Media Gateway – sometimes referred to as a gatekeeper in a VoIP network. It was traditionally used for call admission & control and bandwidth management, but this has changed recently. Now, technology has allowed this functionality to co-exist within traditional getaways (described below).
The major function of media gateways is analog-to-digital conversion of voice and creation of voice IP packets (CODEC functions). In addition, media gateways have optional features, such as voice (analog and/or digital) compression, echo cancellation, silence suppression, and statistics gathering.
The media gateway forms the interface that the voice content uses so it can be transported over the IP network. Media gateways are the sources of bearer traffic. Typically, each conversation (call) is a single IP session transported by a Real-time Transport Protocol (RTP) that runs over User Datagram Protocol (UDP).
Media gateways exist in several forms. For example, media gateways could be a dedicated telecommunication equipment chassis, or even a generic PC running VoIP software. Their features and services can include some or all of the following:
- Trunking gateways that interface between the telephone network and a VoIP network. Such gateways typically manage a large number of digital circuits.
- Residential gateways that provide a traditional analog interface to a VoIP network. Examples of residential gateways include cable modem/cable set-top boxes, xDSL devices and broadband wireless devices.
- Access media gateways that provide a traditional analog or digital PBX interface to a VoIP network. Examples include small-scale (enterprise) VoIP gateways.
- Business media gateways that provide a traditional digital PBX interface or an integrated soft PBX interface to a VoIP network.
- Network access servers that can attach a modem to a telephone circuit and provide data access to the Internet.