Installing IP-Centrex

Installing IP-Centrex
In many conventional Centrex installations the service provider, usually the incumbent telephone company, owned the telephone wiring within the customer's building, as well as provided the telephone service. This arrangement meant that the telco was responsible for the quality of service to the user's desktop and, if the telephone was rented as part of the service right up to the user's ear and mouth. The disadvantage of this situation was that the telco was usually unwilling for the unshielded twisted pair (UTP) cabling to be shared between voice and data signals, thus necessitating the installation of separate cables and cross-connect equipment for Centrex service and for the corporate LAN.

Within recent years most telcos in North America and in some European countries have disposed of the telephone cabling in customers' premises, making the building owners responsible for all in-house telecommunication cabling. This development has made fault diagnosis more complex, but has also opened the door to the shared use of the cabling infrastructure within an office area.

The arrival of IP-Centrex carries this shared use trend to completion, in that the voice and signaling packets travel over the same LAN and through the same switches as the corporate data traffic. In most installations, therefore, IP-Centrex will be superimposed on a preexisting LAN, which is likely to be Ethernet operating at 100 Mbps, and those responsible for implementing the service will not be much concerned with the underlying cable infrastructure.

The exceptions will be those cases where IP-Centrex is to be implemented in conjunction with a major LAN upgrade, or when additional cabling runs and outlets are required to service the IT phones.

For these reasons we have included the following discussion of the types of copper cabling that are now generally used for Ethernet networks