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OSN3500 EMS4单板LCAS断纤保护倒换时间是多长

发布时间:2018-04-07

问题描述

OSN3500EMS4单板配置EPL业务,VCTRUNK分别绑定5个VC12业务到两根上光纤传输。使能LCAS功能后,当发生断纤时,数据业务中断150ms左右。客户咨询我们的LCAS在这种场景下的保护倒换时间是多少,有没有标准?


处理过程

1.标准时间计算

VC12的复帧是通过K4字节的b2比特来实现的,32个VC12复帧组成一个虚级联复帧,而每个VC12复帧由4个VC12构成。故由VC12组成的虚级联复帧周期为 32*4*0.125ms = 16ms

根据标准描述,MFI的恢复时间可为3~10个虚级联复帧周期。

VC12的MFI恢复时间即为:

3个MFI恢复复帧周期= 3 * 16ms = 48ms

10个MFI恢复复帧周期= 10 * 16ms = 160ms

2.LCAS保护倒换时间 = 故障检测时间 + 单板业务恢复时间 + LCAS故障处理时间。

1)故障检测时间与现网的实际路径长度相关。

2)单板业务恢复时间在配置VC12的情况下,按照标准定义,恢复时间在48ms~160ms之间。

3)LCAS故障处理时间,EMS4的LCAS任务处理周期为200ms,也就是说LCAS任务最长处理时间是200ms。

4)结合上述计算方式,LCAS倒换时间在200ms左右。


根因

在ITU-T中,LCAS标准中没有定义LCAS保护的倒换时间,然而LCAS协议本身是基于虚级联技术,虚级联技术标准中为了保证业务正确恢复,对业务恢复操作进行了严格的规定。

低阶MFI恢复时间计算如下:

G.783标准描述:

8.2.5.2 VC-11 VC-12 VC-2 virtual concatenation multiframe alignment

Sink direction The extended overhead multiframe is recovered according to 8.2.3.1. The virtual concatenation frame number is recovered from bits 1-5 of the K4[2] multiframe sequence. The process will be in the out of multiframe (OOM) state when either the extended overhead multiframe alignment process is in the OOM

 state or when an error is encountered in the received and expected frame number from bits 1-5 of the K4[2] sequence. The process enters the IM state when the extended overhead multiframe process is in the IM state and two consecutive error-free frame numbers are recovered. The sequence number is recovered from bits 6-11 of the K4[2] sequence. A new sequence number is accepted if the received sequence has the same value in n consecutive extended overhead multiframes, with 3 ≤?n ≤?10. The accepted sequence number is compared with the expected sequence number for detection of the dSQM defect.


建议与总结

LCAS功能在增删绑定的场景下,业务无损(前提:实际流量没有超过删除绑定或者添加绑定后的带宽大小)。而对于中断光纤的场景无法做到无损保护。