3.1.6 - Define the terms: protocol, data, packet.
3.1.7 - Explain why protocols are necessary.
3.1.8 - Explain why the speed of data transmission across a network can vary.
3.1.9 - Explain why compression of data is often necessary when transmitting across a network.
3.1.10 - Outline the characteristics of different transmission media.
3.1.11 - Explain how data is transmitted by package switching
The students at St Julian's School in Portugal have put together some good notes on their wiki for Networking:
3.1.6-Protocol = Set of rules or guidelines to enable different devices to communicate with each other. Data = Anything that is sent over a network, files. Packet = Data that has been broken down to ensure integrity and reliability since packets are smaller than data, which means if you lose a packet you don't need to resend the whole file only the packet which is missing.
3.1-7-
Protocols are necessary as their function is to allow two or more devices to be able to interact with each other. Protocols are a method of neutral mediation. To add, protocols do not need to be public, and can be kept confidential.
3.1.8- Different factors affect the speed of data transmission being: the computer processor speed-a computer with dual Pentium IV processor will most likely get faster connectivity compared to one with a Pentium III or Pentium II processor; internet speed will depend on distance that the data travels, how many servers it has to go through and the different speeds of each server (the shorter the cables or the closer the computers are to the router the faster the connection); heavy traffic on thenetwork (ISPs are allocated a certain amount of bandwidth which is shared among all the incoming and outgoing connections); Malware, Spyware and Viruses hinder the operation of programs, slows down the speed of connectivity; Modem speed- can slow down the speed at which data is transmitted; hardware problems- can seriously reduce the speed of the data being processed by your system; software problems; memory available- each thing you open is using RAM memory and has to write this to the disk and the more memory you are using up to open programs the less memory there is a available to receive data etc.
3.1.9 - Explain why compression of data is often necessary when transmitting across a network.
A network has limited bandwidth, in that only a certain number of bits can be push through it at any one time without losing data.
To reduce the use of bandwidth in a network, and hence ensure that the network does not becomes congested, redundancies in data
can be removed. This process is called compression.
The following excerpt from St. Julians:
You can assure speed in data transmission by compressing data. There are two types of data compression:
Lossy data compression: This type of compression removes the unnecessary data. It is mainly used in pictures, example: conversion of a picture from GIF to JPEG and conversion of an audio file from WAV to MP3. Example of how this works: imagine a picture with a blue sky, almost every pixel in that part of the picture has a different shade of blue even if the change from one shade to another is
lossy.gif
almost null; when you apply lossy compression it takes a number of different shades and turns them into an 'average' shade. It is a very efficient and smart type of data compression because you can't really notice the difference unless you zoom in on the picture. The main difference between this and lossless compression is that with lossy compression you can't get the original file back.
Lossless data compression: This type of compression allows you to recreate the original file. It involves breaking the original file into a smaller version while it is transmitted or stored in a way that when it reaches its destiny it can be put back together and used as before. Example of lossless data compression is when you zip an amount of files into a file (usually done with 7-zip).
3.1.10-Characteristics of different transmission media
3.1.6 - Define the terms: protocol, data, packet.
3.1.7 - Explain why protocols are necessary.
3.1.8 - Explain why the speed of data transmission across a network can vary.
3.1.9 - Explain why compression of data is often necessary when transmitting across a network.
3.1.10 - Outline the characteristics of different transmission media.
3.1.11 - Explain how data is transmitted by package switching
The students at St Julian's School in Portugal have put together some good notes on their wiki for Networking:
http://st-julians-computer-science-2010.wikispaces.com/3.4+Networked+computer+systems
Other links/notes:
http://en.wikipedia.org/wiki/Data_transmission
3.1.6- Protocol = Set of rules or guidelines to enable different devices to communicate with each other.
Data = Anything that is sent over a network, files.
Packet = Data that has been broken down to ensure integrity and reliability since packets are smaller than data, which means if you lose a packet you don't need to resend the whole file only the packet which is missing.
3.1-7-
Protocols are necessary as their function is to allow two or more devices to be able to interact with each other. Protocols are a method of neutral mediation. To add, protocols do not need to be public, and can be kept confidential.
3.1.8- Different factors affect the speed of data transmission being: the computer processor speed-a computer with dual Pentium IV processor will most likely get faster connectivity compared to one with a Pentium III or Pentium II processor; internet speed will depend on distance that the data travels, how many servers it has to go through and the different speeds of each server (the shorter the cables or the closer the computers are to the router the faster the connection); heavy traffic on the network (ISPs are allocated a certain amount of bandwidth which is shared among all the incoming and outgoing connections); Malware, Spyware and Viruses hinder the operation of programs, slows down the speed of connectivity; Modem speed- can slow down the speed at which data is transmitted; hardware problems- can seriously reduce the speed of the data being processed by your system; software problems; memory available- each thing you open is using RAM memory and has to write this to the disk and the more memory you are using up to open programs the less memory there is a available to receive data etc.
3.1.9 - Explain why compression of data is often necessary when transmitting across a network.
A network has limited bandwidth, in that only a certain number of bits can be push through it at any one time without losing data.
To reduce the use of bandwidth in a network, and hence ensure that the network does not becomes congested, redundancies in data
can be removed. This process is called compression.
The following excerpt from St. Julians:
You can assure speed in data transmission by compressing data. There are two types of data compression:
3.1.10-Characteristics of different transmission media
3.1.11-
http://www.teach-ict.com/technology_explained/packet_switching/packet_switching.html