Page 299 - DCAP101_BASIC_COMPUTER_SKILLS

Basic Computer Skills

Notes These cameras can be controlled at a distance to pan left and right, tilt up and down,
and zoom. They became known as PTZ cameras. The console contains all electrical
interfaces, the control computer, and the software or hardware-based codec.
Omnidirectional microphones are connected to the console, as well as a TV monitor
with loudspeakers and/or a video projector. There are several types of dedicated
videoconferencing devices:

(i) Large group videoconferencing are non-portable, large, more expensive devices
used for large rooms and auditoriums.
(ii) Small group videoconferencing are non-portable or portable, smaller, less
expensive devices used for small meeting rooms.
(iii) Individual videoconferencing are usually portable devices, meant for single
users, have fixed cameras, microphones and loudspeakers integrated into the
console.
2. Desktop systems are add-ons (hardware boards, usually) to normal PCs, transforming
them into videoconferencing devices. A range of different cameras and microphones
can be used with the board, which contains the necessary codec and transmission
interfaces. Most of the desktops systems work with the H.323 standard. Videoconferences
carried out via dispersed PCs are also known as e-meetings.
14.5.1 Conferencing Layers

The components within a Conferencing System can be divided up into several different
layers: User Interface, Conference Control, Control or Signal Plane and Media Plane.

Video Conferencing User Interfaces could either be graphical or voice responsive. Many of
us have encountered both types of interfaces, normally we encounter graphical interfaces on
the computer or television, and Voice Responsive we normally get on the phone, where we
are told to select a number of choices by either saying it or pressing a number. User
interfaces for conferencing have a number of different uses; it could be used for scheduling,
setup, and making the call. Through the User Interface the administrator is able to control
the other three layers of the system.

Conference Control performs resource allocation, management and routing. This layer along
with the User Interface creates meetings (scheduled or unscheduled) or adds and removes
participants from a conference.
Control (Signaling) Plane contains the stacks that signal different endpoints to create a call
and/or a conference. Signals can be, but aren’t limited to, H.323 and Session Initiation Protocol
(SIP) Protocols. These signals control incoming and outgoing connections as well as session
parameters.

The Media Plane controls the audio and video mixing and streaming. This layer manages
Real-Time Transport Protocols, User Datagram Packets (UDP) and Real-Time Transport
Control Protocols (RTCP). The RTP and UDP normally carry information such the payload
type which is the type of codec, frame rate, video size and many others. RTCP on the other
hand acts as a quality control Protocol for detecting errors during streaming.
14.5.2 Multipoint Videoconferencing

Simultaneous videoconferencing among three or more remote points is possible by means
of a Multipoint Control Unit (MCU). This is a bridge that interconnects calls from several
sources (in a similar way to the audio conference call). All parties call the MCU unit, or the
MCU unit can also call the parties which are going to participate, in sequence. There are
MCU bridges for IP and ISDN-based videoconferencing. There are MCUs which are pure
software, and others which are a combination of hardware and software. An MCU is
characterised according to the number of simultaneous calls it can handle, its ability to

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