CHANNEL

What is a CHANNEL

• A CHANNEL is a named path that carries data between CICS programs.
• Instead of one flat COMMAREA, a channel carries many named pieces of data called CONTAINERs.
• You load the channel with PUT CONTAINER commands, then pass it with the CHANNEL option.
• Channels can be used on LINK, XCTL, START and RETURN commands.
• The receiving program reads each piece with GET CONTAINER.
• Channels do not need any definition in CICS tables. Just use a name up to 16 characters.

Passing a channel to another program

• First load each data item into the channel with PUT CONTAINER(container-name) CHANNEL(channel-name).
• Then invoke the program with LINK PROGRAM('name') CHANNEL(channel-name).
• The called program reads the items with GET CONTAINER.
• The called program can also change a container. The caller then reads the new value with GET CONTAINER.
• Example:-
  EXEC CICS PUT CONTAINER(CUSTOMER-NO) CHANNEL(INQUIRY-CHANNEL) END-EXEC. EXEC CICS PUT CONTAINER(BRANCH-NO) CHANNEL(INQUIRY-CHANNEL) END-EXEC. EXEC CICS LINK PROGRAM('SERVER1') CHANNEL(INQUIRY-CHANNEL) END-EXEC. EXEC CICS GET CONTAINER(CUSTOMER-RECORD) CHANNEL(INQUIRY-CHANNEL) END-EXEC.

Why CHANNEL is better than COMMAREA

• A COMMAREA is one flat block with a fixed layout. Both programs must agree on every byte.
• A channel holds separate named containers, so each program picks only what it needs.
• Adding a new container does not break existing programs, unlike changing a COMMAREA layout.
• Channels can pass much larger amounts of data than a COMMAREA.
• The called program can update a container and the caller sees the new value.