Matrix ETERNITY NE System Manual 639
Behind the System Application
It is common for small and medium Systems to be connected to larger System systems, where the trunks of the
larger System are connected to the extension ports of the smaller system. This is usually done for the purpose of
expanding the capacity of the large System already in use.
Such configurations are referred to as 'Behind the System Application'.
How it works
Consider the following illustration.
System-A is connected behind SARVAM UCS. In this 'Behind the System' configuration, the Trunk Lines T5, T6, T7
of SARVAM UCS are connected to the Extensions (SLT) S4, S5, S6 of System-A.
However, Trunk lines T1, T2 of System-A are connected directly to the PSTN.
In such application scenarios, implementing toll control restrictions for the trunks becomes difficult for SARVAM
UCS.
For example: Extension Number 21 of SARVAM UCS in the above illustration is not allowed the facility of long
distance dialing. It has access to all the CO trunks.
When the user of Extension 21 wants to access T1, T2 or T3 (which are direct trunks from the PSTN to SARVAM
UCS) the user dials '0' (or the Trunk Access Code assigned) and gets PSTN dial tone. When the user dials the
number, SARVAM UCS applies Toll Control.
Similarly, when the user of Extension 21 tries to grab a trunk T5, T6 or T7 (which are connected to extensions of
System-A) by dialing Trunk Access Code '0', the user gets the dial tone of System-A. This means, the user of
Extension 21 must dial '0' again to grab CO dial tone of the T1/ T2 connected to System-A.
However, when the user dials '0' again, SARVAM UCS applies Toll Control. It detects the dialed number as ‘00’ and
interprets this as an attempt to dial a long distance number. Since Extension 21 is not allowed long distance dialing
in its Toll Control, SARVAM UCS rejects dialing on the trunk and plays an error tone to Extension 21.
To resolve this, SARVAM UCS provides a configurable Pre-PSTN Digit Count (PPDC) for each CO trunk.
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