英语翻译H.323 Terminal,is an endpoint on the network which provi
英语翻译
H.323 Terminal,is an endpoint on the network which provides for real-time,two-way communications with
another H.323 terminal,Gateway,or Multipoint Control Unit.A terminal may provide speech only,speech and
data,speech and video,or speech,data and video.The block functional structure of an H.323 terminal is
shown in the Figure 3.
· H.323 Gateway (GW),is an endpoint on the H.323 network which provides for real time,two-way
communications between H.323 Terminals and other ITU Terminals connected,for example,to PSTN,ISDN,
broadband ISDN (ATM),or QoS enhanced LANs.The purpose of the Gateway is to reflect the characteristics
of a network endpoint to a Switch Circuits Network (SCN) endpoint,and the reverse,in a transparent way.
Functions like translation between transmission formats and between communications procedures must be
provided.
· Multipoint Control Unit (MCU),is an endpoint on the network which provides the capability for three or
more terminals and Gateways to participate in a multipoint conference.It may also connect two terminals in a
point-to-point conference which may be later developed into a multipoint conference.The MCU consists of
two parts:a mandatory Multipoint Controller (MC) which provides capability negotiation between all terminals
to achieve common levels of communications and optional Multipoint Processors (MP),which performs mixing
or switching of audio,video and data.This functionality could be integrated in an H.323 terminal.
· GateKeeper (GK),is an H.323 entity on the network that provides call control services to the H.323
endpoints.This element is the key block of the H.323 architecture for development of services and for the
application of this technology in a medium-large environment.In principle the GK is an optional block of the
architecture -that was decided in order to boost the development of H.323 terminals without the requirement
of a complex element-,but without this element the model is quite limited.GK provides important services
like:address translation and directory services,admission and bandwidth control,call control signalling or call
authorization.