Troubleshooting guide

Section 5, User Interface Guide - UIG-535, STS-1 Loopbacks
61186003L1-1D 5-97
Figure 5-65. Tributary Loopback Test
Analog Network
An Analog Network loopback test loops the selected T1/E1 back to the network (STS-1). The
T1/E1 is completely demultiplexed, looped back at the T1/E1 line interface unit (LIU) through
the LIU drivers and receivers, and multiplexed back onto the STS-1 network stream. See
Figure 5-66 for an illustration of this test.
Figure 5-66. Analog Network Loopback
Digital Line/Net
A Digital Line/Net loopback performs a loopback of the selected T1/E1 in both the network
and local loop directions. Both loopbacks occur at the T1/E1 LIU. The network side loopback
occurs deep into the LIU through the receiver, receive equalizer, transmit jitter attenuator,
and finally, through the T1/E1 transmit drivers. See Figure 5-67 for an illustration of this
test.
STS-1
MAPPER
T1/E1 LIU
(1 of 28)
T1/E1 LIU
(28 of 28)
STS-1
LIU
CODEC
(1 of 28)
CODEC
(28 of 28)
STS-1
MAPPER
T1/E1 LIU
(1 of 28)
T1/E1 LIU
(28 of 28)
STS-1
LIU
CODEC
(1 of 28)
CODEC
(28 of 28)