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Path Overhead
The Path Overhead (POH) is a 1 byte field in a DS3 PLCP frame that provides
specific functions. The Z bytes (Z1-Z6) are reserved for future functions. The B1
byte is used for Bit Interleaved Parity (BIP-8) which checks for errors and
performance conditions. The G1 byte is used for the PLCP Path Status which
controls error conditions. The C1 byte provides for bit stuffing.
Path Overhead Identifier (POI)
The Path Overhead Identifier (POI) is the label for the function of each Path
Overhead byte in a PLCP frame.
POI - POI Value (8 bit) POH
P11- 00101100 Z6
P10- 00101001 Z5
P9 - 00100101 Z4
P8 - 01000000 Z3
P7 - 00011100 Z2
P6 - 00011001 Z1
P5 - 00010101 X
P4 - 00010000 B1
P3 - 00001101 G1
P2 - 00001000 X
P1 - 00000100 X
P0 - 00000001 C1
Payload
The payload of an ATM cell is the 48 bytes available for data. This field is also
called the Cell Payload or Data Payload.
Payload Type (PT)
A field in the header of an ATM cell used to identify the type of information being
transported that may require different handling by the network or terminating
equipment.