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2.4 Exchanges
2-4
Figure 2.3
Data Frame
Start
Frame
of
Header
Frame
(4)
(24)
( ) = Number of Bytes
In FC, an Ordered Set is a group of four 10-bit characters that provide
low level Link functions, such as frame demarcation and signaling
between two ends of a Link. All frames start with a Start-of-Frame (SOF)
and end with an End-of-Frame (EOF) Ordered Set. Each frame contains
at least a 24-byte header defining such things as Destination and Source
ID, Class of Service and type of frame (e.g., FCP or FC-LE). The biggest
field within a frame can be the payload field. If the frame is a Link Control
frame, then there is no payload. If it is a Data frame, then the frame will
contain a Payload field of up to 2112 bytes. Finally, the frame includes a
Cyclic Redundancy Check (CRC) field used for detection of transmission
errors, followed by the EOF Ordered Set.
Figure 2.4
outlines the FC hierarchical Data structures. At the most
elemental level, four 8b/10b encoded characters make up a FC Word. A
FC Frame is a collection of FC words. A FC Sequence is made up of
one or more frames, and a FC Exchange is made up of one or more
sequences.
Fibre Channel Overview
Copyright © 2000, 2001 by LSI Logic Corporation. All rights reserved.
Data Field
(Optional Headers and
Payload)
(0 to 2112)
CRC
End
of
Frame
(4)
(4)
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