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Computer Networks Chapter 1 - Introduction. Spring 2006Computer Networks2 Välkommen till Datornätverk A, 5p! Denna kurs avser att ge dig grundläggande.

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En presentation över ämnet: "Computer Networks Chapter 1 - Introduction. Spring 2006Computer Networks2 Välkommen till Datornätverk A, 5p! Denna kurs avser att ge dig grundläggande."— Presentationens avskrift:

1 Computer Networks Chapter 1 - Introduction

2 Spring 2006Computer Networks2 Välkommen till Datornätverk A, 5p! Denna kurs avser att ge dig grundläggande förståelse för hur Internet och lokala nätverk är uppbyggda. Kursens karta är TCP/IP- och OSI-modellerna. Målsättningen är att ge dig grundläggande teoretiska och praktiska kunskaper om datakommunikationsprotokoll, nätutrustning, nättopologier, transmissionsmedier, grundläggande adresserings- och routingbegrepp samt enklare verktyg för felsökning av nät.

3 Spring 2006Computer Networks3 Fler kurser inom området Kursen ingår i flera av våra utbildningsprogram. Det finns flera påbyggnadskurser inom området, bl.a. följande distanskurser:  Datateknik A, Nätverksövervakning och drift.  Datateknik B, Trådlös Internetaccess.  Datateknik C, TCP/IP-nätverk. Överlappande kurser Kursen överlappar till stor del med följande kurser, och kan därför INTE ingå i samma examen:  Datateknik A, Internet och datakommunikation 5 poäng  Datateknik A, Datakommunikation och drift av nätverk  Datateknik B, Multimedie- och kommunikationssystem 4 poäng

4 Spring 2006Computer Networks4 Kursuppläggning  Kurslitteratur: Forouzan, ”Data communications and networking”, 3rd edition, eller senare.  Kurswebbplats: webct.miun.se.  Besvara samtliga ”quizzar” (automaträttade felvalsfrågor) med minst 60% rätt svar.  Två laborationstillfällen  En avslutande proejektuppgift. Muntlig redovisning för campusstudenter.  Tentamen: Ta med miniräknare.  Lektionsplanering och slides: Se WebCT.

5 Spring 2006Computer Networks5 Chapter 1 Introduction

6 Spring 2006Computer Networks6 Amount of information -Think about a number between 0 and 15. I am now going to guess it using as few yes and no questions as possible. I start by asking: Is the number larger than or equal to 8? -Yes -Is the it larger than or equal to 12? (The interval is successively divided by 2.) -No. -Is the number larger than or equal to 10? -Yes -Is the number larger than or equal to 9? -Yes. -The amount of information you give me when you tell me that the number is 9 is 4 bits, because the amount of information in bits is the minimum number of yes and no questions that are required. We had 16 options, which is = 2 4 = 2·2·2·2, corresponding to 4 bits. If the number of options was 32 = 2 5, it would require 5 bits. -If yes is represented by the binary digit ”1”, and no by ”0”, the value in the above example can be represented by

7 Spring 2006Computer Networks7 Bits and Bytes  N bit can represent M=2 N different values.  M values can be represented by N = 2 log M =log M / log 2 values  Example: The N=7 bit ASCII character code consists of M=128 codes.  8 bits = 1 byte (a unit for measuring amount of data)  1 kbit = 1000 bit (previously 1024 bit).  1 Mbit = 1000 kbit (previously 1024 kbit).  1 Gbit = 1000 Mbit.  1 Tbit = 1000 Gbit.

8 Spring 2006Computer Networks8 Punkt-till-punkt-förbindelser MikrofonHögtalare KällkodningKällavkodning Digitalisering, komprimering 0110 Felhantering Lägger till fel- rättande eller felupptäckande kod, t.ex. checksumma. Felupptäckt och omsändning, eller felrättning Bitfel Flödesstyrning Buffert Handskakning ModulationDemodulation Elektrisk representation NACK ACK Nivå 6 Nivå 2 Nivå 1 Nivå 7

9 Spring 2006Computer Networks9 Figure 2.17 The OSI seven layer model

10 Spring 2006Computer Networks10 The TCP/IP five layer model

11 Spring 2006Computer Networks11 TCP/IP-modellen TCP, UDP IP Ethernet SMTP, HTTP Exempel:

12 Spring 2006Computer Networks12 The Key Elements of a Protocol  Syntax  referes to the structure of data, meaning the order in which they are presented  Semantics  refferes to the meaning of each section of bits, how a particular pattern to be interpreted and which action should be taken based on the interpretation  Timing  refferes to when data should be sent and how fast they can be sent

13 Spring 2006Computer Networks13 Standards  Standards provide guidelines to the manufacturers, vendors, goverment agencies and other service providers to ensure connectivity between different entities  Development of standards is a very slow process  Two types of standards:  De jure (by law) – legislated by an officially recognized body, for example IEEE or ETSI.  De facto (by fact) – that are actually implemented into the products)  propriatory (closed)  nonpropriatory (open)

14 Spring 2006Computer Networks14 Data Representation  Text – using different codes  Each character is represented by certain number of bits  The number of bits in the code determins the number of different characters  ASCII (7 bits), Extended ASCII (8 bits), Unicode (16 bits), ISO (32 bits)  Numbers – Binary number system  Images – A matrix of pixels represented by bit patterns  Video – A combination of images  Audio – Digitized voice and music

15 Spring 2006Computer Networks15 Direction of Data Flow  Simplex channel  The transmission is only in one direction  Half-duplex channel  The transmission is in both directions, but only one at a time (both directions cannot be used at the same time)  Duplex channel  The transmission is in both directions without limitation

16 Spring 2006Computer Networks16 Figure 1.2 Simplex Example: Video monitor. TV and radio broadcasting.

17 Spring 2006Computer Networks17 Figure 1.3 Half-duplex Example: Communication radio. 2-wire Ethernet.

18 Spring 2006Computer Networks18 Figure 1.4 Full-duplex Example: Telephony. 4-wire Ethernet.

19 Spring 2006Computer Networks19 Different Line Configurations  Point-to-point  Two devices on a single channel (dedicated channel)  Multipoint  Many devices on a single channel (shared channel) Example: Bus network Wireless Network

20 Spring 2006Computer Networks20 Topology of Networks Topology Bus Star Full Mesh Ring Partial Mesh  Topology defines the arrangement of links in a network

21 Spring 2006Computer Networks21 Figure 1.9 Star topology or switch

22 Spring 2006Computer Networks22 Figure 1.10 Bus topology

23 Spring 2006Computer Networks23 Figure 1.11 Ring topology

24 Spring 2006Computer Networks24 LAN, MAN och WAN Lokalt nätverk Stadsnät Globalt nätverk

25 Spring 2006Computer Networks25 Computer Networks Classification 0.1 m 1 m 10 m 100 m 1 km 10 km Circuit board System Room Building Campus Local area Network (LAN) Data flow machine Multicomputer City Country Continent Planet Metropolitan Area Network (MAN) Wide Area Network (WAN) The Internet 100 km 1000 km 10,000 km

26 Spring 2006Computer Networks26 Nättopologier för WAN Hopkopplade LAN och WAN = internetwork T.ex. Internet. Växlat WAN (stjärnnät) T.ex. X.25 eller ATM Växel. Kopplar ihop punkt-till-punkt-länkar. Datorer, terminaler, skrivare, etc. Router=vägväljare, kopplar ihop nätverk med olika teknologier. Nätnoder:

27 Spring 2006Computer Networks27 Internetworking Concept and Model  The goal is to build a unified, cooperative interconnection of networks that supports a universal communication service  Detaches the notions of communication from the details of network technologies, and hides low level details from the user  Provides a mechanism that delivers packet from their source to their ultimate destination in real time

28 Spring 2006Computer Networks28 The Internet Today  Communication is possible by using a common Internet protocol that glues different networks.  Internet emerged from the academic community and therefore has no central governance so far.

29 Spring 2006Computer Networks29 The internet versus the Internet  Internetowork or internet (small ”i”) – generic term to mean an interconnection of networks  Internet (Uppercase I) – the specific worldwide network that uses the IP protocol (Internet protocol)


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