Testing; Table D. All-1S Repeater Release Code Sequence - ADTRAN T400 DDST III Installation And Maintenance Manual

3. TESTING

Loopback Testing
Loopback tests can be performed from the CO to verify
proper loop and DDST III operation. The DDST III
provides a network loopback in response to sealing
current reversal initiated from a CSU latching or non-
latching loopback command. The DDST III also provides
both Manual and NIE latching loopback capabilities at all
rates. Repeater loopback operation functions in
accordance with TR-TSY-000476.
Repeater Loopback (56 kbps)
A Repeater loopback code transmitted from a remote or
local test system causes the OCU or OCU DP to reverse
the sealing current direction on the loop. Upon detection
of sealing current reversal, the DDST III operates relays
that cause a loopback toward the network by connecting
the customer-side transmit and receive pairs together.
Circuit integrity can then be verified by transmitting Bit
Error Rate (BER) data from the test system and examining
the returning data for synchronization and errors.
While in loopback, the DDST III can detect the All-1s
Repeater Release Code sequence, and upon recognition
of this sequence, drops its loopback and allows the
reversed sealing current condition to pass to the next
downstream device. The All-1s Repeater Release Code
may be transmitted in two separate iterations from a test
system to release any looping devices that may exist on
the loop between the CO and the customer DSU/CSU.
The All-1s Repeater Release Code sequence is described
in Table D.

Table D. All-1s Repeater Release Code Sequence

Function
. . . following CSU alternating or CSU latching loopback
command sequences . . .
CLEAR loopback
CSU loopback code
on first repeater
alternating with All-1s byte
CSU/All-1s/CSU/All-1s . . .
WAIT
CSU loopback code
alternating with data byte
(i.e., 2047 test pattern)
CSU/data/CSU/data . . .
CLEAR loopback CSU/All-1s/CSU/All-1s . . .
on second
repeater
WAIT
CSU/data/CSU/data . . .
CLEAR loopback
on Nth repeater
Repeat CLEAR and WAIT sequence
N times.
4
Time
Byte Code
Duration
1 to 2
seconds
1 second
1 to 2
seconds
1 second
Section 61212021L3-5, Issue 3
Some test systems and test sets support both a CSU
(Channel loopback) and a 56 kbps Repeater loopback.
If Repeater loopback is available, it only loops the
repeater. When CSU or Channel loopback is selected,
some test systems automatically send the All-1s Repeater
Release Code to release loopbacks from any repeaters
on the loop. If the test system or test set does not support
a 56 kbps Repeater loopback, a CSU or Channel loopback
should be selected and the All-1s Repeater Release
Code data injected for approximately two seconds to
release any repeater loopbacks prior to looping the CSU.
The repeater is transparent to all other test commands.
CSU Latching Loopback
Some test systems embed All-1s Repeater Release
Codes within the CSU Latching Loopback command to
bypass loop repeaters and directly access the DSU/
CSU. If a latching loopback at the DDST III is desired,
see subsection Network Interface Equipment Latching
Loopback .
For test systems or test sets that do not support automatic
release of CSU latching loopback from the repeaters or
network interface devices, use the following procedures.
Initiating CSU Latching Loopback to Loop DDST III
(SW2-1 LBK enabled)
• From a test system or set, send a CSU latching
loopback sequence. This instructs the OCU DP to
reverse sealing current and loop the DDST III.
• Send a selected test pattern and test for error-free
operation.
Upon completion of this test, advance to Terminating
•
CSU Latching Loopback to DDST III or CSU for
latching loopback termination.
Initiating CSU Latching Loopback to Loop a DSU/
CSU (SW2-1 LBK enabled)
• From a test system or set, send a CSU latching
loopback sequence. This instructs the OCU DP to
reverse sealing current and causes the DDST III to
loop.
• To release the DDST III from latching loopback and
pass reversed sealing current to the DSU/CSU,
send the non-latching CSU loopback code alternating
with an all-1s data pattern for approximately two
seconds. The DSU/CSU should loop when reversed
sealing current is detected.
• Send a selected test pattern and test for error-free
operation.
Upon completion of this test, advance to Terminating
•
CSU Latching Loopback to DDST III or CSU for
latching loopback termination.
61212.021L3-5C