If you want to start the transmission group trace during startup, list the trace and appropriate options from the system console during startup. For more information about starting the NCP transmission group trace during startup, see z/OS Communications Server: SNA Operation.

If you want to start the trace from the host processor, issue the appropriate command for your access method after VTAM® is started.

You can activate VTAM traces when VTAM is started or as needed. Use the TRACE option on the START command to begin the trace when VTAM is started. Use the MODIFY TRACE command to begin the trace when VTAM is already running. The TRACE start option and the MODIFY TRACE command have additional parameters unique to the type of trace being started.

Before you start the transmission group trace for VTAM, start the generalized trace facility (GTF) with the USR option; otherwise, none of the trace data is recorded. For information about starting GTF, see z/OS MVS Diagnosis: Tools and Service Aids.

You can stop the NCP transmission group trace with the same procedure you used to start the trace. To stop the trace from the host processor, specify the NOTRACE parameter of the MODIFY command.

For more information about the transmission group trace, TRACE start option, and MODIFY TRACE command, see z/OS Communications Server: SNA Operation.

To interpret and print trace data, see ACF/TAP information in ACF/TAP and trace data.

The PRDMP system service aid to print the NCP line trace data is not supported for the IBM® 3720, 3725, and 3745 Communication Controllers. For more information about PRDMP, see z/OS Communications Server: SNA Diagnosis Vol 2, FFST Dumps and the VIT.