User Manual

Architecture
Nortel Networks Confidential
3–18
PE/DCL/DD/0063
411–9001–063
Standard 12.07/EN September 2000
GSM/BSS V12
Fault detection
The DSC receives two threshold values from the CSWM that give the overload
situation in message transmission queues. When queue thresholds are reached, the
DSC issues start and end–of–alarm messages to the CSWM on the O&M bus.
3.2.3 PCM Interface (PCMI)
The PCMI interfaces and synchronizes incoming and outgoing PCM links. It
converts the external PCM coming from the BSC into internal PCM used by the
BSC, and vice versa.
Each PCMI handles one external PCM link. A PCMI unit does the following:
converts external PCM links into internal PCM for BTS use
verifies link quality using error detection codes
matches impedance on the type of PCM link used by the operator
3.2.3.1 Configuration
The PCMI can operate without CSWM involvement. However, the CSWM sends
a configuration message on the O&M bus that contains the following:
the number of erroneous seconds, which defines a window used to evaluate PCM
alarms
threshold M1 for frame alignment error counters
threshold M2 for the CRC error counter
threshold M3 for coding type error counters
3.2.3.2 Monitoring
The PCMI monitors its own equipment and PCM links, and issues fault messages
concerning hardware alarms or PCM alarms.
3.2.3.3 PCM alarm management
Managing PCM alarm involves frame, multiframe, submultiframe, zero time slot,
and frame alignment; CRC is not managed yet.
A frame interval is 125 µs.
The duration of a multiframe is 2 ms, representing the time of 16 frames.
The length of a submultiframe is 1 ms.
The TS0 is set aside for the frame alignment signal, multiframe alignment bits, CRC
bits, and alarm sending.