Line Loopback; Digital Loopback; Figure 6-9. Line Loopback Test; Figure 6-10.Digital Loopback - ADTRAN MX2800 M13 User Manual

MX2800 M13 Multiplexer User Manual

Line Loopback

Line Loopback performs a loop of the DS3 back to the network. This loopback occurs just prior to the DS3
framer and B3ZS decoder, but it makes full use of the DS3 LIU in both receive and transmit directions;
therefore, any coding violations received by the DS3 will be inserted back into the network without
modification. See Figure 6-9
If a Line loopback is active when the MX2800 is operating in the Local
timing mode, the timing source for the DS3 is effectively removed from
the circuit. Therefore, it is up to the test equipment or network to provide
DS3 timing into the circuit for the duration of the test.
DSX-3 DSX-3
LIU LIU

Digital Loopback

A Digital Loopback loops the entire DS3 back to the local loop side. The end effect of this test is a
loopback of all T1/E1s after being fully multiplexed and de-multiplexed to and from a DS3. The incoming
DS3 data is ignored, and the outgoing DS3 stream is substituted in its place just prior to exiting the DS3
framer. This test is illustrated in
DSX-3 DSX-3
LIU LIU
61200290L1-1G
on page 6-7 for an illustration of this test.
NOTE
F F
M12/G.747 M12/G.747
R R
D D
A A
MUX/DMUX MUX/DMUX
S S
F F
M M
2 2
R R
E E
M23 M23
D D
A A
R R
S S
M M
MUX/DMUX MUX/DMUX
3 3
E E
R R

Figure 6-9. Line Loopback Test

Figure 6-10.
F F
M12/G.747 M12/G.747
R R
D D
A A
S S MUX/DMUX MUX/DMUX
F F
M M
2 2
R R
E E
M23 M23
D D
A A
R R
S S
M M
MUX/DMUX MUX/DMUX
3 3
E E
R R
Figure 6-10. Digital Loopback
CODEC CODEC
(1 of 28) (1 of 28)
(1 of 7) (1 of 7)
CODEC CODEC
(28 of 28) (28 of 28)
CODEC CODEC
(1 of 28) (1 of 28)
(1 of 7) (1 of 7)
CODEC CODEC
(28 of 28) (28 of 28)
Loopbacks, Section 6
T1/E1 LIU T1/E1 LIU
(1 of 28) (1 of 28)
T1/E1 LIU T1/E1 LIU
(28 of 28) (28 of 28)
T1/E1 LIU T1/E1 LIU
(1 of 28) (1 of 28)
T1/E1 LIU T1/E1 LIU
(28 of 28) (28 of 28)
6-7