The document discusses different types of transmission media used for communication, including guided (wired) media like twisted pair, coaxial cable, and optical fiber, as well as unguided (wireless) transmission. It provides details on the characteristics of each medium, such as their bandwidth capabilities, applications, advantages and limitations. Overall, the document compares various physical transmission paths and how they enable data transmission over different distances and environments.

1. Transmission Media
Transmission medium
{ Physical path between transmitter and receiver
{ May be guided (wired) or unguided (wireless)
{ Communication achieved by using em waves
Characteristics and quality of data transmission
{ Dependent on characteristics of medium and signal
{ Guided medium
Medium is more important in setting transmission parameters
{ Unguided medium
Bandwidth of the signal produced by transmitting antenna is important in setting transmission pa-rameters
Signal directionality
Lower frequency signals are omnidirectional
Higher frequency signals can be focused in a directional beam
Design of data transmission system
{ Concerned with data rate and distance
{ Bandwidth
Higher bandwidth implies higher data rate
{ Transmission impairments
Attenuation
Twisted pair has more attenuation than coaxial cable which in turn is not as good as optical

2. ber
{ Interference
Can be minimized by proper shielding in guided media
{ Number of receivers
In a shared link, each attachment introduces attenuation and distortion on the line
Guided transmission media
Transmission capacity (bandwidth and data rate) depends on distance and type of network (point-to-point or
multipoint)
Twisted pair
{ Least expensive and most widely used
{ Physical description
Two insulated copper wires arranged in regular spiral pattern
Number of pairs are bundled together in a cable
Twisting decreases the crosstalk interference between adjacent pairs in the cable, by using dierent
twist length for neighboring pairs
{ Applications
Most common transmission media for both digital and analog signals

3. Transmission Media 25
Less expensive compared to coaxial cable or optical

4. ber
Limited in terms of data rate and distance
Telephone network
Individual units (residence lines) to local exchange (end oce)
Subscriber loops
Supports voice trac using analog signaling
May handle digital data at modest rates using modems
Communications within buildings
Connection to digital data switch or digital pbx within a building
Allows data rate of 64 kbps
{ Transmission characteristics
Requires ampli

5. ers every 5-6 km for analog signals
Requires repeaters every 2-3 km for digital signals
Attenuation is a strong function of frequency
Higher frequency implies higher attenuation
Susceptible to interference and noise
Improvement possibilities
Shielding with metallic braids or sheathing reduces interference
Twisting reduces low frequency interference
Dierent twist length in adjacent pairs reduces crosstalk
{ Unshielded and shielded twisted pairs
Unshielded twisted pair (utp)
Ordinary telephone wire
Subject to external electromagnetic interference
Shielded twisted pair (stp)
Shielded with a metallic braid or sheath
Reduces interference
Better performance at higher data rates
More expensive and dicult to work compared to utp
{ Category 3 and Category 5 utp
Most common is the 100-ohm voice grade twisted pair
Most useful for lan applications
Category 3 utp
Transmission characteristics speci

6. ed up to 16 mhz
Voice grade cable in most oce buildings
May have data rates up to 16 Mbps over limited distances
Typical twist length 7.5 to 10 cm
Category 4 utp
Transmission characteristics speci

7. ed up to 20 mhz
Category 5 utp
Transmission characteristics speci