700-712-100-01, Revision 01
Functional Description
UTU-712 and ETU-762 List 1
May 10, 1999
17
Figure 10.
Loopback Operations
The following applies to LTU and NTU loopbacks:
•
No inband loopback codes are recognized or generated.
•
A remote HDSL loopback is not available from the local console screen as it causes the HDSL link to go down
and requires user action at the remote unit to disengage the loopback.
•
The DTE should supply timing for local Nx64k interface loopbacks (internal timing supplied by the local
HDSL unit may not function correctly).
Table 9.
Loopbacks Selected at Front Panel Pushbutons and Console Screens
Loopback
Description
The two loopbacks that follow can be selected from the LOC and REM front-panel pushbuttons, the console screens, the Local
Loopback (LL)/Remote Loopback (RL) control lines at the DTE, or the management unit interface.
LOC Pushbutton—Local
HDSL Loopback
This is an analog loopback implemented in both HDSL transceivers, and enables a complete checkout
of the local equipment by looping back data at the furthest point before the transmission media. The
HDSL link goes down as a result of this loopback, and is therefore not selectable from the remote unit
console screens. The LL control line, when asserted from the local DTE, also engages this loopback.
REM Pushbutton—Remote
Loopback
Data is transmitted across the HDSL link and looped back at the remote interface ports. The HDSL
link must be up for this loopback to be available. With no HDSL link up, the REM button will not enable
any loopbacks. The RL control line, when asserted from the local DTE, also engages this loopback.
The three loopbacks that follow are available exclusively from the console screens or management unit interface.
Local Interface Loopback
Data is looped back at the closest point in the local unit toward customer equipment. This loopback
is useful for verification of a proper connection at the local interface between your DTE and the local
HDSL card. The HDSL link is maintained during this loopback.
Local or Interface Loopback
Away from the Local
Equipment
Data is looped back at the local unit or remote unit back toward the remote DTE equipment. This is
equivalent to pressing the REM button on the remote unit’s front panel, and is made available at the
local console screen for ease of installation. The injected test data and loopback verification must still
be performed at the remote unit site. Local equipment outputs an AIS for the duration of this test.
Remote Interface Away
from the Local Equipment
Data is looped back at the remote unit toward the remote DTE equipment. This is available at the local
console screen for the duration of this test. The injected test data and loopback verification must still
be performed at the remote unit site. Local equipment outputs an AIS for the duration of this test.
Nx64k
Nx64k
NTU Interface
LTU Interface
HDSL
HDSL
Single-pair
HDSL loop
