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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,

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Presentasjon om: "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,"— Utskrift av presentasjonen:

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 local ISP company networks regional ISP What is the Internet? 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 router workstation server mobile unit

3 End systems –Run application programs –E.g., web browser, web server, –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; client/server Peer-to-peer model –Interactions are symmetrical –E.g. telephone conferences

4 What is a protocol? 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 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 TCP/IP - protocol stack 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” physical link network transport application

7 physical link network transport session application OSI - model 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 presentation application

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

9 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 application transport network link physical application transport network link physical source destination M M M M H t H t H n H t H n H l M M M M H t H t H n H t H n H l message segment datagram frame

10 Access network and physical media 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?

11 Physical medium 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.

12 Core networks 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

13 Fysisk Lag 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 Den primære oppgaven Fysisk

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

15 Linklaget Innramming av nyttelasten Transport av rammer over mediet – Adressering Feilh å ndtering: –Feildeteksjon –Feilkorreksjon Flytkontroll

16 Normalt en feed-back (tilbakemelding) protokoll der mottaker informerer senderen om sin buffer-kapasitet To vanlige tiln æ rminger: –1. sender stopper n å r 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 f å r ny beskjed (kredittbasert flytkontroll)

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

18 Broer: – knytter sammen lokalnett p å link-niv å – framsending basert p å 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 Network layer: IP 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

21 Adressering og ruting hver “ ting ” vi vil finne frem til, m å 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 Rutetabell Pre- Pross Ruting prosess Fremsender

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

24 IP addresses and hostnames Hostnames –More exactly fully qualified host names –Look like niu.ifi.uio.no Host niu In subdomain ifi, Institutt for Informatik In domain uio, Universitet i Oslo In top level domain no, Norway Who decided this? –.no- IANA gave it to Uninett (”Internet Assigned Numbers Authority”) –.uio- Uninett gave it to UiO –.ifi- USIT, UiO’s drift, gave it to IFI –niu- IFI drift gave it to the machine

25 Subnetting Nett 1 : Destin-addr: subnett 1: Nett-maske = subnett 2: subnett 3: & > 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

26 Transportlaget

27 TCP yforbindelses-orientert  st ø tter en oktett-str ø m mellom to prosesser yfull dupleks yflyt-kontroll  hindrer sender å oversv ø mme mottaker ydemultipleksing ymetnings-kontroll  hindrer sender å oversv ø mme nettet

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

29 UDP forbindelsesfri transport (datagram transport) “ best-effort ” overf ø ring – ingen garanti for vellykket overf ø ring: pakker kan bli borte (sjekksumfeil & rutefeil) pakker kan komme frem i gal rekkef ø lge pakker kan dupliseres pakker kan forsinkes unormalt

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

31 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

32 Overf ø rings-syntaks inhomogene ende-systemer – ulik hardware – ulike operativsystemer – ulike programerings-spr å k kommunikasjonen over nettet m å foreg å i en syntaks som begge sider oppfatter p å samme m å ten

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


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