Multimedia Communication VTU unit 1

MULTIMEDIA COMMUNICATION

(VTU) - 10EC841

UNIT 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 Education, 2004.

Special Thanks To:

1. Ramisuniverse for providing free 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.

Multimedia Communication Raghudathesh G P Asst Professor

Department ECE [email protected] Page No -1

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Unit 1 Multimedia Communication

Introduction:

Multimedia communication includes a range of applications and networking infrastructures.

Definition1: The term "multimedia" is used to indicate that the information/data being transferred over the network 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, 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 high-fidelity 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 digitally manipulated means. A multimedia

project development requires creative, technical, organizational, 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 applications may involve either of the 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 personal computer (PC).

2. These Digital device are located either in homes or offices.



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3. Basically system is a server containing a collection of files or documents - each comprising digitized text, images, audio, and video information either

singly or integrated together in some way alternatively It may also contain -

a library of digitized 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.

Networking infrastructure: provided using a number of different types of 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 of different other services.

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 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 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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Applications involving text and images: comprise the short request for a file. Ex.: file contents being returned, the duration of the overall transaction is relatively

short.

Applications involving Audio and Video Signals: Vary continuously with time as the amplitude of the speech, audio, or video signal 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 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.

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 other media types.

Digitization of an audio signal: produces a digital signal with amplitude of the signal varies continuously with time and is of relatively high bit rate, is measured

by bps (bits per second) and for speech signal a typical bit rate of 64 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 these media types in a digital form hence we go for compression.

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 others.



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Multimedia Networks:

Five basic types of communication networks are used to provide multimedia communication services:

1. Telephone networks. 2. Data networks. 3. Broadcast television networks. 4. Integrated services digital networks. 5. Broadband multiservice networks.

1,2, and 3 networks are initially designed to provide just a single type of service as listed as below:

1. Telephone networks: telephony 2. Data networks: data communications 3. Broadcast television networks: broadcast television

Technological developments enabled these networks to provide additional 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 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 such networks spanned just a single country later, telephone networks of 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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Local Exchange/End Office: telephones located in the home or in a small business are connected directly to their nearest 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. Provides a (free) 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 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 from 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 PBX were designed to carry the 2-way analog signals associated with a call.



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Hence, within the PSTN all the switches and the transmission circuits that interconnect them operate in digital mode to carry a digital signal a stream 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 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 circuits and is sufficient, to support various applications comprising of text and

images integrated together and also services that comprise speech 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 and also a wide range of other multimedia communication applications.



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Data 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, or an 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 communication protocols.

Communication protocol: an agreed set of rules that are adhered to by all communicating parties for the exchange of information.

Rules define the sequence of messages that are exchanged between the communication parties and the syntax of these messages.

By using, the same set of 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".

Figure below shows a selection of the different types of interconnected network.



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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 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 backbone network 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 connected to the network are the same

as those defined for use with Internet.

Enterprise network (Intranet): all internal services are provided by using the same set of communication 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 unit connects IBN and the different types 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 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 PCs: have become available that support a range of other applications. Ex.: with the addition of microphone and a pair of speakers with sound card and

associated software to digitize the speech PCs now are used to support telephony and other

speech-related applications with the addition of video camera and associated hardware and

software a range of other applications 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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Packet-mode networks and the Internet in particular: support general data communication applications and also a range of other multimedia communication

applications involving speech, audio, and video currently.

Broadcast Television Networks:

Designed to support the diffusion of analog television and radio programs throughout wide geographical areas.

Cable distribution network sued as broadcast medium, normally in large town or city. Satellite network (Terrestrial broadcast network): broadcast medium for large areas

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 games, home shopping, and etc.,).

Figure below shows the general architecture of a cable distribution network and a satellite/terrestrial broadcast network.

General architecture of a cable distribution network: Consist of set top box : attached to the cable distribution network Provides:

1. Control of the television channels - that are received. 2. Access to other services.

Ex.: Cable modem: integrated into the STB provides a low bit rate channel and a high bit rate channel from the 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 to the Internet. Cable distribution network: provide basic broadcast radio and television services access

to the range of multimedia communication services that are available with both PSTN and

Internet.

Figure below shows the general architecture of the satellite and terrestrial broadcast networks.



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Satellite and terrestrial broadcast networks: integrated into the STB provides the subscriber with an interaction channel 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 channels over these circuits allow users either to have two different telephone calls in progress simultaneously or two different calls such as

a telephone call and a data call.

Access circuit with ISDN: known as DSL (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

the digital mode of operation of the network transparent to the subscriber phone.

Digitization of a telephone-quality analog speech signal - produces a constant bit rate binary stream 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 to be set up through the switching network independently hence, to synchronize 2

separate 64kbps bitstreams into a single 128kbps stream requires an additional box of

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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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 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 communication applications.

Broadband: term used to indicate the circuits associated with a call could have 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 networks since, were designed to be an enhanced ISDN.

N-ISDN (Narrow Integrated Services Digital Networks): alternate name for ISDN. B-ISDN: when in first technology associated with the digitization of the video signal 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 communication applications that includes video, and also can the other 3 types

of network combined effect, the slow down considerably the deployment of B-ISDN.



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Number of the basic design features associated with the B-ISDN: have been used as the basis of other broadband 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 were initially designed to provide a single type of service.

To have this flexibility: 1. All the different media types associated with a particular application are first

converted in the source equipment into a digital form.

2. These to be integrated 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 the multimedia information associated with a the different types of application.

Ex.: Transmission terms in: cells relating to the different applications can be integrated together more flexibly.

Use of fixed-sized cells: means the switching of cells can be carried out much faster than, if 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.

Ex.: ATM LANs - span a single site, ATM MANs span large town or city. Ex.: For broadband multiservice network is shown in the Figure below



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Being used as a high-speed backbone network to interconnect a number of LANs 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 applications:

1. Interpersonal communications.

2. Interactive applications over the Internet.

3. Entertainment applications.

In many instances networks used to support applications were 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 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 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 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 of using PC, instead of conventional 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. Circuits bandwidth is more (providing access circuits to the network has sufficient capacity).

3. Integration of telephony with all the other networked services are possible by PC. 4. In addition to Telephony many public and private networks support additional

services.

Ex.: Voice-mail and Teleconferencing Voice-mail: Used when the called party being unavailable Spoken message is then be left

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.

Teleconferencing: Calls involve multiple interconnected telephones/PCs. Person can hear and talk to all of the others involved in the call called the conference call/teleconference



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call since, it involves a telephone network or audio conference call which require an

audio bridge - a central 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 are used same way as for a data 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 packets 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).

Telephony gateway: Its a Interworking unit to connect the PC connected to the Internet and a telephone connected to the PSTN/ISDN - since both operate in the circuit mode PC

user sends a request to make a telephone call to a preallocated telephony gateway using the

latters internet Address Gateway requests from the source PC the telephone number of 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 party 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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Assuming the called party answers called gateway signals back to the PC user through the

source gateway that the call can commence. Similar procedure followed to clear the call on

completion.

Image Only:

Exchange of electronic images of documents is an alternate form of interpersonal communications over PSTN/ISDN known as Facsimile (Simply, fax).

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 its 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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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 is normally are normally a PC or a workstation. 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 contain a mailbox

for each user connected to that network User can both create and 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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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 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 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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Shared whiteboard: Window on each persons display is used as the shared workspace, display comprises integrated text and 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, a member of the group updates the contents of whiteboard.

Update-control part: Present in each of the other PCs/workstations obtain above change information in turn, proceed to update the contents of their copy of the whiteboard.

Speech and 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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In Cases of Home use: Terminals used normally dedicated to providing the videophone service.

In Cases of Office Use: Single multimedia PC/workstation is used to provide videophone service together with a range of other 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 using a window of the PC/workstation screen to display the moving image of

the called party.

Network must provide two-way communication channel between 2 parties of sufficient BW to support the integrated 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 participants PC/workstation should be used to display video image of all the other participants.

Needed to implement displaying of video image of all the other participants on screen of each participant this requires:

1. Multiple integrated speech-and-video communication channels, one for each participant, being sent to each of the other participants needed to do this 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.

Ex.: voice-activated MCU MCU whenever detects a participant speaking it relays the information stream from the

participants to all the other participants so, a single 2-way communication channel is

needed between each location and the MCU is needed thereby reducing the

communication bandwidth needed considerably.



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Some Networks such as LANs and the Internet supports Multicasting where all transmissions from any of the PCs/workstations belonging to a predefined multicast group

are received by all the other members of the group Possible to hold a conferencing 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 are involved owing to the high load it places on the network.

In Figure below a person at one location is communicating with a group of people at another 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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speech-and-video to enable the lecturer to both see and hear the members of the class at

the remote 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 lecturers 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 example of videoconferencing. Normally, a group of people are present

at each location.

Videoconferencing studios: Specially equipped rooms are used which contain all the necessary audio and video equipment, comprising of one or more video cameras, a large-

screen display, and associated audio equipment, all of which are connected to a unit called

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 is shown. as the central facility within the network and hence,

only a single 2-way communications channel is required for each access circuit of the

network. Ex.: this type of arrangement, with a telecommunications-provider 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, the stream from

which must be broadcast to all of the other sites.

Multimedia:

Assumption: The information content of each e-mail message consisted of text only used in the earlier discussed.

Ex.: In addition an mail containing, other media types such as images, audio, and 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 there is a voice-mail server associated with each network, in addition to e-mail

server.

Figure below Shows this



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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 recipients 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 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 applications.



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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 and linkages between the pages are known as 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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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.

URL (Uniform Resource Locator) is a Documents unique address which identifies both 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 information on all the web servers.

A Browser is a Client function and there are number of user-friendly browsers available to explore visited servers and to open up a dialog with a particular server at the click of the

mouse. Once the desired document has been located, the user simply clicks on an anchor

point within a page of the document to activate the linkage information stored at that point

Possible to return to the previous anchor at any time.

With the hypertext 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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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 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 Server must provide additional transaction processing support for,

say, ordering and purchasing since, this will also often involve financial transaction, more

rigorous security procedures are required for access and 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/resolution. Since, wide-screen televisions and 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 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 to the other switched services that the PSTN supports.

Figure below. Shows the general operating scheme in both the cases.



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Information stored on the server: collection of digitized movies/videos. Normally, subscriber terminal comprises a conventional television with device for interaction

purposes. User interactions are relayed through the server through a set-top box which also

contains the 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 of the movie by using 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 flow rate from it.



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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 mode in which requests for a particular movie are not played out immediately but instead are queued until the start of the next play out time of that 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 stream can then be displayed directly on the screen of a 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.

STB (Set-Top 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 rate connection to the Internet.



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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. Through

the connection to the PSTN subscriber is able to actively respond to the information being

broadcast its the origin of the term interaction 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 high-

speed modem to provide the connections to the PSTN and the Internet.

Media types:

Figure below shows a selection of the terms used with multimedia.



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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 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 with the bit rate of the communication channel that is used must

be compatible with the rate the source 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 are used to 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 block of information that is created in a time

independent way.

2. Ex.: block of text representing an e-mail or computer program a 2-D matrix of pixel values that 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 at a time determined by the requesting application program.

4. Bit rate of the communications channel need not be constant but, such that, when a block is requested.

RTD (Round-Trip Delay): delay between the request being made and the contents of the

block being output at the destination is within an acceptable time interval - RTD for HCI

(Human-Computer Interface): can be no more than a few seconds.



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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. Ex.: transmission of photographic images from a deep-space probe at predetermined times

Involves unidirectional flow of 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.

Duplex (Two-way simultaneous) :



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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.

Ex.: broadcast of a television program over a cable network as all the television receivers that are connected to the network receive the same set of programs.

Multicast:



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Similar to broadcast except, information output by the source is received by only a specific subset of the nodes that are connected to the network (multicast group).

Ex.: video conferencing involving a predefined group of terminals/computers connected to 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) and a web server: 1. Low bit rate channel from the browser to the web server is required for

request and 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

There are TWO types of communications channel associated with the various network 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 bit rate service - actual rate is

determined by the variable transfer rate of packets across the network.



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Circuit-mode:

Figure below shows 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 information source set up 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 uses this to set up a connection through the

network to the switching office/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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Packet-mode:

Types of packet-mode networks:

1. Connection-Oriented(CO) 2. Connectionless(CL)

Connection-Oriented(CO):

Figure below shows principle of operation of a CO network.

Comprises an 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 the addresses of the source and 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 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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Each PSE maintains a table which specifies the outgoing 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 identifier (VCI) for this link is then selected and two entries are made in a routing table.

1. First entry: Specifies incoming link/VCI and the corresponding outgoing link/VCI.

2. Second entry: To route packets in the reverse direction (the inverse of 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 clear packet along the 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 to route the packet onto the appropriate outgoing link.



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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 its 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. 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 because it depends on the number of packets that are currently present in the queue when a new packet arrives for forwarding this mode of operation is known as

packet store-and-forward.

There is a packet store-and-forward delay in each PSE/router. Sum of the store-and-forward delays in each PSE/router contributes to the overall transfer delay of the packet

across the network.



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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 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:

Features in many interpersonal applications including audio and video conferencing, data sharing, and computer supported cooperative working.

These involve exchange of information between 3 or more terminals/computers. Multipoint conferencing is implemented in one of following 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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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 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 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 makes up the conference are attached to different network types.



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Figure above. Shows Ex.: conference comprises 4 terminals/computers 2 attached to a 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.

Types of conferencing based on media Type:

1. Data conferencing

2. Audio conferencing

3. Videoconferencing

4. Multimedia conferencing

Data conferencing: Involves data only. Ex.: include data sharing and computer-supported cooperative working.

Audio conferencing: Involves audio (speech) only. Videoconferencing: Involves speech and video synchronized and integrated together. Multimedia conferencing: Involves speech, video, and data 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 the other 3 types of conferencing the information flows demand the use of special purpose units.

Audio 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 with both network types.



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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.

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 MCU 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 window on the screen of the participants terminal/computer, in the second window the face of the remote

participant who is currently talking. When another participant starts to talk face of the new

speaker replaces the face of the current remote participant. In the event two or more

participants starting to talk at the same time MCU normally selects 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 participants.



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Network QoS:

Definition: Operational parameters associated with a communications channel through a network collectively determine the suitability of the channel in relation to its use for a

particular 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 error rate 3. 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 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 in other applications it is 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. 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 into blocks the maximum size of which

is determined by the mean BER of the communications channel.

Ex.: if mean BER is 10-3 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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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.

Assuming: random errors: PB=1-(1-P)N, which approximates to NxP if, NxP

PROBLEM

Drive the maximum block size that should be used over a channel which has a mean BER

probability of 10-4

if the probability of a block containing an error and hence being discarded

is to be 10-1

.

ANSWER:

PB=1-(1-P)N

Hence 0.1=1-(1-10-4

)N and N=950bits

Alternatively, PB=N x P

Hence 0.1=Nx10-4

and N=1000bits

Packet-switched network:

QoS parameters associated with a packet-switched network include 1. Maximum packet size 2. Mean packet transfer rate 3. Mean packet error rate 4. Mean packet transfer delay 5. Worst-case jitter 6. Transmission delay

Packet-switched network: rate of packets transfer across the network influenced strongly by bit rate of the interconnecting links due to, 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 in each PSE/router which, it encounters 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.



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PROBLEM:

Determine the propagation delay associated 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.

Assume that the velocity of propagation of a signal in the case of (1) and (2) is 2x108ms

-1 and in

the case of (3) 3x108ms

-1

ANSWER:

1.

2.

3.

Application QoS

Network QoS parameters define what the particular network being used provides rather what

application requires. Application has its own QoS parameters requirement associated with it:

Application involving images: Ex.: parameters may include minimum image resolution and size.

Application involving video: Ex.: parameters may include digitization format and refresh rate.

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 5. Maximum round-trip delay

Applications involving transfer of constant bit rate stream: Parameters important are:

Required bit rate/mean packet transfer rate End-to-end delay



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Delay variation/jitter (can cause problem in the destination decoder if the rate of arrival of the bit stream is variable)

For interactive applications following points 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 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 network should appear to be most appropriate since, call setup delay is not often important

and channel provides a constant bit rate service of 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 (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 bit rate of shared channel: 27Mbps, number of concurrent users of the channel may be several hundred. So, if there are 270 concurrent users each user would get a mean data

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 28.8kbps modem: 57.8 minutes 2. ISDN at 64kpbs: 26 minutes 3. ISDN at 128kpbs: 13 minutes 4. cable modem at 27Mbps: 3.7 seconds



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If other transfer request occurs during the time the file is being transmitted then, completion time of each transfer request will increase as they share the use of 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 is very fast and for many applications, quite acceptable.

For constant bit rate applications: Providing equivalent mean bit rate, provided by the network > input bit rate maximum jitter < defined value 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



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buffer before output starts is determined by the worst-cast jitter and the bit rate of the

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 delay of the channel.

To minimize overall input-to-output delay, packet size used for application is kept small, but of sufficient size to overcome the effect of the worst-case jitter.

To simplify determining a particular network which can meet the QoS requirement of an application: Number of standard application service classes have been defined.

Each service class with specific set of QoS parameters associated for network, can either meet this or not.

Networks support a number of different service classes. Ex.: Internet to ensure, the QoS parameters associated with each class is met packets

relating to each class are given a different priority then, each class packets can be

differently treated.

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.



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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 and start

play out of the bitstream after the 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 if the computed packet size exceeds the network maximum packet size, then the

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.



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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