Computer networks--network

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  • 1. 15-1Networking• Computer network A collection ofcomputing devices that are connected invarious ways in order to communicate andshare resourcesUsually, the connections betweencomputers in a network are made usingphysical wires or cablesHowever, some connections are wireless,using radio waves or infrared signals
  • 2. 15-2Networking• The generic term node or host refers toany device on a network• Data transfer rate The speed with whichdata is moved from one place on anetwork to another• Data transfer rate is a key issue incomputer networks
  • 3. 15-3Networking• Computer networks have opened up anentire frontier in the world of computingcalled the client/server modelFigure 15.1 Client/Server interaction
  • 4. 15-4Networking• File server A computer that stores andmanages files for multiple users on anetwork• Web server A computer dedicated toresponding to requests (from the browserclient) for web pages
  • 5. 15-5Types of Networks• Local-area network (LAN) A networkthat connects a relatively small number ofmachines in a relatively closegeographical area
  • 6. 15-6Types of Networks• Various configurations, called topologies, havebeen used to administer LANs– Ring topology A configuration that connects allnodes in a closed loop on which messages travel inone direction– Star topology A configuration that centers aroundone node to which all others are connected andthrough which all messages are sent– Bus topology All nodes are connected to a singlecommunication line that carries messages in bothdirections
  • 7. Types of Networks• A bus technology called Ethernet has become theindustry standard for local-area networksFigure 15.2 Various network topologies15-10
  • 8. 15-8Types of Networks• Wide-area network (WAN) A network thatconnects two or more local-area networks over apotentially large geographic distanceOften one particular node on a LAN is set up to serveas a gateway to handle all communication goingbetween that LAN and other networksCommunication between networks is calledinternetworkingThe Internet, as we know it today, is essentially theultimate wide-area network, spanning the entire globe
  • 9. 15-9Types of Networks• Metropolitan-area network (MAN) Thecommunication infrastructures that havebeen developed in and around large cities
  • 10. 15-10So, who owns the Internet?Well, nobody does. No single person orcompany owns the Internet or evencontrols it entirely. As a wide-areanetwork, it is made up of many smallernetworks. These smaller networks areoften owned and managed by a person ororganization. The Internet, then, is reallydefined by how connections can be madebetween these networks.
  • 11. 15-11Types of NetworksFigure 15.1 Local-area networks connected across a distance tocreate a wide-area network
  • 12. 15-12Internet Connections• Internet backbone A set of high-speednetworks that carry Internet trafficThese networks are provided bycompanies such as AT&T, GTE, and IBM• Internet service provider (ISP) Acompany that provides other companiesor individuals with access to the Internet
  • 13. 15-13Internet Connections• There are various technologies available that you canuse to connect a home computer to the Internet– A phone modem converts computer data into an analogaudio signal for transfer over a telephone line, and then amodem at the destination converts it back again into data– A digital subscriber line (DSL) uses regular copper phonelines to transfer digital data to and from the phone company’scentral office– A cable modem uses the same line that your cable TVsignals come in on to transfer the data back and forth
  • 14. 15-14Internet Connections• Broadband A connection in which transferspeeds are faster than 128 bits per second– DSL connections and cable modems are broadbandconnections– The speed for downloads (getting data from theInternet to your home computer) may not be the sameas uploads (sending data from your home computerto the Internet)
  • 15. Packet Switching• To improve the efficiency of transferring information overa shared communication line, messages are divided intofixed-sized, numbered packets• Network devices called routers are used to directpackets between networksFigure 15.4Messagessent bypacketswitching15-18
  • 16. 15-16Open Systems• Proprietary system A system that usestechnologies kept private by a particularcommercial vendorOne system couldn’t communicate with another,leading to the need for• Interoperability The ability of software andhardware on multiple machines and frommultiple commercial vendors to communicateLeading to• Open systems Systems based on a commonmodel of network architecture and a suite ofprotocols used in its implementation
  • 17. 15-17Open Systems• The InternationalOrganization forStandardization (ISO)established the OpenSystemsInterconnection (OSI)Reference Model• Each layer deals with aparticular aspect ofnetwork communicationFigure 15.5 The layers of the OSI Reference Model
  • 18. 15-18Network Protocols• Network protocols are layered such thateach one relies on the protocols thatunderlie it• Sometimes referred to as a protocolstackFigure 15.6 Layering of key network protocols
  • 19. 15-19TCP/IP• TCP stands for Transmission Control ProtocolTCP software breaks messages into packets,hands them off to the IP software for delivery,and then orders and reassembles the packetsat their destination• IP stands for Internet ProtocolIP software deals with the routing of packetsthrough the maze of interconnected networksto their final destination
  • 20. 15-20TCP/IP (cont.)• UDP stands for User Datagram Protocol– It is an alternative to TCP– The main difference is that TCP is highlyreliable, at the cost of decreasedperformance, while UDP is less reliable, butgenerally faster
  • 21. 15-21High-Level Protocols• Other protocols build on the foundationestablished by the TCP/IP protocol suite– Simple Mail Transfer Protocol (SMTP)– File Transfer Protocol (FTP)– Telnet– Hyper Text Transfer Protocol (http)
  • 22. 15-22MIME Types• Related to the idea of network protocolsand standardization is the concept of afile’s MIME type– MIME stands for Multipurpose Internet MailExtension– Based on a document’s MIME type, anapplication program can decide how to dealwith the data it is given
  • 23. 15-23MIME TypesFigure 15.7Someprotocols andthe ports theyuse
  • 24. 15-24Firewalls• Firewall A machine and its software thatserve as a special gateway to a network,protecting it from inappropriate access– Filters the network traffic that comes in,checking the validity of the messages asmuch as possible and perhaps denying somemessages altogether– Enforces an organization’s access controlpolicy
  • 25. 15-25FirewallsFigure 15.8 A firewall protecting a LAN
  • 26. 15-26Network Addresses• Hostname A unique identification thatspecifies a particular computer on theInternetFor examplematisse.csc.villanova.educondor.develocorp.com
  • 27. 15-27Network Addresses• Network software translates a hostnameinto its corresponding IP addressFor example205.39.145.18
  • 28. 15-28Network Addresses• An IP address can be split into– network address, which specifies a specific network– host number, which specifies a particular machine inthat networkFigure 15.9An IP address isstored in fourbytes
  • 29. 15-29Domain Name System• A hostname consists of the computer namefollowed by the domain name• csc.villanova.edu is the domain name– A domain name is separated into two or moresections that specify the organization, and possibly asubset of an organization, of which the computer is apart– Two organizations can have a computer named thesame thing because the domain name makes it clearwhich one is being referred to
  • 30. 15-30Domain Name System• The very last section of the domain is called itstop-level domain (TLD) nameFigure 15.10 Top-level domains, including some relatively new ones
  • 31. 15-31Domain Name System• Organizations based in countries other than theUnited States use a top-level domain thatcorresponds to their two-letter country codesFigure 15.11Some of the top-level domainnames based on country codes
  • 32. 15-32Domain Name System• The domain name system (DNS) ischiefly used to translate hostnames intonumeric IP addresses– DNS is an example of a distributed database– If that server can resolve the hostname, itdoes so– If not, that server asks another domain nameserver