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There is nothing fundamentally wrong with premicells [aka FCTs].
SJG are the UK Experts in automatic route selection and, as such, have been called in to resolve issues concerning premicells. This page deals with many of these problems and, in doing so, will prevent you from making the same mistakes and answer some of the points raised on previous pages.
No automatic routing
On smaller / older systems no auto route selection is available this means the premicells are selected by pressing a line key or dialling a code for access [eg 7]. This leads to all sorts of problems on larger sites. However, it has been found that most small sites usually can live with the situation.
There is no easy answer here, each application has to be examined and the implementation of the premicells thoroughly discussed before deployment. Whether they can be used or not depends largely on the system type - even switches with ARS can often not handle the required routing.
Unable to dial out, constant busy, calls not going over cellular network, inappropriate cellular traffic going to the premicells
Incorrect ARS programming causes all of these problems, often compounded by insufficient premicells.
It is a comfort for all of us at SJG that we are yet to see a correctly programmed switch using premicells unless we have done it.
Unable to use premicells on Isdn switches
Switches using isdn may, at first glance, not be able to use premicells. For instance, a switch may have isdn30 with no analogue exchange lines. To use the premicell would mean upgrading the switch to take an analogue exchange card purely for the premicell [each premicell is the equivalent of an analogue exchange line]. This may even mean adding a cabinet to hold the new analogue exchange card.
The solution here can be to use Premicells fitted to analogue extension ports. However, the switch must be capable of sophisticated ars to auto target the premicells where appropriate.
More good news for ISDN switches: New ISDN2 & ISDN30e premicells are now available which connect to the switch via an SoBus for isdn2 or via dedicated/shared isdn trunk ports for isdn2 & 30. Again, hardware considerations may constrain this. For example, does the switch require a Bri card to drive the SoBus?
In theory, all isdn switches can have premicells but implementation is dictated by the site's / system's individual characteristics.
Least Cost Routing
On switches capable of automatic route selection the premicell must be given its own route and dialling plan. Many switches with lcr will not allow multiple routes. The manual, the brochure and the customer may say the application is possible but it is not: the switch will allow different codes to be auto inserted before transmission to the pstn based on the number dialled but this is not what is required: the call must go out to a particular line/line group without modification.
The solution here is dependent on the type of switch.
Carrier Pre Selection
CPS has no fundamental bearing on premicell implementation .
The solution here is dependent on the type of switch.
Mis-routing
Number churn & portability is the culprit and, except for in-house, cannot be overcome. Individual numbers & number ranges can be dealt with depending on the type of switch - however this can lead to an administrative nightmare.
Calls Hanging
Some premicells have a reluctance to let go of some types of calls - usually abandoned calls [eg to voicemail]. Undetected hanging calls can lead to large call charges. This 'fault' is blamed on the premicell by the PBX manufacturer and on the PBX by the premicell manufacturer. The blame lies with the PBX manufacturer: the cure lies with SJG.
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