1. DATA COMMUNICATION AND NETWORKING Chapter 12

2. Communication sending or receiving information Beating of drums Mirrors reflecting sunlight Homing pigeons Telegraph, telephone Computers … Data Communication

4. DATA COMMUNICATION Exchange of data between two devices wired or wireless transmission medium Communication system (collection of hardware, software …) Transfer of dataMethod of transfer Preservation of the data during the transfer process Delivery The system must deliver data to the correct or the intended destination. Accuracy The system must deliver data accurately (error free). Timeliness The system must deliver data in a timely manner without enough time lags.

5. Five components of a data communication System It is the information to be communicated. Popular forms of information include text, pictures, audio, video etc. 1. Message It is the device which sends the data messages. It can be a computer, workstation, telephone handset etc. 2. Sender It is the device which receives the data messages. It can be a computer, workstation, telephone handset etc. 3. Receiver It is the physical path by which a message travels from sender to receiver. Some examples include twisted-pair wire, coaxial cable, radiowaves etc. 4. Transmission Medium It is a set of rules that governs the data communications. It represents an agreement between the communicating devices. Without a protocol, two devices may be connected but not communicating. 5. Protocol

6. Data Transmission Modes Data in a simplex channel is always one way. Simplex channels are not often used because it is not possible to send back error or control signals to the transmit end. An example of a simplex channel in a computer system is the interface between the keyboard and the computer, in that key codes need only be sent one way from the keyboard to the computer system. Simplex A half duplex channel can send and receive, but not at the same time. Its like a one-lane bridge where two way traffic must give way in order to cross. Only one end transmits at a time, the other end receives. Half Duplex Data can travel in both directions simultaneously. There is no need to switch from transmit to receive mode like in half duplex. Its like a two lane bridge on a two-lane highway. Full Duplex

7. Analog & Digital Transmission information changes continuously and can take on many different values. An analog clock’s hands move constantly, displaying time on a continuous scale. Analog information is characterized by discrete states. A light bulb, for example, is on or off. A digital clock represents the time in one- minute intervals and doesn’t change its numbers again until the next minute. A digital clock can represent exact minutes but not the seconds that pass in between. Digital

8. Analog & Digital Transmission … Analog Signals- Sine waves Amplitude Frequency Wavelength Digital

9. Data Communication Measurement Narrowband Services 64 Kbps or less channels Wideband Services 1.5 Mbps to 45 Mbps (North American) 2 Mbps to 34 Mbps (International) Broadband Services 45 Mbps or greater (North American) 34 Mbps or greater (International) It Changes

10. Transmission Media

12. Radio Frequency Propogation

14. Modulation

15. Multiplexing

16. Multiplexing …

17. Synchronization- Controlling time Asynchronous Transmission Each character of data is treated independently Synchronous Transmission For sending large blocks of data Control schemes Character-oriented Bit-oriented 6.17

18. Switching …