Business Data Communications
Business Data Communications INFO 3229
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This 66 page Class Notes was uploaded by Lloyd Smith on Sunday October 25, 2015. The Class Notes belongs to INFO 3229 at University of North Carolina - Charlotte taught by Subramaniam in Fall. Since its upload, it has received 12 views. For similar materials see /class/228943/info-3229-university-of-north-carolina-charlotte in Management Information Systems at University of North Carolina - Charlotte.
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Date Created: 10/25/15
Chapter 2 Outline Role and expectations of Application Layer Application Architectures HostBased ClientBased and ClientServer Architectures Choosing Architectures World Wide Web How the Web Works Inside an HTTP Request amp HTTP Response Electronic Mail How EMail Works Inside an SMTP Packet Listserv Attachments in MIME Other Applications Copyright 2010 John Wiley amp Sons Inc Application Layer Introduction Applications migl n ilirl eg email web l word processing Transport Layer Network Layer Application architecture The way in which the functions of the application layer software are spread among the clients and servers on the network Functions of Application Layer Data storage Storing of data generated by programs eg files records Data access logic Processing required to access stored data eg SQL Application logic Business logic such as word processors spreadsheets Presentation logic Presentation of info to user amp acceptance of user commands Copyright 2010 John Wiley amp Sons Inc 2 2 Clients and Servers Clients Servers Microcomputer Mainframe Terminal Microcomputer Network computer Cluster Transaction terminal Virtua server Handheld Middleware Makes life easier for clients amp servers to communicate Copyright 2010 John Wiley amp Sons Inc 2 3 Application Architectures Determined by how functions of application programs are spread among clients and servers Hostbased Architectures Server performs almost all functions Clientbased architectures Client performs most functions Clientserver architectures Functions shared between client and server Copyright 2010 John Wiley amp Sons Inc 2 4 HostBased Architectures Server ient mainframe camp39utrer iE i mi il Tal j or a PC running a 7 a a terminal emulation program a J 1 Cient captu res key strokes FmsE t then sends them to the y 7 an lagquot mainframe ppl l aatl n I le Client displays information Data 333353 I319 according to the server s Data gtgragg instructions 39 39 Copyright 2010 John Wiley amp Sons Inc 2 5 Hostbased Architecture Problems Host becoming a bottleneck All processing done by the host which can severely limit network performance Host upgrades typically expensive and lumpy Available upgrades require large scale and often costly jumps in processing and memory Network demand grows more incrementally than does the host capacity May see poor fit too much or too little between host performance and network demand Copyright 2010 John Wiley amp Sons Inc 2 ClientBased Architectures Client f Sewer mi cmrz mputary micmmrnwpmen M w 4 wili i EfSQEL iLUSiQEKZTSLPC L 2nd storing zlata f les on a 39 server Presentatiqn Ingeicz atasi rage RDDI IEH HM Iag ir Data amass 139i Copyright 2010 John Wiley amp Sons Inc 2 ClientBased Architecture Problems Data traffic must travel back and forth between server and client Example when the client program is making a database query the ENTIRE database must travel to the client before the query can be processed Often the large file sizes moving across the LAN can yield a poor result in network performance Copyright 2010 John Wiley amp Sons Inc 2 8 ClientServer Architectures Client Server PC mini mainframe Piaaantatian lagia Applicationlagia Example Using a Web browser to obtain web pages uses logic balanced between a a the client and server 399 quot Data acaaaa logic Dataataraga Copyright 2010 John Wiley amp Sons Inc 2 9 ClientServer Architectures Advantages More efficient because of distributed processing Allow hardware and software from different vendors to be used together Disadvantages Difficulty in getting software from different vendors to work together smoothly May require Middleware a third category of software Copyright 2010 John Wiley amp Sons Inc 10 Middleware client application programs a standard I I I I I I Manages way of l I message translating traquot3fers b tw l VFQ MII I Z W G e een IIULQAQJE k JfIg nsuates network 15301 tw cll39e changes from the rofm l clients eg 0quot erent I I I I I I adding a new vendors server application programs server Examples of standards for Middleware Distributed Computing Environment DCE Common Object Request Broker Architecture CORBA Open Database Connectivity ODBC Copyright 2010 John Wiley amp Sons Inc 2 11 Multitier Architectures Involve more than two computers in distributing application program logic 2tier architecture Uses clients and servers in a balance very popular approach in simple LANs 3tier architecture 3 sets of computers involved Ntier architecture More than three sets of computers used more typical across complex organizations Allows load balancing across servers Copyright 2010 John Wiley amp Sons Inc 12 3tier Architecture Databasa SEWET Applicatinn micrmmputan Client aewar minimmputer micmcumpmm rnirir cmmputm Dr mainframe Presentati n I gic applicati n Vl g xitr Damaamaal ghc Dalastmage Copyright 2010 John Wiley amp Sons Inc 2 13 Ntier Architecture Client A Web server microcomputer microcomputer In Presentation logic Application 1091 Database Server microcnmputen Applicatian server minimmpgter micmccmpu t 7 or mainframe D23 I 19 39 39 7 Applicatign I Ggic Data amass logic Data storage Copyright 2010 John Wiley amp Sons Inc 2 14 Multitier Architectures Advantages Better load balancing More evenly distributed processing eg application logic distributed between several servers More scalable Only servers experiencing high demand need be upgraded Disadvantages Heavily loaded network More distributed processing necessitates more data exchanges Difficult to program and test due to increased complexity Copyright 2010 John Wiley amp Sons Inc 2 15 Thin and Thick Clients Classification depends on how much of the application logic resides on the client or server Thin client Little or no application logic on client Becoming popular because easier to manage only the server application logic generally needs to be updated The best example World Wide Web architecture uses a twotier thin client architecture Thick client All or most of the application logic resides on the client Copyright 2010 John Wiley amp Sons Inc 16 ThinClient Example Web Architecture Client Web Server PC mini mainframe Presentation logic Application Lic Data Access logic Data Storage Copyright 2010 John Wiley amp Sons Inc 2 17 Peer to Peer Architecture All computers can serve as a client and a server Increased popularity in the last decade due to the rise of P2P services such as Napster Advantages Data can be stored anywhere on the network Very resilient to failure Disadvantages Finding data Security Copyright 2010 John Wiley amp Sons Inc 2 18 Criteria for Choosing Architecture Infrastructure Cost Cost of servers clients and circuits lVlainframes very expensive terminals PCs Inexpensive Development Cost Mainly cost of software development Software expensive to develop offtheshelf software Inexpensive Scalability Ability to increase or decrease in computing capacity as network demand changes Mainframes not scalable PCs highly scalable Copyright 2010 John Wiley amp Sons Inc 2 19 Choosing an Architecture HostBased ClientBased ClientServer Cost of lnfrastructu re High Medium Low Cost of Development Low Medium Medium Scalability Low Medium High Copyright 2010 John Wiley amp Sons Inc 2 20 Applications Layer Examples World Wide Web Email File Transfer Videoconferencing Instant Messaging Copyright 2010 John Wiley amp Sons Inc 21 World Wide Web Web began with two innovative ideas Hypertext A document containing links to other documents Uniform Resource Locators URLs A formal way of identifying links to other documents Invention of WW 1989 By Tim BernersLee at CERN in Switzerland First graphical browser Mosaic 1993 By Marc Andressen at NCSA in USA later founded Netscape CERN Conseil Europ en pour la Recherche Nucl aire B eeeee sLee T 2000 Weaving the Web NewYork HarperCullins P 4 NCSA National Center for Supercomputing Applications Copyright 2010 John Wiley amp Sons Inc 2 22 How the Web Works Main Web communications protocol Server Computer HTTP Hypertext Transfer Protocol Web Sewer l re HTTP Request 7 Emma Client Computer i a 3 r I a r WED Er ws er l internal quot1 H 139 39quot39quotquotquot quotIuh Mull quot i HTTP Response A requestresponse cvcle includes multiple steps since web Clicking on a hyperlink or pages often contaInembeded typing a URL into a browser f39les sUCh as graph39cs eac starts a requestresponse cycle requ39r39quot9 a separate response39 Copyright 2010 John Wiley amp Sons Inc 2 23 HTTP Request Message Request line command URL HTTP version number requ39red If the user types in the Request header optional 3122 es information on the browser v f thequot the date and the re errIng page referring page is blank Request body information sent to the server Optional such as from a form Copyright 2010 John Wiley amp Sons Inc 2 24 Example of an HTTP Request RequestUne GET adrennishomehtm HTTP11 igt HOST wwwkelleyiuedu DATE Mon 07 Aug 2006 173546 GMT User Agent Mozilla40 meegHemmr Referrer httpwwwindianaeduisdeptfacu1tyhtm Note that this HTTP Request message has no Body part Copyright 2010 John Wiley amp Sons Inc 2 25 HTTP Response Message Response status http version number status code reason Optlonal Response header op onal information on the server date URL of the page retrieved format used Response body required requested web page Copyright 2010 John Wiley amp Sons Inc 2 26 Example of an HTTP Response Response Slams RPSHOHS Hamlet HTTP1 1 200 OK Data Mon 07 Aug 200 173602 9 Senrer Apache Location httpm kallay indinna aduardannisham hm texthm Contentr l ype Response Bouy lttit1egthlan R Dennisltltitlegt ltheadgt ltbodygt ltH2gtAlan R Dennis ltH2gt ltPgtWelcome to the ham pnga of Alan Dennisltlpgt ltbodygt lthtm1gt Copyright 2010 John Wiley amp Sons Inc HTML Hypertext Markup Language A language used to create Web pages Also developed at CERN initially for text files Tags are embedded in HTML documents include information on how to format the file Extensions to HTML needed to format multimedia files XML Extensible Markup Language A new markup language becoming popular Copyright 2010 John Wiley amp Sons Inc 2 28 Email Standards SMTP Simple Mail Transfer Protocol Main email standard for Originating user agent and the mail transfer agent Between mail transfer agents Originally written to handle only text files Usually used in twotier clientserver architectures Post Office Protocol POP and Internet Mail Access Protocol IMAP Main protocols used between the receiver user agent and mail transfer agent Main difference with IMAP messages can be left at the server after downloading them to the client Other competing standards Common Messaging Calls CMC X400 Copyright 2010 John Wiley amp Sons Inc 2 29 TwoTier Email Architecture User agent is another word for an email client application Run on client computers Send email to email servers Download email from mailboxes on those servers Examples Eudora Outlook Netscape Messenger Mail transfer agent is another word for the mail server application Used by email servers Send email between email servers Maintain individual mailboxes Copyright 2010 John Wiley amp Sons Inc 30 Host Based email Architectures An old method used on UNIX based hosts Similar to clientserver architecture except Client PC replaced by a terminal or terminal emulator Sends all keystrokes to the server Display characters received from the server All software resides on the server Takes client keystrokes and understand user s commands Creates SMTP packets and sends them to next mail server Useful when traveling in locations with poor internet facilities Copyright 2010 John Wiley amp Sons Inc 2 31 Webbased email Server computer with HTTP vquotr 39quotl39 Web server Client computer requeSt fquotquot quotquotquotquot f software Web browser LAN SMTP packet I Server computer wrth quot email server software response packet Internet SMTP paCket Server computer HTTP gt39 with email server Client computer request r software with web browser gee response packet wegierver g so are 232 Copyright 2010 John Wiley amp Sons Inc Sample SMTP Message FROM quotAlan Dennisquot ltardennisindianaedugt To quotPat Someonequot ltsomeonesomewherecomgt DATE Mon 07 Aug 2006 190303 GMT SUBJECT Sample Note ATA This is an example of an e mail message Note that this SMTP message has no attachments Copyright 2010 John Wiley amp Sons Inc massageID lt4120000623164823009f5e80IMAPIUEDUgt Header Body Multipurpose Internet Mail Extension A graphics capable mail transfer agent protocol to send graphical information in addition to text SMTP was designed years ago for text transfer only MIME software is included as part of an email client Translates graphical information into text allowing the graphic to be sent as part of an SMTP message as a special attachment Receiver s email client then translates the MIME attachment from text back into graphical format MIME example Copyright 2010 John Wiley amp Sons Inc 2 34 Listserv Discussion Groups Mailing lists of users who join to discuss some special topic eg cooking typing networking Some permit any member to post messages some are more restricted Parts of listserv Listserv Processor Processes commands Listserv Mailer Receives and distributes messages Example Learning Technology Newsletter To subscribe send the message subscribe LEARNINGTECHNOLOGY ltYour Email Addressgt to majordomomaiordomoieeeorq To send email thelistmaiordomoieeeorg Copyright 2010 John Wiley amp Sons Inc 2 35 File Transfer Protocol FTP Enables sending and receiving files over the Internet Requires an application program on the client computer and a FTP server program on a server Commonly used today for uploading web pages Many packages available using FTP WSFTP a graphical FTP software FTP sites Closed sites Requires account name and password Anonymous sites Account name anonymous password email address Copyright 2010 John Wiley amp Sons Inc 2 36 Telnet Allows one computer to log into another computer Remote login enabling full control of the host Requires an application program on the client computer and a Telnet server program on the server Client program emulates a dumb terminal off the server Many packages available conforming Telnet EWAN Requires account name and password Anonymous sites similar to FTP approach Account name anonymous password email address Copyright 2010 John Wiley amp Sons Inc 2 37 Instant Messaging IM A clientserver program that allows realtime typed messages to be exchanged Client needs an IM client software Server needs an IM server package Some types allow voice and video packets to be sent Like a telephone Examples include AOL and ICQ Two step process Telling IM server that you are online Chatting Copyright 2010 John Wiley amp Sons Inc 2 38 How Instant Messaging Works Client computer v packet with email client software 1 LAN Sender sends a request to the IM server telling it that sender is online Ifafriend connects the IM server sends39a packet to sender s IM client and vice versa Client computer with IM client software Internet IM packet LAN When the sender types in text the IM client sends the text in a packet to the IM server which relays it to the receiver computerwith witth LAN 7 f server software IM packet If a chat session has more than two clients multiple packets are sent by the IM server IM servers can also relay information to other IM servers Copyright 2010 John Wiley amp Sons Inc Videoconferencing Provides real time transmission of video and audio signals between two or more locations Allows people to meet at the same time in different locations Saves money and time by not having to move people around Typically involves matched special purpose rooms with cameras and displays Desktop videoconferencing Low cost application linking small video cameras and microphones together over the Internet No need for special rooms Example Net Meeting software on clients communicating through a common videoconference server Copyright 2010 John Wiley amp Sons Inc 2 40 Videoconferencing Standards Proprietary early systems Common standards in use today H320 Designed for roomtoroom videoconferencing over highspeed phone lines H323 Family of standards designed for desktop videoconferencing and just simple audio conferencing over Internet MPEG2 Designed for faster connections such as LAN or privately owned WANs Copyright 2010 John Wiley amp Sons Inc 41 Implications for Management Network may be used to provide a worryfree environment for applications Network is the critical infrastructure over which the wide variety of strategic applications enable an organization to compete in its environment The applications running on the network have the potential for changing the organization Dramatic increase in number and type of applications Rapid growth in amount and type of networking traffic over time Different implication on network design and management Increased operating cost for the network function Copyright 2010 John Wiley amp Sons Inc 2 42 Plan for Chapter 1 82510 Brief history of Data Communications Network Components and Types Internet Intranet Extranet The Layered Communications Model Standards and Protocols Trends in Data Communications Management Implications Copyright 2010 John Wiley amp Sons Inc The Collapsing Information Lag sped up the rate and volume of transmission of information telegraph 11850 1900 1950 2009 gt Information took days InIormation large quantities of or weeks to be transmitted in information transmitted in transmitted minutes or hours a fraction of a second J 1 irew im Ugmmmmu Globalization of networks Copyright 2010 John Wiley amp Sons Inc Advances in Phone Technology firsttrans Te39Sta39 continental Telecommunications packetswitched and via satellite Fax data transatlantlc services digital communications Phone phone transmission T invented quotquote t39 quots carriers 1 12276 1935 1948 19552 1976 gt 39 39 19i9 T 39 199 39 19534 Strowger stepper Microwave l switch trunk39mes Picturefone Cellular rotarydial phones canada failed telephone enabling automatic connections commercially Copyright 2010 John Wiley amp Sons Inc 1 3 US Telecom Act of 1996 Replaced all current laws FCC regulations 1984 consent decree and overrules state laws Main goal open local markets to competition To date though local and long distance competition slow to take hold Large lXCs expected to move into the local markets happening only recently Likewise RBOCs expected to move into long distance markets happening only recently Copyright 2010 John Wiley amp Sons Inc 1 Emergence of Internet NSFNet commercial Originally called created as access to ARPANET the Internet US Internet began as a military the Internet academic network bacjbone begins 19 9 19 3 19 6 1990 1994 2097 ARPANET splits Government Worldwide Milnet for military funding of the over 1 billion Internet academic backbone Internet users education and research ends purposes only Copyright 2010 John Wiley amp Sons Inc 1 5 History of Information Systems Online realtime Batch transaction oriented PC LANS processing systems replaced batch become mainframes Processmg DBMSS common become common 1 19350 19550 1970 19 o 1990 2090 gt PC revolutlon Data communlcatlons over Networklng phone lInes became everywhere common and mainframes became multiuser systems Copyright 2010 John Wiley amp Sons Inc 1 6 Datacomm Convergence Telecommunications Transmission of voice video andor data Implies longer distances Broad term Data Communications Movement of computer information by means of electrical or optical transmission systems convergence Broadband Communications Copyright 2010 John Wiley amp Sons Inc Components of a Local Area Network To other networks eg Internet Servers 7 Client Computers Circuits 7 Printer Copyright 2010 John Wiley amp Sons Inc 1 8 Network Types based on Scale Local Area Networks LAN room building a group of PCs that share a circuit Backbone Networks BN less than few kms a high speed backbone linking together organizational LANs at various locations Metropolitan Area Networks MAN more than a few kms connects LANs and BNs across different locations Often uses leased lines or other services used to transmit data Wide Area Networks WANs far greater than 10 kms Same as MAN except wider scale Copyright 2010 John Wiley amp Sons Inc 1 9 The InterNetwork v m MKS met He He RC ulev C1 We sews HUB me E sewEv HUB ab Chem sews W mme39s W Chem e3 sewe1 computevs Punter PHH sewev Pnrtev 7 jun 39 L sewEv 7 V Intranet vs Extranet Intranet A LAN that uses the Internet technologies within an organization Open only those inside the organization Example insurance related information provided to employees over an intranet Extranet A LAN that uses the Internet technologies across an organization including some external constituents Open only those invited users outside the organization Accessible through the Internet Example Suppliers and customers accessing inventory information in a company over an extranet Copyright 2010 John Wiley amp Sons Inc 1 11 Layered Communications Model n 0 Single layer 3 implementation 3 2 Networking with a 1 large components 3 g is complex to g g understand and 393 implement Multi layer implementation Breaking down into smaller components Easier to implement Copyright 2010 John Wiley amp Sons Inc 1 12 Multilayer Network Models The two most important such network models OSI and Internet Open Systems Interconnection Model Created by International Standards Organization ISO as a framework for computer network standards in 1984 Based on 7 layers Internet Model Created by DARPA originally in early 70 s Developed to solve to the problem of internetworking Based on 5 layers Based on Transmission Control Protocol Internet Protocol TCPIIP suite Copyright 2010 John Wiley amp Sons Inc 1 13 Message Transmission Example Sender Receiver AppIication Application mm mm Layer TCP HTTP TCF HTTP Request V quot New 39 Layer IP TCP HTrP Layer IFquot TCP m rp gt 3quot quot D quotquot Layer Ethernet F TOP HTI39P Layer Ethernet llP TCP H39I I39P Physicai m Physidal Layer Copyright 2010 John Wiley amp Sons Inc 1 14 7Layer Model of OSI I Physicall INetworkITransport ISession IPresentation Ikppllication Elease ot Iouch teve s Eef alligatorsquot Application Layer set of utilities used by application programs Presentation Layer formats data for presentation to the user provides data interfaces data compression and translation between different data formats Session Layer initiates maintains and terminates each logical session between sender and receiver Copyright 2010 John Wiley amp Sons Inc 1 15 7Layer Model of OSI Transport Layer deals with endtoend issues such as segmenting the message for network transport and maintaining the logical connections between sender and receiver Network Layer responsible for making routing decisions Data Link Layer deals with message delineation error control and network medium access control Physical Layer defines how individual bits are formatted to be transmitted through the network Copyright 2010 John Wiley amp Sons Inc 1 16 Internet s 5Layer Model IPhysicalI INetworkITransportIApplicatiOIn Elease o r Iouch Alligators Application Layer used by application program Transport Layer responsible for establishing endtoend connections translates domain names into numeric addresses and segments messages Network Layer same as in OSI model Data Link Layer same as in OSI model Physical Layer same as in OSI model Copyright 2010 John Wiley amp Sons Inc 1 17 Communications over Internet Network Connections Host Host A Router Router B Stack Connections Application 4 A A A gt Application 1 Peertopeer T Transport 4 A A gt Transport Internet Internet Internet Internet Link Link Link Link L Fiber J Ethernet Satellite Ethernet e C Image source wwwwikipediaorg 1 18 Comparison of Network Models 08 Model Internet Model Groups of Layers Examples 7 Application Layer Application Internet Explorer 6 Presentation Layer 5 Appllcatron Layer Layer and Web pages 5 Session Layer 4 Transport Layer 4 Transport Layer quotteigezrwk TCPIP Software 3 Network Layer 3 Network Layer y 2 Data Link Layer 2 Data Link Layer Ethernet Po Hardware Ethernet cables Layer and Ethemei 1 Physical Layer 1 Physical Layer software drivers Copyright 2010 John Wiley amp Sons Inc Pros and Cons of Layers Layers allow simplicity of networking in some ways Easy to develop new software that fits each layer Relatively simple to change the software at any level Matching layers communicate between different computers and computer platforms Accomplished by standards that we all agree on eg Physical layer at the sending computer must match up with the same layer in the receiving computer Somewhat inefficient Involves many software packages and packets Packet overhead slower transmission processing time Interoperability achieved at the expense of perfectly streamlined communication Copyright 2010 John Wiley amp Sons Inc 1 20 Standards Importance Provide a fixed way for hardware andor software systems different companies to communicate Help promote competition and decrease the price Types of Standards Formal standards Developed by an industry or government standards making body Defacto standards Emerge in the marketplace and widely used Lack official backing by a standardsmaking body Copyright 2010 John Wiley amp Sons Inc 1 21 Some Data Comm Standards Layer 5 Application layer Common Standards HTTP HTML Web MPEG H323 audiovideo IMAP POP email TCP Internet 4 Trans ort la er p y SPX Novell LANs 3 Network layer IP Internet IPX Novell LANs Ethernet LAN 2 Data link layer Frame Relay WAN 1 Physical layer T1 MAN and WAN RS232c cable LAN Category 5 twisted pair LAN V92 56 kbps modem Copyright 2010 John Wiley amp Sons Inc 22 Emerging Trends in Networking Pervasive Networking Integration of Voice Video and Data New Information Services Cloud Computing Locationbased Services Convergence of Mobile and Fixed Services Copyright 2010 John Wiley amp Sons Inc 1 23 Implications for Management Embrace change and actively seek to use new aspects of networks toward improving your organization Information moved quickly and easily anywhere and anytime Information accessed by customers and competitors globally Use a set of industry standard technologies Can easily mix and match equipment from different vendors Easier to migrate from older technologies to newer technologies Smaller cost by using a few well known standards Copyright 2010 John Wiley amp Sons Inc 24
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