Network Working Group D. Tsiang
Request for Comments: 2892 G. Suwala
Category: Informational Cisco Systems
August 2000
Network Working Group D. Tsiang
Request for Comments: 2892 G. Suwala
Category: Informational Cisco Systems
August 2000
The Cisco SRP MAC Layer Protocol
Cisco SRP MAC层协议
Status of this Memo
本备忘录的状况
This memo provides information for the Internet community. It does not specify an Internet standard of any kind. Distribution of this memo is unlimited.
本备忘录为互联网社区提供信息。它没有规定任何类型的互联网标准。本备忘录的分发不受限制。
Copyright Notice
版权公告
Copyright (C) The Internet Society (2000). All Rights Reserved.
版权所有（C）互联网协会（2000年）。版权所有。
Abstract
摘要
This document specifies the MAC layer protocol, "Spatial Reuse Protocol" (SRP) for use with ring based media. This is a second version of the protocol (V2).
本文档规定了MAC层协议“空间重用协议”（SRP），用于基于环的媒体。这是协议（V2）的第二个版本。
The primary requirements for SRP are as follows:
SRP的主要要求如下：
- Efficient use of bandwidth using: spatial reuse of bandwidth local reuse of bandwidth minimal protocol overhead - Support for priority traffic - Scalability across a large number of nodes or stations attached to a ring - "Plug and play" design without a software based station management transfer (SMT) protocol or ring master negotiation as seen in other ring based MAC protocols [1][2] - Fairness among nodes using the ring - Support for ring based redundancy (error detection, ring wrap, etc.) similar to that found in SONET BLSR specifications. - Independence of physical layer (layer 1) media type.
- 带宽的高效利用利用：带宽的空间复用带宽的本地复用最小的协议开销-支持优先级流量-可扩展性连接到环的大量节点或站点-“即插即用”设计，无需基于软件的站点管理传输（SMT）其他基于环的MAC协议[1][2]中的协议或环主协商-使用环的节点之间的公平性-支持类似于SONET BLSR规范中的基于环的冗余（错误检测、环包装等）。-物理层（第1层）介质类型的独立性。
This document defines the terminology used with SRP, packet formats, the protocol format, protocol operation and associated protocol finite state machines.
本文档定义了SRP、数据包格式、协议格式、协议操作和相关协议有限状态机使用的术语。
Table of Contents
目录
1. Differences between SRP V1 and V2 ....................... 3
2. Terms and Taxonomy ...................................... 4
2.1. Ring Terminology .................................. 4
2.2. Spatial Reuse ..................................... 5
2.3. Fairness .......................................... 6
2.4. Transit Buffer .................................... 7
3. SRP Overview ............................................ 8
3.1. Receive Operation Overview ........................ 8
3.2. Transmit Operation Overview ....................... 8
3.3. SRP Fairness Algorithm (SRP-fa) Overview .......... 9
3.4. Intelligent Protection Switching (IPS) Protocol
Overview .......................................... 9
4. Packet Formats .......................................... 13
4.1. Overall Packet Format ............................. 13
4.2. Generic Packet Header Format ...................... 14
4.2.1. Time To Live (TTL) ......................... 14
4.2.2. Ring Identifier (R) ........................ 15
4.2.3. Priority Field (PRI) ....................... 15
4.2.4. MODE ....................................... 15
4.2.5. Parity Bit (P-bit) ......................... 16
4.2.6. Destination Address ........................ 16
4.2.7. Source Address ............................. 16
4.2.8. Protocol Type .............................. 16
4.3. SRP Cell Format ................................... 16
4.4. SRP Usage Packet Format ........................... 17
4.5. SRP Control Packet Format ......................... 18
4.5.1. Control Ver ................................ 19
4.5.2. Control Type ............................... 19
4.5.3. Control TTL ................................ 19
4.5.4. Control Checksum ........................... 19
4.5.5. Payload .................................... 20
4.5.6. Addressing ................................. 20
4.6. Topology Discovery ................................ 20
4.6.1. Topology Length ............................ 22
4.6.2. Topology Originator ........................ 22
4.6.3. MAC bindings ............................... 22
4.6.4. MAC Type Format ............................ 22
4.7. Intelligent Protection Switching (IPS) ............ 23
4.7.1. Originator MAC Address ..................... 23
4.7.2. IPS Octet .................................. 24
4.8. Circulating packet detection (stripping) .......... 24
5. Packet acceptance and stripping ......................... 25
5.1. Transmission and forwarding with priority ......... 27
5.2. Wrapping of Data .................................. 28
6. SRP-fa Rules Of Operation ............................... 28
6.1. SRP-fa pseudo-code ................................ 30
1. Differences between SRP V1 and V2 ....................... 3
2. Terms and Taxonomy ...................................... 4
2.1. Ring Terminology .................................. 4
2.2. Spatial Reuse ..................................... 5
2.3. Fairness .......................................... 6
2.4. Transit Buffer .................................... 7
3. SRP Overview ............................................ 8
3.1. Receive Operation Overview ........................ 8
3.2. Transmit Operation Overview ....................... 8
3.3. SRP Fairness Algorithm (SRP-fa) Overview .......... 9
3.4. Intelligent Protection Switching (IPS) Protocol
Overview .......................................... 9
4. Packet Formats .......................................... 13
4.1. Overall Packet Format ............................. 13
4.2. Generic Packet Header Format ...................... 14
4.2.1. Time To Live (TTL) ......................... 14
4.2.2. Ring Identifier (R) ........................ 15
4.2.3. Priority Field (PRI) ....................... 15
4.2.4. MODE ....................................... 15
4.2.5. Parity Bit (P-bit) ......................... 16
4.2.6. Destination Address ........................ 16
4.2.7. Source Address ............................. 16
4.2.8. Protocol Type .............................. 16
4.3. SRP Cell Format ................................... 16
4.4. SRP Usage Packet Format ........................... 17
4.5. SRP Control Packet Format ......................... 18
4.5.1. Control Ver ................................ 19
4.5.2. Control Type ............................... 19
4.5.3. Control TTL ................................ 19
4.5.4. Control Checksum ........................... 19
4.5.5. Payload .................................... 20
4.5.6. Addressing ................................. 20
4.6. Topology Discovery ................................ 20
4.6.1. Topology Length ............................ 22
4.6.2. Topology Originator ........................ 22
4.6.3. MAC bindings ............................... 22
4.6.4. MAC Type Format ............................ 22
4.7. Intelligent Protection Switching (IPS) ............ 23
4.7.1. Originator MAC Address ..................... 23
4.7.2. IPS Octet .................................. 24
4.8. Circulating packet detection (stripping) .......... 24
5. Packet acceptance and stripping ......................... 25
5.1. Transmission and forwarding with priority ......... 27
5.2. Wrapping of Data .................................. 28
6. SRP-fa Rules Of Operation ............................... 28
6.1. SRP-fa pseudo-code ................................ 30
6.2. Threshold settings ................................ 32
7. SRP Synchronization ..................................... 32
7.1. SRP Synchronization Examples ...................... 33
8. IPS Protocol Description ................................ 34
8.1. The IPS Request Types ............................. 35
8.2. SRP IPS Protocol States ........................... 36
8.2.1. Idle ....................................... 36
8.2.2. Pass-through ............................... 36
8.2.3. Wrapped .................................... 36
8.3. IPS Protocol Rules ................................ 36
8.3.1. SRP IPS Packet Transfer Mechanism .......... 36
8.3.2. SRP IPS Signaling and Wrapping Mechanism ... 37
8.4. SRP IPS Protocol Rules ............................ 38
8.5. State Transitions ................................. 41
8.6. Failure Examples .................................. 41
8.6.1. Signal Failure - Single Fiber Cut Scenario . 41
8.6.2. Signal Failure - Bidirectional Fiber Cut
Scenario ................................... 43
8.6.3. Failed Node Scenario ....................... 45
8.6.4. Bidirectional Fiber Cut and Node Addition
Scenarios .......................................... 47
9. SRP over SONET/SDH ...................................... 48
10. Pass-thru mode .......................................... 49
11. References .............................................. 50
12. Security Considerations ................................. 50
13. IPR Notice .. ........................................... 50
14. Acknowledgments ......................................... 50
15. Authors' Addresses ...................................... 51
16. Full Copyright Statement ................................ 52
6.2. Threshold settings ................................ 32
7. SRP Synchronization ..................................... 32
7.1. SRP Synchronization Examples ...................... 33
8. IPS Protocol Description ................................ 34
8.1. The IPS Request Types ............................. 35
8.2. SRP IPS Protocol States ........................... 36
8.2.1. Idle ....................................... 36
8.2.2. Pass-through ............................... 36
8.2.3. Wrapped .................................... 36
8.3. IPS Protocol Rules ................................ 36
8.3.1. SRP IPS Packet Transfer Mechanism .......... 36
8.3.2. SRP IPS Signaling and Wrapping Mechanism ... 37
8.4. SRP IPS Protocol Rules ............................ 38
8.5. State Transitions ................................. 41
8.6. Failure Examples .................................. 41
8.6.1. Signal Failure - Single Fiber Cut Scenario . 41
8.6.2. Signal Failure - Bidirectional Fiber Cut
Scenario ................................... 43
8.6.3. Failed Node Scenario ....................... 45
8.6.4. Bidirectional Fiber Cut and Node Addition
Scenarios .......................................... 47
9. SRP over SONET/SDH ...................................... 48
10. Pass-thru mode .......................................... 49
11. References .............................................. 50
12. Security Considerations ................................. 50
13. IPR Notice .. ........................................... 50
14. Acknowledgments ......................................... 50
15. Authors' Addresses ...................................... 51
16. Full Copyright Statement ................................ 52
This document pertains to SRP V2. SRP V1 was a previously published draft specification. The following lists V2 feature differences from V1:
本文件适用于SRP V2。SRP V1是先前发布的规范草案。以下列出了V2与V1的功能差异：
- Reduction of the header format from 4 bytes to 2 bytes.
- 将标头格式从4字节减少到2字节。
- Replacement of the keepalive packet with a new control packet that carries usage information in addition to providing a keepalive function.
- 将keepalive数据包替换为一个新的控制数据包，该控制数据包除了提供keepalive功能外，还携带使用信息。
- Change bit value of inner ring to be 1 and outer to be 0.
- 将内圈的位值更改为1，外圈的位值更改为0。
- Reduction in the number of TTL bits from 11 to 8.
- 将TTL位的数量从11位减少到8位。
- Removal of the DS bit.
- 删除DS位。
- Change ordering of CRC transmission to be most significant octet first (was least significant octet in V1). The SRP CRC is now the same as in [5].
- CRC传输的变化顺序首先是最重要的八位字节（V1中是最不重要的八位字节）。SRP CRC现在与[5]中的相同。
- Addition of the SRP cell mode to carry ATM cells over SRP.
- 添加了SRP信元模式，以便在SRP上承载ATM信元。
- Changes to the SRP-fa to increase the usage field width and to remove the necessity of adding a fixed constant when propagating usage messages.
- 更改SRP fa以增加使用字段宽度，并在传播使用情况消息时消除添加固定常量的必要性。
SRP uses a bidirectional ring. This can be seen as two symmetric counter-rotating rings. Most of the protocol finite state machines (FSMs) are duplicated for the two rings.
SRP使用双向环。这可以看作是两个对称的反向旋转环。大多数协议有限状态机（FSM）是为两个环复制的。
The bidirectional ring allows for ring-wrapping in case of media or station failure, as in FDDI [1] or SONET/SDH [3]. The wrapping is controlled by the Intelligent Protection Switching (IPS) protocol.
双向环允许在媒体或站点出现故障时进行环包装，如FDDI[1]或SONET/SDH[3]中所述。包装由智能保护交换（IPS）协议控制。
To distinguish between the two rings, one is referred to as the "inner" ring, the other the "outer" ring. The SRP protocol operates by sending data traffic in one direction (known as "downstream") and it's corresponding control information in the opposite direction (known as "upstream") on the opposite ring. Figure 1 highlights this graphically.
为了区分这两个环，一个称为“内环”，另一个称为“外环”。SRP协议通过在一个方向（称为“下游”）上发送数据流量，并在相反的环上在相反的方向（称为“上游”）上发送相应的控制信息来运行。图1以图形方式突出显示了这一点。
FIGURE 1. Ring Terminology
图1。环术语
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Spatial Reuse is a concept used in rings to increase the overall aggregate bandwidth of the ring. This is possible because unicast traffic is only passed along ring spans between source and destination nodes rather than the whole ring as in earlier ring based protocols such as token ring and FDDI.
空间重用是环中使用的一个概念，用于增加环的总体聚合带宽。这是可能的，因为单播通信量只在源节点和目标节点之间沿环跨传递，而不是像早期基于环的协议（如令牌环和FDDI）中那样沿整个环传递。
Figure 2 below outlines how spatial reuse works. In this example, node 1 is sending traffic to node 4, node 2 to node 3 and node 5 to node 6. Having the destination node strip unicast data from the ring allows other nodes on the ring who are downstream to have full access to the ring bandwidth. In the example given this means node 5 has full bandwidth access to node 6 while other traffic is being simultaneously transmitted on other parts of the ring.
下面的图2概述了空间重用的工作原理。在此示例中，节点1正在向节点4发送通信量，节点2向节点3发送通信量，节点5向节点6发送通信量。将目标节点从环中剥离单播数据允许环上下游的其他节点完全访问环带宽。在给定的示例中，这意味着节点5对节点6具有全带宽访问，而其他业务正在环的其他部分上同时传输。
Since the ring is a shared media, some sort of access control is necessary to ensure fairness and to bound latency. Access control can be broken into two types which can operate in tandem:
由于环是一个共享介质，因此需要某种访问控制来确保公平性并限制延迟。访问控制可以分为两种类型，它们可以串联运行：
Global access control - controls access so that everyone gets a fair share of the global bandwidth of the ring.
全局访问控制-控制访问，使每个人都能公平地分享环的全局带宽。
Local access control - grants additional access beyond that allocated globally to take advantage of segments of the ring that are less than fully utilized.
本地访问控制-授予超出全局分配的额外访问权限，以利用未充分利用的环段。
As an example of a case where both global and local access are required, refer again to Figure 2. Nodes 1, 2, and 5 will get 1/2 of the bandwidth on a global allocation basis. But from a local perspective, node 5 should be able to get all of the bandwidth since its bandwidth does not interfere with the fair shares of nodes 1 and 2.
作为同时需要全局和本地访问的示例，请再次参考图2。节点1、2和5将在全局分配的基础上获得1/2的带宽。但从本地角度来看，节点5应该能够获得所有带宽，因为其带宽不会干扰节点1和2的公平共享。
FIGURE 2. Global and Local Re-Use
图2。全球和本地再利用
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To be able to detect when to transmit and receive packets from the ring, SRP makes use of a transit (sometimes referred as insertion) buffer as shown in Figure 3 below. High priority packets and low priority packets can be placed into separate fifo queues.
为了能够检测何时从环发送和接收数据包，SRP使用了传输（有时称为插入）缓冲区，如下图3所示。高优先级数据包和低优先级数据包可以放入单独的fifo队列中。
FIGURE 3. Transit buffer
图3。中转缓冲区
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Receive Packets entering a node are copied to the receive buffer if a Destination Address (DA) match is made. If a DA matched packet is also a unicast, then the packet will be stripped. If a packet does not DA match or is a multicast and the packet does not Source Address (SA) match, then the packet is placed into the Transit Buffer (TB) for forwarding to the next node if the packet passes Time To Live and Cyclic Redundancy Check (CRC) tests.
如果目标地址（DA）匹配，则进入节点的接收数据包将复制到接收缓冲区。如果DA匹配的数据包也是单播的，则该数据包将被剥离。如果数据包不匹配DA或是多播，且数据包的源地址（SA）不匹配，则如果数据包通过生存时间和循环冗余校验（CRC）测试，则将数据包放入传输缓冲区（TB）以转发到下一个节点。
Data sent from the node is either forwarded data from the TB or transmit data originating from the node via the Tx Buffer. High priority forwarded data always gets sent first. High priority transmit data may be sent as long as the Low Priority Transit Buffer (LPTB) is not full.
从节点发送的数据要么是来自TB的转发数据，要么是通过Tx缓冲区传输来自节点的数据。高优先级转发的数据总是先发送。只要低优先级传输缓冲区（LPTB）未满，就可以发送高优先级传输数据。
A set of usage counters monitor the rate at which low priority transmit data and forwarded data are sent. Low priority data may be sent as long as the usage counter does not exceed an allowed usage governed by the SRP-fa rules and the LPTB has not exceeded the low priority threshold.
一组使用计数器监控低优先级传输数据和转发数据的发送速率。只要使用计数器不超过SRP fa规则规定的允许使用量，并且LPTB未超过低优先级阈值，就可以发送低优先级数据。
If a node experiences congestion, then it will advertise to upstream nodes via the opposite ring the value of its transmit usage counter. The usage counter is run through a low pass filter function to stabilize the feedback. Upstream nodes will adjust their transmit rates so as not to exceed the advertised values. Nodes also propagate the advertised value received to their immediate upstream neighbor. Nodes receiving advertised values who are also congested propagate the minimum of their transmit usage and the advertised usage.
如果一个节点遇到拥塞，那么它将通过相反的环向上游节点通告其传输使用计数器的值。使用计数器通过低通滤波器功能运行，以稳定反馈。上游节点将调整其传输速率，以便不超过公布的值。节点还将接收到的播发值传播到其直接的上游邻居。接收播发值且拥塞的节点传播其传输使用率和播发使用率的最小值。
Congestion is detected when the depth of the low priority transit buffer reaches a congestion threshold.
当低优先级传输缓冲区的深度达到拥塞阈值时，检测到拥塞。
Usage messages are generated periodically and also act as keepalives informing the upstream station that a valid data link exists.
使用消息定期生成，并充当keepalives，通知上游站点存在有效的数据链路。
An SRP Ring is composed of two counter-rotating, single fiber rings. If an equipment or fiber facility failure is detected, traffic going towards and from the failure direction is wrapped (looped) back to go in the opposite direction on the other ring (subject to the protection hierarchy). The wrap around takes place on the nodes adjacent to the failure, under control of the IPS protocol. The wrap re-routes the traffic away from the failed span.
SRP环由两个反向旋转的单光纤环组成。如果检测到设备或光纤设施故障，则从故障方向进出的通信量将被包裹（循环）回另一个环上的相反方向（取决于保护等级）。在IPS协议的控制下，环绕发生在故障附近的节点上。包裹将重新路由通信量，使其远离故障跨距。
An example of the data paths taken before and after a wrap are shown in Figures 4 and 5. Before the fiber cut, N4 sends to N1 via the path N4->N5->N6->N1.
图4和图5显示了包裹前后的数据路径示例。在光纤切断之前，N4通过路径N4->N5->N6->N1发送到N1。
If there is a fiber cut between N5 and N6, N5 and N6 will wrap the inner ring to the outer ring. After the wraps have been set up, traffic from N4 to N1 initially goes through the non-optimal path N4->N5->N4->N3->N2->N1->N6->N1.
如果N5和N6之间有光纤切割，N5和N6将把内圈包裹到外圈。设置包裹后，从N4到N1的流量最初通过非最佳路径N4->N5->N4->N3->N2->N1->N6->N1。
Subsequently a new ring topology is discovered and a new optimal path is used N4->N3->N2-N1 as shown in Figure 6. Note that the topology discovery and the subsequent optimal path selection are not part of the IPS protocol.
随后发现一个新的环形拓扑，并使用一个新的最优路径N4->N3->N2-N1，如图6所示。请注意，拓扑发现和随后的最佳路径选择不是IPS协议的一部分。
FIGURE 4. Data path before wrap, N4 -> N1
图4。换行前的数据路径，N4->N1
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----- -----
| N | | N |
| 6 | | 2 |
----- -----
^ | ^ |
# | | |
# | | |
# | | |
# | | |
# | | |
# v | v
----- -----
| N | | N |
| 5 | | 3 |
----- -----
# | | |
# | ----- | |
# -------------->| N |--------------- |
#################| 4 |<----------------
-----
-----
################>| N |-----------------
# ---------------| 1 |<-------------- |
# | ----- | |
# | | |
----- -----
| N | | N |
| 6 | | 2 |
----- -----
^ | ^ |
# | | |
# | | |
# | | |
# | | |
# | | |
# v | v
----- -----
| N | | N |
| 5 | | 3 |
----- -----
# | | |
# | ----- | |
# -------------->| N |--------------- |
#################| 4 |<----------------
-----
The ring wrap is controlled through SONET BLSR [3][4] style IPS signaling. It is an objective to perform the wrapping as fast as in the SONET equipment or faster.
环包裹通过SONET BLSR[3][4]样式的IPS信令进行控制。目标是以与SONET设备相同的速度或更快的速度进行包裹。
The IPS protocol processes the following request types (in the order of priority, from highest to lowest):
IPS协议处理以下请求类型（按优先级顺序，从高到低）：
1. Forced Switch (FS): operator originated, performs a protection switch on a requested span (wraps at both ends of the span)
1. 强制开关（FS）：由操作员发起，在请求的量程上执行保护开关（在量程两端缠绕）
2. Signal Fail (SF): automatic, caused by a media Signal Failure or SRP keep-alive failure - performs a protection switch on a requested span
2. 信号故障（SF）：自动，由媒体信号故障或SRP保持活动故障引起-在请求的量程上执行保护开关
FIGURE 5. Data path after the wrap, N4 -> N1
图5。换行后的数据路径，N4->N1
-----
################>| N |-----------------
# ###############| 1 |<############## |
# # ----- # |
# v # |
----- -----
| N | | N |
| 6 | | 2 |
----- -----
^ # wrap ^ |
### # |
_________ # |
fiber cut # |
--------- # |
### # |
# v wrap # v
----- -----
| N | | N |
| 5 | | 3 |
----- -----
# # # |
# # ----- # |
# ##############>| N |############### |
#################| 4 |<----------------
-----
################>| N |-----------------
# ###############| 1 |<############## |
# # ----- # |
# v # |
----- -----
| N | | N |
| 6 | | 2 |
----- -----
^ # wrap ^ |
### # |
_________ # |
fiber cut # |
--------- # |
### # |
# v wrap # v
----- -----
| N | | N |
| 5 | | 3 |
----- -----
# # # |
# # ----- # |
# ##############>| N |############### |
#################| 4 |<----------------
3. Signal Degrade (SD): automatic, caused by a media Signal Degrade (e.g. excessive Bit Error Rate) - performs a protection switch on a requested span
3. 信号降级（SD）：自动，由媒体信号降级（如误码率过高）引起-在请求的范围内执行保护切换
4. Manual Switch (MS): operator originated, like Forced Switched but of a lower priority
4. 手动开关（MS）：由操作员发起，与强制开关类似，但优先级较低
5. Wait to Restore (WTR): automatic, entered after the working channel meets the restoration criteria after SF or SD condition disappears. IPS waits WTR period before restoring traffic in order to prevent protection switch oscillations
5. 等待恢复（WTR）：自动，在SF或SD条件消失后，工作通道满足恢复标准后输入。IPS在恢复流量之前等待WTR周期，以防止保护开关振荡
If a protection (either automatic or operator originated) is requested for a given span, the node on which the protection has been requested issues a protection request to the node on the other end of the span using both the short path (over the failed span, as the failure may be unidirectional) and the long path (around the ring).
如果针对给定范围请求保护（自动或操作员发起），则请求保护的节点使用短路径（在故障范围内，因为故障可能是单向的）和长路径（环周围）向范围另一端的节点发出保护请求。
FIGURE 6. Data path after the new topology is discovered
图6。发现新拓扑后的数据路径
-----
-----------------| N |-----------------
| ---------------| 1 |<############## |
| | ----- # |
| v # |
----- -----
| N | | N |
| 6 | | 2 |
----- -----
^ | wrap ^ |
-- # |
_________ # |
fiber cut # |
--------- # |
-- # |
| v wrap # v
----- -----
| N | | N |
| 5 | | 3 |
----- -----
| | # |
| | ----- # |
| -------------->| N |############### |
-----------------| 4 |<----------------
-----
-----
-----------------| N |-----------------
| ---------------| 1 |<############## |
| | ----- # |
| v # |
----- -----
| N | | N |
| 6 | | 2 |
----- -----
^ | wrap ^ |
-- # |
_________ # |
fiber cut # |
--------- # |
-- # |
| v wrap # v
----- -----
| N | | N |
| 5 | | 3 |
----- -----
| | # |
| | ----- # |
| -------------->| N |############### |
-----------------| 4 |<----------------
-----
As the protection requests travel around the ring, the protection hierarchy is applied. If the requested protection switch is of the highest priority e.g. Signal Fail request is of higher priority than the Signal Degrade than this protection switch takes place and the lower priority switches elsewhere in the ring are taken down, as appropriate. If a lower priority request is requested, it is not allowed if a higher priority request is present in the ring. The only exception is multiple SF and FS switches, which can coexist in the ring.
当保护请求在环中传播时，将应用保护层次结构。如果请求的保护开关具有最高优先级，例如，信号故障请求的优先级高于信号降级，则发生此保护开关，并视情况取下环中其他位置的低优先级开关。如果请求较低优先级的请求，则如果环中存在较高优先级的请求，则不允许这样做。唯一的例外是多个SF和FS开关，它们可以在环中共存。
All protection switches are performed bidirectionally (wraps at both ends of a span for both transmit and receive directions, even if a failure is only unidirectional).
所有保护开关都是双向执行的（在传输和接收方向的跨度两端缠绕，即使故障只是单向的）。
This section describes the packet formats used by SRP. Packets can be sent over any point to point link layer (e.g. SONET/SDH, ATM, point to point ETHERNET connections). The maximum transfer unit (MTU) is 9216 octets. The minimum transfer unit for data packets is 55 octets. The maximum limit was designed to accommodate the large IP MTUs of IP over AAL5. SRP also supports ATM cells. ATM cells over SRP are 55 octets. The minimum limit corresponds to ATM cells transported over SRP. The minimum limit does not apply to control packets which may be smaller.
本节介绍SRP使用的数据包格式。数据包可以通过任何点对点链路层（例如SONET/SDH、ATM、点对点以太网连接）发送。最大传输单元（MTU）为9216个八位字节。数据包的最小传输单元为55个八位字节。最大限值旨在容纳AAL5上IP的大型IP MTU。SRP还支持ATM信元。SRP上的ATM信元是55个八位字节。最小限制对应于通过SRP传输的ATM信元。最小限制不适用于可能更小的控制数据包。
These limits include everything listed in Figure 7: but are exclusive of the frame delineation (e.g. for SRP over SONET/SDH, the flags used for frame delineation are not included in the size limits).
这些限制包括图7中列出的所有内容：但不包括帧划分（例如，对于SONET/SDH上的SRP，用于帧划分的标志不包括在大小限制中）。
The following packet and cell formats do not include any layer 1 frame delineation. For SRP over POS, there will be an additional flag that delineates start and end of frame.
以下分组和单元格式不包括任何第1层帧描绘。对于SRP over POS，将有一个额外的标志来描绘帧的开始和结束。
The overall packet format is show below in Figure 7:
整体数据包格式如图7所示：
FIGURE 7. Overall Packet Format
图7。总体数据包格式
---------------------------------
| SRP Header |
---------------------------------
| Dest. Addr. |
---------------------------------
| Source Addr. |
---------------------------------
| Protocol Type |
---------------------------------
| Payload |
| |
| |
| |
---------------------------------
| FCS |
---------------------------------
---------------------------------
| SRP Header |
---------------------------------
| Dest. Addr. |
---------------------------------
| Source Addr. |
---------------------------------
| Protocol Type |
---------------------------------
| Payload |
| |
| |
| |
---------------------------------
| FCS |
---------------------------------
The frame check sequence (FCS) is a 32-bit cyclic redundancy check (CRC) as specified in RFC-1662 and is the same CRC as used in Packet Over SONET (POS - specified in RFC-2615). The generator polynomial is:
帧校验序列（FCS）是RFC-1662中规定的32位循环冗余校验（CRC），与SONET上的数据包（RFC-2615中规定的POS）中使用的CRC相同。生成器多项式为：
CRC-32:
CRC-32：
x32 + x26 + x23 + x22 + x16 + x12 + x11 + x10 + x8 + x7 + x5 + x4 +
x2 + x + 1
x32 + x26 + x23 + x22 + x16 + x12 + x11 + x10 + x8 + x7 + x5 + x4 +
x2 + x + 1
The FCS is computed over the destination address, source address, protocol type and payload. It does not include the SRP header.
FCS根据目标地址、源地址、协议类型和有效载荷进行计算。它不包括SRP标头。
Note that the packet format after the SRP header is identical to Ethernet Version 2.
请注意，SRP报头之后的数据包格式与以太网版本2相同。
Each packet has a fixed-sized header. The packet header format is shown in Figure 8.
每个数据包都有一个固定大小的报头。包头格式如图8所示。
FIGURE 8. Detailed Packet Header Format
图8。详细数据包头格式
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Time to Live |R| MOD | PRI |P| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Destination Address |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Source Address +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | Protocol Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| Payload |
. .
. .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Time to Live |R| MOD | PRI |P| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Destination Address |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Source Address +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | Protocol Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| Payload |
. .
. .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The fields are described below.
这些字段描述如下。
This 8 bit field is a hop-count that must be decremented every time a node forwards a packet. If the TTL reaches zero it is stripped off the ring. This allows for a total node space of 256 nodes on a ring. However, due to certain failure conditions (e.g. when the ring is
此8位字段是一个跳数，每次节点转发数据包时，该跳数必须递减。如果TTL达到零，则从环上剥离。这允许环上的总节点空间为256个节点。但是，由于某些故障条件（例如，当环
wrapped) the total number of nodes that are supported by SRP is 128. When a packet is first sent onto the ring the TTL should be set to at least twice the total number of nodes on the ring.
包装）SRP支持的节点总数为128。当数据包第一次发送到环上时，TTL应设置为环上节点总数的至少两倍。
This single bit field is used to identify which ring this packet is designated for. The designation is as follows:
此单位字段用于标识此数据包指定用于哪个环。名称如下：
TABLE 1. Ring Indicator Values
表1。环形指示器值
Outer Ring 0 Inner Ring 1
外圈0内圈1
This three bit field indicates the priority level of the SRP packet (0 through 7). The higher the value the higher the priority. Since there are only two queues in the transit buffer (HPTB and LPTB) a packet is treated as either low or high priority once it is on the ring. Each node determines the threshold value for determining what is considered a high priority packet and what is considered a low priority packet. However, the full 8 levels of priority in the SRP header can be used prior to transmission onto the ring (transmit queues) as well as after reception from the ring (receive queues).
此三位字段表示SRP数据包的优先级（0到7）。值越高，优先级越高。由于传输缓冲区中只有两个队列（HPTB和LPTB），因此数据包在环上时将被视为低优先级或高优先级。每个节点确定用于确定什么被认为是高优先级分组和什么被认为是低优先级分组的阈值。但是，SRP报头中的全部8级优先级可在传输到环之前（传输队列）以及从环接收之后（接收队列）使用。
This three bit field is used to identify the mode of the packet. The following modes are defined in Table 2 below.
此三位字段用于标识数据包的模式。下表2中定义了以下模式。
TABLE 2. MODE Values
表2。模式值
Value Description
值描述
000 Reserved 001 Reserved 010 Reserved 011 ATM cell 100 Control Message (Pass to host) 101 Control Message (Locally Buffered for host) 110 Usage Message 111 Packet Data
000保留001保留010保留011 ATM信元100控制消息（传递到主机）101控制消息（为主机本地缓冲）110使用消息111数据包
These modes will be further explained in later sections.
这些模式将在后面的章节中进一步解释。
The parity bit is used to indicate the parity value over the 15 bits of the SRP header to provide additional data integrity over the header. Odd parity is used (i.e. the number of ones including the parity bit shall be an odd number).
奇偶校验位用于指示SRP报头15位上的奇偶校验值，以在报头上提供额外的数据完整性。使用奇数奇偶校验（即包括奇偶校验位的奇数）。
The destination address is a globally unique 48 bit address assigned by the IEEE.
目标地址是IEEE分配的全局唯一48位地址。
The source address is a globally unique 48 bit address assigned by the IEEE.
源地址是IEEE分配的全局唯一48位地址。
The protocol type is a two octet field like that used in EtherType representation. Current defined values relevant to SRP are defined in Table 3 below.
协议类型是一个两个八位字节的字段，类似于EtherType表示中使用的字段。与SRP相关的当前定义值见下表3。
TABLE 3. Defined Protocol Types
表3。定义的协议类型
Value Protocol Type
值协议类型
0x2007 SRP Control 0x0800 IP version 4 0x0806 ARP
0x2007 SRP控制0x0800 IP版本4 0x0806 ARP
SRP also supports the sending of ATM cells. The detailed cell format is shown below:
SRP还支持发送ATM信元。详细的单元格格式如下所示：
FIGURE 9. SRP Cell Format
图9。SRP单元格式
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Time to Live |R| MOD | PRI |P| VPI/VCI |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| VCI | PTI |C| HEC | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
| |
. .
. ATM Payload .
. ( 48 Bytes ) +-+-+-+-+-+-+-+-+
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Time to Live |R| MOD | PRI |P| VPI/VCI |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| VCI | PTI |C| HEC | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
| |
. .
. ATM Payload .
. ( 48 Bytes ) +-+-+-+-+-+-+-+-+
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Packet nodes would typically ignore (never receive or strip) and always forward ATM-cells. The idea is that ATM switches and routers could coexist in a ring. Note that SRP cells do not contain an FCS. Data integrity is handled at the AAL layer.
数据包节点通常会忽略（从不接收或剥离）并始终转发ATM信元。这个想法是ATM交换机和路由器可以在一个环中共存。请注意，SRP单元不包含FCS。数据完整性在AAL层处理。
SRP usage packets are sent out periodically to propagate allowed usage information to upstream nodes. SRP usage packets also perform a keepalive function. SRP usage packets should be sent approximately every 106 usec.
定期发送SRP使用数据包，将允许的使用信息传播到上游节点。SRP使用数据包还执行keepalive功能。SRP使用数据包应大约每106 usec发送一次。
If a receive interface has not seen a usage packet within the keepalive timeout interval it will trigger an L2 keepalive timeout interrupt/event. The IPS software will subsequently mark that interface as faulty and initiate a protection switch around that interface. The keepalive timeout interval should be set to 16 times the SRP usage packet transmission interval.
如果接收接口在keepalive超时间隔内未看到使用数据包，它将触发L2 keepalive超时中断/事件。IPS软件随后将该接口标记为故障，并启动该接口周围的保护开关。keepalive超时间隔应设置为SRP使用数据包传输间隔的16倍。
FIGURE 10. Usage Packet Format
图10。使用数据包格式
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Time to Live |R| MOD | PRI |P| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Originator MAC Address +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Usage |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Time to Live |R| MOD | PRI |P| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Originator MAC Address +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Usage |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
A USAGE of all ones indicates a value of NULL.
使用all ones表示值为NULL。
If the MODE bits are set to 10X (SRP control) then this indicates a control message. Control messages are always received and stripped by the adjacent node. They are by definition unicast, and do not need any addressing information. The destination address field for control packets should be set to 0's. The source address field for a control packet should be set to the source address of the transmitting node.
如果模式位设置为10X（SRP控制），则表示控制消息。控制消息总是由相邻节点接收和剥离。根据定义，它们是单播的，不需要任何寻址信息。控制数据包的目标地址字段应设置为0。控制包的源地址字段应设置为发送节点的源地址。
Two types of controls messages are defined : Pass to host and Locally buffered. Pass to host messages can be passed to the host software by whatever means is convenient. This is most often the same path used to transfer data packets to the host. Locally buffered control messages are usually reserved for protection messages. These are normally buffered locally in order to not contend for resources with data packets. The actual method of handling these messages is up to the implementor.
定义了两种类型的控件消息：传递到主机和本地缓冲。传递到主机消息可以通过任何方便的方式传递到主机软件。这通常是用于将数据包传输到主机的相同路径。本地缓冲控制消息通常保留用于保护消息。这些数据包通常在本地缓冲，以避免与数据包争夺资源。处理这些消息的实际方法取决于实现者。
The control packet format is shown in Figure 11.
控制包格式如图11所示。
FIGURE 11. Control Packet Format
图11。控制包格式
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Time to Live |R| MOD | PRI |P| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Destination Address |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Source Address +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | Protocol Type = 0x2007 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Control Ver | Control Type | Control Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Control TTL | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
. .
. Payload .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Time to Live |R| MOD | PRI |P| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Destination Address |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Source Address +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | Protocol Type = 0x2007 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Control Ver | Control Type | Control Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Control TTL | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
. .
. Payload .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The priority (PRI) value should be set to 0x7 (all one's) when sending control packets and should be queued to the highest priority transmit queue available. The Time to Live is not relevant since all
发送控制数据包时，优先级（PRI）值应设置为0x7（所有人），并应排队到可用的最高优先级传输队列。生活的时间并不重要，因为
packets will be received and stripped by the nearest downstream neighbor and can be set to any value (preferably this should be set to 001).
数据包将由最近的下游邻居接收和剥离，并且可以设置为任何值（最好设置为001）。
This one octet field is the version number associated with the control type field. Initially, all control types will be version 0.
此八位字节字段是与控件类型字段关联的版本号。最初，所有控件类型都将是版本0。
This one octet field represents the control message type. Table 4 contains the currently defined control types.
此八位字节字段表示控制消息类型。表4包含当前定义的控件类型。
TABLE 4. Control Types
表4。控制类型
Control Type Description
控件类型说明
0x01 Topology Discovery
0x01拓扑发现
0x02 IPS message
0x02 IPS消息
0x03- 0xFF Reserved
0x03-0xFF保留
The Control TTL is a control layer hop-count that must be decremented every time a node forwards a control packet. If a node receives a control packet with a control TTL <= 1, then it should accept the packet but not forward it.
控制TTL是一个控制层跳数，每次节点转发控制数据包时都必须减少该跳数。如果节点接收到控制TTL<=1的控制数据包，那么它应该接受该数据包，但不转发它。
Note that the control layer hop count is separate from the SRP L2 TTL which is always set to 1 for control messages.
请注意，控制层跃点计数与SRP L2 TTL是分开的，SRP L2 TTL对于控制消息总是设置为1。
The originator of the control message should set the initial value of the control TTL to the SRP L2 TTL normally used for data packets.
控制消息的发起人应将控制TTL的初始值设置为通常用于数据包的SRP L2 TTL。
The checksum field is the 16 bit one's complement of the one's complement sum of all 16 bit words starting with the control version. If there are an odd number of octets to be checksummed, the last octet is padded on the right with zeros to form a 16 bit word for checksum purposes. The pad is not transmitted as part of the segment. While computing the checksum, the checksum field itself is replaced with zeros. This is the same checksum algorithm as that used for TCP. The checksum does not cover the 32 bit SRP FCS.
校验和字段是从控制版本开始的所有16位字的补码和中的16位一的补码。如果要进行校验和的八位字节数为奇数，则最后一个八位字节在右侧用零填充，以形成一个16位字，用于校验和。pad不作为段的一部分传输。计算校验和时，校验和字段本身被替换为零。这与TCP使用的校验和算法相同。校验和不包括32位SRP FCS。
The payload is a variable length field dependent on the control type.
有效负载是一个可变长度字段，取决于控制类型。
All nodes must have a globally unique IEEE 48 bit MAC address. A multicast bit is defined using canonical addressing conventions i.e. the multicast bit is the least significant bit of the most significant octet in the destination address. It is acceptable but not advisable to change a node's MAC address to one that is known to be unique within the administrative layer 2 domain (that is the SRP ring itself along with any networks connected to the SRP ring via a layer 2 transparent bridge).
所有节点必须具有全局唯一的IEEE 48位MAC地址。使用规范寻址约定定义多播位，即多播位是目标地址中最高有效八位字节的最低有效位。可以接受但不建议将节点的MAC地址更改为已知在管理层2域内唯一的地址（即SRP环本身以及通过层2透明网桥连接到SRP环的任何网络）。
FIGURE 12. Multicast bit position
图12。多播比特位置
Destination Address
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |M| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
^
|----Multicast bit
Destination Address
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |M| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
^
|----Multicast bit
Note that for SONET media, the network order is MSB of each octet first, so that as viewed on the line, the multicast bit will be the 8th bit of the destination address sent. (For SRP on Ethernet media, the multicast bit would be sent first).
请注意，对于SONET媒体，网络顺序首先是每个八位字节的MSB，因此从线路上看，多播位将是发送的目标地址的第8位。（对于以太网介质上的SRP，将首先发送多播位）。
Each node performs topology discovery by sending out topology discovery packets on one or both rings. The node originating a topology packet marks the packet with the egressing ring id, appends the node's mac binding to the packet and sets the length field in the packet before sending out the packet. This packet is a point-to-point packet which hops around the ring from node to node. Each node appends its mac address binding, updates the length field and sends it to the next hop on the ring. If there is a wrap on the ring, the wrapped node will indicate a wrap when appending its mac binding and wrap the packet. When the topology packets travel on the wrapped section with the ring identifier being different from that of the topology packet itself, the mac address bindings are not added to the packet.
每个节点通过在一个或两个环上发送拓扑发现数据包来执行拓扑发现。发起拓扑分组的节点用出口环id标记分组，将节点的mac绑定附加到分组，并在发送分组之前在分组中设置长度字段。此数据包是一个点对点数据包，在环上从一个节点跳到另一个节点。每个节点附加其mac地址绑定，更新长度字段并将其发送到环上的下一跳。如果环上有包裹，则包裹的节点在附加其mac绑定并包裹数据包时将指示包裹。当拓扑数据包在包装部分上传输，且环标识符不同于拓扑数据包本身的环标识符时，mac地址绑定不会添加到数据包中。
Eventually the node that generated the topology discovery packet gets back the packet. The node makes sure that the packet has the same ingress and egress ring id before excepting the packet. A topology map is changed only after receiving two topology packets which indicate the same new topology (to prevent topology changes on transient conditions).
最终，生成拓扑发现数据包的节点返回数据包。节点在排除数据包之前，确保数据包具有相同的入口和出口环id。只有在接收到指示相同新拓扑的两个拓扑数据包后，才会更改拓扑图（以防止在瞬态条件下更改拓扑）。
Note that the topology map only contains the reachable nodes. It does not correspond to the failure-free ring in case of wraps and ring segmentations.
请注意，拓扑图仅包含可到达的节点。在缠绕和环分段的情况下，它不对应于无故障环。
FIGURE 13. Topology Packet Format
图13。拓扑数据包格式
Topology
拓扑学
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Time to Live |R| MOD | PRI |P| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Destination Address |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Source Address +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | Protocol Type = 0x2007 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Control Ver=0 | Control Type=1| Control Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Control TTL | Topology Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Originator's Globally Unique |
+ MAC Address (48 bits) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | MAC Type | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
| MAC Address (48 bits) |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | Other MAC bindings |
+-+-+-+-+-+-+-+-+ +
| |
+ +
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Time to Live |R| MOD | PRI |P| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Destination Address |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Source Address +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | Protocol Type = 0x2007 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Control Ver=0 | Control Type=1| Control Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Control TTL | Topology Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Originator's Globally Unique |
+ MAC Address (48 bits) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | MAC Type | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
| MAC Address (48 bits) |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | Other MAC bindings |
+-+-+-+-+-+-+-+-+ +
| |
+ +
Note that the Source address should be set to the source address of the TRANSMITTING node (which is not necessarily the ORIGINATING node).
注意，源地址应设置为发送节点（不一定是发起节点）的源地址。
This two octet field represents the length of the topology message in octets starting with the first MAC Type/MAC Address binding.
此两个八位字节字段表示拓扑消息的长度，以八位字节为单位，从第一个MAC类型/MAC地址绑定开始。
A topology discovery packet is determined to have been originated by a node if the originator's globally unique MAC address of the packet is that node's globally unique MAC address (assigned by the IEEE).
如果发起方的数据包的全局唯一MAC地址是该节点的全局唯一MAC地址（由IEEE分配），则拓扑发现数据包被确定为由该节点发起。
Because the mac addresses could be changed at a node, the IEEE MAC address ensures that a unique identifier is used to determine that the topology packet has gone around the ring and is to be consumed.
由于mac地址可以在节点上更改，因此IEEE mac地址确保使用唯一标识符来确定拓扑数据包已绕过环并将被使用。
Each MAC binding shall consist of a MAC Type field followed by the node's 48 bit MAC address. The first MAC binding shall be the MAC binding of the originator. Usually the originator's MAC address will be it's globally unique MAC Address but some implementations may allow this value to be overridden by the network administrator.
每个MAC绑定应包括一个MAC类型字段，后跟节点的48位MAC地址。第一个MAC绑定应为发起人的MAC绑定。通常，发起人的MAC地址将是其全局唯一的MAC地址，但某些实现可能允许网络管理员覆盖此值。
This 8 bit field is encoded as follows:
该8位字段编码如下：
TABLE 5. MAC Type Format
表5。MAC类型格式
Bit Value
位值
0 Reserved 1 Ring ID (1 or 0) 2 Wrapped Node (1) / Unwrapped Node (0) 3-7 Reserved
0保留1个环ID（1或0）2个已包装节点（1）/未包装节点（0）3-7保留
Determination of whether a packet's egress and ingress ring ID's are a match should be done by using the Ring ID found in the MAC Type field of the last MAC binding as the ingress ring ID rather than the R bit found in the SRP header. Although they should be the same, it is better to separate the two functions as some implementations may not provide the SRP header to upper layer protocols.
应使用在最后一个MAC绑定的MAC类型字段中找到的环ID作为入口环ID，而不是在SRP报头中找到的R位，来确定数据包的出口环ID和入口环ID是否匹配。尽管它们应该是相同的，但最好将这两个功能分开，因为某些实现可能不向上层协议提供SRP头。
The topology information is not required for the IPS protection mechanism. This information can be used to calculate the number of nodes in the ring as well as to calculate hop distances to nodes to determine the shortest path to a node (since there are two counter-rotating rings).
IPS保护机制不需要拓扑信息。此信息可用于计算环中的节点数，以及计算到节点的跳距，以确定到节点的最短路径（因为有两个反向旋转环）。
The implementation of the topology discovery mechanism could be a periodic activity or on "a need to discover" basis. In the periodic implementation, each node generates the topology packet periodically and uses the cached topology map until it gets a new one. In the need to discover implementation, each node generates a topology discovery packet whenever they need one e.g., on first entering a ring or detecting a wrap.
拓扑发现机制的实现可以是周期性的活动，也可以是“需要发现”的基础。在周期性实现中，每个节点周期性地生成拓扑包，并使用缓存的拓扑图，直到获得新的拓扑图。在需要发现实现中，每个节点在需要时（例如，在第一次进入环或检测到包裹时）生成拓扑发现包。
IPS is a method for automatically recovering from various ring failures and line degradation scenarios. The IPS packet format is outlined in Figure 14 below.
IPS是一种从各种环路故障和线路退化情况中自动恢复的方法。IPS数据包格式如下图14所示。
FIGURE 14. IPS Packet Format
图14。IPS数据包格式
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Time to Live |R| MOD | PRI |P| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Destination Address |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Source Address +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | Protocol Type = 0x2007 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Control Ver=0 | Control Type=2| Control Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Control TTL | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
| Originator MAC Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Ips Octet | Rsvd Octet |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Time to Live |R| MOD | PRI |P| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Destination Address |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Source Address +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | Protocol Type = 0x2007 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Control Ver=0 | Control Type=2| Control Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Control TTL | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
| Originator MAC Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Ips Octet | Rsvd Octet |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The IPS specific fields are detailed below.
IPS特定字段的详细信息如下。
This is the MAC address of the originator of the IPS message. It is not necessarily the same as the SRP Header Source Address as a node may be simply propagating an IPS message (see the section "SRP IPS Protocol Rules" Rule P.8 as an example).
这是IPS消息发起人的MAC地址。它不一定与SRP报头源地址相同，因为节点可能只是传播IPS消息（例如，请参阅“SRP IPS协议规则”规则第P.8节）。
The IPS octet contains specific protection information. The format of the IPS octet is as follows:
IPS八位字节包含特定的保护信息。IPS八位字节的格式如下：
FIGURE 15. IPS Octet Format:
图15。IPS八位字节格式：
Bits Values (values not listed are reserved)
位值（未列出的值保留）
0-3 IPS Request Type
0-3 IPS请求类型
1101 - Forced Switch (FS) 1011 - Signal Fail (SF) 1000 - Signal Degrade (SD) 0110 - Manual Switch (MS) 0101 - Wait to Restore (WTR) 0000 - No Request (IDLE)
1101-强制开关（FS）1011-信号故障（SF）1000-信号降级（SD）0110-手动开关（MS）0101-等待恢复（WTR）0000-无请求（空闲）
4 Path indicator
4路径指示器
0 - short (S) 1 - long (L)
0-短（S）1-长（L）
5-7 Status Code
5-7状态代码
010 - Protection Switch Completed - traffic Wrapped (W) 000 - Idle (I)
010-保护开关完成-流量包裹（W）000-空闲（I）
The currently defined request types with values, hierarchy and interpretation are as used in SONET BLSR [3], [4], except as noted.
当前定义的具有值、层次结构和解释的请求类型与SONET BLSR[3]、[4]中使用的相同，除非另有说明。
Packets continue to circulate when transmitted packets fail to get stripped. Unicast packets are normally stripped by the destination station or by the source station if the destination station has failed. Multicast packets are only stripped by the source station. If both the source and destination stations drop out of the ring while a unicast packet is in flight, or if the source node drops out while its multicast packet is in flight, the packet will rotate around the ring continuously.
当传输的数据包无法剥离时，数据包继续循环。单播数据包通常由目的站剥离，如果目的站出现故障，则由源站剥离。多播数据包仅由源站剥离。如果源站和目的站都在单播数据包飞行时退出环，或者如果源节点在其多播数据包飞行时退出环，则数据包将围绕环连续旋转。
The solution to this problem is to have a TTL or Time To Live field in each packet that is set to at least twice the number of nodes in the ring. As each node forwards the packet, it decrements the TTL. If the TTL reaches zero it is stripped off of the ring.
该问题的解决方案是在每个数据包中设置一个TTL或生存时间字段，该字段至少设置为环中节点数的两倍。当每个节点转发数据包时，它减少TTL。如果TTL达到零，它将从环上剥离。
The ring ID is used to qualify all stripping and receive decisions. This is necessary to handle the case where packets are being wrapped by some node in the ring. The sending node may see its packet on the reverse ring prior to reaching its destination so must not source strip it. The exception is if a node is in wrap. Logically, a node in wrap "sees" the packet on both rings. However the usual implementation is to receive the packet on one ring and to transmit it on the other ring. Therefore, a node that is in the wrap state ignores the ring ID when making stripping and receiving decisions.
环ID用于确认所有剥离和接收决策。这对于处理数据包被环中的某个节点包装的情况是必要的。在到达目的地之前，发送节点可能会在反向环上看到其数据包，因此不能对其进行源剥离。例外情况是节点处于包裹状态。从逻辑上讲，wrap中的节点“看到”两个环上的数据包。然而，通常的实现是在一个环上接收数据包，并在另一个环上传输数据包。因此，处于包裹状态的节点在做出剥离和接收决策时会忽略环ID。
A potential optimization would be to allow ring ID independent destination stripping of unicast packets. One problem with this is that packets may be delivered out of order during a transition to a wrap condition. For this reason, the ring ID should always be used as a qualifier for all strip and receive decisions.
一个潜在的优化是允许单播数据包的独立于环ID的目的地剥离。这样做的一个问题是，在转换到包装条件期间，数据包可能会无序交付。因此，环ID应始终用作所有条带和接收决策的限定符。
A series of decisions based on the type of packet (mode), source and destination addresses are made on the MAC incoming packets. Packets can either be control or data packets. Control packets are stripped once the information is extracted. The source and destination addresses are checked in the case of data packets. The rules for reception and stripping are given below as well as in the flow chart in Figure 16.
基于数据包类型（模式）、源地址和目标地址，对MAC传入数据包进行一系列决策。数据包可以是控制数据包，也可以是数据包。一旦信息被提取，控制包就被剥离。对于数据包，检查源地址和目标地址。下面给出了接收和剥离规则，以及图16中的流程图。
1. Decrement TTL on receipt of a packet, discard if it gets to zero; do not forward.
1. 收到数据包时减少TTL，如果达到零则丢弃；不要转发。
2. Strip unicast packets at the destination station. Accept and strip "control" packets.
2. 在目的站剥离单播数据包。接受并剥离“控制”数据包。
3. Do not process packets other than for TTL and forwarding if they have the "wrong" ring_id for the direction in which they are received unless the node is in wrap. If the node is in wrap then ignore the ring_id.
3. 如果数据包在接收方向上具有“错误”的环_id，则不要处理除TTL和转发以外的数据包，除非节点处于包裹状态。如果节点处于包裹状态，则忽略环id。
4. Do not process packets other than for TTL and forwarding if the mode is not supported by the node (e.g. reserved modes, or ATM cell mode for packet nodes).
4. 如果节点不支持TTL和转发模式（例如，保留模式或数据包节点的ATM信元模式），则不要处理除TTL和转发以外的数据包。
5. Packets accepted by the host because of the destination address should be discarded at the upper level if there is CRC error.
5. 如果存在CRC错误，则主机因目标地址而接受的数据包应在上层丢弃。
6. Control messages are point to point between neighbors and should always be accepted and stripped.
6. 控制消息是邻居之间的点对点消息，应始终被接受和剥离。
7. Packets whose source address is that of the receiving station and whose ring_id matches should be stripped. If a node is in wrap then ignore the ring_id.
7. 源地址为接收站地址且环id匹配的数据包应剥离。如果节点处于包裹状态，则忽略环id。
FIGURE 16. SRP Receive Flowchart (Packet node)
图16。SRP接收流程图（数据包节点）
if (MODE == 4,5)-------------------------------->[to host]--->|
| |
v |
if (MODE == 6)---------------------------------->[strip]----->|
| |
v |
if (!WRAPPED |
& WRONG_RING_ID)-------------------------------------------|--->|
| | |
v | |
if (MODE == 0,1,2,3)------------------------------------------|--->|
| | |
v | |
if (DA MATCH)--------------->if !(SA MATCH)----->[to host]--->| |
| | | |
| v | |
| if (unicast)------->[to host]--->| |
| | | |
| v | |
if (SA MATCH)-------------------->[strip]-------------------->| |
| | |
| | v
|--------------------------->|<-----------------------|----|
| |
v |
if (ttl < 2)------->[strip]----->|
| |
v |
[decrement ttl] |
| |
[fwd pkt to tb] |
| v
|<-----------------------|
v
[back to top]
if (MODE == 4,5)-------------------------------->[to host]--->|
| |
v |
if (MODE == 6)---------------------------------->[strip]----->|
| |
v |
if (!WRAPPED |
& WRONG_RING_ID)-------------------------------------------|--->|
| | |
v | |
if (MODE == 0,1,2,3)------------------------------------------|--->|
| | |
v | |
if (DA MATCH)--------------->if !(SA MATCH)----->[to host]--->| |
| | | |
| v | |
| if (unicast)------->[to host]--->| |
| | | |
| v | |
if (SA MATCH)-------------------->[strip]-------------------->| |
| | |
| | v
|--------------------------->|<-----------------------|----|
| |
v |
if (ttl < 2)------->[strip]----->|
| |
v |
[decrement ttl] |
| |
[fwd pkt to tb] |
| v
|<-----------------------|
v
[back to top]
Notes: Host is responsible for discarding CRC errored packets. Conditionals (if statements) branch to the right if true and branch down if false.
注意：主机负责丢弃CRC错误数据包。条件句（if语句）如果为true则向右分支，如果为false则向下分支。
A node can transmit four types of packets:
节点可以传输四种类型的数据包：
1. High priority packets from the high priority transit buffer.
1. 来自高优先级传输缓冲区的高优先级数据包。
2. Low priority packets from the low priority transit buffer.
2. 来自低优先级传输缓冲区的低优先级数据包。
3. High priority packets from the host Tx high priority fifo.
3. 来自主机Tx的高优先级数据包高优先级fifo。
4. Low priority packets from the host Tx low priority fifo.
4. 来自主机Tx低优先级fifo的低优先级数据包。
High priority packets from the transit buffer are always sent first. High priority packets from the host are sent as long as the low priority transit buffer is not full. Low priority packets are sent as long as the transit buffer has not crossed the low priority threshold and the SRP-fa rules allow it (my_usage < allowed_usage). If nothing else can be sent, low priority packets from the low priority transit buffer are sent.
来自传输缓冲区的高优先级数据包始终首先发送。只要低优先级传输缓冲区未满，主机就会发送高优先级数据包。只要传输缓冲区未超过低优先级阈值且SRP fa规则允许（my_usage<allowed_usage），就会发送低优先级数据包。如果不能发送其他内容，则发送来自低优先级传输缓冲区的低优先级数据包。
This decision tree is shown in Figure 17.
该决策树如图17所示。
FIGURE 17. SRP transmit flowchart
图17。发送流程图
if (TB_High has pkt)----------->[send pkt from TB_high]-->|
| |
v |
if (TB_Low full)------------------------------------------|---->|
| | |
v | |
if (Tx_High has pkt)----------->[send pkt from Tx_high]-->| |
| | |
v | |
if (TB_Low > Hi threshold)--------------------------------|---->|
| | |
v | |
if (my_usage >= allowed_usage)----------------------------|---->|
| | |
v | |
if (Tx_Low has pkt)------------>[send pkt from Tx_low]--->| |
| | |
| | v
|<------------------------------------------------|-----|
| |
v |
if (TB_Low has pkt)------------>[send pkt from TB_low]--->|
| v
|<------------------------------------------------|
|
v
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if (TB_High has pkt)----------->[send pkt from TB_high]-->|
| |
v |
if (TB_Low full)------------------------------------------|---->|
| | |
v | |
if (Tx_High has pkt)----------->[send pkt from Tx_high]-->| |
| | |
v | |
if (TB_Low > Hi threshold)--------------------------------|---->|
| | |
v | |
if (my_usage >= allowed_usage)----------------------------|---->|
| | |
v | |
if (Tx_Low has pkt)------------>[send pkt from Tx_low]--->| |
| | |
| | v
|<------------------------------------------------|-----|
| |
v |
if (TB_Low has pkt)------------>[send pkt from TB_low]--->|
| v
|<------------------------------------------------|
|
v
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Notes: Conditionals (if statements) branch to the right if true and branch down if false.
注意：如果条件语句（if语句）为true，则向右分支；如果为false，则向下分支。
Normally, transmitted data is sent on the same ring to the downstream neighbor. However, if a node is in the wrapped state, transmitted data is sent on the opposite ring to the upstream neighbor.
通常，传输的数据在同一个环上发送到下游邻居。但是，如果节点处于包裹状态，则传输的数据将在相反的环上发送到上游邻居。
The SRP-fa governs access to the ring. The SRP-fa only applies to low priority traffic. High priority traffic does not follow SRP-fa rules and may be transmitted at any time as long as there is sufficient transit buffer space.
SRP fa管理对环的访问。SRP fa仅适用于低优先级流量。高优先级流量不遵循SRP fa规则，只要有足够的传输缓冲空间，就可以随时传输。
The SRP-fa requires three counters which control the traffic forwarded and sourced on the SRP ring. The counters are my_usage (tracks the amount of traffic sourced on the ring), forward_rate (amount of traffic forwarded on to the ring from sources other than the host) and allowed_usage (the current maximum transmit usage for that node).
SRP fa需要三个计数器来控制SRP环上转发和来源的流量。计数器是my_使用率（跟踪环上来源的通信量）、forward_rate（从主机以外的来源转发到环上的通信量）和allowed_使用率（该节点的当前最大传输使用量）。
With no congestion all nodes build up allowed usage periodically. Each node can send up to max_usage. Max_usage is a per node parameter than limits the maximum amount of low priority traffic a node can send.
在没有拥塞的情况下，所有节点都会定期建立允许的使用率。每个节点最多可发送最大使用量。Max_usage是一个每个节点的参数，它限制了节点可以发送的低优先级流量的最大数量。
When a node sees congestion it starts to advertise its my_usage which has been low pass filtered (lp_my_usage).
当一个节点发现拥塞时，它会开始公布其已低通过滤的my_使用情况（lp_my_使用情况）。
Congestion is measured by the transit buffer depth crossing a congestion threshold.
通过穿过拥塞阈值的传输缓冲区深度来测量拥塞。
A node that receives a non-null usage message (rcvd_usage) will set its allowed usage to the value advertised. However, if the source of the rcvd_usage is the same node that received it then the rcvd_usage shall be treated as a null value. When comparing the rcvd_usage source address the ring ID of the usage packet must match the receiver's ring ID in order to qualify as a valid compare. The exception is if the receive node is in the wrap state in which case the usage packet's ring ID is ignored.
接收非空用法消息（rcvd_用法）的节点将其允许的用法设置为播发的值。但是，如果rcvd_使用的来源与接收到它的节点相同，则rcvd_使用应视为空值。在比较rcvd_使用源地址时，使用数据包的环ID必须与接收器的环ID匹配，才能作为有效的比较。例外情况是，如果接收节点处于包裹状态，则忽略使用数据包的环ID。
Nodes that are not congested and that receive a non-null rcvd_usage generally propagate rcvd_usage to their upstream neighbor else propagate a null value of usage (all 1's). The exception is when an opportunity for local reuse is detected. Additional spatial reuse (local reuse) is achieved by comparing the forwarded rate (low pass filtered) to allow_usage. If the forwarded rate is less than the allowed usage, then a null value is propagated to the upstream neighbor.
未拥塞且接收非空rcvd_使用的节点通常会将rcvd_使用传播到其上游邻居，否则会传播空使用值（全部为1）。异常情况是检测到本地重用的机会时。额外的空间重用（本地重用）是通过比较转发速率（低通过滤）来实现的，以允许使用。如果转发速率小于允许的使用率，则向上游邻居传播空值。
Nodes that are congested propagate the smaller of lp_my_usage and rcvd_usage.
拥塞的节点传播lp_my_用法和rcvd_用法中较小的一种。
Convergence is dependent upon number of nodes and distance. Simulation has shown simulation convergence within 100 msec for rings of several hundred miles.
收敛取决于节点数和距离。模拟显示，数百英里环的模拟收敛速度在100毫秒以内。
A more precise definition of the fairness algorithm is shown below:
公平算法的更精确定义如下所示：
Variables:
变量：
lo_tb_depth low priority transit buffer depth
lo_tb_深度低优先级传输缓冲区深度
my_usage count of octets transmitted by host lp_my_usage my_usage run through a low pass filter my_usage_ok flag indicating that host is allowed to transmit
主机lp发送的八位字节的my_usage计数my_usage my_usage通过低通过滤器运行my_usage_ok标志指示允许主机发送
allow_usage the fair amount each node is allowed to transmit
allow_usage允许每个节点传输的公平数量
fwd_rate count of octets forwarded from upstream lp_fwd_rate fwd_rate run through a low pass filter
从上游lp_fwd_速率fwd_速率通过低通滤波器转发的八位字节的fwd_速率计数
congested node cannot transmit host traffic without the TB buffer filling beyond its congestion threshold point.
如果TB缓冲区填充超过拥塞阈值点，拥塞节点无法传输主机流量。
rev_usage the usage value passed along to the upstream neighbor
rev_usage传递给上游邻居的使用值
Constants:
常数：
MAX_ALLOWANCE = configurable value for max allowed usage for this node
MAX_allowment=此节点的最大允许使用量的可配置值
DECAY_INTERVAL = 8000 octet times @ OC-12, 32,000 octet times @ OC-48
DECAY_INTERVAL = 8000 octet times @ OC-12, 32,000 octet times @ OC-48
AGECOEFF = 4 // Aging coeff for my_usage and fwd_rate
AGECOEFF = 4 // Aging coeff for my_usage and fwd_rate
LP_FWD = 64 // Low pass filter for fwd_rate
LP_MU = 512 // Low pass filter for my usage
LP_ALLOW = 64 // Low pass filter for allow usage auto increment
LP_FWD = 64 // Low pass filter for fwd_rate
LP_MU = 512 // Low pass filter for my usage
LP_ALLOW = 64 // Low pass filter for allow usage auto increment
NULL_RCVD_INFO = All 1's in rcvd_usage field
NULL\u RCVD\u INFO=RCVD\u用法字段中的所有1
TB_LO_THRESHOLD // TB depth at which no more lo-prio host traffic
// can be sent
TB_LO_THRESHOLD // TB depth at which no more lo-prio host traffic
// can be sent
MAX_LRATE = AGECOEFF * DECAY_INTERVAL = 128,000 for OC-48, 32000 for OC-12
最大速率=年龄系数*衰减间隔=OC-48为128000，OC-12为32000
THESE ARE UPDATED EVERY CLOCK CYCLE:
=====================================
THESE ARE UPDATED EVERY CLOCK CYCLE:
=====================================
my_usage is incremented by 1 for every octet that is transmitted by the host (does not include data transmitted from the Transit Buffer).
主机传输的每个八位字节的my_使用量增加1（不包括从传输缓冲区传输的数据）。
fwd_rate is incremented by 1 for every octet that enters the Transit Buffer
对于进入传输缓冲区的每个八位组，fwd_速率增加1
if ((my_usage < allow_usage) &&
!((lo_tb_depth > 0) && (fwd_rate < my_usage)) &&
(my_usage < MAX_ALLOWANCE))
// true means OK to send host packets
my_usage_ok = true;
if ((my_usage < allow_usage) &&
!((lo_tb_depth > 0) && (fwd_rate < my_usage)) &&
(my_usage < MAX_ALLOWANCE))
// true means OK to send host packets
my_usage_ok = true;
UPDATED WHEN USAGE_PKT IS RECEIVED:
===================================
UPDATED WHEN USAGE_PKT IS RECEIVED:
===================================
if (usage_pkt.SA == my_SA) &&
[(usage_pkt.RI == my_RingID) || (node_state == wrapped)]
rcvd_usage = NULL_RCVD_INFO;
else
rcvd_usage = usage_pkt.usage;
if (usage_pkt.SA == my_SA) &&
[(usage_pkt.RI == my_RingID) || (node_state == wrapped)]
rcvd_usage = NULL_RCVD_INFO;
else
rcvd_usage = usage_pkt.usage;
THE FOLLOWING IS CALCULATED EVERY DECAY_INTERVAL:
==================================================
THE FOLLOWING IS CALCULATED EVERY DECAY_INTERVAL:
==================================================
congested = (lo_tb_depth > TB_LO_THRESHOLD/2)
congested = (lo_tb_depth > TB_LO_THRESHOLD/2)
lp_my_usage = ((LP_MU-1) * lp_my_usage + my_usage) / LP_MU
lp_my_usage = ((LP_MU-1) * lp_my_usage + my_usage) / LP_MU
my_usage is decremented by min(allow_usage/AGECOEFF, my_usage/AGECOEFF)
my_usage is decremented by min(allow_usage/AGECOEFF, my_usage/AGECOEFF)
lp_fwd_rate = ((LP_FWD-1) * lp_fwd_rate + fwd_rate) / LP_FWD
lp_fwd_rate = ((LP_FWD-1) * lp_fwd_rate + fwd_rate) / LP_FWD
fwd_rate is decremented by fwd_rate/AGECOEFF
fwd_比率由fwd_比率/年龄系数递减
(Note: lp values must be calculated prior to decrement of non-lp values).
（注：lp值必须在非lp值递减之前计算）。
if (rcvd_usage != NULL_RCVD_INFO)
allow_usage = rcvd_usage;
else
allow_usage += (MAX_LRATE - allow_usage) / (LP_ALLOW);
if (rcvd_usage != NULL_RCVD_INFO)
allow_usage = rcvd_usage;
else
allow_usage += (MAX_LRATE - allow_usage) / (LP_ALLOW);
if (congested)
{
if (lp_my_usage < rcvd_usage)
rev_usage = lp_my_usage;
else
rev_usage = rcvd_usage;
}
else if ((rcvd_usage != NULL_RCVD_INFO) &&
(lp_fwd_rate > allow_usage)
rev_usage = rcvd_usage;
else
rev_usage = NULL_RCVD_INFO
if (congested)
{
if (lp_my_usage < rcvd_usage)
rev_usage = lp_my_usage;
else
rev_usage = rcvd_usage;
}
else if ((rcvd_usage != NULL_RCVD_INFO) &&
(lp_fwd_rate > allow_usage)
rev_usage = rcvd_usage;
else
rev_usage = NULL_RCVD_INFO
if (rev_usage > MAX_LRATE) rev_usage = NULL_RCVD_INFO;
如果（rev_usage>MAX_LRATE）rev_usage=NULL_RCVD_INFO；
The low priority transit buffer (TB_LO_THRESHOLD) is currently sized to about 4.4 msec or 320 KB at OC12 rates. The TB_HI_THRESHOLD is set to about 870 usec higher than the TB_LO_THRESHOLD or at 458 KB at OC12 rates.
低优先级传输缓冲区（TB_LO_阈值）当前的大小约为4.4毫秒或320 KB（以OC12速率）。TB_HI_阈值设置为比TB_LO_阈值高约870 usec，或在OC12速率下设置为458 KB。
The high priority transit buffer needs to hold 2 to 3 MTUs or about 30KB.
高优先级传输缓冲区需要容纳2到3个MTU或大约30KB。
Each node operates in "free-run" mode. That is, the receive clock is derived from the incoming receive stream while the transmit clock is derived from a local oscillator. This eliminates the need for expensive clock synchronization as required in existing SONET networks. Differences in clock frequency are accommodated by inserting a small amount of idle bandwidth at each nodes output.
每个节点在“自由运行”模式下运行。也就是说，接收时钟从传入接收流导出，而发送时钟从本地振荡器导出。这消除了对现有SONET网络中所需的昂贵时钟同步的需要。通过在每个输出节点插入少量空闲带宽来调节时钟频率的差异。
The clock source for the transmit clock shall be selected to deviate by no more than 20 ppm from the center frequency. The overall outgoing rate of the node shall be rate shaped to accommodate the worst case difference between receive and transmit clocks of adjacent nodes. This works as follows:
发射时钟的时钟源应选择为偏离中心频率不超过20 ppm。节点的整体传出速率应为速率形状，以适应相邻节点的接收和发送时钟之间的最坏情况差异。这项工作如下：
A transit buffer slip count (tb_cnt) keeps track of the amount of octets inserted into the TB minus the amount of octets transmitted and is a positive integer.
传输缓冲区滑动计数（tb_cnt）跟踪插入tb的八位字节数减去传输的八位字节数，是一个正整数。
To account for a startup condition where a packet is being inserted into an empty TB and the node was otherwise idle the tb_cnt is reset if the transmit interface is idle. Idle is defined as no data being sent even though there is opportunity to send (i.e. the transmit interface is not prohibited from transmitting by the physical layer).
为了说明一种启动条件，即数据包正在插入到空TB中，而节点在其他情况下处于空闲状态，如果传输接口处于空闲状态，则重置TB_cnt。空闲被定义为即使有机会发送也不发送数据（即，传输接口不被物理层禁止传输）。
An interval counter defines the sample period over which rate shaping is performed. This number should be sufficiently large to get an accurate rate shaping.
间隔计数器定义执行速率成形的采样周期。该数字应足够大，以获得准确的速率成形。
A token_bucket counter implements the rate shaping and is a signed integer. We increment this counter by one of two fixed values called quantums each sample period. Quantum1 sets the rate at (Line_rate - Delta) where delta is the clock inaccuracy we want to accommodate.
令牌桶计数器实现速率整形，是一个有符号整数。在每个采样周期，我们将这个计数器增加两个固定值之一，称为量子。Quantum1将速率设置为（Line_rate-Delta），其中Delta是我们想要适应的时钟不准确度。
Quantum2 sets the rate at (Line_rate + Delta). If at the beginning of a sample period, tb_cnt >= sync_threshold, then we set the rate to Quantum2. This will allow us to catch up and causes the TB slip count to eventually go < sync_threshold. If tb_cnt is < sync_threshold then we set the rate to Quantum1.
Quantum2将速率设置为（行速率+增量）。如果在采样周期开始时，tb\u cnt>=sync\u threshold，则我们将速率设置为Quantum2。这将使我们能够迎头赶上，并导致结核滑脱计数最终达到<sync_阈值。如果tb_cnt小于sync_阈值，则我们将速率设置为Quantum1。
When the input rate and output rates are exactly equal, the tb_cnt will vary between sync_threshold > tb_cnt >= 0. This will vary for each implementation dependent upon the burst latencies of the design. The sync_threshold value should be set so that for equal transmit and receive clock rates, the transmit data rate is always Line_rate-Delta and will be implementation dependent.
当输入速率和输出速率完全相等时，tb_cnt将在sync_threshold>tb_cnt>=0之间变化。根据设计的突发延迟，每个实现都会有所不同。应设置sync_阈值，以便对于相等的发送和接收时钟速率，发送数据速率始终为Line_rate-Delta，并将取决于实现。
The token_bucket is decremented each time data is transmitted. When token_bucket reaches a value <= 0, a halt_transmit flag is asserted which halts further transmission of data (halting occurs on a packet boundary of course which can cause token_bucket to become a negative number).
每次传输数据时，令牌存储桶都会递减。当token_bucket达到小于等于0的值时，断言暂停发送标志，该标志停止进一步的数据传输（当然，在分组边界上发生暂停，这可能导致token_bucket变为负数）。
Assume an interval of 2^^18 or 262144 clock cycles. A Quantum1 value
must be picked such that the data rate will = (LINE_RATE - DELTA). A
Quantum2 value must be picked and used if the tb_cnt shows that the
incoming rate is greater than the outgoing rate and is = (LINE_RATE +
DELTA). Assume that the source of the incoming and outgoing rate
clocks are +/- 100 ppm.
Assume an interval of 2^^18 or 262144 clock cycles. A Quantum1 value
must be picked such that the data rate will = (LINE_RATE - DELTA). A
Quantum2 value must be picked and used if the tb_cnt shows that the
incoming rate is greater than the outgoing rate and is = (LINE_RATE +
DELTA). Assume that the source of the incoming and outgoing rate
clocks are +/- 100 ppm.
For an OC12c SPE rate of 600 Mbps and a system clock rate of 800 Mbps (16 bits @ 50 Mhz). The system clock rate is the rate at which the system transmits bytes to the framer (in most cases the framer transmit rate is asynchronous from the rate at which the system transfers data to the framer).
对于600 Mbps的OC12c SPE速率和800 Mbps的系统时钟速率（50 Mhz时为16位）。系统时钟速率是系统向成帧器传输字节的速率（在大多数情况下，成帧器传输速率与系统向成帧器传输数据的速率是异步的）。
Quantum1/Interval * 800 Mbps = 600 Mbps(1 - Delta)
Quantum1 = Interval * (600/800) * (1 - Delta)
Quantum1 = Interval * (600/800) * (1 - 1e-4) = 196588
Quantum1/Interval * 800 Mbps = 600 Mbps(1 - Delta)
Quantum1 = Interval * (600/800) * (1 - Delta)
Quantum1 = Interval * (600/800) * (1 - 1e-4) = 196588
Quantum2/Interval * 800 Mbps = 600 Mbps(1 + Delta)
Quantum2 = Interval * (600/800) * (1 + Delta)
Quantum2 = Interval * (600/800) * (1 + 1e-4) = 196628
Quantum2/Interval * 800 Mbps = 600 Mbps(1 + Delta)
Quantum2 = Interval * (600/800) * (1 + Delta)
Quantum2 = Interval * (600/800) * (1 + 1e-4) = 196628
Note: The actual data rate for OC-12c is 599.04 Mbps.
注：OC-12c的实际数据速率为599.04 Mbps。
An SRP ring is composed of two counter-rotating, single fiber rings. If an equipment or fiber facility failure is detected, traffic going towards and from the failure direction is wrapped (looped) back to go in the opposite direction on the other ring. The wrap around takes place on the nodes adjacent to the failure, under software control. This way the traffic is re-routed from the failed span.
SRP环由两个反向旋转的单光纤环组成。如果检测到设备或光纤设施故障，则从故障方向进出的通信量将被包裹（循环）回另一个环上的相反方向。在软件控制下，环绕发生在故障附近的节点上。通过这种方式，流量将从发生故障的范围重新路由。
Nodes communicate between themselves using IPS signaling on both inner and outer ring.
节点之间通过内环和外环上的IPS信令进行通信。
The IPS octet contains specific protection information. The format of the IPS octet is as follows:
IPS八位字节包含特定的保护信息。IPS八位字节的格式如下：
FIGURE 18. IPS Octet format:
图18。IPS八位字节格式：
0-3 IPS Request Type
0-3 IPS请求类型
1101 - Forced Switch (FS) 1011 - Signal Fail (SF) 1000 - Signal Degrade (SD) 0110 - Manual Switch (MS) 0101 - Wait to Restore (WTR) 0000 - No Request (IDLE)
1101-强制开关（FS）1011-信号故障（SF）1000-信号降级（SD）0110-手动开关（MS）0101-等待恢复（WTR）0000-无请求（空闲）
4 Path indicator
4路径指示器
0 - short (S) 1 - long (L)
0-短（S）1-长（L）
5-7 Status Code
5-7状态代码
010 - Protection Switch Completed -traffic Wrapped (W) 000 - Idle (I)
010-保护开关完成-流量包裹（W）000-空闲（I）
The IPS control messages are shown in this document as:
IPS控制消息在本文档中显示为：
{REQUEST_TYPE, SOURCE_ADDRESS, WRAP_STATUS, PATH_INDICATOR}
{请求类型、源地址、包装状态、路径指示符}
The following is a list of the request types, from the highest to the lowest priority. All requests are signaled using IPS control messages.
以下是从最高优先级到最低优先级的请求类型列表。所有请求都使用IPS控制消息发出信号。
1. Forced Switch (FS - operator originated)
1. 强制开关（FS-操作员发起）
This command performs the ring switch from the working channel to the protection, wrapping the traffic on the node at which the command is issued and at the adjacent node to which the command is destined. Used for example to add another node to the ring in a controlled fashion.
此命令执行从工作通道到保护的环切，将发出命令的节点上的通信量和命令发送到的相邻节点上的通信量包裹起来。例如，用于以受控方式将另一个节点添加到环中。
2. Signal Fail (SF - automatic)
2. 信号故障（SF-自动）
Protection caused by a media "hard failure" or SRP keep- alive failure. SONET examples of SF triggers are: Loss of Signal (LOS), Loss of Frame (LOF), Line Bit Error Rate (BER) above a preselected SF threshold, Line Alarm Indication Signal (AIS). Note that the SRP keep-alive failure provides end-to-end coverage and as a result SONET Path triggers are not necessary.
由介质“硬故障”或SRP保持活动故障引起的保护。SF触发器的SONET示例包括：信号丢失（LOS）、帧丢失（LOF）、高于预选SF阈值的线路误码率（BER）、线路报警指示信号（AIS）。请注意，SRP保持活动故障提供端到端覆盖，因此不需要SONET路径触发器。
3. Signal Degrade (SD - automatic)
3. 信号降级（SD-自动）
Protection caused by a media "soft failure". SONET example of a SD is Line BER or Path BER above a preselected SD threshold.
由介质“软故障”引起的保护。SD的SONET示例是高于预选SD阈值的线路BER或路径BER。
4. Manual Switch (MS - operator originated)
4. 手动开关（MS-操作员发起）
Like the FS, but of lower priority. Can be used for example to take down the WTR.
与FS类似，但优先级较低。例如，可用于取下WTR。
5. Wait to Restore (WTR - automatic)
5. 等待恢复（WTR-自动）
Entered after the working channel meets the restoration threshold after an SD or SF condition disappears. IPS waits WTR timeout before restoring traffic in order to prevent protection switch oscillations.
在SD或SF条件消失后，工作通道满足恢复阈值后输入。IPS在恢复流量之前等待WTR超时，以防止保护开关振荡。
Each node in the IPS protocol is in one of the following states for each of the rings:
IPS协议中的每个节点对于每个环都处于以下状态之一：
In this mode the node is ready to perform the protection switches and it sends to both neighboring nodes "idle" IPS messages, which include "self" in the source address field {IDLE, SELF, I, S}
在此模式下，节点准备好执行保护切换，并向两个相邻节点发送“空闲”IPS消息，其中包括源地址字段{idle，self，I，S}中的“self”
Node participates in a protection switch by passing the wrapped traffic and long path signaling through itself. This state is entered based on received IPS messages. If a long path message with not null request is received and if the node does not strip the message (see Protocol Rules for stripping conditions) the node decrements the TTL and retransmits the message without modification. Sending of the Idle messages is stopped in the direction in which the message with not null request is forwarded.
节点通过自身传递包裹的流量和长路径信令来参与保护交换机。此状态是根据收到的IPS消息输入的。如果接收到带有not null请求的长路径消息，并且如果节点未剥离该消息（有关剥离条件，请参阅协议规则），则节点将减少TTL并在不修改的情况下重新传输该消息。在具有not null请求的消息被转发的方向上停止发送空闲消息。
Node participates in a protection switch with a wrap present. This state is entered based on a protection request issued locally or based on received IPS messages.
节点参与一个保护开关，并存在一个包裹。此状态是根据本地发出的保护请求或接收到的IPS消息输入的。
R T.1:
R.T.1：
IPS packets are transferred in a store and forward mode between adjacent nodes (packets do not travel more than 1 hop between nodes at a time). Received packet (payload portion) is passed to software based on interrupts.
IPS数据包在相邻节点之间以存储转发模式传输（数据包在节点之间一次传输不超过1跳）。接收到的数据包（有效负载部分）根据中断传递给软件。
R T.2:
R.T.2：
All IPS messages are sent to the neighboring nodes periodically on both inner and outer rings. The timeout period is configurable 1-600 sec (default 1 sec). It is desirable (but not required) that the timeout is automatically decreased by a factor of 10 for the short path protection requests.
所有IPS消息在内环和外环上定期发送到相邻节点。超时时间可配置为1-600秒（默认为1秒）。对于短路径保护请求，超时自动减少10倍是可取的（但不是必需的）。
R S.1:
R.S.1：
IPS signaling is performed using IPS control packets as defined in Figure 14 "IPS Packet Format".
IPS信令使用图14“IPS数据包格式”中定义的IPS控制数据包执行。
R S.2:
R.S.2：
Node executing a local request signals the protection request on both short (across the failed span) and long (around the ring) paths after performing the wrap.
执行本地请求的节点在执行换行后，在短（跨故障范围）和长（环周围）路径上发出保护请求的信号。
R S.3:
R.S.3：
Node executing a short path protection request signals an idle request with wrapped status on the short (across the failed span) path and a protection request on the long (around the ring) path after performing the wrap.
执行短路径保护请求的节点发出空闲请求的信号，该请求在短（跨故障跨度）路径上具有包裹状态，在执行包裹后在长（环周围）路径上具有保护请求。
R S.4:
R.S.4：
A node which is neither executing a local request nor executing a short path request signals IDLE messages to its neighbors on the ring if there is no long path message passing through the node on that ring.
如果没有长路径消息通过环上的节点，则既不执行本地请求也不执行短路径请求的节点向环上的邻居发送空闲消息信号。
R S.5:
R.S.5：
Protection IPS packets are never wrapped.
保护IP数据包从不被包装。
R S.6:
R.S.6：
If the protocol calls for sending both short and long path requests on the same span (for example if a node has all fibers disconnected), only the short path request should be sent.
如果协议要求在同一跨度上同时发送短路径和长路径请求（例如，如果节点断开了所有光纤），则只应发送短路径请求。
R S.7:
R.S.7：
A node wraps and unwraps only on a local request or on a short path request. A node never wraps or unwraps as a result of a long path request. Long path requests are used only to maintain protection hierarchy. (Since the long path requests do not trigger protection, there is no need for destination addresses and no need for topology maps)
节点仅在本地请求或短路径请求时包装和展开。节点从不因长路径请求而进行包装或展开。长路径请求仅用于维护保护层次结构。（由于长路径请求不会触发保护，因此不需要目标地址和拓扑图）
In Figure 19, Node A detects SF (local request/ self-detected request) on the span between Node A and Node B and starts sourcing {SF, A, W, S} on the outer ring and {SF, A, W, L} on the inner ring. Node B receives the protection request from Node A (short path request) and starts sourcing {IDLE, B, W, S} on the inner ring and {SF, B, W, L} on the outer ring.
在图19中，节点A在节点A和节点B之间的跨度上检测到SF（本地请求/自检测请求），并开始在外圈上寻找{SF，A，W，S}，在内圈上寻找{SF，A，W，L}。节点B接收来自节点A的保护请求（短路径请求），并开始在内环上寻找{IDLE，B，W，S}，在外环上寻找{SF，B，W，L}。
FIGURE 19. SRP IPS Signaling
图19。SRP-IPS信令
{SF,A,W,S}
-------------------------------
| -----X--------------------- |
| | fiber | |
| v cut {IDLE,B,W,S}| v
----- -----
| A | | B |
| | | |
----- -----
^ | {SF,A,W,L} i ^ | o {SF,B,W,L}
| | n | | u
| | n | | t
| | e | | e
| v r | v r
{SF,A,W,S}
-------------------------------
| -----X--------------------- |
| | fiber | |
| v cut {IDLE,B,W,S}| v
----- -----
| A | | B |
| | | |
----- -----
^ | {SF,A,W,L} i ^ | o {SF,B,W,L}
| | n | | u
| | n | | t
| | e | | e
| v r | v r
R P.1:
R.P.1：
Protection Request Hierarchy is as follows (Highest priority to the lowest priority). In general a higher priority request preempts a lower priority request within the ring with exceptions noted as rules. The 4 bit values below correspond to the REQUEST_TYPE field in the IPS packet.
保护请求层次结构如下（最高优先级到最低优先级）。一般来说，较高优先级的请求优先于环内较低优先级的请求，例外情况作为规则记录。下面的4位值对应于IPS数据包中的请求类型字段。
1101 - Forced Switch (FS) 1011 - Signal Fail (SF) 1000 - Signal Degrade (SD) 0110 - Manual Switch (MS) 0101 - Wait to Restore (WTR) 0000 - No Request (IDLE): Lowest priority
1101-强制开关（FS）1011-信号故障（SF）1000-信号降级（SD）0110-手动开关（MS）0101-等待恢复（WTR）0000-无请求（空闲）：最低优先级
R P.2:
R P.2：
Requests >= SF can coexist.
请求>=SF可以共存。
R P.3:
R P.3：
Requests < SF can not coexist with other requests.
小于SF的请求不能与其他请求共存。
R P.4:
R P.4：
A node always honors the highest of {short path request, self detected request} if there is no higher long path message passing through the node.
如果没有更高的长路径消息通过节点，则节点始终接受{short-path request，self-detected request}中的最高值。
R P.5:
R P.5：
When there are more requests of priority < SF, the first request to complete long path signaling will take priority.
当有更多优先级<SF的请求时，完成长路径信令的第一个请求将优先。
R P.6:
R P.6：
A Node never forwards an IPS packet received by it which was originally generated by the node itself (it has the node's source address).
节点从不转发其接收的最初由节点自身生成的IPS数据包（它具有节点的源地址）。
R P.7:
R P.7：
Nodes never forward packets with the PATH_INDICATOR set to SHORT.
当PATH_指示符设置为SHORT时，节点从不转发数据包。
R P.8:
R P.8：
When a node receives a long path request and the request is >= to the highest of {short path request, self detected request}, the node checks the message to determine if the message is coming from its neighbor on the short path. If that is the case then it does not enter pass-thru and it strips the message.
当节点接收到长路径请求且该请求大于等于{short-path request，self-detected request}中的最高值时，节点将检查消息以确定消息是否来自短路径上的邻居。如果是这种情况，那么它不会进入pass-thru，并且会剥离消息。
R P.9:
R P.9：
When a node receives a long path request, it strips (terminates) the request if it is a wrapped node with a request >= than that in the request; otherwise it passes it through and unwraps.
当一个节点接收到一个长路径请求时，如果它是一个请求>=大于请求中的请求的包装节点，它将剥离（终止）该请求；否则，它将穿过并展开。
R P.10:
R P.10：
Each node keeps track of the addresses of the immediate neighbors (the neighbor node address is gleaned from the short path IPS messages).
每个节点跟踪直接邻居的地址（邻居节点地址从短路径IPS消息中收集）。
R P.11:
R P.11：
When a wrapped node (which initially detected the failure) discovers disappearance of the failure, it enters WTR (user-configurable WTR time-period). WTR can be configured in the 10-600 sec range with a default value of 60 sec.
当包装节点（最初检测到故障）发现故障消失时，它将进入WTR（用户可配置的WTR时间段）。WTR可在10-600秒范围内配置，默认值为60秒。
R P.12:
R P.12：
When a node is in WTR mode, and detects that the new neighbor (as identified from the received short path IPS message) is not the same as the old neighbor (stored at the time of wrap initiation), the node drops the WTR.
当节点处于WTR模式，并且检测到新邻居（从接收到的短路径IPS消息中识别）与旧邻居（在包裹启动时存储）不同时，节点丢弃WTR。
R P.13:
R P.13：
When a node is in WTR mode and long path request Source is not equal to the neighbor Id on the opposite side (as stored at the time of wrap initiation), the node drops the WTR.
当节点处于WTR模式且长路径请求源不等于另一侧的邻居Id（在wrap启动时存储）时，节点将丢弃WTR。
R P.14:
R P.14：
When a node receives a local protection request of type SD or SF and it cannot be executed (according to protocol rules) it keeps the request pending. (The request can be kept pending outside of the protection protocol implementation).
当节点收到SD或SF类型的本地保护请求且无法执行（根据协议规则）时，它会将该请求保持挂起状态。（请求可以在保护协议实现之外保持挂起状态）。
R P.15:
R P.15：
If a local non-failure request (WTR, MS, FS) clears and if there are no other requests pending, the node enters idle state.
如果本地非故障请求（WTR、MS、FS）清除，并且没有其他未决请求，则节点进入空闲状态。
R P.16:
R P.16：
If there are two failures and two resulting WTR conditions on a single span, the second WTR to time out brings both the wraps down (after the WTR time expires a node does not unwrap automatically but waits till it receives idle messages from its neighbor on the previously failed span)
如果在一个跨度上有两个故障和两个产生的WTR条件，则第二个等待超时的WTR会同时进行两次换行（在WTR时间到期后，节点不会自动展开，而是等待，直到它从先前发生故障的跨度上的邻居处接收到空闲消息）
R P.17:
R P.17：
If a short path FS request is present on a given side and a SF/SD condition takes place on the same side, accept and process the SF/SD condition ignoring the FS. Without this rule a single ended wrap condition could take place. (Wrap on one end of a span only).
如果给定端存在短路径FS请求，且同一侧发生SF/SD情况，则接受并处理SF/SD情况，忽略FS。如果没有此规则，可能会发生单端包裹情况。（仅在跨度的一端缠绕）。
Figure 20 shows the simplified state transition diagram for the IPS protocol:
图20显示了IPS协议的简化状态转换图：
FIGURE 20. Simplified State Transitions Diagram
图20。简化状态转换图
Local FS,SF,SD,MS req.
--------- or Rx{REQ,SRC,W,S} from mate
| IDLE |-------------------------------------------
| |<---------------------------------------- |
--------- Local REQ clears | |
^ | or Rx{IDLE,SRC,I,S} | |
| | | |
| | | |
| | | |
| | | |
Rx{IDLE,SRC,I,S}| | Rx{REQ,SRC,W,L} | |
| | | |
| | | |
| v Local FS,SF,SD,MS REQ > Active req. | v
--------- or Rx{REQ,SRC,W,S},REQ > Active req. ---------
| PASS |------------------------------------>| WRAPPED |
| THRU |<------------------------------------| |
--------- ---------
Forwards Tx{REQ,SELF,W,S} for local REQ
{REQ,SRC,W,L} Tx{IDLE,SELF,W,S} for mate REQ
& Tx{REQ,SELF,W,L}
Local FS,SF,SD,MS req.
--------- or Rx{REQ,SRC,W,S} from mate
| IDLE |-------------------------------------------
| |<---------------------------------------- |
--------- Local REQ clears | |
^ | or Rx{IDLE,SRC,I,S} | |
| | | |
| | | |
| | | |
| | | |
Rx{IDLE,SRC,I,S}| | Rx{REQ,SRC,W,L} | |
| | | |
| | | |
| v Local FS,SF,SD,MS REQ > Active req. | v
--------- or Rx{REQ,SRC,W,S},REQ > Active req. ---------
| PASS |------------------------------------>| WRAPPED |
| THRU |<------------------------------------| |
--------- ---------
Forwards Tx{REQ,SELF,W,S} for local REQ
{REQ,SRC,W,L} Tx{IDLE,SELF,W,S} for mate REQ
& Tx{REQ,SELF,W,L}
Legend: Mate = node on the other end of the affected span
REQ = {FS | SF | SD | MS}
Legend: Mate = node on the other end of the affected span
REQ = {FS | SF | SD | MS}
Sample scenario in a ring of four nodes A, B, C and D, with unidirectional failure on a fiber from A to B, detected on B. Ring is in the Idle state (all nodes are Idle) prior to failure.
在由四个节点a、B、C和D组成的环中，在B上检测到从a到B的光纤发生单向故障的示例场景。环在故障前处于空闲状态（所有节点都处于空闲状态）。
Signal Fail Scenario
信号失败场景
1. Ring in Idle, all nodes transmit (Tx) {IDLE, SELF, I, S} on both rings (in both directions)
1. 在空闲环中，所有节点在两个环上传输（Tx）{Idle，SELF，I，S}（在两个方向上）
FIGURE 21. An SRP Ring with outer ring fiber cut
图21。带外环光纤切割的SRP环
fiber cut
---------X-----------------------------
| ----------------------------------- |
| | | |
| v | v
----- -----
| A | | B |
| | | |
----- -----
^ | ^ |
o | | i | |
u | | n | |
t | | n | |
e | | e | |
r | | r | |
| v | v
----- -----
| D | | C |
| | | |
----- -----
| | | |
| | | |
| ----------------------------------- |
---------------------------------------
fiber cut
---------X-----------------------------
| ----------------------------------- |
| | | |
| v | v
----- -----
| A | | B |
| | | |
----- -----
^ | ^ |
o | | i | |
u | | n | |
t | | n | |
e | | e | |
r | | r | |
| v | v
----- -----
| D | | C |
| | | |
----- -----
| | | |
| | | |
| ----------------------------------- |
---------------------------------------
2. B detects SF on the outer ring, transitions to Wrapped state (performs a wrap), Tx towards A on the inner ring/short path: {SF, B, W, S} and on the outer ring/long path: Tx {SF, B, W, L}
2. B检测外环上的SF，转换到包裹状态（执行包裹），Tx在内环/短路径：{SF，B，W，S}上朝向a，在外环/长路径：Tx{SF，B，W，L}
3. Node A receives protection request on the short path, transitions to Wrapped state, Tx towards B on short path: {IDLE, A, W, S} (message does not go through due to the failure) and on the long path: Tx {SF, A, W, L}
3. 节点A在短路径上接收保护请求，转换为包裹状态，在短路径上向B发送：{IDLE，A，W，S}（由于故障消息未通过），在长路径上发送{SF，A，W，L}
4. As the nodes D and C receive a switch request, they enter a pass-through mode (in each direction) which mean they stop sourcing the Idle messages and start passing the messages between A an B
4. 当节点D和C接收到交换请求时，它们进入直通模式（在每个方向上），这意味着它们停止寻找空闲消息，并开始在a和B之间传递消息
5. Steady state is reached
5. 达到稳定状态
Signal Fail Clears
信号失效清除
1. SF on B clears, B does not unwrap, sets WTR timer, Tx {WTR, B, W, S} on inner and Tx {WTR, B, W, L}
1. B上的SF清除，B不展开，设置WTR定时器，Tx{WTR，B，W，S}在内部和Tx{WTR，B，W，L}
2. Node A receives WTR request on the short path, does not unwrap, Tx towards B on short path: {IDLE, A, W, S} (message does not go through due to the failure) and on the long path: Tx {WTR, A, W, L}
2. 节点A在短路径上接收WTR请求，不展开，在短路径上向B发送：{IDLE，A，W，S}（由于故障消息未通过），在长路径上发送{WTR，A，W，L}
3. Nodes C and D relay long path messages without changing the IPS octet
3. 节点C和D在不更改IPS八位字节的情况下中继长路径消息
4. Steady state is reached
4. 达到稳定状态
5. WTR times out on B. B transitions to idle state (unwraps) Tx {IDLE, B, I, S} on both inner and outer rings
5. WTR在B时超时。B转换到空闲状态（展开）Tx{idle，B，I，S}在内环和外环上
6. A receives Rx {IDLE, B, I, S} and transitions to Idle
6. A接收Rx{IDLE，B，I，S}并转换到IDLE
7. As idle messages reach C and D the nodes enter the idle state (start sourcing the Idle messages)
7. 当空闲消息到达C和D时，节点进入空闲状态（开始寻找空闲消息）
8. Steady state it reached
8. 它达到了稳定状态
Sample scenario in a ring of four nodes A, B, C and D, with a bidirectional failure between A and B. Ring is in the Idle state (all nodes are Idle) prior to failure.
四个节点a、B、C和D组成的环中的示例场景，a和B之间存在双向故障。环在故障前处于空闲状态（所有节点都处于空闲状态）。
Signal Fail Scenario
信号失败场景
1. Ring in Idle, all nodes transmit (Tx) {IDLE, SELF, I, S} on both rings (in both directions)
1. 在空闲环中，所有节点在两个环上传输（Tx）{Idle，SELF，I，S}（在两个方向上）
2. A detects SF on the outer ring, transitions to Wrapped state (performs a wrap), Tx towards B on the inner ring/short path: {SF, A, W, S} and on the outer ring/long path: Tx {SF, A, W, L}
2. A在外圈上检测SF，转换到包裹状态（执行包裹），在内圈/短路径：{SF，A，W，S}上向B发送Tx，在外圈/长路径：Tx{SF，A，W，L}
3. B detects SF on the outer ring, transitions to Wrapped state (performs a wrap), Tx towards A on the inner ring/short path: {SF, B, W, S} and on the outer ring/long path: Tx {SF, B, W, L}
3. B检测外环上的SF，转换到包裹状态（执行包裹），Tx在内环/短路径：{SF，B，W，S}上朝向a，在外环/长路径：Tx{SF，B，W，L}
FIGURE 22. An SRP Ring with bidirectional fiber cut
图22。具有双向光纤切割的SRP环
fiber cut
---------X-----------------------------
| -------X--------------------------- |
| | fiber cut | |
| v | v
----- -----
| A | | B |
| | | |
----- -----
^ | ^ |
o | | i | |
u | | n | |
t | | n | |
e | | e | |
r | | r | |
| v | v
----- -----
| D | | C |
| | | |
----- -----
| | | |
| | | |
| ----------------------------------- |
---------------------------------------
fiber cut
---------X-----------------------------
| -------X--------------------------- |
| | fiber cut | |
| v | v
----- -----
| A | | B |
| | | |
----- -----
^ | ^ |
o | | i | |
u | | n | |
t | | n | |
e | | e | |
r | | r | |
| v | v
----- -----
| D | | C |
| | | |
----- -----
| | | |
| | | |
| ----------------------------------- |
---------------------------------------
4. As the nodes D and C receive a switch request, they enter a pass-through mode (in each direction) which mean they stop sourcing the Idle messages and start passing the messages between A an B
4. 当节点D和C接收到交换请求时，它们进入直通模式（在每个方向上），这意味着它们停止寻找空闲消息，并开始在a和B之间传递消息
5. Steady state is reached
5. 达到稳定状态
Signal Fail Clears
信号失效清除
1. SF on A clears, A does not unwrap, sets WTR timer, Tx {WTR, A, W, S} towards B and Tx {WTR, A, W, L} on the long path
1. A上的SF清除，A不展开，设置WTR定时器，Tx{WTR，A，W，S}朝向B，Tx{WTR，A，W，L}在长路径上
2. SF on B clears, B does not unwrap. Since it now has a short path WTR request present from A it acts upon this request. It keeps the wrap, Tx {IDLE, B, W, S} towards A and Tx {WTR, B, W, L} on the long path
2. B上的SF清除，B不打开。由于它现在有一个短路径WTR请求，它会根据该请求进行操作。它使换行，Tx{IDLE，B，W，S}朝向长路径上的A和Tx{WTR，B，W，L}
3. Nodes C and D relay long path messages without changing the IPS octet
3. 节点C和D在不更改IPS八位字节的情况下中继长路径消息
4. Steady state is reached
4. 达到稳定状态
5. WTR times out on A. A enters the idle state (drops wraps) and starts transmitting idle in both rings
5. WTR在A上超时。A进入空闲状态（丢弃包裹）并开始在两个环中传输空闲
6. B sees idle request on short path and enters idle state
6. B在短路径上看到空闲请求并进入空闲状态
7. Remaining nodes in the ring enter the idle state
7. 环中的其余节点进入空闲状态
8. Steady state is reached
8. 达到稳定状态
FIGURE 23. An SRP Ring with a failed node
图23。具有故障节点的SRP环
---------------------------------------
| ----------------------------------- |
| | | |
| v | v /
----- ----/
| A | | C/| failed
| | | / | node C
----- -/---
^ | /^ |
o | | i | |
u | | n | |
t | | n | |
e | | e | |
r | | r | |
| v | v
----- -----
| D | | B |
| | | |
----- -----
| | | |
| | | |
| ----------------------------------- |
---------------------------------------
---------------------------------------
| ----------------------------------- |
| | | |
| v | v /
----- ----/
| A | | C/| failed
| | | / | node C
----- -/---
^ | /^ |
o | | i | |
u | | n | |
t | | n | |
e | | e | |
r | | r | |
| v | v
----- -----
| D | | B |
| | | |
----- -----
| | | |
| | | |
| ----------------------------------- |
---------------------------------------
Sample scenario in a ring where node C fails. Ring is in the Idle state (all nodes are Idle) prior to failure.
环中节点C失败的示例场景。环在发生故障之前处于空闲状态（所有节点都处于空闲状态）。
Node Failure (or fiber cuts on both sides of the node)
节点故障（或节点两侧的光纤切断）
1. Ring in Idle, all nodes transmit (Tx) {IDLE, SELF, I, S} on both rings (in both directions)
1. 在空闲环中，所有节点在两个环上传输（Tx）{Idle，SELF，I，S}（在两个方向上）
2. Based on the source field of the idle messages, all nodes identify the neighbors and keep track of them
2. 根据空闲消息的源字段，所有节点识别邻居并跟踪它们
3. B detects SF on the outer ring, transitions to Wrapped state (performs a wrap), Tx towards C on the inner ring/short path: {SF, B, W, S} and on the outer ring/long path: Tx {SF, B, W, L}
3. B检测到外圈上的SF，转换到包裹状态（执行包裹），Tx在内圈/短路径：{SF，B，W，S}上朝向C，在外圈/长路径：Tx{SF，B，W，L}
4. A detects SF on the inner ring, transitions to Wrapped state (performs a wrap), Tx towards C on the outer ring/short path: {SF, A, W, S} and on the inner ring/long path: Tx {SF, A, W, L}
4. A检测内环上的SF，转换到包裹状态（执行包裹），Tx在外环/短路径：{SF，A，W，S}上朝向C，在内环/长路径：Tx{SF，A，W，L}
5. As the nodes on the long path between A and B receive a SF request, they enter a pass-through mode (in each direction), stop sourcing the Idle messages and start passing the messages between A an B
5. 当A和B之间的长路径上的节点接收到SF请求时，它们进入直通模式（在每个方向），停止寻找空闲消息并开始在A和B之间传递消息
6. Steady state is reached
6. 达到稳定状态
Failed Node and One Span Return to Service
失败的节点和一个跨度返回服务
Note: Practically the node will always return to service with one span coming after the other (with the time delta potentially close to 0). Here, a node is powered up with the fibers connected and fault free.
注意：实际上，节点将始终返回服务，一个跨度接一个跨度（时间增量可能接近0）。在这里，节点通过连接的光纤通电且无故障。
1. Node C and a span between A and C return to service (SF between A and C disappears)
1. 节点C和a与C之间的跨度返回服务（a与C之间的SF消失）
2. Node C, not seeing any faults starts to source idle messages {IDLE, C, I, S} in both directions.
2. 如果节点C没有发现任何故障，则开始在两个方向上发送空闲消息{idle，C，I，S}。
3. Fault disappears on A and A enters a WTR (briefly)
3. 故障在A上消失，A进入WTR（短暂）
4. Node A receives idle message from node C. Because the long path protection request {SF, B, W, L} received over the long span is not originating from the short path neighbor (C), node A drops the WTR and enters a PassThrough state passing requests between C and B
4. 节点A从节点C接收空闲消息。因为在长跨度上接收到的长路径保护请求{SF，B，W，L}不是来自短路径邻居（C），节点A丢弃WTR并进入直通状态，在C和B之间传递请求
5. Steady state is reached
5. 达到稳定状态
Second Span Returns to Service
第二个跨度恢复使用
The scenario is like the Bidirectional Fiber Cut fault clearing scenario.
该场景类似于双向光纤切割故障清除场景。
FIGURE 24. An SRP Ring with a failed node
图24。具有故障节点的SRP环
wrap
----->|--------------------------------
| -<--|------------------------------ |
| | | |
| v | v
----- ----
| A | | C | Added
| | | | node
----- -----
^ | ^ |
o | | i | |
u | | n | |
t | | n | |
e | | e --- wrap
r | | r ^ |
| v | v
----- -----
| D | | B |
| | | |
----- -----
| | | |
| | | |
| ----------------------------------- |
---------------------------------------
wrap
----->|--------------------------------
| -<--|------------------------------ |
| | | |
| v | v
----- ----
| A | | C | Added
| | | | node
----- -----
^ | ^ |
o | | i | |
u | | n | |
t | | n | |
e | | e --- wrap
r | | r ^ |
| v | v
----- -----
| D | | B |
| | | |
----- -----
| | | |
| | | |
| ----------------------------------- |
---------------------------------------
Sample scenario in a ring where initially nodes A and B are connected. Subsequently fibers between the nodes A and B are disconnected and a new node C is inserted.
环中最初连接节点a和B的示例场景。随后，断开节点A和B之间的光纤，并插入新节点C。
Bidirectional Fiber Cut
双向光纤切割
1. Ring in Idle, all nodes transmit (Tx) {IDLE, SELF, I, S} on both rings (in both directions)
1. 在空闲环中，所有节点在两个环上传输（Tx）{Idle，SELF，I，S}（在两个方向上）
2. Fibers are removed between nodes A and B
2. 在节点A和B之间移除光纤
3. B detects SF on the outer ring, transitions to Wrapped state (performs a wrap), Tx towards A on the inner ring/short path: {SF, B, W, S} and on the outer ring/long path: Tx {SF, B, W, L}
3. B检测外环上的SF，转换到包裹状态（执行包裹），Tx在内环/短路径：{SF，B，W，S}上朝向a，在外环/长路径：Tx{SF，B，W，L}
4. A detects SF on the inner ring, transitions to Wrapped state (performs a wrap), Tx towards B on the inner ring/short path: {SF, A, W, S} and on the outer ring/long path: Tx {SF, A, W, L}
4. A检测内环上的SF，转换到包裹状态（执行包裹），Tx在内环/短路径：{SF，A，W，S}上朝向B，在外环/长路径：Tx{SF，A，W，L}
5. As the nodes on the long path between A and B receive a SF request, they enter a pass-through mode (in each direction), stop sourcing the Idle messages and start passing the messages between A an B
5. 当A和B之间的长路径上的节点接收到SF请求时，它们进入直通模式（在每个方向），停止寻找空闲消息并开始在A和B之间传递消息
6. Steady state is reached
6. 达到稳定状态
Node C is Powered Up and Fibers Between Nodes A and C are Reconnected
节点C通电，节点A和C之间的光纤重新连接
This scenario is identical to the returning a Failed Node to Service scenario.
此场景与将故障节点返回服务场景相同。
Second Span Put Into Service
第二跨投入使用
Nodes C and B are connected. The scenario is identical to Bidirectional Fiber Cut fault clearing scenario.
节点C和B是连接的。该场景与双向光纤切断故障清除场景相同。
Although SRP is media independent it is worth noting how SRP is used with a layer 1 media type. SRP over SONET/SDH is the first media type perceived for SRP applications.
尽管SRP与介质无关，但值得注意的是SRP是如何与第1层介质类型一起使用的。SONET/SDH上的SRP是SRP应用的第一种媒体类型。
Flag delimiting on SONET/SDH uses the octet stuffing method defined for POS. The flags (0x7E) are packet delimiters required for SONET/SDH links but may not be necessary for SRP on other media types. End of a packet is delineated by the flag which could also be the same as the next packet's starting flag. If the flag (0x7E) or an escape character (0x7D) are present anywhere inside the packet, they have to be escaped by the escape character when used over SONET/SDH media.
SONET/SDH上的标志定界使用为POS定义的八位字节填充方法。标志（0x7E）是SONET/SDH链路所需的数据包定界符，但对于其他媒体类型上的SRP可能不是必需的。一个数据包的结束由标志表示，该标志也可以与下一个数据包的开始标志相同。如果标志（0x7E）或转义字符（0x7D）出现在数据包内的任何位置，则在SONET/SDH介质上使用时，必须使用转义字符对其进行转义。
SONET/SDH framing plus POS packet delimiting allows SRP to be used directly over fiber or through an optical network (including WDM equipment).
SONET/SDH成帧加POS分组定界允许直接通过光纤或通过光纤网络（包括WDM设备）使用SRP。
SRP may also connect to a SONET/SDH ring network via a tributary connection to a SONET/SDH ADM (Add Drop Multiplexor). The two SRP rings may be mapped into two STS-Nc connections. SONET/SDH networks typically provide fully redundant connections, so SRP mapped into two STS-Nc connections will have two levels of protection. The SONET/SDH network provides layer 1 protection, and SRP provides layer 2 protection. In this case it is recommended to hold off the SRP Signal Fail IPS triggers (which correspond to failures which can be
SRP还可以通过SONET/SDH ADM（增放多路复用器）的支路连接连接到SONET/SDH环网。两个SRP环可映射为两个STS Nc连接。SONET/SDH网络通常提供完全冗余连接，因此映射到两个STS Nc连接的SRP将具有两级保护。SONET/SDH网络提供第1层保护，SRP提供第2层保护。在这种情况下，建议暂停SRP信号故障IPS触发器（对应于可能发生的故障
protected by SONET/SDH) for about 100 msec in order to allow the SONET/SDH network to protect. Only if a failure persists for over 100 msec (indicating SONET/SDH protection failure) should the IPS protection take place.
由SONET/SDH保护）约100毫秒，以允许SONET/SDH网络进行保护。仅当故障持续超过100毫秒（表示SONET/SDH保护故障）时，IPS保护才会发生。
Since multiple protection levels over the same physical infrastructure are not very desirable, an alternate way of connecting SRP over a SONET/SDH network is configuring SONET/SDH without protection. Since the connection is unprotected at layer 1, SRP would be the sole protection mechanism.
由于同一物理基础设施上的多个保护级别不是很理想，通过SONET/SDH网络连接SRP的另一种方法是配置SONET/SDH而不进行保护。由于连接在第1层不受保护，因此SRP将是唯一的保护机制。
Hybrid SRP rings may also be built where some parts of the ring traverse over a SONET/SDH network while other parts do not.
混合SRP环也可以在环的某些部分通过SONET/SDH网络而其他部分不通过的情况下构建。
Connections to a SONET/SDH network would have to be synchronized to network timing by some means. This can be accomplished by locking the transmit connection to the frequency of the receive connection (called loop timing) or via an external synchronization technique.
到SONET/SDH网络的连接必须通过某种方式与网络定时同步。这可以通过将发送连接锁定到接收连接的频率（称为循环定时）或通过外部同步技术来实现。
Connections made via dark fiber or over a WDM optical network should utilize internal timing as clock synchronization is not necessary in this case.
通过暗光纤或WDM光网络进行的连接应利用内部定时，因为在这种情况下不需要时钟同步。
An optional mode of operation is pass-thru mode. In pass-thru mode, a node transparently forwards data. The node does not source packets, and does not modify any of the packets that it forwards. Data should continue to be sorted into high and low priority transit buffers with high priority transit buffers always emptied first. The node does not source any control packets (e.g. topology discovery or IPS) and basically looks like a signal regenerator with delay (caused by packets that happened to be in the transit buffer when the transition to pass-thru mode occurred).
可选的操作模式是直通模式。在直通模式下，节点透明地转发数据。节点不发送数据包，也不修改它转发的任何数据包。应继续将数据分类为高优先级和低优先级传输缓冲区，高优先级传输缓冲区始终首先清空。该节点不产生任何控制数据包（例如拓扑发现或IP），基本上看起来像一个具有延迟的信号再生器（由转换到直通模式时恰好在传输缓冲区中的数据包引起）。
A node can enter pass-thru mode because of an operator command or due to a error condition such as a software crash.
由于操作员命令或软件崩溃等错误情况，节点可以进入直通模式。
[1] ANSI X3T9 FDDI Specification
[1] ANSI X3T9 FDDI规范
[2] IEEE 802.5 Token Ring Specification
[2] IEEE 802.5令牌环规范
[3] Bellcore GR-1230, Issue 4, Dec. 1998, "SONET Bidirectional Line-Switched Ring Equipment Generic Criteria".
[3] Bellcore GR-1230，1998年12月第4期，“SONET双向线路交换环形设备通用标准”。
[4] ANSI T1.105.01-1998 "Synchronous Optical Network (SONET) Automatic Protection Switching"
[4] ANSI T1.105.01-1998“同步光网络（SONET）自动保护切换”
[5] Malis, A. and W. Simpson, "PPP over SONET/SDH", RFC 2615, June 1999.
[5] Malis，A.和W.Simpson，“SONET/SDH上的PPP”，RFC 26151999年6月。
[6] Simpson, W., "PPP in HDLC-like Framing", STD 51, RFC 1662, July 1994.
[6] 辛普森，W.“HDLC类框架中的PPP”，STD 51，RFC 16621994年7月。
As in any shared media, packets that traverse a node are available to that node if that node is misconfigured or maliciously configured. Additionally, it is possible for a node to not only inspect packets meant for another node but to also prevent the intended node from receiving the packets due to the destination stripping scheme used to obtain spatial reuse. Topology discovery should be used to detect duplicate MAC addresses.
与在任何共享媒体中一样，如果节点配置错误或恶意配置，则穿过该节点的数据包可供该节点使用。此外，由于用于获得空间重用的目的地剥离方案，节点不仅可以检查意欲用于另一节点的分组，而且还可以防止意欲节点接收分组。拓扑发现应用于检测重复的MAC地址。
The IETF has been notified of intellectual property rights claimed in regard to some or all of the specification contained in this document. For more information consult the online list of claimed rights.
IETF已收到关于本文件所含部分或全部规范的知识产权声明。有关更多信息，请查阅在线权利主张列表。
The authors would like to acknowledge Hon Wah Chin who came up with the original version of the SRP-fa. Besides the authors, the original conceivers of SRP include Hon Wah Chin, Graeme Fraser, Tony Bates, Bruce Wilford, Feisal Daruwalla, and Robert Broberg.
作者要感谢提出SRP fa原始版本的韩华钦。除了作者之外，SRP的最初构思者包括韩华钦、格雷姆·弗雷泽、托尼·贝茨、布鲁斯·威尔福德、费萨尔·达鲁瓦拉和罗伯特·布罗伯格。
Comments should be sent to the authors at the following addresses:
评论应发送至以下地址的作者：
David Tsiang Cisco Systems 170 W. Tasman Drive San Jose, CA 95134
David Tsiang Cisco Systems 170 W.塔斯曼大道圣何塞，加利福尼亚州95134
Phone: (408) 526-8216 EMail: tsiang@cisco.com
电话：（408）526-8216电子邮件：tsiang@cisco.com
George Suwala Cisco Systems 170 W. Tasman Drive San Jose, CA 95134
乔治苏瓦拉思科系统170 W.塔斯曼大道圣何塞，加利福尼亚州95134
Phone: (408) 525-8674 EMail: gsuwala@cisco.com
电话：（408）525-8674电子邮件：gsuwala@cisco.com
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Acknowledgement
确认
Funding for the RFC Editor function is currently provided by the Internet Society.
RFC编辑功能的资金目前由互联网协会提供。