自动化系计算机网络配套全册教学课件.ppt

1、自动化系计算机网络配套全册自动化系计算机网络配套全册 教学课件教学课件 2 Computer Networking Zhu Li 3 What is network rThe architecture of interconnecting end systems rmultiple networks: mTelecommunication networks mTV networks mComputer networks r21 century is information time centralized on network mDigitalizing, networking, inform

2、ation mIndustry economy knowledge based economy rInternet is the greatest innovation of human communication from printing 4 What is this course about? Introductory (first) course in computer networking rlearn concepts of computer networking rlearn principles of computer networking rlearn practice of

3、 computer networking rInternet architecture/protocols as case study by the time you are finished Goals: rlearn a lot (not just concepts, but principles and practice) rhave fun (well, it should be interesting, at least) 5 Course Information rIntroductory (first) course in computer networking rWho is

4、this course for? mUndergrads, MS students rPrerequisites: mAlgorithms, Operating Systems, programming skills rCourse materials: mtext: Computer Networking: A Top Down Approach, J. Kurose hosts, access net, physical media rnetwork core: packet/circuit switching, Internet structure rperformance: loss,

5、 delay, throughput rsecurity rprotocol layers, service models rhistory Whats the Internet rThe Internet is a world-wide computer network rThe Internet is a public network mA network that interconnects millions of computing devices throughout the world rInternet Architecture mHardware Ends system Cor

6、es links mSoftware Protocols Networking OS 1-20 1- 21 Whats the Internet: “nuts and bolts” view rmillions of connected computing devices: hosts = end systems m running network apps Home network Institutional network Mobile network Global ISP Regional ISP router PC server wireless laptop cellular han

7、dheld wired links access points qcommunication links vfiber, copper, radio, satellite vtransmission rate = bandwidth qrouters: forward packets (chunks of data) Introduction1- 22 “Cool” internet appliances Worlds smallest web server http:/www-ccs.cs.umass.edu/shri/iPic.html IP picture frame http:/ We

8、b-enabled toaster + weather forecaster Internet phones 1- 23 Whats the Internet: “nuts and bolts” view rprotocols control sending, receiving of msgs me.g., TCP, IP, HTTP, Skype, Ethernet rInternet: “network of networks” mloosely hierarchical mpublic Internet versus private intranet rInternet standar

9、ds mRFC: Request for comments mIETF: Internet Engineering Task Force Home network Institutional network Mobile network Global ISP Regional ISP 1- 24 Whats the Internet: a service view rcommunication infrastructure enables distributed applications: mWeb, VoIP, email, games, e- commerce, file sharing

10、rcommunication services provided to apps: mreliable data delivery from source to destination m“best effort” (unreliable) data delivery 1- 25 Whats a protocol? network protocols: rmachines rather than humans rall communication activity in Internet governed by protocols rProtocols are running everywhe

11、re in the Internet, different protocols are used to accomplish different communication tasks protocols define format, order of msgs and actions taken on msg transmission, receipt 1- 26 A closer look at network structure: rnetwork edge: applications and hosts qaccess networks, physical media: wired,

12、wireless communication links qnetwork core: vinterconnected routers vnetwork of networks 1- 27 The network edge: rend systems (hosts): mrun application programs me.g. Web, email mat “edge of network” client/server peer-peer qclient/server model vclient host requests, receives service from always-on

13、server ve.g. Web browser/server; email client/server qpeer-peer model: v minimal (or no) use of dedicated servers ve.g. Skype, BitTorrent 1- 28 Access networks and physical media Q: How to connect end systems to edge router? rresidential access nets rinstitutional access networks (school, company) r

14、mobile access networks Keep in mind: rbandwidth (bits per second) of access network? rshared or dedicated? telephone networkInternet home dial-up modem ISP modem (e.g., AOL) home PC central office vUses existing telephony infrastructure vHome is connected to central office vup to 56Kbps direct acces

15、s to router (often less) vCant surf and phone at same time: not “always on” Dial-up Modem 1-29 telephone network DSL modem home PC home phone Internet DSLAM Existing phone line: 0-4KHz phone; 4-50KHz upstream data; 50KHz-1MHz downstream data splitter central office Asymmetric Digital Subscriber Line

16、 (ADSL) vAlso uses existing telephone infrastruture vup to 1 Mbps upstream (today typically 256 kbps) vup to 8 Mbps downstream (today typically 10 active at same time is less than .0004 Packet switching allows more users to use network! N users 1 Mbps link Q: how did we get value 0.0004? 1- 52 Packe

17、t switching versus circuit switching rgreat for bursty data mresource sharing msimpler, no call setup rMore users carried rexcessive congestion: packet delay and loss mprotocols needed for reliable data transfer, congestion control rPoor real time mStore and forward Is packet switching a “slam dunk

18、winner?” 1- 53 Internet structure: network of networks rroughly hierarchical rat center: “tier-1” ISPs (e.g., Verizon, Sprint, AT password: foo Man-in-the-middle attack rBad guy is inserted into the communication path between two entities mDelete or modify msgs A B Introduction1- 80 Internet History

19、 r1961: Kleinrock - queueing theory shows effectiveness of packet- switching r1964: Baran - packet- switching in military nets r1967: ARPAnet conceived by Advanced Research Projects Agency r1969: first ARPAnet node operational r1972: mARPAnet public demonstration mNCP (Network Control Protocol) firs

20、t host-host protocol mfirst e-mail program mARPAnet has 15 nodes 1961-1972: Early packet-switching principles Introduction1- 81 Internet History r1970: ALOHAnet satellite network in Hawaii r1974: Cerf and Kahn - architecture for interconnecting networks r1976: Ethernet at Xerox PARC rate70s: proprie

21、tary architectures: DECnet, SNA, XNA rlate 70s: switching fixed length packets (ATM precursor) r1979: ARPAnet has 200 nodes Cerf and Kahns internetworking principles: mminimalism, autonomy - no internal changes required to interconnect networks mbest effort service model mstateless routers mdecentra

22、lized control define todays Internet architecture 1972-1980: Internetworking, new and proprietary nets Introduction1- 82 Internet History r1983: deployment of TCP/IP r1982: smtp e-mail protocol defined r1983: DNS defined for name-to-IP- address translation r1985: ftp protocol defined r1988: TCP cong

23、estion control rnew national networks: Csnet, BITnet, NSFnet, Minitel r100,000 hosts connected to confederation of networks 1980-1990: new protocols, a proliferation of networks Introduction1- 83 Internet History rEarly 1990s: ARPAnet decommissioned r1991: NSF lifts restrictions on commercial use of

24、 NSFnet (decommissioned, 1995) rearly 1990s: Web mhypertext Bush 1945, Nelson 1960s mHTML, HTTP: Berners-Lee m1994: Mosaic, later Netscape mlate 1990s: commercialization of the Web Late 1990s 2000s: rmore killer apps: instant messaging, P2P file sharing rnetwork security to forefront rest. 50 millio

25、n host, 100 million+ users rbackbone links running at Gbps 1990, 2000s: commercialization, the Web, new apps Introduction1- 84 Internet History 2007: r500 million hosts rVoice, Video over IP rP2P applications: BitTorrent (file sharing) Skype (VoIP), PPLive (video) rmore applications: YouTube, gaming

26、 rwireless, mobility Introduction1- 85 Introduction: Summary Covered a “ton” of material! rInternet overview rwhats a protocol? rnetwork edge, core, access network mpacket-switching versus circuit-switching mInternet structure rperformance: loss, delay, throughput rlayering, service models rsecurity

27、 rhistory You now have: rcontext, overview, “feel” of networking rmore depth, detail to follow! Exercises In a new network installation, the network administrator has decided to use a medium that is not affected by electrical noise. Which cable type will best meet this standard? qa) coaxial b) scree

28、ned twisted pair c) shielded twisted pair d) unshielded twisted pair e) fiber optic Select the necessary information that is required to compute the estimated time it would take to transfer data from one location to another. (Choose two.) qa) file size b) data format c) network in use d) type of med

29、ium e) bandwidth of the link Which protocol functions at the internet layer of the TCP/IP protocol suite? q a) File Transfer Protocol (FTP) b) Trivial File Transfer Protocol (TFTP) c) Transmission Control Protocol (TCP) d) Internet Protocol (IP) e) User Datagram Protocol (UDP) f) Simple Mail Transpo

30、rt Protocol (SMTP) Exercises Which of the following is the Layer 4 PDU? q a) bit b) frame c) packet d) segment Which OSI layer encapsulates data into packets? q a) session b) transport c) network d) data link Why are internets necessary? (Choose three.) qa) to overcome LAN scalability limitations b)

31、 to overcome LAN speed limitations c) to overcome LAN distance limitations d) to prevent collision and congestion conditions e) to network networks Submitting Exercises qExplain precisely following abbreviations: vTCP, HTTP, SMTP,DNS,FTP,ATM,ISDN,ADSL,HFC,ISP,WAP, LAN,WAN,MAN,WLAN,ISO,OSI qExplain f

32、ollowing concepts: vTCP/IP vCircuit switching,Packet switching,Message switching,Virtual circuits qP93: review questions: 11,12,14,19; qP95:problems 5,12,14. 2: Application Layer89 Chapter 2: Application Layer Our goals: rconceptual, implementation aspects of network application protocols mtransport

33、-layer service models mclient-server paradigm mpeer-to-peer paradigm rlearn about protocols by examining popular application-level protocols mHTTP mFTP mSMTP / POP3 / IMAP mDNS rprogramming network applications msocket API 2: Application Layer90 Some network apps re-mail rweb rinstant messaging rrem

34、ote login rP2P file sharing rmulti-user network games rstreaming stored video clips rsocial networks rvoice over IP rreal-time video conferencing rgrid computing 2: Application Layer91 Creating a network app write programs that mrun on (different) end systems mcommunicate over network me.g., web ser

35、ver software communicates with browser software No need to write software for network-core devices mNetwork-core devices do not run user applications mapplications on end systems allows for rapid app development, propagation application transport network data link physical application transport netw

36、ork data link physical application transport network data link physical 2: Application Layer92 Application architectures rClient-server mIncluding data centers / cloud computing rPeer-to-peer (P2P) rHybrid of client-server and P2P 2: Application Layer93 Client-server architecture server: malways-on

37、host mpermanent IP address mserver farms for scaling clients: mcommunicate with server mmay be intermittently connected mmay have dynamic IP addresses client/server Google Data Centers rEstimated cost of data center: $600M rGoogle spent $2.4B in 2007 on new data centers rEach data center uses 50-100

38、 megawatts of power 2: Application Layer95 Pure P2P architecture rno always-on server rarbitrary end systems directly communicate rpeers are intermittently connected and change IP addresses Highly scalable but difficult to manage peer-peer 2: Application Layer96 Hybrid of client-server and P2P Skype

39、 mvoice-over-IP P2P application mcentralized server: finding address of remote party: mclient-client connection: direct (not through server) Instant messaging mchatting between two users is P2P mcentralized service: client presence detection/location user registers its IP address with central server

40、 when it comes online user contacts central server to find IP addresses of buddies 2: Application Layer97 Processes communicating Process: program running within a host. rwithin same host, two processes communicate using inter-process communication (defined by OS). rprocesses in different hosts comm

41、unicate by exchanging messages Client process: process that initiates communication Server process: process that waits to be contacted 2: Application Layer98 Sockets rprocess sends/receives messages to/from its socket rsocket analogous to door msending process shoves message out door msending proces

42、s relies on transport infrastructure on other side of door which brings message to socket at receiving process process TCP with buffers, variables socket host or server process TCP with buffers, variables socket host or server Internet controlled by OS controlled by app developer rAPI: (1) choice of

43、 transport protocol; (2) ability to fix a few parameters 2: Application Layer99 Addressing processes rto receive messages, process must have identifier rhost device has unique 32-bit IP address rExercise: use ipconfig from command prompt to get your IP address (Windows) rQ: does IP address of host o

44、n which process runs suffice for identifying the process? mA: No, many processes can be running on same rIdentifier includes both IP address and port numbers associated with process on host. rExample port numbers: mHTTP server: 80 mMail server: 25 2: Application Layer100 App-layer protocol defines r

45、Types of messages exchanged, me.g., request, response rMessage syntax: mwhat fields in messages transfer starting r425 Cant open data connection r452 Error writing file 2: Application Layer130 Electronic Mail Three major components: ruser agents rmail servers rsimple mail transfer protocol: SMTP Use

46、r Agent ra.k.a. “mail reader” rcomposing, editing, reading mail messages re.g., Eudora, Outlook, elm, Mozilla Thunderbird routgoing, incoming messages stored on server user mailbox outgoing message queue mail server user agent user agent user agent mail server user agent user agent mail server user

47、agent SMTP SMTP SMTP 2: Application Layer131 Electronic Mail: mail servers Mail Servers rmailbox contains incoming messages for user rmessage queue of outgoing (to be sent) mail messages rSMTP protocol between mail servers to send email messages mclient: sending mail server m“server”: receiving mail

48、 server mail server user agent user agent user agent mail server user agent user agent mail server user agent SMTP SMTP SMTP 2: Application Layer132 Electronic Mail: SMTP RFC 2821 ruses TCP to reliably transfer email message from client to server, port 25 rdirect transfer: sending server to receivin

49、g server rthree phases of transfer mhandshaking (greeting) mtransfer of messages mclosure rcommand/response interaction mcommands: ASCII text mresponse: status code and phrase rmessages must be in 7-bit ASCII 2: Application Layer133 Scenario: Alice sends message to Bob 1) Alice uses UA to compose me

50、ssage and “to” bobsomeschool.edu 2) Alices UA sends message to her mail server; message placed in message queue 3) Client side of SMTP opens TCP connection with Bobs mail server 4) SMTP client sends Alices message over the TCP connection 5) Bobs mail server places the message in Bobs mailbox 6) Bob