User Manual

Architecture
Nortel Networks Confidential
3–20
PE/DCL/DD/0063
411–9001–063
Standard 12.07/EN September 2000
GSM/BSS V12
One cause is associated with each seriously erroneous second. The alarm cause is
defined in the following descending order of severity: NOS, AIS, LOS, RRA, FE,
CRC, and SKP.
When the number of seriously erroneous consecutive seconds reaches the number
of erroneous seconds (NBSEC) defined in the configuration message, the PCM is
designated in fault condition and a message is sent to the CSW.
The end–of–fault condition is the number NBSEC of consecutive seconds without
errors and the end–of–fault message is sent to the CSW.
3.2.4 Synchronization (SYNC)
The synchronization unit must synchronize the DRXs on a single reference time,
GSM time. It supervises the different defense stages. There are two identical
synchronization units, that have the same software (see Figure 3–5).
3.2.4.1 GSM time
The network supplies the reference time via three PCMI units. The CSWM selects
one of the six clocks and sends it to the synchronization unit. The clock selected
must have good long–term accuracy because it is used by the synchronization
module to generate reference time for the radio interface with an accuracy of
5 x l0
–8
.
If the external reference signal is absent, the CSWM selects a local clock derived
from the SYNC module active in “free running” mode.
3.2.4.2 Monitoring
The synchronization unit is monitored by its own control and monitoring
mechanisms, which check that the unit is operating correctly and GSM time is
available on the GSM TIME bus.
Alarms are as follows:
SYNO unit outage
CSWM clock failure
reference clock failure