21-12-2012, 05:55 PM
CS 1302- Data Communications and Networking
Data Communications.ppt (Size: 1.58 MB / Downloads: 26)
Relation to Internet Model
Actually located below the physical layer
Directly controlled by the physical layer
Introduction
Data must be converted into electromagnetic signals to be transmitted from device to device
Signals can travel through a vacuum, air, or other media
May be in the form of power, voice, radio waves, infrared light, and gamma rays
Categories of Media
Broad categories:
Guided Media – media with a physical boundary
Twisted pair, coaxial, and fiber-optic
Unguided Media – no physical boundaries
Radio waves, infrared light, visible light and gamma rays
Sent by microwave, satellite, and cellular transmission
Twisted-Pair Cable
Two conductors surrounded by insulating material
One wire used to carry signals; other used as a ground reference
Twisting wires reduces the effect of noise interference or crosstalk since both wires will likely be equally affected
More twists = better quality
Limits interfences
No. of twists / unit length determines the quality of the cable