Media Technology I

1
Media Technology I

• Lecture Notes and Tutorials on
• Web www.staff.city.ac.uk/raj

2
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, m-commerce and others)

3
Syllabus

• Multimedia Communications
• - Multimedia information representation
• - Multimedia Networks (Telephone, Data,
  Broadcast, ISDN, Broadband)
• Multimedia Communications
• - 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)

4
Syllabus

• Multimedia Information Representation
• - Digitization principles (analogueue
  signals, encoder design, decoder design)
• - Text (unformatted text, formatted text,
  hypertext). Images (Graphics, digitized
  documents, digitized pictures)
• Multimedia Information Representation
• - Audio(PCM speech, CD-quality audio,
  synthesized audio).
• - Video (Broadcast Television, Digital Video,
  PC Video, Video Content)

5
Syllabus

• Text and Image Compression
• - Compression Principles (source encoders and
  destination decoders, lossless and lossy
  compression, entropy encoding, source encoding)
• - Text compression (Arithmetic coding, LZW
  coding)
• - Image compression (GIF format, TIF format,
  digitized documents, digitized pictures, JPEG)
• Audio and video compression
• - 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..)

6
Syllabus

• Standards for multimedia communications
• - Reference models (TCP/IP, protocol basics)
• - Standards relating to interpersonal
  communications (circuit networks, packet-switched
  networks, e-mail)
• Network management Network operations centre
• Performance management, Configuration
  management, Billing, fault management, security
  management
• Standards for multimedia communications
• - Standards relating to interactive
  applications (information browsing, e-commerce,
  intermediate systems, Java and JavaScript)
• - Standards for entertainment applications
  (Movie/Video-on-demand, iTV)

7
Syllabus

• Digital Communications
• - Transmission media (two-wire open lines,
  twisted-pair lines, coaxial cables, optical
  fibre, satellites, microwave communications,
  signal propagation delay)
• New multimedia technologies
• - UpnP
• - Zigbee
• - Jini
• - smart homes
• - mobile web services
• - IMS (IP Multimedia Subsystems)

8
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
• CDs
• - Video (Moving images and complete
• movies/films)

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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)

10
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

11
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

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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

13
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

14
Telephone Networks

• PSTN Now known as Plain Old Telephone Service
  (POTs)
• The term switched means a subscriber can make a
  call to any other telephone on the total
  network

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PSTN

• PSTN (public switched telephone network) is the
  world's collection of interconnected
  voice-oriented public telephone networks, both
  commercial and government-owned.
• 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

16
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.

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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)

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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 two-way analogue signals
  associated with a call

19
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

20
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

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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)

22
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)

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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

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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

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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 cable modem integrated into the STB
  (set-top-box) 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 back to the cable
  head-end

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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.

27
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

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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.

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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

30
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

31
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)

32
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)

33
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

34
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)

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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

36
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

37
Additional services supported by the public and
private networks

• Internet telephony initially supported
  computer-to-computer communications
• Today the technology is extend so that
  computer-to-telephony is possible

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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.

39
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

40
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

41
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)

42
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

43
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

44
Text and images

• An example of an application that involves both
  text and images integrated together is
  computer-supported cooperative working (CSCW)
• The network used is Intranet, Internet or LAN

45
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)

46
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

47
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

48
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
49
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
  large-display, and associated audio equipment.
  These will be connected to a central unit called
  the videoconferencing system

50
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 recipients
  voice-mail server then relays this to the local
  recipient the next time he logs in

51
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

52
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.

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Entertainment Applications

• Entertainment applications are classified into
• - Movie/video-on-demand
• - Interactive television

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Movie/video-on-demand

• The entertainment applications require higher
  quality / resolution for video and audio since
  wide-screen televisions and stereophonic sound
  are often used

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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-on-demand
  or Video-on-demand.

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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)
57
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)

58
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

59
Interactive television (Satellite/terrestrial
broadcast network)

• The STB associated requires a high speed modem
  to provide the connections to the PSTN and the
  Internet

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Terms used with Multimedia
61
Media Types

• The information associated with the different
  applications can be either continuous or
  block-mode
• Continuous The information is played out
  directly as it is received continuously (called
  streaming or real-time media) (E.g Audio and
  video)
• Block-mode The source information is created in
  a time-independent way and is often stored at the
  source in, say, a file
• When requested it will be transferred across the
  network and displayed at a time specified by the
  requesting application (called downloading) (e.g.
  email consisting of a block of text)

62
Communication Modes

• Simplex The information associated with the
  application flows in one direction only.
• Half-Duplex Information flows in both
  directions but alternatively (two-way
  alternative).
• Duplex Information flows in both directions
  simultaneously (Two-way simultaneous).

63
Communication Modes

• Broadcast The information output by a single
  node is received by all the other nodes connected
  to the same network
• Multicast The information output by the source
  is received by only a specific subset of the
  nodes (Latter form known as multicast group)

64
Communication Modes
65
Communication mode Examples

• In half-duplex and duplex communications, the
  bit rate associated with the flow of information
  in each direction can be equal (symmetric) or
  different (asymmetric).
• Video Telephony Symmetric duplex communication
• Web browsing Asymmetric half-duplex mode (as
  different bit rates for downloading and
  uploading)

66
Network Types (Circuit-mode)

• This operates in a time-dependent manner and
  comprises an interconnected set of switching
  offices/exchanges to which the subscriber
  terminals/computers are connected

67
Circuit-mode- Operational Principle
Step1 The source must set up the connection
first through the network Step2 Each subscriber
terminal has a unique network wide address and to
make a call the source first enters this number
of the intended communication partner Step3 The
local switching office uses this number to set up
a connection. Depending on the availability of
the destination the connection will be
estabilished Step4 Finally at the end of
information exchange the call will be terminated
by the source or the destination
68
Circuit-mode- Terminology

• Signalling messages The messages associated
  with the setting up and clearing of a connection
• Call/Connection setup delay The delay
  associated with the connection procedures
• Examples of Circuit-mode operation PSTN and
  ISDN
• PSTN setup delay varies from fraction of a
  second to few seconds for international
  connections
• ISDN setup delay ranges from tens of
  milliseconds through to several hundred
  milliseconds

69
Packet mode

• There are two types of packet-mode network
• - Connection Oriented (CO)

PSE Packet Switching Exchanges

• As the name implies a connection is established
  prior to information interchange
• The connection utilizes only a variable portion
  of the bandwidth of each link and known as
  virtual circuit (VC)

70
Packet mode Operational Principle

• To set up a VC the source terminal sends a call
  request control packet to the local PSE which in
  addition to the source and destination addresses
  holds a short identifier known as virtual circuit
  identifier (VCI)
• Each PSE maintains a table that specifies the
  outgoing link to use to reach the network address
• On receipt of the call request the PSE uses the
  destination address within the packet to
  determine the outgoing link
• The next free identifier (VCI) for this link is
  selected and two entries are made in the routing
  table

71
Packet mode Connectionless

• In connectionless network, the establishment of
  a connection is not required and they can
  exchange information as and when they arrive
• Each packet must carry the full source and
  destination address in its header in order for
  each PSE to route the packet onto the appropriate
  outgoing link (router term used rather than PSE)

72
Packet mode Summary

• In both types each packet is stored in a
  memory buffer and a check is performed to
  determine if any transmission errors are present
  in the received message. (i.e 0 instead of a 1 or
  vice versa)
• If an error is detected then the packet is
  discarded known as best-effort service.
• All packets are transmitted at the maximum link
  bit rate
• As packets may need to use the same link to
  transfer information an operation known as
  store-and-forward is used.

73
Packet mode Summary

• The sum of the store and forward delays in
  each PSE/router contributes to the overall
  transfer delay of the packets and the mean of
  this delay is known as the mean packet transfer
  delay.
• The variation about the mean are known as the
  delay variation or jitter
• Example of connectionless mode Internet
• Examples of connection oriented network X.25
  (text) and ATM (multimedia)

74
Multipoint Conferencing

• Multipoint conferencing is implemented in one
  of two ways
• - Centralized mode
• - Decentralized mode
• Centralized mode
• This mode is used with circuit switched networks
  such as PSTN and ISDN

75
Multipoint Conferencing Centralized mode

• With this mode a central server is used
• Prior to sending any information each terminal
  needs to set up a connection to the server
• The terminal then sends the information to the
  server.
• The server then distributes this information to
  all the other terminals connected in the
  conference

76
Multipoint Conferencing Decentralized mode

• The decentralized mode is used with
  packet-switched networks that support multicast
  communications
• E.g LAN, Intranet, Internet

77
Decentralized mode Operation

• The output of each terminal is received by all
  the other members of the conference/multicast
  group
• Hence a conference server is not required and it
  is the responsibility of each terminal to manage
  the information streams that they receive from
  the other members

78
Hybrid Mode

• This type of mode is used when the terminals are
  connected to different network types
• In this mode the server determines the output
  stream to be sent to each terminal

79
Network Qos

• Network Quality of Service parameters
  Operational parameters associated with a
  communication channel through a network that
  determine the suitability of the channel in
  relation to its use for a particular application
• Circuit-switched network Bit Error Rate (BER)
  is the probability of a bit being corrupted
  during its transmission in a defined time
  interval. The transmission delay is determined
  by the bit rate used plus the codes (network
  interfaces) and propagation delay of the digital
  signal
• Packet-switched network Mean packet transfer
  rate is a measure of the average number of
  packets transferred per second. Mean Packet Error
  Rate (PER) is the probability of a received
  packet containing one or more bit errors

80
Network Qos

• Most networks (circuit and packet switched)
  provide an unreliable service which is also known
  as a best-try or best-effort service
• If the application accepts only error free
  blocks then it is necessary for the sending
  terminal to divide the source information into
  blocks of a defined maximum size and the
  destination to detect any missing blocks
• When a block is missing then the destination must
  request for a copy of the block from the source.
  The service is then called a reliable service

81
Application Qos

• Transmission of a constant bit rate stream over
  a packet switched network

• The startup delay defines the amount of time
  that elapses between an application making a
  request to start a session and the confirmation
  being received at the destination

82
Application Qos

• To transfer a large file from the server to your
  home computer using the packet switched (PW) and
  circuit switched (CS) networks
• - PSTN (28.8kbps) and ISDN (64/128kbps) operate
  in CS mode and provide constant bit rate channel
• - Cable modem operate in PS mode and the bit
  rate of the shared channel is 27Mbps

83
Application Qos

• Assuming the file size is 100Mbits, the minimum
  time to transmit the file using the different
  Internet access modes is
• - PSTN and 28.8 kbps modem 57.8 minutes
• - ISDN at 64 kbps 26 minutes
• - ISDN at 128 kbps 13 minutes
• - cable modem at 27 Mbps 3.7 seconds

84
Application Qos

• The application quality of service is different
  from the network QoS
• For example in an application involving images
  the parameters may include a minimum image
  resolution and size while a video may include the
  digitization format and the refresh rate

85
Application QoS - Parameters

• The required bit rate or mean packet transfer
  rate
• The maximum startup delay
• The maximum end-to-end delay
• The maximum delay variation/jitter
• The maximum round-trip delay

86
Application Qos

• To overcome the effect of jitter a technique
  known as buffering is used
• The effect of jitter is overcome by retaining a
  defined number of packets in a memory buffer at
  the destination before playout of the information
  bit stream is started

87
Application QoS - Summary

• In order to determine whether a particular
  network can meet the QoS requirements of an
  Application a number of standard application
  service classes have been defined
• Each service class has an associated set of QoS
  parameters defined
• For networks that support different service
  classes ( i.e internet), the packets relating to
  each class are assigned a different priority
• Real time streams have higher priority than
  packets relating to email

88
Summary


89
Summary


90
Summary Multimedia Communication Network and
Services


91
Multimedia Information Representation

• Multimedia Information is stored and processed
  within a computer in a digital form
• Codeword Combination of a fixed number of bits
  that represents each character, in the case of
  textual information
• analogue signal Signal whose amplitude
  (magnitude of the sound/image intensity) varies
  continuously with time
• Signal encoder Electrical circuit used for the
  conversion of an analogue signal into a digital
  form
• Signal decoder Electrical circuit that converts
  stored digitized samples into time-varying
  analogue form

92
analogue Signals

• As mentioned earlier the amplitude of the signal
  varies continuously with time
• The Fourier analysis can be used to show that
  any time varying signal is made up of infinite
  number of single-frequency sinusoidal components
• The range of frequencies of the sinusoidal
  components that make up the signal is called the
  signal bandwidth
• Speech bandwidth 50Hz 10kHz
• Music Bandwidth 15Hz 20kHz

93
analogue Signals Signal Properties


94
analogue Signals Signal Properties

• To transmit an analogue signal through a network
  the bandwidth of the transmission channel should
  be equal to or greater than the signal bandwidth
• If the bandwidth of the channel is less than the
  signal bandwidth than channel is called the
  bandlimiting channel

95
Encoder Design

• The Encoder consists of bandlimiting filter and
  an analogue-to-digital converter (ADC) (
  comprising sample and hold quantizer)

96
Encoder Design

• Bandlimiting filter Removes the selected higher
  frequency components from the source signal
• Sample and hold Circuit Samples amplitude of
  the filtered signal at regular intervals and
  holds the sampled amplitudes between samples
• Quantizer Converts the samples into their
  corresponding binary form

97
Encoder Design Data representation

• The most significant bit of the codeword
  represents the sign of the sample
• A binary 0 indicates a positive value and a
  binary 1 indicates a negative value
• The signal must be sampled at a much higher rate
  than the maximum rate of change of the signal
  amplitude
• The number of quantization levels should be as
  large as possible to represent the signal
  accurately

98


Sampling Rate

• Nyquist sampling theorem To obtain an accurate
  representation of a time-varying analogue signal,
  its amplitude must be sampled at a minimum that
  is equal to or greater than twice the highest
  sinusoidal frequency component that is present in
  the signal
• Nyquist rate is represented either in Hz or more
  correctly in samples per seconds (sps)
• Antialiasing filter Another name for
  bandlimiting filter. Since it passes frequencies
  that are within the Nyquist rate

99

Alias signal generation due to
undersampling

• In reality the transmission channel used often
  has a lower bandwidth
• To avoid distortion the source signal is first
  passed through the BLF which is designed to pass
  only the frequency components that are within the
  channel bandwidth
• This avoids alias signals caused by undersampling

100

Quantization Intervals

• Representation of the analogue samples require
  an infinite number of digits

101

Quantization Intervals

• Three bits are used to represent each sample ( 1
  bit for the sign and two bits to represent the
  magnitude)
• If Vmax is the maximum positive and negative
  signal amplitude and n is the number of binary
  bits used then the quantization interval, q, is
  defined as
• q 2Vmax/ 2n
• A signal anywhere within the quantization
  interval will be represented by the same binary
  codeword
• Each cordword is at the centre of the
  corresponding quantization interval
• Therefore a difference of ?q/2 from the actual
  signal level is present. This difference is
  known as the quantization error

102

Quantization noise
polarity

• Quantization error is the difference between the
  actual signal amplitude and the corresponding
  nominal amplitude (also known as quantization
  noise since values vary randomly)

103

Dynamic Range

• With high-fidelity music it is important to be
  able to hear very quiet passages without any
  distortion created by quantization noise
• Dynamic range is defined as the ratio of the
  maximum signal amplitude to the minimum.
• D 20 log10 (Vmax/Vmin) dB

104

Decoder Design



Encoderdecode Codec

• A signal decoder is an electronic circuit that
  performs the conversion prior to their output
  back again into their analogue form through a
  digital-to-analogue converter and a low pass
  filter
• Low-pass filter Only passes those frequency
  components that were filtered through the
  bandlimiting filter in the encoder

105

Text

• Unformatted text Known as plain text enables
  pages to be created which comprise strings of
  fixed-sized characters from a limited character
  set
• Formatted Text Known as richtext enables pages
  to be created which comprise of strings of
  characters of different styles, sizes and shape
  with tables, graphics, and images inserted at
  appropriate points
• Hypertext Enables an integrated set of
  documents (Each comprising formatted text) to be
  created which have defined linkages between them

106

Unformatted Text The basic ASCII character set

• Control characters
• (Back space, escape, delete, form feed etc)
• Printable characters
• (alphabetic, numeric, and punctuation)

• The American Standard Code for Information
  Interchange is one of the most widely used
  character sets and the table includes the binary
  codewords used to represent each character (7 bit
  binary code)

107

Unformatted Text Supplementary set of Mosaic
characters

• The characters in columns 010/011 and 110/111
  are replaced with the set of mosaic characters
  and then used, together with the various
  uppercase characters illustrated, to create
  relatively simple graphical images

108

Unformatted Text Examples of
Videotext/Teletext

• Although in practice the total page is made up
  of a matrix of symbols and characters which all
  have the same size, some simple graphical symbols
  and text of larger sizes can be constructed by
  the use of groups of the basic symbols

109

Formatted Text

• It is produced by most word processing packages
  and used extensively in the publishing sector for
  the preparation of papers, books, magazines,
  journals and so on..
• Documents of mixed type (characters, different
  styles, fonts, shape etc) possible.
• Format control characters are used

110

Hypertext Electronic Document in hypertext

• Hypertext can be used to create an electronic
  version of documents with the index, descriptions
  of departments, courses on offer, library, and
  other facilities all written in hypertext as
  pages with various defined hyperlinks

111

Hypertext Electronic Document in hypertext

• An example of a hypertext language is HTML used
  to describe how the contents of a document are
  presented on a printer or a display other
  mark-up languages are Postscript, SGML (Standard
  Generalized Mark-up language, Tex, Latex

112

Images

• Images include computer-generated images
  (referred to as computer graphics or simply
  graphics) and digitized images of both documents
  and pictures
• All types of images are displayed in the form of
  a two-dimensional matrix of individual picture
  elements (pixels or pels), but represented
  differently within the computer memory (file)
• Each type of these images is created differently

113

Graphics

• VGA is a common type of display that consists of
  a matrix of 640 horizontal pixels by 480 vertical
  pixels with for example, 8 bits per pixel which
  allows each pixel to have one of 256 different
  colours

114

Graphics

• Colouring a solid block with the same colour is
  known as rendering

• All objects are made up of a series of lines
  that are connected to each other and, what appear
  as a curved line, in practice is a series of
  short lines each made up of a string of pixels
• Each object has a number of attributes
  associated with it. These include its shape,
  size in terms of pixel position, colour of the
  border etc..

115

Graphics - Conclusions

• There are two forms of representation
• - high-level representation (similar to a
  source code of a program) requires less memory
  to store the image and less bandwidth for
  transmission
• - actual picture image of the graphic (
  similar to the low-level machine code and
  generally known as bit-map format) e.g. GIF
  (graphical interchange format), TIFF ( tagged
  image format)
• A graphic can be transferred over the network in
  either form
• A software called SRGP (simple raster graphics
  package) - used to convert high-level form into
  a pixel-image form

116

Digitized Documents- Fax Principles

• The scanner associated with fax machines
  operates by scanning each complete page from left
  to right to produce a sequence of scan lines that
  start at the top of the page and end at the
  bottom
• Vertical resolution is either 3.85 (100 lines)
  or 7.7 mm (200 lines)

117

Digitized Documents- Digitization format

• Fax machines uses a single binary digit to
  represent each pel, a 0 for a white pel and a 1
  for a black pel. Hence the digital representation
  of a scanned page produces a stream about 2
  million bits
• Single binary digit per pel means fax machines
  are best suited for bitonal images

118

Colour Derivative Principles additive colour
mixing ( R G B)

• Black is produced when all three primary colours
  (R,G,B) are zero.
• Useful for producing a colour image on a black
  surface as is the case in display applications

119

Digitised Pictures- Subtractive colour mixing

• White is produced when the three chosen primary
  colours cyan,magenta and yellow are all zero
• Useful for producing a colour image on a white
  surface as is the case in printing applications

120

Digitized Pictures- Television/computer monitor
principles

• The picture tubes used in most television sets
  operate using what is known as a raster-scan
  this involves a finely-focussed electron beam
  being scanned over the complete screen

121

Digitized Pictures- Raster Scan

• Progressive scanning is performed by repeating
  the scanning operation that starts at the top
  left corner of the screen and ends at the bottom
  right corner follows by the beam being deflected
  back again to the top left corner

122

Digitized Pictures Raster scan display
architecture






123

Digitized Pictures-Pixel format on each scan

• The set of three related colour-sensitive
  phospors associated with each pixel is called a
  phospor triad and the typical arrangement of the
  triads on each scan line is shown

124

Digitized Pictures Concepts

• Frame Each complete set of horizontal scan
  lines (either 525 for North South America and
  most of Asia, or 625 for Europe and other
  countries)
• Flicker Caused by the previous image fading from
  the eye retina before the following image is
  displayed, after a low refresh rate ( to avoid
  this a refresh rate of 50 times per second is
  required)
• Pixel depth Number of bits per pixel that
  determines the range of different colours that
  can be produced
• Colour Look-up Table (CLUT) Table that stores
  the selected colours in the subsets as an address
  to a location reducing the amount of memory
  required to store an image

125

Digitized Pictures

• Aspect Ratio This is the ratio of the screen
  width to the screen height ( television tubes and
  PC monitors have an aspect ratio of 4/3 and wide
  screen television is 16/9)

126

Digitized Pictures Screen Resolutions

• NTSC 525 lines per frame (480 Visible)
• PAL,CCIR,SECAM625 lines ( 576 visible)
• Example display resolutions VGA (640x480x8), XGA
  (1024x768x8) and SVGA (1024x768x24)

127

Digitized Pictures Colour Image Capture
Schematic

• Typical arrangement that is used to capture and
  store a digital image produced by a scanner or a
  digital camera (either a still camera or a video
  camera)

128

Digitized Pictures Colour Image Capture
Schematic

• Photosites Silicon chip which consists of a two
  dimensional grid of light-sensitive cells, which
  stores the level of intensity of the light that
  falls on it
• Charge-coupled devices (CCD) Image sensor that
  converts the level of light intensity on each
  photosites into an equivalent electrical charge