Next-Generation Network

Description

Next-generation networks, however, are architected quite differently. In particular, the telephone exchange is decomposed into a number of components separated by standardized protocols, and each of these components can be supplied by a different vendor. The main components of an NGN architecture, although sometimes called different names by the various standards bodies, are the softswitch (equivalent to call control), application sever (features and applications), media server (service circuits), and media gateway (line and trunk cards).

The four key elements of the NGN architecture can be mapped into four quadrants isolating signaling (the signaling gateway) and control (the application server) from transport and media features (the media gateway and media server). Likewise, this architecture also separates gateway functions between the legacy PSTN world and the new IP packet world (the signaling and media gateways) from pure IP devices (the application and media servers).

A media server is a slave media processing device that is connected to an IP network and controlled by a call agent of some kind, for example, a softswitch or application server. The media server performs media processing manipulations on RTP streams such as announcements, IVR, recording and playback, bridging/ mixing, automatic speech recognition (ASR), text to speech (TTS), fax handling, and video processing (for example, playing, recording, and conferencing). A media server does not contain any application logic and is therefore a multipurpose component reusable for all media processing tasks in the network.

A media server is controlled by a softswitch or application server using a control protocol. The most common control protocol in use today is SIP, used in conjunction with with XML-based scripting languages such as VoiceXML (used for IVR dialogs), or Media Server Markup Language (MSML – a an XML scripting language for feature-rich conferencing control). Alternative control protocols include MGCP or H.248.

In real deployments, the IP media server also connects to additional devices including storage devices for voice mails and ring tones, speech servers, and session border controllers. And because the IP media server is discrete from the rest of the VoIP architecture, it’s relatively easy to add a new service or feature, as these service introductions are now isolated to the application layer of the architecture.

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