Path overhead
The Path Overhead (POH) is generated for all plesiochronous tributary signals in
accordance with ITU-T Rec. G.709. The POH provides for integrity of communication
between the point of assembly of a Virtual Container VC and its point of disassembly.
The following table shows the POH bytes and their functions.
Byte Location and Function
J1 Path Trace Identifier byte
B3 Path Bit Interleaved Parity (BIP-8)
Provides each path performance monitoring. This byte is calculated
over all bits of the previous payload before scrambling.
C2 Signal Label
All ″0″ means unequipped; other and ″00000001″ means equipped
G1 Path Status
Conveys the STM-1 path terminating status, performance, and remote
defect indication (RDI) signal conditions back to an originating path
terminating equipment.
F2, F3 User Data Channel
Reserved for user communication.
H4 Multiframe Indicator
Provides a general multiframe indicator for VC-structured payloads.
K3 VC Trail protection.
N1 Tandem connection OH
AU pointer
The AU pointer together with the last 261 columns of the STM-1 frame forms an AUG
(Administrative Unit Group). An AUG may contain one AU-4 or three
byte-multiplexed AU-3s (an AU-3 is exactly one third of the size of an AU-4). AU-3s
are also compatible with the SONET standard (Synchronous Optical NETwork) which
is the predecessor of SDH (and still the prevailing technology within the USA). Three
byte-multiplexed STS frames (SONET frame), each containing one AU-3 can be
mapped into one STM-1.
An SDH overview
SDH frame structure
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A-10
Alcatel-Lucent - Proprietary
See notice on first page
365-312-801R7.2
Issue 3, May 2007
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