Guided Media

Twisted pair
Coaxial cable
Fiber optics



Twisted Pair

copper cable
Types: UTP and STP
originally used for P.O.T.S.
Type of Twisted Pair
cat 3 - used for analog
cat 5 - used for both analog and digital



Types Twisted Pair

Category 1- Basic twisted pair wire for telephone use. Not recommended for data – Original – found in old buildings today


Category 2- For unshielded, solid twisted pair. Certified for data transmission to 4 Mbps.


Category 3- At least three twists per foot. About the same as normal telephone cable installed in most office buildings. Certified for data transmission to 10 Mbps but with proper design and over limited distances, may work to 16 Mbps. If there is more than one pair in the same jack, it must not have the same number of twists per foot in order to minimize cross-talk.


Category 4- Similar to Category 3, but more twists per foot, and certified to 16 Mbps.


Category 5- Three to four twists per inch. Data-grade cable certified for data transmission to 100 Mbps.


Category 5E (5 extended)- An extension of the standard for Category 5 cable designed to handle data transmission up to 1 Gbps. Recommended for all new cable installations in office buildings.


Twisted Pair

used for data transmission over short distances


Advantages:
cheap
easy to install
is already there
3. Disadvantages:

low data transmission rates over long distances
very susceptible to noise never use in a factory to transmit data


Concept Past: Fiber to the curb

            Twisted pair is from the trunk line to the subscriber

Today being installed: Fiber to the subscriber done in metropolitan areas

Trunk - high capacity link


Coaxial Cable

operate on a wide range of frequencies
supports higher data transmission rates
installed by cable TV reason why they wanted to get into the communications business
used to transmit electromagnetic signals
Frequencies 100 KHz to 500 KHz
RG = Radio Government -> denotes the physical specifications
Have a core copper that is enclosed in an insulating sheath
Pieces:
Plastic cover
Metal shield
Insulation
Copper core
Uses:
RG 8 – used in thick Ethernet
RG 9 – Used in thick Ethernet
RG 58 – used in thin Ethernet
RG 59 – used for cable TV



Fiber Optic

transmission of light
light waves are much faster than electromagnetic waves so that reduce propagation delay
not susceptible to noise - get high  data transmission rates since less prone to error
used just for digital signal -> for voice the analog wave must be converted to digital wave done by codec with performs Pulse Code Modulation
light is transmitted through a silicon cable (glass)
Snell's Law - index of refraction -> how light bends going thru different media
I is the angle of incidence
R is the angle of refraction
Parts of fiber optic cable
core - is the silicon where the light travels
cladding - provides the reflection of the light
jacket - provides protection of the cable
modal dispersion - controlled by the quality of the silicon and by the cladding
light transmits data in the giga-byte range and can support large numbers of simulations conversations
SONET = Synchronous Optical Networks
protocol or rules that are used to transmit data by light
uses a loop structure to lay out the cable
primary and secondary (backup) cable
use of secondary cable is to prevent the link going down due to cable cuts
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--Parts of Twisted Pair----------------
  Outside Layer - Jacket (Provides projection)
  Next Layer - Cladding (Reflective Area)
  Center Layer - Core (Transmits light wave, consists of glass/plastic)

Snells Law - N1Sin0 - N2Sin0
           - N = Refractive Index = C/V
           - C = Speed of Light
           - V = Speed in a material

If the angle of Incedence is greater than the critical angle, you get reflection
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RG = Radio Government -> denotes the physical specifications
MTSO = Mobile Telephone Switch Office
Cell is the area of communication -> region
    -size of cell is controlled by the population density

Hand off
  -MTSO constantly monitors at set intervals the strength of the signal
  -If weak the channel is changed or signal is handed off to a new channel.  This is transparent to the user

Receiving
  -The CO send the number to the MTSO
  -Paging the MTSO’s are searched for the source of the signal -> querry the cells

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MTU = Maximum Transmission Unit - determined by hardware
MTU determine the size of the PDU = Protocol Data Unit (packet) -> is a function of software protocol
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modem - modulator/demodulator - converted a digital signal to analog and reconstructed the signal


Techniques to Encode Information


Modulation - process of encoding information on to a signal

Types of modulation
Amplitude Modulation (AM)
Frequency Modulation (FM)
Phase Modulation
Pulse Code Modulation – used for analog to digital (PCM)
Wave Division Modulation – used for fiber optic transmission (WDM)


Amplitude Modulation

amplitude of the wave is used to represent the data
electro-magnetic signals very inefficient because it is prone to noise
used for digital data over fiber optic in a form


Frequency Modulation
   Binary values are represented by two different frequencies in the modulated signal
   Modulated signal is transmitted from source to the destination by the carrier signal
   Used to transmit digital data by electromagnetic signal
Advantages:
Frequency modulation is not as susceptible to noise as amplitude modulation
Supports full duplex


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DTE = Digital Terminal Equipment
DCE = Digital Communications Equipment
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nyquest therom - how often to sample signal to get sufficient daa to be able to regenerate signal


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Parity

It is a very primitive error checking
Types:
odd parity
even parity
operates: count the number of ones in the data and the parity bit, it does NOT count the start bit and the stop bit
If odd parity - the number of ones must be odd or there is an error
If even parity - the number of ones must be even or there is an error
Source and destination MUST agree as to the type of parity being used
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Snell's Law - index of refraction -> how light bends going thru different media
I is the angle of incidence
R is the angle of refraction

When light goes from less dense (Air) to more dense (Water) the angle of refraction gets smaller.