問(wèn)題描述

OSN3500用EMS4單板配置EPL業(yè)務(wù)，VCTRUNK分別綁定5個(gè)VC12業(yè)務(wù)到兩根上光纖傳輸。使能LCAS功能后,當(dāng)發(fā)生斷纖時(shí),數(shù)據(jù)業(yè)務(wù)中斷150ms左右?？蛻糇稍兾覀兊腖CAS在這種場(chǎng)景下的保護(hù)倒換時(shí)間是多少，有沒(méi)有標(biāo)準(zhǔn)？

處理過(guò)程

1.標(biāo)準(zhǔn)時(shí)間計(jì)算

VC12的復(fù)幀是通過(guò)K4字節(jié)的b2比特來(lái)實(shí)現(xiàn)的，32個(gè)VC12復(fù)幀組成一個(gè)虛級(jí)聯(lián)復(fù)幀，而每個(gè)VC12復(fù)幀由4個(gè)VC12構(gòu)成。故由VC12組成的虛級(jí)聯(lián)復(fù)幀周期為 32*4*0.125ms = 16ms

根據(jù)標(biāo)準(zhǔn)描述，MFI的恢復(fù)時(shí)間可為3~10個(gè)虛級(jí)聯(lián)復(fù)幀周期。

VC12的MFI恢復(fù)時(shí)間即為：

3個(gè)MFI恢復(fù)復(fù)幀周期= 3 * 16ms = 48ms

10個(gè)MFI恢復(fù)復(fù)幀周期= 10 * 16ms = 160ms

2.LCAS保護(hù)倒換時(shí)間 = 故障檢測(cè)時(shí)間 + 單板業(yè)務(wù)恢復(fù)時(shí)間 + LCAS故障處理時(shí)間。

1）故障檢測(cè)時(shí)間與現(xiàn)網(wǎng)的實(shí)際路徑長(zhǎng)度相關(guān)。

2）單板業(yè)務(wù)恢復(fù)時(shí)間在配置VC12的情況下，按照標(biāo)準(zhǔn)定義，恢復(fù)時(shí)間在48ms~160ms之間。

3）LCAS故障處理時(shí)間,EMS4的LCAS任務(wù)處理周期為200ms，也就是說(shuō)LCAS任務(wù)最長(zhǎng)處理時(shí)間是200ms。

4）結(jié)合上述計(jì)算方式,LCAS倒換時(shí)間在200ms左右。

根因

在ITU-T中，LCAS標(biāo)準(zhǔn)中沒(méi)有定義LCAS保護(hù)的倒換時(shí)間，然而LCAS協(xié)議本身是基于虛級(jí)聯(lián)技術(shù)，虛級(jí)聯(lián)技術(shù)標(biāo)準(zhǔn)中為了保證業(yè)務(wù)正確恢復(fù)，對(duì)業(yè)務(wù)恢復(fù)操作進(jìn)行了嚴(yán)格的規(guī)定。

低階MFI恢復(fù)時(shí)間計(jì)算如下：

G.783標(biāo)準(zhǔn)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.

建議與總結(jié)

LCAS功能在增刪綁定的場(chǎng)景下，業(yè)務(wù)無(wú)損(前提：實(shí)際流量沒(méi)有超過(guò)刪除綁定或者添加綁定后的帶寬大小)。而對(duì)于中斷光纖的場(chǎng)景無(wú)法做到無(wú)損保護(hù)。