Extreme Networks WM-4T1i manual Monitoring T1 Physical Link, Loopback

Configuring the T1 Physical Link

Monitoring T1 Physical Link

T1 devices have a built-in facility designed for troubleshooting the physical link, called loopback. The T1 link can also be monitored using show commands to display the current configuration of the link, any alarms on the link, link statistics, and link errors.

Loopback

The T1 device can be set up to loopback, that is, return a transmitted signal back to the sender so it can be compared with the original. There are several different types of loopback available to test different parts of the device and the line, specified in the T1 standards.

Local T1 Port Remote T1 Port

Data in	Data out
Data out	Data in
Framer	Framer

Data with framing

Figure 2-1:Normal operation of T1 link

XM_010

During normal operation of a T1 link, as the local data stream enters the framer, the appropriate framing bits are inserted into the data, and the framed signal is transmitted to the remote end. At the remote end, the process is reversed as the framing bits are discarded and the data stream is passed to the remote system.

Loopback can be enabled on the near-end or the far-end of the link. The near-end loopback modes are controlled directly by the hardware on the near-end. Far-end loopback modes require the cooperation of the far-end hardware. A message is sent to the far-end to cause it to enter a far-end loopback mode. When loopback is enabled on a T1 port, the green port LED will blink.

2-6 WM-4T1i Module Installation and User Guide