Paradyne 3551 manual Bilateral Loopback, DTE Loopback, Remote Digital Loopback, Digital Test

COMSPHERE 3550 Series Data Service Units

NOTE

To issue a Local Loopback to a tributary DSU, the DSU must have a DBM installed or a Conflict w/ Environ message will appear. The DBM is required to call the tributary and abort the Local Loopback.

If the NMS is to abort the loopback, the tributary's DBM must be in Idle or Standby mode. If in Dial Backup mode and the NMS issues the Abort command, the command will not be recognized. The loopback will have to be aborted from the DSU's control panel.

point-to-point or multipoint network, whereas a tributary DSU can originate Remote Digital Loopback in a point-to-point network only.

When a DSU (control or tributary) originates Remote Digital Loopback, both the originating DSU and the targeted DSU enter Test mode. No other test can be run at the originating DSU or the targeted DSU until the Remote Digital Loopback is aborted.

The DSU does not generate test results.

Bilateral Loopback

Bilateral Loopback (Bilat Lpbk) is a combination of DTE and Digital Loopbacks operating simultaneously in the same DSU. Both Bilateral and Digital Loopbacks are selected from the General (Gen) option set.

DTE Loopback

DTE Loopback (DTE) loops back the data path at the DTE interface on a per-port basis without affecting the operation of the remaining ports. This loopback is used to verify that the DTE connection and the cable are good.

NOTE

If Bilat Lpbk is enabled, requesting a Remote Digital Loopback or Digital Test will automatically initiate a DTE Loopback, as well.

Digital Loopback

Digital Loopback (DL) allows manual testing of the remote end of the circuit. Data coming in is immediately transmitted back. For example, a Digital Loopback may be required in order to complete an external bit error rate test (BERT) from the remote DSU. The local DSU receives test data, loops it back to the transmitter before the DTE interface, and returns it to the network.

Digital Loopback can also be initiated by receiving a V.54 pattern to go into Digital Loopback. Enable configuration options V.54 Lpbk (V.54 Loopback) and RespondRDL (Respond to Remote Digital Loopback).

Remote Digital Loopback

Remote Digital Loopback (RL), sometimes referred to as RDL, typically supports testing using an external device, like a protocol analyzer that is connected to the local DSU's DTE interface. A test message from the external device is looped back from the receiver to the transmitter in the remote DSU and returned to the local DSU.

In Remote Digital Loopback, the local DSU (control or tributary) puts the remote DSU into Digital Loopback. A control DSU can originate Remote Digital Loopback in a

Digital Test

The Digital Test (DT) checks the functionality of a pair of DSUs and the data circuit between them. This test can also be run on a DBM over a backup connection to a remote DBM for point-to-point testing.

The remote DSU is placed in Digital Loopback, then the local DSU transmits the 511-bit test pattern over the network to the remote DSU for an operator-specified length of time. In a multipoint network (where only a control DSU can originate a Digital Test), tributary DSUs not involved in the test are placed in Test mode for the duration of the test.

During the test, the TXD, RXD, and RTS LED indicators show the states of the leads at the DTE interface. At the conclusion of the test, the local DSU releases the remote DSU from Digital Loopback.

To review the results of the test, select Displ (Display)

and press the key to scroll through the results shown in Table 4-3.

When the test is over, the top line displays Final instead of Active.

4-10 December 1996 3550-A2-GB20-20