A-2
Section 61246001L2-5, Issue 2
61246001L2-5B
Loopback Process Description
In general, the loopback process for the HDSL system
elements is modeled on the corresponding DS1
system process. Specifically, the HTU-C loopback is
similar to an Intelligent Office Repeater loopback and
the HTU-R loopbacks are similar to an inline T1
Repeater loopback.
Each HDSL system element is independently
described by the state diagram shown in Figure 17.
The four states are disarmed, loop-up, armed, and
loop-up/timeout disable.
State transitions result from in-band and ESF Data
Link sequences as well as timeout operations. The
sequences and timeout values are as follows:
1.
Arming Sequence (in-band and ESF)
2.
Activation Sequence
3.
Deactivation Sequence
4.
Disarming Sequence (in-band and ESF)
5.
Loop-up Timeout
6.
Arming Timeout
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.
States and State Transitions
A summary of timeout and control sequences is given
in Table A-1.
In all control code sequences presented, the in-
band codes are shown left-most bit transmitted
first, and the ESF data link codes with right-most
bit transmitted first.
Name
Arming (In-band)
Arming (ESF)
Activation
(HTU-C)
Activation
(HDSL Range Extender #1)
Activation
(HDSL Range Extender #2)
Activation
(HTU-R)
Deactivation
(all HDSL elements)
Disarming (In-band)
Disarming (ESF)
Arming Timeout
Loop-up Timeout
Table A-1. HDSL Loopback Control Codes
Detection Time
5 Seconds
4 Repetitions
> 4 Seconds
> 4 Seconds
> 4 Seconds
> 4 Seconds
> 5 Seconds
5 Seconds
4 Repetitions
2 Hours
Programmable from HTU-C:
None, 20, 60, or 120 minutes
Code
11000
0001 0010 1111 1111
1101 0011 1101 0011
1100 0111 0100 0001
1100 0111 0101 0100
1100 0111 0100 0010
1001 0011 1001 0011
11100
0010 0100 1111 1111
N/A
N/A
Comments
Signal sent in-band or over ESF data link.
HDSL elements in disarmed state make
transition to armed state. Detection of either
code results in Smartjack loop-up, if NIU
loopback is enabled.
Signal sent in-band. HDSL elements in
armed state make transition to loop-up state.
Loop-up state timeout is programmable from
the HTU-C.
Signal sent in-band. HDSL element in loop-
up state makes transition to armed state.
Signal sent in-band or over ESF data link.
HDSL elements in any state make transition
to disarmed state.
HDSL element in loop-up makes transition to
armed state.
