Home > IT Infrastructure, Unified Communications (IPT) > What is a VoIP Gateway?

What is a VoIP Gateway?

A VoIP gateway converts telephony traffic from analog (Time Division Multiplexing, or TDM) to digital (Internet Protocol, or IP) and vice-versa.

Traffic coming in from the public switched telephone network (PSTN) is fed through a gateway and converted to digital packets so it can be transported over a local area network (LAN) or other IP-based network.

Conversely, digital IP traffic is fed back through a VoIP gateway for conversion back to analog so it can be transported out over the PSTN.

In other words, a VoIP gateway acts as a bridge between an IP network and the PSTN.

Things get a bit more complex when considering two other factors: VoIP protocols and voice codecs. A protocol is a method of transporting voice packets across a network. A voice codec is a method of encoding and/or decoding digital data streams or signals.

For a VoIP gateway to work properly, the protocol and codec employed must be compatible with the VoIP phone system and/or VoIP service being used. Incompatible protocols and codecs can cause the system to not work at all, or can result in decreased call quality.

Most VoIP gateways support a single protocol. The most common are Session Initiation Protocol (SIP), Cisco Skinny Client Control Protocol (CSCCP, proprietary for Cisco equipment), MGCP (mostly outdated), and H.323 (mostly outdated).

Most VoIP gateways support multiple codecs. The codec used determines how much the voice stream or signal is compressed, and this affects both call quality and bandwidth needed. More compression means lower voice quality but also less bandwidth demanded.

The most common voice codecs used by VoIP gateways are GSM (13 Kbps), iLBC (15 Kbps), G.711 (64 Kbps), G.722 (48/56/64 Kbps), G726 (16/24/32/40 Kbps), G.728 (16 Kbps) and G.729 (8 Kbps).

VoIP gateways come in two types: analog and digital. Analog gateways connect traditional phones to a VoIP phone system, or a VoIP phone system to the PSTN. Digital gateways connect a VoIP phone system to digital voice lines (e.g. a T1) or to connect a traditional PBX system to an IP network.

Originally posted at: http://www.tmcnet.com/channels/voip-equipment/articles/167773-what-a-voip-gateway.htm

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