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01/12/06

VoIP Technologies/ IP Telephony

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Content of this page: Architecture of the VOIP systems and applicable technologies.

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Architecture

Basic architecture of the VoiP systems following presented:

IP Telephone: is a set of telephonic terminals of VoIP system, whatever it is: IP telephone, analogical telephone with VoIP adapter (ATA) and PC's with softphone;
Gateway (GW):is the functionality responsible by inter-operation between VoIP network and public telephonic network. Execute the media conversion in real time (Analogical Voice x Digital Voice compressed) and the conversion of signaling to the telephonic calls that get in and out of VoIP network;
Gatekeeper (GK): is the functionality responsible by the management of IP telephones. It main functions are: execute the translation of many terminal address, control the access and the terminal calls in the network and control the used band;
Application Server (AS): is the functionality that provide additional services of VoIP Network. Between those services can be: Pobox, Interactive Voice Response (IVR), telephonic agenda services, and others.

Protocols used in VoIP/Telefonia IP

VoIP systems use the set of protocols following presented:

Protocol IP and TCP/UDP

The protocols: IP and TCP/UDP are basic IP net components used by VoiP systems.

Signalling Protocols (Call Control)

H.323 - Packet Based Multimedia Communications Systems (ITU-T). Used by IP telephones, computers, IP adapters, Signalling controllers (soft-switches and call managers) and gateways to establishment, controll and finishing of the calls. It's a old and complex protocol older and complex, nowadyas has been less used by the IP telephonic systems.
SIP - Session Initiation Protocol (IETF). Has the same utilization of H.323, although it is more modern and less complex, and has been adopted with even more by the VoiP systems.

Gateway Protocol Control (Signaling)

MGCP - Media Gateway Control Protocol (IETF). Used by gateways contollers to establishment, control and ending of the calls.
MEGACO - Media Gateway Control Protocol (IETF/ITU-T). Has the same purpose of MCGP, although was developed to be an alternative to this protocol, adjusting also to controllers distributed of gateways, multipoint controllers (Conference) and the interactive units of audible reply.

Media Protocols (Voice Transport)

RTP - Real-Time Transport Protocol (IETF). Protocol responsible for voice transport in real time between computers and gateways. Is the standard used nowadays to this situation.
RTCP - Real-Time Transport Control Protocol (IETF). Protocol responsible for the control of voice transport realized by RTP in the VoIP systems.

Audio Codecs

Os Codecs de Áudio são os programas responsáveis pela conversão e compressão dos sinais de Voz para uso nos sistemas VoIP. De acordo com o nível de compressão do sinal final, pode-se fazer uma sintonia adequada para a relação banda x qualidade de voz para cada sistema VoIP.

Audio Codecs are programs responsible for the conversion and compression of the voice signals to use in the VoiP systems. According with the compression level of the final signal, can be done adequate tunning to the band relation x voice quality for each VoiP system.