ascom Ascotel 2025/2045/2065
3.26 Planning a PBX HBT_20321104_03/B0_en
4.5 Important Planning Information
4.5.1 Clock Synchronization
The clock frequency of a PBX is provided (synchronized) by the public network via
the basic accesses T and the primary rate accesses T2.
Should synchronization by the public network fail (due, for example, to exchange
line interruptions), the PBX will use its own clock. This frequency deviates at most
by 5 ppm from the nominal value, which ensures that the Ascotel DECT system
also remains available.
In a private leased-line network, PINXs that are synchronized by the public net-
work pass on the clock reference to PINXs that are not connected directly to the
public network.
Synchronization in the private fixed network has to be carefully planned to ensure
there are no synchronization loops (see Page 3.97).
All the private leased-line network connections and public exchange line circuits
are automatically in a shared clock reference table when the PBX is configured for
the first time.
If a PBX is not networked in a PISN, the clock reference table can be left as it is;
only the initial reference may have to be assigned differently.
4.5.2 Emergency Operation
In the event of a PBX failure in the PISN, telephony operations can be maintained
by configuring alternative paths in all the neighbouring PINXs (see Page 3.95).
In the event of a 230V mains failure, the uninterruptible power system takes over
the power supply to the PBX without disrupting telephony operations (see "Unin-
terruptible Power Supply (UPS)", Page 4.13).
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