Instruction manual

FEATURES AND SERVICES
Tandem Trunking
Description
Tandem trunking provides an enhanced networking capability for System 25. With this
feature, tie trunks can be used to call through System 25 to reach another switching system
(CO or PBX). Calls may be completed over on-network or off-network facilities.
To be treated as tandem trunks, tie trunks must be assigned trunk numbers beginning with
the digit 9. Incoming calls on these trunks may route out of System 25 over ground start,
loop start, or tie trunks. Tandem trunks can gain access to outgoing facilities either indirectly
(by the ARS feature) or directly (by dial access).
System 25’s Tandem Trunking feature does not support traveling class marks or centralized
attendant service.
Users cannot activate most System 25 features or services at either the
tandem or far-end terminating switch.
Considerations
The use of tandem
between branches.
Interactions
trunking with tie trunks provides a cost-effective alternative to toll calling
The following features interact with Tandem Trunking.
Automatic Route Selection: Tandem trunk calls that route outbound via ARS receive the
same treatment as calls originated by a System 25 station, with one exception. If all facilities
in a routing pattern are busy, call queuing is not provided.
In this case, busy tone is returned
to the calling party.
The second digit of the trunk number is used to specify the trunk’s “station” Facility
Restriction Level (FRL) for use with ARS.
FRLs may be specified as follows:
Trunk Number
Second Station
Range Digit FRL
9000-9199
0 or 1
0
9200-9399 2 or 3 1
9400-9599
4 or 5
2
9600-9999 6, 7, 8, 3
or 9
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