Line trace

The line trace, a joint function of VTAM® and the NCP, records the status of a line each time the NCP receives data from or sends data to that line. Although the trace is controlled by VTAM, the information in the trace records is collected by the NCP. The NCP sends the data to VTAM in a PIU. A trace type indicator in the PIU indicates whether the trace is a byte line trace (type 2 scanner) or a block line trace (type 3 scanner).

Note: If the data is not from a type 1, 2, or 3 scanner, VTAM will not process the data. You must use ACF/TAP.

The line trace collects the operating parameters of a line each time a level 2 interruption occurs on that line.

For a 3705 communication controller with a type 2 communication scanner, a level 2 interruption occurs each time a byte of data is sent or received across the line.
For a 3705 communication controller with a type 3 communication scanner, a level 2 interruption occurs each time an NCP buffer is filled and the buffer data is sent or received across the line.
For a 3720, 3725, or 3745 communication controller, a level 2 interruption occurs each time a message (an entire PIU) is sent or received.

You can use the line trace only for lines attached to a communication controller and operating in network control mode.

For each 3705 communication controller, as many as eight line traces can be active at a time. For each 3720, 3725, or 3745 communication controller, a combination of eight line or scanner interface traces can be active at one time.

The number of active line traces to be allowed is specified during NCP generation (default is 2). In a cross-domain network in which the communication controller is connected to more than one host processor, the number of active traces allowed is distributed among the connected host processors on a first-come, first-served basis.

Note: As the number of active line traces increases, the system becomes less efficient.