Carrier Access Broadmore 1750 - Manual (Page 207)

Broadmore 1750 - Release 4.6 8-19
Maintenance and Troubleshooting
Port Loopback
Port Loopback
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
7-37 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.
CAUTION! T HE TERMINAL OPTION IS RESERVED FOR C ARRIER
A CCESS ENGINEERS AND SHOULD NOT BE USED .
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.