First of all, we will describe the characteristics of SNCP subnet protection for OSN2500 equipment, SNCP subnet connection protection, the way of double sending and receiving, channel protection ring is also called PP ring, the way of the same double sending and receiving, that is, often referred to as, the west optical port to receive the east optical port to send, that is, sending and receiving inconsistent routing, in the sender sends to the east and west directions, and in the receiving end to select and receive, that is, the PP ring service is the whole ring. In fact, PP ring is only a special case of SNCP protection, the difference is mainly in the different single boards participating in the protection, for example, SNCP realizes the double-issue is completed by the line board, while the PP ring is completed by the branch board, but are based on the protection of 2M level channel services. The difference between SNCP and PP ring you can check yourself, I do not have ready information, the following is the difference between the channel protection ring and the multiplexing segment protection, the reversal time: PP is the failure of the channel for the reversal, the reversal speed is faster, generally 15ms; MSP is generally in 25ms or so, the MSP reversal and the size of the service has nothing to do with the size of the entire multiplexing segment layer for the reversal; The following gives you a case to introduce.

Case:

The network is shown in the figure below, A-B-C-D-E-F-G-H-I-J-K-L-M-A form a 2.5GSNCP ring, A is the center site, there are Ethernet services between all sites and A. Site A is configured for EPLAN, and the other sites are configured for EPL, and on a certain day, the fiber optic cable from station A to station M is interrupted, and the service is normally reversed, and after the fiber optic cable failure has been repaired for 10 minutes, the VCTRUNK of station A to station M reports a VCAT_LOA alarm. Ten minutes after the cable failure is repaired, the VCTRUNK from station A to station M reports a VCAT_LOA alarm, and the Ethernet service from station M to station A is interrupted.

Alarm message

VCAT_LOA

Processing

1.VCAT_LOA alarm is reported on VCTRUNK of EFS0 board, which indicates that the configured VCTRUNK time slots have passed through physical links with different distances, check the SDH paths of bound time slots from station A to station M(5VC12 ), and the paths are all the shortest paths , A-M, and there is no problem.

2. Before the fiber optic cable is interrupted business is normal, after the fiber optic cable is interrupted business services can be normal inversion, basically exclude the possibility of single board failure.

3. 10 minutes after the cable repair before generating VCAT_LOA alarms, just after the recovery of SNCP switching, may be part of the channel SNCP switching has not been restored, check the abnormal events, and sure enough, bound to the fiveVC12two are still in the state of SNCP switching, in the SNCP service control menu to view the twoVC12 for the non-restoration of the configuration.

FaultCause

Two of the fiveVC12 time slots bound by VCTRUNK are configured as non-recovery for SNCP inversion recovery, and these two time slots are not inverted back to the working path after SNCP inversion is recovered, resulting in the five time slots passing through physical links with different distances, while the protection path passes through longer distances and more network elements, and the delay time exceeds the time allowed by the virtual cascade delay, resulting in service interruption.

Solution

Under the SNCP service control menu, change the SNCP inversion recovery method of these 2 channels to recovery, the service is inverted to the working path, and the service returns to normal.

Recommendation and Summary

When configuring SDH services, try to ensure that the inversion recovery method of SNCP services at both ends is the same, so as to avoid sending and receiving paths going through different routes. When configuring Ethernet services, be sure to ensure that the physical links passed through the configured time slots are the same, so as to avoid service interruption caused by too large a delay in the virtual cascade.