61179512L2-5A
Section 61179512L2-5, Issue 1
A-1
HDSL MAINTENANCE MODES
This Appendix 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.
Loopback Process Description
In general, the loopback process for the HDSL
system elements is modeled on the corresponding
DS1 system process. Specifically, the ICOT
loopback is similar to an Intelligent Office Repeater
loopback, and the HLIU loopbacks are similar to an
inline T1 Repeater loopback.
In-band control code sequences are transmitted over
the DS1 link by either the
insert
or
overwrite
method. The HDSL elements respond to either
method. The insert method produces periodic
control sequences that are not overwritten by the
DS1 framing bits. 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.
Loopback Control Codes
NOTE
In all control code sequences presented, the
in-band codes are shown with the left-most bit
transmitted first, and the ESF data link codes
with right-most bit transmitted first.
Control sequences are summarized below.
Arm/ 11000 (also known as a 2-in-5 pattern)
The HLIU will loop up toward the network. No
AIS or errors will be sent as a result of this
loopback. The ICOT and HRE will arm. When
sent from the customer, this code will arm all units.
Appendix A
HDSL Loopbacks
Arm/ FF48 (1111 1111 0100 1000)
ESF facility data link: ESF only; when sent from the
network, all units will be armed and an HLIU
network loopback will be activated. This code has
no functionality when sent from the customer.
Disarm/11100 (also known as a 3-in-5
pattern)
All units are removed from the armed state. If any
of the units are in loopback when the 11100 pattern
is received, they will loop down.
Disarm/ FF24 (1111 1111 0010 0100)
ESF facility data link: disarms and/or loop down all
units.
ICOT Network Loop Up/ D3D3 (1101 0011
1101 0011)
If the units have been armed and no units are in
loopback, the ICOT will loop up toward the
network, 2-second of AIS (all 1’s) will be sent,
5-second of data will pass, and then 231-bit errors
will be injected into the DSX-1 signal. As long as
the pattern continues to be sent, 231-errors will be
injected every 20-second. When the pattern is
removed, the unit will remain in loopback. If the
pattern is reinstated, the injection of 231-bit errors
will resume at 20-second intervals.
HRE Network Loop Up/ C741 (1100 0111
0100 0001)
If an HRE is present, the units have been armed, the
HRE will loop up toward the network, 2-second of
AIS (all 1’s) will be sent, 5-second of data will pass,
and then 10-bit errors will be injected into the
DSX-1 signal. As long as the pattern continues to
be sent, 10 errors will be injected every 20-second.
When the pattern is removed, the unit will remain in
loopback. If the pattern is reinstated, the injection
of 10-bit errors will resume at 20-second intervals.
HLIU Loop-up/C742 (1100 0111 0100 0010)
ESF facility Data link: ESF only; when sent from
the network, an HLIU network loopback is activated
and a 20-bit error confirmation is sent. When sent
from the customer, an HLIU customer loopback is
activated with a 20-bit error confirmation.
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