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Date Created: 11/01/15
MIS 301 Study Guide Chapter 1 Introduction to Data Communications Exam 1 Data Communication Networks a n 039 Data Communications movement of computer information from one point to another via electrical or optical transmission systems ex data communication networks Telecommunications includes transmission of voice video data over long distances Components of a Networks 3 hardware components Server host computer stores data software that can be accessed by clients Several can work together over network w client computer to support business application 1 Typically microcomputers can be minicomputers or mainframes 2 Client inputoutput hardware device at user s end of a communication circuit Not technically necessary on all networks ie peertopeer networks provides users with access to network and software on the server Circuit pathway that messages travel Typically copper wire fiberoptic and wireless are becoming common LAN Network To other neworks e g me inxemei File server Chem compuiers Clients 4 microcomputers Circuit hub and cables Router connects two or more networks File Server stores data software Print Server manages printing requests from clients NP P PP P Web Server stores documents graphics that can be accessed from a web browser can respond from requests from networks on any computer on internet d Types of Networks i Local Area Network LAN group of microcomputers located in same general area 1 Covers clearly defined small area ie one floor single building etc Use shared circuits computers take turns to use Support highspeed data transmission lOOMbps Most connected to a backbone network BN 2 3 4 5 Intranet LAN private to those wo access used in organizations MIS 301 Study Guide I Network Models Exam 1 Chapter 1 Introduction to Data Communications 6 Extranet provided to users outside organization provides info to those privy ie usernamepassword protected Backbone Network BN larger central network connecting several LANS other BN s MANs WANs 1 Span from 100ft to several miles 2 Very high speed data transmission 1001000Mbps Metropolitan Area Network MAN connects LANs BNs located in different areas to each other also connects to WANs 1 Span bw 330miles 2 Moderately fast data transmission costly to install operate over long distances Wide Area Networks WANs connect BNs and MANs 1 Companies lease circuits from IXCs ATampT MCI Sprint etc 2 Span hundreds to thousands of miles 3 Data transmission rates from 64Kbps to lonps l OSI Model Internet Model Groups of Layers Examples 7 Application Layer Application Internet Explorer P L s reseniation ayer 5 Appllcalian Layer Layer and Web pages 5 Session Layer 4 Transport Layer 4 Transport Layer 39quot equot r39 k TCPIP Software 3 Network Layer 3 Network Layer ya 2 Data Link Layer 2 Data Link Layer Ememe pon Hardwane Ethernet cables Layer and Ethemez 1 Physical Layer 1 Physical Layer Schwara ddvers a b OSI Model Open Systems Interconnection Reference Model E lt S 5 viii Created by ISO International Organization for Standardization 1984 Framework of standards for CZC communication Not widely used not adopted however is most talked about and referred to network model Physical Layer 1 Defines data bit 0110010 rules for transmission ex voltages of electricity bits per second etc Data Link Layer 1 Corrects transmission errors from Physical Layer marks message boundaries 2 Performs error detection and correction 3 Decides transmit times so two computers don t transmit at same time Network Layer 1 Performs routing Transport Layer 1 Procedures for enteringleaving network 2 Reduces packet size eliminates duplicate packets etc 3 Can perform error correction as in Data Link layer Session Layer 1 Managesstructuresall sessions 2 Handles session accounting so correct party receives bill MIS 301 Study Guide Exam 1 Chapter 1 Introduction to Data Communications ix Presentation Layer 1 Formats data for presentation to user 2 Accommodates different interfaces on different terminalscomputers so the application program need not worry about them a Displaying formatting editing user inputs and outputs x Application Layer 1 End user s access to the network 2 Ex web browser c Internet Model i Most widely used model Message Transmission Using Layers a Protocol a set of rules that define what the layer will do and that provides a clearly defined set of messages that software at the layer needs to understand i Ex HTTP b Protocol Data Unit PDU i Contains information needed to transmit the message through a network ie Packet Sender PDU Receiver Application packer Application Layer Layer Transport Transpun Layer Segment Layer l Netwark Nslwnrk Law Packet Layer Darn Link Dim Link Layer Fame L Physical ML Physical Layer Layer Ell C IV Network Standards Layer Common Standards 5 Application layer HTTP HTML Web MPEG H323 audiovideo SMTP IMAP POP email 4 Transport layer TCP Internet and LANS SPX Novell LANs 3 Network layer IP Internet and LANs PX Novel LANs 2 Data link layer Ethernet LAN Frame relay WAN T1 MAN and WAN Gate 0 I v92 56 Kbp s mo ldem MIS 301 Study Guide Exam 1 Chapter 2 Application Layer I Application Architectures a The way in which the functions of the application layer software are spread among the clients and servers in the network b 4 Application Program Functions four basic building blocks to any application Data Storage Data Access Logic processing required to access data ie SQL Application Logic business logic 2 Presentation Logic presentation of info to the user and acceptance of the user s commands Hostbased Architectures a See pg 42 b First data communication networks in 1960 s were hostbased c The clients usually terminals enabled users to send receive messages to and from host computer server usually a mainframe computer i Client captured keystrokes sent to server for processing accepted returned instructions on what to display d Application software is developed stored on the one server along with data e Problems i Server must process all messages ie demanding workload overload l Prioritizing users access is difficult slower response time i High costs for upgrading Clientbased Architectures a See page 43 b Clients are microcomputers on a LAN server is another microcomputer on same network c Application software on client computer responsible for presentation logic application logic data access logic while server simply stores data d Ex saved a word document file on a server ie G drive e Problems i All data on the server must travel to client for processing ie run query for all employees with company life insurance 1 Can overload network circuits bc far more data is transmitted from server to client than client actually needs V ClientServer Architectures a See page 43 b Most organizations are moving to this architecture c Attempts to balance the processing between client and server by having both do some logic d Client responsible for presentation logic Server responsible for data access logic data storage i Application logic resides either on server on client or split between both e Examples i Using a web browser to get pages from a web server ii Writing a program that uses SQL to talk to a database on a server f Advantages i Enables software hardware from different vendors be used together 1 Doubleedged sword difficult to get software from diff vendors to work together MIS 301 Study Guide Exam 1 Chapter 2 Application Layer a Solution middleware software that sits between application software on client and application software on server i Provides a standard way of communicating that translates between different softwa res ii Manages message transfer from clients to servers vice versa so clients need not know specific server that contains the applications data g TwoTier ThreeTier and nTier Architectures i TwoTier only two sets of computers one set of clients and one set of servers ii ThreeTier three sets of computers see page 45 1 Software on client computer responsible for presentation logic 2 Application server responsible for application logic 3 DB server responsible for data access logic data storage iii nTier 1 See page 46 2 Uses 4 sets of computers 3 Client responsible for presentation logic DB server responsible for data access logic and data storage application logic spread across 2 different sets of computers 4 TCBWorks groupware product 4 Major Components a 1 Web Browser on client computer i Used to access the system and enter commands presentation logic b 2 Web Server i Responds to users requests by providing HTML pages and graphics application logic or by sending request to third component c 3 Set of 38 C programs i Perform various functions such as adding comments or voting application logic d 4 DB Server i Stores all data data access logic data storage e Each component is separate thus easy to spread different components on different servers and to partition the application logic on two different servers 5 Advantage over two or three tier a Separates out processing that occurs to better balance the load on the different servers more scalable 6 Disadvantages over two or three tier a Puts a greater load on the network requires more communication among servers generating more network traffic thus needing a high capacity network b Increased difficulty to program and test software more devices must communicate to complete a user s transaction h Thin Clients vs Thick Clients MIS 301 Study Guide Exam 1 Chapter 2 Application Layer Methods of classifying clientserver architectures by examining level of application logic placed on client computer ThinClient 1 Places little to no application logic on client see Fig 25 pg 46 2 Easier to manage if an application changes only server with the application logic needs to be updated 3 The Web is one of the biggest forces favoring thin clients ThickClient 1 Places all or almost all of the application logic on client 2 Software on all of the clients would need to be updated V PeertoPeer Architectures P2P a Old but modern design became popular early 200 s with P2P file sharing apps ie Napster b All computers act as both a client and server thus all computers perform all 4 functions c User uses the presentation application data logic installed on their computer to access data stored on another computer in the network d Advantage i Data can be installed anywhere on network storage spread throughout network thus resilient to failure of any one computer Only challenge is finding the data 1 Need a central server enabling one to find data you need a Thus often combined with a clientserver architecture e Disadvantage i Security concern thus not used in most organization except for specialized computing needs ie grid computing VI Choosing between Architectures see Fig 23 pg 48 a Cost of Infrastructure b Cost of Development c Scalability I World Wide Web a Web is a TwoTier clientserver architecture V i Each client computer needs an application layer software ie Web Browser ii Each server on network that will act as a Web Server needs an application layer software package ie Web Server b Need protocol for requests from Web browser to be understood by the Web server i HTTP Hypertext Transfer Protocol ii Web browser issues an HTTP request a special packet to Web server which receives and processes request sends back an HTTP response either requested page or error message see Fig 29 pg 49 SO 1 Occurs for every file transferred between client server 2 Ex Web page with 2 graphics 3 requestresponse pairs one for web page two separate s for both graphics c Inside an HTTP Request Fig 210 pg 51 i 3 parts lSt two parts required 3rd part optional 1 Request Line a Provides the Web page and ends with HTTP version number that the browser understands 2 Request Header MIS 301 Study Guide Exam 1 Chapter 2 Application Layer a Optional information including Web browser used and date 3 Request Body a Contains information sent to server ie info the user has typed into a form d Inside an HTTP Response Fig 211 pg 52 i 3 parts lSt two required 3rd part optional 1 Response Status a HTTP version number the server used b A status code 200 means Okay 404 means not found c Reason phrase text description of status code 2 Response Header a Optional information such as Web server used date exact URL of page in the response 3 Response Body a The Web page itself V Electronic Mail a One of earliest applications on internet b Several standards developed to ensure compatibility between different email software packages i Many email packages send using one standard but can understand messages sent in other standards ii SMTP Simple Mail Transfer Protocol 1 Most commonly used standard 2 Email standard used on internet 3 Usually implemented as a twotier thick clientserver application 4 Covers message transmission between mail servers and between originating email client and its mail server c How Email Works i TwoTier Email Architecture see Fig 212 pg 55 1 Each client computer runs an application layer software package Mail User Agent ie email client Outlook Eudora etc 2 User creates email message in client formats message into SMTP packet sends packet to a mail server running a Mail TransferAgent mail server software 3 Email server then reads SMTP packet to find destination address sends packet through network usually the internet from mail server to mail server until destination 4 Mail Transfer Agent on destination server stores message in receivers mailbox on that server 5 POP Post Office Protocol a Email message copied to client computers HDD then deleted from mail server 6 IMAP Internet Message Access Protocol a Email messages remain stored on mail server after they are read ii Hostbased Email Architectures 1 Client computer terminal sends all of users keystrokes to server for processing server then sends characters back to terminal for display a All software resides on server MIS 301 Study Guide Exam 1 Chapter 2 Application Layer b Software takes user s keystrokes creates SMTP packet sends it to next mail server 39ii ThreeTier Thin ClientServer Architecture see Fig 213 pg 57 1 Uses a Web server and Web browser to provide email access no need for email client 2 Web browser connects to page on Web server that allows one to write email message in a form a Click send information from Web browser sent to Web server inside an HTTP request b Web server runs a program C or Perl takes information from HTTP request builds SMTP packet containing email message c Web server sends SMTP packet to mail server through network until it arrives inbox d Receiver uses Web browser to send HTTP request to Web server to check mail Web server processes request sends appropriate IMAP or POP request to mail server e Mail server responds with IMAP or POP packet then a program on Web server converts HTTP response and sends to client f Client then displays email message in Web browser 3 More complicated complex than twotier a More simple than installing email client individually on each computer iv Inside an SMTP Packet see Fig 214 pg 58 1 Header a Lists source destination email addresses address itself date subject etc 2 Body a DATA message itself v Listserv Discussion Groups 1 Mailing list of users whojoined together to discuss same topic 2 2 Parts a Listserv processor processes commands ie requests to subscribe unsubscribe b Listserv mailer messages sent to listserv mailer are resent to everyone on mailing list vi Attachments in Multipurpose Internet Mail Extension 1 MIME Multipurpose Internet Mail Extension a Standard used for nontext files within emails ie graphics attachments b Exists as part of the email client c Takes nontext files translates each byte into special code that looks like regular text Encoded quottextquot is labeled with series of special fields understood by SMTP as identifying a MIMEencoded attachment and specifying info about attachment ie name file type Receivers email client recognizes MIME quottextquot uses MIME software to translate file form MIME quottextquot to original format
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