35 - Centrex

Abstract

Centrex is a service offered by telephone companies that gives their customers the capabilities of a sophisticated voice and data private branch exchange (PBX) without the need to purchase and maintain on-premises switching equipment. The PBX is connected to the public telephone network operator's (PTO) main exchange by voice and data channels called trunks. Voice and data traffic to and from the public network travels over these trunks, while traffic internal to a customer's site is routed by the PBX. Centrex is an alternative for businesses that do not wish to buy and run their own private telecommunications system. As the name implies, it is a Central Office Exchange with the lines from individual telephones and data terminals connected directly to the PTO's exchange rather than a PBX. Centrex is also attractive to businesses that do not have enough lines to justify the purchase of a PBX, yet need the sophisticated voice and data services an expensive PBX can offer, such as automatic call distribution (ACD) and integrated voice mail (IVM). The network and PBX approaches offer comparable features and benefits. When both options are available, as in North America, hybrid networks are frequently found with a vast majority of Centrex users using a PBX somewhere in their network. Centrex has voice features helping ensure that calls are answered quickly and routed appropriately and cost effectively within the network.