2G1316

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• 2G1316 2G1317
• Data Communications and Computer Networks

Peter Sjödin KTH IMIT
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Introduction

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

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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

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Related Courses
2G1325 (5p)Practical Voice over IP SIP and
related protocols
2G1316 (4p)Data communications and computer
networks
2G1305 (4p)Internetworking
2G1330 (5p) Wireless and mobile network
architectures
2G1318 (4p)Queuing theory and teletraffic
systems
2G1332 (5p) Management of networks and
networked systems
2G1501 (6p)Communication systems
2G1507 (6p)Communication systems advanced course
2G1333 (4p)Network services and Internet-based
applications
Laboratory for Communication Systems,
www.lcn.imit.kth.se
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Course Planning

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

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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

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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!

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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.

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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

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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

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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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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

• 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
• ...

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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

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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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Point-to-point Connections
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Multipoint Connection
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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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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

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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

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Network Types

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

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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

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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

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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

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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 local 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 slow down migration

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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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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