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Introduction

Introduction. A quick look at network fundamentals. F. M. Marchetti, Ph.D. CSE / Rm 353 fmm@engr.smu.edu. Introduction. Transmission Fundamentals Factors that determine the best way to connect Cost of connection Speed Immunity to interference Security

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Introduction

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  1. Introduction A quick look at network fundamentals F. M. Marchetti, Ph.D. CSE / Rm 353 fmm@engr.smu.edu CSE 7344

  2. Introduction Transmission Fundamentals • Factors that determine the best way to connect • Cost of connection • Speed • Immunity to interference • Security • Logistics CSE 7344

  3. Purpose of a Network To deliver data from one entity to another Factors to consider: • Need for reliable transmission • Quality of Service • Need for transmission of real-time data CSE 7344

  4. Maximum intercomputer distance Computer located in same … Example 1 m System Multicomputer 10 m / 100 m / 1 km Room / building / campus Local area network (LAN) 10 km City Metropolitan area network 100 km / 1000 km Country / Continent Wide area netwok (WAN) 10000 km Planet The Internet Types of Network CSE 7344

  5. LANs CSE 7344

  6. WANs CSE 7344

  7. The Internet CSE 7344

  8. Forms of Data Transmission Data must be converted to a physical signal for transmission • Analog transmission (such as speech over telephone lines) • Suffers from degradation which cannot be reconstructed • Digital transmission (such as VoIP) • Suffers from all-or-none degradation CSE 7344

  9. Digital vs. Analog • Digital less susceptible to distortion and interference compared to Analog • Digital signals can be regenerated to extend the length of the cable • Extremely low error rate (BER) • Cheaper CSE 7344

  10. Data Encoding Techniques Analog Signals Digital Data • Amplitude shift keying (ASK) • Frequency shift keying (FSK) • Phase shift keying CSE 7344

  11. Digital Data, Digital Signals • Non-return-to-Zero Level (NRZ-L) • NRZ - I • Manchester Encoding • Differential Manchester encoding Disadvantages of NRZ • Synchronization is difficult • DC component CSE 7344

  12. Digital Data, Digital Signal (cont’d) • Advantages of Differential encoding • Easy detection • Can keep track of the polarity • Advantages of bi-phase encoding • Synchronization • No dc component • Error detection CSE 7344

  13. Analog Data, Digital Signal • Based on the sampling theorem • Nyquist Limit • Pulse code modulation (PCM) • ADPCM (more compressed) • Delta modulation • Only the change of information is sent CSE 7344

  14. Parallel vs. Serial Transmission Parallel • Dedicated functions to the wires • Higher speed for short distance interconnections • Not feasible for long distances (more than 100m ) • Reduction in performance • Cross talk in long cables • Cost CSE 7344

  15. Parallel vs. Serial Serial • Serialize the data • Add control characters • Format the data into frames • Two types of transmission: • asynchronous: transmitter and receiver clocks are independent • synchronous: transmitter and receiver are synchronized CSE 7344

  16. Direction of Transmission • Simplex • Transmission in one direction only • Half-Duplex • Transmission in one direction at a time • Full-Duplex • Transmission in both directions CSE 7344

  17. Synchronous vs. Asynchronous Asynchronous • One character at a time • One start bit – one or more stop bits • No clock – receiver resynchronizes after each stop code • Cheap but inefficient – large overhead (20% or more) • Relatively low data rates (up to 115.2 kbps, in practice  38.4 kbps) • Uses: • suitable for data transmitted at random intervals (e.g. keyboard to computer) • simplicity and availability: UART and RS232 are present in any PC • used in the great majority of dial-up connections CSE 7344

  18. Synchronous vs. Asynchronous Synchronous • Arrival time of each bit is predictable • To prevent timing drift the receiver and transmitter clock are synchronized • Preamble and Postamble SYNC characters • Character Oriented • Clock signal transmitted either: • over a separate line (see V.35, RS232 lines) • or encoded into the data (Manchester, differential Manchester encoding) to allow a single line for both data and clock CSE 7344

  19. Transmission Media • Guided Media • Twisted Pair of Cables • Coaxial Cables • Optical Fibers • Unguided Media • Radio • Microwave • Satellite CSE 7344

  20. Multiplexing Link Sharing • For cost-effective transmission • The medium carries multiple signals simultaneously • Commonly used techniques: • FDM - Frequency Division Mux • TDM - Time Division Mux (STDM) • WDM - Wavelength Division Mux • CDM - Code Division Mux (frequency hopping and spread spectrum techniques) CSE 7344

  21. Statistical MUX • Link is shared over time (like STDM) • Scan the buffer and create a variable-size frame • Transmission-on-demand • Also called Concentrator CSE 7344

  22. Dedicated Virtual Communication Switching Techniques Spectrum of Switching Techniques • Circuit switching • Multi-rate circuit switching • Cell relay • Frame relay • Packet switching CSE 7344

  23. Circuit Switching • Dedicated communication path between two stations • Three Phases • Check also whether the destination is ready to accept the request • Data transfer • Could be either digital or analog signaling • Generally full duplex • Circuit disconnect CSE 7344

  24. Packet Switching • Greater line efficiency • Data rate conversion • Connection request is always accepted irrespective of the traffic • Dynamic routing and priority assignment possible CSE 7344

  25. Packet Switching - Approaches • Datagram • Virtual Circuit CSE 7344

  26. Packet Switching - Approaches Datagram • Each packet is treated independently • The packets may be received out of sequence • Some packets may be lost in the event of some node crashes CSE 7344

  27. Packet Switching - Approaches Virtual Circuit • A preplanned route is established before the data is sent • At any time, each station can have more than one VC to any other station and can have VCs to more than one station • Provides sequencing, error control, and flow control • If an intermediate node fails, all virtual circuits going through that node may be lost - less reliable when compared to datagrams CSE 7344

  28. Frame relay • Too much overhead built into packet switching • Frame relays take advantage of the low error rates of networking facilities • Cell Relay • ATM • Fixed length packets CSE 7344

  29. OSI Layers • Application • provides electronic mail, file transfers etc. • Presentation • Translates data format, encrypts and decrypts data • Session • Synchronizes communicating users, recovers from errors CSE 7344

  30. OSI Layers (cont’d) • Transport • Determines network, may assemble and reassemble packets • Network • Determines routes, manages billing information • Data Link • Detects or correct errors, defines frames • Physical • Transmits physical data CSE 7344

  31. End of Class 1 CSE 7344

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