The CRC field is calculated on the Frame Header and Data Field prior to encoding for transmission and after decoding
upon reception
Frame Delimiters
A frame delimiter is an
Ordered Set
that immediately precedes or follows the contents of a frame. Separate and distinct delimiters
shall identify the start of a frame and the end of a frame and shall be recognized when a single Ordered Set is detected. An Ordered
set is described below.
Ordered Set
An Ordered Set is a four-character combination of data and special Transmission Characters. Ordered Sets provide the ability to
obtain bit and word synchronization that also establishes word boundary alignment. The three types of Ordered Sets are:
Frame Delimiters
(SOF)
Start-of-Frame
(EOF)
End-of-Frame
Primitive Signals
A Primitive Signal is an Ordered Set designated to have special meaning. All FC_Ports shall at a minimum recognize R_RDY
and IDLE Primitive Signals. All Primitive Signals not recognized by the FC_Port shall be treated as an IDLE.
Idle:
Idle is a Primitive Signal transmitted on the link to indicate that link initialization is complete and to maintain link
synchronization
(R_RDY)
Receiver Ready
Primitive Sequence
(OLS)
Off-line
(NOS)
Not Operational
(LR)
Link Reset
(LRR)
Link Reset Response
Start of Frame (SOF) and End of Frame (EOF) Delimiter setup
The Start-of-Frame (SOF) delimiter is an Ordered Set that immediately precedes the frame content. There are multiple SOF delimiters
defined for Sequence control. SOF indicates that a Frame will immediately follow and indicates which class of service the Frame will
use.
The value of the SOF field determines the class of service associated with the FC frame. Several Classes of service are specified in
Fiber Channel but only Classes 1,2,3 & 4 are described below. Classes 1, 2, and 3 are topology independent, however, Classes 4 and
6 require a Fabric. If the Fabric is not present, the service is provided as a special case of point-to-point. FC_Ports are not required to
support all classes of service.
Class 1:
Dedicated physical connection with delivery confirmation. This class of service has three phases:
Setting up the connection
Transferring the information
Closing down the connection
Class 2:
Frame multiplexed service with delivery confirmation. No dedicated connection between the two communication parties
is established. This class of service allows a stream of frames to be sent to different destinations quickly. Class 2 also requires
frame confirmations by the recipient.
Class 3:
Is sometimes called "datagram". It is "connectionless" service with the Fabric multiplexing frames at frame boundaries,
if a Fabric is present. If a Fabric is not present, this service becomes a special case of point-to point.
Class 4:
Is a service that uses a virtual circuit established within a Fabric and between two communicating Nx_Ports to
transmit frames to each other using a fabric-managed fractional bandwidth allocation protocol. This service requires a Fabric.
The following SOF Service Class selections are available:
SOF Initiate
(SOFix)
A Sequence shall be initiated and identified by using SOFi1, SOFi2, SOFi3, or SOFi4 in the first frame. SOFix is used to
represent these four SOF delimiters.
SOF_i3:
Contains a code value of 0x2E indicating SOF Initiate Class 3. A SOFi3 should be used on the first frame of a
Sequence for Class 3 Service.
SOF Normal
(SOFnx)
The following delimiters identify the start of all frames other than the first frame of a Sequence based on class of service.
SOFnx is used to indicate SOFn1, SOFn2, SOFn3 and SOFn4.
SOF_n3:
Contains a code value of 0x36 indicating SOF Normal Class 3. The SOFn3 shall be used for all frames except
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