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TRDDB Bidirectional Loopback Support
The TRDDB will execute a bidirectional loopback
when performing a DS0 loopback at the TRDDB
(Figure 7). If the TROCU-R detects a bidirectional
loopback during power up synchronization, the
TROCU-R allows data to pass on the 4-wire interface
by entering pass-thru mode (Figure 7). This allows a
standard portable DDS test set, connected to the 4-
wire customer interface of the TROCU-R, to verify
the integrity of the 2-wire loop by transmitting a test
pattern and examining the returning data for
synchronization and errors. The TRDDB LBK
indicator will illuminate during a TRDDB
bidirectional loopback in pass-thru mode. The
latching and alternating loopback sequences are
defined in Table 5 and Table 6.
TRDDB
Bidirectional
loopback
Figure 7. TRDDB Bidirectional Loopback
Pass-Thru Mode
Table 5. Latching Loopback Activation
Sequence
S
q e
u
n e
e c
B
F
F
F
F
F
u
u
u
u
u
n
n
n
n
n
t c
t c
t c
t c
t c
o i
o i
o i
o i
o i
n
n
n
n
n
C
e l
r a
e
i x
i t s
g n
T
a r
s n
i t i
l
o o
b p
c a
s k
p
o r
r g
s e
X
0
1 1
0 1
d I
n e
i t
y f
e d
i v
e c
L
o
p o
a b
o t
e b
o l
p o
d e
o c
e d
L (
X
1
1 0
1 0
X
0
1 1
0 0
X
1
0 0
0 0
X
0
0 0
1 0
P
e r
a p
e r
o t
l
o o
; p
L
o
p o
a b
e s
d n
M
A
P
o c
e d
L (
B
) E
a
t f
r e
0 3
b
t y
s e
X
1
1 0
1 0
A
i t c
a v
e t
F
r a
E -
o l
p o
a b
k c
F (
E
V
)
X
1
1 0
0 1
M
i
i n
m
u
m
f o
5 3
T
P I
b
t y
s e
a l
c t
i h
g n
l
o o
b p
c a
. k
X
=
D
o
t ' n
C
a
e r
b
t i
6
TR
OCU-R
Test
Unit
Data
Pass-Thru
N
u
m
b
r e
y
e t
C
o
e d
R
R
R
R
R
e
e
e
e
e
e c
e c
e c
e c
e c
v i
v i
v i
v i
v i
d e
d e
d e
d e
d e
n o
n i
M
i
i n
m
u
m
( s
I T
) P
T
P I
b
t y
0 1
k c
e s
e l
t c
M
i
i n
m
u
m
S
) C
L
S
C
b
t y
1 0
-
O
C
U
1 0
-
C
S
U
1 0
-
N
I E
1 0
-
D
S
0
k c
e
a n
l b
d e
M
i
i n
m
u
m
1
0 0
L
B
E
0 1
d n
v
i o
e c
M
i
i n
m
u
m
F
E
V
b
t y
0 1
e r
u q
r i
d e
o t
d
s i
b a
e l
e
t s
b a
61291004L2-5, Issue 2
Table 6. Alternating Loopback Activation
S
q e
u
n e
e c
A
i t c
e v
o l
p o
a b
M
a
n i
a t
n i
o l
p o
t
s e
f t
r o
b
t i
r e
o r
C
e l
r a
o l
p o
a b
k c
X
=
D
o
t ' n
a c
e r
If a DS0 loopback is invoked after the TROCU-R
achieves synchronization, some TROCU-R units will
not pass or receive data from the CPE or DDS test set.
These OCU-Rs will send a MUX-Out-Of-Sync code
downstream on the 4-wire customer loop. This is
consistent with current DDS testing methods and is
referred to as the bidirectional loopback normal mode
(Figure 8). For testing purposes, the installer may
choose to initiate the TROCU-R pass-thru mode. Once
the bidirectional loopback is executed in normal
mode, unseat and reseat the TROCU-R and allow the
unit to train. Once trained, the unit will revert to
f o
pass-thru mode for further testing.
B
B
B
B
B
t y
t y
t y
t y
t y
s e
s e
s e
s e
s e
f o
5 3
s e
TRDDB
f o
5 3
s e
Bidirectional
Figure 8. TRDDB Bidirectional Loopback
f o
b
t y
s e
f o
2 3
s e
i l
h s
d e
Sequence
F
u
n
t c
o i
n
R
e
e c
k c
F
o
r u
c
n o
e s
u c
p s
c e
i f i
d e
o l
X
0
0 1
0 1
0 1
-
X
0
0 1
0 1
0 0
-
X
0
0 1
1 1
0 0
-
a b
k c
a
d n
D
a
a t
y b
e t
a
s r
o l
p o
a b
k c
o c
e
a x
m
p
: e l
X
D
D
D
D
D
D
F
o
r u
c
n o
e s
u c
w
t i
o h
t u
C
S
b
t i
TR
OCU-R
loopback
Normal Mode
v i
d e
B
t y
s e
i t
e v
b
t y
s e
f o
p o
a b
k c
o c
e d
O
C
U
C
S
U
D
S
U
e t l
n r
i t a
g n
i w
h t
e d
1
X /
0
0 1
0 1
0 1
i t
e v
a d
a t
b
t y
s e
U
o l
p o
a b
k c
o c
e d
DSU/
CSU
MOS
61291004L2-5B
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