Generic Framing Procedure

Generic Framing Procedure (GFP ) is a multiplexing technique which is defined in the ITU-T G.7041. It makes it possible to route data streams by applications from a higher network layer via a transport network such as SONET / SDH, the packet size may be variable.

Variations

The packets may Protocol Data Unit (PDU ) to be oriented, such as IP / PPP or Ethernet Media Access Control, or they can be block-oriented, such as Fibre Channel. GFP has two modes: Generic Framing Procedure - Framed ( GFP -F) and Generic Framing Procedure - Transparent ( GFP -T):

  • GFP -F maps each application package into a single GFP package. GFP -F is used when the protocol of the application packetization is performed.
  • GFP- T, however, it more efficient to pack 8B/10B block- coded application data streams in a common 64B/65B block code that is transported with GFP allowed.

GFP uses a length / HEC - based mechanism is more robust than that of high-level Data Link Control (HDLC ), which is based on single octet flags.

Nortel implements two types of GFP- packages: a GFP client frame and a GFP control frame. The former may be, in turn, a data or a management frame for the application and in any case be transported application data. The control frame, however, transported point- to-point management information such as signal loss, etc. It can also contain only header information and no user data to fill gaps in the data stream of the application if it transmits slower than the medium can carry. One also speaks of idle frames.

Packet format

A GFP- package consists of:

  • Core header
  • Data header
  • GFP payload
  • Optional Frame Check Sequence (FCS )
  • Optional extension headers.

Modes

  • Framed GFP ( GFP -F) uses bandwidth optimally, at the expense of latency. It encapsulates a complete application packages (eg Ethernet) and provides them with a GFP header.
  • Transparent GFP ( GFP -T) used one to transport block- encoded data such as Gigabit Ethernet, Fibre Channel, ESCON, FICON and Digital Video Broadcasting (DVB ) with low latency. Here possibly also smaller groups are transported from 8B/10B-Symbolen, instead of waiting for the achievement of a complete packet size.
Point-to-Point Protocol Frame (networking)
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