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MX2800 M13 Multiplexer User Manual Loopbacks, Section 6
61200290L1-1G 6-3
Figure 6-3. Tributary Loopback Test
Analog Network
An Analog Network loopback test loops the selected T1/E1 back to the network (DS3). 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 DS3 network stream. See Figure 6-4 for an illustration of this
test.
Figure 6-4. 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 at the edge of the
LIU while the T1/E1 loop side loopback occurs deep into the LIU through the receiver, receive equalizer,
transmit jitter attenuator, and the T1/E1 transmit drivers. See Figure 6-5 on page 6-3 for an illustration of
this test.
Figure 6-5. Digital Line/Network Loopback
DSX-3
LIU
M23
MUX/DMUX
M12/G.747
MUX/DMUX
(1 of 7)
F
R
A
M
E
R
D
S
2
F
R
A
M
E
R
D
S
3
....
....
T1/E1 LIU
(1 of 28)
CODEC
(28 of 28)
CODEC
(1 of 28)
T1/E1 LIU
(28 of 28)
DSX-3
LIU
M23
MUX/DMUX
M12/G.747
MUX/DMUX
(1 of 7)
F
R
A
M
E
R
D
S
2
F
R
A
M
E
R
D
S
3
....
T1/E1 LIU
(1 of 28)
CODEC
(28 of 28)
CODEC
(1 of 28)
T1/E1 LIU
(28 of 28)
DSX-3
LIU
M23
MUX/DMUX
M12/G.747
MUX/DMUX
(1 of 7)
F
R
A
M
E
R
D
S
2
F
R
A
M
E
R
D
S
3
....
....
T1/E1 LIU
(1 of 28)
CODEC
(28 of 28)
CODEC
(1 of 28)
T1/E1 LIU
(28 of 28)
DSX-3
LIU
M23
MUX/DMUX
M12/G.747
MUX/DMUX
(1 of 7)
F
R
A
M
E
R
D
S
2
F
R
A
M
E
R
D
S
3
....
T1/E1 LIU
(1 of 28)
CODEC
(28 of 28)
CODEC
(1 of 28)
T1/E1 LIU
(28 of 28)
DSX-3
LIU
M23
MUX/DMUX
M12/G.747
MUX/DMUX
(1 of 7)
F
R
A
M
E
R
D
S
2
F
R
A
M
E
R
D
S
3
....
....
T1/E1 LIU
(1 of 28)
CODEC
(28 of 28)
CODEC
(1 of 28)
T1/E1 LIU
(28 of 28)
DSX-3
LIU
M23
MUX/DMUX
M12/G.747
MUX/DMUX
(1 of 7)
F
R
A
M
E
R
D
S
2
F
R
A
M
E
R
D
S
3
....
T1/E1 LIU
(1 of 28)
CODEC
(28 of 28)
CODEC
(1 of 28)
T1/E1 LIU
(28 of 28)