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COMSPHERE DualFlow Data Service Units
4-10 December 1996 3615-A2-GB20-20
NOTE
To abort a loopback on the
tributary DSU from the NMS,
establish a dial connection with
the control DSU, then issue a
subnetwork abort command
from the NMS to the control.
Local Loopback
Only available to a DSU, Local Loopback (LL) is
session-disruptive; that is, performing the test will disrupt
data. It permits the DTE or router to run a test to
determine whether the DTE or router connection to the
DSU and the DSU itself are functioning properly. The
DSU must be connected to the DTE or router, but the
network connection to the DSU is not required.
While the DSU is in Local Loopback, any data
transmission by the DTE or router is returned as received
data. An operator can send a test pattern and verify correct
reception of the test. The DSU does not monitor this
testing.
NOTE
If the NMS is to abort the Local
Loopback, the tributary’s DBM
must be in 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.
DTE Loopback
DTE Loopback (DTE
) loops back the data path at the
DTE interface without affecting operation of the other
port. This loopback is used to verify that the DTE or
router connection and the cable are good.
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 (BER
T) from the remote DSU. The local DSU
receives test data, loops it back to the transmitter before
the DSU’s 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) in the
DSU option set, and
RespondRDL
(Respond to Remote
Digital Loopback).
Remote Digital Loopback
Only
available to the DBM, the 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 DBM and returned to the local DBM.
In Remote Digital Loopback, the local DBM (control
or tributary) puts the remote DBM into Digital Loopback.
496-14493a
DSU
DTE
LL
COMSPHERE 3610
NETWORK
DL or
RL on
Aggregate
DL or
RL on a
Port
COMSPHERE 3610
DSU
DTE
(ROUTER)
DTE
(ROUTER)
Figure 4-3. Loopbacks