Network Working Group S. Yasukawa
Request for Comments: 5439 NTT
Category: Informational A. Farrel
Old Dog Consulting
O. Komolafe
Cisco Systems
February 2009
Network Working Group S. Yasukawa
Request for Comments: 5439 NTT
Category: Informational A. Farrel
Old Dog Consulting
O. Komolafe
Cisco Systems
February 2009
An Analysis of Scaling Issues in MPLS-TE Core Networks
MPLS-TE核心网的扩展问题分析
Status of This Memo
关于下段备忘
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。
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版权公告
Copyright (c) 2009 IETF Trust and the persons identified as the document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/ license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document.
本文件受BCP 78和IETF信托有关IETF文件的法律规定的约束(http://trustee.ietf.org/ 许可证信息）在本文件发布之日生效。请仔细阅读这些文件，因为它们描述了您对本文件的权利和限制。
Abstract
摘要
Traffic engineered Multiprotocol Label Switching (MPLS-TE) is deployed in providers' core networks. As providers plan to grow these networks, they need to understand whether existing protocols and implementations can support the network sizes that they are planning.
流量工程多协议标签交换（MPLS-TE）部署在提供商的核心网络中。当提供商计划发展这些网络时，他们需要了解现有协议和实现是否能够支持他们计划的网络规模。
This document presents an analysis of some of the scaling concerns for the number of Label Switching Paths (LSPs) in MPLS-TE core networks, and examines the value of two techniques (LSP hierarchies and multipoint-to-point LSPs) for improving scaling. The intention is to motivate the development of appropriate deployment techniques and protocol extensions to enable the application of MPLS-TE in large networks.
本文分析了MPLS-TE核心网络中标签交换路径（LSP）数量的一些扩展问题，并探讨了两种技术（LSP层次结构和多点对点LSP）在改进扩展方面的价值。其目的是促进适当部署技术和协议扩展的开发，以便在大型网络中应用MPLS-TE。
This document only considers the question of achieving scalability for the support of point-to-point MPLS-TE LSPs. Point-to-multipoint MPLS-TE LSPs are for future study.
本文档仅考虑实现点对点MPLS-TE LSP支持的可伸缩性问题。点对多点MPLS-TE LSP有待进一步研究。
Table of Contents
目录
1. Introduction ....................................................3
1.1. Overview ...................................................3
1.2. Glossary of Notation .......................................5
2. Issues of Concern for Scaling ...................................5
2.1. LSP State ..................................................5
2.2. Processing Overhead ........................................6
2.3. RSVP-TE Implications .......................................6
2.4. Management .................................................7
3. Network Topologies ..............................................8
3.1. The Snowflake Network Topology .............................9
3.2. The Ladder Network Topology ...............................11
3.3. Commercial Drivers for Selected Configurations ............14
3.4. Other Network Topologies ..................................15
4. Required Network Sizes .........................................16
4.1. Practical Numbers .........................................16
5. Scaling in Flat Networks .......................................16
5.1. Snowflake Networks ........................................17
5.2. Ladder Networks ...........................................18
6. Scaling Snowflake Networks with Forwarding Adjacencies .........22
6.1. Two-Layer Hierarchy .......................................22
6.1.1. Tuning the Network Topology to Suit the
Two-Layer Hierarchy ................................23
6.2. Alternative Two-Layer Hierarchy ...........................24
6.3. Three-Layer Hierarchy .....................................25
6.4. Issues with Hierarchical LSPs .............................26
7. Scaling Ladder Networks with Forwarding Adjacencies ............27
7.1. Two-Layer Hierarchy .......................................27
7.2. Three-Layer Hierarchy .....................................28
7.3. Issues with Hierarchical LSPs .............................29
8. Scaling Improvements through Multipoint-to-Point LSPs ..........30
8.1. Overview of MP2P LSPs .....................................30
8.2. LSP State: A Better Measure of Scalability ................31
8.3. Scaling Improvements for Snowflake Networks ...............32
8.3.1. Comparison with Other Scenarios ....................33
8.4. Scaling Improvements for Ladder Networks ..................34
8.4.1. Comparison with Other Scenarios ....................36
8.4.2. LSP State Compared with LSP Numbers ................37
8.5. Issues with MP2P LSPs .....................................37
9. Combined Models ................................................39
10. An Alternate Solution .........................................39
10.1. Pros and Cons of the Alternate Solution ..................40
11. Management Considerations .....................................42
12. Security Considerations .......................................42
13. Recommendations ...............................................42
1. Introduction ....................................................3
1.1. Overview ...................................................3
1.2. Glossary of Notation .......................................5
2. Issues of Concern for Scaling ...................................5
2.1. LSP State ..................................................5
2.2. Processing Overhead ........................................6
2.3. RSVP-TE Implications .......................................6
2.4. Management .................................................7
3. Network Topologies ..............................................8
3.1. The Snowflake Network Topology .............................9
3.2. The Ladder Network Topology ...............................11
3.3. Commercial Drivers for Selected Configurations ............14
3.4. Other Network Topologies ..................................15
4. Required Network Sizes .........................................16
4.1. Practical Numbers .........................................16
5. Scaling in Flat Networks .......................................16
5.1. Snowflake Networks ........................................17
5.2. Ladder Networks ...........................................18
6. Scaling Snowflake Networks with Forwarding Adjacencies .........22
6.1. Two-Layer Hierarchy .......................................22
6.1.1. Tuning the Network Topology to Suit the
Two-Layer Hierarchy ................................23
6.2. Alternative Two-Layer Hierarchy ...........................24
6.3. Three-Layer Hierarchy .....................................25
6.4. Issues with Hierarchical LSPs .............................26
7. Scaling Ladder Networks with Forwarding Adjacencies ............27
7.1. Two-Layer Hierarchy .......................................27
7.2. Three-Layer Hierarchy .....................................28
7.3. Issues with Hierarchical LSPs .............................29
8. Scaling Improvements through Multipoint-to-Point LSPs ..........30
8.1. Overview of MP2P LSPs .....................................30
8.2. LSP State: A Better Measure of Scalability ................31
8.3. Scaling Improvements for Snowflake Networks ...............32
8.3.1. Comparison with Other Scenarios ....................33
8.4. Scaling Improvements for Ladder Networks ..................34
8.4.1. Comparison with Other Scenarios ....................36
8.4.2. LSP State Compared with LSP Numbers ................37
8.5. Issues with MP2P LSPs .....................................37
9. Combined Models ................................................39
10. An Alternate Solution .........................................39
10.1. Pros and Cons of the Alternate Solution ..................40
11. Management Considerations .....................................42
12. Security Considerations .......................................42
13. Recommendations ...............................................42
14. Acknowledgements ..............................................43
15. Normative References ..........................................43
16. Informative References ........................................43
14. Acknowledgements ..............................................43
15. Normative References ..........................................43
16. Informative References ........................................43
Network operators and service providers are examining scaling issues as they look to deploy ever-larger traffic engineered Multiprotocol Label Switching (MPLS-TE) networks. Concerns have been raised about the number of Label Switched Paths (LSPs) that need to be supported at the edge and at the core of the network. The impact on control plane and management plane resources threatens to outweigh the benefits and popularity of MPLS-TE, while the physical limitations of the routers may constrain the deployment options.
网络运营商和服务提供商正在研究扩展问题，因为他们希望部署更大的流量工程多协议标签交换（MPLS-TE）网络。人们对网络边缘和核心需要支持的标签交换路径（LSP）的数量提出了担忧。对控制平面和管理平面资源的影响可能超过MPLS-TE的好处和普及程度，而路由器的物理限制可能会限制部署选项。
Historically, it has been assumed that all MPLS-TE scaling issues can be addressed using hierarchical LSP [RFC4206]. However, analysis shows that the improvement gained by LSP hierarchies is not as significant in all topologies and at all points in the network as might have been presumed. Further, additional management issues are introduced to determine the end-points of the hierarchical LSPs and to operate them. Although this does not invalidate the benefits of LSP hierarchies, it does indicate that additional techniques may be desirable in order to fully scale MPLS-TE networks.
历史上，假设所有MPLS-TE扩展问题都可以使用分层LSP[RFC4206]解决。然而，分析表明，LSP层次结构所获得的改进在网络中的所有拓扑和所有点上都不如预期的那样显著。此外，还引入了其他管理问题，以确定分层LSP的端点并对其进行操作。尽管这不会使LSP层次结构的优点无效，但它确实表明，为了完全扩展MPLS-TE网络，可能需要其他技术。
This document examines the scaling properties of two generic MPLS-TE network topologies and investigates the benefits of two scaling techniques.
本文研究了两种通用MPLS-TE网络拓扑的扩展特性，并研究了两种扩展技术的优点。
Physical topology scaling concerns are addressed by building networks that are not fully meshed. Network topologies tend to be meshed in the core but tree-shaped at the edges, giving rise to a snowflake design. Alternatively, the core may be more of a ladder shape with tree-shaped edges.
通过构建未完全网格化的网络来解决物理拓扑缩放问题。网络拓扑趋向于在核心处网状，但在边缘处呈树状，从而形成雪花状设计。或者，核心可以是更具树状边缘的梯形。
MPLS-TE, however, establishes a logical full mesh between all edge points in the network, and this is where the scaling problems arise since the structure of the network tends to focus a large number of LSPs within the core of the network.
然而，MPLS-TE在网络中的所有边缘点之间建立了一个逻辑全网格，这就是出现缩放问题的地方，因为网络结构往往将大量LSP集中在网络核心内。
This document presents two generic network topologies (the snowflake and the ladder) and attempts to parameterize the networks by making some generalities. It introduces terminology for the different scaling parameters and examines how many LSPs might be required to be carried within the core of a network.
本文档介绍了两种通用的网络拓扑（雪花和阶梯），并试图通过一些概括来对网络进行参数化。它介绍了不同缩放参数的术语，并检查了网络核心内可能需要携带多少LSP。
Two techniques (hierarchical LSPs and multipoint-to-point LSPs) are introduced and an examination is made of the scaling benefits that they offer as well as of some of the concerns with using these techniques.
介绍了两种技术（分层LSP和多点对点LSP），并对它们提供的扩展优势以及使用这些技术的一些问题进行了检查。
Of necessity, this document makes many generalizations. Not least among these is a set of assumptions about the symmetry and connectivity of the physical network. It is hoped that these generalizations will not impinge on the usefulness of the overview of the scaling properties that this document attempts to give. Indeed, the symmetry of the example topologies tends to highlight the scaling issues of the different solution models, and this may be useful in exposing the worst case scenarios.
当然，本文件作了许多概括。其中最重要的是关于物理网络的对称性和连通性的一组假设。希望这些概括不会影响本文件试图给出的标度特性概述的有用性。事实上，示例拓扑的对称性倾向于突出不同解决方案模型的缩放问题，这可能有助于揭示最坏情况。
Although protection mechanisms like Fast Reroute (FRR) [RFC4090] are briefly discussed, the main body of this document considers stable network cases. It should be noted that make-before-break re-optimisation after link failure may result in a significant number of 'duplicate' LSPs. This issue is not addressed in this document.
虽然对快速重路由（FRR）[RFC4090]等保护机制进行了简要讨论，但本文的主体部分考虑了稳定的网络情况。应注意的是，链路故障后的先通后断重新优化可能会导致大量“重复”LSP。本文件未涉及这一问题。
It should also be understood that certain deployment models where separate traffic engineered LSPs are used to provide different services (such as layer 3 Virtual Private Networks (VPNs) [RFC4110] or pseudowires [RFC3985]) or different classes of service [RFC3270] may result in 'duplicate' or 'parallel' LSPs running between any pair of provider edge nodes (PEs). This scaling factor is also not considered in this document, but may be easily applied as a linear factor by the reader.
还应了解，某些部署模型使用单独的流量工程LSP来提供不同的服务（例如第3层虚拟专用网络（VPN）[RFC4110]或伪线[RFC3985]）或不同类别的服务[RFC3270]可能导致在任何一对提供程序边缘节点（PE）之间运行“重复”或“并行”LSP。本文件中也未考虑该比例因子，但读者可将其作为线性因子轻松应用。
The operation of security mechanisms in MPLS-TE networks [MPLS-SEC] may have an impact on the ability of the network to scale. For example, they may increase both the size and number of control plane messages. Additionally, they may increase the processing overhead as control plane messages are subject to processing algorithms (such as encryption), and security keys need to be managed. Deployers will need to consider the trade-offs between scaling objectives and security objectives in their networks, and should resist the temptation to respond to a degradation of scaling performance by turning off security techniques that have previously been deemed as necessary. Further analysis of the effects of security measures on scalability are not considered further in this document.
MPLS-TE网络[MPLS-SEC]中安全机制的运行可能会影响网络的扩展能力。例如，它们可能会增加控制平面消息的大小和数量。此外，由于控制平面消息受制于处理算法（如加密），并且需要管理安全密钥，因此它们可能会增加处理开销。部署人员将需要考虑它们的网络中的缩放目标和安全目标之间的权衡，并且应该抵制通过关闭先前被视为必要的安全技术来响应缩放性能下降的诱惑。本文档不再进一步分析安全措施对可伸缩性的影响。
This document is designed to help service providers discover whether existing protocols and implementations can support the network sizes that they are planning. To do this, it presents an analysis of some of the scaling concerns for MPLS-TE core networks and examines the
本文档旨在帮助服务提供商发现现有协议和实现是否能够支持他们正在规划的网络规模。为此，本文分析了MPLS-TE核心网络的一些扩展问题，并分析了
value of two techniques for improving scaling. This should motivate the development of appropriate deployment techniques and protocol extensions to enable the application of MPLS-TE in large networks.
两种技术对改善缩放效果的价值。这将促使开发适当的部署技术和协议扩展，以便在大型网络中应用MPLS-TE。
This document only considers the question of achieving scalability for the support of point-to-point MPLS-TE LSPs. Point-to-multipoint MPLS-TE LSPs are for future study.
本文档仅考虑实现点对点MPLS-TE LSP支持的可伸缩性问题。点对多点MPLS-TE LSP有待进一步研究。
This document applies consistent notation to define various parameters of the networks that are analyzed. These terms are defined as they are introduced throughout the document, but are grouped together here for quick reference. Refer to the full definitions in the text for detailed explanations.
本文件采用一致性符号来定义所分析网络的各种参数。这些术语的定义贯穿于整个文档，但此处将它们组合在一起以供快速参考。有关详细说明，请参阅本文中的完整定义。
n A network level. n = 1 is the core of the network. See Section 3 for more details on the definition of a level. P(n) A node at level n in the network. S(n) The number of nodes at level n. That is, the number of P(n) nodes. L(n) The number of LSPs seen by a P(n) node. X(n) The number of LSP segment states held by a P(n) node. M(n) The number of P(n+1) nodes subtended to a P(n) node. R The number of rungs in a ladder network. E The number of edge nodes (PEs) subtended below (directly or indirectly) a spar-node in a ladder network. K The cost-effectiveness of the network expressed in terms of the ratio of the number of PEs to the number of network nodes.
n网络级别。n=1是网络的核心。有关标高定义的更多详细信息，请参见第3节。P（n）网络中n级的节点。S（n）级别n上的节点数。即P（n）个节点的数量。L（n）P（n）节点看到的LSP数。X（n）由P（n）节点保持的LSP段状态数。M（n）P（n+1）个节点的子节点数。R阶梯网络中的梯级数。E梯形网络中spar节点下方（直接或间接）子节点的边缘节点（PE）数量。K网络的成本效益，表示为PEs数量与网络节点数量的比率。
This section presents some of the issues associated with the support of LSPs at a Label Switching Router (LSR) or within the network. These issues may mean that there is a limit to the number of LSPs that can be supported.
本节介绍与标签交换路由器（LSR）或网络内的LSP支持相关的一些问题。这些问题可能意味着可以支持的LSP数量有限。
LSP state is the data (information) that must be stored at an LSR in order to maintain an LSP. Here, we refer to the information that is necessary to maintain forwarding plane state and the additional information required when LSPs are established through control plane protocols. While the size of the LSP state is implementation-dependent, it is clear that any implementation will require some data in order to maintain LSP state.
LSP状态是为了维护LSP而必须存储在LSR中的数据（信息）。这里，我们指的是维持转发平面状态所需的信息，以及通过控制平面协议建立LSP时所需的附加信息。虽然LSP状态的大小取决于实现，但很明显，任何实现都需要一些数据来维护LSP状态。
Thus, LSP state becomes a scaling concern because as the number of LSPs at an LSR increases, so the amount of memory required to maintain the LSPs increases in direct proportion. Since the memory capacity of an LSR is limited, there is a related limit placed on the number LSPs that can be supported.
因此，LSP状态成为缩放关注点，因为随着LSR处LSP的数量增加，维持LSP所需的内存量成正比地增加。由于LSR的内存容量是有限的，因此对可支持的LSP数量有相关限制。
Note that techniques to reduce the memory requirements (such as data compression) may serve to increase the number of LSPs that can be supported, but this will only achieve a moderate multiplier and may significantly decrease the ability to process the state rapidly.
注意，减少内存需求的技术（例如数据压缩）可能会增加可支持的LSP的数量，但这只能实现适度的乘数，并且可能会显著降低快速处理状态的能力。
In this document, we define X(n) as "the number of LSP segment states held by a P(n) node." This definition observes that an LSR at the end of an LSP only has to maintain state in one direction (i.e., into the network), while a transit LSR must maintain state in both directions (i.e., toward both ends of the LSP). Furthermore, in multipoint-to-point (MP2P) LSPs (see Section 8), a transit LSR may need to maintain LSP state for one downstream segment (toward the destination) and multiple upstream segments (from multiple sources). That is, we define LSP segment state as the state necessary to maintain an LSP in one direction to one adjacent node.
在本文档中，我们将X（n）定义为“一个P（n）节点所持有的LSP段状态数”。该定义指出，LSP末端的LSR只需在一个方向（即进入网络）上保持状态，而中转LSR必须在两个方向（即朝向LSP的两端）上保持状态。此外，在多点对点（MP2P）LSP（见第8节）中，公交LSR可能需要为一个下游段（朝向目的地）和多个上游段（来自多个来源）保持LSP状态。也就是说，我们将LSP段状态定义为在一个方向上保持到一个相邻节点的LSP所需的状态。
Depending largely on implementation issues, the number of LSPs passing through an LSR may impact the processing speed for each LSP. For example, control block search times can increase with the number of control blocks to be searched, and even excellent implementations cannot completely mitigate this fact. Thus, since CPU power is constrained in any LSR, there may be a practical limit to the number of LSPs that can be supported.
通过LSR的LSP数量可能会影响每个LSP的处理速度，这在很大程度上取决于实现问题。例如，控制块搜索时间会随着要搜索的控制块数量的增加而增加，即使是优秀的实现也无法完全缓解这一事实。因此，由于CPU功率在任何LSR中都受到限制，因此可以支持的LSP的数量可能存在实际限制。
Further processing overhead considerations depend on issues specific to the control plane protocols, and are discussed in the next section.
进一步的处理开销考虑取决于特定于控制平面协议的问题，将在下一节中讨论。
Like many connection-oriented signaling protocols, RSVP-TE (Resource Reservation Protocol - Traffic Engineering) requires that state is held within the network in order to maintain LSPs. The impact of this is described in Section 2.1. Note that RSVP-TE requires that separate information is maintained for upstream and downstream relationships, but does not require any specific implementation of that state.
与许多面向连接的信令协议一样，RSVP-TE（资源预留协议-流量工程）要求在网络中保持状态以维护LSP。第2.1节描述了这一影响。请注意，RSVP-TE要求为上游和下游关系维护单独的信息，但不要求该状态的任何具体实现。
RSVP-TE is a soft-state protocol, which means that protocol messages (refresh messages) must be regularly exchanged between signaling neighbors in order to maintain the state for each LSP that runs between the neighbors. A common period for the transmission (and receipt) of refresh messages is 30 seconds, meaning that each LSR must send and receive one message in each direction (upstream and downstream) every 30 seconds for every LSP it supports. This has the potential to be a significant constraint on the scaling of the network, but various improvements [RFC2961] mean that this refresh processing can be significantly reduced, allowing an implementation to be optimized to remove nearly all concerns about soft-state scaling in a stable network.
RSVP-TE是一种软状态协议，这意味着协议消息（刷新消息）必须在信令邻居之间定期交换，以保持邻居之间运行的每个LSP的状态。刷新消息的传输（和接收）的公共周期为30秒，这意味着对于每个支持的LSP，每个LSR必须每30秒在每个方向（上游和下游）发送和接收一条消息。这有可能成为网络扩展的一个重要约束，但各种改进[RFC2961]意味着可以显著减少此刷新处理，从而允许优化实现，以消除稳定网络中几乎所有关于软状态扩展的担忧。
Observations of existing implementations indicate that there may be a threshold of around 50,000 LSPs above which an LSR struggles to achieve sufficient processing to maintain LSP state. Although refresh reduction [RFC2961] may substantially improve this situation, it has also been observed that under these circumstances the size of the Srefresh may become very large, and the processing required may still cause significant disruption to an LSR.
对现有实现的观察表明，可能存在约50000个LSP的阈值，超过该阈值，LSR将难以实现足够的处理以维持LSP状态。尽管刷新减少[RFC2961]可能会显著改善这种情况，但还观察到，在这些情况下，Srefresh的大小可能会变得非常大，并且所需的处理仍然可能对LSR造成重大中断。
Another approach is to increase the refresh time. There is a correlation between the percentage increase in refresh time and the improvement in performance for the LSR. However, it should be noted that RSVP-TE's soft-state nature depends on regular refresh messages; thus, a degree of functionality is lost by increasing the refresh time. This loss may be partially mitigated by the use of the RSVP-TE Hello message, and can also be reduced by the use of various GMPLS extensions [RFC3473], such as the use of [RFC2961] message acknowledgements on all messages.
另一种方法是增加刷新时间。刷新时间的百分比增加与LSR性能的改善之间存在相关性。然而，应该注意的是，RSVP-TE的软状态性质取决于定期刷新消息；因此，增加刷新时间会丢失一定程度的功能。这种丢失可以通过使用RSVP-TE Hello消息来部分缓解，也可以通过使用各种GMPLS扩展[RFC3473]来减少，例如在所有消息上使用[RFC2961]消息确认。
RSVP-TE also requires that signaling adjacencies be maintained through the use of Hello message exchanges. Although [RFC3209] suggests that Hello messages should be retransmitted every 5 ms, in practice, values of around 3 seconds are more common. Nevertheless, the support of Hello messages can represent a scaling limitation on an RSVP-TE implementation since one message must be sent and received to/from each signaling adjacency every time period. This can impose limits on the number of neighbors (physical or logical) that an LSR supports, but does not impact the number of LSPs that the LSR can handle.
RSVP-TE还要求通过使用Hello消息交换来保持信令邻接。尽管[RFC3209]建议Hello消息应每5毫秒重新传输一次，但实际上，大约3秒的值更为常见。然而，对Hello消息的支持可以表示RSVP-TE实现上的缩放限制，因为每个时间段必须向每个信令邻接发送和接收一条消息。这可以限制LSR支持的邻居（物理或逻辑）数量，但不会影响LSR可以处理的LSP数量。
Another practical concern for the scalability of large MPLS-TE networks is the ability to manage the network. This may be constrained by the available tools, the practicality of managing large numbers of LSPs, and the management protocols in use.
大型MPLS-TE网络可扩展性的另一个实际问题是管理网络的能力。这可能受到可用工具、管理大量LSP的实用性以及使用的管理协议的限制。
Management tools are software implementations. Although such implementations should not constrain the control plane protocols, it is realistic to appreciate that network deployments will be limited by the scalability of the available tools. In practice, most existing tools have a limit to the number of LSPs that they can support. While a Network Management System (NMS) may be able to support a large number of LSPs, the number that can be supported by an Element Management System (EMS) (or the number supported by an NMS per-LSR) is more likely to be limited.
管理工具是软件实现。尽管这样的实现不应限制控制平面协议，但可以理解的是，网络部署将受到可用工具可伸缩性的限制。实际上，大多数现有工具都限制了它们可以支持的LSP数量。虽然网络管理系统（NMS）可能能够支持大量LSP，但元素管理系统（EMS）可以支持的数量（或每个LSR由NMS支持的数量）更有可能受到限制。
Similarly, practical constraints may be imposed by the operation of management protocols. For example, an LSR may be swamped by management protocol requests to read information about the LSPs that it supports, and this might impact its ability to sustain those LSPs in the control plane. OAM (Operations, Administration, and Management), alarms, and notifications can further add to the burden placed on an LSR and limit the number of LSPs it can support.
类似地，管理协议的操作可能会施加实际约束。例如，LSR可能会被管理协议请求淹没，以读取其支持的LSP的信息，这可能会影响其在控制平面中维持这些LSP的能力。OAM（操作、管理和管理）、警报和通知会进一步增加LSR的负担，并限制其支持的LSP数量。
All of these considerations encourage a reduction in the number of LSPs supported within the network and at any particular LSR.
所有这些考虑因素都鼓励减少网络内和任何特定LSR支持的LSP数量。
In order to provide some generic analysis of the potential scaling issues for MPLS-TE networks, this document explores two network topology models. These topologies are selected partly because of their symmetry, which makes them more tractable to a formulaic approach, and partly because they represent generalizations of real deployment models. Section 3.3 provides a discussion of the commercial drivers for deployed topologies and gives more analysis of why it is reasonable to consider these two topologies.
为了对MPLS-TE网络的潜在扩展问题提供一些一般性分析，本文探讨了两种网络拓扑模型。选择这些拓扑部分是因为它们的对称性，这使它们更易于采用公式化方法，部分是因为它们代表了实际部署模型的概括。第3.3节提供了对部署拓扑的商业驱动的讨论，并给出了为什么合理地考虑这两种拓扑的更多的分析。
The first topology is the snowflake model. In this type of network, only the very core of the network is meshed. The edges of the network are formed as trees rooted in the core.
第一种拓扑是雪花模型。在这种类型的网络中，只有网络的核心是网状的。网络的边缘被形成为植根于核心的树。
The second network topology considered is the ladder model. In this type of network, the core of the network is shaped and meshed in the form of a ladder and trees are attached rooted to the edge of the ladder.
考虑的第二种网络拓扑是梯形模型。在这种类型的网络中，网络的核心以阶梯的形式成形和网格化，树扎根于阶梯的边缘。
The sections that follow examine these topologies in detail in order to parameterize them.
以下各节将详细检查这些拓扑，以便对其进行参数化。
The snowflake topologies considered in this document are based on a hierarchy of connectivity within the core network. PE nodes have connectivity to P-nodes as shown in Figure 1. There is no direct connectivity between the PEs. Dual homing of PEs to multiple P-nodes is not considered in this document, although it may be a valuable addition to a network configuration.
本文档中考虑的雪花拓扑基于核心网络内的连接层次结构。PE节点连接到P节点，如图1所示。PEs之间没有直接连接。本文件不考虑PEs对多个P节点的双重归巢，尽管这可能是网络配置的一个有价值的补充。
P
/|\
/ | \
/ | \
/ | \
PE PE PE
P
/|\
/ | \
/ | \
/ | \
PE PE PE
Figure 1 : PE to P-Node Connectivity
图1:PE到P节点的连接
The relationship between P-nodes is also structured in a hierarchical way. Thus, as shown in Figure 2, multiple P-nodes at one level are connected to a P-node at a higher level. We number the levels such that level 1 is the top level (top in our figure, and nearest to the core of the network) and level (n) is immediately above level (n+1); we denote a P-node at level n as a P(n).
P节点之间的关系也是以分层方式构造的。因此，如图2所示，一个级别的多个P节点连接到更高级别的P节点。我们对级别进行编号，使级别1为顶层（图中为顶层，距离网络核心最近），级别（n）位于级别（n+1）的正上方；我们将n级的P节点表示为P（n）。
As with PEs, there is no direct connectivity between P(n+1) nodes. Again, dual homing of P(n+1) nodes to multiple P(n) nodes is not considered in this document, although it may be a valuable addition to a network configuration.
与PEs一样，P（n+1）节点之间没有直接连接。同样，本文档中不考虑P（n+1）节点到多个P（n）节点的双重归宿，尽管这可能是对网络配置的一个有价值的补充。
P(n)
/|\
/ | \
/ | \
/ | \
P(n+1) P(n+1) P(n+1)
P(n)
/|\
/ | \
/ | \
/ | \
P(n+1) P(n+1) P(n+1)
Figure 2 : Relationship between P-Nodes
图2：P节点之间的关系
At the top level, P(1) nodes are connected in a full mesh. In reality, the level 1 part of the network may be slightly less well-connected than this, but assuming a full mesh provides for generality. Thus, the snowflake topology comprises a clique with topologically equivalent trees subtended from each node in the clique.
在顶层，P（1）个节点连接在一个完整的网格中。事实上，网络的1级部分的连接可能比这稍差，但假设一个完整的网格提供了通用性。因此，雪花拓扑包含一个团，该团中的每个节点都包含拓扑上等价的树。
The key multipliers for scalability are the number of P(1) nodes and the multiplier relationship between P(n) and P(n+1) at each level, down to and including PEs.
可伸缩性的关键乘数是P（1）节点的数量，以及P（n）和P（n+1）在每个级别（包括PEs）之间的乘数关系。
We define the multiplier M(n) as the number of P(n+1) nodes at level (n+1) attached to any one P(n). Assume that M(n) is constant for all nodes at level n. Since nodes at the same level are not interconnected (except at the top level), and since each P(n+1) node is connected to precisely one P(n) node, M(n) is one less than the degree of the node at level n (that is, the P(n) node is attached to M(n) nodes at level (n+1) and to 1 node at level (n-1)).
我们将乘数M（n）定义为与任意一个P（n）相连的（n+1）层上P（n+1）个节点的数量。假设M（n）对于n级的所有节点都是常数。由于同一级别的节点没有互连（顶层除外），并且由于每个P（n+1）节点恰好连接到一个P（n）节点，因此M（n）比级别n的节点的次数少一个（即，P（n）节点连接到级别（n+1）的M（n）节点，并连接到级别（n-1）的1个节点）。
We define S(n) as the number of nodes at level (n).
我们将S（n）定义为（n）级的节点数。
Thus:
因此：
S(n) = S(1)*M(1)*M(2)*...*M(n-1)
S(n) = S(1)*M(1)*M(2)*...*M(n-1)
So the number of PEs can be expressed as:
因此，PEs的数量可以表示为：
S(PE) = S(1)*M(1)*M(2)*...*M(n)
S(PE) = S(1)*M(1)*M(2)*...*M(n)
where the network has (n) layers of P-nodes.
其中，网络具有（n）层P节点。
Thus, we may depict an example snowflake network as shown in Figure 3. In this case:
因此，我们可以描述一个示例雪花网络，如图3所示。在这种情况下：
S(1) = 3
M(1) = 3
S(2) = S(1)*M(1) = 9
M(2) = 2
S(PE) = S(1)*M(1)*M(2) = 18
S(1) = 3
M(1) = 3
S(2) = S(1)*M(1) = 9
M(2) = 2
S(PE) = S(1)*M(1)*M(2) = 18
PE PE PE PE PE PE
\ \/ \/ /
PE--P(2) P(2) P(2) P(2)--PE
\ | | /
\| |/
PE--P(2)---P(1)------P(1)---P(2)--PE
/ \ / \
PE \ / PE
\/
P(1)
/|\
/ | \
/ | \
PE--P(2) P(2) P(2)--PE
/ /\ \
PE PE PE PE
PE PE PE PE PE PE
\ \/ \/ /
PE--P(2) P(2) P(2) P(2)--PE
\ | | /
\| |/
PE--P(2)---P(1)------P(1)---P(2)--PE
/ \ / \
PE \ / PE
\/
P(1)
/|\
/ | \
/ | \
PE--P(2) P(2) P(2)--PE
/ /\ \
PE PE PE PE
Figure 3 : An Example Snowflake Network
图3：雪花网络示例
The ladder networks considered in this section are based on an arrangement of routers in the core network that resembles a ladder.
本节中考虑的梯形网络基于核心网络中类似梯形的路由器布置。
Ladder networks typically have long and thin cores that are arranged as conventional ladders. That is, they have one or more spars connected by rungs. Each node on a spar may have:
梯形网络通常具有长而薄的核心，这些核心按照常规梯形排列。也就是说，它们有一个或多个由横档连接的桅杆。spar上的每个节点可能具有：
- connection to one or more other spars, - connection to a tree of other core nodes, - connection to customer nodes.
- 连接到一个或多个其他Spar，-连接到其他核心节点树，-连接到客户节点。
Figure 4 shows a simplified example of a ladder network. A core of twelve nodes makes up two spars connected by six rungs.
图4显示了梯形网络的简化示例。由十二个节点组成的核心由六个横档连接的两个桅杆组成。
PE PE PE PE
PE PE PE | PE | PE PE PE | PE | PE
\| \|/ |/ | \| \|/
PE-P-----P-----P-----P------P-----P--PE
| | | | | |\
| | | | | | PE
| | | | | |
PE-P-----P-----P-----P------P-----P
/| /|\ |\ |\ |\ \
PE PE PE | PE | PE | PE | PE PE
PE PE PE PE
PE PE PE PE
PE PE PE | PE | PE PE PE | PE | PE
\| \|/ |/ | \| \|/
PE-P-----P-----P-----P------P-----P--PE
| | | | | |\
| | | | | | PE
| | | | | |
PE-P-----P-----P-----P------P-----P
/| /|\ |\ |\ |\ \
PE PE PE | PE | PE | PE | PE PE
PE PE PE PE
Figure 4 : A Simplified Ladder Network
图4：简化的梯形网络
In practice, not all nodes on a spar (call them spar-nodes) need to have subtended PEs. That is, they can exist simply to give connectivity along the spar to other spar-nodes, or across a rung to another spar. Similarly, the connectivity between spars can be more complex with multiple connections from one spar-node to another spar. Lastly, the network may be complicated by the inclusion of more than two spars (or simplified by reduction to a single spar).
实际上，并非spar上的所有节点（称为spar节点）都需要有子端PE。也就是说，它们可以简单地存在，以便沿着spar连接到其他spar节点，或者跨横档连接到另一个spar节点。类似地，由于从一个spar节点到另一个spar节点的多个连接，spar之间的连接可能更加复杂。最后，网络可能因包含两个以上的spar而变得复杂（或简化为单个spar）。
These variables make the ladder network non-trivial to model. For the sake of simplicity, we will make the following restrictions:
这些变量使得梯形网络对模型来说非常重要。为了简单起见，我们将作出以下限制：
- There are precisely two spars in the core network.
- 核心网络中正好有两个Spar。
- Every spar-node connects to precisely one spar-node on the other spar. That is, each spar-node is attached to precisely one rung.
- 每个spar节点都精确连接到另一个spar上的一个spar节点。也就是说，每个spar节点恰好连接到一个横档。
- Each spar-node connects to either one (end-spar) or two (core-spar) other spar-nodes on the same spar.
- 每个spar节点连接到同一spar上的一个（端部spar）或两个（核心spar）其他spar节点。
- Every spar-node has the same number of PEs subtended. This does not mean that there are no P-nodes subtended to the spar-nodes, but does mean that the edge tree subtended to each spar-node is identical.
- 每个spar节点都有相同数量的PE子节点。这并不意味着不存在子节点到spar节点的P节点，而是意味着子节点到每个spar节点的边树是相同的。
From these restrictions, we are able to quantify a ladder network as follows:
根据这些限制，我们能够量化梯形网络，如下所示：
R - The number of rungs. That is, the number of spar-nodes on each spar. S(1) - The number of spar-nodes in the network. S(1)=2*R. E - The number of subtended edge nodes (PEs) to each spar-node.
R-梯级的数量。也就是说，每个spar上的spar节点数。S（1）-网络中spar节点的数量。S（1）=2*R.E-每个spar节点的子端边节点（PE）的数量。
The number of rungs may vary considerably. A number less than 3 is unlikely (since that would not be a significantly connected network), and a number greater than 100 seems improbable (because that would represent a very long, thin network).
横档的数量可能会有很大的不同。小于3的数字是不可能的（因为这不是一个显著连接的网络），大于100的数字似乎是不可能的（因为这将代表一个非常长、非常薄的网络）。
E can be treated as for the snowflake network. That is, we can consider a number of levels of attachment from P(1) nodes, which are the spar-nodes, through P(i) down to P(n), which are the PEs. Practically, we need to only consider n=2 (PEs attached direct to the spar-nodes) and n=3 (one level of P-nodes between the PEs and the spar-nodes).
E可以被视为雪花网络。也就是说，我们可以考虑从P（1）节点，通过Pp（i）到p（n），这是PES的多个节点的附着级别。实际上，我们只需要考虑n＝2（PES直接连接到SPAR节点）和n＝3（在PES和SPAR节点之间的一个P节点级别）。
Let M(i) be the ratio of P(i) nodes to P(i-1) nodes, i.e., the connectivity between levels of P-node as defined for the snowflake topology. Hence, the number of nodes at any level (n) is:
设M（i）为P（i）个节点与P（i-1）个节点的比率，即为雪花拓扑定义的P-节点级别之间的连接性。因此，任何级别（n）的节点数为：
S(n) = S(1)*M(1)*M(2)*...*M(n-1)
S(n) = S(1)*M(1)*M(2)*...*M(n-1)
So the number of PEs subtended to a spar-node is:
因此，spar节点子节点的PE数量为：
E = M(1)*M(2)*...*M(n)
E = M(1)*M(2)*...*M(n)
And the number of PEs can be expressed as:
PEs的数量可以表示为：
S(PE) = S(1)*M(1)*M(2)*...*M(n)
= S(1)*E
S(PE) = S(1)*M(1)*M(2)*...*M(n)
= S(1)*E
Thus, we may depict an example ladder network as shown in Figure 5. In this case:
因此，我们可以描述一个示例梯形网络，如图5所示。在这种情况下：
R = 5
S(1) = 10
M(1) = 2
S(2) = S(1)*M(1) = 20
M(2) = 2
E = M(1)*M(2) = 4
S(PE) = S(1)*E = 40
R = 5
S(1) = 10
M(1) = 2
S(2) = S(1)*M(1) = 20
M(2) = 2
E = M(1)*M(2) = 4
S(PE) = S(1)*E = 40
PE PE PE PE PE PE PE PE PE PE PE PE PE PE PE PE
\| \| \| \| |/ |/ |/ |/
P(2) P(2) P(2) P(2) P(2) P(2) P(2) P(2)
\ \ | \ / | / /
PE \ \ | \ / | / / PE
\ \ \| \/ |/ / /
PE-P(2)---P(1)---P(1)---P(1)---P(1)---P(1)---P(2)-PE
| | | | |
| | | | |
| | | | |
PE-P(2)---P(1)---P(1)---P(1)---P(1)---P(1)---P(2)-PE
/ / / | /\ |\ \ \
PE / / | / \ | \ \ PE
/ / | / \ | \ \
P(2) P(2) P(2) P(2) P(2) P(2) P(2) P(2)
/| /| /| /| |\ |\ |\ |\
PE PE PE PE PE PE PE PE PE PE PE PE PE PE PE PE
PE PE PE PE PE PE PE PE PE PE PE PE PE PE PE PE
\| \| \| \| |/ |/ |/ |/
P(2) P(2) P(2) P(2) P(2) P(2) P(2) P(2)
\ \ | \ / | / /
PE \ \ | \ / | / / PE
\ \ \| \/ |/ / /
PE-P(2)---P(1)---P(1)---P(1)---P(1)---P(1)---P(2)-PE
| | | | |
| | | | |
| | | | |
PE-P(2)---P(1)---P(1)---P(1)---P(1)---P(1)---P(2)-PE
/ / / | /\ |\ \ \
PE / / | / \ | \ \ PE
/ / | / \ | \ \
P(2) P(2) P(2) P(2) P(2) P(2) P(2) P(2)
/| /| /| /| |\ |\ |\ |\
PE PE PE PE PE PE PE PE PE PE PE PE PE PE PE PE
Figure 5 : An Example Ladder Network
图5：梯形图网络示例
It is reasonable to ask why these two particular network topologies have been chosen.
有理由问为什么选择这两种特定的网络拓扑。
The most important consideration is physical scalability. Each node (Label Switching Router - LSR) is only able to support a limited number of physical interfaces. This necessarily reduces the ability to fully mesh a network and leads to the tree-like structure of the network toward the PEs.
最重要的考虑因素是物理可伸缩性。每个节点（标签交换路由器-LSR）只能支持有限数量的物理接口。这必然会降低完全网状网络的能力，并导致网络的树状结构朝向PEs。
A realistic commercial consideration for an operator is the fact that the only revenue-generating nodes in the network are the PEs. Other nodes are needed only to support connectivity and scalability. Therefore, there is a desire to maximize S(PE) while minimizing the sum of S(n) for all values of (n). This could be achieved by minimizing the number of levels and maximizing the connectivity at each layer, M(n). Ultimately, however, this would produce a network of just interconnected PEs, which is clearly in conflict with the physical scaling situation.
对于运营商来说，一个现实的商业考虑是，网络中唯一产生收入的节点是PEs。其他节点仅用于支持连接性和可伸缩性。因此，希望最大化S（PE），同时最小化所有（n）值的S（n）之和。这可以通过最小化层的数量和最大化每层M（n）的连通性来实现。然而，最终，这将产生一个仅互连的PEs网络，这显然与物理扩展情况相冲突。
Therefore, the solution calls for a "few" levels with "relatively large" connectivity at each level. We might say that the cost-effectiveness of the network can be stated as:
因此，该解决方案需要在每个级别上具有“相对较大”连接的“少数”级别。我们可以说，网络的成本效益可以表述为：
K = S(PE)/(S(1)+S(2) + ... + S(n)) where n is the level above the PEs
K = S(PE)/(S(1)+S(2) + ... + S(n)) where n is the level above the PEs
We should observe, however, that this equation may be naive in that the cost of a network is not actually a function of the number of routers (since a router chassis is often free or low cost), but is really a function of the cost of the line cards, which is, itself, a product of the capacity of the line cards. Thus, the relatively high connectivity decreases the cost-effectiveness, while a topology that tends to channel data through a network core tends to demand higher capacity (and so, more expensive) line cards.
然而，我们应该注意到，这个等式可能是幼稚的，因为网络的成本实际上不是路由器数量的函数（因为路由器机箱通常是免费或低成本的），而是线路卡成本的函数，而线路卡成本本身就是线路卡容量的乘积。因此，相对较高的连接性降低了成本效益，而倾向于通过网络核心传送数据的拓扑往往需要更高容量（因此，更昂贵）的线路卡。
A further consideration is the availability of connectivity (usually fibers) between LSR sites. Although it is always possible to lay new fiber, this may not be cost-effective or timely. The physical shape and topography of the country in which the network is laid is likely to be as much of a problem. If the country is 'long and thin', then a ladder network is likely to be used.
进一步考虑的是LSR站点之间的连接可用性（通常是光纤）。尽管铺设新的光纤总是可能的，但这可能不划算或不及时。铺设网络的国家的物理形状和地形可能也是一个问题。如果这个国家“又长又瘦”，那么很可能会使用梯形网络。
This document examines the implications for control plane and data plane scalability of this type of network when MPLS-TE LSPs are used to provide full connectivity between all PEs.
本文件探讨了当使用MPLS-TE LSP在所有PE之间提供完全连接时，这种网络的控制平面和数据平面可扩展性的含义。
As explained in Section 1, this document is using two symmetrical and generalized network topologies for simplicity of modelling. In practice, there are two other topological considerations.
如第1节所述，为了简化建模，本文件使用了两种对称和广义网络拓扑。在实践中，还有另外两个拓扑考虑因素。
a. Multihoming It is relatively common for a node at level (n) to be attached to more than one node at level (n-1). This is particularly common at PEs that may be connected to more than one P(n).
a. 多宿主级别（n）上的节点连接到级别（n-1）上的多个节点是比较常见的。这在可能连接到多个P（n）的PEs中尤其常见。
b. Meshing within a level A level in the network will often include links between P-nodes at the same level, including the possibility of links between PEs. This may result in a network that looks like a series of concentric circles with spokes.
b. 网络a级内的网格划分通常包括同一级别的P节点之间的链路，包括PEs之间的链路。这可能导致网络看起来像一系列带辐条的同心圆。
Both of these features are likely to have some impact on the scaling of the networks. However, for the purposes of establishing the ground rules for scaling, this document restricts itself to the consideration of the symmetrical networks described in Sections 2.1 and 2.2. Discussion of other network formats is for future study.
这两个特性都可能对网络的扩展产生一定影响。然而，为了确定缩放的基本规则，本文件仅限于考虑第2.1节和第2.2节中所述的对称网络。其他网络格式的讨论供将来研究。
An important question for this evaluation and analysis is the size of the network that operators require. How many PEs are required? What ratio of P to PE is acceptable? How many ports do devices have for physical connectivity? What type of MPLS-TE connectivity between PEs is required?
评估和分析的一个重要问题是运营商需要的网络规模。需要多少个PEs？可接受的P与PE的比例是多少？设备有多少个物理连接端口？PEs之间需要什么类型的MPLS-TE连接？
Although presentation of figures for desired network sizes must be treated with caution because history shows that networks grow beyond all projections, it is useful to set some acceptable lower bounds. That is, we can state that we are interested in networks of at least a certain size.
尽管必须谨慎对待所需网络大小的数字表示，因为历史表明网络的增长超出了所有预测，但设置一些可接受的下限是有用的。也就是说，我们可以声明我们对至少一定规模的网络感兴趣。
The most important features are:
最重要的特点是：
- The network should have at least 1000 PEs. - Each pair of PEs should be connected by at least one LSP in each direction.
- 网络应至少有1000个PE。-每对PEs应在每个方向上至少连接一个LSP。
In practice, reasonable target numbers are as follows.
在实践中，合理的目标数字如下。
S(PE) >= 1000
Number of levels is 3. That is: 1, 2, and PE.
M(2) <= 20
M(1) <= 20
S(1) <= 100
S(PE) >= 1000
Number of levels is 3. That is: 1, 2, and PE.
M(2) <= 20
M(1) <= 20
S(1) <= 100
Before proceeding to examine potential scaling improvements, we need to examine how well the flat networks described in the previous sections scale.
在继续检查潜在的扩展改进之前，我们需要检查前几节中描述的平面网络的扩展情况。
Consider the requirement for a full mesh of LSPs linking all PEs. That is, each PE has an LSP to and from every other LSP. Thus, if there are S(PE) PEs in the network, there are S(PE)*(S(PE) - 1) LSPs.
考虑全网状LSP连接所有PES的要求。也就是说，每个PE与每个其他LSP之间都有一个LSP。因此，如果网络中存在S（PE）PE，则存在S（PE）*（S（PE）-1）LSP。
Define L(n) as the number of LSPs handled by a level (n) LSR.
将L（n）定义为由级别（n）LSR处理的LSP数。
L(PE) = 2*(S(PE) - 1)
L(PE) = 2*(S(PE) - 1)
There are a total of S(PE) PEs in the network and, since each PE establishes an LSP with every other PE, it would be expected that there are S(PE) - 1 LSPs incoming to each PE and the same number of LSPs outgoing from the same PE, giving a total of 2(S(PE) - 1) on the incident link. Hence, in a snowflake topology (see Figure 3), since there are M(2) PEs attached to each P(2) node, it may tempting to think that L(2) (the number of LSPs traversing each P(2) node) is simply 2*(S(PE) - 1)*M(2). However, it should be noted that of the S(PE) - 1 LSPs incoming to each PE, M(2) - 1 originated from nodes attached to the same P(2) node, and so this value would count the LSPs between the M(2) PEs attached to each P(2) node twice: once when outgoing from the M(2) - 1 other nodes and once when incoming into a particular PE.
网络中总共有S（PE）个PE，由于每个PE与每个其他PE建立一个LSP，预计每个PE将有S（PE）-1个LSP传入，相同数量的LSP从同一PE传出，因此事件链路上总共有2个（S（PE）-1）。因此，在雪花拓扑（见图3）中，由于每个P（2）节点上都连接有M（2）个PE，因此很可能会认为L（2）（穿过每个P（2）节点的LSP数量）只是2*（S（PE）-1）*M（2）。然而，应当注意，在传入到每个PE的S（PE）-1个lsp中，M（2）-1来自连接到相同P（2）节点的节点，因此该值将对连接到每个P（2）节点的M（2）个PE之间的lsp进行两次计数：一次是从M（2）-1其他节点传出时，一次是传入到特定PE时。
There are a total of M(2)*(M(2) - 1) LSPs between these M(2) PEs and, since this value is erroneously included twice in 2*(S(PE) - 1)*M(2), the correct value is:
这些M（2）个PE之间总共有M（2）*（M（2）-1）个LSP，由于该值错误地包含在2*（S（PE）-1）*M（2）中两次，因此正确的值为：
L(2) = 2*M(2)*(S(PE) - 1) - M(2)*(M(2) - 1)
= M(2)*(2*S(PE) - M(2) - 1)
L(2) = 2*M(2)*(S(PE) - 1) - M(2)*(M(2) - 1)
= M(2)*(2*S(PE) - M(2) - 1)
An alternative way of looking at this, that proves extensible for the calculation of L(1), is to observe that each PE subtended to a P(2) node has an LSP in each direction to all S(PE) - M(2) PEs in the rest of the system, and there are M(2) such locally subtended PEs; thus, 2*M(2)*(S(PE) - M(2)). Additionally, there are M(2)*(M(2) - 1) LSPs between the locally subtended PEs. So:
研究这一点的另一种方法是观察到P（2）节点的每一个子节点在每个方向上都有一个LSP指向系统其余部分中的所有S（PE）-M（2）个PE，并且有M（2）个这样的局部子节点；因此，2*M（2）*（S（PE）-M（2））。此外，在本地子端PE之间存在M（2）*（M（2）-1）个LSP。因此：
L(2) = 2*M(2)*(S(PE) - M(2)) + M(2)*(M(2) - 1)
= M(2)*(2*S(PE) - M(2) - 1)
L(2) = 2*M(2)*(S(PE) - M(2)) + M(2)*(M(2) - 1)
= M(2)*(2*S(PE) - M(2) - 1)
L(1) can be computed in the same way as this second evaluation of L(2). Each PE subtended below a P(1) node has an LSP in each direction to all PEs not below the P(1) node. There are M(1)*M(2) PEs below the P(1) node, so this accounts for 2*M(1)*M(2)*(S(PE) - M(1)*M(2)) LSPs. To this, we need to add the number of LSPs that pass through the P(1) node and that run between the PEs subtended below the P(1). Consider each P(2): it has M(2) PEs, each of which has an LSP going to all of the PEs subtended to the other P(2) nodes subtended to the P(1). There are M(1) - 1 such other P(2) nodes, and so M(2)*(M(1) - 1) other such PEs. So the number of LSPs from the PEs below a P(2) node is M(2)*M(2)*(M(1) - 1). And there are M(1) P(2) nodes below the P(1), giving rise to a total of M(2)*M(2)*M(1)*(M(1) - 1) LSPs. Thus:
L（1）的计算方法与L（2）的第二次计算方法相同。P（1）节点下方的每个PE子节点在每个方向上都有一个LSP，指向不在P（1）节点下方的所有PE。在P（1）节点下有M（1）*M（2）个PE，因此这占了2*M（1）*M（2）*（S（PE）-M（1）*M（2））个LSP。为此，我们需要添加通过P（1）节点和在P（1）下的PE子节点之间运行的LSP的数量。考虑每个P（2）：它有M（2）PES，每个都有一个LSP到所有的PES，它们被倾向于P（1）的其他P（2）节点。存在M（1）-1个这样的其他P（2）节点，因此M（2）*（M（1）-1）个这样的其他PEs。因此，来自P（2）节点下方的PE的LSP数量为M（2）*M（2）*（M（1）-1）。在P（1）之下有M（1）个P（2）节点，总共产生M（2）*M（2）*M（1）*（M（1）-1）个lsp。因此：
L(1) = 2*M(1)*M(2)*(S(PE) - M(1)*M(2)) + M(2)*M(2)*M(1)*(M(1) - 1)
= M(1)*M(2)*(2*S(PE) - M(2)*(M(1) + 1))
L(1) = 2*M(1)*M(2)*(S(PE) - M(1)*M(2)) + M(2)*M(2)*M(1)*(M(1) - 1)
= M(1)*M(2)*(2*S(PE) - M(2)*(M(1) + 1))
So, for example, with S(1) = 5, M(1) = 10, and M(2) = 20, we see:
例如，S（1）=5，M（1）=10，M（2）=20，我们看到：
S(PE) = 1000
L(PE) = 1998
L(2) = 39580
L(1) = 356000
S(PE) = 1000
L(PE) = 1998
L(2) = 39580
L(1) = 356000
Alternatively, with S(1) = 10, M(1) = 10, and M(2) = 20, we see:
或者，当S（1）=10、M（1）=10和M（2）=20时，我们看到：
S(PE) = 2000
L(PE) = 3998
L(2) = 79580
L(1) = 756000
S(PE) = 2000
L(PE) = 3998
L(2) = 79580
L(1) = 756000
In both examples, the number of LSPs at the core (P(1)) nodes is probably unacceptably large, even though there are only a relatively modest number of PEs. In fact, L(2) may even be too large in the second example.
在这两个示例中，核心（P（1））节点处的lsp的数量可能大得令人无法接受，即使PEs的数量相对较少。事实上，在第二个例子中，L（2）甚至可能太大。
In ladder networks, L(PE) remains the same at 2*(S(PE) - 1).
在梯形网络中，L（PE）在2*（S（PE）-1）处保持不变。
L(2) can be computed using the same mechanism as for the snowflake topology because the subtended tree is the same format. Hence,
L（2）可以使用与雪花拓扑相同的机制进行计算，因为子端树的格式相同。因此
L(2) = 2*M(2)*(S(PE) - 1) - M(2)*(M(2) - 1)
L(2) = 2*M(2)*(S(PE) - 1) - M(2)*(M(2) - 1)
But L(1) requires a different computation because each P(1) not only sees LSPs for the subtended PEs, but is also a transit node for some of the LSPs that cross the core (the core is not fully meshed).
但L（1）需要不同的计算，因为每个P（1）不仅可以看到子端PE的LSP，而且是穿过核心的一些LSP的中转节点（核心未完全网格化）。
Each P(1) sees:
每个P（1）可以看到：
o all of the LSPs between locally attached PEs, o less those LSPs between locally attached PEs that can be served exclusively by the attached P(2) nodes, o all LSPs between locally attached PEs and remote PEs, and o LSPs in transit that pass through the P(1).
o 本地连接的PE之间的所有LSP，o减去可由连接的P（2）节点专门服务的本地连接的PE之间的LSP，o本地连接的PE和远程PE之间的所有LSP，以及o通过P（1）的传输中的LSP。
The first three numbers are easily determined and match what we have seen from the snowflake network. They are:
前三个数字很容易确定，并且与我们从雪花网络中看到的相符。他们是：
o E*(E-1) o M(1)*M(2)*(M(2)-1) = E*(M(2) - 1) o 2*E*E*(S(1) - 1)
o E*（E-1）oom（1）*M（2）*（M（2）-1）=E*（M（2）-1）oo2*E*E*（S（1）-1）
The number of LSPs in transit is more complicated to compute. It is simplified by not considering the ends of the ladders but by examining an arbitrary segment of the middle of the ladder, such as shown in Figure 6. We look to compute and generalize the number of LSPs traversing each core link (labeled a and b in Figure 6) and so determine the number of transit LSPs seen by each P(1).
在途LSP的数量计算起来更复杂。通过不考虑梯子的端部，而是检查梯子中间的任意部分，如图6所示，可以简化该过程。我们希望计算和概括穿过每个核心链路的LSP的数量（图6中标记为a和b），从而确定每个P（1）看到的中转LSP的数量。
: : : : : :
: : : : : :
P(2) P(2) P(2) P(2) P(2) P(2)
\ | \ / | /
\ | \ / | /
\| \/ |/
......P(1)---P(1)---P(1)......
| a | |
| |b |
| | |
......P(1)---P(1)---P(1)......
/| /\ |\
/ | / \ | \
/ | / \ | \
P(2) P(2) P(2) P(2) P(2) P(2)
: : : : : :
: : : : : :
: : : : : :
: : : : : :
P(2) P(2) P(2) P(2) P(2) P(2)
\ | \ / | /
\ | \ / | /
\| \/ |/
......P(1)---P(1)---P(1)......
| a | |
| |b |
| | |
......P(1)---P(1)---P(1)......
/| /\ |\
/ | / \ | \
/ | / \ | \
P(2) P(2) P(2) P(2) P(2) P(2)
: : : : : :
: : : : : :
Figure 6 : An Arbitrary Section of a Ladder Network
图6：梯形网络的任意部分
Of course, the number of LSPs carried on links a and b in Figure 6 depends on how LSPs are routed through the core network. But if we assume a symmetrical routing policy and an even distribution of LSPs across all shortest paths, the result is the same.
当然，图6中链路a和b上承载的LSP数量取决于LSP如何通过核心网络路由。但是如果我们假设对称的路由策略和LSP在所有最短路径上的均匀分布，结果是相同的。
Now we can see that each P(1) sees half of 2a+b LSPs (since each LSP would otherwise be counted twice as it passed through the P(1)), except that some of the LSPs are locally terminated and so are only included once in the sum 2a+b.
现在我们可以看到，每个P（1）看到2a+b LSP的一半（因为每个LSP在通过P（1）时会被计数两次），除了一些LSP是本地终止的，因此只在2a+b之和中包含一次。
So L(1) = a + b/2 -
(locally terminated transit LSPs)/2 +
(locally contained LSPs)
So L(1) = a + b/2 -
(locally terminated transit LSPs)/2 +
(locally contained LSPs)
Thus:
因此：
L(1) = a + b/2 -
2*E*E*(S(1) - 1)/2 +
E*(E-1) - E*(M(2) - 1)
= a + b/2 +
E*E*(2 - S(1)) - E*M(2)
L(1) = a + b/2 -
2*E*E*(S(1) - 1)/2 +
E*(E-1) - E*(M(2) - 1)
= a + b/2 +
E*E*(2 - S(1)) - E*M(2)
So all we have to do is work out a and b.
所以我们要做的就是算出a和b。
Recall that the ladder length R = S(1)/2, and define X = E*E.
回想一下阶梯长度R=S（1）/2，并定义X=E*E。
Consider the contribution made by all of the LSPs that make n hops on the ladder to the totals of each of a and b. If the ladder was unbounded, then we could say that in the case of a, there are n*2X LSPs along the spar only, and n(n-1)*2X/n = 2X(n-1) LSPs use a rung and the spar. Thus, the LSPs that make n hops on the ladder contribute (4n-2)X LSPs to a. Note that the edge cases are special because LSPs that make only one hop on the ladder cannot transit a P(1) but only start or end there.
考虑所有的LSP所做的贡献，使N跳在阶梯上达到A和B的总数。如果梯子是无界的，那么我们可以说，在a的情况下，沿spar只有n*2X LSP，并且n（n-1）*2X/n=2X（n-1）LSP使用横档和spar。因此，在梯形图上进行n个跃点的LSP为a贡献（4n-2）X LSP。请注意，边缘情况是特殊的，因为在梯形图上仅进行一次跳跃的LSP不能传输P（1），而只能从P（1）开始或结束。
So with a ladder of length R = S(1)/2, we could say:
因此，对于长度为R=S（1）/2的梯子，我们可以说：
R
a = SUM[(4i-2)*X] + 2RX
i=2
R
a = SUM[(4i-2)*X] + 2RX
i=2
= 2*X*R*(R+1)
= 2*X*R*(R+1)
And similarly, considering b in an unbounded ladder, the LSPs that only travel one hop on the LSP are a special case, contributing 2X LSPs, and every other LSP that traverses n hops on the ladder contributes 2n*2X/n = 4X LSPs. So:
类似地，考虑无界阶梯中的b，在LSP上仅移动一个跃点的LSP是一种特殊情况，贡献2X LSP，并且在阶梯上每移动n个跃点的其他LSP贡献2n*2X/n=4X LSP。因此：
R+1 b = 2X + SUM[4X] i=2
R+1b=2X+SUM[4X]i=2
= 2*X + 4*X*R
= 2*X + 4*X*R
In fact, the ladders are bounded, and so the number of LSPs is reduced because of the effect of the ends of the ladders. The links that see the most LSPs are in the middle of the ladder. Consider a ladder of length R; a node in the middle of the ladder is R/2 hops away from the end of the ladder. So we see that the formula for the contribution to the count of spar-only LSPs for a is only valid up to n=R/2, and for spar-and-rung LSPs, up to n=1+R/2. Above these limits, the contribution made by spar-only LSPs decays as (n-R/2)*2X.
事实上，阶梯是有界的，因此由于阶梯末端的影响，LSP的数量减少了。看到大多数LSP的链接在梯子的中间。考虑长度为R的梯子；梯子中间的一个节点是远离梯子末端的R／2跳。因此，我们看到，对于a，仅spar LSP计数的贡献公式仅在n=R/2时有效，对于spar和rung LSP，在n=1+R/2时有效。超过这些限制，仅spar LSP的贡献衰减为（n-R/2）*2X。
However, for a first-order approximation, we will use the values of a and b as computed above. This gives us an upper bound of the number of LSPs without using a more complex formula for the reduction made by the effect of the ends of the ladder.
然而，对于一阶近似，我们将使用上面计算的a和b的值。这为我们提供了LSP数量的上限，而无需使用更复杂的公式来减少阶梯末端的影响。
From this:
由此：
L(1) = a + b/2 +
E*E*(2 - S(1)) - E*M(2)
= 2*X*R*(R+1) +
X + 2*X*R +
E*E*(2 - S(1)) - E*M(2)
= E*E*S(1)*(1 + S(1)/2) +
E*E + E*E*S(1) +
2*E+E - E*E*S(1) - E*M(2)
= E*E*S(1)*(1 + S(1)/2) + 3*E+E - E*M(2)
= E*E*S(1)*S(1)/2 + E*E*S(1) + 3*E*E - E*M(2)
L(1) = a + b/2 +
E*E*(2 - S(1)) - E*M(2)
= 2*X*R*(R+1) +
X + 2*X*R +
E*E*(2 - S(1)) - E*M(2)
= E*E*S(1)*(1 + S(1)/2) +
E*E + E*E*S(1) +
2*E+E - E*E*S(1) - E*M(2)
= E*E*S(1)*(1 + S(1)/2) + 3*E+E - E*M(2)
= E*E*S(1)*S(1)/2 + E*E*S(1) + 3*E*E - E*M(2)
So, for example, with S(1) = 6, M(1) = 10, and M(2) = 17, we see:
例如，S（1）=6，M（1）=10，M（2）=17，我们看到：
E = 170
S(PE) = 1020
L(PE) = 2038
L(2) = 34374
L(1) = 777410
E = 170
S(PE) = 1020
L(PE) = 2038
L(2) = 34374
L(1) = 777410
Alternatively, with S(1) = 10, M(1) = 10, and M(2) = 20, we see:
或者，当S（1）=10、M（1）=10和M（2）=20时，我们看到：
E = 200
S(PE) = 2000
L(PE) = 3998
L(2) = 79580
L(1) = 2516000
E = 200
S(PE) = 2000
L(PE) = 3998
L(2) = 79580
L(1) = 2516000
In both examples, the number of LSPs at the core (P(1)) nodes is probably unacceptably large, even though there are only a relatively modest number of PEs. In fact, L(2) may even be too large in the second example.
在这两个示例中，核心（P（1））节点处的lsp的数量可能大得令人无法接受，即使PEs的数量相对较少。事实上，在第二个例子中，L（2）甚至可能太大。
Compare the L(1) values with the total number of LSPs in the system S(PE)*(S(PE) - 1), which is 1039380 and 3998000, respectively.
将L（1）值与系统S（PE）*（S（PE）-1中的LSP总数（分别为1039380和3998000）进行比较。
One of the purposes of LSP hierarchies [RFC4206] is to improve the scaling properties of MPLS-TE networks. LSP tunnels (sometimes known as Forwarding Adjacencies (FAs)) may be established to provide connectivity over the core of the network, and multiple edge-to-edge LSPs may be tunneled down a single FA LSP.
LSP层次结构[RFC4206]的目的之一是改善MPLS-TE网络的伸缩特性。可以建立LSP隧道（有时称为转发邻接（FAs））以提供网络核心上的连接，并且多个边到边LSP可以沿单个FA LSP隧道向下。
In our network we consider a mesh of FA LSPs between all core nodes at the same level. We consider two possibilities here. In the first, all P(2) nodes are connected to all other P(2) nodes by LSP tunnels, and the PE-to-PE LSPs are tunneled across the core of the network. In the second, an extra layer of LSP hierarchy is introduced by connecting all P(1) nodes in an LSP mesh and tunneling the P(2)-to-P(2) tunnels through these.
在我们的网络中，我们考虑在相同级别的所有核心节点之间的FA LSP网格。我们在这里考虑两种可能性。在第一种方法中，所有P（2）节点通过LSP隧道连接到所有其他P（2）节点，并且PE-to-PE LSP通过隧道穿越网络核心。在第二层中，通过连接LSP网格中的所有P（1）节点并通过隧道将P（2）到P（2）隧道穿过这些节点，引入了LSP层次结构的额外层。
In this hierarchy model, the P(2) nodes are connected by a mesh of tunnels. This means that the P(1) nodes do not see the PE-to-PE LSPs.
在这个层次模型中，P（2）节点通过隧道网格连接。这意味着P（1）节点看不到PE到PE LSP。
It remains the case that:
情况仍然是：
L(PE) = 2*(S(PE) - 1)
L(PE) = 2*(S(PE) - 1)
L(2) is slightly increased. It can be computed as the sum of all LSPs for all attached PEs, including the LSPs between the attached PE (this figure is unchanged from Section 5.1, i.e., M(2)*(2*S(PE) - M(2) - 1)), plus the number of FA LSPs providing a mesh to the other P(2) nodes. Since the number of P(2) nodes is S(2), each P(2) node sees 2*(S(2) - 1) FA LSPs. Thus:
L（2）略有增加。它可以计算为所有连接PE的所有LSP的总和，包括连接PE之间的LSP（该数字与第5.1节相同，即M（2）*（2*S（PE）-M（2）-1）），加上为其他P（2）节点提供网格的FA LSP的数量。由于P（2）节点的数量是S（2），因此每个P（2）节点看到2*（S（2）-1）个FA lsp。因此：
L(2) = M(2)*(2*S(PE) - M(2) - 1) + 2*(S(2) - 1)
L(2) = M(2)*(2*S(PE) - M(2) - 1) + 2*(S(2) - 1)
L(1), however, is significantly reduced and can be computed as the sum of the number of FA LSPs to and from each attached P(2) to each other P(2) in the network, including (but counting only once) the FA LSPs between attached P(2) nodes. In fact, the problem is identical to the L(2) computation in Section 5.1. So:
然而，L（1）显著减少，并且可以计算为网络中每个连接的P（2）到彼此的P（2）的FA lsp的数量之和，包括（但仅计数一次）连接的P（2）节点之间的FA lsp。事实上，该问题与第5.1节中的L（2）计算相同。因此：
L(1) = M(1)*(2*S(2) - M(1) - 1)
L(1) = M(1)*(2*S(2) - M(1) - 1)
So, for example, with S(1) = 5, M(1) = 10, and M(2) = 20, we see:
例如，S（1）=5，M（1）=10，M（2）=20，我们看到：
S(PE) = 1000
S(2) = 50
L(PE) = 1998
L(2) = 39678
L(1) = 890
S(PE) = 1000
S(2) = 50
L(PE) = 1998
L(2) = 39678
L(1) = 890
Alternatively, with S(1) = 10, M(1) = 10, and M(2) = 20, we see:
或者，当S（1）=10、M（1）=10和M（2）=20时，我们看到：
S(PE) = 2000
S(2) = 100
L(PE) = 3998
L(2) = 79778
L(1) = 1890
S(PE) = 2000
S(2) = 100
L(PE) = 3998
L(2) = 79778
L(1) = 1890
So, in both examples, potential problems at the core (P(1)) nodes caused by an excessive number of LSPs can be avoided, but any problem with L(2) is made slightly worse, as can be seen from the table below.
因此，在这两个示例中，都可以避免由于lsp数量过多而导致的核心（P（1））节点的潜在问题，但是L（2）的任何问题都会稍微恶化，如下表所示。
Example| Count | Unmodified | 2-Layer
| | (Section 5.1) | Hierarchy
-------+-------+---------------+----------
A | L(2) | 39580 | 39678
| L(1) | 356000 | 890
-------+-------+---------------+----------
B | L(2) | 79580 | 79778
| L(1) | 756000 | 1890
Example| Count | Unmodified | 2-Layer
| | (Section 5.1) | Hierarchy
-------+-------+---------------+----------
A | L(2) | 39580 | 39678
| L(1) | 356000 | 890
-------+-------+---------------+----------
B | L(2) | 79580 | 79778
| L(1) | 756000 | 1890
Clearly, we can reduce L(2) by selecting appropriate values of S(1), M(1), and M(2). We can do this without negative consequences, since no change will affect L(PE) and since a large percentage increase in L(1) is sustainable now that L(1) is so small.
显然，我们可以通过选择适当的S（1）、M（1）和M（2）值来减少L（2）。我们可以在没有负面影响的情况下做到这一点，因为没有任何变化会影响L（PE），而且L（1）的大幅增加是可持续的，因为L（1）非常小。
Observe that:
注意：
L(2) = M(2)*(2*S(PE) - M(2) - 1) + 2*(S(2) - 1)
L(2) = M(2)*(2*S(PE) - M(2) - 1) + 2*(S(2) - 1)
where S(PE) = S(1)*M(1)*M(2) and S(2) = S(1)*M(1). So L(2) scales with M(2)^2 and we can have the most impact by reducing M(2) while keeping S(PE) constant.
其中S（PE）=S（1）*M（1）*M（2）和S（2）=S（1）*M（1）。因此，L（2）与M（2）^2成比例，我们可以通过减少M（2），同时保持S（PE）恒定来产生最大的影响。
For example, with S(1) = 10, M(1) = 10, and M(2) = 10, we see:
例如，当S（1）=10、M（1）=10和M（2）=10时，我们看到：
S(PE) = 1000
S(2) = 100
L(PE) = 1998
L(2) = 20088
L(1) = 1890
S(PE) = 1000
S(2) = 100
L(PE) = 1998
L(2) = 20088
L(1) = 1890
And similarly, with S(1) = 20, M(1) = 20, and M(2) = 5, we see:
同样，当S（1）=20，M（1）=20，M（2）=5时，我们看到：
S(PE) = 2000
S(2) = 400
L(PE) = 3998
L(2) = 20768
L(1) = 15580
S(PE) = 2000
S(2) = 400
L(PE) = 3998
L(2) = 20768
L(1) = 15580
These considerable scaling benefits must be offset against the cost-effectiveness of the network. Recall from Section 3.3 that:
这些可观的扩展优势必须与网络的成本效益相抵消。回顾第3.3节：
K = S(PE)/(S(1)+S(2) ... + S(n))
K = S(PE)/(S(1)+S(2) ... + S(n))
where n is the level above the PEs, so that for our network:
其中n是PEs之上的级别，因此对于我们的网络：
K = S(PE) / (S(1) + S(2))
K = S(PE) / (S(1) + S(2))
Thus, in the first example the cost-effectiveness has been halved from 1000/55 to 1000/110. In the second example, it has been reduced to roughly one quarter, changing from 2000/110 to 2000/420.
因此，在第一个例子中，成本效益从1000/55降低到了1000/110。在第二个例子中，它已减少到大约四分之一，从2000/110变为2000/420。
So, although the tuning changes may be necessary to reach the desired network size, they come at a considerable cost to the operator.
因此，尽管可能需要调整更改以达到所需的网络大小，但对运营商来说，这些更改会带来相当大的成本。
An alternative to the two-layer hierarchy presented in Section 6.1 is to provide a full mesh of FA LSPs between P(1) nodes. This technique is only of benefit to any nodes in the core of the level 1 network. It makes no difference to the PE and P(2) nodes since they continue to see only the PE-to-PE LSPs. Furthermore, this approach increases the burden at the P(1) nodes since they have to support all of the PE-to-PE LSPs as in the flat model plus the additional 2*(S(1) - 1) P(1)-to-P(1) FA LSPs. Thus, this approach should only be considered where there is a mesh of P-nodes within the ring of P(1) nodes, and is not considered further in this document.
第6.1节中介绍的两层层次结构的替代方案是在P（1）节点之间提供完整的FA LSP网格。此技术仅对1级网络核心中的任何节点有利。这对PE和P（2）节点没有区别，因为它们继续只看到PE到PE LSP。此外，这种方法增加了P（1）节点的负担，因为它们必须支持平面模型中的所有PE-to-PE lsp加上额外的2*（S（1）-1）P（1）-to-P（1）FA lsp。因此，仅当P（1）节点环内存在P节点网格时，才应考虑该方法，本文件中不再进一步考虑。
As demonstrated by Section 6.2, introducing a mesh of FA LSPs at the top level (P(1)) has no benefit, but if we introduce an additional level in the network (P(3) between P(2) and PE) to make a four-level snowflake, we can introduce a new layer of FA LSPs so that we have a full mesh of FA LSPs between all P(3) nodes to carry the PE-to-PE LSPs, and a full mesh of FA LSPs between all P(2) nodes to carry the P(3)-to-P(3) LSPs.
如第6.2节所示，在顶层（P（1））引入FA LSP网格没有任何好处，但是如果我们在网络中引入一个额外的层（P（3）在P（2）和PE之间）来形成一个四层雪花，我们可以引入一个新的FA LSP层，以便在所有P（3）节点之间有一个完整的FA LSP网格来承载PE到PE LSP，以及在所有P（2）节点之间的FA lsp的完整网格，以承载P（3）到P（3）lsp。
The number of PEs is S(PE) = S(1)*M(1)*M(2)*M(3), and the number of PE-to-PE LSPs at a PE remains L(PE) = 2*(S(PE) - 1).
PE的数量为S（PE）=S（1）*M（1）*M（2）*M（3），并且PE处的PE-to-PE LSP数量保持为L（PE）=2*（S（PE）-1）。
The number of LSPs at a P(3) can be deduced from Section 6.1. It is the sum of all LSPs for all attached PEs, including the LSPs between the attached PE, plus the number of FA LSPs providing a mesh to the other P(3) nodes.
P（3）处的LSP数量可从第6.1节中推导得出。它是所有连接PE的所有LSP的总和，包括连接PE之间的LSP，加上为其他P（3）节点提供网格的FA LSP的数量。
L(3) = M(3)*(2*S(PE) - M(3) - 1) + 2*(S(3) - 1)
L(3) = M(3)*(2*S(PE) - M(3) - 1) + 2*(S(3) - 1)
The number of LSPs at P(2) can also be deduced from Section 6.1 since it is the sum of all LSPs for all attached P(3) nodes, including the LSPs between the attached PE plus the number of FA LSPs providing a mesh to the other P(2) nodes.
P（2）处的LSP数量也可以从第6.1节推导得出，因为它是所有连接的P（3）节点的所有LSP的总和，包括连接的PE之间的LSP加上为其他P（2）节点提供网格的FA LSP数量。
L(2) = M(2)*(2*S(3) - M(2) - 1) + 2*(S(2) - 1)
L(2) = M(2)*(2*S(3) - M(2) - 1) + 2*(S(2) - 1)
Finally, L(1) can be copied straight from 6.1.
最后，L（1）可以直接从6.1中复制。
L(1) = M(1)*(2*S(2) - M(1) - 1)
L(1) = M(1)*(2*S(2) - M(1) - 1)
For example, with S(1) = 5, M(1) = 5, M(2) = 5, and M(3) = 8, we see:
例如，当S（1）=5、M（1）=5、M（2）=5和M（3）=8时，我们看到：
S(PE) = 1000
S(3) = 125
S(2) = 25
L(PE) = 1998
L(3) = 16176
L(2) = 1268
L(1) = 220
S(PE) = 1000
S(3) = 125
S(2) = 25
L(PE) = 1998
L(3) = 16176
L(2) = 1268
L(1) = 220
Similarly, with S(1) = 5, M(1) = 5, M(2) = 8, and M(3) = 10, we see:
类似地，当S（1）=5，M（1）=5，M（2）=8，M（3）=10时，我们看到：
S(PE) = 2000
S(3) = 200
S(2) = 25
L(PE) = 3998
L(3) = 40038
L(2) = 3184
L(1) = 220
S(PE) = 2000
S(3) = 200
S(2) = 25
L(PE) = 3998
L(3) = 40038
L(2) = 3184
L(1) = 220
Clearly, there are considerable scaling improvements with this three-layer hierarchy, and all of the numbers (even L(3) in the second example) are manageable.
显然，在这个三层层次结构中有相当大的扩展改进，并且所有的数字（在第二个示例中甚至是L（3））都是可管理的。
Of course, the extra level in the network tends to reduce the cost-effectiveness of the networks with values of K = 1000/155 and K = 2000/230 (from 1000/55 and 2000/110) for the examples above. That is a reduction by a factor of 3 in the first case and 2 in the second case. Such a change in cost-effectiveness has to be weighed against the desire to deploy such a large network. If LSP hierarchies are the only scaling tool available, and networks this size are required, the cost-effectiveness may need to be sacrificed.
当然，对于上述示例，网络中的额外级别倾向于降低值为K＝1000/155和K＝2000/230（从1000/55和2000/110）的网络的成本效益。这是第一种情况下减少了3倍，第二种情况下减少了2倍。这种成本效益的变化必须与部署如此庞大网络的愿望相权衡。如果LSP层次结构是唯一可用的扩展工具，并且需要这种规模的网络，则可能需要牺牲成本效益。
A basic observation for hierarchical scaling techniques is that it is hard to have any impact on the number of LSPs that must be supported by the level of P(n) nodes adjacent to the PEs (for example, it is hard to reduce L(3) in Section 6.3). In fact, the only way we can change the number of LSPs supported by these nodes is to change the scaling ratio M(n) in the network -- in other words, to change the number of PEs subtended to any P(n). But such a change has a direct effect on the number of PEs in the network and so the cost-effectiveness is impacted.
分层缩放技术的一个基本观察结果是，很难对邻近PEs的P（n）节点级别必须支持的LSP数量产生任何影响（例如，很难在第6.3节中减少L（3））。事实上，我们改变这些节点所支持的LSP数量的唯一方法是改变网络中的缩放比M（n）——换句话说，改变对任意P（n）的PE数量。但这种变化会直接影响网络中的PE数量，从而影响成本效益。
Another concern with the hierarchical approach is that it must be configured and managed. This may not seem like a large burden, but it must be recalled that the P(n) nodes are not at the edge of the network -- they are a set of nodes that must be identified so that the FA LSPs can be configured and provisioned. Effectively, the operator must plan and construct a layered network with a ring of P(n) nodes giving access to the level (n) network. This design activity is open to considerable risk as failing to close the ring (i.e., allowing a node to be at both level (n+1) and at level (n)) may cause operational confusion.
分层方法的另一个问题是必须对其进行配置和管理。这似乎不是一个很大的负担，但必须记住，P（n）节点不在网络的边缘——它们是一组必须识别的节点，以便可以配置和供应FA lsp。有效地，运营商必须规划和构建一个分层网络，其中P（n）个节点环允许访问n级网络。此设计活动存在相当大的风险，因为未能关闭环（即允许节点同时处于级别（n+1）和级别（n））可能会导致操作混乱。
Protocol techniques (such as IGP automesh [RFC4972]) have been developed to reduce the configuration necessary to build this type of multi-level network. In the case of automesh, the routing protocol is used to advertise the membership of a 'mesh group', and all members of the mesh group can discover each other and connect with LSP tunnels. Thus, the P(n) nodes giving access to level (n) can advertise their existence to each other, and it is not necessary to configure each with information about all of the others. Although this process can help to reduce the configuration overhead, it does not eliminate it, as each member of the mesh group must still be planned and configured for membership.
协议技术（如IGP automesh[RFC4972]）已经开发出来，以减少构建此类多级网络所需的配置。在automesh的情况下，路由协议用于公布“mesh组”的成员资格，mesh组的所有成员都可以相互发现并与LSP隧道连接。因此，给予对级别（n）的访问权的P（n）节点可以相互通告它们的存在，并且不必使用关于所有其他节点的信息来配置每个节点。尽管此过程有助于减少配置开销，但并不能消除配置开销，因为网格组的每个成员仍然必须针对成员身份进行规划和配置。
An important consideration for the use of hierarchical LSPs is how they can be protected using MPLS Fast Reroute (FRR) [RFC4090]. FRR may provide link protection either by protecting the tunnels as they traverse a broken link or by treating each level (n) tunnel LSP as a link in level (n+1) and providing protection for the level (n+1) LSPs (although in this model, fault detection and propagation time may be an issue). Node protection may be performed in a similar way, but protection of the first and last nodes of a hierarchical LSP is particularly difficult. Additionally, the whole notion of scaling with regard to FRR gives rise to separate concerns that are outside the scope of this document as currently formulated.
使用分层LSP的一个重要考虑因素是如何使用MPLS快速重路由（FRR）[RFC4090]保护它们。FRR可以通过在隧道穿越断开的链路时保护隧道，或者通过将每个（n）级隧道LSP视为（n+1）级中的链路并为（n+1）级LSP提供保护来提供链路保护（尽管在此模型中，故障检测和传播时间可能是一个问题）。节点保护可以以类似的方式执行，但是对分层LSP的第一个和最后一个节点的保护特别困难。此外，与FRR有关的整个比例概念引起了单独的关注，这些关注超出了当前制定的本文件的范围。
Finally, observe that we have been explaining these techniques using conveniently symmetrical networks. Consider how we would arrange the hierarchical LSPs in a network where some PEs are connected closer to the center of the network than others.
最后，请注意，我们一直在使用方便的对称网络来解释这些技术。考虑一下我们将如何安排一个网络中的分层LSP，其中一些PES被连接到比其他网络更靠近网络的中心。
In Section 6.2, we observed that there is no value to placing FA LSPs between the P(1) nodes of our example snowflake topologies. This is because those LSPs would be just one hop long and would, in fact, only serve to increase the burden at the P(1) nodes. However, in the ladder model, there is value to this approach. The P(1) nodes are the spar-nodes of the ladder, and they are not all mutually adjacent. That is, the P(1)-to-P(1) hierarchical LSPs can create a full mesh of P(1) nodes where one does not exist in the physical topology.
在第6.2节中，我们观察到在示例雪花拓扑的P（1）节点之间放置FA LSP没有任何价值。这是因为这些LSP只有一跳长，实际上只会增加P（1）节点的负担。然而，在阶梯模型中，这种方法是有价值的。P（1）节点是梯形图的spar节点，它们并非相互相邻。也就是说，P（1）到P（1）分层LSP可以创建物理拓扑中不存在的P（1）节点的完整网格。
The number of LSPs seen by a P(1) node is then:
P（1）节点看到的LSP数量为：
o all of the tunnels terminating at the P(1) node, o any transit tunnels, and o all of the LSPs due to subtended PEs.
o 终止于P（1）节点的所有隧道，o任何传输隧道，以及o由于子端接的PE而导致的所有LSP。
This is a substantial reduction; all of the transit LSPs are reduced to just one per remote P(1) that causes any transit LSP. So:
这是一个大幅度的削减；所有中转LSP都减少到每个远程P（1）只有一个，导致任何中转LSP。因此：
L(1) = 2*(S(1) - 1) +
O(S(1)*S(1)/2) +
2*E*E*(S(1) - 1) + E*(E-1) - E*(M(2) - 1)
L(1) = 2*(S(1) - 1) +
O(S(1)*S(1)/2) +
2*E*E*(S(1) - 1) + E*(E-1) - E*(M(2) - 1)
where O(S(1)*S(1)/2) gives an upper bound order of magnitude. So:
其中O（S（1）*S（1）/2）给出了一个上界数量级。因此：
L(1) = S(1)*S(1)/2 + 2*S(1) + 2*E*E*(S(1) - 1) - E*M(2) - 2
L(1) = S(1)*S(1)/2 + 2*S(1) + 2*E*E*(S(1) - 1) - E*M(2) - 2
So, in our two examples:
因此，在我们的两个例子中：
With S(1) = 6, M(1) = 10, and M(2) = 17, we see:
当S（1）=6，M（1）=10，M（2）=17时，我们看到：
E = 170
S(PE) = 1020
L(PE) = 2038
L(2) = 34374
L(1) = 286138
E = 170
S(PE) = 1020
L(PE) = 2038
L(2) = 34374
L(1) = 286138
Alternatively, with S(1) = 10, M(1) = 10, and M(2) = 20, we see:
或者，当S（1）=10、M（1）=10和M（2）=20时，我们看到：
E = 200
S(PE) = 2000
L(PE) = 3998
L(2) = 79580
L(1) = 716060
E = 200
S(PE) = 2000
L(PE) = 3998
L(2) = 79580
L(1) = 716060
Both of these show significant improvements over the previous L(1) figures of 777410 and 2516000. But the numbers are still too large to manage, and there is no improvement in the L(2) figures.
这两个数字都比以前的L（1）数字777410和2516000有显著改善。但数字仍然太大，无法管理，L（2）数字也没有改善。
We can also apply the three-layer hierarchy to the ladder model. In this case, the number of LSPs between P(1) nodes is not reduced, but tunnels are also set up between all P(2) nodes. Thus, the number of LSPs seen by a P(1) node is:
我们还可以将三层层次结构应用于阶梯模型。在这种情况下，P（1）个节点之间的lsp的数量没有减少，但是在所有P（2）个节点之间也建立了隧道。因此，P（1）节点看到的lsp的数量是：
o all of the tunnels terminating at the P(1) node, o any transit tunnels between P(1) nodes, and o all of the LSPs due to subtended P(2) nodes.
o 终止于P（1）节点的所有隧道，o P（1）节点之间的任何传输隧道，以及o由于子端接的P（2）节点而导致的所有lsp。
No PE-to-PE LSPs are seen at the P(1) nodes.
在P（1）节点上看不到PE到PE LSP。
L(1) = 2*(S(1) - 1) +
O(S(1)*S(1)/2) +
2*(S(1) - 1)*M(1)*M(1) + M(1)*(M(1) - 1)
L(1) = 2*(S(1) - 1) +
O(S(1)*S(1)/2) +
2*(S(1) - 1)*M(1)*M(1) + M(1)*(M(1) - 1)
where O(S(1)*S(1)/2) gives an upper bound order of magnitude. So:
其中O（S（1）*S（1）/2）给出了一个上界数量级。因此：
L(1) = S(1)*S(1)/2 + 2*S(1) + 2*M(1)*M(1)*S(1) - M(1)(M(1) + 1) - 2
L(1) = S(1)*S(1)/2 + 2*S(1) + 2*M(1)*M(1)*S(1) - M(1)(M(1) + 1) - 2
Unfortunately, there is a small increase in the number of LSPs seen by the P(2) nodes. Each P(2) now sees all of the PE-to-PE LSPs that it saw before and is also an end-point for a set of P(2)-to-P(2) tunnels. Thus, L(2) increases to:
不幸的是，P（2）节点看到的lsp的数量略有增加。每个P（2）现在可以看到它以前看到的所有PE到PE LSP，并且也是一组P（2）-到P（2）隧道的终点。因此，L（2）增加到：
L(2) = 2*M(2)*(S(PE) - 1) - M(2)*(M(2) - 1) + 2*(S(1)*M(1) - 1)
L(2) = 2*M(2)*(S(PE) - 1) - M(2)*(M(2) - 1) + 2*(S(1)*M(1) - 1)
So, in our two examples:
因此，在我们的两个例子中：
With S(1) = 6, M(1) = 10, and M(2) = 17, we see:
当S（1）=6，M（1）=10，M（2）=17时，我们看到：
E = 170
S(PE) = 1020
L(PE) = 2038
L(2) = 34492
L(1) = 1118
E = 170
S(PE) = 1020
L(PE) = 2038
L(2) = 34492
L(1) = 1118
Alternatively, with S(1) = 10, M(1) = 10, and M(2) = 20, we see:
或者，当S（1）=10、M（1）=10和M（2）=20时，我们看到：
E = 200
S(PE) = 2000
L(PE) = 3998
L(2) = 79778
L(1) = 1958
E = 200
S(PE) = 2000
L(PE) = 3998
L(2) = 79778
L(1) = 1958
This represents a very dramatic decrease in LSPs across the core.
这意味着整个核心的LSP大幅下降。
The same issues exist for hierarchical LSPs as described in Section 6.4. Although dramatic improvements can be made to the scaling numbers for the number of LSPs at core nodes, this can only be done at the cost of configuring P(2) to P(2) tunnels. The mesh of P(1) tunnels is not enough.
如第6.4节所述，分层LSP也存在同样的问题。尽管可以对核心节点上LSP数量的缩放数量进行显著改进，但这只能以配置P（2）到P（2）隧道为代价。P（1）隧道的网格不够。
But the sheer number of P(2) to P(2) tunnels that must be configured is a significant management burden that can only be eased by using a technique like automesh [RFC4972].
但是，必须配置的P（2）到P（2）隧道的绝对数量是一个巨大的管理负担，只有使用automesh之类的技术才能减轻这一负担[RFC4972]。
It is significant, however, that the scaling problem at the P(2) nodes cannot be improved by using tunnels and that the only solution to ease this in the hierarchical approach would be to institute another layer of hierarchy (that is, P(3) nodes) between the P(2) nodes and the PEs. This is, of course, a significant expense.
然而，重要的是，使用隧道无法改善P（2）节点处的缩放问题，并且在分层方法中缓解此问题的唯一解决方案是在P（2）节点和PEs之间建立另一层分层（即P（3）节点）。当然，这是一笔巨大的开支。
An alternative (or complementary) scaling technique has been proposed using multipoint-to-point (MP2P) LSPs. The fundamental improvement in this case is achieved by reducing the number of LSPs toward the destination as LSPs toward the same destination are merged.
提出了一种使用多点对点（MP2P）LSP的替代（或补充）缩放技术。在这种情况下，基本的改进是通过减少朝向目的地的lsp的数量来实现的，因为朝向相同目的地的lsp被合并。
This section presents an overview of MP2P LSPs and describes their applicability and scaling benefits.
本节概述MP2P LSP，并描述其适用性和扩展优势。
Note that the MP2P LSPs discussed here are for MPLS-TE and are not the same concept familiar in the Label Distribution Protocol (LDP) described in [RFC5036].
请注意，此处讨论的MP2P LSP用于MPLS-TE，与[RFC5036]中描述的标签分发协议（LDP）中熟悉的概念不同。
Traffic flows generally converge toward their destination and this can be utilized by MPLS in constructing an MP2P LSP. With such an LSP, the Label Forwarding Information Base (LFIB) mappings at each LSR are many-to-one so that multiple pairs {incoming interface, incoming label} are mapped to a single pair {outgoing interface, outgoing label}. Obviously, if per-platform labels are used, this mapping may be optimized within an implementation.
业务流通常向其目的地汇聚，这可由MPLS用于构建MP2P LSP。使用这样的LSP，每个LSR处的标签转发信息库（LFIB）映射是多对一的，因此多个对{传入接口，传入标签}被映射到单个对{传出接口，传出标签}。显然，如果使用每个平台的标签，则可以在实现中优化此映射。
It is important to note that with MP2P MPLS-TE LSPs, the traffic flows are merged. That is, some additional form of identifier is required if de-merging is required. For example, if the payload is IP traffic belonging to the same client network, no additional de-merging information is required since the IP packet contains sufficient data. On the other hand, if the data comes, for example, from a variety of VPN client networks, then the flows will need to be labeled in their own right as point-to-point (P2P) flows, so that traffic can be disambiguated at the egress of the MP2P LSPs.
需要注意的是，使用MP2P MPLS-TE LSP时，业务流被合并。也就是说，如果需要解合并，则需要某种附加形式的标识符。例如，如果有效载荷是属于同一客户端网络的IP通信量，则不需要额外的解合并信息，因为IP分组包含足够的数据。另一方面，例如，如果数据来自各种VPN客户端网络，则流本身需要被标记为点对点（P2P）流，以便可以在MP2P lsp的出口处消除通信量的歧义。
Techniques for establishing MP2P MPLS-TE LSPs and for assigning the correct bandwidth downstream of LSP merge points are out of the scope of this document.
建立MP2P MPLS-TE LSP和分配LSP合并点下游正确带宽的技术不在本文档的范围内。
Consider the network topology shown in Figure 3. Suppose that we establish MP2P LSP tunnels such that there is one tunnel terminating at each PE, and that that tunnel has every other PE as an ingress. Thus, a PE-to-PE MP2P LSP tunnel would have S(PE)-1 ingresses and one egress, and there would be S(PE) such tunnels.
考虑图3所示的网络拓扑结构。假设我们建立了MP2P LSP隧道，使得每个PE有一个隧道终止，并且该隧道将每个其他PE作为入口。因此，PE到PE MP2P LSP隧道将有S（PE）-1个入口和一个出口，并且将有S（PE）这样的隧道。
Note that there still remain 2*(S(PE) - 1) PE-to-PE P2P LSPs that are carried through these tunnels.
请注意，仍然有2*（S（PE）-1）个PE-to-PE P2P LSP通过这些隧道传输。
Let's consider the number of LSPs handled at each node in the network.
让我们考虑在网络中每个节点处理的LSP数目。
The PEs continue to handle the same number of PE-to-PE P2P LSPs, and must also handle the MP2P LSPs. So:
PEs继续处理相同数量的PE-to-PE P2P LSP，并且还必须处理MP2P LSP。因此：
L(PE) = 2*(S(PE) - 1) + S(PE)
L(PE) = 2*(S(PE) - 1) + S(PE)
But all P(n) nodes in the network only handle the MP2P LSP tunnels. Nominally, this means that L(n) = S(PE) for all values of n. This would appear to be a great success with the number of LSPs cut to completely manageable levels.
但是网络中的所有P（n）节点仅处理MP2P LSP隧道。名义上，这意味着对于n的所有值，L（n）=S（PE）。随着LSP数量削减到完全可管理的水平，这似乎是一个巨大的成功。
However, the number of LSPs is not the only issue (although it may have some impact for some of the scaling concerns listed in Section 4). We are more interested in the amount of LSP state that is maintained by an LSR. This reflects the amount of storage required at the LSR, the amount of protocol processing, and the amount of information that needs to be managed.
然而，LSP的数量并不是唯一的问题（尽管它可能会对第4节中列出的一些扩展问题产生一些影响）。我们更感兴趣的是LSR维护的LSP状态的数量。这反映了LSR所需的存储量、协议处理量以及需要管理的信息量。
In fact, we were also interested in this measure of scalability in the earlier sections of this document, but in those cases we could see a direct correlation between the number of LSPs and the amount of LSP state since transit LSPs had two pieces of state information (one on the incoming and one on the outgoing interface), and ingress or egress LSPs had just one piece of state.
事实上，在本文档的前面部分中，我们也对这种可伸缩性度量感兴趣，但在这些情况下，我们可以看到LSP数量和LSP状态量之间的直接相关性，因为transit LSP有两条状态信息（一条在传入接口上，一条在传出接口上），入口或出口LSP只有一个状态。
We can quantify the amount of LSP state according to the number of LSP segments managed by an LSR. So (as above), in the case of a P2P LSP, an ingress or egress has one segment to maintain, while a transit has two segments. Similarly, for an MP2P LSP, an LSR must maintain one set of state information for each upstream segment (which, we can assume, is in a one-to-one relationship with the number of upstream neighbors) and exactly one downstream segment -- ingresses obviously have no upstream neighbors, and egresses have no downstream segments.
我们可以根据LSR管理的LSP段的数量来量化LSP状态的数量。因此（如上所述），在P2P LSP的情况下，入口或出口有一个要维护的段，而传输有两个段。类似地，对于MP2P LSP，LSR必须为每个上游段维护一组状态信息（我们可以假设，它与上游邻居的数量成一对一的关系），并且只有一个下游段——入口显然没有上游邻居，出口没有下游段。
So we can start again on our examination of the scaling properties of MP2P LSPs using X(n) to represent the amount of LSP state held at each P(n) node.
因此，我们可以再次开始检查MP2P LSP的缩放特性，使用X（n）表示每个P（n）节点上保持的LSP状态量。
At the PEs, there is only connectivity to one other network node: the P(2) node. But note that if P2P LSPs need to be used to allow disambiguation of data at the MP2P LSP egresses, then these P2P LSPs are tunneled within the MP2P LSPs. So X(PE) is:
在PEs上，只有与另一个网络节点的连接：P（2）节点。但是请注意，如果需要使用P2P LSP来允许在MP2P LSP出口处消除数据歧义，那么这些P2P LSP将在MP2P LSP内进行隧道传输。所以X（PE）是：
X(PE) = 2*(S(PE) - 1) if no disambiguation is required,
X（PE）=2*（S（PE）-1）如果不需要消除歧义，
and
和
X(PE) = 4*(S(PE) - 1) if disambiguation is required.
如果需要消除歧义，则X（PE）=4*（S（PE）-1。
Each P(2) node has M(2) downstream PEs. The P(2) sees a single MP2P LSP targeted at each downstream PE with one downstream segment (to that PE) and M(2) - 1 upstream segments from the other subtended PEs. Additionally, each of these LSPs has an upstream segment from the one upstream P(1). This gives a total of M(2)*(1 + M(2)) LSP segments.
每个P（2）节点有M（2）个下游PEs。P（2）看到单个MP2P LSP针对每个下游PE，具有一个下游段（到该PE）和来自其他子端PE的M（2）-1个上游段。此外，这些lsp中的每一个都具有来自一个上游P（1）的上游段。这给出了总共M（2）*（1+M（2））个LSP段。
There are also LSPs running from the subtended PEs to every other PE in the network. There are S(PE) - M(2) such PEs, and the P(2) sees one upstream segment for each of these from each subtended PE. It also has one downstream segment for each of these LSPs. This gives (M(2) + 1)*(S(PE) - M(2)) LSP segments.
还存在从子终端PE到网络中每一个其他PE的LSP。有S（PE）-M（2）个这样的PE，P（2）从每个子端PE中看到每个PE的一个上游段。每个LSP也有一个下游段。这给出了（M（2）+1）*（S（PE）-M（2））LSP段。
Thus:
因此：
X(2) = M(2)*(1 + M(2)) + (M(2) + 1)*(S(PE) - M(2))
= S(PE)*(M(2) + 1)
X(2) = M(2)*(1 + M(2)) + (M(2) + 1)*(S(PE) - M(2))
= S(PE)*(M(2) + 1)
Similarly, at each P(1) node there are M(1) downstream P(2) nodes and so a total of M(1)*M(2) downstream PEs. Each P(1) is connected in a full mesh with the other P(1) nodes and so has (S(1) - 1) neighbors.
类似地，在每个P（1）节点上有M（1）个下游P（2）节点，因此总共有M（1）*M（2）个下游PEs。每个P（1）与其他P（1）节点在全网格中连接，因此具有（S（1）-1）个邻居。
The P(1) sees a single MP2P LSP targeted at each downstream PE. This has one downstream segment (to the P(2) to which the PE is connected) and M(1) - 1 upstream segments from the other subtended P(2) nodes. Additionally, each of these LSPs has an upstream segment from each of the P(1) neighbors. This gives a total number of LSP segments of M(1)*M(2)*(M(1) + S(1) - 1).
P（1）看到一个针对每个下游PE的MP2P LSP。这有一个下游段（PE连接到的P（2））和来自其他子端P（2）节点的M（1）-1个上游段。此外，这些lsp中的每一个具有来自P（1）个邻居中的每一个的上游段。这给出了M（1）*M（2）*（M（1）+S（1）-1的LSP段总数。
There are also LSPs running from each of the subtended PEs to every
other PE in the network. There are S(PE) - M(1)M(2) such PEs, and
the P(1) sees one upstream segment for each of these from each
There are also LSPs running from each of the subtended PEs to every
other PE in the network. There are S(PE) - M(1)M(2) such PEs, and
the P(1) sees one upstream segment for each of these from each
subtended P(2) (since the aggregation from the subtended PEs has already happened at the P(2) nodes). It also has one downstream segment to the appropriate next hop P(1) neighbor for each of these LSPs. This gives (M(1) + 1)*(S(PE) - M(1)*M(2)) LSP segments.
子端P（2）（因为子端PE的聚合已经在P（2）节点上发生）。对于这些lsp中的每一个，它还具有到适当的下一跳P（1）邻居的一个下游段。这就给出了（M（1）+1）*（S（PE）-M（1）*M（2））LSP段。
Thus:
因此：
X(1) = M(1)*M(2)*(M(1) + S(1) - 1) +
(M(1) + 1)*(S(PE) - M(1)*M(2))
= M(1)*M(2)*(S(1) - 2) + S(PE)*(M(1) + 1)
X(1) = M(1)*M(2)*(M(1) + S(1) - 1) +
(M(1) + 1)*(S(PE) - M(1)*M(2))
= M(1)*M(2)*(S(1) - 2) + S(PE)*(M(1) + 1)
So, for example, with S(1) = 10, M(1) = 10, and M(2) = 10, we see:
例如，S（1）=10，M（1）=10，M（2）=10，我们看到：
S(PE) = 1000
S(2) = 100
X(PE) = 3996 (or 1998)
X(2) = 11000
X(1) = 11800
S(PE) = 1000
S(2) = 100
X(PE) = 3996 (or 1998)
X(2) = 11000
X(1) = 11800
And similarly, with S(1) = 20, M(1) = 20, and M(2) = 5, we see:
同样，当S（1）=20，M（1）=20，M（2）=5时，我们看到：
S(PE) = 2000
S(2) = 400
X(PE) = 5996 (or 2998)
X(2) = 12000
X(1) = 39800
S(PE) = 2000
S(2) = 400
X(PE) = 5996 (or 2998)
X(2) = 12000
X(1) = 39800
For comparison with the examples in Sections 5 and 6, we need to convert those LSP-based figures to our new measure of LSP state.
为了与第5节和第6节中的示例进行比较，我们需要将这些基于LSP的数据转换为我们对LSP状态的新度量。
Observe that each LSP in Sections 5 and 6 generates two state units at a transit LSR and one at an ingress or egress. So we can provide conversions as follows:
注意，第5节和第6节中的每个LSP在运输LSR处生成两个状态单元，在入口或出口处生成一个状态单元。因此，我们可以提供如下转换：
Section 5 (flat snowflake network)
第5节（扁平雪花网络）
L(PE) = 2*(S(PE) - 1)
L(2) = M(2)*(2*S(PE) - M(2) - 1)
L(1) = M(1)*M(2)*(2*S(PE) - M(2)*(M(1) + 1))
X(PE) = 2*(S(PE) - 1)
X(2) = 2*M(2)*(2*S(PE) - M(2) - 1)
X(1) = 2*M(1)*M(2)*(2*S(PE) - M(2)*(M(1) + 1))
L(PE) = 2*(S(PE) - 1)
L(2) = M(2)*(2*S(PE) - M(2) - 1)
L(1) = M(1)*M(2)*(2*S(PE) - M(2)*(M(1) + 1))
X(PE) = 2*(S(PE) - 1)
X(2) = 2*M(2)*(2*S(PE) - M(2) - 1)
X(1) = 2*M(1)*M(2)*(2*S(PE) - M(2)*(M(1) + 1))
For the example with S(1) = 10, M(1) = 10, and M(2) = 10, this gives a comparison table as follows:
对于S（1）=10、M（1）=10和M（2）=10的示例，这给出了如下比较表：
Count | Unmodified | MP2P
------+-------------+----------
X(PE) | 1998 | 3996
X(2) | 39780 | 11000
X(1) | 378000 | 11800
Count | Unmodified | MP2P
------+-------------+----------
X(PE) | 1998 | 3996
X(2) | 39780 | 11000
X(1) | 378000 | 11800
Clearly, this technique is a significant improvement over the flat network within the core of the network, although the PEs are more heavily stressed if disambiguation is required.
显然，与网络核心内的平面网络相比，这种技术是一种显著的改进，尽管如果需要消除歧义，PEs会受到更大的压力。
Section 6.1 (two-layer hierarchy snowflake network)
第6.1节（双层雪花网络）
L(PE) = 2*(S(PE) - 1)
L(2) = M(2)*(2*S(PE) - M(2) - 1) + 2*(S(2) - 1)
L(1) = M(1)*(2*S(2) - M(1) - 1)
X(PE) = 2*(S(PE) - 1)
X(2) = 2*M(2)*(2*S(PE) - M(2) - 1) + 2*(S(2) - 1)
X(1) = 2*M(1)*(2*S(2) - M(1) - 1)
L(PE) = 2*(S(PE) - 1)
L(2) = M(2)*(2*S(PE) - M(2) - 1) + 2*(S(2) - 1)
L(1) = M(1)*(2*S(2) - M(1) - 1)
X(PE) = 2*(S(PE) - 1)
X(2) = 2*M(2)*(2*S(PE) - M(2) - 1) + 2*(S(2) - 1)
X(1) = 2*M(1)*(2*S(2) - M(1) - 1)
Note that in the computation of X(2) the hierarchical LSPs only add one state at each P(2) node.
注意，在X（2）的计算中，分层lsp仅在每个P（2）节点处添加一个状态。
For the same example with S(1) = 10, M(1) = 10, and M(2) = 10, this gives a comparison table as follows:
对于S（1）=10、M（1）=10和M（2）=10的相同示例，这给出了如下比较表：
Count | 2-Layer | MP2P
| Hierarchy |
------+-------------+----------
X(PE) | 1998 | 3996
X(2) | 39978 | 11000
X(1) | 3780 | 11800
Count | 2-Layer | MP2P
| Hierarchy |
------+-------------+----------
X(PE) | 1998 | 3996
X(2) | 39978 | 11000
X(1) | 3780 | 11800
We can observe that the MP2P model is better at P(2), but the hierarchical model is better at P(1).
我们可以观察到，MP2P模型在P（2）时更好，但层次模型在P（1）时更好。
In fact, this comparison can be generalized to observe that the MP2P model produces its best effects toward the edge of the network, while the hierarchical model makes most impression at the core. However, the requirement for disambiguation of P2P LSPs tunneled within the MP2P LSPs does cause a double burden at the PEs.
事实上，这种比较可以概括为观察到MP2P模型在网络边缘产生最佳效果，而分层模型在核心产生最大印象。然而，在MP2P LSP中隧道传输的P2P LSP的消歧要求确实会在PEs造成双重负担。
MP2P LSPs applied just within the ladder will not make a significant difference, but applying MP2P for all LSPs and at all nodes makes a very big difference without requiring any further configuration.
仅在梯形图中应用的MP2P LSP不会产生显著差异，但对所有LSP和所有节点应用MP2P会产生非常大的差异，而无需任何进一步的配置。
LSP state at a spar-node may be divided into those LSPs' segments that enter or leave the spar-node due to subtended PEs (local LSP segments), and those that enter or leave the spar-node due to remote PEs (remote segments).
spar节点处的LSP状态可分为由于子端PEs进入或离开spar节点的LSP段（本地LSP段），以及由于远程PEs进入或离开spar节点的LSP段（远程段）。
The local segments may be counted as:
局部段可计算为：
o E LSPs targeting local PEs o (S(1)-1)*E*M(1) LSPs targeting remote PEs
o E针对本地PE的LSP o（S（1）-1）*E*M（1）针对远程PE的LSP
The remote segments may be counted as:
远程段可计为：
o (S(1)-1)*E outgoing LSPs targeting remote PEs
o <= 3*S(1)*E incoming LSPs targeting any PE (there are precisely
P(1) nodes attached to any other P(1) node)
o (S(1)-1)*E outgoing LSPs targeting remote PEs
o <= 3*S(1)*E incoming LSPs targeting any PE (there are precisely
P(1) nodes attached to any other P(1) node)
Hence, using X(1) as a measure of LSP state rather than a count of LSPs, we get:
因此，使用X（1）作为LSP状态的度量，而不是LSP计数，我们得到：
X(1) <= E + (S(1)-1)*E*M(1) + (S(1)-1)*E + 3*S(1)*E
<= (4 + M(1))*S(1)*E - M(1)*E
X(1) <= E + (S(1)-1)*E*M(1) + (S(1)-1)*E + 3*S(1)*E
<= (4 + M(1))*S(1)*E - M(1)*E
The number of LSPs at the P(2) nodes is also improved. We may also count the LSP state in the same way so that there are:
P（2）节点上的lsp的数量也得到了改进。我们也可以用同样的方法计算LSP状态，以便：
o M(2) LSPs targeting local PEs, o M(2)*(S(1)*E) LSPs from local PEs to all other PEs, and o S(1)*E - M(2) LSPs to remote PEs.
o 针对本地PE的M（2）个LSP，从本地PE到所有其他PE的o M（2）*（S（1）*E）个LSP，以及从远程PE到o S（1）*E-M（2）个LSP。
So using X(2) as a measure of LSP state and not a count of LSPs, we have:
因此，使用X（2）作为LSP状态的度量，而不是LSP计数，我们得到：
X(2) = M(2) + M(2)*(S(1)*E) + S(1)*E - M(2)
= (M(2) + 1)*S(1)*E
X(2) = M(2) + M(2)*(S(1)*E) + S(1)*E - M(2)
= (M(2) + 1)*S(1)*E
Our examples from Section 5.2 give us the following numbers:
第5.2节中的示例给出了以下数字：
With S(1) = 6, M(1) = 10, and M(2) = 17, we see:
当S（1）=6，M（1）=10，M（2）=17时，我们看到：
E = 170
S(PE) = 1020
X(PE) = 2038
X(2) = 18360
X(1) <= 12580
E = 170
S(PE) = 1020
X(PE) = 2038
X(2) = 18360
X(1) <= 12580
Alternatively, with S(1) = 10, M(1) = 10, and M(2) = 20, we see:
或者，当S（1）=10、M（1）=10和M（2）=20时，我们看到：
E = 200
S(PE) = 2000
X(PE) = 3998
X(2) = 42000
X(1) <= 26000
E = 200
S(PE) = 2000
X(PE) = 3998
X(2) = 42000
X(1) <= 26000
The use of MP2P compares very favorably with all scaling scenarios. It is the only technique able to reduce the value of X(2), and it does this by a factor of almost two. The impact on X(1) is better than everything except the three-level hierarchy.
MP2P的使用与所有缩放场景相比都非常有利。这是唯一一种能够减少X（2）值的技术，它可以减少几乎两倍。对X（1）的影响比除三级层次结构之外的所有东西都好。
The following table provides a quick cross-reference for the figures for the example ladder networks. Note that the previous figures are modified to provide counts of LSP state rather than LSP numbers. Again, each LSP contributes one state at its end points and two states at transit nodes.
下表提供了示例梯形图网络图的快速交叉参考。请注意，前面的数字经过修改，以提供LSP状态的计数，而不是LSP编号。同样，每个LSP在其端点提供一个状态，在传输节点提供两个状态。
Thus, for the all cases we have:
因此，对于我们所有的案例：
X(PE) = 2*(S(PE) - 1) or X(PE) = 4*(S(PE) - 1) if disambiguation is required.
如果需要消歧，则X（PE）=2*（S（PE）-1）或X（PE）=4*（S（PE）-1）。
In the unmodified (flat) case, we have:
在未修改（平面）的情况下，我们有：
X(2) = 2*(M(2)*(2*S(PE) - M(2) - 1))
X(1) = 2*(M(1)*M(2)*(2*S(PE) - M(2)*(M(1) + 1)))
X(2) = 2*(M(2)*(2*S(PE) - M(2) - 1))
X(1) = 2*(M(1)*M(2)*(2*S(PE) - M(2)*(M(1) + 1)))
In the two-level hierarchy, we have:
在两级层次结构中，我们有：
X(2) = 2*(2*M(2)*(S(PE) - 1) - M(2)*(M(2) - 1))
X(1) = S(1)*S(1) + 2*S(1) + 4*E*E*(S(1) - 1) - 2*E*M(2) - 2
X(2) = 2*(2*M(2)*(S(PE) - 1) - M(2)*(M(2) - 1))
X(1) = S(1)*S(1) + 2*S(1) + 4*E*E*(S(1) - 1) - 2*E*M(2) - 2
In the three-level hierarchy, we have:
在三级层次结构中，我们有：
X(2) = 2*(2*M(2)*(S(PE) - 1) - M(2)*(M(2) - 1)) + 2*(S(1)*M(1) - 1)
X(1) = S(1)*S(1) + 2*S(1) + 4*M(1)*M(1)*S(1) - 2*M(1)(M(1) + 1) - 2
X(2) = 2*(2*M(2)*(S(PE) - 1) - M(2)*(M(2) - 1)) + 2*(S(1)*M(1) - 1)
X(1) = S(1)*S(1) + 2*S(1) + 4*M(1)*M(1)*S(1) - 2*M(1)(M(1) + 1) - 2
Example A: S(1) = 6, M(1) = 10, and M(2) = 17
Example B: S(1) = 10, M(1) = 10, and M(2) = 20
Example A: S(1) = 6, M(1) = 10, and M(2) = 17
Example B: S(1) = 10, M(1) = 10, and M(2) = 20
Example| Count | Unmodified | 2-Level | 3-Level | MP2P
| | | Hierarchy | Hierarchy |
-------+-------+------------+------------+-------------+-------
A | X(2) | 68748 | 68748 | 68866 | 18360
| X(1) | 1554820 | 572266 | 2226 | 12580
-------+-------+------------+------------+-------------+-------
B | X(2) | 159160 | 159160 | 159358 | 42000
| X(1) | 5032000 | 1433998 | 3898 | 26000
Example| Count | Unmodified | 2-Level | 3-Level | MP2P
| | | Hierarchy | Hierarchy |
-------+-------+------------+------------+-------------+-------
A | X(2) | 68748 | 68748 | 68866 | 18360
| X(1) | 1554820 | 572266 | 2226 | 12580
-------+-------+------------+------------+-------------+-------
B | X(2) | 159160 | 159160 | 159358 | 42000
| X(1) | 5032000 | 1433998 | 3898 | 26000
Recall that in Section 8.3, the true benefit of MP2P was analyzed with respect to the LSP segment state required, rather than the actual number of LSPs. This proved to be a more accurate comparison of the techniques because the MP2P LSPs require state on each branch of the LSP, so the saving is not linear with the reduced number of LSPs.
回想一下，在第8.3节中，MP2P的真正好处是根据所需的LSP段状态而不是LSP的实际数量进行分析的。这被证明是对这些技术更准确的比较，因为MP2P LSP需要LSP的每个分支上的状态，因此节省与LSP数量的减少不是线性的。
A similar analysis could be performed here for the ladder network. The net effect is that it increases the state by an order of two for all transit LSPs in the P2P models, and by a multiplier equal to the degree of a node in the MP2P model.
这里可以对梯形网络进行类似的分析。其净效果是，它将P2P模型中所有中转LSP的状态增加了两个数量级，并将MP2P模型中节点的程度增加了一个乘数。
A rough estimate shows that, as with snowflake networks, MP2P provides better scaling than the one-level hierarchical model and is considerably better at the core. But MP2P compares less will with the two-level hierarchy especially in the core.
粗略估计表明，与雪花网络一样，MP2P提供了比一级层次模型更好的可伸缩性，并且在核心方面也有相当好的表现。但MP2P与两级层次结构相比，意愿更少，尤其是在核心。
The biggest challenges for MP2P LSPs are the provision of support in the control and data planes. To some extent, support must also be provided in the management plane.
MP2P LSP面临的最大挑战是在控制和数据平面提供支持。在某种程度上，还必须在管理层提供支持。
Control plane support is just a matter of defining the protocols and procedures [MP2P-RSVP], although it must be clearly understood that this will introduce some complexity to the control plane.
控制平面支持只是定义协议和过程[MP2P-RSVP]的问题，尽管必须清楚地理解这将给控制平面带来一些复杂性。
Hardware issues may be a little more tricky. For example, the capacity of the upstream segments must never (allowing for statistical over-subscription) exceed the capacity of the downstream segment. Similarly, data planes must be equipped with sufficient buffers to handle incoming packet collisions.
硬件问题可能有点棘手。例如，上游段的容量不得（允许统计超额订阅）超过下游段的容量。类似地，数据平面必须配备足够的缓冲区来处理传入的数据包冲突。
The management plane will be impacted in several ways. Firstly, the management applications will need to handle LSPs with multiple senders. This means that, although the applications need to process fewer LSPs, they will be more complicated and will, in fact, need to
管理层将受到多方面的影响。首先，管理应用程序需要处理具有多个发送方的LSP。这意味着，尽管应用程序需要处理更少的LSP，但它们将更加复杂，并且实际上需要
process the same number of ingresses and egresses. Other issues like diagnostics and OAM would also need to be enhanced to support MP2P, but might be borrowed heavily from LDP networks.
处理相同数量的入口和出口。其他问题，如诊断和OAM，也需要增强以支持MP2P，但可能会大量借鉴LDP网络。
Lastly, note that when the MP2P solution is used, the receiver (the single egress PE of an MP2P tunnel) cannot use the incoming label as an indicator of the source of the data. Contrast this with P2P LSPs. Depending on deployment, this might not be an issue since the PE-PE connectivity may in any case be a tunnel with inner labels to discriminate the data flows.
最后，请注意，当使用MP2P解决方案时，接收器（MP2P隧道的单出口PE）不能使用传入标签作为数据源的指示符。这与P2P LSP形成对比。根据部署情况，这可能不是问题，因为PE-PE连接在任何情况下都可能是带有内部标签的隧道，用于区分数据流。
In other deployments, it may be considered necessary to include additional PE-PE P2P LSPs and tunnel these through the MP2P LSPs. This would require the PEs to support twice as many LSPs. Since PEs are not usually as fully specified as P-routers, this may cause some concern; however, the use of penultimate hop popping on the MP2P LSPs might help to reduce this issue.
在其他部署中，可能认为有必要包括额外的PE-PE P2P LSP，并通过MP2P LSP对其进行隧道传输。这将要求PEs支持两倍于LSP的LSP。由于PEs通常不像P路由器那样完全指定，这可能会引起一些担忧；然而，在MP2P LSP上使用倒数第二跳可能有助于减少此问题。
In all cases, care must be taken not to confuse the reduction in the number of LSPs with a reduction in the LSP state that is required. In fact, the discussion in Section 8.3 is slightly optimistic since LSP state toward the destination will probably need to include sender information and so will increase depending on the number of senders for the MP2P LSP. Section 8.4, on the other hand, counts LSP state rather than LSPs. This issue is clearly dependent on the protocol solution for MP2P RSVP-TE, which is out of scope for this document.
在所有情况下，必须注意不要将LSP数量的减少与所需LSP状态的减少混为一谈。事实上，第8.3节中的讨论有些乐观，因为朝向目的地的LSP状态可能需要包括发送方信息，因此将根据MP2P LSP的发送方数量而增加。另一方面，第8.4节统计LSP状态，而不是LSP。这个问题显然取决于MP2P RSVP-TE的协议解决方案，这超出了本文档的范围。
MPLS Fast Reroute (FRR) [RFC4090] is an attractive scheme for providing rapid local protection from node or link failures. Such a scheme has, however, not been designed for MP2P at the time of writing, so it remains to be seen how practical it could be, especially in the case of the failure of a merge node. Initial examination of this case suggests that FRR would not be a problem for MP2P, given that each flow can be handled separately.
MPLS快速重路由（FRR）[RFC4090]是一种很有吸引力的方案，用于提供针对节点或链路故障的快速本地保护。然而，在撰写本文时，这种方案还没有针对MP2P设计，因此它的实用性还有待观察，尤其是在合并节点出现故障的情况下。对该案例的初步检查表明，鉴于每个流程可以单独处理，FRR对MP2P来说不会是一个问题。
As a final note, observe that the MP2P scenario presented in this document may be optimistic. MP2P LSP merging may be hard to achieve between LSPs with significantly different traffic and Quality of Service (QoS) parameters. Therefore, it may be necessary to increase the number of MP2P LSPs arriving at an egress.
最后，请注意，本文档中呈现的MP2P场景可能是乐观的。MP2P LSP合并可能很难在具有显著不同的流量和服务质量（QoS）参数的LSP之间实现。因此，可能需要增加到达出口的MP2P lsp的数量。
There is nothing to prevent the combination of hierarchical and MP2P solutions within a network.
没有任何东西可以阻止在网络中结合分层和MP2P解决方案。
Note that if MP2P LSPs are tunneled through P2P FA LSPs across the core, none of the benefit of LSP merging is seen for the hops during which the MP2P LSPs are tunneled.
请注意，如果MP2P LSP通过P2P FA LSP在核心上进行隧道传输，则MP2P LSP隧道传输期间的跳数看不到LSP合并的任何好处。
On the other hand, it is possible to construct solutions where MP2P FA LSPs are constructed within the network, resulting in savings from both modes of operation.
另一方面，可以构造在网络内构造MP2P FA lsp的解决方案，从而从两种操作模式中节省成本。
A simple solution to reducing the number of LSP tunnels handled by any node in the network has been proposed. In this solution it is observed that part of the problem is caused purely by the total number of LSP in the network, and that this is a function of the number of PEs since a full mesh of PE-PE LSPs is required. The conclusion of this observation is to move the tunnel end-points further into the network so that, instead of having a full mesh of PE-PE tunnels, we have only a full mesh of P(n)-P(n) tunnels.
提出了一种减少网络中任何节点处理的LSP隧道数量的简单解决方案。在该解决方案中，可以观察到部分问题纯粹由网络中的LSP总数引起，并且这是PE数量的函数，因为需要PE-PE LSP的完整网格。这一观察的结论是将隧道端点进一步移动到网络中，这样，我们就没有PE-PE隧道的完整网格，而只有P（n）-P（n）隧道的完整网格。
Obviously, there is no change in the physical network topology, so the PEs remain subtended to the P(n) nodes, and the consequence is that there is no TE on the links between PEs and P(n) nodes.
显然，物理网络拓扑结构没有变化，因此PEs仍然是P（n）节点的子节点，其结果是PEs和P（n）节点之间的链路上没有TE。
In this case, we have already done the hard work for computing the number of LSPs in the previous sections. The power of the analysis in the earlier sections is demonstrated by its applicability to this new model -- all we need to do is make minor changes to the formulae. This is most simply done by removing a layer from the network. We introduce the term "tunnel end-point" (TEP) and replace the P(n) nodes with TEPs. Thus, the example of a flat snowflake network in Figure 3 becomes as shown in Figure 7. Corresponding changes can be made to all of the sample topologies.
在本例中，我们已经完成了前面章节中计算LSP数量的艰苦工作。前面几节中的分析的威力体现在它对这个新模型的适用性上——我们所需要做的只是对公式做一些小的修改。最简单的方法是从网络中删除一层。我们引入术语“隧道端点”（TEP）并用TEP替换P（n）节点。因此，图3中扁平雪花网络的示例如图7所示。可以对所有样例拓扑进行相应的更改。
PE PE PE PE PE PE
\ \/ \/ /
PE--TEP TEP TEP TEP--PE
\ | | /
\| |/
PE--TEP---P(1)------P(1)---TEP--PE
/ \ / \
PE \ / PE
\/
P(1)
/|\
/ | \
/ | \
PE--TEP TEP TEP--PE
/ /\ \
PE PE PE PE
PE PE PE PE PE PE
\ \/ \/ /
PE--TEP TEP TEP TEP--PE
\ | | /
\| |/
PE--TEP---P(1)------P(1)---TEP--PE
/ \ / \
PE \ / PE
\/
P(1)
/|\
/ | \
/ | \
PE--TEP TEP TEP--PE
/ /\ \
PE PE PE PE
Figure 7 : An Example Snowflake Network with Tunnel End-Points
图7：具有隧道端点的雪花网络示例
To perform the scaling calculations we need only replace the PE counts in the formulae with TEP counts, and observe that there is one fewer layer in the network. For example, in the flat snowflake network shown in Figure 7, we can see that the number of LSPs seen at a TEP is:
要执行缩放计算，我们只需将公式中的PE计数替换为TEP计数，并观察到网络中少了一层。例如，在图7所示的扁平雪花网络中，我们可以看到在TEP上看到的LSP数量为：
L(TEP) = 2*(S(TPE) - 1)
L(TEP) = 2*(S(TPE) - 1)
In our sample networks, S(TPE) is typically of the order of 50 or 100 (the original values of S(2)), so L(TEP) is less than 200, which is quite manageable.
在我们的示例网络中，S（TPE）通常为50或100（S（2）的原始值），因此L（TEP）小于200，这是可以管理的。
Similarly, the number of LSPs handled by a P(1) node can be derived from the original formula for the number of LSPs seen at a P(2) node, since all we have done is reduce n in P(n) from 2 to 1. So our new formula is:
类似地，P（1）节点处理的LSP数量可以从P（2）节点上看到的LSP数量的原始公式中推导出来，因为我们所做的只是将P（n）中的n从2减少到1。因此，我们的新公式是：
L(1) = M(1)*(2*S(TEP) - M(1) - 1)
L(1) = M(1)*(2*S(TEP) - M(1) - 1)
With figures for M(1) = 10 and S(TEP) = 100, this gives us L(1) = 1890. This is also very manageable.
用M（1）=10和S（TEP）=100的数字，我们得到L（1）=1890。这也是非常容易管理的。
On the face of it, this alternate solution seems very attractive. Simply by contracting the edges of the tunnels into the network, we have shown a dramatic reduction in the number of tunnels needed, and there is no requirement to apply any additional scaling techniques.
从表面上看，这种替代解决方案似乎非常有吸引力。仅仅通过将隧道边缘收缩到网络中，我们已经显示出所需隧道数量的大幅减少，并且不需要应用任何额外的缩放技术。
But what of the PE-P(n) links? In the earlier sections of this document, we have assumed that there was some requirement for PE-PE LSPs with TE properties that extended to the PE-P(n) links at both ends of each LSP. That means that there was a requirement to provide reservation-based QoS on those links, to be able to discriminate traffic flows for priority-based treatment, and to be able to distinguish applications and sources that send data based on the LSPs that carry the data.
但PE-P（n）链接是什么？在本文件的前几节中，我们假设对具有TE属性的PE-PE LSP有一些要求，这些PE-PE LSP扩展到每个LSP两端的PE-P（n）链路。这意味着需要在这些链路上提供基于预约的QoS，能够区分基于优先级的处理的流量，并且能够区分基于承载数据的LSP发送数据的应用程序和源。
It might be argued that, since the PE-P(n) links do not offer any routing options (each such link provides the only access to the network for a PE), most of the benefits of tunnels are lost on these peripheral links. However, TE is not just about routing. Just as important are the abilities to make resource reservations, to prioritize traffic, and to discriminate between traffic from different applications, customers, or VPNs.
有人可能会争辩说，由于PE-P（n）链路不提供任何路由选择（每个这样的链路为PE提供对网络的唯一访问），隧道的大部分好处在这些外围链路上丢失。然而，TE不仅仅是路由问题。同样重要的是，能够进行资源预订、确定流量优先级以及区分来自不同应用程序、客户或VPN的流量。
Furthermore, in multihoming scenarios where each PE is connected to more than one P(n) or where a PE has multiple links to a single P(n), there may be a desire to pre-select the link to be used and to direct the traffic to that link using a PE-PE LSP. Note that multihoming has not been considered in this document.
此外，在每个PE连接到多个P（n）或PE具有到单个P（n）的多个链路的多归属场景中，可能希望预先选择要使用的链路，并使用PE-PE LSP将业务定向到该链路。请注意，本文档中未考虑多主定位。
Operationally, P(n)-P(n) LSPs offer the additional management overhead that is seen for hierarchical LSPs described in Section 6. That is, the LSPs have to be configured and established through additional configuration or management operations that are not carried out at the PEs. As described in Section 6, automesh [RFC4972] could be used to ease this task. But it must be noted that, as mentioned above, some of the key uses of tunnels require that traffic is classified and placed in an appropriate tunnel according to its traffic class, end-points, originating application, and customer (such as client VPN). This information may not be readily available for each packet at the P(n) nodes since it is PE-based information. Of course, it is possible to conceive of techniques to make this information available, such as assigning a different label for each class of traffic, but this gives rise to the original problem of larger numbers of LSPs.
在操作上，P（n）-P（n）LSP提供了第6节中描述的分层LSP的额外管理开销。也就是说，必须通过PEs未执行的其他配置或管理操作来配置和建立LSP。如第6节所述，可以使用automesh[RFC4972]简化此任务。但必须注意的是，如上所述，隧道的一些关键用途要求根据流量类别、端点、原始应用程序和客户（如客户端VPN）对流量进行分类并将其放置在适当的隧道中。该信息对于P（n）节点处的每个分组可能不容易获得，因为它是基于PE的信息。当然，可以设想使这些信息可用的技术，例如为每一类流量分配不同的标签，但这会导致LSP数量增加的原始问题。
Our conclusion is, therefore, that this alternate technique may be suitable for the general distribution of traffic based solely on the destination, or on a combination of the destination and key fields carried in the IP header. In this case, it can provide a very satisfactory answer to the scaling issues in an MPLS-TE network. But if more sophisticated packet classification and discrimination is required, this technique will make the desired function hard to
因此，我们的结论是，这种替代技术可能适用于仅基于目的地或基于目的地和IP报头中携带的关键字段的组合的一般流量分布。在这种情况下，它可以为MPLS-TE网络中的扩展问题提供非常令人满意的答案。但是，如果需要更复杂的数据包分类和鉴别，这种技术将使所需的功能难以实现
achieve, and the trade-off between scaling and feature-level will swing too far towards solving the scaling issue at the expense of delivery of function to the customer.
实现，并且扩展和功能级别之间的权衡将过于偏重于以向客户交付功能为代价来解决扩展问题。
The management issues of the models presented in this document have been discussed in-line. No one solution is without its management overhead.
本文件中介绍的模型的管理问题已进行了在线讨论。没有一个解决方案没有它的管理开销。
Note, however, that scalability of management tools is one of the motivators for this work and that network scaling solutions that reduce the active management of LSPs at the cost of additional effort to manage the more static elements of the network represent a benefit. That is, it is worth the additional effort to set up MP2P or FA LSPs if it means that the network can be scaled to a larger size without being constrained by the management tools.
但是，请注意，管理工具的可扩展性是这项工作的动力之一，网络扩展解决方案可以减少LSP的主动管理，但需要付出额外的努力来管理网络中更静态的元素，这是一个好处。也就是说，如果这意味着网络可以扩展到更大的规模而不受管理工具的限制，那么设置MP2P或FA LSP是值得的。
The MP2P technique may prove harder to debug through OAM methods than the FA LSP approach.
MP2P技术可能比FA LSP方法更难通过OAM方法进行调试。
The techniques described in this document use existing or yet-to-be-defined signaling protocol extensions and are subject to the security provided by those extensions. Note that we are talking about tunneling techniques used within the network and that both approaches are vulnerable to the creation of bogus tunnels that deliver data to an egress or consume network resources.
本文档中描述的技术使用现有的或尚未定义的信令协议扩展，并受这些扩展提供的安全性的约束。请注意，我们讨论的是网络中使用的隧道技术，这两种方法都容易受到创建虚假隧道的攻击，这些隧道将数据传送到出口或消耗网络资源。
The fact that the MP2P technique may prove harder to debug through OAM methods than the FA LSP approach is a security concern since it is important to be able to detect misconnections.
MP2P技术可能比FA LSP方法更难通过OAM方法进行调试，这是一个安全问题，因为能够检测错误连接很重要。
General issues of the relationship between scaling and security are covered in Section 1.1, but the details are beyond the scope of this document. Readers are referred to [MPLS-SEC] for details of MPLS security techniques.
第1.1节介绍了伸缩性和安全性之间关系的一般问题，但详细信息超出了本文件的范围。有关MPLS安全技术的详细信息，请参阅[MPLS-SEC]。
The analysis in this document suggests that the ability to signal MP2P MPLS-TE LSPs is a desirable addition to the operator's MPLS-TE toolkit.
本文中的分析表明，向MP2P MPLS-TE LSP发送信号的能力是运营商MPLS-TE工具包的理想补充。
At this stage, no further recommendations are made, but it would be valuable to consult more widely to discover:
在这一阶段，没有提出进一步的建议，但有必要进行更广泛的咨询，以发现：
- The concerns of other service providers with respect to network scalability.
- 其他服务提供商对网络可扩展性的关注。
- More opinions on the realistic constraints to the network parameters listed in Section 4.
- 关于第4节所列网络参数的实际约束的更多意见。
- Desirable values for the cost-effectiveness of the network (parameter K).
- 网络成本效益的理想值（参数K）。
- The applicability, manageability, and support for the two techniques described.
- 描述了这两种技术的适用性、可管理性和支持。
- The feasibility of combining the two techniques, as discussed in Section 9.
- 结合这两种技术的可行性，如第9节所述。
- The level of concern over the loss of functionality that would occur if the alternate solution described in Section 10 was adopted.
- 如果采用第10节中所述的替代解决方案，则会出现功能丧失的关注程度。
The authors are grateful to Jean-Louis Le Roux for discussions and review input. Thanks to Ben Niven-Jenkins, JP Vasseur, Loa Andersson, Anders Gavler, Ben Campbell, and Tim Polk for their comments. Thanks to Dave Allen for useful discussion of the math.
作者感谢Jean-Louis Le Roux的讨论和评论意见。感谢Ben Niven Jenkins、JP Vasseur、Loa Andersson、Anders Gavler、Ben Campbell和Tim Polk的评论。感谢戴夫·艾伦对数学的有益讨论。
[RFC4206] Kompella, K. and Y. Rekhter, "Label Switched Paths (LSP) Hierarchy with Generalized Multi-Protocol Label Switching (GMPLS) Traffic Engineering (TE)", RFC 4206, October 2005.
[RFC4206]Kompella，K.和Y.Rekhter，“具有通用多协议标签交换（GMPLS）流量工程（TE）的标签交换路径（LSP）层次结构”，RFC 4206，2005年10月。
[RFC2961] Berger, L., Gan, D., Swallow, G., Pan, P., Tommasi, F., and S. Molendini, "RSVP Refresh Overhead Reduction Extensions", RFC 2961, April 2001.
[RFC2961]Berger，L.，Gan，D.，Swallow，G.，Pan，P.，Tommasi，F.，和S.Molendini，“RSVP刷新开销减少扩展”，RFC 29612001年4月。
[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V., and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP Tunnels", RFC 3209, December 2001.
[RFC3209]Awduche，D.，Berger，L.，Gan，D.，Li，T.，Srinivasan，V.，和G.Swallow，“RSVP-TE：LSP隧道RSVP的扩展”，RFC 3209，2001年12月。
[RFC3270] Le Faucheur, F., Wu, L., Davie, B., Davari, S., Vaananen, P., Krishnan, R., Cheval, P., and J. Heinanen, "Multi-Protocol Label Switching (MPLS) Support of Differentiated Services", RFC 3270, May 2002.
[RFC3270]Le Faucheur，F.，Wu，L.，Davie，B.，Davari，S.，Vaananen，P.，Krishnan，R.，Cheval，P.，和J.Heinanen，“区分服务的多协议标签交换（MPLS）支持”，RFC 32702002年5月。
[RFC3473] Berger, L., Ed., "Generalized Multi-Protocol Label Switching (GMPLS) Signaling Resource ReserVation Protocol-Traffic Engineering (RSVP-TE) Extensions", RFC 3473, January 2003.
[RFC3473]Berger，L.，Ed.“通用多协议标签交换（GMPLS）信令资源预留协议流量工程（RSVP-TE）扩展”，RFC 3473，2003年1月。
[RFC3985] Bryant, S., Ed., and P. Pate, Ed., "Pseudo Wire Emulation Edge-to-Edge (PWE3) Architecture", RFC 3985, March 2005.
[RFC3985]Bryant，S.，Ed.，和P.Pate，Ed.，“伪线仿真边到边（PWE3）架构”，RFC 39852005年3月。
[RFC4090] Pan, P., Ed., Swallow, G., Ed., and A. Atlas, Ed., "Fast Reroute Extensions to RSVP-TE for LSP Tunnels", RFC 4090, May 2005.
[RFC4090]Pan，P.，Ed.，Swallow，G.，Ed.，和A.Atlas，Ed.，“LSP隧道RSVP-TE快速重路由扩展”，RFC 40902005年5月。
[RFC4110] Callon, R. and M. Suzuki, "A Framework for Layer 3 Provider-Provisioned Virtual Private Networks (PPVPNs)", RFC 4110, July 2005.
[RFC4110]Callon，R.和M.Suzuki，“第3层提供商提供的虚拟专用网络（PPVPN）框架”，RFC 4110，2005年7月。
[RFC4972] Vasseur, JP., Ed., Leroux, JL., Ed., Yasukawa, S., Previdi, S., Psenak, P., and P. Mabbey, "Routing Extensions for Discovery of Multiprotocol (MPLS) Label Switch Router (LSR) Traffic Engineering (TE) Mesh Membership", RFC 4972, July 2007.
[RFC4972]Vasseur，JP.，Ed.，Leroux，JL.，Ed.，Yasukawa，S.，Previdi，S.，Psenak，P.，和P.Mabbey，“发现多协议（MPLS）标签交换路由器（LSR）流量工程（TE）网状成员资格的路由扩展”，RFC 4972，2007年7月。
[RFC5036] Andersson, L., Ed., Minei, I., Ed., and B. Thomas, Ed., "LDP Specification", RFC 5036, October 2007.
[RFC5036]Andersson，L.，Ed.，Minei，I.，Ed.，和B.Thomas，Ed.，“LDP规范”，RFC 5036，2007年10月。
[MP2P-RSVP] Yasukawa, Y., "Supporting Multipoint-to-Point Label Switched Paths in Multiprotocol Label Switching Traffic Engineering", Work in Progress, October 2008.
[MP2P-RSVP]Yasukawa，Y.，“支持多协议标签交换流量工程中的多点到点标签交换路径”，正在进行的工作，2008年10月。
[MPLS-SEC] Fang, L., Ed., "Security Framework for MPLS and GMPLS Networks", Work in Progress, November 2008.
[MPLS-SEC]Fang，L.，Ed.，“MPLS和GMPLS网络的安全框架”，正在进行的工作，2008年11月。
Authors' Addresses
作者地址
Seisho Yasukawa NTT Corporation 9-11, Midori-Cho 3-Chome Musashino-Shi, Tokyo 180-8585 Japan Phone: +81 422 59 4769 EMail: s.yasukawa@hco.ntt.co.jp
日本东京武藏寺3-Chome-Musashino-Shi靖川正雄NTT公司9-11 180-8585电话：+81 422 59 4769电子邮件：s。yasukawa@hco.ntt.co.jp
Adrian Farrel Old Dog Consulting EMail: adrian@olddog.co.uk
Adrian Farrel老狗咨询电子邮件：adrian@olddog.co.uk
Olufemi Komolafe Cisco Systems 96 Commercial Street Edinburgh EH6 6LX United Kingdom EMail: femi@cisco.com
Olufemi Komolafe思科系统96商业街爱丁堡EH6 6LX英国电子邮件：femi@cisco.com