VeEX VePAL TX300, User Manual

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The OTU framing is divided into two portions: FAS and MFAS.
Frame Alignment Signal (FAS)
Uses the first six bytes and, similar to SONET/SDH, it is used to provide framing for the entire signal
In order to provide enough 1/0 transitions for synchronization, scrambling is used over the entire OTU frame, except
for the FAS bytes
MultiFrame Alignment Signal (MFAS)
Byte is used to extend command and management functions over several frames
The MFAS counts from 0 to 255, providing a 256 multiframe structure
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9.2.2 Optical Transport Unit (OTU) Analysis
The OTU overhead is comprised of the SM, GCC0, and RES bytes.
Section Monitoring (SM)
Bytes are used for the Trail Trace Identifier (TTI), Parity (BIP-8) and the Backward Error Indicator (BEI) (also known
as the Backward Incoming Alignment Error [BIAE]), Backward Defect Indicator (BDI), and Incoming Alignment Error
(IAE).
The TTI is distributed over the multiframe and is 64 bytes in length. It is repeated four times over the multiframe.
SM TTI Type
General Communication Channel 0 (GCC0)
Clear channel used for transmission of information between OTU termination points
GCCO Type
TX300/e_e-manual_D07-00-033P_RevG00