3Com SuperStack II, NETBuilder SI manual Performing a Loopback Test on a Serial Port

144APPENDIX A: TROUBLESHOOTING

Performing a Loopback Test on a Serial Port

This section describes how to perform a loopback test on a serial port.

Figure 14 shows the data flow that occurs when a loopback test is performed on a serial line. A modem or CSU/DSU is required in this configuration.

Figure 14 Serial Loopback Testing

Before running the serial loopback test, complete the following tasks:

■Attach a console or Telnet to your bridge/router.

■Place the modem or CSU/DSU in local loopback test mode. For information, see the documentation that accompanies your modem or CSU/DSU.

■Verify the path and port number of the serial port you are testing by referring to Table 14 or Table 15 on page 69.

To perform a loopback test on the serial port, follow these steps:

1Set the line type to Leased using:

SETDefault !<path> -PATH LineType = Leased

2Set the owner of the serial port you are testing to LoopBack using:

SETDefault !<port> -PORT OWNer = LoopBack

3Select the loopback test mode by entering:

DLTest TestMode LoopBack

4Specify the number of seconds that the test should run using:

DLTest TestDuration <seconds>

If you do not enter a value, the test will run indefinitely. However, use caution when running the test for a specified duration. The test ends abruptly as soon as the time duration expires, and a discrepancy between the number of packets transmitted and the number received may result.

5Start the serial loopback test by entering:

DLTest START