Path Overhead Layer
The following is a partial list of POH bytes and their corresponding functions;
J1 byte (STS path trace)
- High Order STS-N path trace byte
- An unique message is assigned to each path in a SONET network – therefore the path trace can be used to
check continuity between any location on a transmission path and the path source
- This user programmable byte repeatedly transmits a 15 byte string plus 1 (CRC-7) byte so that a receiver can
continually verify its connection with the transmitter
- A 64 byte free-format string is also permitted
- The message is transmitted one byte per STS-3 frame
B3 byte
- Even code parity which determines if a transmission error has occurred over a path
- Its value is calculated over all the bits of the previous STS-3
- The computed checksum is placed in the B3 byte before scrambling
TX150 e-Manual D07-00-023 Rev A02
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