| Generic
Framing Procedure |
Generic Framing Procedure (GFP) is defined by ITU-T G.7041. This allows mapping
of variable length, higher-layer client signals over a transport network like
SDH/SONET. The client signals can be protocol data unit (PDU) oriented (like IP/PPP
or Ethernet Media access control [MAC]) or can be block-code oriented (like fiber
channel).
There are two modes of GFP, viz., GFP-F and GFP-T. GFP-F maps each
client frame into a single GFP frame. GFP-T, on the other hand, allows mapping
of multiple 8B/10B client data frames into an efficient 64B/65B block code for
transport within a GFP frame.
GFP utilizes a length/HEC-based frame delineation
mechanism that is more robust than that used by HDLC (High-level Data Link Control),
which is single octet flag based.
There are two types of GFP frames: a GFP
client frame and a GFP control frame.
A GFP client frame can be further classified
as either a client data frame or a client management frame. The former is used
to transport client data, while the latter is used to transport point-to-point
management information like loss of signal, etc. Client management frames can
be differentiated from the client data frames based on the payload type indicator.
The GFP control frame consists only of a core header field with no payload area.
This frame is used to compensate for the gaps between the client signal where
the transport medium has a higher capacity than the client signal.
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