A-2
Section 61246045L1-5, Issue 2
61246045L1-5B
Upon deactivation of a loopback, the HDSL system
will synchronize automatically. It should be noted
that the synchronization process of the HDSL system
upon deactivation of the HRE loopback, could take up
to 15 seconds to ensure all system elements are
synchronized.
Loopback Process
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 A-2.
The four states are disarmed, loop-up, armed, and
loop-up/timeout-disable.
State transitions result from in-band, ESF data link
sequences, and timeout operations. The sequences
and timeouts are as follows:
Figure A-2. HDSL Element State Diagram
ACTIVATION
LOOP-UP
TIMEOUT
ARMING
TIMEOUT
DEACTIVATION
DISARM
LOOP-UP
TIMEOUT
DISABLE*
*The Loop-up Timeout Disable function is currently not supported.
LOOP-UP / TIMEOUT
STATE
ARMED
STATE
LOOP-UP / NO TIMEOUT
STATE
DISARMED
STATE
• Arming (in-band and ESF)
• Activation
• Deactivation
• Disarming (in-band and ESF)
• Loop-up Timeout
• Arming Timeout
A summary of timeout and control sequences is
given in
Table A-1 and A-2
.
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.
