ES154 Communications and Media 2001-2002
UNIVERSITY OF WARWICK
Lecture 12
School of Engineering
Networked multimedia communication systems and services
D.D.Udrea
Aims and Objectives
- Explain the concept of a multimedia
- Explain the concept of a multimedia service network
- Give examples of Wide Area Service Networks
Multimedia
The term “multimedia” represents information that is being transferred over a network, which contains
two or more of the following media type:
Text: in the form of strings of characters, either formatted or unformatted;
Binary data: in the form of binary representation of numbers of a specific type and precision;
Images (still images or animations): in the form of computer generated graphics or digitised pictures or
documents;
Audio: in the form of speech (low fidelity sound) or music and voice (high fidelity sound);
Video: in the form of short sequences of moving images or complete movies.
Multimedia applications involve either person-to-person communication or person-to-system
communication.
(e.g. two people talking to each other on the phone or a person watching a broadcast movie on TV or a
person viewing a web page).
Bandwidth requirement of multimedia
Examples of services in three different categories -voice, data
and video - and the approximate bandwidth ranges of the
services.
[http://www.ericsson.com/about/telecom/part-a/a-2-8.shtml]
? How long it takes to transmit a file of 100 Mbit over the following lines:
-PSTN (14.4, 28.8, 33.6 or 56 kb/s)
-ISDN (64, 128 kb/s)
-ADSL (16-640 kb/s upstream, 1.544-8.448 Mb/s downstream)
-CATV(20-40 Mb/s)
-Ethernet (10, 100, 1000 Mb/s)
transfer time = file size / bit rate
Answer
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Transmission time = File size/Transmission rate
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ES154 Communications and Media 2001-2002
UNIVERSITY OF WARWICK
Lecture 12
School of Engineering
Networked multimedia communication systems and services
D.D.Udrea
? What are the uncompressed bit rates for the following multimedia sources
Source
Bandwidth
Hz
Sampling rate
Samples/s
Bits per sample
Bit rate
kb/s
Telephone voice
Wideband speech
Wideband audio
Colour image
CCIR TV
HDTV
200-3400
50-7000
20-20000
8000
16000
44100
512 x 512
750 x 576 x 30
1280 x 720 x 60
12
14
16/channel
24
24
24
96
224
1412
6300
300000
1327000
Multimedia communication networks
There a number of different types of network that are used to provide the networking infrastructure. Some
of these networks were originally designed to provide one single type of service and have evolved to
provide more services; some other networks were originally designed to provide multimedia
communications.
In the first category, one examples is the PSTN (Public Switched Telephone Network), originally
designed to provide low quality voice service, now provides a more advanced range of services, due to
the technological advances in hardware and software.
A second example are old data networks like the ARPANET (Advanced Research Projects Agency
Network of the US Defence Department), originally for basic data applications and e-mail, which evolved
to become the Internet.
In the second category, the ISDN (Integrated Services Digital Network) or the ATM (Asynchronous
Transfer Mode) multiservice network were, from the onset, specified for voice and data services,
respectively for broadband digital services.
A complete multimedia network can be functionally represented by the following components, as shown
in the figure below:
Source
Source
Terminal
Destination
Terminal
Access
Network
Backbone
Network
Components of a multimedia
communication network
[Gibson 2001, Chapter 1]
Delivery
Network
The Source is the media to be transmitted (voice, text, data, audion, video), often represented in digital
form. One of the most important characteristics of the source is the bandwidth.
The Source Terminal, for example telephone, computer, PDA (Personal Digital Assistant), is the device
that converts the Source into an appropriate form in order to be correctly transmitted and received at the
destination. Its role is to ensure that the information is transmitted at the required rate, that it is packaged
in a way that ensures reliability etc.
The Access Network is the physical line that the Source terminal is connected to, such as an Analogue
telephone line, a 56 Kbit/s modem line, an ADSL (Asymmetric Digital Subscriber Line), or a LAN (Local
Area Network).
The Backbone Network is the main interconnection network (or networks) comprising of physical lines
and additional hardware, which performs functions like routing, switching and billing. The connection
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ES154 Communications and Media 2001-2002
UNIVERSITY OF WARWICK
Lecture 12
School of Engineering
Networked multimedia communication systems and services
D.D.Udrea
provided can be a physical circuit-switched connection, a dedicated virtual path through a packetswitched network or a general TCP/IP type connection. Some important connection characteristics are
bandwidth, jitter, delay, packet loss, guaranteed service.
The Delivery Network is the physical line that the Destination Terminal is connected to. It may be
identical or only compatible to the access network, with respect to the service it supports.
The Destination Terminal may be identical or compatible to the Source Terminal and its role is to
reproduce the information in its original form or in a very close representation.
Let’s consider several examples of multimedia communication networks and the services they provide.
Telephony or POTS (Plain Old Telephone Service)
Telephony is a service which allows two (or multiple) users to have a conversation with each other, in
real time and simultaneously ( a full-duplex transmission), from remote locations.
In this case, the Source is voice or low definition sound with a frequency bandwidth between 200 and
3400 Hz. In its most traditional form, the Source and Destination terminals are telephone sets, the Access
and Delivery networks are analogue lines which connect the terminals to a switching office, known as
Local Exchange - for private, individual users - or PBX (Private Branch Exchange) - for companies or
offices. The PBX enables free calls between any two telephones connected to it. The Backbone network
to which the exchanges belong is called the PSTN (Public Switched Telephone Network). The National
PSTNs also contain centres for switching international calls. These are called IGEs (International
Gateway Exchanges).
The figure below shows a simple diagram of a traditional telephone network.
The PSTN of the 1960s
[http://www.ericsson.com/about/telecom/
part-b/b-1-2.shtml]
Over the years, the PSTN has evolved to accept other types of terminals and services, such as Fax,
cordless phones, Data terminals and computers, as show in the figure below.
Modern PBX with different terminals
and lines to the local exchange (PSTN).
The PBX and the Local Exchange are
connected through a digital line which
uses PCM (Pulse Code Modulation) to
encode the original audio signal.
[http://www.ericsson.com/about/telecom/
part-b/b-1-3.shtml]
Other services over PSTN
Various terminals have emerged which took advantage of the telephone networks already in place.
However, they had to adapt their type of information to the analog transmission line of the Access
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ES154 Communications and Media 2001-2002
UNIVERSITY OF WARWICK
Lecture 12
School of Engineering
Networked multimedia communication systems and services
D.D.Udrea
network. The figure below shows the types of terminal connected to the PSTN and the type of source they
transmit.
One example of service which uses the existing PSTN infrastructure is Internet access. Most individual
users connect to the Internet through their phone lines. In this case, the Source and Destination terminals
are computers, the Access Network is a modem connected to an analog telephone line, the Backbone
network is formed by a PSTN exchange which connects either digitally to the ISP (Internet Service
Provider) network through a PSTN-TCP/IP Gateway or through an ISP modem (as shown in the figure
below).
Connecting a computer to the Internet
over the PSTN
[http://www.ericsson.com/about/telecom/
part-b/b-1-3.shtml]
Typical modem transmission rates are 14.4, 28.8, 33.6 or 56 kbit/s. However, if we combine a line bit rate
of 33.6 kbit/s with a modern compression algorithm, we can now achieve a transfer rate of 230 kbit/s.
This rate allows high rate services to be provided.
Telephony and data N-ISDN (Narrowband-Integrated Services Digital Network)
[http://www.ericsson.com/about/telec
om/part-b/b-1-3.shtml]
The ISDN (see above) was created from the beginning with the purpose to provide multimedia services to
the users. In theory, ISDN can handle all services that require a bandwidth of up to 1,920 kbit/s.
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ES154 Communications and Media 2001-2002
UNIVERSITY OF WARWICK
Lecture 12
School of Engineering
Networked multimedia communication systems and services
D.D.Udrea
It provided an alternative, all digital, connection for telephone, fax and data, to the PSTN service. The
Backbone network is very similar to the PSTN, directly compatible and sometimes interlinked. The main
difference is in the equipment used for user access (digital) and the transmission rate from/to the user.
The typical transmission rate from the user is termed Basic rate access (BRA). It consists of two main
transmission channels of 64 kbit/s (termed B channels) and one data channel of 16 kbit/s (termed D
channel), used for sinchronisation and signalling on the network, a total of 144 kbit/s.
An enhanced service can be received if the user has Primary rate access (PRA) which provides 30 B
channels of 64 kbit/s and a larger D channel of 64 kbit/s, a total of 1984 kbit/s.
In analogy with the general network model, the Source and Destination terminals are digital telephone
sets, fax machines or computers, termed TE1s (Terminal Equipment type 1) or analog telephones and fax
machines, termed TE2s (Terminal Equipment type 2 – non ISDN). The Access and Delivery networks are
Network Terminals (NT), sometimes also called User Network Interfaces (UNIs), attached to digital lines
or, in the case of non-ISDN terminals, Terminal adapters (TAs) interfacing the terminals with the
Network Terminals. The Backbone Network is the ISDN (Integrated Services Digital Network).
Summary of multimedia communication networks and their services
Telephony Voice Facsimile Internet Video
Speech and Entertainment
(fixed and mail
(fax)
Acces
telephony videoconfe (video on demand,
mobile)
rencing
interactive TV)
Multimedia Email and file Videoconfe Information retrieval
The Internet Speech and
videotelephony mail
transfer
rencing
and e-commerce
Access to the
Internet Acces
Analog/digital Interactive CD and video
Cable
PSTN
audio and TV TV
on demand
networks
Analog/digital audio and TV broadcast
Interactive Near-video on
Broadcast
TV
demand
networks
Internet Acces
LAN
Narrowband Digital telephony Video telephony and
and fax
conferencing
interconnection
ISDN
All interpersonal and interactive
High speed network interconnections
Broadband
applications
ISDN
Telephone
networks
References:
Halsall, Fred – Multimedia communications: Applications, Networks, Protocols and Standards – Addison Wesley, 2001, ISBN
0-201-39818-4 QA 78.51.H2
Gibson, Jerry, ed. – Multimedia communications; Directions & innovations – Academic Press, 2001, ISBN 0-12-282160-2,
QA 78.51.M8
Comer, Douglas - Computer networks and Internets with Internet applications / Douglas E. Co. - 3rd ed. - Upper Saddle River,
N.J.; London: Prentice Hall, 2001. – ISBN 0-13-091449-5 QA 74.2.C6
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