G.8032/Y.1344 2010/03
Summary APS
protection switching mechanisms(characteristics, architectures) ETH layer Ethernet ring topologies incorporates Amendment 1 (2010),
Appendix X (minimizing segmentation in interconnected rings)
multiple faults that could cause segmentation in a network of interconnected rings. uses additional management information and configuration of MEP Appendix XI (end-to-end service resilience) ring protection to interact with the full service protection ITU-T G.8031/Y.1342
1 Scope APS
Protection switching mechanisms for ETH layer Ethernet Ring topologies The ETH layer ring maps to the physical layer ring structure.
2 References [ITU-T G.805] [ITU-T G.806] 2009版 [ITU-T G.808.1] [ITU-T G.809] [ITU-T G.870] [ITU-T G.8010] [ITU-T G.8021] [ITU-T Y.1731] [IEEE 802.1Q]
3 Definitions
3.1 Terms defined elsewhere
和1相比，唯一的区别是G.8021中多定义了一个ETHDi/ETH adaptation function (ETHDi/ETH_A)
3.2 Terms defined in this Recommendation 3.2.1 Ethernet ring 由ring node形成的一个物理上闭合的回路，每个ring node和邻接的ring node相连。注意表述中说的是ethernet ring和ethernet ring node, 并非erp ring或erp ring
node,即讨论物理层，Ethernet层面，环的组成和连接，erp ring 和node 映射到该ring物理结构上，实际情况中，如果其中有非支持erp的ring node，应视为透明的link；由此产生的单通状态【如cc单通，或一侧link单通】按erp单通逻辑处理。 3.2.2 Ethernet ring node A network element which implements at least the following functionalities: ETH_C+ ETH_FF for forwarding APS Two ring ports, including ETHDi/ETH adaptation function ERP control process controlling the blocking and unblocking of traffic over the ring ports. 上述几个function在G.8021中定义，需要进一步学习 3.2.3 ERP instance 3.2.4 interconnection node 表述相当拗口，逻辑还是简单的，简单说互联节点，就是连接多个ring的节点；多个ring中，一个是major ring,每个互联节点有2个ring port参与，其它都是sub-ring，每个互联节点有且只有一个ring port参与. Be common to 与…共有 互联节点和共享节点不同，共享节点是多个ring共享该节点，各个ring彼此独立，每个ring，有2个ring port参与 在没有定义major ring和sub ring的时候抛出interconnection node的概念,又没有图说明，是不妥当滴。 3.2.5 major ring 物理和逻辑上都闭合的环，共享link属于major ring，每个共享节点有2个ring port参与 3.2.6 R-APS virtual channel 叙述相当稀烂；ERPS中有2种通道，traffic channel和R-APS channel，在多环的情况下，子环物理和逻辑上未闭合，v1a1中引入virtual channel的概念，让sub ring的R-APS message在主环中透传，从而实现子环逻辑上的闭合 3.2.7 ring MEL 3.2.8 ring protection link (RPL) 3.2.9 RPL neighbour node: 逻辑很容易理解，但引入neighbour不过是能 block rpl的另一端，有什么现实意义？减少无效流量侵占带宽？ 3.2.10 RPL owner node Owner如何相应FS/MS请求？ 3.2.11 sub-ring 3.2.12 sub-ring link Span这里如何翻译？node之间的间距？ 3.2.13 wait to block timer
4 Abbreviations 新增BPR，FS,MS,ID,TCM,VPLS 5 Conventions 5.1 Representation of octets
多个8位元组表达一个2进制数，低位在前，高位在后
BIN HEX 0000 001001101100 6C 02
8位元组内部，高位在前，低位在后
6 Introduction Mechanisms, APS apply on ETH ring wide-area multipoint connectivity,moreeconomically(reduced number of links) highly reliable and stable protection,never form loops ring protection switching architecture loop avoidance at any time, traffic may flow on all but one of the ring links. Ethernet flow forwarding function (ETH_FF) this Recommendation shall be applicable for a multi-ring/ladder network, if the following principles are adhered to:
a) R-APS channels are not shared across Ethernet ring interconnections;[独立RAPS通道] b) On each ring port, each traffic channel and each R-APS channel are controlled (e.g., for blocking or flushing) by the Ethernet ring protection control process (ERP control process) of only one Ethernet ring;[各环有独立控制的ring port, tc, rc，不共享] c) Each major ring or sub-ring must have its own RPL.[独立RPL]
7 Ring protection characteristics
7.1 Monitoring methods and conditions Switching trigger condition: Condition就是SF, SF or OK,其它方式没有定义
SF trigger switching
SF defined in 8021,SF or no failed, not defined other condition, i.e. SD SF defined on transport entity of each ring link SF检测有three monitoring methods Inherent --- physical layer trail Sub-layer --- tandem connection monitoring (TCM). Test trail --- extra test trail (CCM?) 对于ERP进程而言，不知道采用的何种defects monitoring 方式，只知道传输实体(ring link)SF或OK
7.2 Ethernet traffic and bandwidth consideration 无论ERP出于何种状态，都应该能提供足够的带宽保证业务和RAPS Care should be taken that ring link capacity can continue to support all ring APS (R-APS) and service traffic that is protected after protection switching 7.3 Ethernet ring protection switching performance Single ring(switch completion time = transfer time)<50ms
without congestion all nodes in idle status
<1200km fibre circumference, <16node
single link failure
所有其它情况不保证倒换时间小于50ms
特别提到子环虚通道场景，性能部分受主环性能影响，如果节点数，距离超
过上述标准，则达不到50ms
8 Ring protection conditions and commands
Conditions，这里conditions如何翻译？条件，状态或其它？似乎状态比较合理，ring 可以出于2种状态,故障和无故障状态，从宏观上说环的状态用idle和protection表述更合适，并且ring也不止idle和protection状态，不知道这里用2种消息来表述环的状态是什么意思，当然另一种理解是，当环上检测到SF，则SF消息在环上传播遍历所有节点，恢复时NR消息传遍所有节点，这是从微观角度看环的状态
Signal fail (SF) No request (NR) Commands Forced switch (FS)[FS或MS可以同时配多处吗？假如可以同时多处配FS或MS，那么环上同时多个堵点，从实际工作上说同时配多处没有意义，但又可能不做检查允许这样做]
Manual switch (MS) Clear a) Clearing an active local administrative command (e.g., forced switch or manual switch).[clear优先级高, 假定可以同时多配FS/MS,仍然清除所有FS/MS的配置]
b) Triggering reversion before the WTR or WTB timer expires in case of revertive operation.[在WTR或WTR超时前触发恢复]
c) Triggering reversion in case of non-revertive operation. 下面3种命令没有实现
Lockout of protection – This command disables the protection group.
Replace the RPL – This command moves the RPL by blocking a different ring link and unblocking the RPL permanently.
Exercise signal – Exercise of the R-APS protocol. The signal is chosen so as not to modify the position of the blocked ring port.
9 Ring protection architectures
9.1 Revertive and non-revertive switching Switch conditions cleared(SF is removed, ms/fs is cleared) Revertive(WTR->switch over to working transport entity) Advantage: working transport entity may be optimized Disadvantage: the expense of an additional traffic interruption Non-revertive(no switch) Advantage: not the expense of an additional traffic interruption Disadvantage: may use the non-optimizedtransport entity 9.2 Protection switching triggers 3个倒换触发来源，SF,RAPS, operator control。ERP控制进程消息输入包括本地消息和外部消息，各种消息优先级不同，任意时候，只响应最高优先级的消息
a. SF, it has a higher priority b. the received R-APS message requests to switch and it has a higher priority than any otherlocal request（i.e.假定故障恢复，wtr超时，某个故障邻接node将收到owner的NRRB消息，此时如果NRRB消息优先级最高，就会触发倒换） c. initiated by operator control (e.g., forced switch, manual switch) if it has a higher prioritythan any other local request or far-end request 9.2.1 Signal fail declaration conditions
SF is defined in 8021
9.3 Protection switching models on a single Ethernet ring
举了一个4 nodes单环的例子，每个环节点抽象为应用了若干function ETHcharacteristic information (ETH_CI)即以太的报文 ETH_FF某个特定的vlan
Ethernet flow point (ETH_FP)某个端口
对图中的圆圈可以理解为某个ETH_FF，若干端口加入其中，上面承载的是ETH_CI的业务，ERP Process控制ETH_FF实现对ring端口block或unblock，flush db等 图1 正常情况 图2 SF
图3 引入CCM, MEP 图4 解释CCM如何工作
If a MEP detects a defect, which contributes to an SF defect condition, it informs the ERP control process that a failure condition has been detected.
An ERP control function uses the ETH_CI_SSF information, forwarded from the ETHx/ETH-m_A_Sk, to assert the SF condition of the ring link. R-APS protocol用R-APS message交换消息
ETHDi/ETH_A功能模块负责解析和生成R-APS message To ERP process: R-APS to ETH_CI_RAPS, To ring port: ETH_CI_RAPS to R-APS
注意：ERP process收到的为ETH_CI_RAPS除了送ERP处理，还会通过RAPS-FF向下游转发
A received R-APS message is also forwarded to the ETH_FF
9.4 Traffic channel blocking
Blocking traffic is supported by excluding the connection point from the ETH_FF functions for theone or more VLAN IDs of the traffic channel controlled by the ERP Instance
Each ERP instance shall only block orunblock the VLAN IDs of the traffic channels of the set of VLANs assigned for protection by thatERP instance. 9.5 R-APS channel blocking
R-APS channel VLAN traffic forwarding is always blocked at the same ring ports where the trafficchannel is blocked, except on sub-rings without R-APS virtual channel
除了子环w/o vc情况下，traffic channel和raps channel block不同以外，其它情况blocking或unblocking都保持一致,并且二者blocking的逻辑相同 但blocking时一些细节不同