Hello everyone!
Today, I'm going to share with you some information about the VC4 server trail. I hope you like it!
What is the VC4 server trail?
VC4 server trail exists between line boards of SDH equipment. It is used to carry VC12 and VC3 service trails. It depends on the establishment of the MS trail. Before the MS trail is created, you cannot create it on the NMS.
Position of the VC4 server trail in the SDH trail hierarchy:
Why is the VC4 server trail required?
1. VC12 and VC3 trails cannot be directly created on MS trails. We need to add a shell to them to implement adaptation between trails at different levels.
2. The basic reason is to save lower-order cross-connection resources.
As shown in the following figure, if there is no VC-4 server trail and multiple VC-12 or VC-3 trails are created, multiple lower-order cross-connections need to be created on the NEs that traverse the trail.
If a VC4 server trail is created between site A and site C, only one higher-order VC4 cross-connection is consumed at site B. (One VC-4 higher-order cross-connection can accommodate three VC-3 trails or 63 VC-12 trails).
As shown in the preceding figure, the VC12/VC3 trails attached to the VC4 server trail are traversed through higher-order cross-connections at site B. This greatly saves lower-order cross-connection resources.
Restrictions on VC4 server Trails
1. When creating a VC4 server trail on the protection network, ensure that the VC4 sequence number of each MS trail must be the same. Otherwise, the VC12/VC3 trail cannot be created successfully.
2. If a trail traverses multiple VC4 server trails, lower-order cross-connections are used on the NEs connected to the two server trails (the NEs at the end of the service trail). Therefore, we need to plan the server trails and set up the server trails where VC4 pass-through is available. Otherwise, lower order cross-connection resources are severely consumed.
3. When a VC4 server trail is created, VC4 SDH services are configured at the intermediate site, but no actual services are configured at the source and sink sites. If VC-12 trails are configured, VC-12 cross-connections are generated at the source and sink sites, and the intermediate sites use the newly created VC-4 cross-connections to provide pass-through.
4. An intermediate site cannot use the pass-through VC4 server trail to create a VC12 trail with its source and sink ends. As shown in the preceding figure, site B is the pass-through station of the VC4 service trail. Therefore, you cannot use the VC4 service trail to create a VC12/VC3 trail with B as the source or sink.
That's all, welcome to discuss and learn about transmission networks together!
Thank you!
