System information

FCD 901 48
Issue R2A, 07.2009
XMP1 Release 5.5 System Description
Clock Supply
Aastra Proprietary Information Page 2-13
2.3 Clock Supply
The PCM network represents a synchronous network. In such a network, a
network node can supply the network clock. If this network clock source
fails, another network node must take over network synchronization.
However, it is also possible that individual or all network nodes recover their
clock from T3in or use an Rx clock.
In the standard procedure of the XMP1 system, a network node provides
the clock for all other network nodes (see Section 2.3.3, Clock priority
control ).
To increase clock supply flexibility in the network, the XMP1 system offers
further clock control options:
• Separation of clock ranges at different connections
• Clock supply regionalization (using debugging functions)
• Manual entry of clock trees
• Preferred or fixed connection of individual nodes to specified clock
sources
The clock sources available for network synchronization are recorded and
administered by the Network Management software. The Network
Management software also informs the network node on its clock sources
and numbers of its clock priorities.
2.3.1 Clock sources
The following clock sources can be used:
• internal clock T
INT
• external T3in clock
• receive clocks of port modules
• receive clock of ISDN interfaces
• SDH clock
Clock generator 2.048 MHz
A clock generator with a frequency of 2.048 MHz is used as internal source
for system clock supply.
Clock interface T3in
Clock interface T3in can be used to supply the XMP1 Flexible Multiplexer
with the 2048 kHz reference frequency required for synchronous operation.
The input impedance of the T3in interface is
1.6 KOhms  16 pF. In order
to avoid reflections on the clock line, the input can be terminated with
120 Ohms.
The clock interface T3out (output) is used to connect a reference frequency
distributor.