Computer Networks

Computer Networks Chapter 1 - Introduction

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. Välkommen till Datornätverk A, 5p! Computer Networks

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 Computer Networks

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. Computer Networks

Chapter 1 Introduction Computer Networks

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 = 24 = 2·2·2·2, corresponding to 4 bits. If the number of options was 32 = 25 , 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 1 0 1 1. Computer Networks

Bits and Bytes • N bit can represent M=2N different values. • M values can be represented by N = 2log 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. Computer Networks

Nivå 7 Digitalisering, komprimering Källkodning Källavkodning Nivå 6 0110 0110 Felhantering Felupptäckt och omsändning, eller felrättning Felhantering Lägger till fel- rättande eller felupptäckande kod, t.ex. checksumma. Nivå 2 0110010 0100010 Bitfel Flödesstyrning Buffert Handskakning Flödesstyrning Nivå 1 Modulation Elektrisk representation Demodulation Punkt-till-punkt-förbindelser Mikrofon Högtalare NACK 0110010 ACK Computer Networks

Figure 2.17The OSI seven layer model Computer Networks

The TCP/IP five layer model Computer Networks

TCP/IP-modellen Exempel: SMTP, HTTP TCP, UDP IP Ethernet Computer Networks

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 Computer Networks

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) Computer Networks

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 Computer Networks

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 Computer Networks

Figure 1.2Simplex Example: Video monitor. TV and radio broadcasting. Computer Networks

Figure 1.3Half-duplex Example: Communication radio. 2-wire Ethernet. Computer Networks

Figure 1.4Full-duplex Example: Telephony. 4-wire Ethernet. Computer Networks

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 Computer Networks

Topology of Networks • Topology defines the arrangement of links in a network Topology Ring Bus Full Mesh Partial Mesh Star Computer Networks

Figure 1.9Star topology or switch Computer Networks

Figure 1.10Bus topology Computer Networks

Figure 1.11Ring topology Computer Networks

LAN, MAN och WAN Lokalt nätverk Globalt nätverk Stadsnät Computer Networks

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

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

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 Computer Networks

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. Computer Networks

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) Computer Networks

Computer Networks