The DQM channel control function

The channel control function provides the administration and control of message channels using CICS between WebSphere MQ for z/OS and compatible systems. See Figure 28 for a conceptual picture.

The channel control function consists of CICS panels and programs, a sequence number queue, a channel command queue, and a VSAM file for the channel definitions. The following is a brief description of the components of the channel control function.

• The channel definition file (CDF):
  • Is a VSAM file
  • Is indexed on channel name
  • Holds channel definitions
  • Must be available to the CICS regions in which the channel control program runs, and where the message channel agent (MCA) programs run
• You use channel definition panels to:
  • Create, copy, display, alter, find, and delete channel definitions
  • Start channels, reset channel sequence numbers, stop channels, ping channels, resync channels, and resolve in-doubt messages when links cannot be re-established
  • Display status information about channels

  The panels are CICS basic-mapping support maps.

• Sequence numbers and logical unit of work IDs (LUWIDs) are stored in the sequence number queue, SYSTEM.CHANNEL.SEQNO, and are used for channel re-synchronization purposes.
• A channel command queue, SYSTEM.CHANNEL.COMMAND, is used to hold certain commands for channels.
• The programs are a series of CICS transactions, which include transactions for the MCAs. There are different MCAs available for each type of channel. The names are contained in the following table. Other transactions provide channel control, command handling, and trigger monitoring.
  

  Table 35. Program and transaction names
  

  Program name	Channel type	CICS transaction ID
  CSQKMSGS	Sender	CKSG
  CSQKMSGR	Receiver	CKRC
  CSQKMSGQ	Requester	CKRQ
  CSQKMSGV	Server	CKSV

• A transient data queue CKMQ for error messages.

CICS regions

Figure 50 shows a configuration of two CICS regions, connected to a single queue manager. The regions have multiregion operation (MRO) links to one another, for function shipping of EXEC CICS START commands from the channel control program.

Figure 50. Sample configuration of channel control and MCA. MRO is used for an EXEC CICS START of the MCA, and for an EXEC CICS READ of the channel definition file by the MCA. Communication with the remote queue manager is through CICS ISC, not MRO.

Starting DQM panels

You invoke DQM panels with the CKMC CICS transaction. On invocation, DQM presents you with the main Message Channel List panel. All activity with the other panels follows from selections made on this panel.