Appendix A, HDSL Loopbacks - HDSL Maintenance Modes
61247026L1-5A
A-3
In-band control code sequences are transmitted over the DS1 link by either the unframed or
overwrite method. The HDSL elements respond to either method.
The unframed method produces periodic control sequences and the normal DS1 framing bit is
omitted.
The overwrite method produces periodic control sequences. However, once per frame, the
framing bit overwrites one of the bits in the control sequence.
The unit can detect the loopback activation or deactivation code sequence only if an error rate
of 1E-03 or better is present.
HDSL Loopback Codes
A summary of HDSL loopback codes are given in
Table A-1. HDSL Loopback Control Codes
Function
Code (Binary/Hex)
Response
Arming (In-band)
11000
(2 in 5)
Signal sent in-band or over ESF data link.
Arming (ESF)
1111 1111 0100 1000/
FF48
HDSL elements in disarmed state make transition
to armed state. Detection of either code results in
Smartjack loop up, if NIU loopback is enabled.
Activation (HTU-C)
1101 0011 1101 0011/
D3D3
Signal sent in-band. HDSL elements in armed state
make transition to loop up state. Loop up state time
out is programmable from the HTU-C. Sends 231
bit errors every 20 seconds.
Arm
Source: Network
100000
(1 in 6)
Signal sent in-band. HDSL elements in disarmed
state transition to armed state. Detection of the
code results in an HTUR network loopback if New
England Loopback (NELB) is enabled.
Disarming (In-band)
11100
(3 in5)
Signal sent in-band. HDSL elements loopdown and
transition to disarmed state.
Disarming (ESF)
1111 1111 0010 0100/
FF24
Signal sent in the FDL. HDSL elements loopdown
and transition to disarmed state.
Deactivation
1001 0011 1001 0011/
9393
Signal sent in-band. HDSL elements loopdown and
transition to disarmed state. If NIU is enabled, the
HTU-R does not loopdown.
Disarm
Source: Network or
Customer
100
(1 in 3)
Signal sent in-band. HDSL elements loopdown and
transition to disarmed state.
Activation (HTU-C)
Source: Network
1111 1111 0001 1110/
FF1E
Signal sent in-band. HTU-C loops back the T1 data
to the network equipment.
Activation (HTU-C)
Source: Network
1111000
(4 in 7)
Signal sent in-band. HTU-C loops back the T1 data
to the network equipment.
