QT2022/32 - Data Sheet: DS3051
7.1.3 Line Overhead
The Line layer is responsible for the reliable transport of the Path layer payload and overhead. Line overhead is
accessed where SPEs are multiplexed or protection switching is performed.
Table 10: Line Overhead Definitions
Overhead
Octet
Description
Value (Bits 1...8)
Function
H1-H2
Pointer
NDF field = 0110
SS field = 00
Pointer = 10000 01010
The pointer marks the beginning of the STS-192c SPE. It also
indicates a concatenated payload. On reset the New data flag is also
set.
H3
B2
Pointer action
Line BIP-8
00000000
This byte is provided for frequency justification purposes. In the
transmit direction this byte serves no purpose. In the receive
direction if a negative stuff operation has been indicated by the
pointer bytes this byte will contain valid payload data.
Varies
Used for line error monitoring functionality. This is a bit-interleaved
parity-8 code using even parity and is calculated over all bits of the
line overhead and STS-1 Envelope capacity of the previous STS-1
frame before scrambling. The computed B2 is placed in the line
overhead of each STS-1 frame before scrambling. When using the
TOH Serial interface, the inserted value of B2 represents an
inversion mask. An inserted value of all zeroes preserves the
calculated B2 octet.
K1-K2
Automatic
Protection Switch
(APS) Channel
K1 - 00000001
K2[1...5] - 00010
K2[6...8] - Varies
These bytes are allocated for APS signalling between Line level
entities. These bytes are only defined for STS-1 number 1 in the
STS-192c frame. K2[6...8] transports either an RDI-L encoding or is
set to 000.
D4-D12
Line Data
Communications
Channel (DCC)
All octets set to
00000000
Unsupported, not required by IEEE 802.3 Clause 50.
S1
Synchronization
messaging
00001111
00000000
Unsupported, not required by IEEE 802.3 Clause 50.
Unsupported, not required by IEEE 802.3 Clause 50.
M0
STS-1 Line
Remote Error
Indication (REI)
M1
STS-N line REI
Varies
This octet is used for conveying the number of errors detected by
the Line BIP-8 (B2) bytes. The count has legal values from 0 to 255.
If greater than 255 errors are detected by the Line BIP-8 the count is
set to 255.
Z1
Z2
E2
Reserved for line
growth
00000000
00000000
00000000
Unsupported, not required by IEEE 802.3 Clause 50.
Unsupported, not required by IEEE 802.3 Clause 50.
Unsupported, not required by IEEE 802.3 Clause 50.
Reserved for line
growth
Orderwire
38
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