Cabinet/Carrier Expansion Requirements

PBX system cabinet and carrier costs, without housed printed circuit boards, can account for 10 to 15 percent of the total system price. To keep system costs down, customers should seek PBXs based on cabinet/carrier designs that limit the necessary common equipment hardware. Carriers with many port card slots may be more cost effective than carriers with fewer card slots. Multicarrier cabinets with more carrier shelves may be more cost effective than cabinets that house fewer carriers. Regardless of the number of installed cabinets or available card slots at system cutover, customers will likely be required to purchase additional common equipment over the life of the system.

The following are the most common reasons for installing additional cabinets and/or carriers.

Port Growth

The most common reason for cabinet/carrier expansion is port capacity growth requirements for stations and/or trunks. Current carriers can typically support a few hundred ports, and cabinets can usually support more than 1,000 ports.

Increased Traffic Requirements

Some PBX systems require additional port cabinets/carrier common equipment to satisfy customer traffic engineering requirements even if port capacity does not increase. This is a common requirement for PBX systems based on blocking switch network designs, such as the Avaya Definity ECS and Nortel Networks Meridian 1 Option 61C/81C models.

Increased Call Processing Requirements

Although the call processing capacity of most PBX systems is based on the main common control complex, a few systems with distributed call processing designs require additional control cabinets to satisfy increased customer call processing capacity needs. The Ericsson MD-110 is a good example of a distributed call processing PBX system design with limited call processing capacity per LIM cabinet but significant collective call processing capacity across multiple configured LIMs.

New Application Requirements

An important PBX design trend during the 1990s was offloading of call processing–intensive applications, such as ACD, from the common control complex to adjunct applications servers. With rare exceptions, most current PBX systems require an adjunct server to support advanced ACD features. All PBXs require an adjunct server to support advanced ACD MIS reporting capabilities. Other applications that may require dedicated carriers or adjunct servers include messaging, wireless communications, and systems administration.