Understanding Transmission Media in Networks and Communication Department
Learn about different types of transmission media such as guided and unguided media, their characteristics, design factors, and transmission characteristics of guided media like twisted pair, coaxial cable, and optical fiber.
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Presentation Transcript
1 TRANSMISSION MEDIA Networks and Communication Department
Overview Transmission medium: is the physical path between transmitter and receiver. Transmission media can be classified as : 1. guided media- wire : electromagnetic waves are guided along a solid medium, such as copper twisted pair, copper coaxial cable, and optical fiber 2. unguided media wireless: wireless transmission occurs through the atmosphere, outer space, or water.
3 Characteristics and quality determined by medium and signal: in unguided media - bandwidth produced by the antenna is more important in guided media - medium is more important Design Factors: 1. Bandwidth 2. Transmission impairments 3. Interference 4. number of receivers in guided media 10-Jun-25 Networks and Communication Department
Design Factors key concerns are data rate and distance 1. Bandwidth higher bandwidth gives higher data rate 2. Transmission impairments For unguided media attenuation, limit the distance. For guided media, twisted pair generally suffers more impairment than coaxial cable, which in turn suffers more than optical fiber.
Design Factors 3. Interference Interference from competing signals in overlapping frequency bands can distort or wipe out a signal. Interference is of particular concern for unguided media. For guided media, interference can be caused by emanations from nearby cables. For example, twisted pairs . 4. number of receivers -in guided media each attachment introduces some attenuation and distortion on the line, limiting distance and/or data rate . -more receivers (multi-point) introduces more attenuation, limiting distance and data rate.
Guided Medium 7 10-Jun-25 Networks and Communication Department
Transmission Characteristics of Guided Media Frequency Range Typical Attenuation Typical Delay Repeater Spacing Twisted pair (with loading) 0 to 3.5 kHz 0.2 dB/km @ 1 kHz 50 s/km 2 km Twisted pairs (multi-pair cables) Coaxial cable 0 to 1 MHz 0.7 dB/km @ 1 kHz 5 s/km 2 km 0 to 500 MHz 7 dB/km @ 10 MHz 4 s/km 1 to 9 km Optical fiber 186 to 370 THz 0.2 to 0.5 dB/km 5 s/km 40 km
Twisted Pair physical description: A twisted pair consists of two insulated copper wires arranged in a regular spiral pattern. The twisting tends to decrease the crosstalk interference between adjacent pairs in a cable. Twisted pair is much less expensive than the other easier to work with.
Twisted Pair Application: Most common medium Telephone network Between house and local exchange Within buildings . For local area networks (LAN)
Twisted Pair - Transmission Characteristics analog needs amplifiers every 5km to 6km digital needs a repeater every 2-3km limited distance limited bandwidth (1MHz) limited data rate (100 Mbps) susceptible to interference and noise
Unshielded vs Shielded TP Twisted pair comes in two varieties: unshielded and shielded. unshielded Twisted Pair (UTP) ordinary telephone wire cheapest easiest to install suffers from external EM interference shielded Twisted Pair (STP) metal braid or sheathing that reduces interference more expensive harder to handle (thick, heavy) in a variety of categories - see EIA-568
14 Unshielded vs Shielded TP 10-Jun-25 Networks and Communication Department
UTP Categories Cat 3 (up to 16 MHz) Twist length of 7.5 cm to 10 cm Cat 5 (up to 100MHz) Twist length 0.6 cm to 0.85 cm Tighter twist -> more expensive, But better performance Cat 5E (Enhanced), Cat 6 & Cat 7
Near End Crosstalk Near-end crosstalk it applies to twisted pair wiring systems is the coupling of the signal from one pair of conductors to another pair. These conductors may be the metal pins in a connector or wire pairs in a cable. It is coupling of signal from one pair to another occurs when transmit signal entering the link couples back to receiving pair
2. Coaxial cable Coax cable carries signals of higher frequency ranges than those in Twisted pair cable because the two media are constructed quite differently. The outer conductor serves both as a shield against noise and as second conductor, which complete the circuit 7.17
Coaxial Cable - Transmission Characteristics Coaxial cable is used to transmit both analog and digital signals. It has frequency characteristics that are superior to those of twisted pair and can hence be used effectively at higher frequencies and data rates. performance limited by attenuation & noise analog signals amplifiers every few km with closer spacing required if higher frequency is used The usable spectrum for analog signaling extends up to 500MHz digital signals repeater every 1km closer for higher data rates
3. Fiber Optic Cable 7.21 Is made of glass or plastic and transmit signals in the form of light. Light travels in a straight line as long as it is moving through a single uniform substance. If a ray of light traveling through one substance enters another substance of different density , the ray change direction as shown:
Optical fiber 7.22 Fiber Optical : uses reflection to guide light through a channel. A glass or plastic core is surrounded by a cladding of less dense glass or plastic Back to the book for advantages and disadvantages
Applications for Fiber Optic cable 7.23 Used in : 1.Cable TV network: hybrid network use a combination of optical fiber and coax cable. Optical provides the backbone while coaxial cable provide the connation to the user. 2.Local area networks such as ( fast Ethernet) 3.Backbone networks because its wide bandwidth
Propagation modes using fiber optics 24 Multimode Fiber: any light ray incident on the boundary above the critical angle will be reflected internally, many different rays will be bouncing around at different angles. Single-mode Fiber: light can propagate only in a straight line, without bouncing.
Optical Fiber - Benefits greater capacity data rates of hundreds of Gbps smaller size & weight lower attenuation electromagnetic isolation greater repeater spacing 10s of km at least
Optical Fiber - Transmission Characteristics uses total internal reflection to transmit light effectively acts as wave guide for 1014 to 1015 Hz can use several different light sources Light Emitting Diode (LED) cheaper, wider operating temp range, longer operational life Injection Laser Diode (ILD) more efficient, has greater data rate There is a relationship among the wavelength employed, the type of transmission, and the achievable data rate.
Difference between Guided Media Twisted pair Coaxial cable Fiber optics Data rate Few Mbps (1 km) 100 Mbps to 10 Gbps (tens of meters) Hundreds of Mbps (1 km) Hundreds of Gbps ( tens of km) Attenuation high low Very low Electro- magnetic isolation affected affected Not effected by external electromagnet ic fields. No crosstalk Repeater Every few kilometers Every few kilometers Every tens or hundreds of kilometers
Transmission Medium 31 Data and Computer Communications, Ninth Edition by William Stallings, Chapter 4 References 10-Jun-25 Networks and Communication Department
