61245.001L7-5A
Section 61245001L7-5, 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. 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 inline 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.
Appendix A
HDSL LOOPBACKS
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.
DDS Latching Loopback Operation
If the unit is optioned for FT1 mode, then DDS Latching
Loopback operation is supported as described in
Bellcore TA-TSY-000077, Issue 3, Section 5.1.3. The
HTU-C and any HRE units which are in the HDSL
circuit are treated as Identical Tandem Dataports and
the HTU-R is treated as a Different Tandem Dataport.
For a complete description of the DDS Latching
Loopback codes, refer to Bellcore TA-TSY-000077,
Issue 3, Section 5.1.3.
Loopback Control Codes
A summary of control sequences is given in Tables A-1
and A-2.
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.
Table A-1. HDSL Enhanced Loopback Control Codes
Type
Source Code
Name
(N)
3in7 (1110000) ...... Loopback data from network toward network in the HTUR.
(N)
4in7 (1111000) ...... Loopback data from network toward network in the HTUC.
Abbreviated (N)
2in6 (110000) ........ Loopback data from network toward network in first HRE.
(C )
6in7 (1111110) ...... Loopback data from customer toward customer in HTUC.
(C )
5in7 (1111100) ...... Loopback data from customer toward customer in HTUR.
(C )
4in6 (111100) ........ Loopback data from customer toward customer in first HRE.
(N)
FF1E ...................... Loopback data from network toward network at HTUC.
(C)
3F1E ...................... Loopback data from customer toward customer at HTUC.
(N)
FF04 ...................... Loopback data from network toward network at HRE1.
(C)
3F04 ...................... Loopback data from customer toward customer at HRE1.
Wescom
(N)
FF02 ...................... Loopback data from network toward network at HTUR.
(C)
3F02 ...................... Loopback data from customer toward customer at HTUR
(N)
1in6 (100000) ........ Loopback data from network toward network at HTUR.
(N)
FF48 (ESF-DL) ...... Loopback data from network toward network at HTUR.
(N/C)
1in3 (100) .............. Loopdown everything.
(N/C)
FF24 (ESF-DL) ...... Loopdown everything.
Notes:
The Source column indicates which side of the interface the control codes are sent from.
For example, an (N) indicates a network sourced code while a (C) indicates a customer
sourced code.
All codes are inband unless labeled ESF-DL.
All codes listed above must be sent for a minimum of 5 seconds in order for them to be
detected and acted upon.
