1 / 18

CS 313 Introduction to Computer Networking & Telecommunication

CS 313 Introduction to Computer Networking & Telecommunication. Theoretical Basis of Data Communication. Topics. Data Communication Performance Measurements Analog/Digital Signals Time and Frequency Domains Bandwidth and Channel Capacity. Data Communication Performance Measurements.

harding-herman
Download Presentation

CS 313 Introduction to Computer Networking & Telecommunication

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. CS 313 Introduction to Computer Networking & Telecommunication Theoretical Basis of Data Communication Chi-Cheng Lin, Winona State University

  2. Topics • Data Communication Performance Measurements • Analog/Digital Signals • Time and Frequency Domains • Bandwidth and Channel Capacity

  3. Data Communication Performance Measurements • Throughput • How fast data can pass through an entity • Number of bits passing through an imaginary wall in a second • Bit time • Duration of a bit (time for a bit ejected into network) • 1 / throughput • Propagation time (propagation delay) • Time required for one bit to travel from one point to another • Propagation speed depends on medium and signal frequency

  4. Message Transmission Delay Total transmission delay = (size_of_message / throughput) + propagation_time Time Sender 01101… Receiver 01101… t0 t1 t2 t3 first bit sent last bit sent first bit arrived last bit arrived propagation_time

  5. Message Transmission Delay - Example • What is the transmission delay of a 2 KB message transmitted over a 2 km cable that has a throughput 40 Mbps and a propagation delay of 8 µs/km? • Answer: Total transmission delay = (size_of_message / throughput) + propagation_time = (2048 x 8 bits / 40x106 bits/sec) + 8 µs/km x 2 km = 409.6 x 10-6 sec + 16 µs = 425.6 µs What is the bit time? 5

  6. Signals • Information must be transformed into electromagnetic signals to be transmitted • Signal forms • Analog or digital

  7. Analog/Digital Signals • Analog signal • Continuous waveform • Can have a infinite number of values in a range • Digital signal • Discrete • Can have only a limited number of values • E.g., 0 and 1, i.e., two levels, for binary signal

  8. Time Vs. Frequency Domain • A signal can be represented in either the time domain or the frequency domain.

  9. Period (Time) and Frequency

  10. Composite Signals • A composite signal can be decomposed into component sine waves - harmonics • The decomposition is performed by FourierAnalysis • DC component is the one with frequency 0.

  11. Frequency Spectrum and Bandwidth • Frequency spectrum • Collection of all component frequencies it contains • Bandwidth • Width of frequency spectrum

  12. Digital Signal - Decomposition • A digital signal can be decomposed into an infinite number of simple sine waves (harmonics) A digital signal is a composite signal with an infinite bandwidth. • More harmonics components = better approximation • Animation • Significant spectrum • Components required to reconstruct the digital signal

  13. Bandwidth-Limited Signals • (a) A binary signal and its root-mean-square Fourier amplitudes.

  14. Bandwidth-Limited Signals (2) • (b) – (e) Successive approximations to the original signal.

  15. Channel Capacity • Channel capacity • Maximum bit rate a transmission medium can transfer • Nyquist theorem for noiseless channels • C = 2H log2V where C: channel capacity (bit per second) H: bandwidth (Hz) V: signal levels (2 for binary) • C is proportional to H  bandwidth puts a limit on channel capacity

  16. Channel Capacity • Shannon Capacity for noisy channels • C = H log2(1 + S/N) where C: (noisy) channel capacity (bps) H: bandwidth (Hz) S/N: signal-to-noise ratio dB = 10 log10S/N • In practice, we have to apply both for determining the channel capacity.

  17. Examples • Noiseless channel. Consider a noiseless channel with a bandwidth of 3000 Hz transmitting a signal with two signal levels. What is the maximum bit rate of this channel? • Noiseless channel. Consider the same noiseless channel, transmitting a signal with four signal levels (for each level, we send two bits). What is the maximum bit rate of this channel? • Extremely noisy channel. Consider an extremely noisy channel in which the value of the signal-to-noise ratio is almost zero. In other words, the noise is so strong that the signal is faint. What is the channel capacity of this channel?

  18. Examples • Theoretical highest bit rate of a regular telephone line. A telephone line normally has a bandwidth of 3000 Hz (300 Hz to 3300 Hz). The signal-to-noise ratio is usually 35dB, i.e., 3162. What is the capacity of this channel? • Applying both theorems. We have a channel with a 2 MHz bandwidth. The S/N for this channel is 127; what is the appropriate bit rate and signal level?

More Related