The IMS node sends
a bit stream to IMS, which schedules
one of its programs to process the message. The program generates
a message, which IMS sends back
to the IMS node, as illustrated
in the following diagram.
The bit stream contains the routing information that IMS needs so that it can schedule
a program to receive that bit stream. The structure of the bit stream
varies depending on whether it is a request or response bit stream.
The structure of the different bit streams are described in the following
sections.
Request bit stream
The structure of the
request bit stream is illustrated by the following diagram.
- LLZZ is a four-byte field. The first two bytes
indicate the length of the bit stream, and the other two bytes are
reserved for use by IMS.
- The transaction code can contain up to eight characters. If the
code contains less than eight characters, the transaction code must
be delimited by a space. When the transaction code is less than eight
bytes, IMS reads only the transaction
code and one space. The response segments do not need to have the
transaction name, but an IMS program
can add it.
- The rest of the bit stream comprises the data that the IMS program needs.
IMS reads the first twelve
bytes of the bit stream, but it passes the entire bit stream to the IMS program.
Response bit stream
The structure of the
response bit stream is illustrated by the following diagram.
Commands
You can also use bit streams to
run commands. The structure of the response bit stream is illustrated
by the following diagram.
The first character after LLZZ
is the slash (/) character, which is followed by the command verb
and any arguments. For commands, the response bit stream has the same
format as the response bit stream for transactions: LLZZ is followed
by the response data.
For more information about IMS concepts,
see the following topics: