User Manual

Architecture
Nortel Networks Confidential
3–12
PE/DCL/DD/0063
411–9001–063
Standard 12.07/EN September 2000
GSM/BSS V12
3.2.1.4 Synchronization management
At start–up, the CSWM chooses the first correct clock from among six. During
LAPD connection, the BTS forces the clock on the PCM carrying the LAPD.
3.2.1.5 Switching matrix management
The switching matrix management includes the following:
initialization
configuration
monitoring/defense
The switching matrix has 16 PCM links. Each PCM link has the following:
transmission test interface
reception test interface
idle interface
All 2n PCM time slots are connected to 2n+ 1 PCM time slots to allow PCM links
to be routed when the BTS are chained together (drop and insert technique).
Initialization
The 0 time slot on each PCM link is looped back on itself by the transmission test
interface, which is a hardware device that connects the PCM 0 time slot transmission
and reception on the reception interface.
The frames received and transmitted in each TS 0 over each PCM link are frequently
compared to allow the switching matrix to be tested at start–up time and its
performance to be monitored.
Configuration
The switching matrix is configured when the BSC requests the BCF to set up or
release a signaling or traffic channel.
Signaling channels are set up (or broken off) between an DRX signaling time slot
and a non–concentrated link on a signaling concentrator unit. This may entail
(dis)connection between a concentrated link on a signaling concentrator unit and
a PCM link time slot on a PCM interface.
Traffic channels are set up (or broken off) between a DRX traffic time slot and a
PCM link time slot on a PCM interface.
Monitoring/defense
The switching matrix is monitored by endless loops that are activated during the
initialization phase.