Fibre Channel Primer

29 Chapter 4: Physical and Signaling Layer
l A set of generic functions that are common across multiple upper-
layer protocols.
l A built-in protocol to aid in managing the operation of the link,
control the Fibre Channel configuration, perform error recovery,
and recover link and port status information.
l Optional headers that may be used for network routing.
l Control information in the header to assist hardware routing.
l Process to provide segmentation and reassembly of data.
BUILDING BLOCKS
To aid in the transport of upper-layer protocol application data
across the Fibre Channel network, the FC-2 layer defines a set of
four “building blocks” that create logical communication from end
to end.
1. Ordered Set. An ordered set consists of four 10-bit characters,
a combination of data characters and special characters that are used
to provide certain very low-level link functions, such as frame
demarcation and signaling between two ends of a link. This signaling
provides for initialization of the link after power-on and for certain
basic recovery actions.
2. Frame. A frame is the smallest indivisible packet of data
that is sent on the link. Frame protocol/structure is shown in Figure
4.6. Addressing is done within the frame header. Frames are not visible
to the upper-layer protocols and consist of the following fields:
l Start-of-frame delimiter (an ordered set)
l Frame header (defined by FC-2)
l Optional headers (defined by FC-2)
l Variable-length payload containing upper-layer protocol user data
(length 0 to maximum 2112 bytes)
l 32-bit CRC (for error detection)
l End-of-frame delimiter (an ordered set)
Each frame or group of frames can be acknowledged as part of the
flow control scheme. “Busy” and “Reject” messages are also defined
to provide notification of nondelivery of a frame.