A-5
Section 61246026L6-5, Issue 2
61246026L6-5B
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.
Table A-2. HDSL Loopback Control Codes
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.
(N) .... 2in6 (110000) ............... Loopback data from network toward network in first HRE.
(N) .... 3in6 (111000) ............... Loopback data from network toward network in second 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.
(C) .... 5in6 (111110) ............... Loopback data from customer toward customer in second 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.
(N) .... FF06 ............................. Loopback data from network toward network at HRE2.
(C) .... 3F04 .............................. Loopback data from customer toward customer at HRE1.
(C) .... 3F06 .............................. Loopback data from customer toward customer at HRE2.
(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.
Source
Abbreviated
Wescom
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.
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-2 and A-3.
NOTE: 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.
