Multimedia Communication
Raghudathesh G P
Asst Professor
MULTIMEDIA COMMUNICATION (VTU) - 10EC841 U N I T – 1:
MULTIMEDIA COMMUNICATIONS: Introduction, multimedia information representation, multimedia networks, multimedia applications, media types, communication modes, network types, multipoint conferencing, network QoS application QoS. 6 Hours TEXT BOOK:
1. Multimedia Communications: Applications, Networks, Protocols and Standards , Fred Halsall, Pearson Education, Asia, Second Indian reprint 2002. REFERENCE BOOKS:
1. “Multimedia Fundamentals: Vol 1 - Media Coding and Content Processing” , Ralf Steinmetz, Klara Narstedt, Pearson P earson Education, 2004. Special Thanks To:
1. Ramisuniverse for providing providing free e-material. e-material. 2. Students : BY:
RAGHUDATHESH G P Asst Prof ECE Dept, GMIT Davangere 577004 Cell: +917411459249 Mail:
[email protected]
Quotes from Great People : If you judge people, you have no time to love them. The secret of getting ahead is getting started. The man who does not read good books has no advantage over the man who can't read them. Talent wins games, but teamwork and intelligence wins championships. Tell the truth boldly, whether it hurts or not.
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Multimedia Communication
Raghudathesh G P
Asst Professor
Unit 1 – 1 – Multimedia Multimedia Communication Introduction: Multimedia Multimedia communication co mmunication includes includes a range of applications and networking
infrastructures. Definition1: The term "multimedia " is used to indicate that the information/data being
transferred transferred over the network net work may be composed of one or more of the following media types: 1. Text: Includes both Unformatted Text - comprising strings of characters from a limited character set and Formatted Text - comprises strings as used for the structuring, structuring, access, and presentation of electronic documents. 2. Images: Includes Computer Generated Image - comprising lines, curves, and circles, and Digitized Images of documents and pictures. 3. Audio: Includes both low-fidelity speech - as used in telephony and highfidelity speech - stereophonic music as used with compact discs.
4. Video: Includes short sequences of moving images (also known as video clips) and complete movies/films. Definition2: Multimedia is any combination of text, art, sound, animation, and video. It
is delivered to the user by electronic or d igitally igitally manipulated man ipulated means. A multimedia mult imedia project development develop ment requires creative, creat ive, technical, organizational, orga nizational, and business skills. Definition3: Multimedia is the presentation of a (usually interactive) computer
application, incorporating media elements such as text, graphics, video, animation and sound on computer.
Multimedia Multimedia applications may involve involve either e ither of the following: following: 1. Person-to-Person communications or 2. Person-to-System communications
Person-to-Person communicates using suitable Terminal Equipment (TE)
Person-to-System communications:
1. Person interacts with the system using suitable Digital device like workstation or multimedia multimedia personal computer co mputer (PC). 2. These Digital device are located either in homes or offices.
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Multimedia Communication
Raghudathesh G P
Asst Professor
3. Basically system is a server contai co ntaining ning a collection of files or documents each comprising digitized digitized text, t ext, images, images, audio, and video information information either singly or integrated together in some way alternatively It may also co ntain a library of digitized movies/videos. movies/videos. 4. User interacts with the server by means of a suitable selection device connected to the Set-top box (STB) associated with a television or modem used with the computers.
using a number of different different types of Networking infrastructure: provided using network
Networks: Two types
1. Designed initially to provide just a single type of service due to advances in various technologies these networks can now provide a range rang e of differen differentt other other services. service s. a. Ex 1: PSTN (Public Switched Telephone Network) or GSTN
(General
Switched
Telephone
Network) –
designed initially to provide the basic switched telephone service but due to the Advances in digital signal processing hardware and associated software
PSTNs/GSTNs
now
provide a range range of more advanced services involving - text, images, and video. b. Ex 2: Data network: designed initially to support basic data applications - e-mail, file transfers, and others now support a much richer set of applications - which involve images, audio, and video. 2. Designed from the outset to provide multimedia communication services. Ex 1: ATM networks.
Multimedia Information I nformation Representation: Representation:
Applications involving text and images - comprise blocks of digital data units.
Text data - typical unit is block of characters with each character represented by,
fixed number of Binary digits (bits) or Codeword.
Digitized image data - comprises a 2-D block of pixels (picture elements) with
each pixel represented by a fixed number of bits.
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Multimedia Communication
Raghudathesh G P
Asst Professor
Applications involving text and images: comprise the short request for a file.
file contents being returned, the t he duration of the overall transaction is relatively Ex.: file short.
Applications involving Audio and Video Signals: Vary continuously with time as the amplitude amplitude of o f the speech, audio, or video signal varies. varies.
Ex.: Typical telephone conversation can last for several minutes and Movie
(comprising audio and video) can last for a number of hours.
Applications involves of single type of media: Basic form of representation of the
particular particular media type is often used.
Applications involving either text-and-images or audio-and-video: Their Basic
form is often used since the two media types in these applications have the same form of representation. representation.
Applications involving of different media types: We integrated together in some
way as it's necessary to represent all 4 media types in a digital form.
For text and images: This (digital) is their standard form of representation.
For audio and video: since, their basic forms of representations are analog signals
- these must be converted into a corresponding digital form - before they can be integrated with the two ot her media media types.
digital signal with amplitude of the Digitization of an audio signal: produces a digital signal varies continuously with time and is of relatively high bit rate, is measured by bps (bits (bits per second) and for speech signal signal a typical bit bit rate of 64 kbps. kbps.
Applications involving audio can be of a long duration: this bit rate must be sustained for an equally long time period.
Digitization of video signal: the same applies as that of audio signals but, except
that the much higher bit rates and longer time durations are involved.
In general, the communication networks that are used to support applications that involve audio and video cannot support the very high bit rates that are required for representing representing these media types types in a digital digital form hence he nce we go for compression. compress ion.
Compression: It's a technique first applied to the digitized signals in order to
reduce the resulting bit rate to a level which can support be supported by various networks.
Compression to text and images: To reduce the time delay between a requests
being made for some information and the information becoming available on the screen of a computers or over o ver others.
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Multimedia Communication
Raghudathesh G P
Asst Professor
Multimedia Networks:
Five basic types of communication networks are used to provide multimedia communication communication services: services: 1. Telephone networks. 2. Data networks. 3. Broadcast television television networks. 4. Integrated services digital networks. 5. Broadband multiservice networks.
single type of service as listed listed 1,2, and 3 networks are initially designed to provide just a single as below: 1. Telephone networks: telephony 2. Data networks: data communications 3. Broadcast television networks: broadcast television
Technological developments developments enabled these networks to provide additional services. services. 4, and 5 networks: Designed from the outset to provide multiple services.
Telephone networks:
Public Switched Telephone network (PSTNs) has been in existence for many years and have gone through many changes over the t he time.
Designed to provide a basic switched telephone service which, with the advent of the other network types has become known as POTS (Plain Old Telephone Service).
'Switched': term is used to indicate that the subscriber can make a call to any other
telephone that is connected to the total network.
Initially Initially such networks net works spanned just a single single country later, telephone networks o f different different countries were interconnected so, that they now provide an international switched service.
Main components of the network are shown in the Fig below.
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Multimedia Communication
Raghudathesh G P
Asst Professor
Local Exchange/End Office: telephones located in the home or in a small business are
connected directly to their nearest LEs/Eos. LEs/Eos.
Private Branch Exchange (PBX):
i.
Telephones located in the medium or large office/site are connected to a PBX or Private switching Office.
ii. ii.
Provides a (free) switched switched service between any two telephones - that are connected to it.
iii.
Connected to its nearest LE (public), which enables the telephone that are connected to the PBX also to make calls through a PSTN.
Cellular Phone Networks: Been introduced which provide the similar service to the
mobile subscribes by means of the handsets that are linked to the cellular phone network infrastructure infrastructure by radio.
MSC (Mobile Switching Center): it's the switch used in the cellular phone network Like
the PBXs also, connected to a switching office in a PSTN which, enables both sets of subscribers to make calls to one another.
IGE (International Gateway Exchange): route and switch the international calls.
General scheme of modem is shown in the Fig below.
Speech signal: is an analog signal varies continuously with time according, to the
amplitude and frequency variations of the sound resulting fro from m the speech.
Microphone: used to convert this into an analog electrical signal. Telephone networks
operate in circuit mode which means, for each call a separate circuit is set up through the network of the necessary capacity for the duration of the call.
Access circuits: link the telephone handsets to a PSTN or P BX were designed designed to carry the
2-way analog analog signals associated with a call.
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Multimedia Communication
Raghudathesh G P
Asst Professor
Hence, within the PSTN all the switches and the transmission transmission circuits that interconnect interconnect them operate in digital digital mode to carry a digital digital signal a stream strea m of binary 1s and 0s over the analog access circuits require the device modem.
Modem:
i.
At the sending side: modem converts the digital signal output by the source digital
device into an analog signal which is, compatible with a normal speech signal it is routed through the network in the same way as a speech signal. ii.
At the receiving side: modem converts the analog signal back again into its digital
form before, relaying this to the destination digital device.
Have the necessary circuits to set up and terminate the call.
Using a pair of modems: at each subscriber access point a PSTN can also be used to
provide a switched switched digital digital service.
Early modems: supported only a very low bit rate service of 300bps.
Modems now support, bit rates of up to 56kbps as the result of advances in digital signal processing processing circuits and is sufficient, sufficient, to support various applications applications comprising comprising of o f text and images integrated together and a lso services that comprise comprise speech speec h and low resolution video modems are now available to use with same access circuits that provide a high bit rate channel which is in addition to the speech channel used for telephony the bit rate of this second channel, typically is such that it can support high resolution audio and video hence, they are used to provide access to servers that support a range of entertainment related applications.
Figure below shows the general scheme of this, and such applications need bit rates in
excess of 1.5 Mbps.
Technological advances in modems area have been made PSTNs can now support speech applications applications and also a wide range of o f other multimedia multimedia communication applications.
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Multimedia Communication
Raghudathesh G P
Asst Professor
Data networks: networks:
Designed to provide basic data communication services such as e-mail and general file transfers.
User equipments - connected to data networks : are the computers such as a PC, a
workstation, workstation, or o r an e-mail/file e-mail/file server.
Two widely deployed types of data networks: 1. X.25 network and
2. Internet.
X.25 network: operational mode is restricted to relatively low bit rate data applications.
Hence, unsuitable for most multimedia applications.
Internet: Made up of a vast collection of interconnected networks all of which operate
using the same set of o f communication communication protocols.
Communication protocol: an agreed set of rules that are adhered to by all communicating communicating
parties for for the exchange of information. information.
Rules define the sequence of messages that are exchanged between the communication parties and and the syntax of these messages. messages.
By using, the same set of communication communication protocols: all the computers that are connected to the Internet can communicate freely with each other irrespective of their type or manufacturer this is the origin of the term "open systems interconnection interconnection ".
Figure below shows a selection of the different types o f interconnected network.
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Multimedia Communication
Raghudathesh G P
Asst Professor
User at home or in a small business access to Internet is through an intermediate: ISP (Internet Service Provider) network normally, this type of user wants access to the
Internet intermittently the user devices are connected to the ISP network either through a PSTN with modems or through an ISDN (Integrated Services Digital Network which provide access at a higher higher bit bit rate).
Business user - obtain access through a site/campus network if, the business comprises
only a single site or obtain access through an enterprise-wide private network if, it comprises multiple sites.
Colleges and Universities In the case of a single site/campus: network is known as a
(private) LAN (Local Area Network), In the case of sites that are interconnected together using an inter-site inter-site backbone network netwo rk to provide a set of enterprise-wide communication services
network is known as an enterprise-wide private network Providing
communication protocols used by all the computers co nnected to the network are the same as those defined for use with Internet.
Enterprise network (Intranet): all internal services services are provided by using the same set o f
communication communication protocols, protocols, as those defined for the Internet.
IBN (Internet Backbone Network): different types of network are all connected to it
through an interworking unit called gateways.
Gateways (Router): an interworking interworking unit connects IBN and the different different types t ypes of network
responsible for routing and relaying all messages to and from the connected network hence, also called as a router.
Packet mode: all data networks operate in this mode.
Packet: container for a block of data and has head in which, address of the intended
recipient recipient computer (which is used to route the packet through the network).
This mode of operation is chosen since, the format of the data associated with data applications is normally in the form of discrete blocks of text or binary data with varying time intervals between each block.
Multimedia Multimedia PCs: have become available available that support support a range o f other applications.
Ex.: with the addition of microphone and a pair of speakers with sound card and
associated software to digitize digitize the speech PCs now are used to support telephony and other speech-related speech-related applications applications with the addition of video camera and associated hardware and software a range of other applications applications involving involving video can be supported.
Due to those availability above of higher bit rate transmission circuits and routing nodes have become available, and also more efficient algorithms to represent speech, audio and video in a digital form.
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Multimedia Communication
Raghudathesh G P
Packet-mode networks and the Internet in particular:
Asst Professor
support general data
communication applications and also a range of other multimedia communication applications involving speech, audio, and video currently. Broadcast Television Networks:
Designed Designed to support the diffusion diffusion of o f analog television and radio programs throughout wide geographical areas.
Cable distribution distribution network sued as broadcast medium, medium, normally in large town to wn or city.
medium for large areas Satellite network (Terrestrial broadcast network): broadcast medium digital television services have become available.
Low bit rate return channel for interaction purposes - with digital television services
provide a range of additional services (like (like games, games, home shopping, shopping, and etc.,).
Figure below shows the general architecture of a cable distribution network and a
satellite/terrestri satellite/terrestrial al broadcast network.
General architecture of a cable distribution network: Consist of set top box : attached
to the cable distribution distribution network Provides: 1. Control of the television channels - that are received. 2. Access to other services. services.
Ex.: Cable modem: integrated into the STB provides a low bit rate channel and a high bit
rate channel from fro m the subscriber subscriber back to the cable head end.
Low bit rate channel: used to connect the subscriber to a PSTN.
High bit rate channel: used to connect the subscriber subscriber to the Internet.
television services access Cable distribution network: provide basic broadcast radio and television to the range of o f multimedia communication communication services that are available available with both bot h PSTN and Internet.
Figure below shows the general architecture of the satellite and terrestrial broadcast
networks.
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Multimedia Communication
Raghudathesh G P
Asst Professor
Satellite and terrestrial broadcast networks: integrated into the STB provides the
subscriber subscriber with an interaction interaction channel c hannel hence, enhancing the range of services is the origin of the term "interactive television". Integrated Services Digital Networks:
Started to be deployed in early 1980s.
Originally designed to provide PSTN users with the capability of having additional services.
Achieved by converting the access circuits that connect user equipment to the network (Ex.: telephone network) into an all digital form.
Providing TWO separate communication communication channels over these circuits allow users either to have two different telephone calls in progress simultaneously or two t wo different calls such as a telephone call and a data call. call.
Access circuit with ISDN: known as DSL (Digital (Digital Subscriber Line).
Subscriber telephone: can either a digital phone or a conventional analog one.
Case of digital phone: electronics that are needed to convert the analog voice and call
setup signals into a digital form are integrated into the phone handset.
Case of analog phone: electronics that are needed to convert the analog voice and call
setup signals into a digital form are located in the network termination equipment making making the digital mode of operation of the network transparent to the subscriber subscriber phone.
Digitization of a telephone-quality analog speech signal - produces a constant bit rate
binary stream normally, normally, referred to as the bitstream of 64kpbs.
BRI (Basic Rate Access or Basic DSL of ISDN): support two 64kbps channels which
can be used either independently (as they were intended) or as a single combined 128kbps channel.
Design of ISDN: Two channels were intended for two different calls require 2 separate
circuits circuits to be set up through the switching network independently independently hence, to synchronize synchronize 2 separate 64kbps bitstreams into a single 128kbps stream requires an additional box of electronics electronics to perform the aggregation function.
PRI (Primary Rate Access): single higher bit rate channel of either 1.5 or 2 Mbps is
used.
More flexible way of obtaining a switched 128kbps service has been introduced by many network operators Service provided has been enhanced and a single switched channel supports now of (p * 64kbps), where p=1,2,3,4...30
Figure below shows the summarization of the various services provided.
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Multimedia Communication
Raghudathesh G P
Asst Professor
ISDN can support a range of multimedia applications Due to the relatively high cost of
digitizing the access circuits: cost of the services associated with an ISDN is higher than the equivalent equivalent service service provided by a PSTN. Broadband multiservice networks:
Designed in mid-1980s for use, as public switched networks to support a wide range of multimedia multimedia communication communication appli app lications. cations.
Broadband: term used to indicate indicate the circuits associated with a call ca ll could have bit bit rates in excess of the maximum bit rate of 2Mbps 30X64kbps provided by an ISDN.
B-ISDN (Broadband Integrated Services Digital Networks): alternate names for
broadband multiservice multiservice networks since, were designed designed to be an enhanced ISDN.
N-ISDN (Narrow Integrated Services Digital Networks): alternate name for ISDN .
B-ISDN: when in first first technology associated with the digitization of the video signal using using
were, in general, an ISD could not support services that included video.
Due to considerable advances in the field of compression from ISDN now support multimedia multimedia communication applications that includes video, and also can the other 3 types of network combined combined effect, the slow down considerably the deployment of B-ISDN.
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Multimedia Communication
Raghudathesh G P
Asst Professor
Number o f the basic design features associated with with the B-ISDN: have been used as the basis of other broadband broadband multiservice multiservice networks.
Ex.: A multiservice network implies that the network must support multiple services.
Different multimedia applications require different bit rates the rate being determined by the types of media that are involved hence, switching and transmission methods that are used within these networks must be more flexible than those used in networks such as a PSTN or ISDN which which were initially initially designed designed to t o provide a single type o f service.
To have this flexibility: 1. All the different media types associated with a particular application are first converted in the source equipmen eq uipmentt into a digital form. 2. These to be integrated together. together. 3. Resulting binary stream is divided into multiple fixed-size packets called cells.
Information streams: of this type provides a more flexible way of both transmitting and
switching switching the t he multimedia information associated with a the different different types t ypes of application.
Ex.: Transmission terms in: cells relating to the different applications can be integrated
together more flexibly.
means the switching o f cells cells can be carried out much faster than, than, Use of fixed-sized cells: means if variable-length variable-length packets were used.
Different multimedia applications generate cell streams of different rates: this mode
of operation in rate of transfer of cells through the network also varies hence, the name: ATM (Asynchronous Transfer Mode) ATM networks (Broadband multiservice
networks) - alternate name: Cell-Switching Networks. Networks.
Ex.: ATM LANs - span a single site , ATM MANs – MANs – span span large town or city.
Ex.: For broadband multiservice network is shown in the Figure below
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Multimedia Communication
Raghudathesh G P
Asst Professor
Being used as a high-speed backbone network to interconnect a number of LANs distributed distributed around a large town or city.
Note: Two of the LANs are ATM LANs and other two are simply higher-speed versions
of older data only LANs. It's the typical of ATM networks which must often interwork with older (legacy) networks.
Multimedia Applications:
Many and varied applications involving of multiple media types present.
Major categories of multimedia multimedia applicati app lications: ons: 1. Interpersonal communications. 2. Interactive applications over the Internet. 3. Entertainment applications.
In many instances networks network s used to support applications applications were initially initially designed to provide the service which involves just the single type of medium and with advances in technology, made multimedia applications support possible along with initial designed of basic services being from those possible and in some applications basic basic designed applications become - still more enhanced form is of possible.
Interpersonal communications: May involve speech, image, text, or video.
Interpersonal communications may involve single type or integrated two or more type of media involved: 1. Speech only 2. Image only 3. Text Only 4. Text and Images 5. Speech and Video 6. Multimedia
Speech Only:
Traditionally, involves involves – – speech, speech, telephony.
Service is provided using telephones which are connected either to PSTN/ISDN/Cellular network or PBX.
Figure below shows the general scheme
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Multimedia Communication
Raghudathesh G P
Asst Professor
Multimedia PC with microphone and speakers, if using user can make telephone calls through PC.
This requires the telephone interface card and associated software called CTI (Computer Telephony Integration).
The advantages adva ntages of using PC, instead of conventional telephone telephone for calls are: 1. User can create his or her own private directory of numbers and initiate a call simply by selecting the desired number on the PC screen. 2. Circuit’s bandwidth is more (providing (providing access circuits to the network has sufficien sufficientt capacity). 3. Integration Integration of telephony with all the t he other networked services are possible possible by PC. 4. In addition to Telephony many public and private networks support additional services.
Ex.: Voice-mail and Teleconferencing
being unavailable unavailable Spoken message is then be left left Voice-mail: Used when the called party being in the voice mail box of the called party Voice mail server, located in the central repository had voice mail boxes, Message can be read by owner of the mailbox the next time he, or she contact the server.
Calls involve multiple interconnected tel t elephones/PCs. ephones/PCs. Person Perso n can hear Teleconferencing: Calls and talk to all of the others o thers involved in the call called the conference call/teleconference
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Multimedia Communication
Raghudathesh G P
Asst Professor
involves a telephone network or audio conference call which require an call since, it involves audio bridge - a central unit unit which supports to set up a conference call automatically.
Internet was used to support telephony. Initially, designed to support computer-to-
computer communications Just (multimedia) PC-to-PC telephony was supported subsequently, extended so that a standard telephone could be used.
Figure below shows telephone over the Internet below
PC-to-PC telephone call: Standard addresses are used to identify individual computers
connected to the internet internet are used same way as for a data transfer transfer application.
Internet: operates in the packet mode Both PCs must have the necessary hardware and
software to convert the speech signal from the microphone into into packets pack ets on input and back again prior to output to the speakers.
Thus Telephony over the Internet is known as Packet voice as the network protocol associated with the internet is called the Internet Protocol (IP), Voice over IP (VoIP).
It’s a Interworking unit to connect the PC connected to the Internet Telephony gateway: It’ and a telephone connected to the PSTN/ISDN - since both operate in the circuit mode PC user sends a request to make make a telephone t elephone call to a preallocated telephony gateway using the latter’s internet latter’s internet Address Gateway requests from the source PC the telephone number o f the called party assuming user is registered for this service. Source gateway on receipt of above initiates the session (call) with the telephony gateway nearest to the called party using the Internet address of the gateway. Called part y then, initiates a call to the recipient telephone using its telephone number and the standard call procedure of the PSTN/ISDN.
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Multimedia Communication
Raghudathesh G P
Asst Professor
t hrough the Assuming the called party answers called gateway signals back to t he PC user through source gateway that that the call can commence. Similar procedure followed followed to clear the call on completion. Image Only:
Exchange of electronic images of documents is an alternate form of interpersonal (Simply, fax). communications communications over PSTN/ISDN known as Facsimile (Simply,
Figure below illustrates facsimile
Communication involves use of the pair of fax machines one at each network termination point.
Document sending: caller keys in the telephone number of the intended recipient, a circuit
is set up through the network in the same way as for a telephone call Two fax machines communicate with each other to establish operational parameters after, which the sending machine starts to scan and digitize each page of the document in turn both fax machines have an integral modem within them and as, each page is scanned it’s digitized it’s digitized image is simultaneously transmitted over the network and as this is received at the called side a printed version of the document is produced after the last page of the document has been sent and received connection through the network is cleared by the calling machine in the normal ways.
PC fax:
PC can be used instead of the normal fax machine to send an electronic version of document stored directly within the PCs memory. Digital image of each page of the document is sent in the same way as the scanned image produced by a conventional fax machine.
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Multimedia Communication
Raghudathesh G P
Asst Professor
With Telephony this requires a telephone interface card and associated software, latter operates in the same way as like the fax machine so, and terminal at the called side can be either a fax machine /another similar PC.
It Is Possible to send (by using LAN interface card and associated software) the digitized document over other network types such as an enterprise network particularly, this mode of operation useful when working with paper-based documents, such as invoices.
Text only:
Ex.: E-mail (Electronic mail).
User terminal t erminal is normally no rmally are norm normall ally y a PC or a workstation. workstat ion.
Figure below shows various operational scenarios
User at home access to the Internet through the PSTN/ISDN, and through an intermediate ISP network.
Business users obtain access either through an enterprise network/site or campus network.
Email servers: One or more associated with each network Collectively Collectively contain a mailbox mailbox
for each user connected to that that network User can both create and deposit deposit mail his/her mailbox read mail from it. Standard Internet communication protocol used by e-mail servers and internetwork gateway.
Figure Below. shows the format of the text-only e-mail message
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Multimedia Communication
Raghudathesh G P
Asst Professor
At the head: unique Internet-wide name of both the sender and recipient of the mail, In
addition present mail copy can be sent to multiple recipients each of whom is listed in the cc part of the mail header ‘cc’ ‘cc’ acronym acronym for the carbon copy the original means of making (paper) copies of documents Text only mails content: comprise unformatted text typically, strings of ASCII characters. Text and Images:
CSCV (Computer-Supported Cooperative Working) application: involves – text and
images integrated.
Network used: enterprise network/LAN/Internet.
Figure below. shows the general scheme
Typically Typically distributed distributed group of people each in the place of work are all working on the same project.
User terminal is either a PC or a workstation.
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Multimedia Communication
Raghudathesh G P
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each person’s ’s display display is used as the shared workspace, Shared whiteboard: Window on each person display comprises integrated text and images. images.
Software associates comprises of whiteboard program, a central program and a linked set of support programs, one in each PC/workstation.
Linked set of supported programs made up of change-notification part and update-control part.
Change-notification part: Sends details of the changes in the whiteboard program
whenever, whenever, a member member of the group updates the contents of whiteboard.
Update-control part: Present in each of the other PCs/workstations obtain above change
information information in turn, proceed to update the contents of their copy of the whiteboard. Speech and Video: Video:
Ex.: video telephony uses integrated speech and video supported now by all the network
types.
Figure below shows the general scheme
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Multimedia Communication
Raghudathesh G P
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In Cases of Home use: Terminals used normally dedicated to providing the videophone
service.
Single multimedia multimedia PC/workstation is used to provide videophone In Cases of Office Use: Single service together with a range of other services services..
In both the cases: video camera, microphone and speaker used for telephony by the terminals/PCs.
Dedicated terminal using a separate screen is used for the display Multimedia PC or workstation workstation using a window o f the PC/workstation screen to display display the moving image of the called party.
Network must must provide two-way communication channel between 2 parties of sufficient sufficient BW to support support the integrated speech-and-video speech-and-video generated by each terminal/PC.
Integration of video and speech: Bandwidth of the access circuits required to support is
higher than that require for speech only.
Desktop videoconferencing call: Telephony like: call may involve not just 2 persons and
so, terminals/PCs several people each located in their own office.
Used widely in large corporations involving multiple geographically distributed sites to minimize the travel between the various locations. Large corporations of this type have enterprise-wide network to link the sites together MCU (Multipoint control unit) is a Central unit to support the videoconferencing. Videoconferencing server associated with the network used in few cases.
Figure above shows separate window on screen of each participa participant’s nt’s PC/workstation
should be used to dis d isplay play video image of all the other partici p articipants. pants.
Needed to implement implement displaying displaying of o f video image image o f all a ll the other ot her participants on screen of each participant this requires: 1. Multiple integrated speech-and-video communication channels, one for each participant, being being sent to each of the t he other participants participants needed to do thi t hiss which
Require more bandwidth than is available. 2. Integrated speech-and-video information stream: from each participant is sent to the MCU which then, selects just a single information stream to send to each participant. participant.
Ex.: voice-activated voice-activated MCU
MCU whenever detects a participant speaking it relays the information stream from the participants participants to all the other participants participants so, a single single 2-way communication channel is needed between each location and the MCU is needed thereby reducing the communication communication bandwidth needed considerably.
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Multimedia Communication
Raghudathesh G P
Asst Professor
Some Networks such as LANs and the Internet supports Multicasting where all transmissions transmissions from any of the PCs/workstations PCs/workstations belonging to a predefined multicast group are received by all the other members of the gro up Possible to hold hold a conferencing session session without an MCU possible with networks that support multicasting.
Figure below shows the principle of this is only feasible when only a limited number of
participants participants are involved involved owing owing to the high load load it places places on the network.
In Figure below a person at one location is communicating with a group of people at another location. location.
Ex.: for this case transmission of a live lecture or seminar, typically information stream,
transferred from the lecturer to the remove class would be integrated speech-and video together with electronic copies of transparencies, and other documents used in the lecture In reverse direction information may comprise just speech for questions or integrated
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Multimedia Communication
Raghudathesh G P
Asst Professor
speech-and-video to enable the lecturer to both see and hear the members of the class at the remote location. location.
Communication requirements in terms, these are similar to those for a two-party videophone call. If the lecturer is relayed to multiple locations a separate communication channel is required to each remote site or MCU is used at the lecturer’s site. lecturer’s site.
Relatively high BW that is involved network is either an ISDN (supports of multiple 64kbps channels) or a broadband multiservice network if one is available.
In Figure above there is a group of people at each location. This type is in use from many years was the first first example of videoconferencing. Normally, Normally, a group gro up of people are present at each location.
used – which which contain all the Videoconferencing studios: Specially equipped rooms are used – necessary audio and video equipment, comprising of one or more video cameras, a largescreen displ display ay,, and associated audio equipment, equipment, all of which are connected co nnected to a unit unit called videoconferencing videoconferencing system.
Conference can involve just 2 locations or more usually, multiple locations (in this latter case an MCU is normally, used to minimize the BW demands on the access circuits to the network) as Figure in MCU MCU is shown. as the central facility facility within the network netwo rk and hence, only a single 2-way communications channel is required for each access circuit of the network. Ex.: this type t ype of o f arrangement, with a telecommunications-provi telecommunications-provider der conference.
If a private network alternately used MCU is normally located at one of the sites Communication requirements, are then more demanding since, it must support multiple input channels one for each of the other sites and a single output channel, channel, the stream from which must be broadcast to all of the other sites.
Multimedia:
Assumption: The information information content of each e-mail message consisted of text only used
in the earlier d iscussed. iscussed.
Ex.: In addition addition an mail containing, containing, other media types such as images, audio, and video video are
also used like voice-mail, video-mail, and multimedia mail.
Voice-mail: Similar in principle to earlier discussed telephone networks. Internet-based
voice-mail server associated with w ith each network, in addition addition to e-mail voice-mail there is a voice-mail server.
Figure below Shows this
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Multimedia Communication
Raghudathesh G P
Asst Professor
User first enters the voice message addressed to the intended recipient local voice-mail server then, relays this to the server associated with the intended recipient’s network recipient’s network stored voice message is then, played out the next time the recipient accesses voice-mailbox.
Same mode of operation is used for video-mail except, the mail message comprises an integrated speech-and video sequence.
Multimedia mail: An extension of text-only mail in as much as the basic content of the
mail comprises comprises textual information.
Textual information is annotated with a digitized image, a speech message, or a video message, as in Figure.
Speech-and-video case in the annotations can be sent either directly to the mailbox of the intended recipient together with the original textual message and, hence stored and played out in the normal way or they may have to be requested specifically by the recipient when the textual message is being read.
Recipient can always receive the basic text-only message but, the multimedia annotations can be received only if the terminal being use by the recipient supports voice and/or video.
Interactive Applications Over The Internet:
Internet is used to support a range of interactive applications along with interpersonal communication appli app lications. cations.
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Multimedia Communication
Raghudathesh G P
Asst Professor
Ex.: WWW (World Wide Web) or simply Web server comprises the linked set of
multimedia information servers that are geographically distributed around the Internet.
Total information stored on all the servers is equivalent to a vast library of document.
Figure below shows the general principle
Each document comprises a linked set of pages a nd linkages between the pages are known as hyperlinks.
Hyperlinks Hyperlinks are pointers also known as references to other pages of the same document or to any other document within the total web so, a reader of the document has the option at well-defined points throughout the pages that make up a document to jump either to a different page of the same document or, to a different document. Also, to return subsequently to a specific point on a page at a later time.
Optional linkage points within documents are defined by the creator of the document and are known as anchors for which the necessary linkage information is attached.
Hypertext are documents comprising only texts and are created using hypertext.
Hypermedia are documents comprising multimedia information and are created using
hypermedia.
Figure below Shows general structure of this type of document.
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Multimedia Communication
Raghudathesh G P
Asst Professor
There is no central authority for the introduction of new documents into the web. On side in anyone create a new document providing the server has been allocated an Internet address, and make hyperlink references from it to any other document on the web.
Document’s unique address which identifies both URL (Uniform Resource Locator) is a Document’s unique location of the server on the Internet, where the first page of the document is stored and also the file reference on the server.
Home page is the First page of the document all the hyperlinks on this and other pages
have similar URLs associated with them physical location of a page is transparent, to the user and in theory can be located anywhere on the web.
A Standard format is used for writing documents is known as HTML (Hyper Text Markup Language) and is also used for writing client software to explore the total
contents of the web, i.e., the contents of the linked linked information information on all the web servers.
A Browser is a Client function and there are number of user-friendly browsers available available to explore visited servers and to open up a dialog with a part icular icular server at the cli c lick ck of the mouse. Once the desired document has been located, the user simply clicks on an anchor point point within a page of the document do cument to activate the linkage linkage information stored at that that point Possible Possible to return to the previous anchor at any time.
With the hypertex h ypertextt document: Anchor is usually, an underlined word or phrase.
With the hypermedia document: Anchor is usually, an icon of an appropriate shape.
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Multimedia Communication
Raghudathesh G P
Asst Professor
Ex.: Loudspeaker for a sound annotation for a video camera for a video clip.
In Some applications client simply wishes to browse through the information stored at a particular particular site. Ex.: Browsing through sales literature, product information, application notes periodicals, newspapers, and so on. In general, no charge for accessing this information however, access to books, journals, and similar documents may be by subscriptions only.
Teleshopping (home shopping)/ Telebanking (home banking) applications: A client
may wish not only to browse through the information at a site but also to initiate an additional transaction transaction Server must provide provide additional transaction processing support for, for, say, ordering and purchasing since, this will also often involve financial transaction, more rigorous security procedures are required for access and authentication authentication purposes. Entertainment Applications:
Entertainment applications can be of 2 types: 1. Movie/video-on-demand 2. Interactive television
Movie/Video-On-Demand:
The video and audio associated with entertainment applications must be of a much higher quality/resoluti quality/resolution. on. Since, wide-screen televisions televisions and stereophonic stereophonic sound are often used.
Digitized movie/video with sound requires a minimum channel bit rate (bandwidth) of 1.5Mbps. Hence, network used to support this application, must be either a PSTN with a high bit bit rate modem or a cable network of this type .
For PSTN: high bit rate channel provided by the modem used only over the access circuit and provides additional services services to the t he other switched switched services services that the PSTN supports.
Shows – the the general operating scheme in both bot h the cases. Figure below. Shows –
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Multimedia Communication
Raghudathesh G P
Asst Professor
Information stored on the server: collection of digitized movies/videos. Normally, subscriber terminal comprises a conventional television with device for interaction purposes. User interactions interactions are relayed relayed through the server server through a set-top box which which also also contains the high high bit rate modem.
MOD (Movie-On-Demand)/VOD (Video-On-Demand): From suitable menu subscriber
is able to browse through the set of movies/videos available and initiate the showing of a selected movie. Subscriber can control the showing o f the movie by using similar similar controls to those used on a conventional VCR (Video Cassette Recorder) i.e., pause, fast-forward, and so on.
Key feature of MOD: a subscriber can initiate showing of a movie selected from a large library of movies at any time of the day or night.
From Figure below, the server must be capable of playing out simultaneously a large number of video streams equal to the number of subscribers currently watching a movie requires the information flow from the server to be extremely high since, it must support not just the transmission of a possibly large number of different movies, but also multiple copies of each movie it is very challenging and costly since, the cost of the server is directly related to the aggregate information information flow rate from it.
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Multimedia Communication
Raghudathesh G P
Asst Professor
Server: if, supporting a large number of subscribers it is common for several subscribers
to request the same movie within a relatively short time interval between each request.
Alternative Alternative mode in which requests for a particular particular movie are not played out immediately immediately but instead are queued until the start of the next play out time of o f that movie movie as shown in Figure below.
N-MOD (Near Movie-On-Demand): in this mode of operation all request for the same
movie which are made during the period up to the next play out time are satisfied simultaneously by the server outputting a single video stream clearly, the viewer is unable to control the play out of the movies.
Similar applications as above been made use in Business environment except, the stored information in the server is typically, training and general educational material, company news, and so on and, thus the number of stored videos is normally much less as is the number of simultaneous users so, video servers required are less sophisticated than those used in public MOD/N-MOD systems.
Stored video streams/programs are often in a different format is as that of CD-ROMs since, the received video video stream can then be displayed displayed directly on the screen o f a multimedia multimedia PC or workstation.
Communication requirements of the private networks are the same as those identified for use with a public networks.
Interactive Television:
Broadcast television networks: include cable, satellite, and terrestrial networks.
Basic service of this network is diffusion of both analog and digital television (and radio)
programs. programs.
STB (Set-T (Set-Top op Box): associated with these networks has a modem within it.
For cable networks as in Figure below. , STB provides both a low bit rate connection to
the PSTN and a high bit bit rate rat e connecti co nnection on to the Internet.
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Multimedia Communication
Raghudathesh G P
Asst Professor
By connecting appropriate TE to the STB a keyboard, telephone, and so on subscriber is able to gain access to all the services provided through the PSTN and the Internet. Throug h the connection to the t he PSTN subscriber subscriber is able to actively actively respond to the information information being broadcast it’s the origin of the term interaction television. television.
Typical uses of the return channel are for voting, participation in games, home shopping, and so on.
As in Figure a similar set of services are available through satellite and terrestrial
broadcast networks except, that the STB associated with these networks requires a highspeed modem to provide the connections to the PSTN and t he Internet. Internet.
Media types:
Figure below shows a selection of the terms used with multimedia. multimedia.
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Multimedia Communication
Raghudathesh G P
Asst Professor
Information flow associated with the different applications can be either continuous or block mode.
Continuous media case:
1. Information stream is generated by the source continuously in a time dependent way. 2. Continuous media media is passed directly to the destination as it is generated, and at the destination, the information stream is played out directly as it is received operation mode of which is called streaming. 3. Continuous media generated in a time-dependent way is called Real-time media . 4. Continuous media media with the bit rate of o f the communication channel that is used must be compatible compatible with the rate the source media media is being generated. 5. Ex.: Media types that guarantee continuous streams of information in real time are audio and video. 6. Bit rate of source information stream can be either CBR (Constant Bit Rate)/ VBR (Variable Bit Rate).
7. Audio: Ex.: Digitized audio stream is generated at a constant bit rate which is determined by the frequency. The audio waveform is sampled and the number of bits that that are used to digitize digitize each sample. 8. Video: Ex.: Individual pictures/frames that make up the video are generated at a constant rate after compression amount of information associated with each frame varies in general, information stream associated with compressed video is generated at fixed time intervals but the resulting bit rate is variable.
Block mode media:
1. Source information comprises single single block of o f information that is created in a time independent way. 2. Ex.: block of text representing representing an e-mail or computer program a 2-D matrix matrix of pixel values values that represents represents an image and so on. 3. Block mode media created in a time-independent way often stored at the source in say, a file Downloading when it is requested block of information is transferred across the network to the destination where it is again stored and subsequently output/displayed output/displayed at a time time determined by the requesting application applicat ion program. 4. Bit rate of the communications channel need not be constant constant but, such that, when a block is requested.
RTD (Round-Trip Delay): delay between the request being being made and the contents of o f the
block being output at the destination destination is within an acceptable acceptable time interval - RTD – for for HCI (Human-Computer Interface): can be no more than a few seconds.
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Multimedia Communication
Raghudathesh G P
Asst Professor
Communication Modes: Transfer of information streams associated with an application can be in 5 modes: 1. Simplex 2. Half-duplex (Two-way alternate) 3. Duplex (Two-way simultaneous) 4. Broadcast 5.
Multicast
Simplex:
Information associated with the application flows in one direction only.
transmission of o f photographic photographic images from a deep-space probe at predetermined times Ex.: transmission Involves unidirectional unidirectional flow of information information from the probe to an earth station.
Half-duplex (Two-way alternate):
Information flows in both directions but, alternatively.
Ex.: user making a request for some information form a remote server, which returns the
requested information. information. Duplex (Two-way (Two-way simultaneous) :
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Multimedia Communication
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Information flows in both directions simultaneously.
Ex.: two-way flow of the digitized speech and video associated with a video telephony
application. Broadcast:
Information output by a single source node is received by all the other nodes, computers, and others which are connected to the same network.
broadcast of a television program over a cable network netwo rk as all the television television receivers Ex.: broadcast that are connected to the network receive the same set of programs.
Multicast:
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Multimedia Communication
Raghudathesh G P
Asst Professor
Similar Similar to broadcast except, except, information information output by the t he source is received by only a specific subset of the nodes that t hat are connected to the network (multicast group). conferencing involving involving a predefined group of terminals/computers terminals/computers connected to Ex.: video conferencing a network exchanging integrated speech and video streams. In half-duplex and duplex communications the bit rate associated with the flow of information in each direction can be same or different. 1. Rate associated, with the flow of information in each direction is equal then is called as Symmetric. 2. Rate associated, with the flow of information in each direction is unequal then is called as Asymmetric. Ex.: Video telephone call: involves exchange of integrated digitized speech and video stream both direction simultaneously so, symmetric duplex communications channel is required. Application involving browser (program) (program) and an d a web server: 1. Low bit rate channel from the browser to the web server is required for request and control control purposes. 2. High bit rate channel from the server to the subscriber for the transfer of, say, and requested file so, asymmetric half-duplex communications channel is required.
Network Types:
Types of information stream associated with the different media types are: 1. Continuous mode 2. Block mode TWO O types of communications channel associated with the various network There are TW types they are: 1. Circuit-mode: operates in a time-dependent way, also called as Synchronous communications channel as it provides a constant bit rate service at a specified rate. 2. Packet-mode: operates in a time-varying way, also called as Asynchronous communications channel provides a variable variable bit rate service service - actual rate is determined by the variable variable transfer rate of packets across the network.
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Multimedia Communication
Raghudathesh G P
Asst Professor
Circuit-mode:
Figure below shows – shows – the the circuit mode network
Circuit-switched networks comprise an interconnected set of switching offices/exchanges for which the subscriber terminals/computers are connected.
Prior sending sending information information source set up u p a connection through the network.
Each subscriber terminal/computer has a unique network-wide number/address associated with it.
To make a call source first enters the number/address of the intended communication partner Local switching office/exchange office/exchange uses this to set up a connection connection through the network to the switching switching offi o ffice/exchange ce/exchange to which destination is connected.
Assuming destination is free and ready to receive a call a message is returned to the
source indicating that it can start to transfer/exchange information. After all the information has been transferred/exchanged either the source or the destination requests for the connection to be cleared.
Bit rate associated with the connection is fixed and, determined by the bit rate that is used over the access circuits that connect the source and destination terminal/computer to the network signaling messages associated with the setting up and clearing of a connection.
Call/connection setup delay is the time delay while a connection is being established.
Ex.: PSTN and ISDN.
PSTN: call setup delay can range from a fraction of a second for a local call through to several seconds for an international call.
ISDN: delay ranges from tens of milliseconds through to several hundred milliseconds.
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Multimedia Communication
Raghudathesh G P
Asst Professor
Packet-mode:
Types of packet-mode networks: 1. Connection-Oriented(CO) 2. Connectionless(CL) Connection-Oriented(CO):
principle of operation of a CO network. Figure below shows principle
Comprises Comprises an interconnected interconnected set of PSEs (Packet-Switching Exchanges).
Connection-Oriented network is also called as Packet-switched network .
Each terminal/computer is connected to the network has a unique network-wide number/address associated with it. Prior to the sending any information connection is first set up through network using using the addresses of the source and destination destination terminals.
Connection/circuit that is set up utilizes only a variable portion of the BW of each link hence, connection is known as Virtual Connection/Virtual Connection/Virtual Circuit (VC) .
VC Set up:
Source terminal/computer sends a call request control packet to its local PSE which contains address of the source and destination terminal/computer and a Virtual Circuit Identifier (VCI) a short identifier.
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Multimedia Communication
Raghudathesh G P
Asst Professor
Each PSE maintains maintains a table which specifies the o utgoing link that should be use dot reach each network address. On receipt of the call request packet PSE uses the destination address within the packet to determine the outgoing link to be used.
Next free identifi identifier er (VCI) for this link is then t hen selected and two entries are made in a routing routing table. t able. 1. First entry: Specifies incoming link/VCI and the corresponding outgoing link/VCI. 2. Second entry: To route route packets in the reverse direction (the inverse o f these as we show in the example in the Figure).
Call request packet is then forwarded on the selected outgoing link. Same procedure is followed at each PSE along the route until the destination terminal/computer is reached VCIs used on the various links form the VC.
At the destination assuming the cal is accepted: A call accepted packet is returned to the source over the same route/VC.
Information transfer phase can start but, since a VC is now in place only the VCI is needed in the packet header instead of the full network-wide address.
Each PSE first uses the incoming link/VCI to determine the outgoing link/VCI from the routing table Existing VCI in the packet header is replaced with that obtained from the routing table Packet is forwarded on the identified outgoing link.
Same procedure is followed to return information in the reverse direction. When all information is transferred/exchanged VC is cleared. Appropriate VCIs are released by passing a call call clear packet packet along the VC. VC.
Connectionless:
In connectionless network: Establishment of connection is not required. Two communicating terminals/computers can communicate and exchange information as and when they wish.
Figure below shows each packet must carry the full source and destination addresses in its
header in order for each PSE PS E to route t he packet onto the appropriate outgoing link.
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Multimedia Communication
Raghudathesh G P
Asst Professor
Router is used, rather than packet switching exchange.
In Both network types (CO and CL): Each packet is received by PSE/router on an
incoming link. It is stored in it’s entirely it’s entirely in a memory buffer. A check is made to determine if any, transmission/bit errors are present in the packet header i.e., the signal that is used to represent a binary 0 is corrupted and is interpreted by the receiver as a binary 1 and vice versa.
Service offered by the packet-switched network is Best-effort service.
If no errors are detected the addresses/VCIs carried in the packet header are read to determine the outgoing link that should be used.
Packet is placed in a queue ready for forwarding on the selected outgoing link. link. All packets are transmitted at the maximum link bit rate.
With this mode of operation it is possible for a sequence of packets to be received on a number of incoming links all of which need forwarding on the same outgoing link. Hence, a packet may experience an additional delay while it is in the output queue for a link waiting to be transmitted.
This delay variable variable because it depends on the number o f packets that are currently present present in the queue when a new packet arrives for forwarding forwarding this mode of operation is known as packet store-and-forward. store-and-forward.
There is a packet store-and-forward delay in each PSE/router. Sum of the store-andforward delays in each PSE/router contributes to the overall transfer delay of the packet across the network.
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Multimedia Communication
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Mean of the above delay is called Mean packet transfer delay and variation about the mean is known as Delay variation (jitter).
Ex.:
1. Internet (Ex.: for packet-switched network – network – that that operates in the CL mode). 2. International X.25 packet-switching network and ATM (Ex.: for networks that operate in the CO mode).
Multipoint Conferencing: Conferencing:
Features in many interpersonal applications including audio and video conferencing, data sharing, and computer supported cooperative cooperative working.
These involve exchange of o f information information between 3 or more terminals/computers. terminals/computers.
Multipoint conferencing is implemented implement ed in one of following follow ing ways: 1. Centralized mode 2. Decentralized mode 3. Hybrid mode
Centralized mode:
Used with circuit-switched networks such as PSTN/ISDN.
Figure Above. shows Centralized conference server is used.
Prior to sending any information, each terminal/computer to be involved in the conference must first set up a connection to the server.
Each terminal/computer then, sends its own media stream comprising, say, audio, video, and data integrated together in some way to the server using the established connection.
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Multimedia Communication
Raghudathesh G P
Asst Professor
Server in turn, distributes either the media stream received from a selected terminal/computer or a mix of the media streams received from several terminals/computers back to all the other terminals/computers that are involved in the conference.
Decentralized mode:
Used with packet-switched networks that support multicast multicast communications.
Ex.: LANs, intranets, and the Internet.
Figure above. Shows output of each terminal/computer is received by all the other
members of the conference/multicast conference/multicast group.
Conference server is not normally used, and instead each terminal/computer manages the information streams that it receives from the other members.
Hybrid mode:
Used when the various terminals/computers that that makes makes up the conference co nference are attached to different different network types.
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Multimedia Communication
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conference compris co mprises es 4 terminals/computers terminals/computers 2 attached attached to a Figure above. Shows Ex.: conference circuit-switched network and 2 to a packet switched network that supports multicasting.
Like in the centralized mode conference server is used output of each terminal/computer is sent to the server either over individual circuits terminals A and B or using multicasting terminals C and D Server that determines output stream(s) to be sent to each terminal. terminal.
Types of conferencing based on media Type: 1. Data conferencing 2. Audio conferencing 3. Videoconferencing 4. Multimedia conferencing
include data sharing and computer-supported Data conferencing: Involves data o nly. Ex.: include cooperative working.
Audio conferencing: Involves audio (speech) only.
Videoconferencing: Involves speech and video synchronized and integrated together.
Multimedia conferencing: Involves speech, video, and dat a integrated together.
Data conferencing:
Information flow between the various parties is relatively infrequent; Conference server is a general-purpose computer with the conference function implemented in software.
With With the other ot her 3 types of conferencing the information flows demand the use of special purpose units.
Audio conferencing: conferencing:
Audio bridge is the unit.
Typical units supporting 6 through 48 conference participants.
Video and multimedia conferencing:
MCU (Multipoint Control Unit) is the unit.
Due to volume and rate of the information being exchanged centralized mode of working is used w ith both bot h network types.
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Multimedia Communication
Raghudathesh G P
Asst Professor
MCU consists of 2 parts:
Multipoint Controller part (MC): Concerned with the establishment of connections
to each of the conference participants and with the negotiation of an agreed set of operational parameters screen resolution, refresh rate, and others.
Multipoint Processor (MP): Concerned with the distribution of the information
streams generated during the conference. Include such functions as the mixing of the various media streams into an integrated stream, voice-activated switching and continuous presence. presence. Audio bridge:
When using a audio bridge, a call is scheduled for a particular date, time, and duration.
Everyone who is to take part in the call is assigned a user ID and password. At appropriate time all participants call in and after verified, they can hear and speak to the other participants.
In the same way MCU when using a call is scheduled as for an audio bridge.
Once the conference starts each participant can hear, see, and share data with the other participants participants MCU with with 1. Dial-in mode: The participants calling in. 2. Dial-out mode: MCU calls the participants provides better security.
Voice-activated switching mode: Face of the participant is displayed in a win w indow dow o n the
screen of the parti the particip cipant’s ant’s terminal terminal/computer, /computer, in the second window the face face of the remote re mote participant participant who is currently talking. When another participant participant starts to talk face of the new speaker replaces replaces the face of the current remote participant. participant. In the event two or more more participants participants starting starting to talk at the same time MCU normally selects person person who speaks the loudest.
Continuous -presence mode: Remote window is divided into a number of smaller
windows each of which displays the face of the last set of participants who spoke or who are currently speaking. With both modes of speech from all participants are normally mixed into a single stream and hence, each participant can always hear what is said by all the other ot her participants. participants.
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Multimedia Communication
Raghudathesh G P
Asst Professor
Network QoS:
associated with a communications communications channel through throug h a Definition: “Operational parameters associated network collectively determine the suitability of the channel in relation to its use for a particular particular application” application”.
QoS parameters are different for circuit-switched and packet-switched networks.
Circuit-Switched Network:
QoS parameters associated with a constant bit rate channel that is set up through a Circuit-switched network are
1. Bit rate 2. Mean bit bit error err or rate 3. Transmission Transmission delay Bit rate:
In digital telecommunication, the bit rate is the number of bits that pass a given point in a telecommunication network in a given amount of time, usually a second.
A bit rate is usually measured in some multiple of bits per second.
The term bit rate is a synonym for data transfer rate (or simply
data rate ).
Mean BER (Mean Bit Bi t Error Rate) of a channel:
Probability of a bit being corrupted during its transmission across the channel in a defined time interval.
For constant bit rate channel: Mean BER is the probability of a bit being corrupted in a
defined number of bits Mean BER of 10-3 means, on average for every 1000 bits that are transmitted, 1 of these bits is corrupt.
Some applications providing the occurrence of bit errors is relatively infrequent their presence is acceptable while while in other applications it it is imperative imperative that no residual bit errors are present in the received information.
Ex.:
1. If the application involves speech then, an occasional bit error will go unnoticed. unnoticed. 2. If the application involves transfer say, financial information it is essential that the received information contains no errors in such applications, prior to transmission the source information is normally divided divided into blocks the maximum size of which is determined determined by the mean BER of the communica co mmunications tions channel.
-3
Ex.: if mean BER is 10 number of bits in a block must be considerably < 1000,
otherwise, on an average every block will contain an error and will be discarded.
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Page No -43
Multimedia Communication
Raghudathesh G P
Asst Professor
Normally bit errors occur randomly hence, even with a block size of (say 100 bits) blocks may still contain an error but, the probability of this occurring is considerably less.
In general, BER probability is P, Number of bits in a block is N, Probability of a block containing a bit error is PB.
N which approximates to NxP if, if, NxP<1. Assuming: random errors: PB=1-(1-P) , which
In practice, both circuit-switched and packet-switched provide unreliable service (besttry or best-effort service).
Unreliable service (Best-try/Best-effort service) is a type of service where any blocks
containing bit errors will be discarded either with the network (packet-switched network) or in the network interface at the destination (both packet-switched and circuit switched networks).
Application dictates that only error-free blocks are acceptable, it is necessary for sending terminal/computer terminal/computer to divide the source information information into blocks blocks of o f a defined maximum size and for the destination to detect when a block is missing.
When the above occurs destination must request source send another copy of the missing block. This This type type of service service is is called called Reliable service.
Due to above abo ve case delay is introduced so, that retransmission retransmission procedure should be invoked relatively infrequently which dictates a small block size. This leads to high overheads since, each block must contain additional information that is associated with the transmission transmission procedure. pro cedure.
So, choice of o f block size compromise compromise between increased delay resulting from a large large block size hence, retransmission and the loss of transmission BW from the high overheads of using a small block size.
Transmission delay:
Associated with the channel is determined by: 1. Bit rate used 2. Delays Delays occur in the terminal/computer terminal/computer network interfaces (codec delays) + propagation delay of the d igital, igital, as they t hey pass from source to destination, across the network.
The above is determined by physical separation of 2 communicating devices and velocity 8
of propagation of a signal, across the transmission medium (free space: 3*10 m/s and a 8
fraction of this in physical media, a typical value 2*10 m/s).
Propagation delay: in each case is independent of the bit rate of the communication
channel. Assuming codec delay remains constant; propagation delay remains same whether bit rate is 1kpbs, 1Mbps, or 1Gbps.
Department ECE
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Page No -44
Multimedia Communication
Raghudathesh G P
Asst Professor
PROBLEM
Drive the maximum block size that should be used over a channel which has a mean BER -4
probability of 10 if the probability of a block containing an error – error – and and hence being discarded – discarded – -1
is to be 10 . ANSWER: N
PB=1-(1-P) -4 N
Hence 0.1=1-(1-10 )
and N=950bits
Alternatively, PB=N x P Hence
-4
0.1=Nx10
and N=1000bits
Packet-switched network:
QoS param p arameters eters – associated with a packet-switched network include – associated 1. Maximum packet size 2. Mean packet transfer rate 3. Mean packet error rate 4. Mean packet transfer delay 5. Worst-case or st-case jitter 6. Transmission Transmission delay
Packet-switched network: rate of packets transfer across the network influenced strongly by bit rate rat e of the interconnecting interconnecting links due to, variable variable store-and-forward delays in each PSE/router. Actual rate of transfer of packets across the network is also variable.
Mean packet transfer rate: Measure of the average number of packets transferred across
the network/second coupling with packet size being used determines equivalent mean bit rate of the channel.
Mean PER (Mean Packet Error Rate): Probability of a received packet containing one
or more bit errors. It is same as block error rate, associated with a circuit-switched network. Thus related to both maximum packet size and worst-case BER of the transmission links which interconnects PSEs/routers that make up the network.
Mean packet transfer delay: Summation of the mean store-and-forward delay that a
packet experiences experiences in each PSE/router which, which, it it encounters along along a rout.
Jitter: Worst-case variation in the mean packet transfer delay.
Transmission delay: Same for network operates in the packet mode or a circuit mode
Includes: Codec delay, in each of the two-communicating computers and Signal propagation delay.
Department ECE
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Page No -45
Multimedia Communication
Raghudathesh G P
Asst Professor
PROBLEM:
Determine the propagation delay associated assoc iated with the following communication channels: 1. A connection through a private telephone network of the 1km, 2. A connection through a PSTN of 200km, 3. A connection over a satellite channel of 50 000km. 8
-1
Assume that the velocity of propagation propagat ion of a signal in the ca se of (1) and (2) is 2x10 ms and in 8
-1
the case of (3) 3x10 ms ANSWER :
1.
2.
3.
Application QoS Network QoS parameters define define what the particular particular network being being used provides rather what application requires. Application has its own QoS parameters requirement associated with it: Application involving images: Ex.: parameters parameters may include include minimum minimum image image resolution resolution and size. size.
may include include digitization digitization forma formatt and refresh refresh rate. Application involving video: Ex.: parameters may Application QoS parameters relate to the network include:
1. Required bit rate or mean packet transfer rate 2. Maximum startup delay 3. Maximum end-to-end delay 4. Maximum delay variation/jitter variation/jitter 5. Maximum round-trip delay Applications involving – involving – transfer transfer of constant bit rate stream: Parameters important are:
Required bit rate/mean packet transfer rate
End-to-end delay
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Page No -46
Multimedia Communication
Raghudathesh G P
Asst Professor
Delay variation/jitter (can cause problem – problem – in in the destination decoder – decoder – if if the rate of arrival of the bit stream is variable)
For interactive applications applications following points p oints are prime factor:
1. Startup delay: Amount of time that elapses between an application making a request to start a session and the confirmation being received from the application at the destination from a server. Ex.: it is prepared to accept the request so, it includes time required to establish a
network connection + If required, delay introduced in both the source and destination destination computers while negotiating that session can take place. 2. Round-trip delay: Delay between a request for some information being made and the start of the information being received/displayed. It is Important for HCI (human-computer interaction) to be successful. It should be as short as possible ideally, less than a few seconds.
For applications involving, transfer of constant bit rate stream: Circuit-switched
should appear to be most appropriate since, call setup delay is not often important network should and channel provides a constant bit bit rate rat e service service of o f known rate.
For interactive applications connection-less packet-switched network is appropriate
since, no network call setup delay and any variation in the packet transfer delay are not important.
For PSTN and ISDN: Operation is circuit-switched provide a constant bit rate channel in
the order of 28.8kbps 28. 8kbps (PSTN with modem) and 64/128kbps (ISDN).
For cable modem: Operation is packet-switched. Modems in each of homes in a cable
region are time-share, uses a single high bit rate channel/circuit.
Typical Typical bit rate of shared channel: channel: 27Mbps, number of concurrent users of the channel may be several hundred. So, if the there re are are 270 concurrent users each user would get a mean data dat a rate of 100 kbps.
In these applications: main parameter of interest is not mean data/bit rate, but times to transmit the complete file With PSTN/ISDN: it is related to channel bit rate and the size of the file.
Cable modems: time-shares the use of 27Mbps channel, when they gain access to it, file transfer takes place at full rate.
Assuming: File size is 100Mbits minimum time to transmit the file using different Internet
access modes is: 1. PSTN and and 28.8kbps 28.8kbps modem: modem: 57.8 minutes 2. ISDN at 64kpbs:
26 minutes
3. ISDN at 128kpbs:
13 minutes
4. cable modem at 27Mbps:
3.7 seconds
Department ECE
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Page No -47
Multimedia Communication
Raghudathesh G P
Asst Professor
If other transfer request occurs during the time the file is being transmitted then, completion completion time of o f each transfer request will increase as they share the use o f the channel here, probability of multiple users requesting a transfer in this short window of time is relatively low.
For interactive applications: Ex.: call setup delay with an ISDN or an ATM network, and
a PSTN for local calls – calls – is is very fast – fast – and and for many applications, quite acceptable.
Providing equivalent mean bit rate, provided by the For constant bit rate applications: – Providing network > input bit rate maximum jitter < defined value – value – then, then, a packet-switched network can be used
Buffering: Used to overcome the effect of jitter
Fig. shows the general principle
Effect of jitter is overcome by retaining a defined number of packets in a memory buffer at the destination before play out of the information bitstream is started. Memory buffer operates using a first-in, first-out (FIFO) discipline. Number of packets retained in the
Department ECE
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Page No -48
Multimedia Communication
Raghudathesh G P
Asst Professor
buffer buffer before output starts is determined determined by the worst-cast jitter jitter and the bit rate of the information information stream.
Figure shows when using the packet-switched network for this type of application
additional delay is incurred at the source as the information bitstream is converted into packets.
Packetization delay: Additional delay, incurred at the source as the information bitstream
is converted into packets adds to the transmission transmission delay of the channel.
To minimize overall input-to-output delay, packet size used for application is kept small, but of suffici sufficient ent size to overcome the effect effect of the worst-case jitter. jitter.
To simplify determining a particular network which can meet the QoS requirement of an application: application: Number of standard application service classes have h ave been defined.
Each service class with specific set o f QoS parameters associated – associated – for for network, can either meet this or not.
Networks sup suppor portt a number number of differe different nt service classes. Internet – to to ensure, the QoS parameters associated with with each class is met – met – packets packets Ex.: Internet – relating to each class are given a different priority then, each class packets can be differently differently treated. t reated.
Internet packets relating to multimedia applications involving real-time streams are given higher priority than, packets relating to applications such as e-mail.
Packets containing real-time streams such as radio and video are more sensitive to delay and jitter, than the packets containing textual information. Hence, during periods of congestion packets containing real-time streams are transmitted first packets containing video are more sensitive to packet loss than, packets containing audio hence are given more priority.
Department ECE
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Page No -49
Multimedia Communication
Raghudathesh G P
Asst Professor
PROBLEM:
A packet-switch network with a worst-case jitter of 10ms is to be used for a number of applications each of which involves a constant bit rate information stream. Determine the minimum amount of memory that is required at the destination and a suitable packet size for each of the following input bit rate. It can be assumed that the main packet transfer network exceeds the equivalent input bit rate in each case. (1) 64kbps (2) 256kbps (3) 1.5Mbps ANSWER :
(1) At 64kbps, 10ms=640bits Hence chose a packet size of, say, 800 bits with a FIFO buffer of 1600 bits -2 packet – packet – and and start play out of the bitstream after the first first packet has been received. (2) At 256kbps, 10ms=2560 bits Hence chose a packet size of, say, 2800 bits with a FIFO buffer of 4800 bits. (3) AT 1.5Mbps, 10ms=15000 bits Hence choose a packet size of, say, 16000 bits with a FIFO buffer of 32000 bits. NOTICE: that t hat if the computed packet size exceeds e xceeds the t he network maximum packet size, then t hen the t he equivalent number of packet must be sent before play out starts for example, if the maximum network packet size was 800 bits , then for case (3) above play out would not start until two packets have received and the FIFO buffer should hold four packets.
Department ECE
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Page No -50
Multimedia Communication
Raghudathesh G P
Asst Professor
Question Bank VTU BE 1. With the help of a diagram, describe the main components of PSTN and show how a high
speed modem provides multiple service in addition to basic telephony. May 2010 (10 M) 2. Explain the working of CO packet switched network including routing table. May 2010 (8M)
3. Briefly explain the following operation modes of a communication channel: 1. Duplex 2. Multicast.
May 2010 (2 M)
4. Define the term multimedia communication. State the basic form of representing different media types.
December 2010 (4 M)
5. Explain why most data networks operate in a packet mode. Hence explain why services involving audio and video are supported.
December 2010 (4 M)
6. Identify and explain the meaning of the key QOS parameters associated with : 1. Circuit Switching. 2. Packet Switching.
December 2010 (8 M)
7. A wed page of 10 Mb is being retrieved from a wed server. Neglecting server and trunk delays, calculate the time to transfer the page over a 1. PSTN modem operating at 28.8 kbps. 2. Primary rate ISDN access line of 1.5 Mbps. 3. Cable modem operating at 27 Mbps.
December 2010 (4 M)
8. With a neat diagram, explain how voice mail and teleconferencing is supported in relation
to speech only interpersonal communication involving both public (PSTN/ISDN) and private network. network. Also, Also, explain explain the role of voice voice mail mail server server audio audio bridge. December 2011(10 M) 9. Explain with a neat diagram, the interactive television application for both cable and
satellite network.
December 2011(7 M)
10. Determine the propagation delay associated with the following communication channels: 1. A communication through a private telephone network of 1 km 2. A communication through a PSTN of 200 km 3. A communication over a satellite channel of 50000 km Assume the velocity of propagation delay of a signal in the case of 1 and 2 is 2 x 108 ms-1 and 8
-1
in the case of 3 is 2 x 10 ms
Department ECE
December 2011, June 2013(7 M)
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Page No -51
Multimedia Communication
Raghudathesh G P
Asst Professor
11. With the help of a diagram, describe the main components of PSTN and show how a high
speed modem provides multiple services in addition to basic telephony. June 2012 (10 M)
12. Explain the working principle of a circuit-mode and packet-mode of operation of multimedia networks. List out salient features of each type of networks. June 2012 (10 M)
13. Explain operational modes of multipoint conference.
June 2013 (7 M)
14. Explain multimedia data networks.
June 2013 (7 M)
15. What are the basic types of multimedia communication networks? Explain satellite and
terrestrial broadcast network with a neat figure.
December 2013 (10 M)
16. With the aid of diagrams, explain the following modes of communication and multipoint conferencing methods: 1. Unicast 2. Multicast 3. Centralized 4. Decentralized 5. Hybrid
December 2013 (10 M)
17. List the five basic of communication network that are used to provide multimedia services. Explain with a neat diagram 1. Broadcast television network 2. Integrated service digital network.
June/July 2014(12 Marks)
18. Explain, with neat diagram diagram of multipo multipoint int conferencing modes and types of conferencing. June/July 2014 (08 Marks)
19. With the aid aid of diagrams, explain the meaning of the foll following owing operational operat ional modes modes of a communication system : i. simplex ii. Duplex iii. Broadcast iv. Multicast v. Asymmetric and symmetric. December 2014 (10 M)
Department ECE
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Page No -52
Multimedia Communication
Raghudathesh G P
Asst Professor
Question Bank VTU M-Tech Multimedia, Give media types associated a ssociated with with it, also explain its applications. applications. 1. Define Multimedia, December 2008 (10 M), December 2009 (10 M), December 2011 (08 M)
2. Bring out the salient features of different types of networks employed employed in multimedia communication December 2009 (10 M), 3. Explain different types of communication network that are used to provide multimedia
communication services. December 2011 (10 M), December 2013 (10 M) 4. Determine the propagation delay associated with the following communication channels: 5. A connection through a private telephone network of 10 km. 6. A connection through a PSTN of 500 km. 7. A connection through a satellite channel of 75.000 km. 8. Assume that the velocity of propagation of a signal in the case of (i) & (ii) is 2x10 8 ms-1 8
-1
and in the case of (iii) 3x10 ms . December 2008 (08 M), December 2013 (04 M), December 2011 (06 M) 9. Differentiate between voice-operated switching mode and continuous-presence mode. December 2011 (04 M), December 2013 (06 M) 10. Explain the network QoS associated with different types of network. December 2011 (10 M)
11. With the aid of a diagram, explain the meaning of the following terms relating two packetswitched network: i)packetization delay ii) mean packet transfer delay iii)jitter 12. Describe how the effects on a constant bit-rate stream of packetization delay and jitter can,
be overcome overcome by bufferi buffering. ng. December 2011 (10 M) 13. With the help of a diagram, describe the main components of PSTN and show how a high
speed
modem provides multiple multiple services in addition to basic telephony. December 2011
(08 M) 14. Briefly explain the following operational modes of a communication channel i) Simplex ii)
Duplex iii) Broadcast iv) Multicast. December 2011 (04 M) 15. With a neat diagram, explain the working of circuit switched and packet switched
networks. December 2011 (08 M) 16. Briefly explain the network QOS associated with the circuit switched and packet switched
networks. December 2011 (08 M) 17. Drive the maximum block size that should be used over a channel which has a mean BER -4
probability probability of 10 if the probability of a block containing an error – and and hence being -1
discarded – discarded – is is to be 10 . December 2009 (04 M), December 2011 (04 M) 18. Explain the different operational modes of a communication channel. December 2012 (08 M)
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Page No -53
Multimedia Communication
Raghudathesh G P
Asst Professor
19. Describe the essential features of the network types initially designed to provide single type of services and discuss the technological development that has enabled them to provide additional services. December 2012 (08 M) 20. Explain the key parameters associated with application QOS. Describe how the effects on a constant bit rate stream of packetization delay and jitter can be overcome. December 2012 (08 M) 21. Briefly explain five basic types of communication network that are used to provide
multimedia communication service. June 2009 (10 M) 22. Explain different types of net works June 2009 (10 M) 23. Define entropy, bit rate, sampling frequency, quantization and Niquist rate. June 2009 (10 M) 24. The term mu1timedia composed of many media types. Explain them. December 2008 (08 M)
25. Explain briefly the entertainment applications applications of multimedia. multimedia. December 2008 (08 M) network QoS associated with different types of network. December 2013 (08 26. Explain the network M) 27. A web page of 10 M bytes is being retried from a Web-server. Assuming negligible delays,
calculate time to transfer the page over. i)A modem operating op erating at28.8Kbps at28. 8Kbps
ii)ISDN
access line of 1.5Mbps iii) Cable modern operating at 27Mbps. December 2008 (04 M) 28. Mention different modes of multipoint conferencing. December 2008 (08 M) 29. How are multimedia applications classified? classified? Discuss. December 2009 (08 M)
30. What are quality quality of service in multimedia multimedia systems? Explain. December 2013 (10 M) 31. With the aid of diagram explain the meaning of the following terms relating to packet
switching network: i) Packetization delay ii) mean packet transfer delay iii) jitter. Describe, how the effects on a constant bit-rate stream of packetization delay and jitter can be overcome by buffering. December 2013 (10 M) 32. Define the term multimedia. List different types of multimedia networks. Explain any two networks in detail. December 2014 (10 M) 33. Identify and explain the meaning of key QOS parameters associated with circuit and packet switching. December 2014 (10 M)
Department ECE
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Page No -54
Multimedia Communication
Raghudathesh G P
Asst Professor
Additional Questions: 1. Give a definition of multimedia and a multimedia system.? [02] 2. Define Multimedia; what is a multimedia PC hence list list the application of multimedia and List out the benefits of multimedia? [06] 3. List some of Multimedia applications.[05] 4. What are the various input and output devices that can be used in a Multimedia PC? Explain in detail. [08] 5. Explain the building blocks of multimedia. [08] 6. List the multimedia communication networks.[05] 7. State Nyquist sampling theorem & Nyquist rate.[05] 8. What do you mean by Hypertext?[04] 9. What is compression? [03] 10. Compare lossy & lossless compression.[07] 11. State & explain the basic form of representation Text, Image, Audio, Video?[10] 12. Explain the meaning of bps in relation to digitized audio & video.[05] 13. Explain the meaning of compression & why it is used?[08] 14. Explain the meaning of POTS, local exchange office, PBX, mobile switching centre, international gateway exchange.[08] 15. Explain why most data networks operate in a packet mode. Hence explain why services involving audio and video are supported?[10] 16. Explain “Broadband” in relation to B -ISDN and why deployment has been delayed?[08] 17. Describe the principal operation of a fax machine & why modems are required. What is the meaning of PC fax?[10] 18. With aid of block diagram explain CSCW?[10] 19. Explain a Web server, a browser, WWW?[05]
20. Explain web page, home page, hyperlink, URL, HTML?[10] 21. Explain the principle of movie/video-on-demand?[06] 22. Explain the principle operation of a circuit mode network?[06] 23. Explain briefly different modes of multipoint conferencing?[08] 24. Identify & explain the meaning of the key parameters associated with the application QOS ?[10] 25. Discuss the term “application service classes”?[05]
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Page No -55
