Generic Framing Procedure
Encyclopedia
Generic Framing Procedure (GFP) is a multiplexing
technique defined by ITU-T
G.7041. This allows mapping of variable length, higher-layer client signals over a circuit switched transport network like OTN
, SDH/SONET
or PDH
. The client signals can be protocol data unit
(PDU) oriented (like IP
/PPP
or Ethernet
Media Access Control
) or can be block-code oriented (like fibre channel
).
There are two modes of GFP: Generic Framing Procedure - Framed (GFP-F) and Generic Framing Procedure - Transparent (GFP-T):
GFP utilizes a length/HEC-based frame delineation
mechanism that is more robust than that used by High-Level Data Link Control
(HDLC), 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 currently 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, and is better known as an idle frame.
Multiplexing
The multiplexed signal is transmitted over a communication channel, which may be a physical transmission medium. The multiplexing divides the capacity of the low-level communication channel into several higher-level logical channels, one for each message signal or data stream to be transferred...
technique defined by ITU-T
ITU-T
The ITU Telecommunication Standardization Sector is one of the three sectors of the International Telecommunication Union ; it coordinates standards for telecommunications....
G.7041. This allows mapping of variable length, higher-layer client signals over a circuit switched transport network like OTN
Optical Transport Network
ITU-T defines an Optical Transport Network as a set of Optical Network Elements connected by optical fibre links, able to provide functionality of transport, multiplexing, switching, management, supervision and survivability of optical channels carrying client signals...
, SDH/SONET
Sonet
Sonet may refer to:* Sonet Records, European record label* Synchronous optical networking * Saab Sonett...
or PDH
Plesiochronous Digital Hierarchy
The Plesiochronous Digital Hierarchy is a technology used in telecommunications networks to transport large quantities of data over digital transport equipment such as fibre optic and microwave radio systems...
. The client signals can be protocol data unit
Protocol data unit
In telecommunications, the term protocol data unit has the following meanings:#Information that is delivered as a unit among peer entities of a network and that may contain control information, address information, or data....
(PDU) oriented (like IP
Internet Protocol
The Internet Protocol is the principal communications protocol used for relaying datagrams across an internetwork using the Internet Protocol Suite...
/PPP
Point-to-Point Protocol
In networking, the Point-to-Point Protocol is a data link protocol commonly used in establishing a direct connection between two networking nodes...
or Ethernet
Ethernet
Ethernet is a family of computer networking technologies for local area networks commercially introduced in 1980. Standardized in IEEE 802.3, Ethernet has largely replaced competing wired LAN technologies....
Media Access Control
Media Access Control
The media access control data communication protocol sub-layer, also known as the medium access control, is a sublayer of the data link layer specified in the seven-layer OSI model , and in the four-layer TCP/IP model...
) or can be block-code oriented (like fibre channel
Fibre Channel
Fibre Channel, or FC, is a gigabit-speed network technology primarily used for storage networking. Fibre Channel is standardized in the T11 Technical Committee of the InterNational Committee for Information Technology Standards , an American National Standards Institute –accredited standards...
).
There are two modes of GFP: Generic Framing Procedure - Framed (GFP-F) and Generic Framing Procedure - Transparent (GFP-T):
- GFP-F maps each client frame into a single GFP frame. GFP-F is used where the client signal is framed or packetized by the client protocol.
- GFP-T, on the other hand, allows mapping of multiple 8B/10B8B/10B encodingIn telecommunications, 8b/10b is a line code that maps 8-bit symbols to 10-bit symbols to achieve DC-balance and bounded disparity, and yet provide enough state changes to allow reasonable clock recovery. This means that the difference between the count of 1s and 0s in a string of at least 20 bits...
block-coded client data streams into an efficient 64B/65B block code for transport within a GFP frame.
GFP utilizes a length/HEC-based frame delineation
CRC-based framing
The concept of CRC-based framing was developed by StrataCom, Inc. in order to improve the efficiency of a pre-standard Asynchronous Transfer Mode link protocol. This technology was ultimately used in the principal link protocols of ATM itself and was one of the most significant developments of...
mechanism that is more robust than that used by High-Level Data Link Control
High-Level Data Link Control
High-Level Data Link Control is a bit-oriented synchronous data link layer protocol developed by the International Organization for Standardization...
(HDLC), 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 currently 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, and is better known as an idle frame.
Frame format
A GFP frame consists of:- a core header
- a payload header
- an optional extension header
- a GFP payload
- an optional payload frame check sequenceFrame Check SequenceA frame check sequence refers to the extra checksum characters added to a frame in a communication protocol for error detection and correction. Frames are used to send upper-layer data and ultimately the user application data from a source to a destination. The data package includes the message...
(FCS).
Modes
- Framed GFP (GFP-F) is optimized for bandwidth efficiency at the expense of latency. It encapsulates complete Ethernet (or other types of) frames with a GFP header.
- Transparent GFP (GFP-T) is used for low latency transport of block-coded client signals such as Gigabit EthernetGigabit EthernetGigabit Ethernet is a term describing various technologies for transmitting Ethernet frames at a rate of a gigabit per second , as defined by the IEEE 802.3-2008 standard. It came into use beginning in 1999, gradually supplanting Fast Ethernet in wired local networks where it performed...
, Fibre ChannelFibre ChannelFibre Channel, or FC, is a gigabit-speed network technology primarily used for storage networking. Fibre Channel is standardized in the T11 Technical Committee of the InterNational Committee for Information Technology Standards , an American National Standards Institute –accredited standards...
, ESCONESCONESCON is a data connection created by IBM, and is commonly used to connect their mainframe computers to peripheral devices such as disk storage and tape drives. ESCON is an optical fiber, half-duplex, serial interface. It originally operated at a rate of 10 Mbyte/s, which was later increased to...
, FiCONFICONFICON is the IBM proprietary name for the ANSI FC-SB-3 Single-Byte Command Code Sets-3 Mapping Protocol for Fibre Channel protocol. It is a FC layer 4 protocol used to map both IBM’s antecedent channel-to-control-unit cabling infrastructure and protocol onto standard FC services and infrastructure...
, and Digital Video Broadcast (DVB). In this mode, small groups of 8B/10B symbols are transmitted rather than waiting for a complete frame of data.