
Configuring WAN Line Services
4-8 117021-A Rev. A
Remote Digital Loopback (RL)
Remote Digital Loopback (CCITT V.54 Loopback) tests the local router
DSU/CSU, the Telco circuit, and the remote DSU/CSU. The local DSU/CSU
sends a V.54 loop-up code to the remote DSU/CSU to initiate a Digital Loop, and
then sends a test pattern through the loop to check for returned data errors.When
the remote DSU/CSU receives the V.54 loop-up code, it provides the loopback
path shown in F
igure 4-6.
Figure 4-6. Remote Digital Loopback (CCITT V.54 Loopback)
Local Analog Loopback (AL)
Local Analog Loopback is a self-diagnostic local test, shown in F
igure 4-7.
Figure 4-7. Analog Loopback
While operating the local loop test, the CSU transmits data to the network to avoid
causing a carrier alarm.
Network
AN/ANH/ARN
DSU
CSU
LS0024A
Network
AN/ANH/ARN
DSU
CSU
LS0023A
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