Guided Transmission Media
Twister-pair cable
One popular form of wire is the twisted pair. These are usually broken up into two major
categories: Unshielded Twisted Pair (UTP), and Shielded Twisted Pair (STP).
The UTP wire is the cheapest and most common wire, which would explain why most
LANs use UTP. There are several “categories” of UTP cable that have been standardized.
1. Category 1: Basic twisted pair; used for the old telephone system. Unsuitable for data
communications (unless very low-speed).
2. Category 2: Better than Category 1. Suitable for data communications up to 4Mbps.
3. Category 3: Required to have at least 3 twists per foot, and can be used for data
communications up to 10Mbps. Modern telephone wire.
4. Category 4: Improved version of Category 3, can be used for data communications up
to 16Mbps.
5. Category 5: Can be used for data transmission of up to 100Mbps.
The STP cable has a foil of metal mesh covering the pair of wires, eliminating crosstalk.
Coaxial cable
Commonly known as coax carries a signal at much higher frequencies than twisted pair.
Instead of having two wires, there is a primary ‘core’ wire in the center, with an insulator,
and an outer conductor that serves as a shield and insulator. Cable TV uses Coaxial Cable.
There are a few standards:
1. RG-8: Used in Thick Ethernet.
2. RG-9: Used in Thick Ethernet.
3. RG-11: Used in Thick Ethernet.
4. RG-58: Used for Thin Ethernet.
5. RG-59: Used for TV.
Fiber-Optic cable
There are many different kinds of fiber wires, as well as many different ways of sending
data through them. The whole concept is that light tends to bend or reflect when hitting
something of different density. For example, light tends to refract when hitting a pool of
water; the same light, if hitting the pool at a different angle, might make the water appear
like a mirror (will reflect instead of refract).
The same thing happens if you have two glass (or plastic) layers of different densities. In
fiber optic cable, you have an inner ‘core’ of glass (or plastic) of higher density, and an outer
layer (cladding) of lower density glass (or plastic).
Propagation Modes: There are several ways of arranging the wire:
• Multimode, step-index: The thick inner core of glass of constant density is surrounded
by cladding of lower density. When the beam hits the cladding, it is reflected.
Coaxial cable
Commonly known as coax carries a signal at much higher frequencies than twisted pair.
Instead of having two wires, there is a primary ‘core’ wire in the center, with an insulator,
and an outer conductor that serves as a shield and insulator. Cable TV uses Coaxial Cable.
There are a few standards:
1. RG-8: Used in Thick Ethernet.
2. RG-9: Used in Thick Ethernet.
3. RG-11: Used in Thick Ethernet.
4. RG-58: Used for Thin Ethernet.
5. RG-59: Used for TV.
Fiber-Optic cable
There are many different kinds of fiber wires, as well as many different ways of sending
data through them. The whole concept is that light tends to bend or reflect when hitting
something of different density. For example, light tends to refract when hitting a pool of
water; the same light, if hitting the pool at a different angle, might make the water appear
like a mirror (will reflect instead of refract).
The same thing happens if you have two glass (or plastic) layers of different densities. In
fiber optic cable, you have an inner ‘core’ of glass (or plastic) of higher density, and an outer
layer (cladding) of lower density glass (or plastic).
Propagation Modes: There are several ways of arranging the wire:
• Multimode, step-index: The thick inner core of glass of constant density is surrounded
by cladding of lower density. When the beam hits the cladding, it is reflected.
