Ficon Concepts - Brocade Communications Systems 1606 Administrator's Manual

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FICON concepts

FICON concepts
Figure 1
environment. The logical path of the traffic is defined as frames moving from the channel to the
switch to the control unit. FICON traffic moves from an LPAR (logical partition) and through the
channel, through a Fibre Channel link to the switch through the control unit, and ending at the
device. This is also called a channel path, which is a single interface between a central processor
and one or more control units along which signals and data can be sent to perform I/O requests.
The channel path uses the logical path to traverse the Fibre Channel fabric. The channel path is
defined using an ID, called the channel path ID (CHPID). This information is stored in the
Input/Output Configuration Program (IOCP) so that the same path is used. The IOCP is a z/OS
program that defines to a system the channels, I/O devices, paths to the I/O devices, and the
addresses of the I/O devices. The output is normally written to a z/OS or zSeries Input/Output
Configuration Data Set (IOCDS). The data set in the z/OS and zSeries processor (in the support
element) contains an I/O configuration definition built by the IOCP Work Load Manager.
FIGURE 1
The traffic on the channel path communicates using channel command words (CCWs) that direct
the device to perform device specific actions, such as Seek, Read, or Rewind. In a FICON
environment, CCWs use the buffer credit process for information unit (IU) pacing. IU pacing is a
mechanism that limits the number of CCWs, and therefore the number of IUs, that can either
transmit (write) or solicit (read) without the need for additional control-unit-generated
acknowledgements called command responses. There are times when there are no more buffer
credits to pass back to the other end and a frame pacing delay occurs. This is the number of
intervals of 2.5 microsecond duration that a frame had to wait to be transmitted due to a lack of
available buffer credits.
FICON introduces the following concepts:
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shows how the traffic in a switched point-to-point configuration flows in a FICON
FICON traffic
FICON Control Unit Port (CUP)
The internal port in a switch that assumes an FC address such that it is the FC DID used to
direct FICON traffic to the FICON Management Server.
FICON Manager
Host communication includes control functions such as blocking and unblocking ports, as well
as monitoring and error-reporting functions.
FICON Administrator's Guide
53-1001771-01