TRANSMISSION MEDIUM

Session 3

TRANSMISSION MEDIA Transmission

media are located below the physical layer

Computers use signals to represent data.

Signals are ransmitted in form of electromagnetic energy.

TRANSMISSION MEDIATransmission Media and Physical Layer

Classes of transmission media

FACTORS TO BE CONSIDERED WHILE CHOOSING TRANSMISSION MEDIUM

Transmission Rate

Cost and Ease of Installation

Resistance to Environmental Conditions

Distances

GUIDED MEDIAGUIDED MEDIA

Guided media, which are those that provide a conduit from one device to another, include twisted-pair cable, coaxial cable, and fiber-optic cable.

TWISTED PAIR CABLE

This cable is the most commonly used and is cheaper than others. It is lightweight, cheap, can be installed easily, and they support many different types of network

Twisted Pair is of two types : Unshielded Twisted Pair (UTP)

Shielded Twisted Pair (STP)

UNSHIELDED VERSUS SHIELDED TWISTED-PAIR CABLE

UTP and STP cables

UNSHIELDED TWISTED PAIR (UTP)Adv:• Ordinary telephone wire• Cheapest• Easiest to install• It has high speed capacity• 100 meter limit

Dis adv:• Bandwidth is low when compared

with Coaxial Cable• Provides less protection from

interference.

SHIELDED TWISTED PAIR (STP)Adv:• Metal braid or sheathing

that reduces interference• Easy to install• Eliminates crosstalk• Higher capacity than

unshielded twisted pair• Increases the signaling rate

Disadv:• More expensive• Harder to handle (thick, heavy)• Difficult to manufacture

GUIDED MEDIA - UTP Applications:

Telephone lines connecting subscribers to the central office

DSL lines LAN – 10Base-T and 100Base-T

TWISTED PAIR - APPLICATIONS Most common medium Telephone network Within buildings For local area networks (LAN)

TWISTED PAIR - PROS AND CONS Cheap Easy to work with Low data rate Short range

GUIDED MEDIA – COAXIAL CABLECoaxial Cable

COAXIAL CABLE

COAXIAL CABLE Inner conductor is a

solid wire outer conductor serves both as a shield

against noise and a second conductor

TYPES OF COAXIAL CABLES 

Baseband : Which is used for digital transmission. It is mostly used for LAN’s. Baseband transmits a single signal at a time with very high speed.

Broadband : This uses analog transmission on standard cable television cabling. It transmits several simultaneous signal using different frequencies.

COAXIAL CABLE PROS Bandwidth is high Used in long distance telephone lines. Television distribution Can carry 10,000 voice calls simultaneously Short distance computer systems links Local area networks Data transmission without distortion.

CONS Single cable failure can fail the entire

network.

Difficult to install and expensive when compared with twisted pair.

GUIDED MEDIA – COAXIAL CABLE

Applications:

Analog telephone networks

Cable TV networks

Traditional Ethernet LAN – 10Base2, 10Base5

FIBER OPTICS• Higher bandwidth• Less expensive• Immune to electrical noise• More secure – easy to notice an attempt to

intercept signal• Physical characterizes

– Glass or plastic fibers– Very thin (thinner than human hair)– Material is light

OPTICAL FIBER - PROS• greater capacity

– data rates of hundreds of Gbps• smaller size & weight• lower attenuation(Reduction in signal) • Used for both analog and digital signals.

CONS It is expensive.

Difficult to install.

Maintenance is expensive and difficult

GUIDED MEDIA – OPTICAL FIBER CABLE

Applications: Backbone networks – SONET

Cable TV – backbone

LAN 100Base-FX network (Fast Ethernet)

100Base-X

UNGUIDED MEDIA Wireless transmission waves

BROADCAST RADIO Its frequency is between 10 kHz to 1GHz. It is simple to install and has high

attenuation. FM radio

UHF and VHF television still need line of sight suffers from multipath interference

reflections from land, water, other objects

UNGUIDED MEDIA – INFRARED Frequencies between 300 GHz to 400 THz.

Can not penetrate walls.

Used for short-range communication in a closed area using line-of-sight propagation.

INFRARED are blocked by walls no licenses required typical uses

TV remote control IRD port

MICROWAVE TRANSMISSION

Line-of-site

High speed

Cost effective

Easy to implement

Weather can cause interference

STRAIGHT THROUGH AND CROSSOVER WIRING

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Wiring within a twisted pair cable is configured as either Straight through, where each wire (or pin) is attached

to the same contact point at each end Crossover, where transmit contacts on each end of the

cable are connected to the receive contact at the other end

STRAIGHT THROUGH WIRING

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CROSSOVER WIRING

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UTP STRAIGHT-THROUGH CABLE

The cable that connects from the switch port to the computer NIC port is called a straight-through cable.

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Host or RouterHub or Switch

UTP STRAIGHT-THROUGH CABLE

Host or RouterHub or Switch

UTP CROSS-OVER CABLE

The cable that connects from one switch port to another switch port is called a crossover cable.

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UTP CROSS-OVER CABLE

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UTP ROLLOVER CABLE

The cable that connects the RJ-45 adapter on the com port of the computer to the console port of the router or switch is called a rollover cable.

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