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ArchitectureNortel Networks Confidential 3–55
S8000/S8002/S8006 BTS Reference Manual
Synchronization management
At the start–up, the BTS selects the clock. During LAPD connection, the BTS forces
the clock onto the PCM carrying the LAPD.
Switching matrix management
Each PCM link managed by the switching matrix has a transmission test interface,
reception test interface, and an idle interface
The switching matrix is configured when the BSC requests to set up or to release
a signaling or traffic channel from the BTS.
Signaling channels are set up (or broken) between a transmission signaling TS and
a non–concentrated link. This operation may entail (dis)connection between a a
concentrated link TS coming from the BTS and a PCM link TS on the PCM
interface.
Traffic channels are set up (or broken) between a transmission traffic TS and a PCM
link TS on the PCM interface.
Data signaling concentration function
The BTS uses this function to set up the communication between the BSC and the
other entities that make up the BTS. This function is implemented with the LAPD
protocol that serves concentrator and routing functions.
Time base
The time base regenerates the GSM_TIME bus with information issued from the
GSM_TIME channel.
If, for any reason, the GSM time is not distributed to the time base, this one
maintains the GSM_TIME bus signals locally and continues to provide the GSM
time to the logic unit.
Synchronization function
The synchronization function must synchronize the transmissions on a single
reference time: GSM _TIME.
The network provides a radio reference clock via two PCM links. This clock
selected has good long–term accuracy. It’s the reason that the synchronization
module to generate an exact reference time for the radio interface uses this clock..
If the external reference signal is missing, the BTS selects the local clock.
The synchronization function is monitored by internal control and monitoring
mechanisms. They check that the synchronization is operating correctly and that the
GSM time is available on the GSM_TIME bus.