Computer Networks

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Computer Networks

• Chapter 1 - Introduction

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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.

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• 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

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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.

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Chapter 1
Introduction
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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 2222,
  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.

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Bits and Bytes

• N bit can represent M2N different values.
• M values can be represented by N 2log M log
  M / log 2 values
• Example The N7 bit ASCII character code
  consists of M128 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.

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Punkt-till-punkt-förbindelser
Mikrofon
Högtalare
NACK
0110010
ACK
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Figure 2.17 The OSI seven layer model
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The TCP/IP five layer model
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TCP/IP-modellen
Exempel
SMTP, HTTP
TCP, UDP IP
Ethernet
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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

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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)

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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

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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

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Figure 1.2 Simplex
Example Video monitor. TV and radio
broadcasting.
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Figure 1.3 Half-duplex
Example Communication radio. 2-wire Ethernet.
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Figure 1.4 Full-duplex
Example Telephony. 4-wire Ethernet.
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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
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Topology of Networks

• Topology defines the arrangement of links in a
  network

Topology
Ring
Bus
Full Mesh
Partial Mesh
Star
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Figure 1.9 Star topology
or switch
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Figure 1.10 Bus topology
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Figure 1.11 Ring topology
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LAN, MAN och WAN
Lokalt nätverk
Globalt nätverk
Stadsnät
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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
Planet
The Internet
10,000 km
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Nättopologier för WAN

• Hopkopplade LAN och WAN internetwork T.ex.
  Internet.

• Växlat WAN (stjärnnät)T.ex. X.25 eller ATM

Nätnoder
Växel. Kopplar ihop punkt-till-punkt-länkar.
Routervägväljare, kopplar ihop nätverk med olika
teknologier.
Datorer, terminaler, skrivare, etc.
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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

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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.

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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)