COMMUNICATION

Communication is a process whereby information is enclosed in a package and is channeled and imparted by a sender to a receiver via some medium.

Sender: The One who sends the message idea or concept

Receiver: The one for whom the message is made or to one the message is delivered

A Communication channels is a path way over which information can be conveyed

It may be defined a physical wire that connects communication devices

Features of Communication Four things required

Sender, receiver, medium, and message Types of messages

File Request Response Status Control Correspondence

Understandability Error Detection

Data Communication Is the process of transmitting data from

one computer to another Focus is on transmission medium,

different signal levels and data coding

Information Transmission

Data are entities that convey information and are being exchanged

A signal is an encoded form of data using a physical mean.E.g. voltage.

Two domain of signalTimeFrequency

Transmission Medium Provides the path for data

communication Allows a bit stream to be transported

from one machine to another Can be categorized as

○ Guided media○ Unguided media

Guided Media

Copper WiresTwisted Pair

○ UTP○ STP

Coaxial Cable

Fiber Optics

Twisted Pair Consist of two insulated copper wires. Wires are twisted together each other. Commonly used in Telephone lines. Can run several meters without amplification. For longer distances Repeaters are used. Used for analog and Digital transmission. Cat-3, cat-5 and cat-6 used in computer

Networks. Commonly referred as UTP.

Types of Twisted Pair

Twisted pair

Unshielded twisted pair○ each wire is insulated with plastic wrap, but

the pair is encased in an outer covering

Benefits of UTP

Inexpensive and readily available Flexible and light weight Easy to work with and install

Disadvantages of UTP

Susceptibility to interference and noise Attenuation problem

For analog, repeaters needed every 5-6kmFor digital, repeaters needed every 2-3km

Relatively low bandwidth (3000Hz)

Unshielded Twisted Pair Connector

The standard connector for unshielded twisted pair cabling is an RJ-45 connector. This is a plastic connector that looks like a large telephone-style connector. A slot allows the RJ-45 to be inserted only one way. RJ stands for Registered Jack, implying that the connector follows a standard borrowed from the telephone industry. This standard designates which wire goes with each pin inside the connector.

The RJ-45 Connector

Shielded Twisted Pair (STP) Cable

A disadvantage of UTP is that it may be susceptible to radio and electrical frequency interference (RFI, EFI).

Shielded twisted pair (STP) is suitable for environments with electrical interference; however, the extra shielding can make the cables quite bulky.

Shielded twisted pair is often used on networks using Token Ring topology.

More expensive, harder to work with.

Baseband Coaxial Cable Commonly known as “coax”. More fast than Twisted pair

and span longer distance due to better shielding.

Consist of Copper wire surrounded by Insulating material which is covered by a mesh of conductor and which is covered by Plastic sheath.

Two types, 50 ohms and 75 ohms.

Used in Cable TV and LANs.

Broadband Coaxial Cable Used for Analog transmission. Can run 300 MHz for long distances. Analog signaling has better S/N than digital

signaling. Interfaces must convert digital signals to

analog and vice versa. Designed for long distances - can use

amplifiers. Commonly used for Cable TVs.

Better shieldingMore resistance to noise and cross talkLonger distances and higher speeds

Fiber Optics Consist of glass core surrounded by

cladding of Glass, covered by a thin plastic Jacket.

Typically grouped together in bundles, protected by an outer sheath.

Types of Fiber Optic

There are two types of Fiber Optic cable.MultimodeSingle-mode fiber

Single-mode fibers are more fast and expensive than Multi-mode because of covering long distance i.e. 50 Gbps for 100km without amplification.

Diameter = 50 microns

Diameter = 8 microns

Unguided Media

Radio Transmission

Radio waves have certain advantage over other Wireless medias. Travel long distance. Obstacles do not effect. Omni-directional

The disadvantages are the Interference among users, interference of Motors and Electrical equipments.

VLF, LF and MF bands are not used for Data communication due to their low bandwidth.

HF and VHF bands are used for communication.

Wireless LAN Technologies

Infrared (IR) Microwave Transmission Satellite Communications

Infrared (IR) Used for short range communication. Remote controls of devices use Infrared. Directional, Cheap and easy to build. Can not pass through Solid objects. No problem of interference between two

Infrared waves.

Microwave Transmission Travels in straight line. Parabolic antennas are used. Problem of Multi-path fading can occur. Antennas at transmitter and receiver must

be aligned (Line of Sight) Long distance links must have repeaters Used commonly in Telecommunication,

Mobiles, TV distribution,

Often the microwave antennas are on towers and buildings.

Why we require SatellitesDue to curvature of earth, signal can not be sent directly between two stations.

dish dish

uplink station downlink station

satellitetransponder

Solution: Satellites

Simply works as a Relay Station / Repeater.

Earth

Satellite

Ground station / Antenna

Ground station / Antenna

Important Terms

Uplink: earth->satellite. Downlink: satellite->earth. Transponder: satellite

electronics converting uplink signal to downlink.

Properties of Satellites

There are several Transponders in the Satellites, which are listening a signal on certain frequency and forwarding on a certain frequency

Satellites have to take care of the Van Allen belts as well, which are actually highly Charged Particles (Magnetic field)

Types of Satellites There are three categories of Satellites.

GEO satellites (Geo-stationary) MEO Satellites (Medium Earth Orbit) LEO Satellites (Lower Earth Orbit)