Australian Government Architecture Reference Models Version 3.0

266
Service Standards Defines Examples
310507
Video
Video conferencing
provides communication
across long distances with
video and audio contact
that may also include
graphics and data
exchange. Digital video
transmission systems
typically consist of
camera, codec (coder
decoder), network access
equipment, network and
audio system.
Australian Government Architecture Reference Models Version 3.0
� integrated services digital network (ISDN): a system of
digital phone connections which has been available for
over a decade. This system allows data to be transmitted
simultaneously across the world using end-to-end digital
connectivity
� T1/T3: T1 service delivers 1.544 Mbps. It typically
channels into 24 DS0s, each capable of carrying a single
voice conversation or data stream. The European T1 or
E1 transmission rate is 2.048 Mbps. A T3 circuit
communicates at 45 Mbps, or 28 T1 lines
� digital subscriber line (DSL): refers collectively to all
types of digital subscriber lines, the two main categories
being ADSL and SDSL. Two other types of DSL
technologies are High data rate DSL (HDSL) and Very
high DSL (VDSL)
� firewall: refers to the network device that is designed to
prevent unauthorised access to or from a private network.
Firewalls can be implemented in both hardware and
software, or a combination of both. Firewalls are
frequently used to prevent unauthorised Internet users
from accessing private networks connected to the
Internet, especially intranets. There are several types of
firewall techniques and firewalls may implement one or
more simultaneously. Packet filtering inspects inbound
and outbound packets, validating against defined
business rules. Application gateways apply security rules
against applications. Circuit level gateways apply security
rules against physical connection attempts to and from
the network. Proxy servers mask the internal requestor by
inspecting and augmenting the packet header. Four
common architectures of firewalls include the packet
filtering router, the screened host firewall system, the
dual-homed host firewall and the screened subnet firewall
(with a DMZ), which is one of the most secure
implementations.
Examples of network devices/standards include:
� bridge: a bridge connects three or more conference sites
so that they can simultaneously pass data, voice or video.
Video conferencing bridges are often called MCUs
(multipoint conferencing units)
� codec: a video codec converts analogue video signals
from a video camera to digital signals for transmission
over digital circuits and then converts the digital signals
back to analogue signals for display
� receiver: an electronic device which enables a particular
videoconference signal to be separated from all others
being received by an earth station and converts the signal
format into a format for video, voice or data.