130 VO IP OVERVIEWThis document is organized as follows:■ “VoIP Overview” on page 2243■ “Voice Subscriber Line Configuration” on page 2245■ “Voice Entity Configuration” on page 2265Introduction to VoIP The voice over IP (VoIP) network is an IP-based packet switched network. Afterdigitization, compression, and packetization, traditional analog voice signals areencapsulated into frames for transmission over the IP network.In a broad sense, VoIP refers to a way to carry data, voice, fax, image and othermultimedia services over an IP data network. In a narrow sense, VoIP refers to away to carry the voice service over an IP data network. The well-known IP phone isa typical VoIP application.Table 75 makes a comparison between plain old telephone service (POTS) withVoIP.Table 75 Comparison between POTS and VoIPPOTS VoIPBased on circuit switching Based on packet switchingPhysical connection. The two parties inconversation each seize a physical connection.Virtual connection. The two parties inconversation share a physical connection.Subject to constraints of communicationprocedure, transmission rate, andencoding/decoding schemeProviding value-added services bycontrolling signalingHigh communication cost Low communication cost
