User`s guide

Performing Loopback Modes and Pattern Tests

6-9

7800-A2-GB26-80

May 1999

As described in

Using Loopback Modes

on page 6-4 and

Using Pattern Tests

page 6-11,

the remote loopback Send V.54 Up Code and Send FT1 Up Code put

a remote device in loopback mode, while Send V.54 Down Code and Send FT1

Down Code take a remote device out of loopback mode. You can use these

codes in troubleshooting, as described in

Using

Pattern Tests

on page 6-11

Use of the Loopback Up Codes and Down Codes

The remote loopback up codes (which put a remote device in loopback mode)

and down codes (which take a remote device out of loopback mode) are in-band

codes that allow remote control of a device. The loopback modes, as well as the

pattern tests, are defined in MIBs, and so any device that supports the

appropriate MIBs is able to go into loopback mode and send/monitor pattern

tests. The LLB up code invokes an LLB in the remote unit while the LLB down

code terminates the remote LLB. The Send V.54 Up/Down and FT1 Up/Down

perform a similar function, but are only sent on the DS0s associated with a

particular data port and will control the remote operation of the DCLB Loopback.

The up and down codes are useful for performing tests from one end of a circuit.

The following example illustrates the use of the codes. You would:

1. Send an LLB up code from the local device to a remote DSU/CSU. The

remote DSU/CSU goes into line loopback.

2. Send a QRSS pattern test from the local device. The remote DSU/CSU will

return the QRSS pattern (because it is in loopback mode).

3. Start a monitor QRSS pattern test in the local 3100 Series device and

monitor the result to determine whether the circuit is operational (In Sync),

marginal (In Sync With Bit Errors), or completely down (Not in Sync). (The

test dialog described in

Running Tests

on page 6-12 reports the results of the

pattern test.)

4. Terminate sending and monitoring the QRSS pattern tests.

5. Send LLB down code from the local device to the remote DSU/CSU. Remote

DSU/CSU terminates the line loopback.