Hi there, Community friends! This time,I would like to continue with the TCM topic that we saw in Introduction to TCM. Hope you like it!
In the SDH transmission hierarchy, the tandem connection monitoring (TCM) serves at a layer between the AU/TU pointer management layer and the HP/LP layer. The TCM uses the N1/N2 bytes in the path overhead (POH) to monitor the quality of transmission paths in a transmission area (that is, a TCM section).
The TCM is available in two modes: Option 1 and Option 2. Currently, Huawei uses the Option 2 mode.
Overheads of TCM
Figure 1 shows the overhead bytes of N1.
Bits 1-4 are used as an incoming error count (IEC), indicating the number of incoming bit errors from the source end.
Bit 5 operates as the TC_REI of the Tandem Connection (TC) to indicate errored blocks caused within the TC.
Bit 6 operates as the outgoing error indication (OEI) to indicate errored blocks that the sink outputs to another network carrier.
Bit 7 and bit 8 indicate the following elements:
Tandem connection monitor trace byte (TC-API), similar to J1.
Remote defect indication (TC_RDI), by using which the sink informs the source of defects in the TC section.
Outgoing defect indication (ODI), by using which the sink informs the source of defects in the outgoing services.
Figure 1 N1 Byte
The overhead bytes of TCM are N1 bytes. Hence, N1 bytes also indicate the overhead bytes of TCM. IEC indicates the number of B3 bit errors. Thus, the maximum value of IEC is 8 because a maximum number of B3 bit errors occur.
That's all, I welcome everyone to leave a message and exchange in the comment area!
