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Transport aspects 2

17.4.1 Mapping of GFP frames into an extended OPU2 payload area

The mapping of generic framing procedure (GFP) frames in an extended OPU2 payload area is performed
by aligning the byte structure of every GFP frame with the byte structure of the extended OPU2 payload
(see Figure 17-7). Since the GFP frames are of variable length (the mapping does not impose any
restrictions on the maximum frame length), a frame may cross the OPU2 frame boundary.

Figure 17-7  OPU2 frame structure and mapping of GFP frames
into an extended OPU2 payload area

GFP frames arrive as a continuous bit stream with a capacity that is identical to the OPU2 payload area, due
to the insertion of GFP-idle frames at the GFP encapsulation stage. The GFP frame stream is scrambled
during encapsulation.
NOTE – There is no rate adaptation or scrambling required at the mapping stage; this is performed by the GFP
encapsulation process.

The OPU2 overhead for the GFP mapping consists of a payload structure identifier (PSI) including the
payload type (PT), a client signal fail (CSF) indicator and 254 bytes plus 7 bits of reserved for future
international standardization (RES).
The extended OPU2 payload for the GFP mapping consists of 4 × 3808 bytes from the OPU2 payload plus 7
bytes from the OPU2 overhead.

17.5 Mapping of test signal into OPU

17.5.1 Mapping of a NULL client into OPU
An OPU payload signal with an all-0s pattern (see Figure 17-8) is defined for test purposes. This is referred
to as the NULL client.

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