Data Communications And Computer Networks

2G1316

Data Communications and Computer Networks Peter Sjödin KTH School of Electrical Engineering Laboratory for Communication Networks

Introduction • Goal • Related courses • Planning and rules ƒ Lectures ƒ Recitations ƒ Laboration

• Material ƒ Book ƒ Exercises with solutions ƒ Lab instructions

• Responsabilities of participants 2

Goal • Basics ƒ Data communications o

How information can be transfered

ƒ Protocols o

How system functions are performed

ƒ Services o

How the networks are used

ƒ Network architectures o

How the pieces are put together

ƒ Design principles and methods

• Introduction to TCP/IP and the Internet 3

Related Courses 2E1624 (5p) Performance Analysis of Communication Networks

2E1623 (5p) Data links and local area networks

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

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

2G1318 (4p) Queuing theory and teletraffic systems

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

2E1633 (5p) Network services and Internet-based applications

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Course Planning • Twelve lectures • Nine recitations • One laboration ƒ Homework ƒ Preparation for the laboration

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Teachers • Lectures

ƒ Peter Sjödin (Swedish)

• Recitation assistants ƒ György Dan (English/Swedish) ƒ Vladimir Vukadinovic (English) ƒ Fetahi Wuhib (English)

• Laborations ƒ Jing Fu ƒ Mikael Rudholm 6

Students • Please meet… ƒ D3, D4 ƒ E3, E4 ƒ I2 ƒ MEDIA2 ƒ Medicinsk Informatik o

Karolinska institutet

ƒ Enstaka kurser… 7

Please Note! • Exam March 13 • Important messages through Bilda ƒ bilda.kth.se ƒ Also at the lectures ƒ You are responsible for staying updated!

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Lectures and Recitations • •

F1: Introduction F2: Layered models ƒ ƒ

•

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

•

Modulation Coding Link technologies

F5 + Ö3: Data link layer ƒ ƒ ƒ

•

Internet OSI

Flow control Error control Data link protocols

•

F7 + Ö5: Wide Area Networks ƒ ƒ ƒ

• •

F8 and F9 + Ö6 and Ö7: Internetworking and IP F10 and F11 + Ö8: End-to-end communication ƒ ƒ

• •

Circuit switching Packet switching Virtual circuits

Transport protocols Applications

F12: — (spare) F13 + Ö9: Summary

F6 + Ö4: Local Area Networks ƒ ƒ

Multiple Access Ethernet (IEEE 802.3)

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Laboration • Purpose ƒ Design and configuration of a computer network ƒ Work with modern Internet equipment

• Laboratorium LQ303, Osquldas väg 10 • Groups with two students • Sign up for lab sessions ƒ (more details later)

• Homework ƒ Must be completed in order to do the lab! ƒ Deadline February 2 ƒ 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: ƒ MEDIA, Medicinsk Informatik o

Track 1 (György)

ƒ D, E, and I o

Track 2 (Vladimir and Fetahi) 11

Course Material • Book ƒ

Behrouz A Forouzan, Data Communications and Networking, 3rd edition, McGraw-Hill. ISBN 007-123241-9.

• Exercises with solutions • Lab instructions • Summary of course modules ƒ Background material

• All material (except for the book) is available on the course web ƒ 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 labs ƒ S3 booking system, see the web

• Course registrations ƒ No separate course registration ƒ When you register for the labs, you also register for the course ƒ If you for some reason are not going to register for the labs, please contact Peter!

• Search the web ƒ Most information available on the course web Course administration

• Course evaluation • Course responsible can be reached through Bilda ƒ Make sure your Bilda profile is up to date

• Be on time for the laborations ƒ And keep the deadline for the homework

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Course Committee (Kursnämnd) • Volounteers? • Meetings ƒ Mid-course ƒ End of course

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Today’s Lecture • Definitions • Signals • Requirements on communication • Communication networks ƒ Connections and topologies ƒ Network types

• Examples of networks 15

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 meanings ƒ Wikipedia (http://www.wikipedia.org) lists five meanings: o o o

1. Negative entropy—the 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 ƒ Representation of information o

Symbols with a certain syntax

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Information • Technical definition ƒ Context known by sender and receiver o

The alternatives are well defined

ƒ Information represents one alternative o

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 information ƒ Has a certain bit rate or data rate (measured in bits per second, b/s, bit/s, bps)

• Time independent information ƒ Consists of a certain amount of bits

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Communication • Sharing or transfer of information • “Telecommunication” ƒ Communication at a distance o

”Tele” is ”far” in Greek

ƒ Traditionally speach ƒ Sound, pictures, text, ...

• “Communications” ƒ With an ’s’ at the end! ƒ “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” ƒ ”[...] 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 link ƒ Signal format

• Addressing ƒ Identify sender and receiver

• Routing ƒ Find a path between sender and receiver

• Buffering ƒ Compensate for differences in speed ƒ Variations in traffic load

• Error detection and control ƒ If data is lost or corrupted

• Congestion control ƒ To protect the network from being overloaded

• Management and network operations

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Signals • Analog signals ƒ Continuous in time ƒ Infinitely many levels o

Continuously varying

• Digital signals ƒ Limited number of levels o o

Discrete Often binary (0 and 1)

ƒ Discrete in time

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Sine Wave • Fully described by ƒ s(t) = A sin(2πft + φ) ƒ A is amplitude, f is frequency, φ is phase

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Time and Frequency Domains • A signal can be represented as ƒ A function of time ƒ 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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Bandwidth • Important property of a medium ƒ Difference between highest and lowest frequency that can pass through the medium ƒ Measured in Hertz [Hz] ƒ Limits the channel’s capacity

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Capacity • Transmission capacity ƒ Measured in bits per second [b/s, bit/s, bps]

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

• Larger units ƒ 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 ƒ Analog information is converted to digital o

Sampling

• Data is transferred using electromagnetic waves ƒ Light, electricity, radio o

Analog signal

o

Modulation

• Information is recreated at the receiver ƒ Errors are corrected or hidden

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Requirements on Communication • Quality ƒ Delay ƒ Information loss and distortion ƒ Reliability ƒ Security

• Connectivity ƒ One-way and twoway o

• Cost ƒ Information ƒ Service o o

Resources (time, capacity) Management — Booking — Directory services — Security

Simplex/duplex

ƒ One to one, one to many

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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 ƒ Signals regeneration and amplification ƒ Different equipment, formats, etc ƒ Sharing of links ƒ Routing, addressing, traffic control, ...

• A set of nodes connected by links ƒ Hosts, switches, routers, stations, …

• Links form a topology • Distributed processing ƒ Tasks are divided among multiple units (computers)

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Physical Topologies

Topology Topology Mesh Mesh

Star Star

Bus Bus

Ring Ring

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Mesh Topology • One link between every pair of nodes • Advantages ƒ Reliable and robust ƒ High capacity

• Disadvantages ƒ High 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 office installation today • Advantages ƒ Less costly than mesh ƒ Easy to install and maintain

• Disadvantages ƒ Hub is single point of failure ƒ One cable from each node to hub

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Bus Topology • Point-to-multipoint • Advantages ƒ Ease of installation ƒ Cost

• Disadvantages ƒ Limited size ƒ Maintainance o

Reconfiguration

o

Fault isolation

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Ring Topology •

Point-to-point links ƒ

• •

Between neighbours

Signals rotate around the ring Advantages ƒ ƒ

Easy to install and reconfigure Cost

• Disdvantages ƒ Robustness

• Dual ring improves robustness and capacity

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Network Types Network Network Local LocalArea AreaNetwork Network (LAN) (LAN)

Metropolitan MetropolitanArea AreaNetwork Network (MAN) (MAN)

Wide WideArea AreaNetwork Network (WAN) (WAN)

• Classification depends on: ƒ Ownership ƒ Size and distance ƒ Physical architecture 40

Local Area Networks (LANs) • Single organization ƒ Office, building, campus, etc

• Resource sharing ƒ Printers, file servers, Internet connection

• One type of medium ƒ Ethernet most common o

10, 100, 1000 Mb/s

ƒ Wireless LANs

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Metropolitan Area Network (MAN) • Connect LANs together • Provide access to WAN • Different kinds of ownership ƒ private company ƒ public company o o

Network operator ”Stadsnät, kommuner, energibolag”

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Wide Area Network (WAN) • International networks • Use different kinds of equipment ƒ Public, leased, private equipment

• International operators (carriers) • Private WAN ƒ ”Enterprise networks”

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Telephone Network • Built for analog voice traffic ƒ Suscriber access via simple pair cable o

Analog signals with low bandwidth, about 3 kHz

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

• Simple terminals with “intelligence in the network” • Services mainly related to connection establishment (“plustjänster") ƒ Call waiting ƒ Call transfer ƒ Group 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 quality ƒ Coaxial cable or optical cable ƒ Bus or star topology

• Alternative Internet access ƒ Higher capacity down link (up to 2000 kb/s today) ƒ Lower capacity uplink (up to 400 kb/s today)

• Owned and operated independently of the telephone network ƒ Competition in the local access networks

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The Internet • Most important computer network ƒ Note: capital I in Internet!

• Many interconnected (independent) networks • Common addressing and transmission format ƒ Internet Protocol (IP)

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

• Information primarily not time-dependent ƒ Mainly text and pictures

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

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Internet Today

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