Multimedia Communication - ECE - VTU - 8th Sem - Unit 1 - Multimedia Communications

Multimedia Communications (10EC841) Unit 1: Multimedia Communications

Ramesh S Asst. Prof.(ECE Dept.), Bengaluru [email protected] cell: +91 9449851913

ELECTIVE –5 (GROUP E) MULTIMEDIA COMMUNICATIONS Subject Code: 10EC841 No. of Lecture Hrs/Week: 04 Exam Hours : 03 IA Marks: 25 Total no. of Lecture Hrs.: 52 Exam Marks : 100 UNIT 1:MULTIMEDIA COMMUNICATIONS: Introduction, multimedia information representation, multimedia networks, multimedia applications, media types, communication modes, network types media types, communication modes, network types, multipoint conferencing, network QoS application QoS. 6 Hrs UNIt 2: MULTIMEDIA INFORMATION REPRESENTATION: Introduction, digital principles, text, images, audio, video. 7 Hrs UNIT 3: TEXT AND IMAGE COMPRESSION: Introduction, compression principles, text compression, image compression. 6 Hrs UNIT 4: AUDIO AND VIDEO COMPRESSION: Introduction, audio compression, DPCM, ADPCM, APC, LPC, video compression, video compression principles, H.261, H.263, MPEG, MPEG-1, MPEG-2, and MPEG-4. 7 Hrs UNIT 5: MULTIMEDIA INFORMATION NETWORKS: Introduction, LANs, Ethernet, Token ring, Bridges, FDDI High-speed LANs, LAN protocol. 6 Hrs UNIT 6: THE INTERNET: Introduction, IP Datagrams, Fragmentation, IP Address, ARP and RARP, QoS Support, IPv8. 7 Hrs UNIT 7: BROADBAND ATM NETWORKS: Introduction, Cell format, Switch and Protocol Architecture ATM LANs. 6 Hrs UNIT 8: TRANSPORT PROTOCOL: Introduction, TCP/IP, TCP, UDP, RTP and RTCP. 7 Hrs TEXT BOOK: 1. Multimedia Communications: Applications, Networks, Protocols and Standards, Fred Halsall, Pearson Education, Asia, Second Indian reprint 2002. REFERENCE BOOKS: 1. Multimedia Information Networking, Nalin K. Sharda, PHI, 2003. 2. Multimedia Fundamentals: Vol 1 - Media Coding and Content Processing, Ralf Steinmetz, Klara Narstedt, Pearson Education, 2004. 3. Multimedia Systems Design, Prabhat K. Andleigh, Kiran Thakrar, PHI, 2004.



UNIT 1:MULTIMEDIA COMMUNICATIONS: Introduction, multimedia information representation, multimedia networks, multimedia applications, media types, communication modes, network types media types, communication modes, network types, multipoint conferencing, network QoS application QoS. 6 Hrs Introduction Multimedia communication had a range of applications and networking infrastructures Definition: 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: Text: Includes both unformatted text - comprising strings of characters from a limited character set formatted text - comprises strings as used for the structuring, access, and presentation of electronic documents Images: Includes computer generated image - comprising lines, curves, and circles, and digitized images of documents and pictures Audio: Includes both low-fidelity speech - as used in telephony high-fidelity speech - stereophonic music as used with compact discs Video: Includes short sequences of moving images (also known as video clips) and complete movies/films Multimedia applications Multimedia applications may be

Person-to-Person communications or Person-to-System communications

Terminal Equipment (TE): used for 2-peoples communication Multimedia Personal Computer (PC) or Workstation: used by a person to interact with a system Typically, these are located either in the home or on a desktop in an office Server: It's the system - containing a collection of files or documents - each comprising digitized text, images, audio, and video information either singly or integrated together in some It may also contain - a library of digitized movies/videos User interacts with the server - by means of a suitable selection device - connected to the Set-top box (STB) - associated with a television Networking infrastructure: provided by - using a number of different types of network Networks: designed from the outset to provide multimedia communication services and designed initially to provide just a single type of service Advances in various technologies: the networks can provide - a range of services Ex.: PSTN (Public Switched Telephone Network) or GSTN (General Switched Telephone Network) - designed initially to provide the basic switched telephone service Advances in digital signal processing hardware and associated software - kept PSTNs/GSTNs provide a range of more advanced services involving - text, images, and video



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 Multimedia Information Representation Applications - involving text and images - comprise blocks of digital data Text data for - 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 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: Audio and video signals: Vary continuously - with time as the amplitude of the speech, audio, or video signal varies Type of signal: analog signal Duration of applications - involve of audio and/or video: can be relatively long Ex.: Typical telephone conversation - can last for several minutes 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 involves 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 involves of different media types integrated together in some way - it's necessary - to represent all 4 media types in a digital form For text and images: this 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 wit time - is of relatively high bit rate - and 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 Compression: It's a technique - first applied to the digitized signals in order to reduce the resulting bit rate to a level - which are various networks - can support Compression to text and images: To reduce the time delay between a request being made for some information and the information becoming available on the screen of a computers or over others



Multimedia Networks Basic types of communication networks - used to provide multimedia communication services – are

Telephone networks Data networks Broadband television networks Integrated services digital networks Broadband multiservice networks

1,2, and 3 networks: Initially designed - to provide just a single type of service - listed as below: Telephone networks: telephony Data networks: data communications Broadband 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 PSTNs - been in existence for many years - have gone through many changes during this 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. 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): Telephones located in the medium or large office/site are connected to a PBX or Private switching Office Provides - a (free) switched service between any two telephones - that are connected to it 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



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 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 General scheme of modem is shown in the Fig.



Modem: 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 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: one 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 Fig. shows the general scheme of this, and such applications need bit rates in excess of 1.5Mbps Technological advances - in modems area - have been made - PSTNs can now support speech applications and also a wide range of other multimedia communication applications

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: X.25 network and 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" Fig. shows a selection of the different types of interconnected network 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 - use the same approach 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 communiction 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 on 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) 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 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: 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.,) Fig. shows the general architecture of a cable distribution network and a satellite/terrestrial broadcast network



General architecture of a cable distribution network: Set-top box: attached to the cable distribution network Provides: Control of the television channels - that are received 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 Fig. shows the general architecture of the satellite and terrestrial broadcast networks 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 were - 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 2 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 Fig. shows the summarization of the various services provided 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 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 Number of the basic design features associated with the B-ISDN: have been used as the basis of other broadband multiservice networks Ex.: Multiservice networks 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 - All the different media types associated with a particular application are first converted in the source

equipment into a digital form These to be integrated together 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 Fig. 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:

Interpersonal communications Interactive applications over the Internet 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 advances in technology - from, 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 in of possible Multimedia communications implies two or more media types involved in it – even then, from the applications perspective – selected examples of applications that these networks were designed, to support even though only a single type of medium is involved – to be to included

Interpersonal communications : May involve speech, image, text, or video Single type or integrated two or more type of media - involved Speech only Image only Text only Text and images Speech and video Multimedia Speech only: Traditionally, involves – speech, telephony

Provided using telephones – which are connected either to PSTN/ISDN/Cellular network or PBX Fig. shows the general scheme Multimedia PC with microphone and speakers, if using – user can make telephone calls through PC – require the telephone interface card and associated software – called CTI (Computer Telephony Integration) Advantages of using PC, instead of conventional telephone – for calls 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 Circuit’s bandwidth – is more (providing access circuits – to the network has sufficient capacity) Integration of telephony with all the other networked services – possible by PC 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 – 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 Each person – can hear and talk to all of the others – involved in the call – called the conference



call/teleconference 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: 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 PC-to-PC telephone call: Standard address – 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 Packet voice: Telephony over the Internet VoIP (Voice over IP - since, IP is the network protocol associated with the Internet): Telephony over the Internet



Telephony gateway: It’s 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 latter’s 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 setup procedure of the PSTN/ISDN Assuming the called party answers - called gateway – signals back t the PC user –through the source gateway – that the call can commence Similar procedure – followed to clear the call on completion Image only:

Facsimile (Simply, fax): Exchange of electronic images of documents – is an alternate form of interpersonal communications over – PSTN/ISDN Fig. 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 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 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 Telephony like- this requires – a telephone interface card and associated software Latter – operates in the same way – as like the fax machine – so, terminal at the called side can be either a fax machine/another similar PC 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 – a PC or a workstation

Fig. shows - various operational scenarios User at home – case in – access to the Internet s 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 Fig. shows – the format of the text-only e-mail message At the head: unique Internet-wide name of both the sender and recipient of the mail – 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 Fig. 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 Shared whiteboard: Window on each person’s display – is used as the shared workspace Display comprises integrated text and images Software associates comprises – 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 Fig. shows – the general scheme Home use cases in: Terminals used – normally, dedicated to providing the videophone service Office use cases in: 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 required 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): Central unit - to support the videoconferencing videoconferencing server – Associated with the network – used in few cases Fig. shows – Separate window – on screen of each participant’s 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: 1. Multiple integrated speech-and-video communication channels, one for each participant, being sent to each of the other participants – needed to do this 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 Multicasting: Networks such as LANs and the Internet – supports: all transmissions – form 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 Fig. shows – the principle of this Principle shown in the Fig. – is only feasible – when only a limited number of participants – are involved – owing to the high load – it places on the network Application, involve: can only a single person at each location or groups of people at one or more of the locations Fig. Shows – the two examples In Fig. – 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 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 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 Fig. – 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 Fig in MCU is shown in Fig. 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 – mail containing, other media types such as images, audio, and video are also used Ex.: 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 Fig. Shows this 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 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 Fig. 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 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 documents Fig. shows – the general principle



Each document: comprises a linked set of pages – and hyperlinks (linkages between the pages) References: Above are pointers or references – either 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: Documents comprising only texts – are created using it Hypermedia: Documents comprising multimedia information - are created using it Fig. Shows – general structure of this type of document No central authority: For the introduction of new documents – into the web Server 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): Document’s 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: 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 Standard format – is used for writing documents – HTML (Hyper Text Markup Language): Is a standard format of writing documents - 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



Browser: Client function 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 Ex.: Loudspeaker – for a sound annotation for a video camera for a video clip Presence of sound and video – annotations brings a document to life and adds value over a simple printed page Some applications: in 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 (homeshopping)/Telebanking (homebanking) 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

Movie/video-on-demand Interactive television

Movie/video-on-demand:

Similar in principal – to that of previous discussion – except, in general, 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 (as in Fig. ) or a cable network of the type (as in Fig. ) 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 Fig. shows – the general operating scheme in both the cases 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 Fig. , 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 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 playout time of that movie as shown in Fig. 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 playout time – are satisfied simultaneously – by the server outputting a single video stream – clearly, the viewer is unable to control the playout of the movies Business environment: similar applications as above been made use – 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 – 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: 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 Fig. , STB provides – both a low bit rate connection to the PSTN and a high bit rate connection to the Internet 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 – it’s the origin of the term interaction television Typical uses of the return channel – are for voting, participation in games, home shopping, and so on Fig. as in – 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 Fig. shows – a selection of the terms used with multimedia Information flow associated – with the different applications – can be either continuous or block-mode

Continuous media case: information stream is generated by the source continuously – in a time-dependent way

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 Real-time media: continuous media is generated in a time-dependent way



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 Ex.: of media types - that guarantee continuous streams of information in real time – are audio and video CBR (Constant Bit Rate)/ VBR (Variable Bit Rate): generation of source information can be – 2 types

Audio with: 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

Video with: 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: Source information comprises – single block of information that is created in a time-

independent way 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 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 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 Communication modes Communication channels – provided by various network types – is shown in Fig.



Transfer of information streams – associated with an application – can be in 5 modes: Simplex Half-duplex (Two-way alternate) Duplex (Two-way simultaneous) Broadcast 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): 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: 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: 2 types: Symmetric: Equal – rate associated, with the flow of information in each direction Asymmetric: Unequal - rate associated, with the flow of information in each direction

Ex.: Video telephone call: involves – exchange of integrated digitized speech and video stream – both directions simultaneously – so, symmetric duplex communications channel is required Application involving browser (program) and a web server: low bit rate channel from the browser to the web server – is required – for request and control purposes



high bit rate channel from the server to the subscriber for the transfer of, say, requested file – so, asymmetric half-duplex communications channel is required

Network types Types of information stream associated with the different media types:

Continuous mode Block mode

Types of communications channel associated wit the various network types:

Circuit-mode: operates in a time-dependent way or Synchronous communications channel: provides a constant bit rate service at a specified rate

Packet-mode: operates in a time-varying way or Asynchronous communications channel: provides a variable bit rate service - actual rate is determined by the variable transfer rate of packets across the network

Circuit-mode

Fig. shows – the circuit mode network Circuit-switched networks - Comprises – 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: Time delay – while a connection is being established Ex.: PSTN and ISDN PSTN: call setup delay – can range form 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



Packet-mode

Fig. shows Types of packet-mode networks: CO (connection-oriented)

CL (connetionless) CO: Fig. shows – principle of operation of a CO network Comprises an interconnected set of PSEs (Packet-Switching Exchanges) Packet-switched network: another name of the CO networks 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 – VC (Virtual Connection/Virtual Circuit) 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 VCI (Virtual Circuit Identifier) – a short identifier 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 First: Specifies – incoming link/VCI and the corresponding outgoing link/VCI Second: To route packets in the reverse direction (the inverse of these – as we show in the example in the Fig. ) 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: Assumption: 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



CL: In conncectionless network: Establishment of connection – is not required Two communicating terminals/computers: can communicate and exchange information as and when they wish Fig. 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 Router: used, rather than packet switching exchange Both network types (CO and CL) in: 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



If an error – is detected, the packet is simply discarded Best-effort service: service offered by the packet-switched network 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 dame 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 Mean packet transfer delay – mean of this delay Delay variation (jitter) – variation about the mean Ex.: Internet (Ex.: for packet-switched network – that operates in the CL mode) International X.25 packet-switching network and ATM (Ex.: for networks that operate in the CO mode) X.25 network:

Used primarily – for the transfer of files – containing text and binary data between large computers Routing of packets is relatively slow – with the effect that X.25 network, is unsuitable for most multimedia applications – because of the packet format that is used ATM network:

Designed from the outset – to support all types of multimedia applications Achieved by high bit rate interconnecting links Once a VC – has been set up, a very small fixed-sized packet of 53bytes is used – to transfer the information – associated with the call Cell: small packet – includes a short 5-byte header, which enables cells to be switched at the very high link bit rates that are used Fast packet-switching networks/Cell-switching networks: other names of ATM 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



Different modes of operation of the two (circuit and packet) network types: multipoint conferencing is implemented in one of two ways:

Centralized mode Decentralized mode Hybrid mode

Centralized mode: Used with circuit-switched networks – such as PSTN/ISDN

Fig. 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 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

Decentalized mode: Used with packet-switched networks – that support multicast communications Ex.: LANs, intranets, and the Internet Fig. 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 manage the information streams that it receives from the other members

Hybrid mode: Used when the various terminals/computers – that make up the conference are attached to different network types

Fig. 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:

Data conferencing Audioconferencing Videoconferencing Multimedia conferencing

Data conferencing: Involves – data only - Ex.: include data sharing and computer-supported cooperative working Audioconferencing: 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 Volume and rate of the information being exchanged, due to – centralized mode of working is used – with both network types MCU: Consists of 2 parts

1. MC (Multipoint Controller) part - 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

MP (Multipoint Processor) part - 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 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, 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 Dial-in mode: The participants calling in 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 participant’s 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 is normally mixed – into a single stream and hence, each participant can always hear what is said by all the other participants Network QoS Network QoS parameters: 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: circuit-switched and packet-switched are different – for

Circuit-switched networks Packet-switched networks

Circiuti-switched: QoS parameters associated – with constant bit rate channel – set up include: Bit rate Mean bit error rate Transmission delay

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.: if the application involves speech – then, an occasional bit error will go unnoticed 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 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<1 In practice, both circuit-switched and packet-switched – provide unreliable service (best-try or best-effort service) Unreliable service (Best-try/Best-effort service): 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) Reliable service: If application – dictates that: only error-free blocks are acceptable – it is necessary for: Sending terminal/computer to divide the source information into blocks of a defined maximum size Destination to detect when a block is missing When this occurs – destination must request – source send another copy of the missing block Introduce delay – so, that retransmission procedure – should be invoked relatively infrequently – which dictates a small block size Leads to high overheads – since, each block must contain additional information – that is associated with the transmission procedure So, choice of block size – compromise between increased delay resulting from a 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 Determined by: Bit rate used Delays occur in the terminal/computer network interfaces (codec delays) + propagation delay of the digital

signals, as they pass from source to destination, across the network Determined – by physical separation of 2 communicating devices and Velocity of propagation of a signal, across the transmission medium (free space: 3*108 m/s and a fraction of this in physical media, a typical value 2*108 m/s) Propagation delay: in each case is independent of the bit rate of the communication channel

assuming: codec delay remains constant – propagation delay, s same whether bit rate is 1kpbs, 1Mbps, or 1Gbps

Packet-switched network QoS parameters – associated with a packet-switched network include: Maximum packet size Mean packet transfer rate Mean packet error rate Mean packet transfer delay Worst-case jitter 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



Same as block error rate, associated with a circuit-switched network 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 route 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 Application QoS Network QoS parameters: define what the particular network being used provides rather – what application requires Application: has QoS parameters also – 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: Required bit rate or mean packet transfer rate Maximum startup delay Maximum end-to-end delay Maximum delay variation/jitter 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 Delay variation/jitter (can cause problem – in the destination decoder – if the rate of arrival of the bit stream is

variable) For interactive applications: 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 – 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 Round-trip delay: Delay between a request for some information being made and the start of the information

being received/displayed Important – for HCI (human-computer interaction) – to be successful Should be as short as possible – ideally, less than a few seconds For applications – involve, 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



Ex.: illustrating the benefits – of a packet-switched network over a circuit-switched network Transfer of a large file of data form server computer – connected to the Internet t a client PC/workstation in a home Fig . Access to the Internet – from home, can be by means of a PSTN (with a modem), an ISDN connection, or a cable modem 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 time-share – use of 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 270 concurrent users – each user would get a mean data rate of 100 kbps In this applications: main parameter of interest: not mean data/bit rate, but time to transmit the complete file With PSTN/ISDN: it is related to channel bit rate and the size of the file Cable modems: time-share 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: PSTN and 28.8kbps modem: 57.8 minutes ISDN at 64kpbs: 26 minutes ISDN at 128kpbs: 13 minutes cable modem at 27Mbps: 3.7 seconds

If other transfer request occur – 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 befor playout of the information bitstream is started Memory buffer – operates using a first-in, first-out (FIFO) discipline Number of packets retained – in the buffer before output starts – is determined by the worst-cast jitter and the bit rate of the information stream Fig. 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 – 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



For neworks – support a number of different service classes Ex.: is Internet – to ensure, the QoS parameters –associated with each class re 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, more priority of



Bibliography: Multimedia Communications: Applications, Networks, Protocols and Standards, Fred Halsall, Pearson Education, Asia, Second Indian reprint 2002.

Multimedia Communication - ECE - VTU - 8th Sem - Unit 1 - Multimedia Communications

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