Ethernet encapsulation with GFP
The generic framing procedure (GFP) is used to adapt the asynchronous Ethernet
payload to the synchronous SDH server layer.
A GFP-header (8 octets) is prepended to each Ethernet frame to indicate frame length
and payload type. Gaps between Ethernet frames are filled with “IDLE” frames (4
octets each).
GFP, standardized by the ITU-T in the recommendations G.7041 and Y.1303, is a very
efficient encapsulation protocol because it has a fixed and small overhead per packet.
In earlier versions (prior to the Garnet network release of June 2002) of the
TransLAN
®
equipment, the Ethernet over SDH (EoS) encapsulation and mapping
method is used for VC-12 and/or VC-3 based designs (10/100BASE-T Ethernet / Fast
Ethernet cards). EoS is a proprietary encapsulation protocol, based on the ANSI
T1X1.5/99-268r1 standard, and can be regarded as a precursor of GFP. EoS and GFP
are both length-based encapsulation methods. EoS is similar to GFP in terms of frame
delineation and mapping (incl. scrambling); differences between the two encapsulation
methods lie in the size and interpretation of the EoS/GFP encapsulation core headers,
as well as the length of the Idle frames.
The generic framing procedure, framed mode (GFP-F) compliant to the ITU-T Rec.
G.7041 is available on all TransLAN
®
products since the Garnet Maintenance /
Mercury network release of January 2003.
LAN
LAN
SDH transport
network
Virtual switch
LAN
ports
WAN
ports
TransLAN physical
Ethernet switch
IDLE
GFP
HEADER
Ethernet frame
IDLE IDLE
GFP
HEADER
GFP
HEADER
Ethernet frame
IDLE IDLE
Ethernet frame
Ethernet Overview
Ethernet over SDH
....................................................................................................................................................................................................................................
11-6
Alcatel-Lucent - Proprietary
See notice on first page
365-312-801R7.2
Issue 3, May 2007
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