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Datakommunikasjon høsten 2002

Datakommunikasjon høsten 2002. Mandag 11. november Repitisjon. Hva skal dere lære?. Hva er Internett Nettverkskort Protokoller Adressering Applikasjoner ISDN LAN WAN ISP ASP. Ethernet ARP TCP/IP Bro Svitsj Ruter FW/Brannmur DNS SNMP SMTP. IN - Node. LAN. Internet.

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Datakommunikasjon høsten 2002

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  1. Datakommunikasjon høsten 2002 Mandag 11. november Repitisjon Datakom høsten 2002

  2. Hva skal dere lære? • Hva er Internett • Nettverkskort • Protokoller • Adressering • Applikasjoner • ISDN • LAN • WAN • ISP • ASP • Ethernet • ARP • TCP/IP • Bro • Svitsj • Ruter • FW/Brannmur • DNS • SNMP • SMTP Datakom høsten 2002

  3. Datakom høsten 2002

  4. IN - Node LAN Internet Telecom Management System GSM Tactical and Strategic Military Networks Tele-/datakommunikasjonsnett PSTN Datakom høsten 2002

  5. Hypertext Transfer ProtocolHTTP • Benyttes av WWW • Protokoll for overføring av HTML • Kan overføre tekst, lyd, bilder osv. • Transaksjonsorientert klient/tjener protokoll • Vanligvis mellom en Web browser (klient) og Web server (tjener) • Benytter TCP • Tilstandsløs • Hver transaksjon behandles separat (Keep-Alive) • En ny TCP forbindelse for hver transaksjon • Terminerer forbindelsen når transaksjonen er komplett Datakom høsten 2002

  6. Telnet og Rlogin • Innlogging fra en maskin til en annen over nettet • Benytter seg av klient-tjener begrepet • Telnet er en standard applikasjon som er implementert i alle TCP/IP applikasjoner • Rlogin kommer fra Berkley Unix og ble utviklet for pålogging mellom to Unix systemer • Telnet er mer kompleks enn Rlogin Datakom høsten 2002

  7. FTP (File Transfer Protocol) • Internett standard for filoverføring • FTP protokoll • Kontroll forbindelse • Server gjør en ”passive open” på port 21 • Klient gjør en ”active open” til port 21 • Data overføres fra port 20 på FTP serveren Datakom høsten 2002

  8. DNS - Domain Name System RFC1034, RFC1035 • Mapper mellom hostnavn og IP-adresse(og omvendt) • Benyttes av TCP/IP applikasjoner • Distribuert, hierarkisk • Benytter både TCP og UDP som transport, port nummer 53 • Eksempler • DNS Query • DNS Reply Datakom høsten 2002

  9. a human protocol and a computer network protocol: TCP connection reply. Get http://gaia.cs.umass.edu/index.htm Got the time? 2:00 <file> time What’s a protocol? Hi TCP connection req. Hi Datakom høsten 2002

  10. A Communications Model • Source • Generates data to be transmitted • Transmitter • Converts data into transmittable signals • Transmission System • Carries data • Receiver • Converts received signal into data • Destination • Takes incoming data Datakom høsten 2002

  11. Simplified Communications Model - Diagram Datakom høsten 2002

  12. Networking • Point to point communication not usually practical • Devices are too far apart • Large set of devices would need impractical number of connections • Solution is a communications network Datakom høsten 2002

  13. Simplified Network Model Datakom høsten 2002

  14. WAN - Wide Area Networks • Store geografiske områder • Består av en rekke noder • Alternative teknologier • Linesvitsjing (Circuit switching) • Pakkesvitsjing (Packet switching) • Frame relay • Asynchronous Transfer Mode (ATM) Datakom høsten 2002

  15. LAN - Local Area Networks • En eller flere bygninger • Eies vanligvis av den som henger utstyr på lokalnettet • Høyere datahastigheter enn WAN • Ethernet 10 eller 100 Mbit/s • Tidligere kun kringasting, dvs alle kan lytte på nettet • Nå mer og mer svitsjede systemer, dvs kan segmentere nettet Datakom høsten 2002

  16. Typical home network components: ADSL or cable modem router/firewall Ethernet wireless access point Home networks wireless laptops to/from cable headend cable modem router/ firewall wireless access point Ethernet (switched) Datakom høsten 2002

  17. Circuit Switching • Dedikert kommunikasjonsvei mellom partene så lenge kommunikasjonen pågår. • Eksempel: Telefonnettet Datakom høsten 2002

  18. Example: 4 users Frequency Division Multiplexing Access frequency time Time Division Multiplexing Access frequency time Circuit Switching: FDMA and TDMA Datakom høsten 2002

  19. Packet Switching • Datapakker sendes enkeltvis • Datapakkene behøver ikke ta samme vei gjennom nettet • Datapakkene sendes fra node til node mellom avsender og mottaker • Brukes mellom datamaskiner • Eksempel: Datapak basert på X.25 Datakom høsten 2002

  20. D E Pakkesvitsjing 10 Mbs Ethernet C A statistical multiplexing 1.5 Mbs B queue of packets waiting for output link 45 Mbs Datakom høsten 2002

  21. Asynchronous Transfer Mode • ATM • Little overhead for error control • Fixed packet (called cell) length • Anything from 10Mbps to Gbps • Constant data rate using packet switching technique Datakom høsten 2002

  22. Integrated Services Digital Network • ISDN • Laget for å erstatte PSTN, dvs analog telefoni • Prøveprosjekt i Norge høsten 1989 • Ble først populært når det kunne benyttes for å koble seg mot Internett Datakom høsten 2002

  23. ISDN kanaler Grunnaksess (Basic Access): 2 B-kanaler 1 D-kanal Utvidet aksess(Primary rate Access): 30 B-kanaler 1 D-kanal Datakom høsten 2002

  24. ADSL – Assymetric Digital Subscriber Line • Telenor tilbyr (hastighet inn/ut): • 384 / 128 Kb/slaste ned lyd og bilde, samt gjøre flere ting på en gang •  704 / 128 Kb/slaste ned filmklipp, programvare og andre store filer •  1024 / 256 Kb/slaste ned og sende ut store filer raskt og effektivt Datakom høsten 2002

  25. application: supporting network applications ftp, smtp, http transport: host-host data transfer tcp, udp network: routing of datagrams from source to destination ip, routing protocols link: data transfer between neighboring network elements ppp, ethernet physical: bits “on the wire” application transport network link physical Internet protocol stack Datakom høsten 2002

  26. Internetworking Protocols Datakom høsten 2002

  27. Application Application Presentation Session Transport Transport Network Network Data Link Data Link Physical Kommunikasjonslagene (referert til OSI) OSI Internet-TCP/IP FTP HTTP SMTP DNS TCP UDP ICMP IP ARP PPP Ethernet Datakom høsten 2002

  28. Sikkerhet • Autentisering (identifikasjon) • Aksesskontroll (aksess til ressurser) • Konfidensialitet (informasjon holdes hemmelig) • Integritetstjeneste (data skal være korrekte) • Tilgjengelighet (informasjonen skal være tilgjengelig for de som er autorisert) • CIA – Confidentiality Integrity Availability Datakom høsten 2002

  29. Symmetrisk kryptering Secret Key Ciphertext Cleartext Cleartext Encryption Algorithm Encryption Algorithm Encipher Decipher Datakom høsten 2002

  30. Asymmetrisk kryptering One Key to Encipher Another Key to Encipher Ciphertext Cleartext Cleartext Encryption Algorithm Encryption Algorithm Encipher Decipher Datakom høsten 2002

  31. IPSec – IP Security • Sikkerhetsmekanisme for beskyttelse av VPN • VPN – Virtual Private Network • VPN over Internett • Mellom avdelingskontorer • Mellom hjemmekontor og jobb • Mellom leverandør og kunde Datakom høsten 2002

  32. IPSec sikkerhetstjenester • Konfidensialitet • Informasjonen krypteres • Integritet • En veis hash funksjon • Autentisering • MAC (hash + hemmelighet) • Digital signatur Datakom høsten 2002

  33. PING ping 193.69.136.8 Pinging 193.69.136.8 with 32 bytes of data: Reply from 193.69.136.8: bytes=32 time=81ms TTL=127 Reply from 193.69.136.8: bytes=32 time=48ms TTL=127 Reply from 193.69.136.8: bytes=32 time=50ms TTL=127 Reply from 193.69.136.8: bytes=32 time=49ms TTL=127 Ping statistics for 193.69.136.8: Packets: Sent = 4, Received = 4, Lost = 0 (0% loss), Approximate round trip times in milli-seconds: Minimum = 48ms, Maximum = 81ms, Average = 57ms Datakom høsten 2002

  34. Informasjon om IP på maskin ipconfig -all Ethernet adapter Local Area Connection: Connection-specific DNS Suffix . : halden.scandpower.noDescription . . . . . . . . . . . : 3Com EtherLink XL 10/100 PCI or Complete PC Management NIC (3C905C-TX) Physical Address. . . . . . . . . : 00-50-DA-DD-2E-5E DHCP Enabled. . . . . . . . . . . : NoIP Address. . . . . . . . . . . . : 193.69.136.78Subnet Mask . . . . . . . . . . . : 255.255.255.0Default Gateway . . . . . . . . . : 193.69.136.54DNS Servers . . . . . . . . . . . : 193.69.136.53 Datakom høsten 2002

  35. ARP - Address Resolution Protocol (IP til MAC adresse) arp -a Interface: 193.69.136.78 on Interface 0x2 Internet Address Physical Address Type 193.69.136.34 00-60-b0-3d-82-74 dynamic 193.69.136.54 00-10-5a-66-21-78 dynamic 193.69.136.60 00-50-da-4f-31-8c dynamic 193.69.136.61 00-60-97-17-2a-48 dynamic 193.69.136.91 00-60-08-49-2a-fe dynamic 193.69.136.115 08-00-09-70-2c-8e dynamic 193.69.136.133 08-00-09-87-fe-29 dynamic Datakom høsten 2002

  36. Traceroute Address: Time: Seq: Results: 192.168.1.1 <10ms 1 56 bytes received. 80.212.232.0 16ms 2 56 bytes received. 146.172.167.65 16ms 3 56 bytes received. 146.172.202.57 31ms 4 168 bytes received. 146.172.202.37 16ms 5 168 bytes received. 146.172.250.229 16ms 6 168 bytes received. 146.172.248.66 31ms 7 56 bytes received. 193.156.90.3 16ms 8 56 bytes received. 193.75.3.62 15ms 9 56 bytes received. www.vg.no [193.69.165.20] 31ms 9 52 bytes received. Datakom høsten 2002

  37. Standards • Required to allow for interoperability between equipment • Advantages • Ensures a large market for equipment and software • Allows products from different vendors to communicate • Disadvantages • Freeze technology • May be multiple standards for the same thing Datakom høsten 2002

  38. Standards Organizations • Internet Society • Internet Architecture Board (IAB) • Internet Engineering Task Force (IETF) • Internet Engineering Steering Group (IESG) • ISO - International Standard for Organization • JTC – Joint Technical Committee • ITU-T (tidligere CCITT) • ITU- International Telecommunication Union • 14 study groups • ATM forum Datakom høsten 2002

  39. Process: program running within a host. within same host, two processes communicate using interprocess communication (defined by OS). processes running in different hosts communicate with an application-layer protocol user agent: software process, interfacing with user “above” and network “below”. implements application-level protocol Web: browser E-mail: mail reader streaming audio/video: media player Network applications: some jargon Datakom høsten 2002

  40. Typical network app has two pieces: client and server request reply application transport network data link physical application transport network data link physical Client-server paradigm Client: • initiates contact with server (“speaks first”) • typically requests service from server, • Web: client implemented in browser; e-mail: in mail reader Server: • provides requested service to client • e.g., Web server sends requested Web page, mail server delivers e-mail Datakom høsten 2002

  41. API: application programming interface defines interface between application and transport layers socket: Internet API two processes communicate by sending data into socket, reading data out of socket Q: how does a process “identify” the other process with which it wants to communicate? IP address of host running other process “port number” - allows receiving host to determine to which local process the message should be delivered Application-layer protocols (cont). Datakom høsten 2002

  42. Data loss some apps (e.g., audio) can tolerate some loss other apps (e.g., file transfer, telnet) require 100% reliable data transfer Timing some apps (e.g., Internet telephony, interactive games) require low delay to be “effective” What transport service does an app need? Bandwidth • some apps (e.g., multimedia) require minimum amount of bandwidth to be “effective” • other apps (“elastic apps”) make use of whatever bandwidth they get Datakom høsten 2002

  43. Transport service requirements of common apps Time Sensitive no no no yes, 100’s msec yes, few secs yes, 100’s msec yes and no Application file transfer e-mail Web documents real-time audio/video stored audio/video interactive games financial apps Data loss no loss no loss loss-tolerant loss-tolerant loss-tolerant loss-tolerant no loss Bandwidth elastic elastic elastic audio: 5Kb-1Mb video:10Kb-5Mb same as above few Kbps up elastic Datakom høsten 2002

  44. TCP service: connection-oriented: setup required between client, server reliable transport between sending and receiving process flow control: sender won’t overwhelm receiver congestion control: throttle sender when network overloaded does not providing: timing, minimum bandwidth guarantees UDP service: unreliable data transfer between sending and receiving process does not provide: connection setup, reliability, flow control, congestion control, timing, or bandwidth guarantee Internet transport protocols services Datakom høsten 2002

  45. Internet apps: application, transport protocols Application layer protocol smtp [RFC 821] telnet [RFC 854] http [RFC 2068] ftp [RFC 959] proprietary (e.g. RealNetworks) NSF proprietary (e.g., Vocaltec) Underlying transport protocol TCP TCP TCP TCP TCP or UDP TCP or UDP typically UDP Application e-mail remote terminal access Web file transfer streaming multimedia remote file server Internet telephony Datakom høsten 2002

  46. transfer file to/from remote host client/server model client: side that initiates transfer (either to/from remote) server: remote host ftp: RFC 959 ftp server: port 21 FTP user interface FTP client FTP server local file system ftp: the file transfer protocol file transfer user at host remote file system Datakom høsten 2002

  47. ftp client contacts ftp server at port 21, specifying TCP as transport protocol two parallel TCP connections opened: control: exchange commands, responses between client, server. “out of band control” data: file data to/from server ftp server maintains “state”: current directory, earlier authentication TCP control connection port 21 TCP data connection port 20 FTP client FTP server ftp: separate control, data connections Datakom høsten 2002

  48. Sample commands: sent as ASCII text over control channel USER username PASS password LISTreturn list of file in current directory RETR filenameretrieves (gets) file STOR filenamestores (puts) file onto remote host Sample return codes status code and phrase (as in http) 331 Username OK, password required 125 data connection already open; transfer starting 425 Can’t open data connection 452 Error writing file ftp commands, responses Datakom høsten 2002

  49. People: many identifiers: SSN, name, passport # Internet hosts, routers: IP address (32 bit) - used for addressing datagrams “name”, e.g., gaia.cs.umass.edu - used by humans Q: map between IP addresses and name ? Domain Name System: distributed database implemented in hierarchy of many name servers application-layer protocol host, routers, name servers to communicate to resolvenames (address/name translation) note: core Internet function, implemented as application-layer protocol complexity at network’s “edge” DNS: Domain Name System Datakom høsten 2002

  50. no server has all name-to-IP address mappings local name servers: each ISP, company has local (default) name server host DNS query first goes to local name server authoritative name server: for a host: stores that host’s IP address, name can perform name/address translation for that host’s name Why not centralize DNS? single point of failure traffic volume distant centralized database maintenance doesn’t scale! DNS name servers Datakom høsten 2002

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