2G1316

Data Communications and Computer Networks

Peter SjödinKTH School of Electrical EngineeringLaboratory for Communication Networks

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Introduction

• Goal• Related courses• Planning and rules

LecturesRecitationsLaboration

• MaterialBookExercises with solutionsLab instructions

• Responsabilities of participants

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Goal

• BasicsData communications

o How information can be transfered

Protocols

o How system functions are performed

Services

o How the networks are used

Network architectures

o How the pieces are put together

Design principles and methods

• Introduction to TCP/IP and the Internet

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Related Courses

2E1623 (5p)Data linksand local area networks

2G1305/2E1605 (4p)Internetworking(2D1392 Protocols and Principles of the Internet)

2G1318 (4p)Queuing theory and teletraffic systems

2E1624 (5p)Performance Analysisof CommunicationNetworks

2E1632 (5p)Management of networks and networked systems

2E1633 (5p)Network services andInternet-based applications

Laboratory for Communication Systems, www.s3.kth.se/lcn

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Course Planning

• Twelve lectures

• Nine recitations

• One laborationHomework

Preparation for the laboration

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Teachers

• LecturesPeter Sjödin (Swedish)

• Recitation assistantsGyörgy Dan (English/Swedish)

Vladimir Vukadinovic (English)

Fetahi Wuhib (English)

• LaborationsJing Fu

Mikael Rudholm

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Students

• Please meet…D3, D4

E3, E4

I2

MEDIA2

Medicinsk Informatiko Karolinska institutet

Enstaka kurser…

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Please Note!

• Exam March 13

• Important messages through Bildabilda.kth.se

Also at the lectures

You are responsible for stayingupdated!

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Lectures and Recitations

• F1: Introduction• F2: Layered models

InternetOSI

• F3 and F4 + Ö1 and Ö2: Physical layer and data transfer

ModulationCodingLink technologies

• F5 + Ö3: Data link layerFlow controlError controlData link protocols

• F6 + Ö4: Local Area NetworksMultiple AccessEthernet (IEEE 802.3)

• F7 + Ö5: Wide Area NetworksCircuit switchingPacket switchingVirtual circuits

• F8 and F9 + Ö6 and Ö7: Internetworking and IP

• F10 and F11 + Ö8: End-to-end communication

Transport protocolsApplications

• F12: — (spare)• F13 + Ö9: Summary

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Laboration

• Purpose

Design and configuration of a computer network

Work with modern Internet equipment

• Laboratorium LQ303, Osquldas väg 10

• Groups with two students

• Sign up for lab sessions

(more details later)

• Homework

Must be completed in order to do the lab!

Deadline February 2

Hand in at lecture or recitation

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Recitations

• There are two parallel recitation groups for 2E1623 and 2G1316

• You do not need to register

• Recommendation:MEDIA, Medicinsk Informatik

o Track 1 (György)

D, E, and Io Track 2 (Vladimir and Fetahi)

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Course Material

• BookBehrouz A Forouzan, Data Communications and Networking, 3rd edition,

McGraw-Hill. ISBN 007-123241-9.

• Exercises with solutions

• Lab instructions

• Summary of course modules

Background material

• All material (except for the book) is available on the course

web

http://www.s3.kth.se/courses/2G1316

• There will be a printed version of exercises and lab

instructions, which you can buy

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Your Responsibilities

• Registration for exams and labsS3 booking system, see the web

• Course registrationsNo separate course registrationWhen you register for the labs, you also register for the courseIf you for some reason are not going to register for the labs, please contact Peter!

• Search the webMost information available on the course web Course administration

• Course evaluation• Course responsible can be reached through Bilda

Make sure your Bilda profile is up to date

• Be on time for the laborationsAnd keep the deadline for the homework

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Course Committee (Kursnämnd)

• Volounteers?

• MeetingsMid-course

End of course

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Today’s Lecture

• Definitions

• Signals

• Requirements on communication

• Communication networksConnections and topologies

Network types

• Examples of networks

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Illustrations in this material are collected from

Behrouz A Forouzan, Data Communications and Networking, 3rd edition, McGraw-Hill.

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Information and Data

• Information—many meaningsWikipedia (http://www.wikipedia.org) lists five meanings:

o 1. Negative entropy—the instructions that are needed to produce order or reduce uncertainty

o ...o 5. Any type of pattern that influences the

formation or transformation of other patterns

• DataRepresentation of information

o Symbols with a certain syntax

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Information

• Technical definitionContext known by sender and receiver

o The alternatives are well defined

Information represents one alternativeo To represent one of N alternatives requires⎡log2N⎤ bits

o Example: The letters in the Swedish alphabet can be represented by 5 bits (25 = 32)

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Information

• Time dependent informationHas a certain bit rate or data rate (measured in bits per second, b/s, bit/s, bps)

• Time independent informationConsists of a certain amount of bits

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Communication

• Sharing or transfer of information• “Telecommunication”

Communication at a distanceo ”Tele” is ”far” in Greek

Traditionally speachSound, pictures, text, ...

• “Communications”With an ’s’ at the end!“The branch of technology concerned with the representation, transfer, interpretation, and processing of data among persons, places, and machines also known as information systems.”

o From http://www.wikipedia.org

• ”Data communications””[...] the exchange of data between two devices over some form of transmission medium”

o Forouzan

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Network Functions

• Ways to transfer information on a linkSignal format

• AddressingIdentify sender and receiver

• RoutingFind a path between sender and receiver

• BufferingCompensate for differences in speedVariations in traffic load

• Error detection and controlIf data is lost or corrupted

• Congestion controlTo protect the network from being overloaded

• Management and network operations

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Signals

• Analog signalsContinuous in timeInfinitely many levels

o Continuously varying

• Digital signalsLimited number of levels

o Discreteo Often binary (0 and 1)

Discrete in time

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Sine Wave

• Fully described bys(t) = A sin(2πft + φ)

A is amplitude, f is frequency, φ is phase

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Time and Frequency Domains

• A signal can be represented asA function of time

A function of frequency

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Composite Signals

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Fourier Analysis

• Any composite signal can be representedas a sum of simple sine waves

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Bandwidth

• Important property of a mediumDifference between highest and lowest frequency that can pass through the medium

Measured in Hertz [Hz]

Limits the channel’s capacity

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Capacity

• Transmission capacityMeasured in bits per second [b/s, bit/s, bps]

• Increased bandwidth can give higher capacityA noiseless analogous channel has infinite capacity

• Larger unitskilo (k) 103, mega (M) 106, giga (G) 109, tera (T) 1012, peta (P) 1015, exa (E) 1018, zetta (Z) 1021, yotta (Y) 1024, … googol 10100, … googolplex 1010100

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Data Communications

• All information is represented as digital dataAnalog information is converted to digital

o Sampling

• Data is transferred using electromagnetic waves

Light, electricity, radioo Analog signal

o Modulation

• Information is recreated at the receiverErrors are corrected or hidden

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Requirements on Communication

• QualityDelayInformation loss and distortionReliabilitySecurity

• ConnectivityOne-way and two-way

o Simplex/duplex

One to one, one to many

• CostInformationService

o Resources (time, capacity)

o Management—Booking—Directory services—Security

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Connectivity

Duplex

Half duplex

Simplex

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Point-to-point Connections

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Multipoint Connection

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Networks

• Need devices between sender and receiverSignals regeneration and amplification

Different equipment, formats, etc

Sharing of links

Routing, addressing, traffic control, ...

• A set of nodes connected by linksHosts, switches, routers, stations, …

• Links form a topology

• Distributed processingTasks are divided among multiple units (computers)

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Physical Topologies

TopologyTopology

MeshMesh StarStar BusBus RingRing

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Mesh Topology

• One link betweenevery pair of nodes

• AdvantagesReliable and robust

High capacity

• DisadvantagesHigh cost

o Installation

o Cabling

o Number of I/O ports

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Star Topology

• All links to a central node(hub)

• Common officeinstallation today

• AdvantagesLess costly than mesh

Easy to install and maintain

• DisadvantagesHub is single point of failure

One cable from eachnode to hub

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Bus Topology

• Point-to-multipoint

• AdvantagesEase of installation

Cost

• DisadvantagesLimited size

Maintainanceo Reconfiguration

o Fault isolation

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Ring Topology

• Point-to-point linksBetween neighbours

• Signals rotate around the ring

• AdvantagesEasy to install and reconfigureCost

• DisdvantagesRobustness

• Dual ring improvesrobustness and capacity

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Network Types

NetworkNetwork

Local Area Network(LAN)

Local Area Network(LAN)

Metropolitan Area Network(MAN)

Metropolitan Area Network(MAN)

Wide Area Network(WAN)

Wide Area Network(WAN)

• Classification depends on:Ownership

Size and distance

Physical architecture

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Local Area Networks (LANs)

• Single organizationOffice, building, campus, etc

• Resource sharingPrinters, file servers, Internet connection

• One type of mediumEthernet most common

o 10, 100, 1000 Mb/s

Wireless LANs

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Metropolitan Area Network (MAN)

• Connect LANs together• Provide access to WAN• Different kinds of ownership

private companypublic company

o Network operatoro ”Stadsnät, kommuner, energibolag”

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Wide Area Network (WAN)

• International networks• Use different kinds of equipment

Public, leased, private equipment

• International operators (carriers)• Private WAN

”Enterprise networks”

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Telephone Network

• Built for analog voice trafficSuscriber access via simple pair cable

o Analog signals with low bandwidth, about 3 kHz

Low delay, low lossData transfer with modem (fax)ISDN – multiservice network, is available but outdated

• Simple terminals with “intelligence in the network”• Services mainly related to connection establishment

(“plustjänster")Call waitingCall transferGroup calls

• xDSL—Higher data rate over existing telephone cables

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Cable TV

• One-way distribution (simplex) of TV signals

• Cabling with high qualityCoaxial cable or optical cable

Bus or star topology

• Alternative Internet accessHigher capacity down link (up to 2000 kb/s today)

Lower capacity uplink (up to 400 kb/s today)

• Owned and operated independently of the telephone network

Competition in the local access networks

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The Internet

• Most important computer networkNote: capital I in Internet!

• Many interconnected (independent) networks• Common addressing and transmission format

Internet Protocol (IP)

• Access via telephone network, cable TV, fiber, …Internet Service Provider (ISP)Limited access speed

• Information primarily not time-dependentMainly text and pictures

• Time-dependent traffic increasesStreaming media (for example Web radio)IP telephony (“Voice over IP”)

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Internet Today