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What is the Internet? What is a protocol? End systems Core networks

What is the Internet? What is a protocol? End systems Core networks Access network and physical media Throughput, loss and delay Protocol layers IP, TCP, UDP Applications. Oversikt:. Internet: “network of networks” Partly hierarchical Public Internet versus private intranet

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What is the Internet? What is a protocol? End systems Core networks

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  1. What is the Internet? What is a protocol? End systems Core networks Access network and physical media Throughput, loss and delay Protocol layers IP, TCP, UDP Applications Oversikt:

  2. Internet: “network of networks” Partly hierarchical Public Internet versus private intranet ISPs: Internet Service Providers Protocols Control sending, receiving of messages E.g., TCP, IP, HTTP, FTP, PPP local ISP regional ISP company networks What is the Internet? router workstation server mobile unit

  3. End systems Run application programs E.g., web browser, web server, email At “the edge” of the net Client/server model Clients ask for, and get a service from the servers E.g. WWW client (browser)/ server; email client/server Peer-to-peer model Interactions are symmetrical E.g. telephone conferences End systems

  4. Human protocols: “What time is it?” “I have a questions” Formal phrases… … are special “messages” that are sent, which lead to … … defined events or actions when the message is received Network protocols: Machine instead of people All communication activity in the Internet is controlled by protocols What is a protocol? Protocols define formats, order of sending and receiving of messages, and the actions that the reception initiates.

  5. Reference models;Why layering? Management of complex systems: • Modularisation simplifies • Design • Maintenance • Updating of a system • Explicit structure allows • Identification of the individual parts • Relations among them • Clear structure: layering • Layered reference model • Goal: different implementation of one layer fit with all implementations of other layers

  6. application: supports network applications ftp, smtp, http Your applications transport: data transfer from end system to end system TCP, UDP network: finding the way through the network from machine to machine IP (data) link: data transfer between two neighbors in the network ppp, ethernet physical: bits “on the wire” TCP/IP - protocol stack application transport network link physical

  7. A standard for layering of communication protocols Open Systems Interconnection by the ISO – International Standardization Institute Two additional layers to those of the Internet stack presentation: translates between different formats XML, XDR provides platform independence session: manages connection, control and disconnection of communication sessions RTP OSI - model application presentation session application transport network link physical

  8. Hode Data, for eks. 10.000 bit Hale M-adresse S-adresse Sjekksum Generelt pakkeformat • rammer • pakker • meldinger • PDU (Protocol Data Unit)

  9. M M H H H H H H H H H H H H t t t t l n l t n n t n M M M M application transport network link physical application transport network link physical M M Protocol layer and data Each layer takes data from next higher layer • Adds header information to create a new data unit (message, segment, frame, packet …) • Send the new data unit to next lower layer source destination message segment datagram frame

  10. How to connect end systems to edge routers? Home network Company network (schools, companies) Mobile access network Keep in mind when choosing a technology: Bandwidth? Shared or dedicated medium? Access network and physical media

  11. Physical link: a sent bit propagates through the link Closed media: Signals propagate in cable media (copper, fiber) Open media: Signals propagate freely, e.g. radio. Physical medium

  12. Graph of interconnected routers One fundamental question: how is data passed through the net? Circuit switching Packet switching Circuit switching Dedicated line through the network Packet switching Discrete data units are sent through the network Core networks

  13. Fysisk Fysisk Fysisk Lag Den primære oppgaven • flytte bits fra avsender til mottaker • krever: • standardisert måte å representere bit inn på transmisjonsmediet • standardisering av kabler og tilkoplingsutstyr • synkronisering av klokketakt mellom sender og mottaker

  14. Multipleksing 1 link n kanaler n kanaler inn n kanaler ut • tids multipleksing • frekvens multipleksing • pakke multipleksing

  15. Linklaget • Innramming av nyttelasten • Transport av rammer over mediet • Adressering • Feilhåndtering: • Feildeteksjon • Feilkorreksjon • Flytkontroll

  16. Flytkontroll • Normalt en feed-back (tilbakemelding) protokoll der mottaker informerer senderen om sin buffer-kapasitet • To vanlige tilnærminger: • 1. sender stopper når spesiell NAK mottas • 2. mottaker informerer senderen om hvor mange pakker/bytes den har plass til, og senderen sender ikke mer data enn oppgitt inntil den får ny beskjed (kredittbasert flytkontroll)

  17. Token Ring Ethernet Konkurranseutsatt Konkurransefri Radio-LAN Konkurranseutsatt Lokalnett strukturer Nøkkelbegrep: Medium Aksess kontroll

  18. Broer: • knytter sammen lokalnett på link-nivå • framsending basert på MAC-adresser • effektivt sammenkoplingsalternativ • kan benyttes til isolering av trafikk • konsumerer ikke IP-nettverks adresser

  19. Tasks of the Network Layer • Responsible for end-to-end transport • Addressing of machines • Forwarding • Connectionless • datagram; no fixed path through the network • Connection-oriented (e.g. X.25 or ATM) • Three phases: connection establishment, data transmission, teardown • Fixed path through the network • Relatively reliable and ordered transmission • Flow control

  20. Datagram switching IP Internet Protocol Datagram service of the Internet RFC 791 IP offers: Datagram service Unreliable Unordered Addressing Routing IP networks can use virtual circuits IPv4: circuit is one hop IPv6: can have a tag Network layer: IP

  21. Adressering og ruting • hver “ting” vi vil finne frem til, må ha en adresse! • adresse: • en streng av bytes som enhetlig identifiserer “tingen” • adressetyper: • unicast; identifiserer et endepunkt (ting) • kringkasting; identifiserer alle • gruppe-kringasting; identifiserer alle i en gruppe

  22. Ruting 2 1 4 3 1 1 Ruting prosess 2 2 Pre- Pross. Rutetabell 3 3 4 4 Fremsender

  23. Formatet til IP-hodet 4 4 8 16 Vers. Hlen TOS Length Ident Flags Offset TTL Proto Checksum SourceAddr DestinationAddr Opsions (variable) Pad Data

  24. Subnetting Nett 1 : 129.240.0.0 Destin-addr: 129.240.002.35 subnett 1: 129.240.1.0 Nett-maske = 255.255.255.0 subnett 2: 129.240.2.0 subnett 3: 129.240.3.0 129.240.002.35 & 255.255.255.0 --> 129.240.002.0 • subnetting innfører et nytt adressenivå • nett-masken identifiserer subnett-adressen • subnett er bare synlige innenfor lokalområdet • det er fullt mulig med flere subnett • på samme fysiske nett

  25. Transportlaget

  26. TCP • forbindelses-orientert • støtter en oktett-strøm mellom to prosesser • full dupleks • flyt-kontroll • hindrer sender å oversvømme mottaker • demultipleksing • metnings-kontroll • hindrer sender å oversvømme nettet

  27. SrcPort DestPort SequenceNum Acknowledgement HdrLen 0 Flags Adv.Window CheckSum UrgPointer Options (variable) Data Segment format Pseudo-header Flags: SYN FIN ACK RESET PUSH URG Checksum: pseudo header + tcp header + data

  28. UDP • forbindelsesfri transport (datagram transport) • “best-effort” overføring • ingen garanti for vellykket overføring: • pakker kan bli borte (sjekksumfeil & rutefeil) • pakker kan komme frem i gal rekkefølge • pakker kan dupliseres • pakker kan forsinkes unormalt

  29. SrcPort DestPort Checksum Length Data Src-address Dest-address 0 Protocol Length Enkel multiplekser/ demultiplekser (UDP) • tilbyr multipleksing og demultipleksing • ved hjelp av “Service aksess punkter” kalt porter; • ingen flytkontroll; • tjener-siden lytter på velkjente porter • checksum: valgbar Pseudo-hode

  30. Funksjonelle behov • applikasjonsprosessenes behov: • navning av maskiner og tjenester • konvertering av navn til addresser • tilgang til kommunikasjonstjenesten (API): • service aksess punkt (SAP); virtuelt tilknytningspunkt mellom applikasjonsprosess og komm.hierarkiet • etablering, bruk, og nedkopling av forbindelser • spesifisere kvalitets-krav

  31. Overførings-syntaks • inhomogene ende-systemer • ulik hardware • ulike operativsystemer • ulike programerings-språk • kommunikasjonen over nettet må foregå i en syntaks som begge sider oppfatter på samme måten

  32. Applications that use TCP: HTTP (WWW) FTP (file transfer) SMTP (email) Telnet (remote login) Applications that use UDP: Streaming media Video conferencing Internet telephony NTP (network time protocol) Applications

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