When the invoker sends a request to the mainframe, it wraps the raw data in a message structure. The LegStar messaging framework is transport independent so that LegStar can evolve to support more transports in the future.

The framework uses a notion of "Address" similar in spirit to SOAP Addressing which allows each request to be correctly routed. The Address identifies the target mainframe.

The message structure is multipart to support host programs with multiple input structures and multiple output structures (for example CICS containers).

When the underlying transport uses LegStar messaging:

Message headers support an open format based on JSON so that more sophisticated message exchange protocols can be built in the future.

On the mainframe side, the data needs to be unwrapped and extracted from the message received. This C/370 program performs such unwrapping.

The following mainframe side C/370 programs provide the message wrapping/unwrapping capabilities:

Some transports (such WebSphere MQ with CICS MQ Bridge) do not use the LegStar messaging and therefore do not need the LegStar z/OS modules to be installed.