A VoIP Gateway, or Voice over IP Gateway, is a network device which helps to convert voice and fax calls, in real time, between an IP network and Public Switched Telephone Network (PSTN). It is a high performance gateway designed for Voice over IP applications. Typically, a VoIP gateway comes with the ability to support at least two T1/E1 digital channels. Most VoIP gateways feature at least one Ethernet and telephone port. Controlling a gateway can be done with the help of the various protocols like MGCP, SIP or LTP.
The main advantage of VoIP gateway is that it can provide connection with your existing telephone and fax machines through the traditional telephone networks, PBXs, and key systems. This makes the process of making calls over the IP network familiar to VoIP customers.
VoIP gateways can end a call from the telephone and can provide user admission control using IVR (Interactive Voice Response) system and provide accounting records for the call. Gateways also help direct outbound calls to a specific destination, or can end the call from another gateway and send the call to the PSTN.
VoIP gateways plays a major role in enhancing carrier services and also supports the simplicity of the telephone calls for less cost and easy access. Flexible call integration has been developed at less cost which enables programmable call progress tones and distinctive ring tones.
The main functions of VoIP gateways include voice and fax compression or decompression, control signaling, call routing, and packetization. VoIP gateways are also power packed with additional features such as interfaces to external controllers like Gatekeepers or Softswitches, network management systems, and billing systems.
Analog telephony adapters are connected to the internet or Local area network using an Ethernet port and have sockets to connect one or more PSTN phones. Such devices are sent out to customers who sign up with various commercial VoIP providers allowing them to continue using their existing PSTN based telephones.
Another type of gateway device acts as a simple GSM base station and regular mobile phones can connect to this and make VoIP calls. While a license is required to run one of these in most countries these can be useful on ships or remote areas where a low-powered gateway transmitting on unused frequencies is likely to go unnoticed.