(VOIP (VoiceOverIP) is a technology that uses IP network as a transmission carrier to realize voice communication. The voice gateway GateWay (GW for short) is located between the public telecommunication network PSTN and the network access site, collects analog voice signals from the PSTN network, converts It becomes a digital signal, compresses and encodes it, and then transmits it to the peer voice gateway through the network. At the same time, it receives the packet voice IP packets from the network. After decompression, it is converted into an analog voice signal of the PSTN network through digital-to-analog conversion. On the router The realization of the VOIP telephone function is actually an expansion of the router function, and it also represents the gradual expansion of the data service to the voice service. IPv6 base header)