Network Working Group J. Boyle
Request for Comments: 3346 PD Nets
Category: Informational V. Gill
AOL Time Warner, Inc.
A. Hannan
RoutingLoop
D. Cooper
Global Crossing
D. Awduche
Movaz Networks
B. Christian
Worldcom
W.S. Lai
AT&T
August 2002
Network Working Group J. Boyle
Request for Comments: 3346 PD Nets
Category: Informational V. Gill
AOL Time Warner, Inc.
A. Hannan
RoutingLoop
D. Cooper
Global Crossing
D. Awduche
Movaz Networks
B. Christian
Worldcom
W.S. Lai
AT&T
August 2002
Applicability Statement for Traffic Engineering with MPLS
MPLS流量工程的适用性声明
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 (2002). All Rights Reserved.
版权所有（C）互联网协会（2002年）。版权所有。
Abstract
摘要
This document describes the applicability of Multiprotocol Label Switching (MPLS) to traffic engineering in IP networks. Special considerations for deployment of MPLS for traffic engineering in operational contexts are discussed and the limitations of the MPLS approach to traffic engineering are highlighted.
本文档描述了多协议标签交换（MPLS）在IP网络流量工程中的适用性。讨论了在操作环境中部署MPLS进行流量工程的特殊注意事项，并强调了MPLS流量工程方法的局限性。
Table of Contents
目录
1. Introduction....................................................2
2. Technical Overview of ISP Traffic Engineering...................3
3. Applicability of Internet Traffic Engineering...................4
3.1 Avoidance of Congested Resources................................4
3.2 Resource Utilization in Network Topologies with Parallel Links..5
3.3 Implementing Routing Policies using Affinities..................5
3.4 Re-optimization After Restoration...............................6
4. Implementation Considerations...................................6
4.1 Architectural and Operational Considerations....................6
4.2 Network Management Aspects......................................7
4.3 Capacity Engineering Aspects....................................8
4.4 Network Measurement Aspects.....................................8
5. Limitations.....................................................9
6. Conclusion.....................................................11
7. Security Considerations........................................11
8. References.....................................................11
9. Acknowledgments................................................12
10. Authors' Addresses.............................................13
11. Full Copyright Statement.......................................14
1. Introduction....................................................2
2. Technical Overview of ISP Traffic Engineering...................3
3. Applicability of Internet Traffic Engineering...................4
3.1 Avoidance of Congested Resources................................4
3.2 Resource Utilization in Network Topologies with Parallel Links..5
3.3 Implementing Routing Policies using Affinities..................5
3.4 Re-optimization After Restoration...............................6
4. Implementation Considerations...................................6
4.1 Architectural and Operational Considerations....................6
4.2 Network Management Aspects......................................7
4.3 Capacity Engineering Aspects....................................8
4.4 Network Measurement Aspects.....................................8
5. Limitations.....................................................9
6. Conclusion.....................................................11
7. Security Considerations........................................11
8. References.....................................................11
9. Acknowledgments................................................12
10. Authors' Addresses.............................................13
11. Full Copyright Statement.......................................14
It is generally acknowledged that one of the most significant initial applications of Multiprotocol Label Switching (MPLS) is traffic engineering (TE) [1][2] in IP networks. A significant community of IP service providers have found that traffic engineering of their networks can have tactical and strategic value [2, 3, 4]. To support the traffic engineering application, extensions have been specified for Interior Gateway Protocols (IGP) IS-IS [5] and OSPF [6], and to signaling protocols RSVP [7] and LDP [8]. The extensions for IS-IS, OSPF, and RSVP have all been developed and deployed in large scale in many networks consisting of multi-vendor equipment.
人们普遍认为，多协议标签交换（MPLS）最重要的初始应用之一是IP网络中的流量工程（TE）[1][2]。大量IP服务提供商发现，他们网络的流量工程具有战术和战略价值[2,3,4]。为了支持流量工程应用，已为内部网关协议（IGP）IS-IS[5]和OSPF[6]以及信令协议RSVP[7]和LDP[8]指定了扩展。IS-IS、OSPF和RSVP的扩展都已在由多供应商设备组成的许多网络中大规模开发和部署。
This document discusses the applicability of TE to Internet service provider networks, focusing on the MPLS-based approach. It augments the existing protocol applicability statements and, in particular, relates to the operational applicability of RSVP-TE [9]. Special considerations for deployment of MPLS in operational contexts are discussed and the limitations of this approach to traffic engineering are highlighted.
本文讨论了TE对Internet服务提供商网络的适用性，重点讨论了基于MPLS的方法。它扩充了现有的协议适用性声明，特别是与RSVP-TE的操作适用性有关[9]。讨论了在操作环境中部署MPLS的特殊注意事项，并强调了这种流量工程方法的局限性。
Traffic engineering (TE) is generally concerned with the performance optimization of operational networks [2]. In contemporary practice, TE means mapping IP traffic flows onto the existing physical network topology in the most effective way to accomplish desired operational objectives. Techniques currently used to accomplish this include, but are not limited to:
流量工程（TE）通常关注运营网络的性能优化[2]。在当代实践中，TE意味着以最有效的方式将IP流量映射到现有的物理网络拓扑上，以实现预期的运营目标。目前用于实现这一目标的技术包括但不限于：
1. Manipulation of IGP cost (metrics) 2. Explicit routing using constrained virtual-circuit switching techniques such as ATM or Frame Relay SPVCs 3. Explicit routing using constrained path setup techniques such as MPLS
1. IGP成本操纵（指标）2。使用受限虚拟电路交换技术（如ATM或帧中继SPVCs）的显式路由3。使用受限路径设置技术（如MPLS）的显式路由
This document is concerned primarily with MPLS techniques. Specifically, it deals with the ability to use paths other than the shortest paths selected by the IGP to achieve a more balanced network utilization, e.g., by moving traffic away from IGP-selected shortest paths onto alternate paths to avoid congestion in the network. This can be achieved by using explicitly signaled LSP-tunnels. The explicit routes to be used may be computed offline and subsequently downloaded and configured on the routers using an appropriate mechanism. Alternatively, the desired characteristics of an LSP (such as endpoints, bandwidth, affinities) may be configured on a router, which will then use an appropriate algorithm to compute a path through the network satisfying the desired characteristics, subject to various types of constraints. Generally, the characteristics associated with LSPs may include:
本文档主要涉及MPLS技术。具体而言，它涉及使用除IGP选择的最短路径以外的路径以实现更平衡的网络利用的能力，例如，通过将业务从IGP选择的最短路径移动到备用路径以避免网络中的拥塞。这可以通过使用显式信号LSP隧道来实现。要使用的显式路由可以离线计算，并且随后使用适当的机制在路由器上下载和配置。或者，可以在路由器上配置LSP的期望特性（例如端点、带宽、亲和力），路由器随后将根据各种类型的约束使用适当的算法来计算通过网络的满足期望特性的路径。通常，与lsp相关联的特征可以包括：
o Ingress and egress nodes o Bandwidth required o Priority o Nodes to include or exclude in the path o Affinities to include or exclude in the path o Resilience requirements
o 入口和出口节点o所需带宽o优先级o在路径中包含或排除的节点o在路径中包含或排除的亲和力o弹性要求
Affinities are arbitrary, provider-assigned, attributes applied to links and carried in the TE extensions for the IGPs. Affinities impose a class structure on links, which allow different links to be logically grouped together. They can be used to implement various types of policies, or route preferences that allow the inclusion or exclusion of groups of links from the path of LSPs. Affinities are unique to MPLS and the original requirement for them was documented in [2].
亲缘关系是任意的、提供者指定的、应用于链接的属性，并在IGP的TE扩展中携带。亲缘关系在链接上施加类结构，允许不同的链接逻辑地分组在一起。它们可用于实现各种类型的策略或路由首选项，允许从LSP路径中包含或排除链路组。亲和力是MPLS所独有的，对它们的原始要求记录在[2]中。
As mentioned in [2] and [7], traffic engineering with MPLS is appropriate to establish and maintain explicitly routed paths in an IP network for effective traffic placement. LSP-tunnels can be used to forward subsets of traffic through paths that are independent of routes computed by conventional IGP Shortest Path First (SPF) algorithms. This gives network operators significant flexibility in controlling the paths of traffic flows across their networks and allows policies to be implemented that can result in the performance optimization of networks. Examples of scenarios where MPLS-based TE capabilities are applicable in service provider environments are given below. The applicability of MPLS is certainly not restricted to these scenarios.
如[2]和[7]所述，使用MPLS的流量工程适用于在IP网络中建立和维护显式路由路径，以实现有效的流量布局。LSP隧道可用于转发通过独立于传统IGP最短路径优先（SPF）算法计算的路径的流量子集。这使网络运营商在控制其网络上的流量路径方面具有极大的灵活性，并允许实施可导致网络性能优化的策略。下面给出了基于MPLS的TE功能适用于服务提供商环境的场景示例。MPLS的适用性当然不限于这些场景。
In order to lower the utilization of congested link(s), an operator may utilize TE methods to route a subset of traffic away from those links onto less congested topological elements. These types of techniques are viable when segments of the network are congested while other parts are underutilized.
为了降低拥塞链路的利用率，运营商可以利用TE方法将业务子集从这些链路路由到拥塞较少的拓扑元素上。当网络的各个部分拥挤而其他部分利用不足时，这些类型的技术是可行的。
Operators who do not make extensive use of LSP-tunnels may adopt a tactical approach to MPLS TE in which they create LSP-tunnels only when necessary to address specific congestion problems. For example, an LSP can be created between two nodes (source and destination) that are known to contribute traffic to a congested network element, and explicitly route the LSP through a separate path to divert some traffic away from the congestion. On the other hand, operators who make extensive use of LSP-tunnels, either for measurement or automated traffic control, may decide to explicitly route a subset of the LSPs that traverse the point of congestion onto alternate paths. This can be employed to respond quickly when the bandwidth parameter associated with the LSPs does not accurately represent the actual traffic carried by the LSPs, and the operator determines that changing the bandwidth parameter values might not be effective in addressing the issue or may not have lasting impact.
未广泛使用LSP隧道的运营商可采用战术方法来实现MPLS TE，即仅在必要时创建LSP隧道以解决特定的拥塞问题。例如，可以在已知为拥塞网元贡献流量的两个节点（源和目的地）之间创建LSP，并通过单独的路径显式地路由LSP以将一些流量从拥塞中转移出去。另一方面，广泛使用LSP隧道（用于测量或自动交通控制）的运营商可能会决定将穿过拥塞点的LSP子集显式路由到备用路径上。当与lsp相关联的带宽参数不能准确地表示lsp承载的实际业务量，并且操作员确定更改带宽参数值可能无法有效地解决问题或者可能不会产生持久影响时，这可被用于快速响应。
There are other approaches that measure traffic workloads on LSPs and utilize these empirical statistics to configure various characteristics of LSPs. These approaches, for example, can utilize the derived statistics to configure explicit routes for LSPs (also known as offline TE [10]). They can also utilize the statistics to set the values of various LSP attributes such as bandwidths, priority, and affinities (online TE). All of these approaches can be used both tactically and strategically to react to periods of congestion in a network. Congestion may occur as a result of many
还有其他方法可以测量LSP上的流量工作负载，并利用这些经验统计数据来配置LSP的各种特性。例如，这些方法可以利用导出的统计信息为LSP配置显式路由（也称为离线TE[10]）。他们还可以利用统计信息来设置各种LSP属性的值，例如带宽、优先级和亲和力（联机TE）。所有这些方法都可以在战术和战略上用于对网络中的拥塞周期作出反应。由于许多原因，可能会出现拥堵
factors: equipment or facility failure, longer than expected provisioning cycles for new circuits, and unexpected surges in traffic demand.
因素：设备或设施故障，新电路的供应周期长于预期，以及交通需求的意外激增。
In practice, many service provider networks contain multiple parallel links between nodes. An example is transoceanic connectivity which is often provisioned as numerous low-capacity circuits, such as NxDS-3 (N parallel DS-3 circuits) and NxSTM-1 (N parallel STM-1 circuits). Parallel circuits also occur quite often in bandwidth-constrained cities. MPLS TE methods can be applied to effectively distribute the aggregate traffic workload across these parallel circuits.
实际上，许多服务提供商网络在节点之间包含多个并行链路。一个例子是越洋连接，它通常被设置为许多低容量电路，例如NxDS-3（N个并行DS-3电路）和NxSTM-1（N个并行STM-1电路）。在带宽受限的城市，并行电路也经常出现。MPLS-TE方法可用于在这些并行电路之间有效地分配聚合流量负载。
MPLS-based approaches commonly used in practice to deal with parallel links include using LSP bandwidth parameters to control the proportion of demand traversing each link, explicitly configuring routes for LSP-tunnels to distribute them across the parallel links, and using affinities to map different LSPs onto different links. These types of solutions are also applicable in networks with parallel and replicated topologies, such as an NxOC-3/12/48 topology.
基于MPLS的方法在实践中通常用于处理并行链路，包括使用LSP带宽参数来控制穿过每个链路的需求比例，明确地为LSP隧道配置路由以将它们分布在并行链路上，以及使用亲和力将不同的LSP映射到不同的链路上。这些类型的解决方案也适用于具有并行和复制拓扑的网络，例如NxOC-3/12/48拓扑。
It is sometimes desirable to restrict certain types of traffic to certain types of links, or to explicitly exclude certain types of links in the paths for some types of traffic. This might be needed to accomplish some business policy or network engineering objectives. MPLS resource affinities provide a powerful mechanism to implement these types of objectives.
有时需要将某些类型的通信量限制为某些类型的链路，或者在某些类型的通信量的路径中明确排除某些类型的链路。这可能是实现某些业务策略或网络工程目标所必需的。MPLS资源亲缘关系为实现这些类型的目标提供了强大的机制。
As a concrete example, suppose a global service provider has a flat (non-hierarchical) IGP. MPLS TE affinities can be used to explicitly keep continental traffic (traffic originating and terminating within a continent) from traversing transoceanic resources.
作为一个具体的例子，假设一个全球服务提供商有一个平面（非层次）IGP。MPLS TE亲和力可用于明确防止大陆流量（源自大陆和终止于大陆的流量）穿越跨洋资源。
Another example of using MPLS TE affinities to exclude certain traffic from a subset of circuits might be to keep inter-regional LSPs off of circuits that are reserved for intra-regional traffic.
使用MPLS-TE亲和力从电路子集排除某些流量的另一个示例可能是使区域间lsp远离为区域内流量保留的电路。
Still another example is the situation in a heterogeneous network consisting of links with different capacities, e.g., OC-12, OC-48, and OC-192. In such networks, affinities can be used to force some types of traffic to only traverse links with a given capacity, e.g. OC-48.
还有另一个例子是由具有不同容量的链路（例如OC-12、OC-48和OC-192）组成的异构网络中的情况。在这样的网络中，亲和力可用于强制某些类型的通信量仅遍历具有给定容量的链路，例如OC-48。
After the occurrence of a network failure, it may be desirable to calculate a new set paths for LSPs to optimizes performance over the residual topology. This re-optimization is complementary to the fast-reroute operation used to reduce packet losses during routing transients under network restoration. Traffic protection can also be accomplished by associating a primary LSP with a set of secondary LSPs, hot-standby LSPs, or a combination thereof [11].
在发生网络故障之后，可能需要为lsp计算新的路径集，以优化剩余拓扑上的性能。这种重新优化是对快速重新路由操作的补充，该操作用于减少网络恢复下路由瞬态期间的数据包丢失。还可以通过将主LSP与一组辅助LSP、热备用LSP或其组合相关联来实现流量保护[11]。
When deploying TE solutions in a service provider environment, the impact of administrative policies and the selection of nodes that will serve as endpoints for LSP-tunnels should be carefully considered. As noted in [9], when devising a virtual topology for LSP-tunnels, special consideration should be given to the tradeoff between the operational complexity associated with a large number of LSP-tunnels and the control granularity that large numbers of LSP-tunnels allow. In other words, a large number of LSP-tunnels allow greater control over the distribution of traffic across the network, but increases network operational complexity. In large networks, it may be advisable to start with a simple LSP-tunnel virtual topology and then introduce additional complexity based on observed or anticipated traffic flow patterns [9].
在服务提供商环境中部署TE解决方案时，应仔细考虑管理策略的影响和将用作LSP隧道端点的节点的选择。如[9]所述，在设计LSP隧道的虚拟拓扑时，应特别考虑与大量LSP隧道相关的操作复杂性和大量LSP隧道允许的控制粒度之间的权衡。换句话说，大量LSP隧道允许对网络上的流量分布进行更大的控制，但增加了网络操作的复杂性。在大型网络中，建议从简单的LSP隧道虚拟拓扑开始，然后根据观察到的或预期的交通流模式引入额外的复杂性[9]。
Administrative policies should guide the amount of bandwidth to be allocated to an LSP. One may choose to set the bandwidth of a particular LSP to a statistic of the measured observed utilization over an interval of time, e.g., peak rate, or a particular percentile or quartile of the observed utilization. Sufficient over-subscription (of LSPs) or under-reporting bandwidth on the physical links should be used to account for flows that exceed their normal limits on an event-driven basis. Flows should be monitored for trends that indicate when the bandwidth parameter of an LSP should be resized. Flows should be monitored constantly to detect unusual variance from expected levels. If an unpoliced flow greatly exceeds its assigned bandwidth, action should be taken to determine the root cause and remedy the problem. Traffic policing is an option that may be applied to deal with congestion problems, especially when some flows exceed their bandwidth parameters and interfere with other compliant flows. However, it is usually more prudent to apply policing actions at the edge of the network rather than within the core, unless under exceptional circumstances.
管理策略应指导分配给LSP的带宽量。可以选择将特定LSP的带宽设置为在一段时间间隔内测量的观测利用率的统计，例如，峰值速率，或观测利用率的特定百分位或四分位。在事件驱动的基础上，应使用物理链路上足够的过度订阅（LSP）或报告带宽不足来解释超过其正常限制的流量。应监控流的趋势，以指示何时应调整LSP的带宽参数。应持续监控流量，以检测与预期水平的异常差异。如果未许可的流大大超过其分配的带宽，则应采取措施确定根本原因并解决问题。流量管理是一种可用于处理拥塞问题的选项，特别是当某些流超过其带宽参数并干扰其他兼容流时。然而，除非在特殊情况下，通常更谨慎的做法是在网络边缘而不是在核心内实施警务行动。
When creating LSPs, a hierarchical network approach may be used to alleviate scalability problems associated with flat full mesh virtual topologies. In general, operational experience has shown that very large flows (between city pairs) are long-lived and have stable characteristics, while smaller flows (edge to edge) are more dynamic and have more fluctuating statistical characteristics. A hierarchical architecture can be devised consisting of core and edge networks in which the core is traffic engineered and serves as an aggregation and transit infrastructure for edge traffic.
在创建LSP时，可以使用分层网络方法来缓解与平面全网格虚拟拓扑相关的可伸缩性问题。一般而言，运营经验表明，非常大的流量（城市对之间）是长期的，具有稳定的特征，而较小的流量（边到边）则更具动态性，具有更多波动的统计特征。可以设计由核心和边缘网络组成的分层体系结构，其中核心是流量工程，用作边缘流量的聚合和传输基础设施。
However, over-aggregation of flows can result in a stream so large that it precludes the constraint-based routing algorithm from finding a feasible path through a network. Splitting a flow by using two or more parallel LSPs and distributing the traffic across the LSPs can solve this problem, at the expense of introducing more state in the network.
然而，流的过度聚集会导致流太大，从而使基于约束的路由算法无法找到通过网络的可行路径。通过使用两个或多个并行LSP拆分流并在LSP之间分配流量可以解决此问题，但代价是在网络中引入更多状态。
Failure scenarios should also be addressed when splitting a stream of traffic over several links. It is of little value to establish a finely balanced set of flows over a set of links only to find that upon link failure the balance reacts poorly, or does not revert to the original situation upon restoration.
在多个链路上拆分流量流时，还应解决故障场景。在一组链路上建立一组精细平衡的流，结果发现链路故障时，平衡反应很差，或者在恢复时没有恢复到原始状态，这是没有什么价值的。
Networks planning to deploy MPLS for traffic engineering must consider network management aspects, particularly performance and fault management [12]. With the deployment of MPLS in any infrastructure, some additional operational tasks are required, such as constant monitoring to ensure that the performance of the network is not impacted in the end-to-end delivery of traffic. In addition, traffic characteristics, such as latency across an LSP, may also need to be assessed on a regular basis to ensure that service-level guarantees are achieved.
用于部署流量工程的MPLS的网络规划必须考虑网络管理方面，特别是性能和故障管理[12 ]。随着MPLS在任何基础设施中的部署，需要执行一些额外的操作任务，例如持续监控，以确保在端到端传输流量时不会影响网络性能。此外，还可能需要定期评估流量特性，例如LSP的延迟，以确保实现服务级别保证。
Obtaining information on LSP behavior is critical in determining the stability of an MPLS network. When LSPs transition or path changes occur, packets may be dropped which impacts network performance. It should be the goal of any network deploying MPLS to minimize the volatility of LSPs and reduce the root causes that induce this instability. Unfortunately, there are very few, if any, NMS systems that are available at this time with the capability to provide the correct level of management support, particularly root cause analysis. Consequently, most early adopters of MPLS develop their own management systems in-house for the MPLS domain. The lack of availability of commercial network management systems that deal specifically with MPLS-related aspects is a significant impediment to the large-scale deployment of MPLS networks.
获取有关LSP行为的信息对于确定MPLS网络的稳定性至关重要。当发生LSP转换或路径更改时，可能会丢弃数据包，从而影响网络性能。任何部署MPLS的网络都应该以最小化LSP的波动性和减少导致这种不稳定性的根本原因为目标。不幸的是，目前只有极少数（如果有的话）NMS系统能够提供正确级别的管理支持，特别是根本原因分析。因此，大多数早期采用MPLS的人在内部为MPLS领域开发自己的管理系统。缺乏专门处理MPLS相关方面的商业网络管理系统是大规模部署MPLS网络的一大障碍。
The performance of an MPLS network is also dependent on the configured values of bandwidth for each LSP. Since congestion is a common cause of performance degradation in operational networks, it is important to proactively avoid these situations. While MPLS was designed to minimize congestion on links by utilizing bandwidth reservations, it is still heavily reliant on user configurable data. If the LSP bandwidth value does not properly represent the traffic demand of that LSP, over-utilization may occur and cause significant congestion within the network. Therefore, it is important to develop, deploy, and maintain a good modeling tool for determining LSP bandwidth size. Lack of this capability may result in sub-optimal network performance.
MPLS网络的性能还取决于为每个LSP配置的带宽值。由于拥塞是运营网络中性能下降的常见原因，因此主动避免这些情况非常重要。虽然MPLS旨在通过利用带宽预留来最小化链路上的拥塞，但它仍然严重依赖于用户可配置的数据。如果LSP带宽值不能正确地表示该LSP的业务需求，则可能发生过度利用，并在网络内造成严重拥塞。因此，开发、部署和维护用于确定LSP带宽大小的良好建模工具非常重要。缺乏这一能力可能会导致次优网络性能。
Traffic engineering has a goal of ensuring traffic performance objectives for different services. This requires that the different network elements be dimensioned properly to handle the expected load. More specifically, in mapping given user demands onto network resources, network dimensioning involves the sizing of the network elements, such as links, processors, and buffers, so that performance objectives can be met at minimum cost. Major inputs to the dimensioning process are cost models, characterization of user demands and specification of performance objectives.
交通工程的目标是确保不同服务的交通性能目标。这要求不同的网络元件尺寸适当，以处理预期负载。更具体地说，在将给定的用户需求映射到网络资源时，网络尺寸确定涉及到网络元素（如链路、处理器和缓冲区）的尺寸确定，以便以最低成本实现性能目标。尺寸确定过程的主要输入是成本模型、用户需求表征和性能目标规范。
In using MPLS, dimensioning involves the assignment of resources such as bandwidth to a set of pre-selected LSPs for carrying traffic, and mapping the logical network of LSPs onto a physical network of links with capacity constraints. The dimensioning process also determines the link capacity parameters or thresholds associated with the use of some bandwidth reservation scheme for service protection. Service protection controls the QoS for certain service types by restricting access to bandwidth, or by giving priority access to one type of traffic over another. Such methods are essential, e.g., to prevent starvation of low-priority flows, to guarantee a minimum amount of resources for flows with expected short duration, to improve the acceptance probability for flows with high bandwidth requirements, or to maintain network stability by preventing performance degradation in case of a local overload.
在使用MPLS时，尺寸确定涉及将资源（如带宽）分配给一组预先选择的LSP以承载流量，并将LSP的逻辑网络映射到具有容量约束的链路的物理网络。尺寸确定过程还确定与使用某些带宽预留方案进行服务保护相关联的链路容量参数或阈值。服务保护通过限制对带宽的访问，或通过优先访问一种类型的流量而不是另一种类型的流量来控制特定服务类型的QoS。这些方法是必不可少的，例如，为了防止低优先级流的饥饿，为了保证具有预期短持续时间的流的最小资源量，为了提高具有高带宽要求的流的接受概率，或者通过防止在本地过载情况下的性能下降来维持网络稳定性。
Network measurement entails robust statistics collection and systems development. Knowing *what* to do with these measurements is often where the secret-sauce is. Examples for different applications of measurements are described in [13]. For instance, to ensure that the QoS objectives have been met, performance measurements and performance monitoring are required so that real-time traffic control
网络测量需要可靠的统计数据收集和系统开发。知道如何处理这些测量通常是秘密所在。[13]中描述了不同测量应用的示例。例如，为了确保满足QoS目标，需要进行性能测量和性能监控，以便实现实时流量控制
actions, or policy-based actions, can be taken. Also, to characterize the traffic demands, traffic measurements are used to estimate the offered loads from different service classes and to provide forecasting of future demands for capacity planning purposes. Forecasting and planning may result in capacity augmentation or may lead to the introduction of new technology and architecture.
可以采取行动或基于策略的行动。此外，为了描述交通需求，交通量测量用于估计不同服务等级的提供负荷，并为容量规划目的提供未来需求预测。预测和规划可能导致容量增加，或可能导致引入新技术和架构。
To avoid QoS degradation at the packet level, measurement-based admission control can be employed by using online measurements of actual usage. This is a form of preventive control to ensure that the QoS requirements of different service classes can be met simultaneously, while maintaining network efficiency at a high level. However, it requires proper network dimensioning to keep the probability for the refusal of connection/flow requests sufficiently low.
为了避免分组级别上的QoS降低，可以通过使用实际使用情况的在线测量来采用基于测量的接纳控制。这是一种预防性控制，以确保不同服务类别的QoS要求可以同时得到满足，同时将网络效率保持在较高水平。然而，它需要适当的网络尺寸，以保持连接/流量请求被拒绝的概率足够低。
Significant resources can be expended to gain a proper understanding of how MPLS works. Furthermore, significant engineering and testing resources may need to be invested to identify problems with vendor implementations of MPLS. Initial deployment of MPLS software and the configurations management aspects to support TE can consume significant engineering, operations, and system development resources. Developing automated systems to create router configurations for network elements can require significant software development and hardware resources. Getting to a point where configurations for routers are updated in an automated fashion can be a time consuming process. Tracking manual tweaks to router configurations, or problems associated with these can be an endless task. What this means is that much more is required in the form of various types of tools to simplify and automate the MPLS TE function.
可以花费大量资源来正确理解MPLS的工作原理。此外，可能需要投入大量的工程和测试资源，以确定MPLS供应商实施中的问题。最初部署MPLS软件和配置管理方面以支持TE可能会消耗大量工程、运营和系统开发资源。开发自动化系统为网络元件创建路由器配置可能需要大量的软件开发和硬件资源。达到路由器配置以自动化方式更新的程度可能是一个耗时的过程。跟踪路由器配置的手动调整，或与之相关的问题可能是一项无休止的任务。这意味着，要简化和自动化MPLS TE功能，还需要各种类型的工具。
Certain architectural choices can lead to operational, protocol, and router implementation scalability problems. This is especially true as the number of LSP-tunnels or router configuration data in a network increases, which can be exacerbated by designs incorporating full meshes, which create O(N^2) number of LSPs, where N is the number of network-edge nodes. In these cases, minimizing N through hierarchy, regionalization, or proper selection of tunnel termination points can affect the network's ability to scale. Loss of scale in this sense can be via protocol instability, inability to change network configurations to accommodate growth, inability for router implementations to be updated, hold or properly process configurations, or loss of ability to adequately manage the network.
某些架构选择可能导致操作、协议和路由器实现可伸缩性问题。当网络中的LSP隧道或路由器配置数据的数量增加时，情况尤其如此，这可能会因包含完整网格的设计而恶化，该设计创建O（N^2）个LSP，其中N是网络边缘节点的数量。在这些情况下，通过层次化、区域化或正确选择隧道端点来最小化N会影响网络的扩展能力。从这个意义上讲，规模的损失可能是由于协议不稳定、无法更改网络配置以适应增长、无法更新路由器实现、保持或正确处理配置，或者无法充分管理网络。
Although widely deployed, MPLS TE is a new technology when compared to the classic IP routing protocols such as IS-IS, OSPF, and BGP. MPLS TE also has more configuration and protocol options. As such, some implementations are not battle-hardened and automated testing of various configurations is difficult if not infeasible. Multi-vendor environments are beginning to appear, although additional effort is usually required to ensure full interoperability.
虽然MPLS-TE被广泛部署，但与is-is、OSPF和BGP等经典IP路由协议相比，它是一种新技术。MPLS TE还具有更多配置和协议选项。因此，一些实现不是经过战斗考验的，各种配置的自动化测试即使不是不可行的，也是困难的。多供应商环境开始出现，尽管通常需要额外的努力来确保完全的互操作性。
Common approaches to TE in service provider environments switch the forwarding paradigm from connectionless to connection oriented. Thus, operational analysis of the network may be complicated in some regards (and improved in others). Inconsistencies in forwarding state result in dropped packets whereas with connectionless methods the packet will either loop and drop, or be misdirected onto another branch in the routing tree.
服务提供商环境中TE的常见方法将转发范式从无连接切换到面向连接。因此，网络的操作分析在某些方面可能比较复杂（在其他方面则有所改进）。转发状态的不一致会导致数据包丢失，而使用无连接方法时，数据包将循环并丢失，或者错误地定向到路由树中的另一个分支上。
Currently deployed MPLS TE approaches can be adversely affected by both internal and external router and link failures. This can create a mismatch between the signaled capacity and the traffic an LSP-tunnel carries.
当前部署的MPLS TE方法可能会受到内部和外部路由器和链路故障的不利影响。这可能导致信号容量与LSP隧道承载的流量不匹配。
Many routers in service provider environments are already under stress processing the software workload associated with running IGP, BGP, and IPC. Enabling TE in an MPLS environment involves adding traffic engineering databases and processes, adding additional information to be carried by the routing processes, and adding signaling state and processing to these network elements. Additional traffic measurements may also need to be supported. In some environments, this additional load may not be feasible.
服务提供商环境中的许多路由器在处理与运行IGP、BGP和IPC相关的软件工作负载时已经处于压力之下。在MPLS环境中启用TE涉及添加流量工程数据库和进程，添加路由进程要承载的附加信息，以及向这些网元添加信令状态和处理。可能还需要支持其他交通测量。在某些环境中，此附加负载可能不可行。
MPLS in general and MPLS-TE in particular is not a panacea for lack of network capacity, or lack of proper capacity planning and provisioning in the network dimensioning process. MPLS-TE may cause network traffic to traverse greater distances or to take paths with more network elements, thereby incurring greater latency. Generally, this added inefficiency is done to prevent shortcomings in capacity planning or available resources path to avoid hot spots. The ability of TE to accommodate more traffic on a given topology can also be characterized as a short-term gain during periods of persistent traffic growth. These approaches cannot achieve impossible mappings of traffic onto topologies. Failure to properly capacity plan and execute will lead to congestion, no matter what technology aids are employed.
一般而言，MPLS，特别是MPLS-TE，并不是解决网络容量不足或在网络规模确定过程中缺乏适当容量规划和供应的灵丹妙药。MPLS-TE可能会导致网络流量穿越更长的距离，或采用具有更多网络元素的路径，从而导致更大的延迟。一般来说，这样做是为了防止在容量规划或可用资源路径方面存在缺陷，从而避免热点。TE在给定拓扑上容纳更多流量的能力也可以被描述为在持续流量增长期间的短期增益。这些方法无法实现不可能的流量到拓扑的映射。无论采用何种技术辅助，如果不能正确规划和执行容量，都将导致拥堵。
The applicability of traffic engineering in Internet service provider environments has been discussed in this document. The focus has been on the use of MPLS-based approaches to achieve traffic engineering in this context. The applicability of traffic engineering and associated management and deployment considerations have been described, and the limitations highlighted.
本文讨论了流量工程在Internet服务提供商环境中的适用性。在这种情况下，重点是使用基于MPLS的方法来实现流量工程。已经描述了流量工程的适用性以及相关的管理和部署注意事项，并强调了局限性。
MPLS combines the ability to monitor point-to-point traffic statistics between two routers and the capability to control the forwarding paths of subsets of traffic through a given network topology. This makes traffic engineering with MPLS applicable and useful for improving network performance by effectively mapping traffic flows onto links within service provider networks. Tools that simplify and automate the MPLS TE functions and activation help to realize the full potential.
MPLS结合了监视两个路由器之间的点到点流量统计信息的能力和通过给定网络拓扑控制流量子集的转发路径的能力。这使得使用MPLS的流量工程变得适用，并且有助于通过有效地将流量映射到服务提供商网络内的链路来提高网络性能。简化和自动化MPLS TE功能和激活的工具有助于实现全部潜力。
This document does not introduce new security issues. When deployed in service provider networks, it is mandatory to ensure that only authorized entities are permitted to initiate establishment of LSP-tunnels.
本文档不会引入新的安全问题。在服务提供商网络中部署时，必须确保仅允许授权实体启动LSP隧道的建立。
1 Rosen, E., Viswanathan, A. and R. Callon, "Multiprotocol Label Switching Architecture," RFC 3031, January 2001.
1 Rosen，E.，Viswanathan，A.和R.Callon，“多协议标签交换体系结构”，RFC 30312001年1月。
2 Awduche, D., Malcolm, J., Agogbua, J., O'Dell, M. and J. McManus, "Requirements for Traffic Engineering Over MPLS," RFC 2702, September 1999.
2 Awduche，D.，Malcolm，J.，Agogbua，J.，O'Dell，M.和J.McManus，“MPLS上的流量工程要求”，RFC 2702，1999年9月。
3 X. Xiao, A. Hannan, B. Bailey, and L. Ni, "Traffic Engineering with MPLS in the Internet," IEEE Network, March/April 2000.
3 X.Xiao，A.Hannan，B.Bailey和L.Ni，“互联网中使用MPLS的流量工程”，IEEE网络，2000年3月/4月。
4 V. Springer, C. Pierantozzi, and J. Boyle, "Level3 MPLS Protocol Architecture," Work in Progress.
4 V.Springer、C.Pierantozzi和J.Boyle，“三级MPLS协议架构”，正在进行中。
5 T. Li, and H. Smit, "IS-IS Extensions for Traffic Engineering," Work in Progress.
5 T.Li和H.Smit，“交通工程的IS-IS扩展”，正在进行中。
6 D. Katz, D. Yeung, and K. Kompella, "Traffic Engineering Extensions to OSPF," Work in Progress.
6 D.Katz、D.Yaung和K.Kompella，“OSPF的交通工程扩展”，正在进行中。
7 Awduche, D., Berger, L., Gan, D.H., Li, T., Srinivasan, V. and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP Tunnels," RFC 3209, December 2001.
7 Awduche，D.，Berger，L.，Gan，D.H.，Li，T.，Srinivasan，V.和G.Swallow，“RSVP-TE：LSP隧道RSVP的扩展”，RFC 3209，2001年12月。
8 Jamoussi, B. (Editor), "Constraint-Based LSP Setup using LDP," RFC 3212, January 2002.
8 Jamoussi，B.（编辑），“使用LDP的基于约束的LSP设置”，RFC 3212，2002年1月。
9 Awduche, D., Hannan, A. and X. Xiao, "Applicability Statement for Extensions to RSVP for LSP-Tunnels," RFC 3210, December 2001.
9 Awduche，D.，Hannan，A.和X.Xiao，“LSP隧道RSVP扩展的适用性声明”，RFC 3210，2001年12月。
10 Awduche, D., Chiu, A., Elwalid, A., Widjaja, I. and X. Xiao, "Overview and Principles of Internet Traffic Engineering", RFC 3272, May 2002.
10 Awduche，D.，Chiu，A.，Elwalid，A.，Widjaja，I.和X.Xiao，“互联网流量工程概述和原则”，RFC 3272，2002年5月。
11 W.S. Lai, D. McDysan, J. Boyle, M. Carlzon, R. Coltun, T. Griffin, E. Kern, and T. Reddington, "Network Hierarchy and Multilayer Survivability," Work in Progress.
11 W.S.Lai，D.McDysan，J.Boyle，M.Carlzon，R.Coltun，T.Griffin，E.Kern和T.Reddington，“网络层次结构和多层生存性”，正在进行中。
12 D. Awduche, "MPLS and Traffic Engineering in IP Networks," IEEE Communications Magazine, December 1999.
12 D.Awduche，“IP网络中的MPLS和流量工程”，IEEE通信杂志，1999年12月。
13 W.S. Lai, B. Christian, R.W. Tibbs, and S. Van den Berghe, "A Framework for Internet Traffic Engineering Measurement," Work in Progress.
13 W.S.Lai，B.Christian，R.W.Tibbs和S.Van den Berghe，“互联网流量工程测量框架”，正在进行中。
The effectiveness of the MPLS protocols for traffic engineering in service provider networks is in large part due to the experience gained and foresight given by network engineers and developers familiar with traffic engineering with ATM in these environments. In particular, the authors wish to acknowledge the authors of RFC 2702 for the clear articulation of the requirements, as well as the developers and testers of code in deployment today for keeping their focus.
MPLS协议在服务提供商网络中用于流量工程的有效性在很大程度上归功于熟悉这些环境中ATM流量工程的网络工程师和开发人员所获得的经验和远见。特别是，作者希望感谢RFC 2702的作者清楚地表达了需求，以及今天部署中的代码开发人员和测试人员保持关注。
Jim Boyle Protocol Driven Networks Tel: +1 919-852-5160 EMail: jboyle@pdnets.com
Jim Boyle协议驱动网络电话：+1 919-852-5160电子邮件：jboyle@pdnets.com
Vijay Gill AOL Time Warner, Inc. 12100 Sunrise Valley Drive Reston, VA 20191 EMail: vijay@umbc.edu
Vijay Gill AOL时代华纳公司，地址：弗吉尼亚州莱斯顿日出谷大道12100号，邮编：20191电子邮件：vijay@umbc.edu
Alan Hannan RoutingLoop Intergalactic 112 Falkirk Court Sunnyvale, CA 94087, USA Tel: +1 408-666-2326 EMail: alan@routingloop.com
Alan Hannan RoutingLoop银河系间112美国加利福尼亚州桑尼维尔市法尔柯克法院94087电话：+1 408-666-2326电子邮件：alan@routingloop.com
Dave Cooper Global Crossing 960 Hamlin Court Sunnyvale, CA 94089, USA Tel: +1 916-415-0437 EMail: dcooper@gblx.net
Dave Cooper Global Crossing 960 Hamlin Court Sunnyvale，CA 94089，美国电话：+1 916-415-0437电子邮件：dcooper@gblx.net
Daniel O. Awduche Movaz Networks 7926 Jones Branch Drive, Suite 615 McLean, VA 22102, USA Tel: +1 703-298-5291 EMail: awduche@movaz.com
Daniel O.Awduche Movaz Networks 7926美国弗吉尼亚州麦克莱恩615号套房邮编22102电话：+1 703-298-5291电子邮件：awduche@movaz.com
Blaine Christian Worldcom 22001 Loudoun County Parkway, Room D1-2-737 Ashburn, VA 20147, USA Tel: +1 703-886-4425 EMail: blaine@uu.net
Blaine Christian Worldcom 22001 Loudoun County Parkway，D1-2-737室，弗吉尼亚州阿什本，邮编20147，美国电话：+1 703-886-4425电子邮件：blaine@uu.net
Wai Sum Lai AT&T 200 Laurel Avenue Middletown, NJ 07748, USA Tel: +1 732-420-3712 EMail: wlai@att.com
美国新泽西州米德尔顿劳雷尔大道200号惠森莱电话电报公司电话：+1732-420-3712电子邮件：wlai@att.com
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Acknowledgement
确认
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