Figure 4. Bidirectional Connections For Loops Greater Than -45 Db; Table C. Faceplate Indicators And Controls - ADTRAN T400 DDST III Installation And Maintenance Manual

Loopback Enable
The DDST III can be optioned to ignore or respond to
CSU latching and non-latching loopback command
sequences. CSU loopback sequences are processed by
the OCU or OCU DP, which in turn reverses sealing
current direction on the DDS loop. The DDST III detects
sealing current reversal and responds with a regenerative
loopback toward the network if LBK is selected. If LBK
is disabled, the DDST III passes the reversed sealing
current condition to the DSU/CSU. The DDST III always
responds to the Network Interface Equipment (NIE)
latching loopback sequence regardless of the position of
the LBK option switch. Loopback command sequences
are described in subsection Testing .
The LBK option does not disable Network
Interface Equipment latching loopback
response.
Repeat
The DDST III can be optioned to regenerate the DDS
loop signal in the network-to-customer direction only.
Because DSU/CSU units are not required to operate on
loops with loss beyond 34 dB, the RPT option can be
enabled to extend the DDS loop to distances
corresponding to 45 dB of loss. If RPT is disabled, loop
signals pass transparently through the DDST III without
regeneration. If the unit is commanded into network
loopback, the incoming signal is regenerated toward the
network at 0 dB, regardless of the RPT setting.
Two DDST III units may be used in the bidirectional
configuration to extend DDS loops beyond 45 dB loss.
The loop loss from the central office may not exceed 45
dB, and the loop loss toward the customer may not
exceed 34 dB. Wiring for this application is described in
Figure 4.
LBK must be disabled on DDST III #2 and LBK
must be enabled in DDST III #1 to
accommodate telco testing.
Display Indicators
The DDST III contains faceplate-mounted LED indicators
which display the operating data rate and status. The
indicators are described in Table C.
61212.021L3-5C
To Network
From Network
Figure 4. Bidirectional Connections for Loops

Table C. Faceplate Indicators and Controls

Indicator
SC
56
SC and 56
38.4
19.2
9.6
4.8
2.4
LOOPBACK
ACTIVE
>34 dB
CHK WIRE
NO SX
Section 61212021L3-5, Issue 3
DDST III #2
(Repeat Option)
DTT
TT 55
41
DTR
TR
49
47
Customer
Network
5
7
RT DRT
15
DRR
RR
13
Loopback
Disabled
DDST III #1
(Repeat Option)
DTT
55
TT 41
To
TR DTR
49
47
Customer
Network
5
7
RT
From DRT
RR
15
DRR
13
Loopback
Enabled
Greater Than -45 dB
Status Explanation
On Secondary Channel enabled
On 56 kbps data rate enabled
Both On 64 kbps or 56 SC data rate
enabled
On 38.4 kbps data rate enabled
On 19.2 kbps data rate enabled
On 9.6 kbps data rate
On
4.8 kbps data rate
On 2.4 kbps data rate
On Loopback is activated
On Loop loss exceeds 34 dB
Flashing Loop pairs are reversed
On
No sealing current detected
Network
Demarcation
Point
DSU/
CSU
3