Media Technology I
Lecture Notes and Tutorials on:
Web : www.staff.city.ac.uk/~raj
Aim of this Module
• Describe the theory and operation of the major
technologies and equipment of relevance to the media and
information industries
• Introduce you to the multimedia communications and its
range of applications and networking infrastructures
• Learn about different media types (text, images, speech,
audio and video) and applications (VoIP, multimedia
electronic mail, interactive television, e-commerce, mcommerce and others)
Syllabus
• Multimedia Communications (Week 1)
- Multimedia information representation
- Multimedia Networks (Telephone, Data, Broadcast,
ISDN, Broadband)
• Multimedia Communications (Week 2)
- Multimedia applications (interpersonal
communications, interactive applications over the
Internet, Entertainment applications)
- Application and Networking Terminology (Media
types, communication modes, Network types, multipoint
conferencing, network QoS, Application QoS)
Syllabus
• Multimedia Information Representation (week 3)
- Digitization principles (analogueue signals, encoder
design, decoder design)
- Text (unformatted text, formatted text, hypertext).
Images (Graphics, digitized documents, digitized
pictures)
• Multimedia Information Representation (Week 4)
- Audio(PCM speech, CD-quality audio, synthesized
audio).
- Video (Broadcast Television, Digital Video, PC Video,
Video Content)
Syllabus
• Text and Image Compression (Week 5)
- Compression Principles (source encoders and
destination decoders, lossless and lossy compression,
entropy encoding, source encoding)
- Text compression (Static Huffman coding, Dynamic
Huffman coding, Arithmetic coding, LZW coding)
- Image compression (GIF format, TIF format, digitized
documents, digitized pictures, JPEG)
• Audio and video compression (Week 6)
- Audio compression (Differential pulse code
modulation, adaptive differential PCM, adaptive predictive
coding, linear predictive coding, MPEG audio coders)
- Video compression (Video compression principles,
H.261, H.263, MPEG-1, MPEG-2 etc..)
Syllabus
• Standards for multimedia communications (Week 7)
- Reference models (TCP/IP, protocol basics)
- Standards relating to interpersonal communications
(circuit networks, packet-switched networks, e-mail)
• Standards for multimedia communications (Week 8)
- Standards relating to interactive applications
(information browsing, e-commerce, intermediate
systems, Java and JavaScript)
- Standards for entertainment applications
(Movie/Video-on-demand, iTV)
Syllabus
• Digital Communications (Week 9)
- Transmission media (two-wire open lines, twistedpair lines, coaxial cables, optical fibre, satellites,
microwave communications, signal propagation delay)
- Sources of signal impairment (Attenuation, limited
bandwidth, delay distortion, noise)
- Asynchronous transmission (bit synchronisation,
character synchronization, frame synchronization)
• Digital Communications (week 10)
- Synchronous transmission (Bit synchronisation,
character-oriented, bit-oriented)
- Error detection methods (Parity, block sum check,
cyclic redundancy check)
- Advanced protocol and specifications
Introduction
• ‘Multimedia’ means the information transferred is
composed of text, images, audio and video
- Text (Unformatted and Formatted)
- Images (Computer-generated, Digitized,
etc.)
- Audio (Low-fidelity speech as in telephony
and high-fidelity stereophonic music as in
CD’s
- Video (Moving images and complete
movies/films)
Introduction
• Person-to-person (communication) – Two
people communicate through suitable
Terminal Equipment (TE)
• Person-to-system (Interactive ) – Using
multimedia Personal computer or
Workstation ( Located at home or in an
office)
Voice and Data Networks
• Public switched telephone networks
(PSTNs) – initially designed to provide
speech services. However, due to the
advances in Digital Signal Processing
(DSP) hardware and software now can
support multimedia applications
• Data networks that initially supported data
applications (email and ftp) now support
much complex multimedia applications
Multimedia Information
Representation
• Text: Block of characters, each represented by a
fixed number of binary digits (bits) known as
codeword
• Digitized image: Two-dimensional block of
picture elements represented by a fixed number of
bits
• Audio and Video: Type of signal is known as an
analogue signal and varies continuously with time
(e.g: a telephone conversation can last for several
minutes while a movie (audio + video) can last for
a number of hours
Multimedia Information
Representation
• Single type of media - basic form of
representation of a specific media type used
• Mixed media – applications involving text
and images or audio and video their basic
form is used
• Integrated media (text,images,audio,video)Must convert all the four media into a
suitable digital form
Multimedia Networks
• Telephone Networks - Telephony
• Data Networks – Data Communications
• Broadcast Television Networks – Broadcast
TV)
• Integrated Services Digital Networks
(ISDN) – Multi service
• Boradband Multiservice Networks – Multi
service
Telephone
Networks
– Now known as Plain Old Telephone
Service (POTs)
• PSTN
• The term switched means a subscriber can make
a call to any other telephone on the ‘total’ network
PSTN
• PSTN (public switched telephone network) is the world's
collection of interconnected voice-oriented public
telephone networks, both commercial and governmentowned.
• It's the aggregation of circuit-switching telephone
networks that has evolved from the days of Alexander
Graham Bell.
• Today, it is almost entirely digital in technology except
for the final link from the central (local) telephone office
to the user
Telephone Networks
• Telephones in the home or in a small business are connected
directly to their nearest local exchange/end office
• Telephones in a large office are connected to a private
switching office known as private branch exchange (PBX)
• PBX provides free service between two telephones that are
connected to it
• A PBX is a telephone system within an enterprise that
switches calls between enterprise users on local lines while
allowing all users to share a certain number of external
phone lines. The main purpose of a PBX is to save the cost
of requiring a line for each user to the telephone company's
central office.
Telephone Networks
• PBX is connected to the local exchange and this
enables phones connected to the PBX to make
calls through PSTN too.
• Cellular phone networks – Provides service to
mobile subscribers
• The switches used in a cellular phone network are
known as Mobile Switching Centers (MSCs)
• International calls are routed to and switched by
international gateway exchanges (IGEs)
Telephone Networks
• Circuit mode – Telephone networks
operate in this mode in which a separate
circuit is set up through the network for
each call for the duration of the call
• Access Circuits – Link the telephone
handsets to a PSTN or PBX and carry twoway analogue signals associated with a call
Telephone Networks
• Today within PSTN all the switches and the
transmission circuits that interconnect them
operate in digital mode. However, to carry a
digital signal (0s and 1s) over the analogue access
circuits a device known as modem is required
• Modem stands for modulation and demodulation
• Modem converts the digital signal to analogue
signal for transmission and then at the receiver end
re-converts it back to digital form before relaying
this back to the destination digital source
• Early modem supported bit rates of 2400 bps.
Today 56 kbps modems are commonly used
Telephone Networks
• Today with high bit-rate channels in addition to the
voice using the same access networks high resolution
audio and video can be downloaded from a range of
entertainment related servers
Data Networks
• Designed to provide basic data communication services
such as email and general file transfer
• Most widely deployed networks: X.25 network (low
bit rate data) not suitable for multimedia and the
Internet (Interconnected Networks)
• Communication protocol: set of rules (defines the
sequence and syntax of the messages) that are adhered
to by all communicating parties for the exchange of
information/data
• Packet: Container for a block of data, at its head, is the
address of the intended recipient computer which is
used to route the packet through the network
Data Networks
• Open systems interconnections (OSI)- is a
standard description or "reference model" for how
messages should be transmitted between any two
points in a telecommunication network
• Access to homes is
through an Internet
Service provider (ISP)
• Access through PSTN
or ISDN (high-bit rate)
Data Networks
• Business users obtain access either through site
network or through an enterprise-wide private
network (multiple sites)
• Universities with single campus use a network
known as the Local Area Network (LAN).
However bigger universities with more than one
campus use enterprise wide network
• If the communication protocols of the computers
on the network are the same as the internet
protocols then the network is known as an
intranet (e.g large companies and universities)
Data Networks
• All types of network are connected using a
gateway (router) to the internet backbone
network
• Router - a router is a device or, in some cases, software
in a computer, that determines the next network point to
which a packet should be forwarded toward its
destination
Data Networks
• Packet mode – Operates by transfer of packets as
defined earlier
• This mode of operation is chosen because
normally the data associated with data applications
is in discrete block format.
• With the new multimedia PCs packet mode
networks are used to support in addition to the
data communication applications a range of
multimedia applications involving audio video and
speech
Broadcast Television Network
• Broadcast television networks support the diffusion
of analogue television programs to a wider
geographical area via a cable distribution network,
a satellite network (a terrestrial broadcast
network)
• A cable modem integrated into the STB (set-topbox) provides both a low bit rate channel (connects
the subscriber to the PSTN ) and a high bit rate
channel (connects to the Internet) from the subscriber
Broadcast Television Network
• A set-top box is a device that enables a television set to
become a user interface to the Internet and also enables a
television set to receive and decode digital television
(DTV) broadcasts. DTV set-top boxes are sometimes called
receivers. A set-top box is necessary to television viewers
who wish to use their current analogue television sets to
receive digital broadcasts. It is estimated that 35 million
homes will use digital set-top boxes by the end of 2006, the
estimated year ending the transition to DTV.
Satellite/terrestrial broadcast network
• In Satellite and broadcast networks by
integrating an H-S modem into the STB a range
of interactive services can be supported. This is
the origin of the term “interactive television”
Integrated Services Digital Networks
• Started to develop in the early 1980s to provide PSTN users
the capability to have additional services
• Integrated Services Digital Network (ISDN) in concept is
the integration of both analogue or voice data together with
digital data over the same network.
• ISDN is a set of ITU standards for digital transmission over
ordinary telephone copper wire as well as over other media.
Home and business users who install an ISDN adapter (in
place of a modem) can see highly-graphic Web pages
arriving very quickly (up to 128 Kbps). ISDN requires
adapters at both ends of the transmission so your access
provider also needs an ISDN adapter. ISDN is generally
available from your phone company.
Digital Subscriber Line (DSL):
• DSL (Digital Subscriber Line) is a technology for bringing
high-bandwidth information to homes and small businesses
over ordinary copper telephone lines.
• Assuming your home or small business is close enough to a
telephone company central office that offers DSL service,
you may be able to receive continuous transmission of
motion video, audio, and even 3-D effects.
• Typically, individual connections will provide from 1.544
Mbps to 512 Kbps downstream and about 128 Kbps
upstream. A DSL line can carry both data and voice signals
and the data part of the line is continuously connected.
• Access circuit that allows users either two different
telephone calls simultaneously or a telephone call and a
data network
Integrated Services Digital Networks
• DSL supports two 64 kbps channels that can be
used independently or as a single combined 128kbps
channel (additional box of electronics). This is
known as the aggregation function
Broadband Multi service Networks
• Broadband – Circuits associate with a call could
have bit rates in excess of the maximum bit rate of
2Mbps – 30X64 kbps – provided by ISDN
• Broadband integrated services digital network
(B-ISDN) – All different media types are
converted in the source equipment into a digital
form, integrated togeather and divided into
multiple fixed-sized packets (cells)
Broadband Multiservice Networks
• Broadband – Circuits associate with a call could
have bit rates in excess of the maximum bit rate of
2Mbps – 30X64 kbps – prvided by ISDN
• Broadband integrated services digital network
(B-ISDN) – All different media types are
converted in the source equipment into a digital
form, integrated togeather and divided into
multiple fixed-sized packets (cells)
Multimedia Applications
• Application that involve multiple media types:
- Interpersonal Communications: May
involve speech, image, text or video
- Interactive Applications over the Internet:
Browsing through sales, literature, newspapers,
etc.
- Entertainment Applications: Movie/Video on
demand, interactive television
Interpersonal Communications
(Speech only)
• Traditional interpersonal
communication involving
speech was provided by using
telephones connected to either
PSTN/ISDN or PBX hub.
• Today multimedia PC
equipped with a microphone
and speakers can be used to
make telephone calls. This
technology is known as
computer telephony
integration (CTI)
Advantages of using CTI
• The users can create their own private
directory of numbers and can initiate a call
simply by selecting the desired numbers
from the PC screen
• Provides access circuit to the network with
more capacity known as the bandwidth
• Integration of the PC based network
services with the telephony is possible
Additional services supported by
the public and private networks
• Voice mail: Used in the event of the called party being
unavailable. The voice mail is saved in the server
mailbox and can be read by the owner next time they
contact the server
• Teleconferencing: Involves multiple interconnected
telephones/PCs. Each person can talk to all the others
involved in the call. This is known as a conference
call. A central unit called an audio bridge provides the
necessary support to set up the call automatically
Additional services supported by the
public and private networks
• Internet telephony initially supported computer-tocomputer communications
• Today the technology is extend so that computerto-telephony is possible
Telephony over the Internet
• To make a PC-to-PC telephone call the standard addresses
that identify the PC on the network are used same as in a
data transfer application
• However, since the internet operates in a packet mode
necessary conversion software and hardware is mandatory
in both the PCs. This type of telephony is known as Voice
over IP (VoIP)
• To make a call using a PC connected to the Internet to a
telephone connected to a PSTN/ISDN an interworking
unit known as telephony gateway is necessary.
Principle of VoIP
• Initially the PC user sends a request to make a telephone
call to a preallocated gateway using its internet address.
• If the user is registered the gateway will request the phone
number to establish the call from the PC
• On receipt of this the source gateway will initiate a call
with the gateway nearest to the called party.
• The called gateway then establishes the call to the
recipient telephone using its telephone number and the call
setup procedures
• If the called party answers then a signal is sent back by the
recipient gateway to the PC user via the source gateway
Image only interpersonal Communication
• Fax: Exchange of electronic images or documents
over PSTN/ISDN
• As shown above this requires use of a pair of
fax machines, one at each termination point
• Both fax machines have an integral modem
within them
Image only interpersonal Communication
• PC can also be used instead of a normal fax
machine
• The PC can send an electronic version of a
document stored directly within the PCs memory
• This requires a telephone interface card and
associated software
• In addition it is possible to send digitised
documents over other enterprise network (LAN
interface card and software required)
Image only interpersonal Communication
Step1: Initially the caller keys in the telephone number of the
intended recipient and a circuit is set up through the
network
Step2: The two fax machines communicate with each other
to establish operational parameters
Step3: The sending machine starts to scan and digitized each
page of the document in turn and is simultaneously
transmitted over the network
Step4: After the final page has been sent/received the
connection through the network is cleared by the
calling machine
Text only interpersonal Communication
• An example of interpersonal communications
involving just text is email
• The user terminal is
normally a PC or a work
station networked
• Associated with each
network is a server/servers.
Each is known as an email
server and they contain
mailboxes for each user
connected to the network
Text and images
• An example of an application that involves both
text and images integrated together is computersupported cooperative working (CSCW)
• The network used is Intranet, Internet or LAN
Text and images
• A distributed group of people working on the
same project can share each others display. This
is known as shared whiteboard.
• The CSCW comprises a central “whiteboard
program” and a linked set of subprograms in
each PC/workstation with a shared window or
workspace (shared whiteboard)
Speech and video
• An example of this type is video telephony
• As can be seen from the figure the
terminals/PCs incorporate a video camera in
addition to the microphone and speaker
•The network must provide sufficient
bandwidth to support the integrated speech and
video generated
Speech and video
• Desktop videoconferencing call – Many
interconnected PC users in geographically
distributed sites can share speech and video between
various locations
• To support video conferencing a central unit called a
multipoint control unit(MCU) is used. This selects a
single information stream to send to each participant
hence reducing the communication bandwidth
Speech and video
• Multicasting – In which all transmissions from any
of the PCs/workstations belong to a predefined
group are received by all the other members of the
group
• Using multicasting eliminates the need for an MCU
unit
Note: Only possible when
there are few participants
involved
Many-to-many videoconferencing
• As group of people present at each location these
rooms must contain audio and video equipments
and are known as videoconferencing studios
• Each studio will have few cameras, a largedisplay, and associated audio equipment. These
will be connected to a central unit called the
videoconferencing system
Many-to-many videoconferencing
• A multimedia email will consist of text, images,
audio and video.
Examples of email applications consisting media
types other than text are Voice-mail, Video mail
and multimedia mail
• Voice-mail: With internet-based voice-mail, there
is an associated voice-mail server.
The user enters a voice message addressed to the
intended recipient and the local recipient’s voicemail server then relays this to the local recipient
the next time he logs in
Interactive applications over the Internet
• Anchor – The optional linkage points within
documents are defined by the creator of the
document and are known as anchors
• Hypertext – Web documents comprising only
text are created using hypertext
•Hypermedia – Web documents comprising
multimedia (Video, Sound) are created using
hypermedia
• Browser – The client function that is used to
explore the total contents of the web
Interactive applications over the Internet
• Applications such as homeshopping,
homebanking, etc.. the user may want to pass on
information back to the server.
• This information might contain credit card details
and personal details and hence a rigorous security
procedure needs to be in place
• This type of two way process is known as
interactive application over the Web.
Entertainment Applications
• Entertainment applications are classified into:
- Movie/video-on-demand
- Interactive television
Movie/video-on-demand
• The entertainment applications require higher
quality / resolution for video and audio since widescreen televisions and stereophonic sound are
often used
Movie/video-on-demand
• Normally the subscriber terminal comprises
television with a selection deive for interation
purposes
• The user interactions are relayed to the server
through a set-top-box (STB) which contains a high
speed modem
• By means of the menu the user can browse
through the movies/videos and initiate the showing
of a selected movie. This is known as Movie-ondemand or Video-on-demand.
Movie/video-on-demand
Key features of MOD
- Subscriber can initate the showing of a movie
from a library of movies at any time of the day or
night
Issues associated with MOD
- The server must be capable of playing out
simultaneously a large number of video streams
equal to the number of subscribers at any one time
- This will require high speed information flow
from the server (multi-movies + multi-copies)
Movie/video-on-demand
• In order to avoid the heavy load there is another
mode of operation used. In which requests are
queued until the start of the next playout time.
• This mode of operation is known as the
near movie-on-demand (N-MOD)
Interactive television (Cable network)
• The set-top box (STB) provides both a low bit
rate connection to the PSTN and a high bit rate
connection to the internet
• Through the connection to the PSTN, the
subscriber is able to actively respond to the
information being broadcast
Interactive television (Satellite/terrestrial
broadcast network)
• The STB associated requires a high speed
modem to provide the connections to the PSTN
and the Internet
Terms used with Multimedia