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Alarms Present 255
Access Server Administrators’ Reference Guide 22 • T1/E1 Link
For E1 links, the Far End Alarm failure is declared when bit 3 of time-slot zero is received set to 1 on two con-
secutive occasions. The Far End Alarm failure is cleared when bit 3 of time-slot zero is received set to zero.
Alarm Indication Signal (AIS) Failure
The Alarm Indication Signal failure is declared when an AIS defect is detected at the input and the AIS defect
still exists after the Loss Of Frame failure (which is caused by the unframed nature of the all-ones signal) is
declared. The AIS failure is cleared when the Loss Of Frame failure is cleared.
Loss Of Frame Failure
For T1 links, the Loss Of Frame failure is declared when an OOF or LOS defect has persisted for T seconds,
where 2 £ T £ 10. The Loss Of Frame failure is cleared when there have been no OOF or LOS defects during
a period T where 0 £ T £ 20. Many systems will perform hit integration within the period T before declaring or
clearing the failure (for more information, see TR 62411 [16]).
For E1 links, the Loss Of Frame Failure is declared when an OOF defect is detected.
Loss Of Signal Failure
For T1, the Loss Of Signal failure is declared upon observing 175 +/- 75 contiguous pulse positions with no
pulses of either positive or negative polarity. The LOS failure is cleared upon observing an average pulse density
of at least 12.5% over a period of 175 ±75 contiguous pulse positions, starting with the receipt of a pulse.
For E1 links, the Loss Of Signal failure is declared when greater than 10 consecutive zeroes are detected (see
O.162 Section 3.4.4).
Loopback Pseudo-Failure
The Loopback Pseudo-Failure is declared when the near end equipment has placed a loopback (of any kind) on
the DS1. This allows a management entity to determine from one object whether the DS1 can be considered
to be in service or not (from the point of view of the near end equipment).
TS16 Alarm Indication Signal Failure
For E1 links, the TS16 Alarm Indication Signal failure is declared when time-slot 16 is received as all ones for
all frames of two consecutive multiframes (see G.732 Section 4.2.6). This condition is never declared for T1.
Loss Of MultiFrame Failure
The Loss Of MultiFrame failure is declared when two consecutive multiframe alignment signals (bits 4 through 7
of TS16 of frame 0) have been received with an error. The Loss Of Multiframe failure is cleared when the first cor
-
rect multiframe alignment signal is received. The Loss Of Multiframe failure can only be declared for E1 links
operating with G.732 [18] framing (sometimes called Channel Associated Signalling mode).
Far End Loss Of Multiframe Failure
The Far End Loss Of Multiframe failure is declared when bit 2 of TS16 of frame 0 is received set to one on two
consecutive occasions. The Far End Loss Of Multiframe failure is cleared when bit 2 of TS16 of frame 0 is
received set to zero. The Far End Loss Of Multiframe failure can only be declared for E1 links operating in
Channel Associated Signalling mode.