Customers who want a single PBX system supporting communications requirements across multiple physical locations can use one of many systems offering a remote port cabinet/carrier option, in addition to systems similar to those described in the preceding paragraph. Even though the Ericsson, Alcatel, Cisco, and Sphere systems have a standard single system image distributed architecture capable of supporting station users dispersed across one or more customer premises, some PBXs can support only remote communications requirements with optional hardware. The first PBX system that supported a remote off-premises port cabinet option was the Northern Telecom SL-1. The SL-1 RPE option was introduced in 1982. Since the original SL-1 option most other leading PBX suppliers have introduced their own remote cabinet/carrier options. Current remote options differ greatly across system platforms. Remote port options may include:

1. Multicarrier port cabinets designed to support up to 1,000 ports

2. Single carrier cabinets designed to support about 300 ports

3. Half-shelf carrier cabinets designed to support about 150 ports

4. Single port interface circuit boards designed to support 24 or 36 ports

Customers with significant remote port requirements would benefit from a system that supports a remote equipment option minimizing the number of cabinets/carriers needed at the remote location, instead of con- figuring 10 or 20 remote interface boards, each with limited port capacities. However, a large remote equipment cabinet would be very expensive if the number of remote ports is limited. Growth requirements at the remote location must be taken...