363-206-295
A SONET Overview
Issue 1
December 1997
A-5
Each SONET layer has a set of overhead bytes as shown in Figure A-3. These
bytes carry information used by various network elements.
■
Section Overhead contains information that is used by all SONET
equipment including repeaters.
■
Line Overhead is used by all SONET equipment except repeaters.
■
Path Overhead is carried within the payload envelope.
— STS-1 path overhead remains with the STS-1 SPE until its
asynchronous signal is extracted (for example, DS-3) or until its
individual VT1.5 signals are demultiplexed.
— VTN (N= 1.5, 2, 3, or 6) path overhead remains with the VTN until
its asynchronous signal is extracted.
Figure A-3.
SONET Frame Format
Data Com
D9
Data Com
D6
H3
APS
K2
D3
F3
Multiframe
H4
User
F2
Channel
Signal Label
C2
Data Com
Path Status
G1
J0
Data Com
Orderwire
E2
K3
Data Com
Data Com
D12
Data Com
Pointer
Orderwire
User
F1
Data Com
N1
BIP-8
B3
Action
STS-1
STS-1 ID
D11
APS
Framing
Trace
J1
M0
S1
Data Com
D10
Data Com
D7
D8
Data Com
D4
D5
BIP-8
B2
K1
Pointer
H1
H2
Framing
A1
A2
BIP-8
B1
E1
Data Com
D1
D2
1
2
3
4
5
6
Section
Overhead
Line
Overhead
Path OH
Transport Overhead
3 Columns
STS-1 Synchronous Payload Envelope (STS-1 SPE)
87 Columns
STS-1 Frame Format
90 Columns
89
90
User
APS
TCM
Line REI
Synch. Status
