Data Transmission

Topic 3. Network

Data transmission


Define the terms: protocol, data packet.

Protocol:

 The rules of communication.
Set of rules for data communication over a network.A protocol defines the format and the order of the messages exchanged between multiple communicating entities.

Data:

Anything in a form that is suitable for use with a computer.

Packet:

Group of bits. May include control signals, error control bites, coded information, as well as the destination for the data.

Data packet:

Data packet is a unit of information in a form suitable to travel between computers.

Explain why protocols are necessary.

Data integrity

Ensuring that the information being sent did not change or gets corrupted either deliberately nor accidentally. Checksum mechanisms provide data integrity.

Flow control

A mechanism that ensures the rate at which a sender is transmitting is in proportion with the receiver’s receiving capabilities so prevents network overload.

Deadlock prevention

Deadlock is a situation in which two or more network competing actions are each waiting for the other to finish, and thus neither ever does.Prevents situation where two or more competing programs or actions are sharing a resource and preventing each other from using it.

Congestion management

Congestion happens when the request on the network resources exceeds the offered capacity. Using protocol to stop both and re-queue them so they won’t occur at the same time / re-queue to be in sequential order.

Error checking

A process to determine the error

Error correction

The ability to repair the error

Explain why the speed of data transmission across a network can vary

1. Bandwidth of the network
2. Speed, technology and capacity of the network server
3. Interferences (e.g. walls, trees...)
4. Number of users and users’ demand at any particular time

Explain why compression of data is often necessary when transmitting across a network.

（Compression has enabled information to be disseminated more rapidly.）
Data compression is the reduction of bits by encoding data using fewer bits than the original representation. It makes the file smaller and the transfer with no data loss because it takes up less bandwidth while all networks have a limited bandwidth.

Lossy data compression:

with this compression method, some loss of information is acceptable and there is no way to get the original file back.(e.g. JPEG, MPEG2)

Lossless data compression:

This compression method reduces the number of bits by first identifying and then eliminating any statistical redundancy.There is no loss of information during lossless compression(e.g. compression-decompression software)

Outline the characteristics of different transmission media.

Metal Conductor

  • Speed
Higher compare to wireless connection.
  • Reliability
High compare to wireless counterpart, as manufactured cables have higher performance due to existence of wired technology since years.
  • Cost
Less as cables are not expensive
  • Security
.Wired networks are more secure than wireless networks This is due to the fact that the network is only accessible with a physical cable connection. 

Fibre optic

  • Speed
The highest because it’s speed is light speed
  • Reliability
A fiber optic internet access does not experience interruptions from electricity disruptions. You’ll still be able to access your fiber-optic network without electricity because the cables are made of glass and do not conduct electricity. This protects the cables from fluctuating power voltages and risk of fires. In other words, a fiber network provides a consistent service.
  • Cost
The fiber-optic internet cost can be more expensive and will depend on your usage, the speed of the internet you want, and your location. You may also need to pay installation and activation fees.
  • Security
Wired networks are more secure than wireless networks . This is due to the fact that the network is only accessible with a physical cable connection. 

Wireless

  • Speed
lower compare to wired networks
  • Reliability
Reasonably high, This is due to failure of router will affect the entire network.
  • Cost
More cost as wireless subscriber stations, wireless routers, wireless access points and adapters are expensive
  • Security
A wireless network is less secure than a wired network. Wireless networks must be secured correctly as accessing a wireless network can be done discreetly and does not require physical access to a building.

Explain how data is transmitted by packet switching.

The original file is divided into packets before transmission and each packet.
Datagram Packet Switching: each packet contains the receiver address. The path that datagrams take between the same source and destination can be different.
Virtual Circuit Packet Switching: a route from source to destination is set up before any transmission takes place.
With packet switching the communication channel can be used more efficiently and delays are minimized.