Communication between devices in a
fibre channel
Fibre Channel (FC) is a high-speed data transfer protocol providing in-order, lossless delivery of raw block data. Fibre Channel is primarily used to connect computer data storage to servers in storage area networks (SAN) in commercial data cen ...
network uses different elements of Fibre Channel standards.
Transmission words and ordered sets
All Fibre Channel communication is done in units of four 10-bit codes. This group of 4 codes is called a transmission word.
An ordered set is a transmission word that includes some combination of control (K) codes and data (D)
codes
In communications and information processing, code is a system of rules to convert information—such as a letter, word, sound, image, or gesture—into another form, sometimes shortened or secret, for communication through a communication c ...
.
AL_PAs
Each device has an
Arbitrated Loop
The arbitrated loop, also known as FC-AL, is a Fibre Channel topology in which devices are connected in a one-way loop fashion in a ring topology. Historically it was a lower-cost alternative to a fabric topology. It allowed connection of man ...
Physical Address (AL_PA). These addresses are defined by an 8-bit field but must have neutral disparity as defined in the
8b/10b coding scheme. That reduces the number of possible values from 256 to 134. The 134 possible values have been divided between the fabric, FC_AL
ports
A port is a maritime facility comprising one or more wharves or loading areas, where ships load and discharge cargo and passengers. Although usually situated on a sea coast or estuary, ports can also be found far inland, such as Ham ...
, and other special purposes as follows:
Meta-data
In addition to the transfer of data, it is necessary for Fibre Channel communication to include some
metadata
Metadata is "data that provides information about other data", but not the content of the data, such as the text of a message or the image itself. There are many distinct types of metadata, including:
* Descriptive metadata – the descriptive ...
. This allows for the setting up of links, sequence management, and other control functions. The meta-data falls into two types, primitives which consist of a 4 character transmission word and non-data frames which are more complex structures.
Primitives
All primitives are four characters in length. They begin with the control character K28.5, followed by three data characters. In some primitives the three data characters are fixed, in others they can be varied to change the meaning or to act as parameters for the primitive. In some cases the last two parameter characters are identical.
Parameters are shown in the table below in the form of their hexadecimal 8-bit values. This is clearer than their full 10-bit (Dxx.x) form as shown in the
Fibre Channel
Fibre Channel (FC) is a high-speed data transfer protocol providing in-order, lossless delivery of raw block data. Fibre Channel is primarily used to connect computer data storage to servers in storage area networks (SAN) in commercial data cen ...
standards:
Note 1: The first parameter byte of the EOF primitive can have one of four different values (8A, 95, AA, or B5). This is done so that the EOF primitive can rebalance the disparity of the whole frame. The remaining two parameter bytes define whether the frame is ending normally, terminating the transfer, or is to be aborted due to an error.
Note 2: The Open selective replicate variant can be repeated a number of times in order to communicate with more than one destination port simultaneously. The Open broadcast replicate variant will allow communication with all ports simultaneously.
Note 3: The SOF primitive contains a pair of control
byte
The byte is a unit of digital information that most commonly consists of eight bits. Historically, the byte was the number of bits used to encode a single character of text in a computer and for this reason it is the smallest addressable unit ...
s (shown as cccc in the table) to designate the type of frame.
Frames
The Fibre Channel protocol transmits data in frames each of which can contain up to 2112 bytes of
payload data
In computing and telecommunications, the payload is the part of transmitted data that is the actual intended message. Headers and metadata are sent only to enable payload delivery.
In the context of a computer virus or worm, the payload is t ...
. The structure of a frame is shown in this table:
In addition to data frames, there are non-data frames that are used for setup and messaging purposes. These fall into three categories:
link control frames, link service frames, and extended link service frames. The following table lists the most common ones:
{, border="1" cellpadding="5" cellspacing="0"
, Mnemonic, , Frame type, , Meaning
, -
, , ABTS, , Link service, , Abort Sequence
, -
, , ACK, , Link control, , Acknowledge data frame (success)
, -
, , BA_ACC, , Link service, , Basic accept
, -
, , BA_RJT, , Link service, , Basic reject
, -
, , F_BSY, , Link control, , Fabric busy
, -
, , F_RJT, , Link control, , Fabric frame reject
, -
, , FLOGI, , Extended link service, , Fabric login
, -
, , NOP, , Link service, , No Operation
, -
, , P_BSY, , Link control, , Port busy
, -
, , P_RJT, , Link control, , Port frame reject
, -
, , PLOGI, , Extended link service, , Port login
, -
, , PRLI, , Extended link service, , Process login
, -
, , PRLO, , Extended link service, , Process logout
, -
, , PRMT, , Link service, , Dedicated connection preempted
, -
, , RMC, , Link service, , Remove connection
, -
, , RSI, , Extended link service, , Request sequence initiative
Fibre Channel
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