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CPEG 419 COMPUTER COMMUNICATION NETWORKS

CPEG 419 COMPUTER COMMUNICATION NETWORKS. Instructor: Stephan Bohacek Course webpage: www.eecis.udel.edu/ ~ bohacek/classes/419 Email: bohacek@ee.udel.edu Office: Evans 315 Phone: 831-4274 TA: Ignjat Kilibarda TA’s email: cmpt@udel.edu. CPEG 419. Textbooks:

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CPEG 419 COMPUTER COMMUNICATION NETWORKS

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  1. CPEG 419 COMPUTER COMMUNICATION NETWORKS Instructor: Stephan Bohacek Course webpage: www.eecis.udel.edu/~bohacek/classes/419 Email: bohacek@ee.udel.edu Office: Evans 315 Phone: 831-4274 TA: Ignjat Kilibarda TA’s email: cmpt@udel.edu U of D CPEG 419

  2. CPEG 419 • Textbooks: • Require textbook: W. Stallings, Data and Computer Communications, 6th edition, Prentice Hall. • Other books: • Peterson and Davie, Computer Networks. • Tanenbaum, Computer Networks. • Grading: • Homework and quizzes (20%) • Midterm (20%) • Project (20%) • Final exam (40%) • Homework consist of short problems, programming and ns simulations. University of Delaware CPEG 419

  3. Who are you? Write the following on a piece of paper • Name, email, Majors, Year. • Why 419? • Do you know what the Fourier transform is? • Do you know how to program? (C, sockets?) • Have you taken any probability? • Circuits? What is an RC circuit? • Do you know what ARP is? • What is 10base-T? • What is the speed of 10base-T? University of Delaware CPEG 419

  4. Course Objectives: • Basic understanding of computer networks and their protocols. • OSI’s 7 layer protocol stack and the TCP/IP protocol suite. • Internet. • LANs. University of Delaware CPEG 419

  5. Course Outline • Introduction • Basic concepts • Layers • OSI • TCP/IP • Physical Layer • Data Link Layer • MAC Layer • Multiplexing • LANs University of Delaware CPEG 419

  6. Outline (cont’d) • Network Layer • Routers versus bridges • Routing and forwarding • Addressing and subnetting • Internetworking • IP: IPv4 and IPv6 • ICMP • Internet routing: RIP, OSPF, BGP • IP Multicast University of Delaware CPEG 419

  7. Outline (cont’d) • Transport Layer • UDP • TCP • End-to-end argument • Error control • Flow and congestion control • Security University of Delaware CPEG 419

  8. Outline (cont’d) • Layer 5 and above • DNS • FTP • E-mail • SNMP • HTTP • Wireless networks (time permitting) University of Delaware CPEG 419

  9. Administration Issues • How late can we start next Tuesday? • Probably no class on Oct 3. University of Delaware CPEG 419

  10. Introduction • Basic concepts • Layers • OSI • TCP/IP University of Delaware CPEG 419

  11. Ubiquitous Computing • Computers everywhere. • Also means ubiquitous communication • Users connected anywhere/anytime. • PC, laptop, palmtop, cell phone, etc. University of Delaware CPEG 419

  12. Computer Network • WHY? • Provide access to local and remote resources (data/information, computing, etc.). • Provide efficient communication (email, voice over IP, chatting, etc.) • HOW? • Collection of interconnected end systems: • Computing devices (mainframes, workstations, PCs, palm tops) • Peripherals (printers, scanners, terminals, sensors). • Applications: location and platform transparency. University of Delaware CPEG 419

  13. Computer Networks (cont’d) • Physical Components: • Nodes • End systems (or hosts), • Routers/switches/bridges, and • Links • twisted pair, • coaxial cable, • fiber, • radio, • etc. University of Delaware CPEG 419

  14. Computer Networks (cont’d) • Protocols – Protocols define a way for the physical components to work together. • Applications – The final result and end product of the network. University of Delaware CPEG 419

  15. The Internet: Some History • Late 1970’s/ early 1980’s: the ARPANET (funded by ARPA). • Connecting university, research labs and some government agencies. • Main applications: e-mail and file transfer. • Features: • Decentralized, non-regulated system. • No centralized authority. • No structure. • Network of networks. University of Delaware CPEG 419

  16. The Internet (cont’d) • Early 1990’s, the Web caused the Internet revolution: the Internet’s killer app! • Today: • Almost 60 million hosts as of 01.99. • Doubles every year. University of Delaware CPEG 419

  17. How the Internet is designed • Internet Society • IAB • IETF • IRTF • Internet draft -> RFC -> Internet standard • There are many other standards that are also used, e.g., IEEE, ISO, ITU-T University of Delaware CPEG 419

  18. Network Architecture (chapter 2) • Protocol layers: divide and conquer. • Main idea: each layer uses the services from lower layer and provide services to upper layer. • Higher layer shielded from the implementation details of lower layers. • Interface between layers must be clearly defined: services provided to upper layer. University of Delaware CPEG 419

  19. Network Layers in Action: An Example Goal: Send a file from a web server (e.g. yahoo.com) to a web client (e.g. your PC). Application e.g. http server Application e.g. http client Transport Layer e.g. TCP source Transport Layer e.g. TCP receiver Network Layer: IP Network Layer: IP Network Layer Network Layer Link Layer e.g., CSMA/CD Link Layer e.g., CSMA/CD Link Layer Link Layer Link Layer Physical Layer e.g., twisted pair Physical Layer e.g., twisted pair Physical Layer Physical Layer Physical Layer University of Delaware CPEG 419

  20. Approach 1: ISO OSI Model • ISO: International Standards Organization • OSI: Open Systems Interconnection. Application Presentation Session Transport Network Data link Physical University of Delaware CPEG 419

  21. OSI ISO 7-Layer Model • Physical layer: transmission of bits/bytes. Deals with electric properties and encoding. • Data link layer: reliable transmission over physical medium; synchronization, error control, flow control; media access in shared medium. • Network layer: routing and forwarding; congestion control; internetworking. University of Delaware CPEG 419

  22. OSI ISO 7-Layer Model (cont’d) • Transport layer: error, flow, and congestion control end-to-end. • Session layer: manages connections (sessions) between end points. • Presentation layer: data representation. • Application layer: provides users with access to the underlying communication infrastructure. University of Delaware CPEG 419

  23. Example 2: TCP/IP Model • Model employed by the Internet. ISO OSI TCP/IP Application Application Presentation Session Transport Transport Internet Network Network Access Data link Physical Physical University of Delaware CPEG 419

  24. TCP/IP Protocol Suite: • Physical layer: same as OSI ISO model. • Network access layer: medium access and routing over single network. • Internet layer: routing across multiple networks, or, an internet. • Transport layer: end-to-end error, congestion, flow control functions. • Application layer: same as OSI ISO model. University of Delaware CPEG 419

  25. Physical Layer (Stallings Chap. 3-6) • Sending raw bits/bytes/words across “the wire”. • Point to point. No routing, no error correction (link layer). • Objective: Transmit a frame from a transmitter to receiver. University of Delaware CPEG 419

  26. Basic Concepts • Signal: electro-magnetic wave carrying information. • Time domain: signal as a function of time. • Analog signal: signal’s amplitude varies continuously over time, ie, no discontinuities. • Digital signal: data represented by sequence of 0’s and 1’s (e.g., square wave). University of Delaware CPEG 419

  27. Digital vs. Analog Signals Digital signals don’t really exists. We interpret analog signals as digital digital signal analog signal 0 0 1 0 0 1 0 0 University of Delaware CPEG 419

  28. Bandwidth vs. Data Rate • Q. What is the bandwidth of 10base-T ethernet? • The data rate is 10Mbs (mega bits per second). • The bandwidth maybe larger than 10Mhz. Let x(t) be the analog signal broadcast. The Fourier transform of x is X(f) is the component of x that has frequency f The bandwidth of x is the fBW such that |X(f)| is small for f > fBW University of Delaware CPEG 419

  29. Bandwidth vs. Data Rate 2 time domain signal 1.5 1 0.5 0 0 10 20 30 40 50 60 70 80 90 2.5 frequency domain signal 2 1.5 1 0.5 0 -0.5 0.98 0.99 1 1.01 1.02 1.03 4 x 10 A single pulse contains all frequencies! University of Delaware CPEG 419

  30. Bandwidth vs. Data Rate Band-limited approximation of the digital signal 0 0 0 1 1 0 1 1 0 0 0 0 1 1 0 1 1 0 0 0 0 1 1 0 1 1 0 sample times threshold 0.3 time the bit-rate 0.5 time the bit-rate 0 0 0 1 1 0 1 1 0 0 0 0 1 1 0 1 1 0 0 0 0 1 1 0 1 1 0 0.75 times the bit-rate 2 times the bit-rate 1 times the bit-rate University of Delaware CPEG 419

  31. Bandwidth vs. Data Rate Suppose the digital signal is … 0 1 0 1 0 1 0 1 0 1 … And a bit is sent every T seconds. University of Delaware CPEG 419

  32. Fourier Series (Fourier Transform for periodic signals) Let x be periodic with period 2T where University of Delaware CPEG 419

  33. Bandwidth vs. Data Rate Suppose the digital signal is … 0 1 0 1 0 1 0 1 0 1 … And a bit is sent every T seconds. The lowest frequency component is at ½ the data rate. What is the lowest bandwidth of the signal that might be able to approximate x? Hence, to transmit a binary signal with data rate 1/T, one must use an analog signal that contains frequencies up to ½1/T. University of Delaware CPEG 419

  34. Multi-level Signals Bit Rate and Baud Rate • The number of bits transmitted can be increased by transmitting more than one bit in one time slot • Baud rate: number of times per second signal changes its value (voltage). • Each value might “carry” more than 1 bit. • Example: 8 values of voltage (0..7); each value conveys 3 bits, ie, number of bits = log2V. • Thus, bit rate = log2V * baud rate. • For 2 levels, bit rate = baud rate. University of Delaware CPEG 419

  35. Last slide University of Delaware CPEG 419

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