The major components of a VOIP network are very similar in functionality to that of a circuit-switched network. There are three major pieces to VOIP networks.

-a VOIP network
-media gateways
-media gateways/signalling controllers

Media gateways are responsible for call origination, call detection, analog-to-digital conversion of voice, and creation of voice packets (CODEC functions).

Media gateways exist in several forms. For example, media gateways could be a dedicated telecommunication equipment chassis, or even 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.
-Residential gateways that provide a traditional analog interface to a VoIP network.
-Business media gateways that provide a traditional digital PBX interface or an integrated soft PBX interface to a VoIP network.
-Access media gateways that provide a traditional analog or digital PBX interface to a VoIP network.
-Discreet IP telephones units.
-Network access servers that can attach a modem to a telephone circuit and provide data access to the Internet.

-Trunking gateways that interface between the telephone network and a VoIP network.
-Residential gateways that provide a traditional analog interface to a VoIP network.
-Business media gateways that provide a traditional digital PBX interface or an integrated soft PBX interface to a VoIP network.
-Access media gateways that provide a traditional analog or digital PBX interface to a VoIP network.
-Discreet IP telephones units.
-Network access servers that can attach a modem to a telephone circuit and provide data access to the Internet.
Media Gateway Controllers
Media gateway controllers house the signaling and control services that coordinate the media gateway functions. 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). Media gateway controllers could be considered similar to that of H.323 gatekeepers.The amount of functionality is based on the particular VoIP enabling products used.

For calls that originate and terminate within the domain of the VoIP network, only a media gateway controller might be needed to complete calls. In a scalable VoIP network, you can breakup the role of a controller into signaling gateway controller and media gateway controller. You could use a signaling gateway controller to directly connect to the SS7 network, while also interfacing to a VOIP network elements.

Knowing the details of how the devices use their suite of protocols is important to designing the IP backbone that is to service the VoIP elements. The services of these devices are defined by the protocols and software they are running. There are several protocols and implementations that any number of vendors could deploy.

You can view a VOIP network as one logical switch. However, this logical switch is a distributed system, rather than that of a single switch entity; the IP backbone provides the connectivity among the distributed elements.Depending on the VoIP protocols used, this system as a whole is sometimes referred to as a softswitch architecture.

Jim Francisto
voip phone service provider