Computer Networks Dr. Miled M. Tezeghdanti October 19, 2010 Dr. - PDF document

Computer Networks Dr. Miled M. Tezeghdanti October 19, 2010 Dr. Miled M. Tezeghdanti () Computer Networks October 19, 2010 1 / 79 Syllabus Basic Concepts OSI Model Data-Link Layer Local Area Networks Network Layer Transport Layer Application Layer Dr. Miled M. Tezeghdanti () Computer Networks October 19, 2010 2 / 79

Bibliography Textbook Computer Networks, Andrew S. Tanenbaum, 4 th edition, Prentice Hall, 2002, ISBN-10: 0130661023, ISBN-13: 978-0130661029. Reference Computer Networking: A Top-Down Approach, James F. Kurose and Keith W. Ross, 5 th edition, Addison Wesley, 2009, ISBN: 0-13-607967-9. Dr. Miled M. Tezeghdanti () Computer Networks October 19, 2010 3 / 79 Outline Network Network Types Network Topology Switching Transmission Digital Encoding Modulation Multiplexing Network Delays Transmission Modes Transmission Media Dr. Miled M. Tezeghdanti () Computer Networks October 19, 2010 4 / 79

Definition A computer network, often simply referred to as a network, is a group of computers and devices interconnected by communications channels that facilitate communications among users and allows users to share resources (from Wikipedia). Goal: Information Exchange Data Voice Video Dr. Miled M. Tezeghdanti () Computer Networks October 19, 2010 5 / 79 Network Types Broadcast Network Each communication is receieved by all network users Examples: Radio Network, TV Network Point-to-Point Network The communication is between two network users Examples: Public Switched Telephone Network (PSTN), Internet Dr. Miled M. Tezeghdanti () Computer Networks October 19, 2010 6 / 79

Network Topology Bus Ring Star Tree Mesh Dr. Miled M. Tezeghdanti () Computer Networks October 19, 2010 7 / 79 Bus Topology All hosts are connected to the same bus The bus can handle a single communication at a given time Cannot be used when the number of hosts is large Each communication could be listened by each host Similar to the FSB (Front Side Bus) of a PC Dr. Miled M. Tezeghdanti () Computer Networks October 19, 2010 8 / 79

Ring Topology All hosts are connected to the same ring Data travels in only one direction Dr. Miled M. Tezeghdanti () Computer Networks October 19, 2010 9 / 79 Star Topology All hosts are connected to a central node Single point of failure Broadcasting Switching Dr. Miled M. Tezeghdanti () Computer Networks October 19, 2010 10 / 79

Tree Topology There is a one and only one path between each two nodes No tolerant to failures Two isolated sub-trees in case of link failure Dr. Miled M. Tezeghdanti () Computer Networks October 19, 2010 11 / 79 Mesh Topology The shortest path is used for the communication Tolerant to failures Economic Solution Dr. Miled M. Tezeghdanti () Computer Networks October 19, 2010 12 / 79

Switching How is data transferred through the network? Circuit Switching Message Switching Packet Switching Cell Switching Dr. Miled M. Tezeghdanti () Computer Networks October 19, 2010 13 / 79 Switching Circuit Switching Public Switched Telephone Network (PSTN) Message Switching Mail/Email Packet Switching Internet Cell Switching Asynchronous Transfer Mode (ATM) Dr. Miled M. Tezeghdanti () Computer Networks October 19, 2010 14 / 79

Circuit Switching End to end dedicated communication circuit Established for the call duration End to end physical circuit must be established before data transfer Example: Telephone Network Dr. Miled M. Tezeghdanti () Computer Networks October 19, 2010 15 / 79 Circuit Switching 1 5 2 6 3 7 4 8 1 3: Circuit Setup Success 4 6: Circuit Setup Success 1: Circuit Setup Failure: User Busy 5 2: Circuit Setup Failure: Network Busy 8 4 6: Circuit Release Success 7: Circuit Setup Success 2 Dr. Miled M. Tezeghdanti () Computer Networks October 19, 2010 16 / 79

Message Switching Does not require circuit setup before conversation Messages are stored and then forwarded Store-and-forward No restriction on the size of transferred messages Intermediate nodes must have huge storage space Example: Mail/Email Dr. Miled M. Tezeghdanti () Computer Networks October 19, 2010 17 / 79 Message Switching Message Switching from: h1@lan1.net from: h1@lan1.net to: h5@lan5.net to: h5@lan5.net subject: MS subject: MS from: h1@lan1.net from: h1@lan1.net Email uses MS Email uses MS to: h5@lan5.net to: h5@lan5.net . . subject: MS subject: MS Email uses MS Email uses MS MTA/MDA MTA/MDA . . MUA MUA LAN LAN MUA MUA Internet MUA MUA LAN LAN MTA/MDA MTA/MDA MUA MUA MAU: Mail User Agent (pine, Outlook, Mozilla, ...) MTA/MDA: Mail Transfer Agent/Mail Delivery Agent (Sendmail, Exchange, ...) LAN: Local Area Network Dr. Miled M. Tezeghdanti () Computer Networks October 19, 2010 18 / 79

Packet Switching Invented to overcome message switching problems Messages are segmented into packets Packets have a maximum size Pipeline: first packet could be transmitted before the arrival of the second one Example: Internet Dr. Miled M. Tezeghdanti () Computer Networks October 19, 2010 19 / 79 Packet Switching Packet Switching from: h1@lan1.net to: h5@lan5.net subject: MS Email uses MS . . 1−>5,5 1−>5,3 to: h5@lan5.net 1−>5,2 Email uses MS 1−>5,4 subject: MS from: h1@lan1.net 1−>5,1 Dr. Miled M. Tezeghdanti () Computer Networks October 19, 2010 20 / 79

Cell Switching Similar to packet switching Messages/Packets are segmented into cells Cells have fixed size Padding bytes in the last cell Good for real time traffic (transmission time is fixed for each cell) Example: ATM Dr. Miled M. Tezeghdanti () Computer Networks October 19, 2010 21 / 79 Transmission Link Characteristics Simplex Transmission in one direction Radio, TV Half-Duplex Transmission in both directions, but in only one direction at a given time Walkie Talkie Full-Duplex Transmission in both directions simultaneously Telephone Dr. Miled M. Tezeghdanti () Computer Networks October 19, 2010 22 / 79

Signal A signal is a varying quantity (voltage, air pressure,) that can be expressed as a continuous function of an independent variable usually time Used for data representation Digital Signal Discrete time signal Discrete values (+5V and 5V) Dr. Miled M. Tezeghdanti () Computer Networks October 19, 2010 23 / 79 Analog Signal Continuous time signal Amplitude varies continuously Dr. Miled M. Tezeghdanti () Computer Networks October 19, 2010 24 / 79

Digital Signal Discrete time signal Discrete values (+5V and 5V) Dr. Miled M. Tezeghdanti () Computer Networks October 19, 2010 25 / 79 Fourier Analysis A periodic signal g ( t ) with frequency f can be written as follows: ∞ ∞ g ( t ) = c � � 2 + a n sin (2 π nft ) + b n cos (2 π nft ) n =1 n =1 � T c = 2 g ( t ) dt T 0 � T a n = 2 g ( t ) sin (2 π nft ) dt T 0 � T b n = 2 g ( t ) cos (2 π nft ) dt T 0 if the signal is not periodic, we can apply Fourier on portions of the signal. Dr. Miled M. Tezeghdanti () Computer Networks October 19, 2010 26 / 79

Fourier Analysis � T a n = 2 g ( t ) sin (2 π nft ) dt T 0 T = 2 � 2 sin (2 π nft ) dt T 0 � T = 2 � 1 2 2 π nf cos (2 π nft ) − T 0 = 2 � 1 �� cos (2 π nf T � 2 ) − cos (0) − T 2 π nf �� �� = − 2 1 cos (2 π nf T 2 ) − cos (0) 2 π nf T = − 1 � � cos ( n π ) − 1 n π = 1 � � 1 − cos ( n π ) n π Dr. Miled M. Tezeghdanti () Computer Networks October 19, 2010 27 / 79 Fourier Analysis � T b n = 2 g ( t ) cos (2 π nft ) dt T 0 T = 2 � 2 cos (2 π nft ) dt T 0 � T = 2 � 1 2 2 π nf sin (2 π nft ) T 0 = 2 � 1 �� sin (2 π nf T � 2 ) − sin (0) T 2 π nf = 2 1 sin (2 π nf T � � 2 ) − sin (0) 2 π nf T = 1 � � sin ( n π ) − 0 n π = 0 Dr. Miled M. Tezeghdanti () Computer Networks October 19, 2010 28 / 79

Fourier Analysis � T c = 2 g ( t ) dt T 0 � T � = 2 2 t T 0 = 2 � T � 2 − 0 T = 2 T 2 T = 1 Dr. Miled M. Tezeghdanti () Computer Networks October 19, 2010 29 / 79 Fourier Analysis ∞ ∞ g ( t ) = c � � 2 + a n sin (2 π nft ) + b n cos (2 π nft ) n =1 n =1 a n = 1 � � 1 − cos ( n π ) n π b n = 0 c = 1 ∞ g ( t ) = 1 1 � � � 2 + 1 − cos ( n π ) sin (2 π nft ) + 0 n π n =1 g ( t ) = 1 2 + 2 π sin (2 π ft ) + 2 3 π sin (6 π ft ) + 2 5 π sin (10 π ft ) + ... Dr. Miled M. Tezeghdanti () Computer Networks October 19, 2010 30 / 79

Fourier Analysis Dr. Miled M. Tezeghdanti () Computer Networks October 19, 2010 31 / 79 Fourier Analysis Dr. Miled M. Tezeghdanti () Computer Networks October 19, 2010 32 / 79

Fading/Attenuation Fading/Attenuation Diminution of the amplitude of the signal Depends on: Frequency of the signal Transmission media Circuit length Dr. Miled M. Tezeghdanti () Computer Networks October 19, 2010 33 / 79 Fading/Attenuation Dr. Miled M. Tezeghdanti () Computer Networks October 19, 2010 34 / 79

Distortion Distortion Signal deformation The signal is constituted by many harmonics with different frequencies Harmonics are transmitted with different speeds Received signal will be distorted Dr. Miled M. Tezeghdanti () Computer Networks October 19, 2010 35 / 79 Distortion Dr. Miled M. Tezeghdanti () Computer Networks October 19, 2010 36 / 79