Data communications and Networking Chapter 4 Transmission media Reading Book Chapter 4 Data and Computer Communications, 8th edition By wIlliam Stallings
1 Data Communications and Networking Chapter 4 Transmission Media Reading: Book Chapter 4 Data and Computer Communications, 8th edition By William Stallings
Transmission media In a data transmission system, the transmission medium is the physical path between transmitter and receiver · Guided mediun Electromagnetic waves are guided along a solid medium Unguided media Wireless transmission occurs through the atmosphere, outer space, or water The characteristics and quality of a data transmission are determined bot by the medium and the signal For guided media, the medium itself is more important in determining the limitations of transmission For unguided media, the bandwidth of the signal produced by the transmitting antenna is more important. One key property of signals transmitted by antenna is directionality Key concerns are data rate and distance: the greater the data rate and distance. the better
2 Transmission Media • In a data transmission system, the transmission medium is the physical path between transmitter and receiver. • Guided medium — Electromagnetic waves are guided along a solid medium. • Unguided media — Wireless transmission occurs through the atmosphere, outer space, or water. • The characteristics and quality of a data transmission are determined both by the medium and the signal. — For guided media, the medium itself is more important in determining the limitations of transmission. — For unguided media, the bandwidth of the signal produced by the transmitting antenna is more important. One key property of signals transmitted by antenna is directionality. • Key concerns are data rate and distance: the greater the data rate and distance, the better
Electromagnetic Spectrum Frequency (Hertz)102 104105 10 10 10 11 12 1011101210 1310 1410 ELF VF VLF LF MF HF VHF UHF SHFEHF Power and telephone Radio Microwave Infrared Visible Rotating generators Radios and televisions Radar asers light Musical instruments Electronic tubes Microwave antennas Guided missiles Voice microphones Integrated circuits Magnetrons Rangefinders Cellular Telephony Twisted Pair Optical Fiber axial cable AM Radio FM Radio Terrestrial and TVand Satellite Transmission Wavelength 10 10 10010-110 3 10 10 In space (meters) ELF EXtremely low frequency MF Medium frequency UHF Ultrahigh frequency VF Voice frequency HF = High frequency SHF = Superhigh frequency VLF Very low frequency VHF Very high frequency EHF Extremely high frequency
3 Electromagnetic Spectrum
Guided transmission media · Twisted pair · Coaxial cable Optical fiber Table 4.1 Point-to-Point Transmission Characteristics of Guided Media [GLov98] Frequency Range Typical Attenuation Typical Delay Re epeater spacing Twisted pair(with 0 to 3.5 kHz 0.2 dB/km a l khz Hs/km 2 km loading) Twisted pairs(multi-pair 0 to I MHz 0.7 dB/km a 1 kHz 5 us/km 2 km axial c 0 to 500 MHz 7 dB/km (a 10 MHz 4 us/km I to 9 km Optical fiber 186 to 370 THz 0.2 to 0.5 dB/km 5 us/km 40 km THz= TeraHerz= 102H
4 Guided Transmission Media • Twisted Pair • Coaxial cable • Optical fiber
Twisted Pair length Separately insulated Twisted together -Often bundled" into cables -Usually installed in building during construction (a)Twisted pair a wire pair acts as a single communication link typically a number of these pairs are bundled together into a cable The twisting tends to decrease the crosstalk interference between adjacent pairs in a cable, which usually contain hundreds of pairs 5
5 Twisted Pair A wire pair acts as a single communication link. Typically, a number of these pairs are bundled together into a cable. The twisting tends to decrease the crosstalk interference between adjacent pairs in a cable, which usually contain hundreds of pairs