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the FC-2 layer through the Sequence and Exchange constructs. The
framing protocol creates the constructs necessary to form frames with
the data being packetized within each frame's payload.
The FC-3 layer provides common services that span multiple N_Ports
(see
Section 2.5, "FC Ports," page
2-7). Some of these services include
Striping, Hunt Groups, and Multicasting. All of these services allow a
single port or fabric to communicate to several N_Ports at one time.
The top layer defined in FC is the FC-4 layer. The FC-4 layer provides a
seamless integration of existing standards. It specifies the mapping of
Upper Layer Protocols (ULPs) to the layers below. Some of these ULPs
include SCSI and IP. Each of these ULPs is defined in its own ANSI
document.
2.3 Frames
There are two types of frames used in FC: Link Control frames and Data
frames. Link Control frames contain no payload and are flow control
responses to Data frames. An example of a Link Control frame is the
ACK frame.
Figure 2.2
Link Control Frame
Start
CRC
End
Frame
of
of
Header
Frame
Frame
(4)
(4)
(4)
(24)
( ) = Number of Bytes
A Data frame is any frame which contains data in the payload field. An
example of a Data frame is the LOGIN frame.
Frames
2-3
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