Digital VoIP Media Gateways


VoIP Media Gateways come in two flavors: Analog VoIP and Digital VoIP. With Digital VoIP transmission, sequences of discrete, distinct pulses represent the data being sent. VoIP Information is encoded as a binary language.

VoIP Media Gateways perform the conversion between TDM voice to Voice over Internet Protocol (VoIP). Because the gateway connects different types of networks, one of its main functions is to convert between the different transmission and coding techniques.

VOIP Media Gateways are used on both near-end and far-end terminations of a VoIP circuit. At the near-end, gateways are typically used to connect an existing analog telephones or faxes to a VoIP circuit, referred to as an FXS port.At the far-end, gateways are used to interface the VoIP circuit to the appropriate TDM voice circuit.


Media gateways are special gateways that are responsible for call origination, call detection, analog-to-digital conversion of voice, and creation of voice packets . In addition, media gateways have optional features, such as voice (analog and/or digital) compression, echo cancellation, silence suppression, and statistics gathering.


Advantages of Digital VoIP Transmission
Advantages of a digital VoIP media approach include lower cost and more flexibility. Sound quality is better and VoIP transmission is more secure. Digital VoIP transmission can also handle data directly but in general, to retrieve the information, the digital VoIP binary code must be converted back to an analog signal

VOIP Media Gateways features and services

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.

Discreet IP telephones units.


Media Gateway Controllers


Media gateway controllers house the signaling and control services that coordinate the media gateway functions. Media gateway controllers could be considered similar to that of H.323 gatekeepers. The media gateway controller has the responsibility for some or all of the call signaling coordination, phone number translations, host lookup, resource management, and signaling gateway services to the PSTN (SS7 gateway). The amount of functionality is based on the particular VoIP enabling products used.


A Media Gateway Controller (MGC) is a system used in certain Voice over IP telephony architectures. An MGC controls a number of dumb terminals, the Media Gateways. The MGC receives signalling information (like dialed digits) from the Media Gateway and can instruct it to alert the called party, to send and receive voice data etc. There are several protocols which can be used between MGC and Media Gateway: SGCP, IPDC, MGCP and Megaco (also known as H.248). The MGC receives also the term Call Agent when referred in the context of MGCP.

If the gateway is decomposed into two parts, separating the call control function from the bearer control function, then the part that controls the call control is referred to as a "Media Gateway Controller". This is also sometimes referred to as a "softswitch".

Media Gateway Controllers also allows the Call Agent to audit the current state of endpoints on a Media Gateway.

The Media Gateway uses Media Gateway Controllers to report events (such as off-hook, or dialed digits) to the Call Agent.