explicit path is "mandatory" or "non-mandatory."
“路径首选项规则”属性应与管理指定的显式路径相关联。路径首选项规则属性是一个二进制变量，它指示管理配置的显式路径是“强制”还是“非强制”
If an administratively specified explicit path is selected with a "mandatory attribute, then that path (and only that path) must be used. If a mandatory path is topological infeasible (e.g. the two endpoints are topologically partitioned), or if the path cannot be instantiated because the available resources are inadequate, then the path setup process fails. In other words, if a path is specified as mandatory, then an alternate path cannot be used regardless of prevailing circumstance. A mandatory path which is successfully instantiated is also implicitly pinned. Once the path is instantiated it cannot be changed except through deletion and instantiation of a new path.
如果使用“强制”属性选择管理指定的显式路径，则必须使用该路径（且仅使用该路径）。如果强制路径在拓扑上不可行（例如，两个端点在拓扑上已分区），或者如果由于可用资源不足而无法实例化该路径，则路径设置过程失败。换句话说，如果将路径指定为强制路径，则无论当前情况如何，都无法使用备用路径。成功实例化的强制路径也会隐式固定。一旦路径实例化除非通过删除和实例化新路径，否则不能对其进行更改。
However, if an administratively specified explicit path is selected with a "non-mandatory" preference rule attribute value, then the path should be used if feasible. Otherwise, an alternate path can be chosen instead by the underlying protocols.
但是，如果使用“非强制性”首选项规则属性值选择管理指定的显式路径，则应在可行的情况下使用该路径。否则，底层协议可以选择替代路径。
In some practical contexts, it can be useful to have the ability to administratively specify a set of candidate explicit paths for a given traffic trunk and define a hierarchy of preference relations on the paths. During path establishment, the preference rules are applied to select a suitable path from the candidate list. Also, under failure scenarios the preference rules are applied to select an alternate path from the candidate list.
在某些实际环境中，能够管理性地为给定的交通干线指定一组候选显式路径，并在路径上定义偏好关系的层次结构是有用的。在路径建立期间，应用偏好规则从候选列表中选择合适的路径。此外，在故障场景下，将应用首选项规则从候选列表中选择备用路径。
Resource class affinity attributes associated with a traffic trunk can be used to specify the class of resources (see Section 6) which are to be explicitly included or excluded from the path of the traffic trunk. These are policy attributes which can be used to impose additional constraints on the path traversed by a given traffic trunk. Resource class affinity attributes for a traffic can be specified as a sequence of tuples:
与流量主干关联的资源类关联属性可用于指定要从流量主干路径显式包括或排除的资源类（参见第6节）。这些是策略属性，可用于对给定流量主干通过的路径施加附加约束。流量的资源类关联属性可以指定为元组序列：
<resource-class, affinity>; <resource-class, affinity>; ..
<resource class，affinity><资源类，关联>。。
The resource-class parameter identifies a resource class for which an affinity relationship is defined with respect to the traffic trunk. The affinity parameter indicates the affinity relationship; that is, whether members of the resource class are to be included or excluded from the path of the traffic trunk. Specifically, the affinity parameter may be a binary variable which takes one of the following values: (1) explicit inclusion, and (2) explicit exclusion.
resource class参数标识一个资源类，为该资源类定义了与流量主干相关的关联关系。亲和参数表示亲和关系；也就是说，资源类的成员是要包括在流量主干的路径中还是要从中排除。具体地说，affinity参数可以是一个二进制变量，它采用以下值之一：（1）显式包含，和（2）显式排除。
If the affinity attribute is a binary variable, it may be possible to use Boolean expressions to specify the resource class affinities associated with a given traffic trunk.
如果affinity属性是二进制变量，则可以使用布尔表达式指定与给定流量主干关联的资源类affinity。
If no resource class affinity attributes are specified, then a "don't care" affinity relationship is assumed to hold between the traffic trunk and all resources. That is, there is no requirement to explicitly include or exclude any resources from the traffic trunk's path. This should be the default in practice.
如果未指定资源类关联属性，则假定在流量主干和所有资源之间存在“不关心”关联关系。也就是说，不需要显式地从流量主干的路径中包括或排除任何资源。这应该是实践中的默认设置。
Resource class affinity attributes are very useful and powerful constructs because they can be used to implement a variety of policies. For example, they can be used to contain certain traffic trunks within specific topological regions of the network.
资源类关联属性是非常有用和强大的构造，因为它们可以用于实现各种策略。例如，它们可用于在网络的特定拓扑区域内包含某些交通干线。
A "constraint-based routing" framework (see section 7.0) can be used to compute an explicit path for a traffic trunk subject to resource class affinity constraints in the following manner:
“基于约束的路由”框架（见第7.0节）可用于以以下方式计算受资源类关联约束的流量主干的显式路径：
1. For explicit inclusion, prune all resources not belonging to the specified classes prior to performing path computation.
1. 对于显式包含，请在执行路径计算之前修剪不属于指定类的所有资源。
2. For explicit exclusion, prune all resources belonging to the specified classes before performing path placement computations.
2. 对于显式排除，请在执行路径放置计算之前修剪属于指定类的所有资源。
Network characteristics and state change over time. For example, new resources become available, failed resources become reactivated, and allocated resources become deallocated. In general, sometimes more efficient paths become available. Therefore, from a Traffic Engineering perspective, it is necessary to have administrative control parameters that can be used to specify how traffic trunks respond to this dynamism. In some scenarios, it might be desirable to dynamically change the paths of certain traffic trunks in response to changes in network state. This process is called re-optimization. In other scenarios, re-optimization might be very undesirable.
网络特性和状态随时间而变化。例如，新资源变为可用，失败的资源变为重新激活，分配的资源变为取消分配。通常，有时会有更有效的路径可用。因此，从交通工程的角度来看，有必要设置管理控制参数，用于指定交通干线如何响应这种动态。在某些情况下，可能需要根据网络状态的变化动态更改某些流量中继的路径。这个过程称为重新优化。在其他情况下，重新优化可能非常不可取。
An Adaptivity attribute is a part of the path maintenance parameters associated with traffic trunks. The adaptivity attribute associated with a traffic trunk indicates whether the trunk is subject to re-optimization. That is, an adaptivity attribute is a binary variable which takes one of the following values: (1) permit re-optimization and (2) disable re-optimization.
自适应属性是与交通干线相关联的路径维护参数的一部分。与交通干线相关联的自适应属性指示是否对干线进行重新优化。也就是说，自适应属性是采用以下值之一的二进制变量：（1）允许重新优化和（2）禁用重新优化。
If re-optimization is enabled, then a traffic trunk can be rerouted through different paths by the underlying protocols in response to changes in network state (primarily changes in resource availability). Conversely, if re-optimization is disabled, then the traffic trunk is "pinned" to its established path and cannot be rerouted in response to changes in network state.
如果启用了重新优化，则底层协议可以根据网络状态的变化（主要是资源可用性的变化）通过不同的路径重新路由流量中继。相反，如果禁用了重新优化，则流量中继将“固定”到其已建立的路径，并且无法响应网络状态的变化而重新路由。
Stability is a major concern when re-optimization is permitted. To promote stability, an MPLS implementation should not be too reactive to the evolutionary dynamics of the network. At the same time, it must adapt fast enough so that optimal use can be made of network assets. This implies that the frequency of re-optimization should be administratively configurable to allow for tuning.
当允许重新优化时，稳定性是一个主要问题。为了提高稳定性，MPLS实现不应该对网络的演化动态做出太大的反应。同时，它必须足够快地适应，以便能够优化使用网络资产。这意味着重新优化的频率应该在管理上可配置，以便进行调优。
It is to be noted that re-optimization is distinct from resilience. A different attribute is used to specify the resilience characteristics of a traffic trunk (see section 5.9). In practice, it would seem reasonable to expect traffic trunks subject to re-optimization to be implicitly resilient to failures along their paths. However, a traffic trunk which is not subject to re-optimization and whose path is not administratively specified with a "mandatory" attribute can also be required to be resilient to link and node failures along its established path
需要注意的是，重新优化不同于弹性。不同的属性用于指定交通干线的弹性特征（见第5.9节）。在实践中，期望经过重新优化的交通干线对其路径上的故障具有隐含的恢复能力似乎是合理的。然而，不受重新优化影响且其路径未通过“强制”属性管理性指定的流量中继也可能需要对其已建立路径上的链路和节点故障具有弹性
Formally, it can be stated that adaptivity to state evolution through re-optimization implies resilience to failures, whereas resilience to failures does not imply general adaptivity through re-optimization to state changes.
形式上，可以说，通过重新优化对状态演化的适应性意味着对故障的恢复能力，而对故障的恢复能力并不意味着通过重新优化对状态变化的一般适应性。
Load distribution across multiple parallel traffic trunks between two nodes is an important consideration. In many practical contexts, the aggregate traffic between two nodes may be such that no single link (hence no single path) can carry the load. However, the aggregate flow might be less than the maximum permissible flow across a "min-cut" that partitions the two nodes. In this case, the only feasible solution is to appropriately divide the aggregate traffic into sub-streams and route the sub-streams through multiple paths between the two nodes.
两个节点之间跨多个并行业务中继的负载分配是一个重要的考虑因素。在许多实际环境中，两个节点之间的聚合流量可能是这样的，即没有单个链路（因此没有单个路径）可以承载负载。但是，总流量可能小于通过分割两个节点的“最小切割”的最大允许流量。在这种情况下，唯一可行的解决方案是将聚合流量适当地划分为子流，并通过两个节点之间的多条路径路由子流。
In an MPLS domain, this problem can be addressed by instantiating multiple traffic trunks between the two nodes, such that each traffic trunk carries a proportion of the aggregate traffic. Therefore, a flexible means of load assignment to multiple parallel traffic trunks carrying traffic between a pair of nodes is required.
在MPLS域中，可以通过实例化两个节点之间的多个业务中继来解决此问题，这样每个业务中继都承载一部分聚合业务。因此，需要一种灵活的方式，将负载分配给在一对节点之间承载业务的多个并行业务中继。
Specifically, from an operational perspective, in situations where parallel traffic trunks are warranted, it would be useful to have some attribute that can be used to indicate the relative proportion of traffic to be carried by each traffic trunk. The underlying protocols will then map the load onto the traffic trunks according to the specified proportions. It is also, generally desirable to maintain packet ordering between packets belong to the same micro-flow (same source address, destination address, and port number).
具体地说，从运营角度来看，在保证平行交通干线的情况下，最好有一些属性可用于指示每个交通干线要承载的交通的相对比例。然后，底层协议将根据指定的比例将负载映射到交通干线上。通常，还希望在属于相同微流（相同的源地址、目的地址和端口号）的分组之间保持分组顺序。
The priority attribute defines the relative importance of traffic trunks. If a constraint-based routing framework is used with MPLS, then priorities become very important because they can be used to determine the order in which path selection is done for traffic trunks at connection establishment and under fault scenarios.
优先级属性定义了交通干线的相对重要性。如果MPLS使用基于约束的路由框架，那么优先级就变得非常重要，因为它们可以用来确定在连接建立和故障场景下对流量中继进行路径选择的顺序。
Priorities are also important in implementations permitting preemption because they can be used to impose a partial order on the set of traffic trunks according to which preemptive policies can be actualized.
优先级在允许抢占的实现中也很重要，因为优先级可用于对流量中继集施加偏序，根据偏序可以实现抢占策略。
The preemption attribute determines whether a traffic trunk can preempt another traffic trunk from a given path, and whether another traffic trunk can preempt a specific traffic trunk. Preemption is useful for both traffic oriented and resource oriented performance
preemption属性确定一个流量主干是否可以从给定路径抢占另一个流量主干，以及另一个流量主干是否可以抢占特定的流量主干。抢占对于面向流量和面向资源的性能都很有用
objectives. Preemption can used to assure that high priority traffic trunks can always be routed through relatively favorable paths within a differentiated services environment.
目标。抢占可用于确保高优先级业务中继始终可以通过差异化服务环境中相对有利的路径进行路由。
Preemption can also be used to implement various prioritized restoration policies following fault events.
抢占还可用于在发生故障事件后实施各种优先恢复策略。
The preemption attribute can be used to specify four preempt modes for a traffic trunk: (1) preemptor enabled, (2) non-preemptor, (3) preemptable, and (4) non-preemptable. A preemptor enabled traffic trunk can preempt lower priority traffic trunks designated as preemptable. A traffic specified as non-preemptable cannot be preempted by any other trunks, regardless of relative priorities. A traffic trunk designated as preemptable can be preempted by higher priority trunks which are preemptor enabled.
抢占属性可用于为流量中继指定四种抢占模式：（1）启用抢占模式，（2）非抢占模式，（3）可抢占模式和（4）不可抢占模式。启用抢占器的流量中继可以抢占指定为可抢占的低优先级流量中继。被指定为不可抢占的流量不能被任何其他中继抢占，无论其相对优先级如何。指定为可抢占的流量中继可以被启用抢占器的高优先级中继抢占。
It is trivial to see that some of the preempt modes are mutually exclusive. Using the numbering scheme depicted above, the feasible preempt mode combinations for a given traffic trunk are as follows: (1, 3), (1, 4), (2, 3), and (2, 4). The (2, 4) combination should be the default.
看到一些抢占模式是相互排斥的，这是不重要的。使用上述编号方案，给定交通干线的可行抢占模式组合如下：（1,3）、（1,4）、（2,3）和（2,4）。（2，4）组合应为默认值。
A traffic trunk, say "A", can preempt another traffic trunk, say "B", only if *all* of the following five conditions hold: (i) "A" has a relatively higher priority than "B", (ii) "A" contends for a resource utilized by "B", (iii) the resource cannot concurrently accommodate "A" and "B" based on certain decision criteria, (iv) "A" is preemptor enabled, and (v) "B" is preemptable.
一条交通干线，如“A”，只有在以下五个条件中的*全部*都成立时，才能抢占另一条交通干线，如“B”：（i）“A”的优先级相对高于“B”；（ii）“A”争夺“B”使用的资源；（iii）根据某些决策标准，该资源不能同时容纳“A”和“B”；（iv）“A”已启用抢占器，且（v）“B”可抢占。
Preemption is not considered a mandatory attribute under the current best effort Internet service model although it is useful. However, in a differentiated services scenario, the need for preemption becomes more compelling. Moreover, in the emerging optical internetworking architectures, where some protection and restoration functions may be migrated from the optical layer to data network elements (such as gigabit and terabit label switching routers) to reduce costs, preemptive strategies can be used to reduce the restoration time for high priority traffic trunks under fault conditions.
在当前尽力而为的Internet服务模式下，抢占虽然很有用，但并不被视为强制属性。然而，在差异化服务场景中，抢占的需求变得更加迫切。此外，在新兴的光互连体系结构中，一些保护和恢复功能可以从光层迁移到数据网元（如千兆位和太比特标签交换路由器）以降低成本，抢占策略可用于减少故障条件下高优先级业务中继的恢复时间。
The resilience attribute determines the behavior of a traffic trunk under fault conditions. That is, when a fault occurs along the path through which the traffic trunk traverses. The following basic problems need to be addressed under such circumstances: (1) fault detection, (2) failure notification, (3) recovery and service restoration. Obviously, an MPLS implementation will have to incorporate mechanisms to address these issues.
弹性属性确定故障条件下交通干线的行为。也就是说，当沿交通干线穿过的路径发生故障时。在这种情况下，需要解决以下基本问题：（1）故障检测，（2）故障通知，（3）恢复和服务恢复。显然，MPLS实现必须包含解决这些问题的机制。
Many recovery policies can be specified for traffic trunks whose established paths are impacted by faults. The following are examples of feasible schemes:
对于已建立的路径受故障影响的交通干线，可以指定许多恢复策略。以下是可行方案的示例：
1. Do not reroute the traffic trunk. For example, a survivability scheme may already be in place, provisioned through an alternate mechanism, which guarantees service continuity under failure scenarios without the need to reroute traffic trunks. An example of such an alternate scheme (certainly many others exist), is a situation whereby multiple parallel label switched paths are provisioned between two nodes, and function in a manner such that failure of one LSP causes the traffic trunk placed on it to be mapped onto the remaining LSPs according to some well defined policy.
1. 不要改变交通干线的路线。例如，可生存性方案可能已经到位，通过备用机制提供，该机制保证故障场景下的服务连续性，而无需重新路由业务中继。这种替代方案的一个示例（当然存在许多其他方案）是这样一种情况，即在两个节点之间提供多个并行标签交换路径，并且其工作方式使得一个LSP的故障导致放置在其上的业务中继根据某个明确定义的策略映射到剩余LSP。
2. Reroute through a feasible path with enough resources. If none exists, then do not reroute.
2. 通过具有足够资源的可行路径重新路由。如果不存在，则不要重新路由。
3. Reroute through any available path regardless of resource constraints.
3. 无论资源限制如何，通过任何可用路径重新路由。
4. Many other schemes are possible including some which might be combinations of the above.
4. 许多其他方案是可能的，包括一些可能是上述方案的组合。
A "basic" resilience attribute indicates the recovery procedure to be applied to traffic trunks whose paths are impacted by faults. Specifically, a "basic" resilience attribute is a binary variable which determines whether the target traffic trunk is to be rerouted when segments of its path fail. "Extended" resilience attributes can be used to specify detailed actions to be taken under fault scenarios. For example, an extended resilience attribute might specify a set of alternate paths to use under fault conditions, as well as the rules that govern the relative preference of each specified path.
“基本”弹性属性表示要应用于路径受故障影响的交通干线的恢复过程。具体而言，“基本”弹性属性是一个二进制变量，用于确定目标流量主干在其路径段失败时是否要重新路由。“扩展”弹性属性可用于指定故障场景下要采取的详细行动。例如，扩展弹性属性可以指定一组在故障条件下使用的备用路径，以及控制每个指定路径的相对首选项的规则。
Resilience attributes mandate close interaction between MPLS and routing.
弹性属性要求MPLS和路由之间进行密切的交互。
The policing attribute determines the actions that should be taken by the underlying protocols when a traffic trunk becomes non-compliant. That is, when a traffic trunk exceeds its contract as specified in the traffic parameters. Generally, policing attributes can indicate whether a non-conformant traffic trunk is to be rate limited, tagged, or simply forwarded without any policing action. If policing is used, then adaptations of established algorithms such as the ATM Forum's GCRA [11] can be used to perform this function.
policing属性确定当流量中继变得不兼容时底层协议应采取的操作。也就是说，当交通干线超过交通参数中规定的合同时。通常，监控属性可以指示是否对不符合要求的流量主干进行速率限制、标记或简单转发，而无需任何监控操作。如果使用了监管，则可以使用ATM论坛的GCRA[11]等已建立算法的调整来执行此功能。
Policing is necessary in many operational scenarios, but is quite undesirable in some others. In general, it is usually desirable to police at the ingress to a network (to enforce compliance with service level agreements) and to minimize policing within the core, except when capacity constraints dictate otherwise.
在许多行动场景中，维持治安是必要的，但在其他一些场景中，这是非常不可取的。一般来说，通常需要在网络入口进行监控（以强制遵守服务级别协议），并尽量减少核心内的监控，除非容量限制另有规定。
Therefore, from a Traffic Engineering perspective, it is necessary to be able to administratively enable or disable traffic policing for each traffic trunk.
因此，从交通工程的角度来看，必须能够在管理上启用或禁用每个交通干线的交通管制。
Resource attributes are part of the topology state parameters, which are used to constrain the routing of traffic trunks through specific resources.
资源属性是拓扑状态参数的一部分，用于通过特定资源约束交通干线的路由。
The maximum allocation multiplier (MAM) of a resource is an administratively configurable attribute which determines the proportion of the resource that is available for allocation to traffic trunks. This attribute is mostly applicable to link bandwidth. However, it can also be applied to buffer resources on LSRs. The concept of MAM is analogous to the concepts of subscription and booking factors in frame relay and ATM networks.
资源的最大分配乘数（MAM）是一个管理上可配置的属性，它决定了可分配到流量中继的资源比例。此属性主要适用于链路带宽。但是，它也可以应用于LSR上的缓冲资源。MAM的概念类似于帧中继和ATM网络中的订阅和预订因素的概念。
The values of the MAM can be chosen so that a resource can be under-allocated or over-allocated. A resource is said to be under-allocated if the aggregate demands of all traffic trunks (as expressed in the trunk traffic parameters) that can be allocated to it are always less than the capacity of the resource. A resource is said to be over-allocated if the aggregate demands of all traffic trunks allocated to it can exceed the capacity of the resource.
可以选择MAM的值，以便资源可以分配不足或分配过度。如果可以分配给资源的所有交通干线（如干线交通参数所示）的总需求总是小于资源的容量，则称资源分配不足。如果分配给资源的所有交通干线的总需求可以超过该资源的容量，则称该资源被过度分配。
Under-allocation can be used to bound the utilization of resources. However,the situation under MPLS is more complex than in circuit switched schemes because under MPLS, some flows can be routed via conventional hop by hop protocols (also via explicit paths) without consideration for resource constraints.
分配不足可以用来约束资源的利用率。然而，MPLS下的情况比电路交换方案更复杂，因为在MPLS下，一些流可以通过传统的逐跳协议（也通过显式路径）路由，而不考虑资源约束。
Over-allocation can be used to take advantage of the statistical characteristics of traffic in order to implement more efficient resource allocation policies. In particular, over-allocation can be used in situations where the peak demands of traffic trunks do not coincide in time.
过度分配可用于利用流量的统计特性，以实现更高效的资源分配策略。特别是，过度分配可用于交通干线高峰需求在时间上不一致的情况。
Resource class attributes are administratively assigned parameters which express some notion of "class" for resources. Resource class attributes can be viewed as "colors" assigned to resources such that the set of resources with the same "color" conceptually belong to the same class. Resource class attributes can be used to implement a variety of policies. The key resources of interest here are links. When applied to links, the resource class attribute effectively becomes an aspect of the "link state" parameters.
资源类属性是管理分配的参数，表示资源的某种“类”概念。资源类属性可以被视为分配给资源的“颜色”，以便具有相同“颜色”的资源集在概念上属于同一类。资源类属性可用于实现各种策略。这里感兴趣的关键资源是链接。当应用于链接时，资源类属性实际上成为“链接状态”参数的一个方面。
The concept of resource class attributes is a powerful abstraction. From a Traffic Engineering perspective, it can be used to implement many policies with regard to both traffic and resource oriented performance optimization. Specifically, resource class attributes can be used to:
资源类属性的概念是一个强大的抽象。从流量工程的角度来看，它可以用于实现许多与流量和面向资源的性能优化相关的策略。具体而言，资源类属性可用于：
1. Apply uniform policies to a set of resources that do not need to be in the same topological region.
1. 对不需要位于同一拓扑区域的一组资源应用统一策略。
2. Specify the relative preference of sets of resources for path placement of traffic trunks.
2. 为交通干线的路径放置指定资源集的相对首选项。
3. Explicitly restrict the placement of traffic trunks to specific subsets of resources.
3. 明确地将交通干线的放置限制为特定的资源子集。
4. Implement generalized inclusion / exclusion policies.
4. 实施普遍的包容/排斥政策。
5. Enforce traffic locality containment policies. That is, policies that seek to contain local traffic within specific topological regions of the network.
5. 强制实施交通区域控制策略。也就是说，寻求在网络的特定拓扑区域内包含本地流量的策略。
Additionally, resource class attributes can be used for identification purposes.
此外，资源类属性可用于标识目的。
In general, a resource can be assigned more than one resource class attribute. For example, all of the OC-48 links in a given network may be assigned a distinguished resource class attribute. The subsets of OC-48 links which exist with a given abstraction domain of the network may be assigned additional resource class attributes in order to implement specific containment policies, or to architect the network in a certain manner.
通常，可以为资源分配多个资源类属性。例如，给定网络中的所有OC-48链路可以被分配一个可分辨资源类属性。存在于网络的给定抽象域中的OC-48链路子集可以被分配额外的资源类属性，以便实现特定的包含策略，或者以某种方式构建网络。
This section discusses the issues pertaining to constraint-based routing in MPLS domains. In contemporary terminology, constraint-based routing is often referred to as "QoS Routing" see [5,6,7,10].
本节讨论与MPLS域中基于约束的路由相关的问题。在当代术语中，基于约束的路由通常被称为“QoS路由”，参见[5,6,7,10]。
This document uses the term "constraint-based routing" however, because it better captures the functionality envisioned, which generally encompasses QoS routing as a subset.
然而，本文档使用术语“基于约束的路由”，因为它更好地捕获了预想的功能，通常将QoS路由作为一个子集。
constraint-based routing enables a demand driven, resource reservation aware, routing paradigm to co-exist with current topology driven hop by hop Internet interior gateway protocols.
基于约束的路由使需求驱动、资源预留感知的路由范式能够与当前拓扑驱动的逐跳互联网内部网关协议共存。
A constraint-based routing framework uses the following as input:
基于约束的路由框架使用以下内容作为输入：
- The attributes associated with traffic trunks.
- 与交通干线关联的属性。
- The attributes associated with resources.
- 与资源关联的属性。
- Other topology state information.
- 其他拓扑状态信息。
Based on this information, a constraint-based routing process on each node automatically computes explicit routes for each traffic trunk originating from the node. In this case, an explicit route for each traffic trunk is a specification of a label switched path that satisfies the demand requirements expressed in the trunk's attributes, subject to constraints imposed by resource availability, administrative policy, and other topology state information.
基于此信息，每个节点上基于约束的路由过程会自动为源自该节点的每个流量主干计算显式路由。在这种情况下，每个业务中继的显式路由是标签交换路径的规范，该路径满足中继属性中表示的需求需求，受资源可用性、管理策略和其他拓扑状态信息施加的约束。
A constraint-based routing framework can greatly reduce the level of manual configuration and intervention required to actualize Traffic Engineering policies.
基于约束的路由框架可以大大降低实现流量工程策略所需的手动配置和干预水平。
In practice, the Traffic Engineer, an operator, or even an automaton will specify the endpoints of a traffic trunk and assign a set of attributes to the trunk which encapsulate the performance expectations and behavioral characteristics of the trunk. The constraint-based routing framework is then expected to find a feasible path to satisfy the expectations. If necessary, the Traffic Engineer or a traffic engineering support system can then use administratively configured explicit routes to perform fine grained optimization.
实际上，流量工程师、操作员甚至自动机将指定流量主干的端点，并为主干分配一组属性，这些属性封装了主干的性能期望和行为特征。然后期望基于约束的路由框架找到一条满足期望的可行路径。如果需要，流量工程师或流量工程支持系统可以使用管理配置的显式路由来执行细粒度优化。
A constraint-based routing framework should at least have the capability to automatically obtain a basic feasible solution to the traffic trunk path placement problem.
基于约束的路由框架至少应能够自动获得交通干线路径布局问题的基本可行解。
In general, the constraint-based routing problem is known to be intractable for most realistic constraints. However, in practice, a very simple well known heuristic (see e.g. [9]) can be used to find a feasible path if one exists:
一般来说，基于约束的路由问题对于大多数现实约束来说是难以解决的。然而，在实践中，如果存在一条可行路径，则可以使用非常简单的众所周知的启发式方法（参见[9]）来找到可行路径：
- First prune resources that do not satisfy the requirements of the traffic trunk attributes.
- 首先修剪不满足流量主干属性要求的资源。
- Next, run a shortest path algorithm on the residual graph.
- 接下来，在残差图上运行最短路径算法。
Clearly, if a feasible path exists for a single traffic trunk, then the above simple procedure will find it. Additional rules can be specified to break ties and perform further optimizations. In general, ties should be broken so that congestion is minimized. When multiple traffic trunks are to be routed, however, it can be shown that the above algorithm may not always find a mapping, even when a feasible mapping exists.
显然，如果单个交通干线存在可行路径，则上述简单过程将找到它。可以指定其他规则来打破联系并执行进一步优化。一般来说，应断开连接，以尽量减少拥挤。然而，当要路由多个业务中继时，可以证明，即使存在可行的映射，上述算法也不一定总能找到映射。
Many commercial implementations of frame relay and ATM switches already support some notion of constraint-based routing. For such devices or for the novel MPLS centric contraptions devised therefrom, it should be relatively easy to extend the current constraint-based routing implementations to accommodate the peculiar requirements of MPLS.
帧中继和ATM交换机的许多商业实现已经支持一些基于约束的路由概念。对于此类设备或由此设计的以MPLS为中心的新型装置，扩展当前基于约束的路由实现以适应MPLS的特殊需求应该相对容易。
For routers that use topology driven hop by hop IGPs, constraint-based routing can be incorporated in at least one of two ways:
对于使用拓扑驱动逐跳IGP的路由器，基于约束的路由至少可以采用以下两种方式之一：
1. By extending the current IGP protocols such as OSPF and IS-IS to support constraint-based routing. Effort is already underway to provide such extensions to OSPF (see [5,7]).
1. 通过扩展现有的IGP协议，如OSPF和IS-IS，以支持基于约束的路由。已经在努力为OSPF提供此类扩展（见[5,7]）。
2. By adding a constraint-based routing process to each router which can co-exist with current IGPs. This scenario is depicted in Figure 1.
2. 通过向每个可以与当前IGP共存的路由器添加基于约束的路由过程。该场景如图1所示。
------------------------------------------
| Management Interface |
------------------------------------------
| | |
------------ ------------------ --------------
| MPLS |<->| Constraint-Based | | Conventional |
| | | Routing Process | | IGP Process |
------------ ------------------ --------------
| |
----------------------- --------------
| Resource Attribute | | Link State |
| Availability Database | | Database |
----------------------- --------------
------------------------------------------
| Management Interface |
------------------------------------------
| | |
------------ ------------------ --------------
| MPLS |<->| Constraint-Based | | Conventional |
| | | Routing Process | | IGP Process |
------------ ------------------ --------------
| |
----------------------- --------------
| Resource Attribute | | Link State |
| Availability Database | | Database |
----------------------- --------------
Figure 1. Constraint-Based Routing Process on Layer 3 LSR
图1。基于约束的第三层LSR路由过程
There are many important details associated with implementing constraint-based routing on Layer 3 devices which we do not discuss here. These include the following:
在第3层设备上实现基于约束的路由有许多重要的细节，我们在这里不讨论这些细节。这些措施包括：
- Mechanisms for exchange of topology state information (resource availability information, link state information, resource attribute information) between constraint-based routing processes.
- 用于在基于约束的路由进程之间交换拓扑状态信息（资源可用性信息、链路状态信息、资源属性信息）的机制。
- Mechanisms for maintenance of topology state information.
- 维护拓扑状态信息的机制。
- Interaction between constraint-based routing processes and conventional IGP processes.
- 基于约束的路由过程和传统IGP过程之间的相互作用。
- Mechanisms to accommodate the adaptivity requirements of traffic trunks.
- 适应交通干线自适应要求的机制。
- Mechanisms to accommodate the resilience and survivability requirements of traffic trunks.
- 适应交通干线的弹性和生存性要求的机制。
In summary, constraint-based routing assists in performance optimization of operational networks by automatically finding feasible paths that satisfy a set of constraints for traffic trunks. It can drastically reduce the amount of administrative explicit path configuration and manual intervention required to achieve Traffic Engineering objectives.
总之，基于约束的路由通过自动找到满足一组交通干线约束的可行路径，有助于运营网络的性能优化。它可以大大减少实现流量工程目标所需的管理显式路径配置和手动干预量。
This manuscript presented a set of requirements for Traffic Engineering over MPLS. Many capabilities were described aimed at enhancing the applicability of MPLS to Traffic Engineering in the Internet.
这篇手稿提出了MPLS流量工程的一系列要求。描述了许多旨在增强MPLS在互联网流量工程中的适用性的功能。
It should be noted that some of the issues described here can be addressed by incorporating a minimal set of building blocks into MPLS, and then using a network management superstructure to extend the functionality in order to realize the requirements. Also, the constraint-based routing framework does not have to be part of the core MPLS specifications. However, MPLS does require some interaction with a constraint-based routing framework in order to meet the requirements.
应该注意，这里描述的一些问题可以通过将最小的构建块集合合并到MPLS中，然后使用网络管理上层结构来扩展功能以实现需求来解决。此外，基于约束的路由框架不必是核心MPLS规范的一部分。然而，MPLS确实需要与基于约束的路由框架进行一些交互，以满足需求。
This document does not introduce new security issues beyond those inherent in MPLS and may use the same mechanisms proposed for this technology. It is, however, specifically important that manipulation of administratively configurable parameters be executed in a secure manner by authorized entities.
除MPLS固有的安全问题外，本文档不会引入新的安全问题，并可能使用针对该技术提出的相同机制。然而，特别重要的是，授权实体应以安全的方式执行管理可配置参数的操作。
[1] Rosen, E., Viswanathan, A. and R. Callon, "A Proposed Architecture for MPLS", Work in Progress.
[1] Rosen，E.，Viswanathan，A.和R.Callon，“MPLS的拟议架构”，正在进行中。
[2] Callon, R., Doolan, P., Feldman, N., Fredette, A., Swallow, G. and A. Viswanathan, "A Framework for Multiprotocol Label Switching", Work in Progress.
[2] Callon，R.，Doolan，P.，Feldman，N.，Fredette，A.，Swallow，G.和A.Viswanathan，“多协议标签交换框架”，正在进行中。
[3] Li, T. and Y. Rekhter, "Provider Architecture for Differentiated Services and Traffic Engineering (PASTE)", RFC 2430, October 1998.
[3] Li，T.和Y.Rekhter，“差异化服务和流量工程的提供商架构（PASTE）”，RFC 2430，1998年10月。
[4] Rekhter, Y., Davie, B., Katz, D., Rosen, E. and G. Swallow, "Cisco Systems' Tag Switching Architecture - Overview", RFC 2105, February 1997.
[4] Rekhter，Y.，Davie，B.，Katz，D.，Rosen，E.和G.Swallow，“思科系统的标签交换架构-概述”，RFC 21052997年2月。
[5] Zhang, Z., Sanchez, C., Salkewicz, B. and E. Crawley "Quality of Service Extensions to OSPF", Work in Progress.
[5] Zhang，Z.，Sanchez，C.，Salkewicz，B.和E.Crawley“OSPF的服务质量扩展”，正在进行中。
[6] Crawley, E., Nair, F., Rajagopalan, B. and H. Sandick, "A Framework for QoS Based Routing in the Internet", RFC 2386, August 1998.
[6] Crawley，E.，Nair，F.，Rajagopalan，B.和H.Sandick，“互联网中基于QoS的路由框架”，RFC 2386，1998年8月。
[7] Guerin, R., Kamat, S., Orda, A., Przygienda, T. and D. Williams, "QoS Routing Mechanisms and OSPF Extensions", RFC 2676, August 1999.
[7] Guerin，R.，Kamat，S.，Orda，A.，Przygienda，T.和D.Williams，“QoS路由机制和OSPF扩展”，RFC 26761999年8月。
[8] C. Yang and A. Reddy, "A Taxonomy for Congestion Control Algorithms in Packet Switching Networks," IEEE Network Magazine, Volume 9, Number 5, July/August 1995.
[8] C.Yang和A.Reddy，“分组交换网络中拥塞控制算法的分类”，《IEEE网络杂志》，第9卷，第5期，1995年7月/8月。
[9] W. Lee, M. Hluchyi, and P. Humblet, "Routing Subject to Quality of Service Constraints in Integrated Communication Networks," IEEE Network, July 1995, pp 46-55.
[9] W.Lee，M.Hluchyi和P.Humblet，“综合通信网络中受服务质量约束的路由”，IEEE网络，1995年7月，第46-55页。
[10] ATM Forum, "Traffic Management Specification: Version 4.0" April 1996.
[10] ATM论坛，“流量管理规范：4.0版”，1996年4月。
The authors would like to thank Yakov Rekhter for his review of an earlier draft of this document. The authors would also like to thank Louis Mamakos and Bill Barns for their helpful suggestions, and Curtis Villamizar for providing some useful feedback.
作者感谢Yakov Rekhter对本文件早期草案的审查。作者还要感谢Louis Mamakos和Bill Barns提出的有益建议，以及Curtis Villamizar提供的一些有用反馈。
Daniel O. Awduche UUNET (MCI Worldcom) 3060 Williams Drive Fairfax, VA 22031
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EMail: mo@uu.net
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EMail: mo@uu.net
Jim McManus UUNET (MCI Worldcom) 3060 Williams Drive Fairfax, VA 22031
Jim McManus UUNET（MCI Worldcom）弗吉尼亚州费尔法克斯威廉姆斯大道3060号，邮编22031
Phone: +1 703-206-5607
EMail: jmcmanus@uu.net
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EMail: jmcmanus@uu.net
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