Chapter 3 : Data transmission Networks and Communication Department Data and Communication book by William stalling

Lecture Contents 3.1 Concepts and Terminology The Physical Layer. Transmission Terminology. Spectrum and Bandwidth. DC component Data Rate an Bandwidth. Digital signal and Bandwidth. 30-Nov-18 Networks and Communication Department

3.1 Concepts and Terminology 30-Nov-18 Networks and Communication Department

The Physical Layer Foundation on which other layers build Properties of wires, fiber, wireless limit what the network can do Key problem is to send (digital) bits using only (analog) signals This is called modulation 30-Nov-18 Networks and Communication Department

Transmission Terminology: The successful transmission of data depends on two factors: quality of the signal being transmitted characteristics of the transmission medium 30-Nov-18 Networks and Communication Department

Transmission Terminology 30-Nov-18 Networks and Communication Department

Transmission Terminology 30-Nov-18 Networks and Communication Department

Transmission Terminology Simplex : signals transmitted in one direction eg : Television Half duplex: both stations transmit, but only one at a time eg : Police radio Full duplex: simultaneous transmissions eg : Telephone 30-Nov-18 Networks and Communication Department

Spectrum & Bandwidth range of frequencies contained in signal spectrum width of spectrum Absolute bandwidth narrow band of frequencies containing most energy often just bandwidth Effective bandwidth component of zero frequency dc component 30-Nov-18 Networks and Communication Department

DC component 30-Nov-18 Networks and Communication Department

DC component No DC component. DC component = 1 30-Nov-18 Networks and Communication Department

Data rate & Bandwidth Data rate: is the amount of data that is moved from one place to another in a given time. (bps) , Data rate=2*f Bandwidth: is the actual speed at which data can be transmitted on a connection. There is a direct relationship between data rate & bandwidth 30-Nov-18 Networks and Communication Department

Data Rate Calculation Suppose that we are using a digital transmission system that is capable of transmitting signals with a bandwidth of 12 MHz From the figures, What data rate can be achieved? 30-Nov-18 Networks and Communication Department

Data Rate Calculation Fig . A : Fig . B : BW = 5f – f 12 MHz = 5f – f  f = 3 MHz Data rate = 2 * f = 2 * 3 = 6 Mbps Fig . B : BW = 7f – f 12 MHz = 7f – f  f = 2 MHz Data rate = 2 * f = 2 * 2 = 4 Mbps 30-Nov-18 Networks and Communication Department

Data rate & Bandwidth relationship any transmission system has a limited band of frequencies this limits the data rate that can be carried on the transmission medium square waves have infinite components and hence an infinite bandwidth most energy in first few components limiting bandwidth creates distortions 30-Nov-18 Networks and Communication Department

Data rate & Bandwidth relationship In general : any digital waveform will have infinite bandwidth. If we attempt to transmit this waveform as a signal over any medium, the transmission system will limit the bandwidth that can be transmitted. On one hand, for any medium, the greater the bandwidth transmitted, the greater the cost. On the other hand limiting the bandwidth creates distortions, and the greater the potential for error by the receiver. 30-Nov-18 Networks and Communication Department

Effect of bandwidth on a digital signal greater the bandwidth transmitted, the greater the quality. 30-Nov-18 Networks and Communication Department

The end Any Question ? 30-Nov-18 Networks and Communication Department