Overview
The fundamental requirement for any computer networking system is the ability to transmit data from one node to another over a link. This requires a medium to carry the signal and some form of signal that represents the information in the messages. This unit attempts to develop a very basic understanding of those things - media and signalling.
Objectives
- Determine the characteristics of an electronic signal.
- Differentiate between analog and digital signaling.
- Understand the capacity of a signal to carry information.
- Establish principles for assessing the information capacity of a signal.
- Review the common types of communication media and their properties.
Preparation
Chapter 1 in the book introduces some of the terms and sections 2.1 and 2.2 are pertinent to this discussion, but the primary source of information is in the notes.
Knowledge, Comprension & Problem Solving
Terms
- 802.11 wireless
- amplitude shift keying
- analog signal
- attenuation
- bandwidth
- category 5 UTP wire
- channel
- coaxial cable
- delay distortion
- discrete (digital) signal
- frequency shift keying
- microwave
- multimode fiber
- noise
- optical fiber
- phase shift keying
- signaling
- single-mode fiber
- synchronization
- twisted pair wire
- wavelength division multiplexing
Questions
- Sketch a diagram of a sine wave with an amplitude of 5 volts, a frequency of 2 Hz and a phase angle of zero.
- On the same sketch, draw a diagram of a sine wave with an amplitude of 3 volts, a frequency of 4 Hz and a phase angle of -90 degrees.
- Sketch the sum of the two waves. What is the bandwidth of the sum signal?
- A carrier has a bandwidth of 20 MHz. What is the maximum capacity of this signal if it encodes 3 bits per baud?
- For the previous problem, what is the maximum capacity if the signal to noise ratio is 20 decibels?
- How long is a full wave in meters at 100 Hz?
- Telephone systems have their bandwidth limited to 4000 Hz. What is the maximum capacity of a telephone line? What must happen to get a 56,000 b/s channel? If the signal-to-noise ratio is 20 dB, what is the rated capacity? How do they get the higher data rates?
Analysis, Synthesis & Evaluation
- Is it correct to say that a Manchester encoded signal requires twice the bandwidth of a Non-return-to-zero signal?
- Suggest a method for encoding 3 bits per baud using FSK and a maximum signal bandwidth of 1000 Hz.
- Suggest a method for encoding 4 bits per baud using PSK and a signal with a frequency of 1000 Hz. What is the maximum bit rate for this method? What is the baud rate?
- Would it be possible to have a voice conversation over a telephone line at the same time that you were transmitting data? How and what are the technical requirements?
- Why do digital signals need repeating more often than a similar analog signal needs amplification?
- Why do you suppose major sound system manufacturers have switched to digital sound rather than analog?
- You have a broadband system carrying some cable television channels, but you think it might be nifty to carry some data on it as well. Think in terms of someone sending data from a computer at a data rate of 1 Mb/s using Manchester encoding and describe how you could do this.
- A telephone line has a loss of 20dB in power due to attenuation. At the input the signal power is 1.0 watt; the noise power is 1 microwatt (10-6). What is the output signal-to-noise ratio?
- Linux typically ships with gnuplot installed. You can graph sinusoids easily with a simple command: like this:
gnuplot
gnuplot> plot 4*sin (2*3.1416*x-30*2*3.1416/360)
which plots a sine function. If you want to control the range displayed, use the xrange and/or yrange commands and help will give you help on any command.