ONEday, the transmission equipment room received switching equipment room response suddenly, the services between central NE1 and all other NEwere interrupted. Through the observation from SBS NM of NE1, it was found that there were large amounts of lower order path errors and performance events such as pointer justifications etc. in No. 1 NEand at the tributaries side of No. 3 and 4 NEs. There was no path protection switching alarm on tributary unit
)Through fault symptoms analysis, it could be judged that switching service interruption was caused by poor transmission performance, bit error or excessive jitter.
2) For path protection ring, the services take unidirectional route, the fault of any NEwill cause the above-mentioned symptom. For the convenience of fault localization, the following measures were taken.
3) Two receiving/sending optical fibers of the westward optical interface unit of No. 1 NEwere pulled out to make path protection work. It was found that the services of No.2 and 3 NEs were recovered, while the service of No.4 NEwas still interrupted. It could be judged that there was something wrong with the eastward optical interface unit of No. 3 NEor No.4 NE.
4) A fiber pigtail was used to make self-loop for the eastward optical interface unit of No. 3 NE, the 2M path leading to No.4 NEfrom No.1 NEwas tested, the result showed it was normal (the path was already looped back). This suggested that the fault point should exist in No.4 NE.
5) Through further observation of performance, there were large amounts of bit errors on the optical interface unit connecting with No.1, 3 NEs and No.4 NE, it can be judged that there might be something wrong with the clock of No.4 NE. After the STG unit of No. 4 NEwas replaced, the normal service was resumed
For path protection ring, unidirectional path protection ring can be reconfiged to bidirectional service chain by means of breaking fiber so that fault could be located.
The transmission networking in a certain office is as illustrated in Fig. 1-2, with a unidirectional path protection ring consisting of four SBS155 equipment; the service is of centralized type, No. 1 NEis the service central point and connects with NM.