A-3
Section 61180405L1-5, Issue 1
61180405L1-5A
The NEI latching loopback is detected in the primary
DS0 of the FT1 circuit to control the looping of the
FT1 circuit. When the FT1 circuit is looped, all DS0s
in use will be looped back toward the network. AIS
will be sent to the customer.
The FNID CPE loopback is a digital loopback toward
customer premises as shown in
Figure A-6
. This
loopback is initiated by the Total Access 1500 craft
interface, when available. When the FT1 circuit is
looped, all DS0s in use will be looped back toward the
customer. The DS0s will be transmitted toward the
network.
3. LOOPBACK ACTIVATION/DEACTIVATION
This section describes loopback activation and
deactivation methods for the ADTRAN Fractional T1
system. Loopback activation and deactivation is
controlled with the pushbutton located on the front
panel, through craft interface, or latching loopback
codes.
The FNID front panel REM LBK pushbutton controls
remote loopback activation. Pressing REM LBK
activates FT1 DP CPE loopback. Remote loopback is
deactivated by again pressing the REM LBK or
waiting for the 20-minute loopback time out, if
enabled.
The FNID has a craft interface located on the front
panel of the device. The FT1 DP is controlled by the
craft interface on the Total Access 1500. The craft
interface allows access to the FT1 device through an
RS-232-type interface. All loopbacks for the FT1 DP
and FNID can be controlled from the craft interface.
The Total Access 1500 craft interface can activate and
deactivate the FT1 DP network loopback and the FT1
DP CPE loopback in the FT1 DP. The Total Access
1500 craft interface can also remotely activate and
deactivate the FNID network loopback, FNID CPE
loopback, and the repeater loopbacks.
The craft interface on the FNID can activate and
deactivate the FNID network loopback and the FNID
CPE loopback. The FNID craft interface can also
remotely activate and deactivate the FT1 DP network
loopback and the FT1 DP CPE loopback and the
repeat loopback.
FT1 DP, FT1 Repeater, and FNID network loopbacks
can be activated by the DDS latching loopback
sequence. The latching loopback sequence is detected
in the primary DS0 of the FT1 system. When the
loopback is activated on the device, the whole FT1
bandwidth is looped. The FT1 DP, FT1 Repeater, and
FNID each respond to a different loopback select code
allowing for sectionalization of the network during
testing.
Table A-1
is a list of FT1 devices and their
loopback select codes.
Latching loopbacks for the FT1 system are activated
by transmitting the following latching loopback
sequence in the primary DS0 of the FT1 system:
A. Minimum of 35 transition in progress (TIP)
bytes (N0111010).
B. Minimum of 35 loopback select code (LSC)
bytes as defined in Table A-1.
C. Minimum of 100 loopback enable (LBE) bytes
(N1010110).
D. Minimum of 35 all 1s bytes (S1111111), plus a
minimum of 100 LBE bytes. (N-1) iterations,
where N is the number of channel units of the
same type (i.e., same LSC) that lie between the
test center and the loopback to be operated.
This step is only used when there are identical
channel units in tandem.
E. Minimum of 32 far end voice (FEV) bytes
(N1011010).
Table A-1. FT1 Loopback Select Codes
Loopback Select
Loopback Select
FT1 Device
Code Name
Code Byte
FT1 DP ............................................................... DDS OCU DP .......................................................... N1010101
FT1 Repeater #1 ................................................. NEI Loopback 1 ...................................................... N1000001
FT1 Repeater #2 ................................................. NEI Loopback 2 ...................................................... N1000001
FNID without Repeater ...................................... NEI Loopback 1 ...................................................... N1000001
FNID with one Repeater .................................... NEI Loopback 2 ...................................................... N1000001
