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.
