IMS nodes

IBM® App Connect Enterprise message flows use IMS nodes to call programs that are running in IMS.

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 diagram shows how request and response bit streams are exchanged with the IMS Program.

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.
The diagram shows the structure of a request bit stream, and is described in the following text.
  • 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.
The diagram shows that the structure of a response bit stream is the same as a request bit stream, but without the transaction code.

Commands

You can also use bit streams to run commands. The structure of the response bit stream is illustrated by the following diagram.
The diagram shows the structure of a response bit stream that is used to run commands.
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: