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.

150

Page 170
Image 170
Agilent Technologies J3919A, J3972A manual Path Overhead Identifier POI, Payload Type PT