Buffer contents trace for the VTAM API and TSC

The buffer contents trace shows the contents of message buffers in the application programming interface (API) and the transmission subsystem component (TSC). When data is sent by an application program (outbound), API is the first component of VTAM® to process it, and TSC is the last component of VTAM to process it. When data is received from the network (inbound), TSC is the first component of VTAM to process it, and API is the last. To enable you to distinguish where in VTAM the trace data was recorded, the output specifies:

Either USER (for data recorded in API) or VTAM (for data recorded in TSC)
If the recorded data is inbound or outbound

The API writes user buffer contents trace records while user data is still in the application program's buffers, before it is copied into VTAM buffers. Only user data is recorded.

TSC writes VTAM buffer contents trace records while the data is in VTAM fixed I/O buffers. The PIU (the transmission header - TH, request/response header - RH, and user data) is recorded.

For a list of the resources for which you may request a buffer contents trace, see z/OS Communications Server: SNA Operation.

Note:

VTAM can start a buffer contents trace only for the resources that it owns. A data host, which does not own any NCPs, cannot start a buffer contents trace for an NCP or any of the NCP's subordinate resources.
If you want to trace a session between an LU and an application program, you must start the trace at the host where the application program resides.
If the buffer contents trace is active for a specific APPC application, the FMH5 is always traced at the user (API) level.
The VTAM TSC component is bypassed for conversation level data exchanged between two VTAM/APPC applications residing on the same host and using the APPCCMD macroinstruction interface to communicate. Thus VTAM buffer contents records are not to be recorded for this data. USER buffer contents records will continue to be recorded.