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. 13-Nov-18 Networks and Communication Department

3.1 Concepts and Terminology 13-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 13-Nov-18 Networks and Communication Department

Transmission medium and physical layer A transmission media defined as anything that carry information between a source to a destination Located below the sender physical layer and is connected to the other receiver physical layer.

Classes of Transmission Media

Transmission Terminology: The successful transmission of data depends on two factors: Quality of the signal being transmitted Characteristics of the transmission medium 13-Nov-18 Networks and Communication Department

Transmission Terminology 13-Nov-18 Networks and Communication Department

Transmission Terminology: Types of connections The term direct link is used to refer to the transmission path between two devices in which signals propagate directly from transmitter to receiver with no intermediate devices, 1-Point –to-point it provides a direct link between two devices and those are the only two devices sharing the medium. 2- Multipoint In which more than two devices share the same medium. 13-Nov-18 Networks and Communication Department

Transmission Terminology: Direction of data flow 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 13-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 13-Nov-18 Networks and Communication Department

Time and Frequency Domain Figure 4-11 Time and Frequency Domain WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998

Examples  The McGraw-Hill Companies, Inc., 1998 Figure 4-12 WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998

Signal with DC Component Figure 4-13 Signal with DC Component WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998

Complex Waveform  The McGraw-Hill Companies, Inc., 1998 Figure 4-14 WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998

Bandwidth  The McGraw-Hill Companies, Inc., 1998 Figure 4-15 WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998

Digital Signal  The McGraw-Hill Companies, Inc., 1998 Figure 4-16 WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998

Amplitude, Period, and Phase Figure 4-17 Amplitude, Period, and Phase for a Digital Signal WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998

Bit Rate and Bit Interval Figure 4-18 Bit Rate and Bit Interval WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998

Harmonics of a Digital Signal Figure 4-19 Harmonics of a Digital Signal WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998

Exact and Significant Spectrums Figure 4-20 Exact and Significant Spectrums However, most of the energy in the signal is contained in a relatively narrow band of frequencies. This band is referred to as the effective bandwidth, or just bandwidth. WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998 Lte Capacity Workstream RMEA | Ericsson Internal | Uen, Rev DRAFT | 18-May-2014 | Page ‹#›

Corruption Due to Insufficient Bandwidth Figure 4-22 Corruption Due to Insufficient Bandwidth WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998

Bandwidth and Data Rate Figure 4-23 Bandwidth and Data Rate Increasing the Bit Rate result in increasing the BW كلما زاد ال bit rate كلما زاد ال لb.w WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998 Lte Capacity Workstream RMEA | Ericsson Internal | Uen, Rev DRAFT | 18-May-2014 | Page ‹#›

DC component 13-Nov-18 Networks and Communication Department

DC component No DC component. DC component = 1 13-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. It is measured in bps , and can be calculated by: 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 13-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? 13-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 13-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 13-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. 13-Nov-18 Networks and Communication Department

Effect of bandwidth on a digital signal greater the bandwidth transmitted, the greater the quality. 13-Nov-18 Networks and Communication Department

Units of period and frequency TABLE 3.1

The end Any Question ? 13-Nov-18 Networks and Communication Department