Carrier Access 1750 Benutzerhandbuch

The loopback function is the primary troubleshooting aid for isolation of circuit 
connectivity problems, both internal and external to the Broadmore 1750. Loopback is 
available on both the NIM and SAM. There are three loopback options on each SAM 
module, four on each NIM, see Figure 8-1. These loopbacks are set as a card 
configuration function (see “Module Configuration” on page

 for details).

Loopbacks provide a means to verify that circuit paths are functioning correctly. For 
example, setting the SAM remote loopback, will take user equipment transmit data 
(Tx) and send it to user equipment receive data (Rx). If a check of the user equipment 
indicates good Tx and Rx, the problem is not between the SAM and user equipment but 
somewhere else in the circuit. This logic can then be extended through the entire circuit 
until problems are isolated and corrected.

The NIM has four loopback options:

1. Normal: no loopback.

2. Local: The user equipment data is looped back after processing by the SONET 

circuitry on the NIM.

3. Remote: The ATM network data is looped back before passing through the 

NIM

4. Terminal: The user equipment data is looped back after passing through the 

NIM framer, but before the Line Interface Unit, LIU. 

The SAM has three loopback options:

1. Normal state is no loopback.

2. Remote: user equipment data is looped back after passing through the SAM 

LIU.

3. Local: ATM network data is looped back to the network after local processing 

by the NIM but before passing through the SAM LIU to user equipment.

These loopback options are shown graphically on the next page. The top view shows a 
simple circuit without any loopbacks. The middle view shows NIM loopbacks breaking 
the circuit connectivity. SAM loopbacks are shown in the following figure.