User Manual

ArchitectureNortel Networks Confidential 3–27
S8000/S8002/S8006 BTS Reference Manual
3.3.1.2 Synchronization
The CMCF provides synchronization to the radio part of the BTS.
Synchronization is obtained through a temperature–controlled oscillator that allows
the selection of timing signal from seven signals (six from the external PCMs, one
from an external source, and one from the CMCF master).
The selected clock signal is routed to a digital phase comparator that authorizes
synchronization operations in a frequency locked loop (CMCF master) or in a phase
locked loop (CMCF slave).
The CMCF slave operates in a phase locked loop so that its H4M clock is
synchronized with that of the CMCF master. This ensures that phase hopping does
not occur during a CMCF switchover.
GSM Time
The processing unit transmits the GSM Time every 60 ms. The GSM Time is
transmitted to the switching matrices of the CMCF master. The CMCF slave reads
the GSM Time in the CMCF master, which allows the synchronization of GSM
Time on both CMCFs.
Figure 3–7 shows the synchronization process on the CMCF board.
Switchover
A switchover occurs in synchronization with the H4M clock. Since the master
CMCF and the slave CMCF are synchronized (H4M and GSM Time), the
switchover does not cause a timing disruption.
The switchover sequence is as follows:
active CMCF becomes inactive
inactive CMCF detects the inactivity
inactive CMCF becomes active
A CMCF processor becomes inactive in the following circumstances:
H16M clock state is NOK and there is dual chain operation
the master request is disabled
master board is not properly connected to the back panel
the active processor is reset while in dual chain operation
Defence and redundancy management
A switchover from one CMCF board to the other in the event of an error on the active
CMCF board ensures redundancy. The hardware supports duplex and simplex
modes.
A redundancy channel between both CMCF boards ensures the exchange of data
between the boards in the event of a switchover.
The defense connectivity is shown in Figure 3–8.