EXFO FTB-8510B Guia Del Usuario página 1264

Glossary
G.709 Optical Transport Network (OTN)
The main attributes of the ODU multiplexer functionality are as follows:
The Asynchronous Mapping Procedure (AMP) is used for multiplexing
the tributary signals; this method uses a modified Justification Control
mechanism which has 2 positive Justification Control bytes and one
negative Justification Control byte.
The new multiplex method also supports the Generic Mapping
Procedure as the Justification Control mechanism is still using the OPU
OH JC bytes.
The Multiplex Structure Identifier (MSI) provides information that is
specific to each type of multiplexer provided.
Can handle multiplex signals with frequency offset of +/- 20 ppm on
every layer for the legacy architecture while the new architecture
(using GMP) can handle frequency offset of +/-100 ppm.
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FTB-8100 Series Transport Blazer