Filter
Top Products
700-701-100-02 Functional Description
UTU-701 and ETU-751 List 1 August 9, 2002 19
LOOPBACKS
An HDSL system maintains several diagnostic loopback configurations, both toward and away from the local unit,
which can be used to verify proper transmission of test data through the local unit, the HDSL facility, and the
remote unit. Figure 8 on page 19 shows all possible loopback paths. Table 12 on page 20 lists available loopbacks.
During loopbacks the system generates an Alarm Indication Signal (AIS) past the loopback point toward the far
unit. Loopbacks can be activated from the LOC (local) and REM (remote) front-panel pushbuttons, the console
Test menus, and the management unit interface. Table 13 on page 21 lists loopback equivalents for different
activation methods. Only one loopback option can be enabled at a time. During a loopback, the Loopback LEDs
on the front panel indicate the type of loopback currently present in the system. See Table 4, “Line and Desktop
Unit Front Panel LED Indications,” on page 6.
The system reverts to normal transmission of payload data after the specified timeout period has elapsed. If a
timeout period is not specified, the loopback must be manually disengaged before normal transmission of data can
resume.
Figure 8. Loopback Operations
Table 11. HDSL Transmission and Application Interface Alarms
Alarm Description
HDSL Alarms HDSL alarms include:
Margin (MAR) Margin has fallen below threshold set for the HDSL interface.
Errored Seconds (ES) Errored seconds count has exceeded threshold set for the HDSL interface.
Loss of Sync Word
(LOSW)
Loss of sync word at the HDSL interface. Remains active during restart, but not a cold start.
G.703 Alarms G.703 alarms include:
Loss of Signal (LOS) Loss of signal at the G.703 input.
Loss of Frame Alignment
(LFA)
Loss of frame alignment at the G.703 input.
Receive Alarm Indication
Signal (AIS)
Alarm indication signal (unframed all ones) received at the G.703 input.
Remote Alarm Indication
Signal (RAI)
Remote alarm indication signal received at the G.703 input (through A-bit).
Loss of Clock (LOC) Applies to loss of external clock when EXT timing is used. The external clock was lost for the
previous second. This alarm is reset when the clock is active again.
Test loopbacks disrupt normal end-to-end transmission of customer data and are the
equivalent of taking the circuit out of service. The circuit does not revert to normal operation
until loopbacks are disengaged manually or until after the specified loopback timeout period
has expired.
Nx64k Nx64k
NTU InterfaceLTU Interface
HDSL HDSL
Single-pair
HDSL loop