Cisco ISDN GW 3241 Manual de usuario descargar pdf (Pagina 12)

Video conferencing today

 H.323 Terminal

The terminal is an endpoint on a network which provides for real-time, two-way communications. A

terminal may provide audio (speech) only, or audio in a combination of video and data.

 H.323 Gatekeeper

A gatekeeper is optional and controls a zone. It provides a directory service allowing services to be

accessed via directory numbers (E.164 numbers) and alphanumeric names. It also provides call

control, routing services, bandwidth management and admission control. It also provides basic security

(authorization) for communications between H.323 elements within its zone.

 H.323 Gateway

A gateway is any device that allows calls to be established between networks, whether of the same or

different types. It may also provide protocol conversion between H.323 endpoints and endpoints that

do not support H.323. For example:

The Codian ISDN GW can route calls to an H.320 ISDN network

The Codian ISDN gateway and VoIP gateways can perform H.323<->PSTN operations, routing

voice over IP (VoIP) calls from an H.323 terminal on to the public switched telephone network

(PSTN) allowing "normal" telephone calls to be made from an H.323 client

The elements can be software based and there can be more than one entity installed on a single computer.

The Codian MCU and IP VCR can act as a gateway to allow direct access to internal features such as

individual conferences or recordings. You can also set up gateway definitions on Codian MCUs and IP VCRs

so that outgoing calls can be routed to gateways.

Video conferencing, networking and telephony

protocols

H.323 encompasses a number of other protocols, including audio (voice) and video codecs, and standards

for passing data and control structures. The following are examples of some protocols supported by Codian

products and included in the H.323 framework that a video conferencing administrator is likely to come

across:

 G.711, G.722, G.723.1, G.728 and G.729 are audio codecs

 H.261, H.263(+) and H.264 are video codecs. H.264 is the most recent video compression standard.

It offers approximately twice the quality of H.263 at the same bandwidth, or the same quality at half

the bandwidth

 H.239 which allows a secondary video channel. It defines how PC desktop graphics is converted in to a

separate media stream and transmitted in parallel with the video stream. This is the protocol that

Codian MCUs use for the data channel in a conference

 H.225 and H.245 are signalling protocols

 Siren14™ is a proprietary audio codec used by Polycom endpoints

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Cisco ISDN GW 3241 Manual de usuario Pagina 12