Physical communication

Explain Coaxial and fiber optic media in detail.

A. Coaxial Cable

• An insulation is provided by coaxial cable is better than twisted pair cable.
• In coaxial cable, the inner inductor is either a solid copper wire or strands of copper.
• It is covered by an insulating plastic foam.
• The foam is surrounded by the outer inductor which is either a wire mesh tube or conductive foil wrap.
• It acts as an EMI shield.
• An insulation sheath of PVC or Teflon cover the entire cable.
• Coaxial cables are very expensive.

B. Fiber Optic Cable

• Fiber optic cable consists of a glass or plastic core which carries light pulses.
• The core is surrounded by layer's of reflective glass called cladding.
• It is in turn surrounded by a protective layer of fibers.
• The entire cable is tough outer sheath.
• Fiber optic cable is light weight than UTP and STP cable.
• It gives best data transfer rate with excellent quality.

Sr. No.	Fiber Optic Cable	Coaxial Cable
1.	It provides more bandwidth than coaxial cable.	It provides less bandwidth than fiber optic cable.
2.	It is eco-friendly. (That means, it does not generate excess heat.)	It is not eco-friendly.
3.	It is fast.	It is slow.
4.	It offers more secure communication.	It offers less secure communication.
5.	It will be able to support more bandwidth intensive activities.	It will not be able to support household Internet demands.
6.	It requires less insulation and jacketing.	It requires more insulation and jacketing.
7.	It is less physically robust.	It is physically robust than fiber optic cables.
8.	It transmits optical signal.	It transmits electrical signal.

What do you mean unguided media? Explain any one in brief.

Unguided Media

• Communication devices that send and receive data signal through air or space is called Unguided Media.
• In unguided media, the data is communicated in the form of wave.
• It provides a mean to transmit data signal but does not guide them along a specific path.
• The data signals are not bounded to a cabling media. Therefore, unguided media is also called Unbounded media.
• Unguided media is used when it is impossible to install the cables. The data can be transmitted all over the world through this medium.
• It is commonly referred to as wireless. The transmission of data is carried out using antenna (Directional and Omni-directional).

Types of Unguided Media

1. Microwave Transmission
2. Satellite Transmission
3. Radio Transmission
4. Mobile Communication

1. Microwave Transmission

• Microwave transmission are high frequency radio waves.
• The data is transmitted through air or space, instead of cables or wires.
• It uses 'line of sight' in order to work properly. A 'line of sight' mean the data signals or radio waves can only travel in straight lines and cannot bend.
• It is also called as relay station or booster.
• It contains an antenna, transmitter, receiver and other equipments that are required for microwave transmission.
• The microwave antennas are placed on the high tower or building. These are placed within 20 to 30 miles of each other.
• Each microwave station receives signals from previous microwave station and transmit to next station. In this way, data is transmitted over larger distances.

• The distance covered by microwave signal is based upon the height of the antenna. In order to increase this coverage each antenna has a built-in repeater that regenerates the signal before passing it on to the next antenna in line. The placement of the antenna to do this is approximately 25 miles.

Advantages of Microwave

• It is used for long distance telephone communication.
• It carries 1000's of voice channel at the same time.
• There is no need of cables.
• Multiple channels are available.
• It has wide bandwidth.

Disadvantages of Microwave

• It is very costly. Towers are expensive to build.
• The 'Line of sight' will be disrupted if any obstacle, such as new buildings are in the way.
• Single absorption by the atmosphere. Microwaves suffer from attenuation due to atmospheric conditions.

2. Satellite Transmission

• Satellite transmission can send and receive data signals.
• It consists of a satellite and several earth stations.
• This transmission requires an unobstructed line of sight. The line-of-sight will be between the orbiting satellite and station on Earth.
• These satellites are typically between 100 and 24,000 miles away.
• The satellites have many purposes including data communications, scientific applications and weather analysis.
• Microwave signals from a satellite can be transmitted to any place on Earth which mean that high quality communication can be made available to remote areas of the world without requiring massive investment in ground-based equipment.

The path that a satellite takes round the Earth is called its orbit.

There are three types of orbit:

1. Low Earth Orbit
2. Geosynchronous Earth Orbit
3. Polar Orbit

1. Low Earth Orbit (LEO)

• These satellites are placed at the top earth's atmosphere between 100 and 1240 miles high.
• It is the simplest and most cost effective type of satellite.
• It provides high bandwidth and low latency.
• It requires several dozen satellites to provide coverage of the entire planet.

2. Geosynchronous Earth Orbit (GEO)

• These satellites orbit are on the Earth at approximately 23,000 miles above the equator and have a period of exactly one day.
• They have their sending and receiving antenna locked to each other to maintain line-of-sight.
• It attains a specific orbit around the equator to keep away from other GEO satellites.
• The distance between GEO satellite is 2 degrees or 1000 miles.

3. Polar Orbit (PO)

• These satellites are generally Low Earth Orbit (LEO) satellites that have an orbit near or over the poles.
It can pass over the north and south poles many times a day at low altitudes of around 600 miles.
• Polar Orbit satellites are used for observation of the Earth and reconnaissance.

Advantages of Satellite Transmission

• It provides high bandwidth.
• It can be cheaper over long distances.
• A large amount of data can be communicated from one country to another.

Disadvantages of Satellite Transmission

• Bad weather can affect the quality of satellite transmission.
• Satellite manufacturing cost is very high.
• Cost of launching satellite is very expensive.

3. Radio Transmission

• This transmission works with or without 'line-of-sight'.
• If the 'line-of-sight' is possible then transmission can take place between sending and receiving antenna.
• If line of sight cannot be implemented then signals can be broadcast to the upper layers or the atmosphere or space and then transmitted back to Earth.
• The electromagnetic spectrum used for radio communication consists of eight distinct ranges which are regulated by government authorities:

Name	Description	Range
VLF	Very low frequency	3 – 30KHz
LF	Low frequency	30 – 300KHz
MF	Middle frequency	300KHz – 3MHz
HF	High frequency	3 – 30MHz
VHF	Very high frequency	30- 300MHz
UHF	Ultra high frequency	300MHz – 3GHz
SHF	Super high frequency	3 – 30GHz
EHF	Extremely high frequency	30 – 300GHz

4. Mobile Communication

• In mobile communication, the data is sent and received from the mobile computers.
• The data is communicated through radio signals from one location to another.
• The computers can be connected to the network through wireless connections or through wires.
• It is a radio-based network.

Explain three switching techniques in brief.

Switching techniques

• A network consist of many switching devices. A switched network is made up of a series of interconnected nodes called switches.
• Long distance transmission is done over a network of switched nodes.

Types of switching techniques

1. Circuit Switching
2. Message Switching
3. Packet Switching

1. Circuit Switching

• In circuit switching, an end to end path or circuit must be established between the communicating machines. The machines have exclusive use of this path until the connection is released.
• It is used in the public networks.
• In this method, the routing decision is made when the path is set up across the given network. After the link has been set in between the sender and receiver then the information is forwarded continuously over the provided link.

• In circuit switching, a dedicated link/path is established across the sender and the receiver which is maintained for the entire duration of conversation.
• It transfers data in real time with only delay being in circuit setup and propagation delay.

It has three phases

I. Circuit Establishment
II. Data Transfer
III. Circuit Disconnect

I. Circuit Establishment:

• Before any data transfer can begin, an end to end path has to be set up.
• Data Transfer: Once the circuit is established, analog or digital can be transmitted depending upon the nature of the network.
• Circuit Disconnect: The circuit can be released by either of the connected station's after data transfer takes place.

Disadvantages of Circuit Switching

• It is more expensive than any other switching techniques, because a dedicated path is required for each connection.
• Inefficient use of the communication channel.

2. Message Switching

• In message switching, it is not necessary to set up a physical path between the sender and the receiver.
• Each message is treated as an independent unit and includes its own destination source address by its own.
• Each complete message is transmitted from one device to another through internetwork.

Advantages of Message Switching

• The sender can send data when it wants to and does not need to check the status of the receiver whether it is busy or idle.
• Not necessary to set up a circuit in advance.

Disadvantages of Message Switching

• It requires large data buffers to hold the messages.
• Complicated routing algorithms are required.

3. Packet Switching

• An alternate method to message switching is to break up the message into several blocks called Packets.
• In this method, messages are broken up into packets and each of which includes a header with source, destination and intermediate node address information.
• It is used for performing data rate conversion.
• In packet switching, bandwidth is reduces by the splitting of data into different routes for a busy circuit.

• Using packet switching, there is a possibility to send data/information simultaneously.
• In the above diagram, information is padded with header that contains addresses of source and destination. This header is detected by intermediate switching nodes to determine their route and destination.
• The long messages breaks into packets. The packets are sent one at a time to the network. They can be handled in two ways, viz. Datagram and virtual circuit.

Advantages of Packet Switching

• It is more flexible.
• Call setup phase is avoided

Disadvantages of Packet Switching

• There is no guarantee that packet's will be delivered.
• It requires more overheads since each packet has to carry a lot of control information.