2G1316

1

• 2G1316 2G1317
• Data Communications and Computer Networks

Peter Sjödin KTH IMIT
2
Introduction

• Goal
• Related courses
• Planning and rules
• Lectures
• Recitations
• Laboration
• Material
• Book
• Exercises with solutions
• Lab instructions
• Responsabilities of participants

3
Goal

• Basics
• Data communications
• How information can be transfered
• Protocols
• How system functions are performed
• Technologies
• How systems are built
• Services
• How the networks are used
• Network architectures
• How the pieces are put together
• Design principles and methods
• Introduction to TCP/IP and the Internet

4
Related Courses
5
Related Courses

• Påbyggnad
• 2G1305 Internetworking
• TCP/IP in depth
• Network services and Internet-based applications
• 2G1318 Köteori och teletrafiksystem
• Network analysis for performance and dimensioning
• 2G1330 Wireless and Mobile Network Architectures
• 2G1331 Management of Network and Networked
  Systems
• Complement
• 2D1490 IP-routning inom enkla datornät
• 2D1491 IP-routning på Internet och andra
  sammansatta nät
• 2E1431 Kommunikationsteori
• 2E1511 Radiokommunikation

6
Course Planning

• Twelve lectures
• Nine recitations
• One laboration
• Homework
• Preparation for the laboration

7
Teachers

• Lectures
• F 1 - F 10 Peter Sjödin
• F 11 Johan Montelius, guest lecturer
• F 12 Course summary, Peter
• Recitation assistants
• Group 1 and 4 Ignacio Más Ivars (English)
• Recommendation MEDIA and I
• Group 2 and 5 Henrik Lundqvist (Swedish)
• Recommendation Others (D, E, Med-IT, ...)
• Group 3 and 6 (if needed)
• Laborations
• Héctor Velayos with assistants

8
Please Note!

• Exam March 11
• Important messages on the course web
• http//www.imit.kth.se/courses/2G1316
• Also at the lectures
• You are responsible for staying updated!

9
Lectures and Recitations

• F1 Introduction
• F2 Layered models
• Internet
• OSI
• F3 and F4 Ö1 and Ö2 Physical layer and data
  transfer
• Modulation
• Coding
• Link technologies
• F5 Ö3 Data link layer
• Flow control
• Error control
• Data link protocols
• F6 Ö4 Local Area Networks
• Multiple Access
• Ethernet (IEEE 802.3)

• F7 Ö5 Wide Area Networks
• Circuit switching
• Packet switching
• Virtual circuits
• F8 and F9 Ö6 and Ö7 Internetworking and IP
• F10 Ö8 End-to-end communication
• Transport protocols
• Applications
• F11 Guest Lecture
• F12 Ö9 Summary

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Laboration

• Purpose
• Design and configuration of a computer network
• Work with modern Internet equipment
• Takes place in Kista (sal 430, KTH Forum)
• Groups with two students
• Sign up for lab sessions at Studentexpeditionen
  (STEX), Q building
• No later than Jan 26 at 1200
• Homework
• Must be completed in order to do the lab!
• Deadline Should be handed in at STEX, Q
  building, by Jan 26 at 1200.

11
Course Material

• Book
• Behrouz A Forouzan, Data Communications and
  Networking, 3rd edition, McGraw-Hill. ISBN
  0072515848.
• 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.imit.kth.se/courses/2G1316
• Printed version of exercises and lab instructions
  can be bought at STEX

12
Your Responsibilities

• Search the web
• Most information available on the course web
  http//www.imit.kth.se/courses/2G1316
• KTH-student http//www.kth.se/student
• Läs- och tentamensscheman
• Course responsible can be reached at
• 2G1316-17_at_imit.kth.se
• Peter does not reply to mail to any other
  address!
• Ask questions at the lectures!
• Be on time for the laborations
• And keep the deadline for the homework

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Course Committee (Kursnämnd)

• Volounteers
• D
• E
• I
• Med-IT
• MEDIA
• Meetings
• After a few lectures
• End of course

14
Todays Lecture

• Definitions
• Signals
• Requirements on communication
• Communication networks
• Connections and topologies
• Network types
• Examples of networks
• Overview of design and analysis methods

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Information and Data

• Informationmany meanings
• Wikipedia (www.wikipedia.org) lists 5 meanings
• 1. Negative entropythe instructions that are
  needed to produce order or reduce uncertainty
• ...
• 5. Any type of pattern that influences the
  formation or transformation of other patterns
• Data
• Representation of information
• Symbols with a certain syntax

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Another Way to Define Information and Data

• Data is a representation of facts, concepts, or
  instructions in a formalized manner suitable for
  communication, interpretation, or processing by
  human beings or by automatic means
• Information is the meaning that is currently
  assigned to data by means of the conventions
  applied to those data
• Dictionary for Information Systems, American
  National Standards Institute, X3.1721990

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Information

• Technical definition
• Context known by sender and receiver
• The alternatives are well defined
• Information represents one alternative
• To represent one of N alternatives requires
  élog2Nù bits
• Example The letters in the Swedish alphabet can
  be represented by 5 bits (25 32)

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Information

• Time dependent information
• Has a certain bit rate or data rate (measured in
  bits per second, b/s, bit/s, bps)
• Time independent information
• Consists of a certain amount of bits

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Information and Knowledge

• Weak relation information can lead to knowledge
• Requires that
• Information has certain qualities
• Receiver has capacity to process the information
  (reflecting)
• Increased information flow
• Could decrease knowledge by overloading
  processing capacity

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Communication

• Sharing or transfer of information
• Telecommunication
• Communication at a distance
• Tele is far in Greek
• Traditionally speach
• Sound, pictures, text, ...
• Communications
• With an s
• The branch of technology concerned with the
  representation, transfer, interpretation, and
  processing of data among persons, places, and
  machines also known as information systems.
• From www.wikipedia.org
• Data communications
• ... the exchange of data between two devices
  over some form of transmission medium
• Forouzan

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ApplicationsWhy Communication?

• Human communication
• Sound, picture,
• Machine communication
• Process control
• Logistics
• Man-machine
• Business
• Shopping, services
• Business to business
• Control status reports (warnings) and commands
• Access to information (databases)
• Simulations and games
• ...

22
Network Functions

• Ways to transfer information on a link
• Signal format
• Addressing
• Identify sender and receiver
• Routing
• Find a path between sender and receiver
• Buffering
• Compensate for differences in speed
• Error detection and control
• If data is lost or corrupted
• Congestion control
• To protect the network from being overloaded
• Management and network operations

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Signals

• Analog signals
• Continuous in time
• Infinitely many amplitude levels
• Continuously variying amplitude
• Digital signals
• Limited number of defined amplitude levels
• Discrete (quantisized)
• Often binary (0 and 1)
• Discrete in time (sampled)

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Sine Wave

• Fully described by
• s(t) A sin(2pft f)
• A is amplitude, f is frequency, f is phase

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Time and Frequency Domains

• A signal can be represented as
• A function of time
• A function of frequency

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Composite Signals
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Fourier Analysis

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

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Frequency Spectrum of a Square Wave
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Bandwidth

• Property of a medium
• Difference between the highest and lowest
  frequency that can pass through the medium
• Bandwidth of an analogous channel is neasured in
  Hertz Hz
• A measure of the channels capacity

30
Capacity

• Transmission capacity
• Measured in bits per second b/s, bit/s, bps
• Increased bandwidth can give higher capacity
• A noiseless analogous channel has infinite
  capacity
• Larger units
• kilo (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 data
• Analog information is converted to digital
• Sampling
• Data is transferred using electromagnetic waves
• Light, electricity, radio
• Modulation
• Information is recreated at the receiver
• Time dependencies are recreated
• Errors are corrected or hidden

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Requirements on Communication

• Quality
• Delay
• Information loss and distortion
• Reliability
• Security
• Connectivity
• One way and two way
• Simplex/duplex
• One to one, one to many

• Cost
• Information
• Service
• Resources (time, capacity)
• Management
• Booking
• Directory services
• Security

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Connectivity
Duplex
Half duplex
Simplex
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Networks

• Need devices between sender and receiver
• Signals regeneration and amplification
• Different equipment, formats, etc
• Sharing of links
• Routing, addressing, traffic control, ...
• A set of nodes connected by links
• Hosts, switches, routers, stations
• Links form a topology
• Distributed processing
• Tasks are divided among multiple units (computers)

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Point-to-point Connections
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Multipoint Connection
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Physical Topologies
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Mesh Topology

• One link between every pair of nodes
• Advantages
• Reliable and robust
• High capacity
• Disadvantages
• High cost
• Installation
• Cabling
• Number of I/O ports

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Star Topology

• All links to a central node (hub)
• Common office installation today
• Advantages
• Less costly than mesh
• Easy to install and maintain
• Disadvantages
• Hub is single point of failure
• One cable from each node to hub

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Bus Topology

• Point-to-multipoint
• Advantages
• Ease of installation
• Cost

• Disadvantages
• Limited size
• Maintainance
• Reconfiguration
• Fault isolation

41
Ring Topology

• Point-to-point links
• Between neighbours
• Signals rotate around the ring
• Advantages
• Easy to install and reconfigure
• Cost

• Disdvantages
• Robustness
• Dual ring improves robustness and capacity

42
Network Types

• Classification depends on
• Ownership
• Size and distance
• Physical architecture

43
Local Area Networks (LANs)

• Single organization
• Office, building, campus, etc
• Resource sharing
• Printers, file servers, Internet connection
• One type of medium
• Ethernet most common
• (10), 100, 1000 Mb/s

44
Multiple-building LAN
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Metropolitan Area Network (MAN)

• Connect LANs together
• Provide access to WAN
• Different kinds of ownership
• private company
• public company
• Network operator
• 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

47
Telephone Network

• Built for analog voice traffic
• Suscriber access via simple pair cable
• Analog signals with low bandwidth, about 3 kHz
• Low delay, low loss
• Data 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 waiting
• Call transfer
• Group calls

48
Cable TV

• One-way distribution (simplex) of TV signals
• Cabling with high quality
• Coaxial cable or optical cable
• Bus or star topology
• Alternative Internet access
• Higher 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 access networks

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The Internet

• Most important computer network
• Note 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 dependent
• Mainly text and pictures
• Video and sound (including voice)
• Increasing
• Problems with delay and loss slows down migration

50
Internet Today
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Future Networks - Mobile Internet

• Internet
• More users
• More services
• Multicast
• Quality to support for audio, video
• Mobility
• Competition among service operators
• Radio access and permanent broadband access
• Spontaneous networks
• Direct communication between mobile units
• Peer to peer

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Framtidens datornät - Mobilt Internet

• Internets nästa generation
• bygger på dagens Internet
• stort och snabbt ökande antal användare
• ökat tjänsteutbud
• Multicast
• Tjänstekvalitet
• Mobilitet
• stor konkurrens bland tjänsteoperatörer
• Från IP version 4 till version 6
• Större adressrymd mm
• Radio- och fast bredbandig anslutning

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Konstruktions- och analysmetoder

• Matematiska redskap
• Matematisk statistik och sannolikhetslära
• köteori prestanda och dimensionering av nät för
  slumpmässiga dataflöden
• informationsteori
• Systemteori, linjär och icke-linjär
• Specifika metoder
• Datorsimulering och prototyper
• Digital signalbehandling
• Elektronik- och mjukvaruutveckling
• för realisering av systemet

54
Design and Analysis Methods

• Mathematical tools
• Mathematical statistics and probability analysis
• Queing theory performance and dimensioning of
  networks with random data flows
• Information theory
• Systems theory, linear and non-linear
• Specific methods
• Computer simulations and prototypes
• Digital signal processing
• Hardware and software development
• For system realization
• Measurements and monitoring
• Active and passive

55
Digitalisering av analoga signaler

• Från tidskontinuerlig till tidsdiskret
• Sampling (utpulsning, pulsamplitud-modulering,
  PAM)
• Från amplitudkontinuerlig till amplituddiskret
• Kvantisering
• Kodning (representation)
• Pulskodmodulation (PCM)
• Differential-PCM (DPCM)
• Deltamodulation (DM)

56
Sampling

• Man läser av signalens amplitud med jämna
  mellanrum

Signalen multipliceras med ett pulståg
Pulståg med varierande amplitud
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Samplingsteoremet Nyquist Shannon

• En tidskontinuerlig signal x(t) med bandbredden B
  Hz
• Ändlig bandbredd innebär att signalen är
  amplitudkontinuerlig (även i samtliga derivator)
• Har signalen okänd bandbredd måste den först
  filtreras genom ett tidskontinuerligt filter med
  känd bandbredd, B Hz
• Signalen måste samplas med frekvensen fs ³ 2B
  för att kunna återskapa utan förlust
• Signalen behöver inte ha spektrumet centrerat
  kring 0 Hz
• Översampling, f gt 2B, ger ingen (teoretisk)
  kvalitetsvinst
• Undersampling förvränger signalens spektrum
• Analoga signalen återvinns med hjälp av ett
  tidskontinuerligt filter med bandbredden B Hz
• Frekvensen 2B Hz kallas ofta för
  Nyquist-frekvensen efter den svenskfödde
  amerikanen Harry

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Undersampling

• Exempel
• Sinussignal med frekvensen f Hz, samplad med fs lt
  2f Hz
• Förvrängningen av signalens spektrum (kallas
  aliasing)

59
Illustration sampling i tidsplanet
T
60
Illustration sampling i frekvensplanet
Xs(f)
T-1
f
fs ³ 2B
2fs
Xs(f)
T-1
f
fs lt 2B
2fs
B
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Återskapande av den kontinuerliga signalen

• Signalen x(t) återfås efter filtering
• Analogt filter, bandbredd B1/2T Hz
• i tidplanet
• i frekvensplanet X(f) Xs(f) H(f)
• H(f) T, för -B f B och H(f) 0 i övrigt

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Kvantisering och kodning

• Sampelvärdena xs(nT) är kontinuerliga (reella
  tal) inom något intervall
• Kvantisering rundar av sampelvärdena nedåt
  (trunkerar) till ett ändligt antal nivåer (N)
• Kvantiseringsnivåerna kan kodas med

63
Digitalisering för telefoni PCM

64
Pulskodmodulering

65
PCM-näthierarki

• Primär PCM-multiplex (sammanlagring)
• Europa 30 talkanaler
• USA och Japan 24 talkanaler

66
DPCM och DM

• Differential-PCM
• Koda skillnaderna mellan sampelvärden
• Ytterligare avrunding av små skillnader kan
  reducera antalet kvantiseringsnivåer
• Deltamodulering
• Koda enbart tecknet på skillnaden i DPCM (en bit)
• Ofta kombinerad med översampling

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Signalspektrum

• En signal kan representeras
• i tidsdomänen, som funktion av tiden
• i frekvensdomänen, som funktion av frekvensen
• Signalens spektrum
• Bandbredd
• skillnaden mellan högsta och lägsta frekvensen i
  signalens spektrum