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Chap 4 Transmission Media

Chap 4 Transmission Media. H1. H2. A transmission medium. Classification Guided media twisted pairs  UTP and STP coaxial cable (Coax) optical fibers Unguided media broadcast radio ( omni-directional , RF transmission)

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Chap 4 Transmission Media

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  1. Chap 4 Transmission Media H1 H2 A transmission medium Classification • Guided media twisted pairs  UTP and STP coaxial cable (Coax) optical fibers • Unguided media broadcast radio (omni-directional, RF transmission) microwave (directional, beyond RF, cannot penetrate metal structures) infrared (limited to small area, e.g, a single room) light from a laser (travels in a straight line, cannot penetrate vegetation, susceptible to snow and fog, has limited use)

  2. Communication Satellites • Geo-synchronous (Geo-stationary) Satellite * synchronous with the rotation of the earth * distance: ~ 36000 Km (22000 miles) above the earth * may consist of several transponders, each with a transmitter and a receiver * angular separation of satellites : 4 - 8 degrees • Low Earth Orbit (LEO) Satellites * distance : 200 – 400 miles above the earth * period of rotation: faster the rotation of the earth * does not appear to stay stationary * needs an array of satellites (66 required to cover the entire earth) * communicating with ground stations and other satellites in the array

  3. Two Important Physical Limits of a TX System • Propagation Delay * Time required for a signal to travel across media * Example: EM radiation travels through space at the speed of light (C = 3 * 10 ^8 m/sec) • Bandwidth * Max. number of changes per second the signal can change * Measured in cycles per second or Hertz (Hz) * Example: If a TX system has a bandwidth of 4000 Hz, then the underlying hardware can transmit any signals that oscillate back and forth at a rate < = 4000Hz * Every physical TX system has a finite bandwidth

  4. Factors that affect data rate & distance • Bandwidth data rate increases as bandwidth increases • Transmission impairments attenuation, distortion, noise reduce the data rate and the distance twisted pair > coax > optical fiber • Interference from adjacent cables or overlapping frequency band may disrupt or prevent normal communication • # of receivers in the guided case each attachment in a multi-point line introduces attenuation and distortion in the line

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