Reference Manual

Synchronization
31 Synchronization
The purpose of this function is to synchronize an RBS internally. The
function is needed to achieve air timeslot synchronization, according to
/GSM:05.10/ and /JTC PCS:7/.
The transition between different states and functions can be seen in the
figure below.
Startup
Free running clock
Establishing
sync. state
Selection of
ref. source
Locking to
ref.source
Hold over time
expired
Hold over
state
Selection of
ref. source
Hold over
operation
ESB
Distribution
(Master mode)
Supervision of
ref. source
Timing
compensation
(Slave mode)
Synchronized
state
Selection of
ref. source
Synchronizing
to ref. source
ESB
Distribution
(Master mode)
Supervision of
ref. source
Timing
compensation
(Slave mode)
Sync.
reestablished
Ref. source
is not usable
P005514B
Sync.
established
Figure 96 Synchronization function states
Short-term stability of the timing is achieved by the RBS itself. The
long-term stability of the RBS will rely on an external or an optional
synchronization reference.
The external synchronization reference is taken from one of the two
PCM interfaces in the transport network interface or from another RBS
via the External Synchronization Bus, ESB.
The optional synchronization reference is taken from an optional
synchronization function in the RBS.
The three possible sources for synchronization are handled in the same
way by the synchronization function. The BSC is able to request that
either the transport network, the optional synchronization function or
another RBS to be used for synchronization.
The synchronization function can have three different modes:
• Stand-alone
EN/LZT 720 0008 R1A
2001-06-26
247 (421)
© Ericsson Radio Systems AB
— All Rights Reserved —