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Chapter 6. Diagnostics
6-4
MX2800 STS-1 User Manual
61200659L1-1
Digital Line/Net
D
IGITAL
 L
INE
/N
ET
 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 6-5 for an illustration of this test.
Figure 6-5.  Digital Line/Network Loopback
Codec Line/Net
C
ODEC
 L
INE
/N
ET
 loopback performs a loopback of the selected 
T1/E1 in both the network and local loop directions. Both 
loopbacks occur at the T1/E1 codec. Both the network and the local 
loop side of the loopback are executed at the edge of the codec, 
completely testing the STS-1 mapper and the T1/E1 LIU. See 
Figure 6-6 for an illustration of this test.
Figure 6-6.  Codec Loopback
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)