A-1Section 61245211L1-5, Issue 161245211L1-5A
APPENDIX A
FT1 LOOPBACKS
1. GENERAL
This Appendix is an overall reference to the
loopback capabilities of the ADTRAN Fractional T1
system. Included in the Appendix is a description of
the FT1 loopbacks and the methods for activating
the FT1 loopbacks.
2. FT1 LOOPBACKS
Figure A-1 shows the application from the central
office (CO) to customer premises. The FT1
Repeater is shown for convenience and not as a
necessary part of the FT1 network. The loopbacks
shown are as follows:
A. FT1 DP network loopback
B. FT1 DP CPE loopback
C. FT1 Repeater network loopback
D. FNID network loopback
E. FNID CPE loopback
There are two loopbacks available to the FT1 DP.
The FT1 DP network loopback loops the FT1 signal
back to the network. The FT1 DP CPE loopback
loops the FT1 signal back to the customer.
The FT1 DP network loopback is a digital loopback
toward the CO (see Figure A-2). This loopback is
initiated by the OCU latching loopback command
(N1010101), by a push-button when available, or by
the craft interface. The OCU latching loopback
code is detected in the primary DS0 of the FT1
circuit -- the channel where the FT1 DP is
physically installed -- to control the FT1 circuit
looping. When the FT1 circuit is looped, all DS0s
in use will be looped back toward the network. The
DS0s will be transmitted on to the customer.
The FT1 DP CPE loopback is a digital loopback
toward customer premises as shown in Figure A-3.
This loopback is initiated by the RLB button on the
FNID, or by the craft interface. When the FT1
circuit is looped, all DS0s in use will be looped back
toward the customer. All DS0s sent toward the
network will be filled with all-1s.
Figure A-1. FT1 Loopbacks
DSX-1
Interface
Central
Office
Customer
Premises
Equipment
FT1 DP
D4
Channel Bank
FT1
Repeater
FNID
T1 NIU
A B
C
D
E
Figure A-2. FT1 DP Network Loopback
DSX-1
Interface
Central
Office
FT1 DP
D4
Channel Bank
FNID
HDSL
Local Loop
DS1
Interface
Customer
Premises
Figure A-3. FT1 DP CPE Loopback
DSX-1
Interface
Central
Office
FT1 DP
D4
Channel Bank
FNID
HDSL
Local Loop
DS1
Interface
Customer
Premises
