Notes for VTU syllabus

1. Multimedia Communications
UNIT I
18EC743

2. Introduction to Multimedia
Dr. Nandhini Vineeth 2
• In networks, the data transferred can be of any of the following Media forms.
• Text
• Formatted text (electronic documents etc.)
• Unformatted text ( email – plain text without any font specifications)
• Images
• Computer generated images –shapes (line/circle etc)
• Digitized images of documents
• Pictures
• Audio
• Low fidelity (Speech - telephony)
• High fidelity (Steoreophonic music)
• Video
• Short sequence of moving images (video clips - advertisements)
• Complete movies ( films )

3. Applications
3
• Person to person communication using Terminal Equipments
• Person to computer communication
• Person -- a MM PC and Computer – server with files (holding single MM type
or Integrated MM)
• Person – a set top box connected to a TV can communicate with MM servers
Applications that initially supported only one type of the MM now with
advanced H/W and S/W supports Integrated MM.
• email supported only text initially now can be sent with any type of media
attached
• Telephone services supported using only speech earlier but now allows all
MM Types.

4. Multimedia Information Representation
• Text and Images
• represented using blocks of digital data
• Text- rep with codewords – fixed number of bits
• Images- picture elements – every pixel is rep using a fixed number of bits
• Transaction duration – less
Audio and Video
• represented as analog signals that vary continuously with time
• Telephonic conversations may take minutes and movie downloads may take
hours
• When they are only type, they take their basic form- analog
• When integrated with other types, they need to be converted to digital form.

5. Multimedia Information Representation
• Speech signal – typical data rate is 64kbps
• Music and Video – higher bit rates are required
• Huge bit rates cannot be supported by all networks
• Compression is the technique applied to the digitized signals to
reduce the time delay for a request / response.

6. Multimedia Networks
6
• Five basic types of Communication Networks
• Telephone Networks
• Data Networks
• Broadcast Television Networks
• Integrated Services Digital Network
• Broadband Multiservice Networks

7. Telephone Networks
7
• POTS-Plain Old Telephone System
• Initially calls were done within a country
• Extended to International calls
• Explanation of the figure in next slide
• PBX – Private Branch Exchange
• LE - Local Exchange
• IGE - International Gateway Exchange
• GMSC – Gateway Mobile Switching Centre
• PSTN- Public Switched Telephone Networks

8. Telephone Networks
8
Dr. Nandhini Vineeth

9. Telephone Networks
9
• Microphone is used to convert speech to analog signal
• Telephone earlier used to work in circuit mode – a separate call is set
up and resources are reserved through out the network during the
duration of the call.
• Handsets were designed to carry two way analog signals to PBX.
• Digital mode is seen within a PSTN.
• MODEM was a significant device used.

10. 10
High speed Modems
• Earlier Modems worked at speed -300bps but now they operate at higher
bit rates.
• 56kbps – sufficient for text, image as well as speech and low resolution
videos
• Digital Signal Processing techniques has helped communication in many
ways.
• Two channels are used with high speed modems – one in which speech is
sent for telephony and the other is a high bit rate one which can carry high
resolution videos and audio

11. Dr. Nandhini Vineeth 11
DATA NETWORKS
• Designed for basic data communication services – Email and file transfers.
• UE- PC/Computer/Workstation
• Two widely deployed networks- X.25 and Internet
• X.25- low bit rate –unsuitable for MM
• Internet- coll of interconn networks operate using the same set of
communication proto
• Comm protocol- set of rules agreed by the comm. Parties for exchange of
infor-this includes syntax of messages.
• Open System Interconnection- Irrespective of the type or manufacturer, all
systems in Internet they communicate

12. Data networks
Dr. Nandhini Vineeth 12

13. Data Networks
13
• Home/Small Offices connect to Internet via Internet Service Provider thro a PSTN via modem or ISDN.
• Site / Campus Network – single site/Multiple sites through an enterprise-wide private network connect to
the Internet
• EWPN – ex. College / University campus
• When these networks use the same set of protocols for internal services used by Internet, they are said to
be Intranets.
• All the above type of networks connect to Internet Backbone Network via a gateway (router)
• Data networks operate in packet mode.
• Packet- container for data – has both head and body. Head contains the control information like the
destination address
• MM PC were introduced which supports Microphones and Speaker, sound card and a supporting software
to digitize the speech.
• Introduction of camera with its supporting H/W and S/W introduced Video.
• The data networks hence initiated the MC applications.

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Broadcast Television N/W
• Designed to support the diffusion of analog television to geographically
wide areas.
• For city/town- the bx medium is a cable distribution network, for larger
areas – a satellite network or a terrestrial broadcast network.
• Digital services started with Home shopping and Game playing.
• The STB in case of cable network, help for control of television channels
(low bit rate) that are received and the cable model in STB give access to
other services where a high bit rate channel is used to connect the
subscriber back to the cable head-end.
• These also provides an “interaction television”- where an interaction
channel helps the subscriber to demand his/her interests.

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16. 16
Integrated Services Digital Network
• Integration of services with PSTN
• Conversion of Telephone Networks into all digital form.
• Two separate communication channels – supporting two telephonic calls simultaneously / one
telephone call and the other data call
• These circuits are termed Digital Subscriber lines (DSL)
• UE can be either an analog or a digital phone.
• Digital phone- all required conversion circuitry seen in handset
• Analog phone- all required conversion circuitry was seen in the network terminal equipment.
• Basic Rate Access – two 64kbps per channel –either independent or combined as one 128kbpsline.
• This definitely requires two separate circuitry setup to support two different calls.
• The synchronization of the two channels into a single 128kbps requires a additional box to dothe
aggregation function.
• Primary rate Access – 1.5 or 2 Mbps data rate channel
• Service provided has now extended top X 64kbps where p =1..30.
• • Supports MM applications with an incre
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compared to PSTN.

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19. Dr. Nandhini Vineeth 19
Broadband Multiservice Networks
• Broadband- Bit rates in excess of the max 2 Mbps – 30 X 64 kbps given by ISDN.
• These are enhanced ISDN and hence termed Broadband-ISDN (B-ISDN) with the simple ISDN
termed as Narrowband or N-ISDN.
• Initial type did not support video. Current ones do with the intro to compression tech.
• As the other three types of networks also started showing improvements with the introduction to
compression techniques, broadband slowed down.
• Multi Service- Multiple services- Different rates were required for different services, hence
flexibility was introduced. Every media type was first converted to digital form and then integrated
together. This is further divided into equal sized cells.
• Uniform size helped in better switching.
• As different MM requires different rates, the rate of transfer of cells also vary and hence termed
Asynchronous transfer modes.
• ATM Networks or Cell switching Networks.
• ATM LANs- single site, ATM MANs- high speed back bone network to inter connect a number of
LANs
• These can also communicate with other types of LANs

20. Dr. Nandhini Vineeth 20

21. URLs explaining in depth working
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• Television Broadcast - https://www.youtube.com/watch?v=bvSDQmo-
Wbk
• Satellite TV -https://www.youtube.com/watch?v=OpkatIqkLO8

22. Multimedia Applications
• Teleconferencing- conference callD
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audio bridge – to setup a conf call automatically 22
• The applications fall under three categories:
• Interpersonal communication
• Interactive applications over the internet
• Entertainment applications
• Interpersonal communication
• Involves all four MM types
• in single form or combined form
• Speech only
• Telephones connected to PBX or a PSTN/ISDN/Celullar networks
• Computers can also be used to make calls
• Computer telephony Integration-requires a telephone interface card and associated software.
• Adv – Phone Directory can be saved and dialling a number is easily done with a click
• Telephony can be integrated with network services provided by the PC
• Additional services: Voice mail and teleconferencing
• Voice mail – in the absence of called party, a message is left for them which is stored in a central server
Which can be read the next time the party contacts the server.

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Dr. Nandhini Vineeth

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Telephony
• Internet also support telephony.
• Initially only PC TO PC Telephony was the only one supported. Later they were
able to include telephones in these networks.
• Here voice signal was converted to packets and hence necessary Hardware and
softwares were required
• Telephone over internet is collect packet voice or Voice over IP (VoIP).
• When a PC is to call a telephone, a request is sent to a Telephony Gateway with
IP address of the called party (CP). This obtains the phone number of the called
party from source PC. A session call is established by this TG to the TG nearest to
CP using internet address of the gateway. This gateway initiates a call set up
procedure to the receiver’s phone.
• When the CP answers, reverse communication happens
• A similar procedure for the closing of the call

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Image only
• Exchange of electronic images of documents. – facsimile / fax
• To send images, a call set up is made as in telephone call
• Two fax machine communicate to establish operational parameters
• Sending machine starts to scan and digitize each page of the document in turn.
• An internal modem transmits the digitized image is simultaneously transmitted over the network
and is received at the called site a printed version of the image is produced.
• After the last page is received, connection is cleared by the calling machine
• PC fax- electronic version of a document stored in a PC can be send. This requires a telephone
interface card and an associated software. The other side of communication can a Fax machine
or a PC.
• With a LAN interface card and associated software, digitized documents can be sent over other
network types like enterprise networks.
• This is mainly useful for sending paper-based documents such as invoices, marks cards and so on.

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Text Only
• Email: Home/Enterprise N/w ISP->receiver
• Email server , mailbox
• Users can create and deposit / read mails into the mailbox.
• Email servers and Internet gateways work on the standard internet
communication protocols.
• Message format- Source and destination – name and address
• cc- carbon copy
• Can contain only text

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30. Text and images
• An application showing this integration is Computer- supported
cooperative working (CSCW).
• A window on each PC is a shared workspace said to be shared
whiteboard.
The software associated with this is a whiteboard program with a linked set
of support programs.
Shared whiteboard has two components- Change notification and Update
control.
Change notification gives an update to the shared whiteboard program
whenever there is a modification done by the user.
This relays the changes to the update-control in each of the other PC and in
turn proceeds to update the contents of their copy of the whiteboard.

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Speech and Video
• Video Telephony – Video camera in addition to microphone is userd.
• A dedicated terminal / MM PC can be used for communication
• An entire display / window in PC is used.
• A two-way communication channel must be provided by the network with sufficient bandwidth to
support this integrated environment.
• Desktop video conferencing call is used in large corporations
• Bandwidth used is more
• Multipoint Control Unit/Videoconferencing server is used (BW –reduced)
• Integrated speech and video is sent from each participant reaches MCU which selects a single
information stream to send to each participant.
• When it detects a participant speaking, it sends that stream to all other participants. Only a
single two way comm channel between each location and the MCU is required.
• Internet supports multicasting- one PC to a predefined group of PCs. MCUs were not used here.
Here number of participants will be limited

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Dr. Nandhini Vineeth

34. Speech and Video- Interpersonal
communication
• Environments : when more number of participants are involved at
one or more locations
• One person may communicate with a group at another location
• Ex. Live lecture
• Lecturer may share notes/ presentation
• Students may only talk or may send video along with speech
• If the students are at same location, it may be like a video phone call (
• IIT-B Live lecture sessions
• When the students are at different locations, either a separate communication channel
is required to each remote site or an MCU is used at lecturer’s site
• Relative high BW is required and hence ISDN or Broadband multiservice n/w suit

35. Speech and Video- Interpersonal
communication
• Group of people at different location Ex. video conferencing
• Specially equipped room called Video conferencing Studios (VS) are used
• Studios may have one or more cameras, microphones(audio equipment), large
screen displays
• Multiple locations when involved, an MCU is used to minimize the BW demands on
the access circuits
• MCU is a central facility within the network and hence only a single two way
communication channel is required. Example : Telecommunication provider
conference
• In Private networks, MCU is located at one of the sites where the comm
requirements are more demanding as it must support multiple input channels, and
an output stream to broadcast to all sites

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37. Multimedia
• Three different types of electronic mail other than text only
• Voice mail:
• Voice mail server is associated with each network.
• User enters a voice message addressed to a recipient
• Local voice mail server relays this to the voice server of the intended recipient network.
• When the recipient logs in to the mailbox next, the message is played out
• Video mail also works the same way – but with video and speech
• Multimedia Mail
• Combination of all four media types
• MIME – Multimedia Internet Mail Extensions
• In case of speech and video, annotations can be sent either directly to mailbox of recipient
with original text message.
• Stored and played in a normal way/ played when the recipients reads out the text message
and the recipient terminal supports audio /video

38. Multimedia E-mail Structure
37

39. Interactive applications over Internet
• World Wide Web
• Linked set of multimedia servers that are geographically distributed
• Total information stored is equivalent to a vast library of documents.
• Pages are linked through Hyperlinks (References to other pages / same page)
• Options available to jump to specific point of pages.
• Anchors used
• HyperText
• HyperMedia
• Uniform Resource Locator- URL –unique identification to a location
• Home Page
• Browser
• HyperText Markup Language
• Free sites / Subscription sites
• Teleshopping, Telebanking- initiate additional transactions

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41. Entertainment Applications
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• Two types:
• Movie/ video – on demand
• Interactive television
• Movie/ video –on demand
• Video / audio applications need to be of much higher quality/resolution
since wide screen or stereophonic sound may be used.
• Min channel bit rate of 1.5 Mbps is used.
• Here a PSTN with high bit rate required / Cable network
• Digitized movies / videos are stored in servers.

42. Entertainment Applications
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• Subscriber end
• Conventional television
• Television with selection device for interactive purpose.
• Movie-on-demand /video-on-demand
• Control of playing of the movies can be taken like Video Casette Recorder
• Any time – User’s choice
• This may result in concurrent access leading to multiple copies in the server
• This may add up to the cost
• Alternate method used is not play the movie immediately after request but defer till the
next time playout time. All request satisfied simultaneously by server outputting a single
video stream. This mode is known as near movie-on-demand or N-MOD.
• Viewer is unable to control the playout of the movie
• Formats of the files also play a significant role

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Dr. Nandhini Vineeth

44. Interactive Television
• Broadcast Television include cable, satellite and terrestrial networks.
• Diffusion of analog and digital television programs
• Set Top Box also has a modem within it
• Cable Networks- STB provides a low bit rate connection to PSTN as well
requests and a high bit rate connection to Internet or broadcasts
• An additional Keyboard, telephone can be connected to the STB to gain
access to services.
• Interaction Television:
• Through the connection to PSTN, users were initially actively able to respond to the
information being broadcast.
• Return channels helped in voting, participation in games, home shopping etc.,
• STB in these networks require a high speed modem.

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46. Network QoS
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• Communication Channel
• Parameters associated – Network QoS
• Suitability of a channel for an application can be decided using these
• Different for Circuit Switched networks and Packet Switched networks
• Circuit-Switched N/w
• Constant bit rate channels
• Parameters
• Bit rate
• Mean bit rate error
• Transmission delay

47. Network QoS - Circuit-Switched N/w
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• Bit error rate
• Probability of the bit being corrupted during transmission
• A BER of 10-3
=1/1000 –
• indicates 1 bit may be corrupted in 1000 bits
• Bit errors occur randomly
• If BER probability is P and the number of bits in a block is N then assuming
random errors, the prob of a block containing a block error PB is given by
PB =1-(1-P)N
Which approximates to N X P if NXP < 1
Ex. If P=1/1000 and N =100 bits, PB =100/1000=1/10

48. Network QoS - Circuit-Switched N/w
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• Both CS and PS provide an unreliable service known as a best effort or best try service
• Erroneous packets are generally dropped either within the network or in the network interface
of the destination.
• If the application demands error free packets, then the sender needs to divide the source
information into blocks of a defined max size and transmits and the destination is to detect if the
block is missing.
• When a block is missed out, destination requests the source to send another copy of the missing
block. This is reliable service.
• A delay is introduced so the retransmission procedure should be invoked relatively infrequently
which dictates a small block size.
• High overheads are also involved since each block contains additional information associated
with retransmission procedure.
• Choice of a block size is a compromise between the increased delay resulting from a larger block
size and hence retransmissions
• When small block sizes is used, loss of transmission bandwidth results from the high overheads

49. Network QoS - Circuit-Switched N/W
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• Transmission delay within a channel is determined not only by the bitrate
but also delays that occur in the terminal/ computer n/w interfaces(codec
delays) + propagation delay
• ie. Transmission delay depends on bitrate + terminal delay + interface
delay + propagation delay
• Determined by the physical separation of the two communicating devices
and the velocity of propagation of a signal across the transmission
medium.
• Speed of light in free space is 3 X 108
m/s
• Physical media – 2 X 108
m/s
• Propagation delay is independent of the bit rate of the communications
channel and assuming that codec delay remains constant, it is the same
whether the bit rate is 1 kbps, 1 Mbps or 1 Gbps

50. From Forouzan
49
• Propagation speed - speed at which a bit travels though the medium
from source to destination.
• Transmission speed - the speed at which all the bits in a message
arrive at the destination. (difference in arrival time of first and last bit)
• Propagation Delay = Distance/Propagation speed
• Transmission Delay = Message size/bandwidth bps
• Latency = Propagation delay + Transmission delay + Queueing time +
Processing time

51. Network QoS -Packet Switched Networks
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• QoS Parameters
• Max Packet Size
• Mean packet Transfer rate
• Mean packet error rate
• Mean packet Transfer delay
• Worst case jitter
• Transmission delay
• Inspite of a constant bit rate supported by most of the networks, the store and
forward delay in router/PSE, the actual rate across network also becomes
variable.

52. Network QoS -Packet Switched Networks
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• Mean packet Transfer rate
• Average number of packets transmitted across the network per second and coupled with packet
size being used, determines the equivalent mean bit rate of the channel
• Summation of mean - store and forward delay that a packet experiences in each PSE/ router in its
route
• Mean packet error rate PER
• Prob of a received packet containing one or more bit errors.
• Same as the block error rate of a CS n/w
• Related to the max packet size and the worst case BER of the transmission links that
interconnect the PSEs/routers that make up the network
• Jitter – worst case - variation in the delay
• Transmission delay is the same in both pkt mode or a circuit mode and includes the codec
delay in each of the communicating computers and the signal propagation delay.

53. Problem – Network QoS
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54. Application QoS
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• In applications depending on the media the parameters may vary
• Ex. Images – parameters may include a minimum image resolution
and size
• Video appln- digitization format and refresh rate may be defined
• Application QoS parameters that relate to network include:
• Required bit rate or Mean packet Transfer rate
• Max startup delay
• Max end to end delay
• Max delay variation/jitter
• Max round trip delay

55. Application QoS
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• For appln demanding a constant bit rate stream, the important parameters are bit
rate/mean packet transfer rate, end to end delay, the delay variation/jitter since at the
destination decoder problems may be caused if the rate of arrival of the bitstream is
variable.
• For applications with constant bit rate, a circuit switched network would be appropriate
as the requirement is that call setup delay is not important, but the channel should be
providing a constant bit rate service of a known rate
• Interactive applications- a connectionless packet switched network would be
appropriate as no call set up delay and any variation in the packet transfer delay are not
important
• For interactive applications, however the startup delay (delay between the application
making a request and the destination (server) responding with an acceptance. Total time
delay includes the connection establishment delay + delay in source and destination.

56. Application QoS
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• Round trip delay is important for a human computer interaction to be
successful-delay between start of a request for some info made and
the start of the information received/displayed should be as short as
possible and should be less than few seconds
• Application that best suits packet switched n/w compared to CS is a
large file transfer from a server to a workstation.
• Devices in home n/w connection can use PSTN, an ISDN connection,
or a cable modem
• PSTN/ISDN – CS constant bit rate channel -28.8kbps(PSTN) and
64/128kbps(ISDN)

57. Application QoS
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• Cable modems operate in Packet switched mode.
• As concurrent users are seen using the channel, 100kbps of mean data rate
can be used.
• Time taken to transfer the complete file is of interest as though 27Mbps
channels are available, as time sharing is used, file transfer happens at the
fullest in the slot allotted.
• Summary, when a file of 100Mbits is to be transferred, the min time taken
by
• PSTN and 28.8kbps modem 57.8min
• ISDN at 64 kbps 26 min
• ISDN at 128kbps 13 min
• Cable modem at 27Mbps 3.7 sec

58. Application QoS
57
• Many situations, depending on the parameters, constant bit stream
applications can pass through packet switching networks also
• Buffering is the technique used to overcome the effects of jitter.
• A defined number of packets is kept in a memory buffer at the
destination before play out.
• FIFO discipline is followed
• Packetization delay adds up to the transmission delay of the channel
• Packet size is chosen appropriately to give an optimized effect

59. Application QoS

60. Application QoS
• To check the suitability of the network to applications to be transmitted
by the end machines, service classes have been defined.
• Every specific set of QoS parameters defined for each service class.
• Internet – includes all classes of services.
• Packets in each class have a different priority and treated differently
• Ex. Packets relating to MM applications are sensitive to delay and jitter and
are given high priority compared to packet with text messages like email
• During network congestion, video packets are transmitted first.
• Video packets are more sensitive to packet loss and hence given a higher
priority than audio.

61. Application QoS

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