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need to exceed 24 seconds to allow detection and
loop-down of up to three HDSL elements and the
Smartjack.
All HDSL elements can be commanded to move
from the armed state into the disarmed state by the
ESF DATA LINK disarming sequence used for NIU
Smartjack loop-down as follows:
ESF Disarm Sequence
0010 0100 1111 1111
for four repetitions per element in loopback
The disarming process ensures race-free operation
of HDSL element disarming and Smartjack
loop-down. Duration of the disarm sequence may
need to exceed 16 repetitions to allow detections
and loop-down of up to three HDSL elements and
the Smartjack. This sequence will loop-down the
Smartjack and the HDSL element.
All HDSL elements will automatically move from
the armed state into the disarmed state when a
default timeout value of two hours is reached.
Arming Timeout
Loop-up State
In the loop-up state, the selected HDSL element
provides continuous loop-up of the DS1 signal.
However, the data flow is monitored for the in-band
deactivation sequence, the in-band disarming
sequence, and the ESF data link disarming
sequence. Also, a loop-up timeout value causes
automatic return to the armed state. All other
control code sequences are igneored in the loop-up
state.
Transition from Loop-up to Armed State
Any HDSL element can be commanded to move
from the loop-up state into the armed state by a
single in-band 16-bit deactivate control code
sequence. The same deactivation sequence as
shown is used for all HDSL elements.
Deactivation after Receiving Sequence
for > 5 seconds
Duration of the deactivation sequence may need to
exceed 18 seconds to allow detection and
loop-down of up to three HDSL elements. The
deactivation sequence does not disarm the HDSL
elements. They can still respond to activation
sequence control codes. All HDSL elements
61246045L1-5B
2 Hours
Section 61246045L1-5, Issue 2
automatically move from the loop-up state into the
armed state when the selected loop-up timeout value
is reached.
Loop-up Timeout
programmable from HTU-C at
None, 20, 60, or 120 minutes
Transition from Loop-up to Disarmed State
All HDSL elements can be simultaneously
commanded to move from the loop-up state into the
disarmed state by either the standard 5-bit in-band
disarming sequence used for NIU Smartjack
loop-down, or by the ESF DATA LINK command,
as previously described.
A-2. ENHANCED LOOPBACKS
HDSL Maintenance Modes
This subsection describes operation of the HDSL
system with regard to detection of in-band and ESF
facility data link loopback codes.
Upon deactivation of a loopback, the HDSL system
will synchronize automatically. Note that the
synchronization process of the HDSL system upon
deactivation of the HRE loopback could take up to
15 seconds, ensuring all system elements are
synchronized.
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 in-line T1 Repeater loopback.
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
deactiviation code sequence only if an error rate of
-03
1E
or better is present.
A-5
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