331: STUDY DATA COMMUNICATIONS AND NETWORKS

 1. Discuss computer networks (5 hrs)  2. Discuss data communications (15 hrs)

 PERFORMANCE STANDARD ◦ Given a network system, identify and illustrate the different data communications components clearly  Objectives: ◦ Define elements of a communication system ◦ Define data communications ◦ Discuss various types of transmission media and their characteristics ◦ Discuss encoding of information for transmission ◦ Discuss types of signal & their characteristics ◦ Relate data capacity of a channel and bandwidth ◦ Classify media based on bandwidth ◦ Discuss channel organization

Discuss types of signal & their characteristics

 Data can be analog or digital. Analog data are continuous and take continuous values. Digital data have discrete states and take discrete value.  Like the data they represent, signals can be either analog or digital.  An analog signal has infinitely many levels of intensity over a period of time. As the wave moves from value A to value B, it passes through and include an infinite number of values along its path

 We seem to live in an analogue world – ◦ things can be louder or quieter, hotter or colder, longer or shorter.  If we record sound on a tape recorder, we’re putting an analogue signal onto the tape.  Digital signals aren’t on a sliding scale – they’re either ON or OFF. (We call these “1” and “0”.) There’s no “in between”.

Analog Signals Continuous Infinite range of values More exact values, but more difficult to work with Digital Signals Discrete Finite range of values (2) Not as exact as analog, but easier to work with Example: A digital thermostat in a room displays a temperature of 72 . An analog thermometer measures the room temperature at . The analog value is continuous and more accurate, but the digital value is more than adequate for the application and significantly easier to process electronically.

 An analog signal can be any time-varying signal.  Minimum and maximum values can be either positive or negative.  They can be periodic (repeating) or non- periodic.

Amplitude (peak-to-peak) Amplitude (peak) Period (T) Frequency:

The power we use at home has a frequency of 60 Hz. The period of this sine wave can be determined as follows:

 Digital signal are commonly referred to as square waves or clock signals.  They can be periodic (repeating) or non- periodic.

Amplitude Time High (t H ) Time Low (t L ) Period (T) Rising Edge Falling Edge Amplitude: For digital signals, this will ALWAYS be 5 volts. Period: The time it takes for a periodic signal to repeat. (seconds) Frequency: A measure of the number of occurrences of the signal per second. (Hertz, Hz) Time High (t H ): The time the signal is at 5 v. Time Low (t L ): The time the signal is at 0 v. Duty Cycle: The ratio of t H to the total period (T). Rising Edge: A 0-to-1 transition of the signal. Falling Edge: A 1-to-0 transition of the signal. Frequency:

 Digital circuits are subject to less distortion and interference  Error correction is possible.  Encryption and privacy is possible  Digital circuit is simple and cheap  The receiver can request a retransmission of bad information

 Interface to analogue is needed.  A digital system requires a greater bandwidth than analogue to carry the same information.  Generally digital communication system require synchronization but analogue do not require.

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