Monday, November 23, 2009

What VoIP H.323 comprises of?

The VoIP/H.323 comprises a set of standards and is supported by a series of protocols covering the different aspects of communication:

* Address:

1. RAS (Registration, Admission and Status). Communications protocol that enables an H.323 station locate another station through the H.323 Gatekeeper.

2. DNS (Domain Name Service). Service name resolution to IP addresses for the same purpose that the RAS protocol but through a DNS server


1. Initial Q.931 Call Signaling

2. H.225 Call Control: signaling, registration and admissions, and packetization / synchronization of the stream (flow) voice

3. H.245 Control Protocol messages to specify opening and closing of channels for voice streams

* Voice Compression:

1. Required: G.711 and G.723

2. Optional: G.728, G.729 and G.722

* Transmission of Voice:

1. UDP. The transmission takes place on UDP packets, but UDP does not provide for data integrity, use of the bandwidth is higher than with TCP.

2. RTP (Real Time Protocol). Manages aspects of timing, scoring UDP packets with the information necessary for the efficient delivery of them at the reception.

* Transmission Control:

* RTCP (Real Time Control Protocol). It is mainly used to detect situations of network congestion and take, where appropriate, corrective action.

VoIP protocol stack

We can now from a number of items already available in the market and, according to different designs allow us to build VoIP applications. These elements are:

IP Phones.

PC Adapters.

Telephone Hubs.

Gateways (gateways PSTN / IP).


Multiple audio units. (MCU Voice)

Directory Services.

For more info read my hub:
Wireless Communication Protocols: GSM, H.323, PBX, PCM, WAN, LAN, Routers

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