In a particular scenario, we have a link of four sites:
A ---- B ---- C --- D
The aim is to create 21 E1 connections between A and D. As per the practical scenario the cross-connections on site A are of VC12 level (21 E1). The cross connections on site-B & site-C are of VC3 level, i.e. we have pass-through one VC3 containing the 21 E1's. And then at the end (site-D) we are dropping on VC12 level on PQ1 card.
Please confirm whether the scenario will work in the presence of VC3 level pass-through at site B&C?
This scenario can not work as VC-12 and VC-3 are both low order and each one has its own LO-POH & LO-PTR
So if you created the service at the start node (Site A)as 21 VC-12 , according to the attached ITU-T multiplexing structure these 21 VC12 services will be encapsulated in an STM-1 frame format but the lower order header will be for each VC-12 multi frame, meanwhile if you created its pass-through service (at site B&C) as a VC-3 pass-through this means that the VC-12 header will be damaged and both the end sites will report TUAIS alarm
Only you can path through the lower order services (VC-12 & VC-3) using the higher order service (VC-4) so that you can keep the lower order headers, but one condition must be achieved in such case (all the equipments participating in this service must have the same service time slot numbering scheme especially if the equipments are from different vendors “ITU-T or Interleaved)” for more details about different numbering schemes you can refer to the attached file)
The service configuration is not right.
The lower order services, VC-12 or VC-3, can be pass-through in the middle station either by making VC-12 or VC-3 respectively services or both of them can be pass through using the higher order service (VC-4).but if you made the pass-through of the VC-12 services using a VC-3 service , both of the end station of the VC-12 service will report TU-AIS