You might use this trace if you suspect a problem with a device attached to a communication controller. If data appears correctly in the line trace but the terminal or printer does not react appropriately, the device itself is probably causing the failure.

Before using a line trace, you should use buffer and I/O traces to verify that the problem is not in VTAM® or an application program. You may also want to use the scanner interface trace (for 3720, 3725, and 3745 communication controllers only), which traces data after it has been processed by the NCP and before it leaves the communication controller. Therefore, it can help determine whether the problem is in the NCP or in the line.

You might want to use a transmission group (TG) trace instead of or in addition to this trace. If there is more than one active line in a transmission group, and you do not know which line is causing the problem, use the transmission group trace. The transmission group trace also shows more data than the line trace.

A line trace can be active for any line in the transmission group. However, a line trace and a transmission group trace cannot be active for the same line, at the same time.