Brief History of UC

Before Voice over IP (VoIP), voice calls were sent over a dedicated network. Each call passed through a dedicated circuit and was switched from one point to the other, hence the term circuit-switched. Although this guaranteed a quality connection, it required dedicated processing power and physical connectivity. For example, the wire that went from your home telephone to the central office (CO) connected you to a physical port on the CO telephone switch. The processor of the CO switch had to constantly monitor each port to determine whether a particular phone (port) made a request to dial a number or access a feature, such as call forwarding.

With a telephone connected to a dedicated network, either the public switched telephone network (PSTN) or an enterprise class private branch exchange (PBX) network, it was difficult for outside influences to affect the quality of a connected call. Although having this separate network held numerous advantages, most notably quality and reliability, individual PBX or CO switches used proprietary protocols limiting interoperability and feature expansion. It also meant, for example, that if you wanted to access your PBX voicemail box from your email client, you were subject to the whim of the PBX voicemail vendor’s decision as to what you could and couldn’t do and what standards were supported.