CAC is a deterministic and informed decision that is made before a voice call is established and is based on whether the required network resources are available to provide suitable QoS for the new call. The purpose of a Call admission controller is to decide, at the time of call arrival, whether or not a new call should be admitted into the network. A new call is admitted if and only if its Quality of Service constraints can be satisfied without jeopardizing the QOS constraints of existing calls in the network.

The term VoIP refers to the transfer of Voice over the Internet Protocol (IP) of the TCP/IP protocol suite. Using "VoIP" technology we can make traditional telephone calls from either computer or phone to other computer or phone using both public switched telephone network (PSTN) and internet (which is packet switched network). All you need is an Internet connection for VoIP. This technology really changes everything because it allows people to receive phone calls from anywhere that an internet connection exists, just in the same way you can receive your emails anywhere that you can connect to the internet. The term "VoIP technology" covers a range of technologies, including voice-over-IP (VoIP) and fax-over-IP services, which are carried over both the Internet and private IP-based networks. VoIP is part of packet voice, which includes voice-over-asynchronous-transmission-mode (ATM) and frame-relay networks, which run faster than IP but are less common. VoIP connects across combinations of PCs, Web-based telephones, and phones connected via public telephone lines to remote voice gateways. Because information travels in discrete packets, it doesn't need to rely on a continuously available switched circuit. Using VoIP we can enhance the traditional PBX by combining voice and data services onto a single network. The end user devices (also called client device) are normally referred to as VoIP phone are used in VoIP. Development of the 'VoIPphone' will require the development of a ' system on a chip' which combines digital signal processing (DSP) functions, micro-controller (MCU) functions, analog interface, telephone user interface and associated glue logic.

CAC is a deterministic and informed decision that is made before a voice call is established and is based on whether the required network resources are available to provide suitable QoS for the new call. The purpose of a Call admission controller is to decide, at the time of call arrival, whether or not a new call should be admitted into the network. A new call is admitted if and only if its Quality of Service constraints can be satisfied without jeopardizing the QOS constraints of existing calls in the network.