Client server and peer-to-peer

• Client-server network


  One or more computers known as clients are connected to a powerful central computer known as the server. Each client may hold some of its own files and resources such as software, and can also access resources held by the server. In a large network, there may be several servers, each performing a different task.
• Types of servers in a client-server network

  • File server
  • Print server
  • Web server
  • Mail server
  • Database server
• Client-server network operation


  1. Client makes a request to the server

  2. Server processes the request
• Advantages of a client-server network

  • Security is better, since all files are stored in a central location and access rights are managed by the server
  • Backups are done centrally so there is no need for individual users to back up their data. If there is a breakdown and some data is lost, recovery procedures will enable it to be restored
  • Data and other resources can be shared
• Disadvantages of a client-server network

  • Expensive to install and manage
  • Professional IT staff needed to maintain the servers and run the network
• Cloud computing


  A growing service-based industry providing access to software or storage over the internet, using the client-server model
• Cloud-based storage services


  • DropBox
  • OneDrive
  • Google Drive
• Software as a Service (SaaS)

  Provision of software applications over the internet, where the company's data and applications are stored offsite
• Cloud-based applications


  • Microsoft Office
  • Accounting packages
• When a user requests a file from cloud-based storage


  The file is provided from the remote servers
• Peer-to-peer network


  A network where individual computers are connected to each other locally or over a wide area network to share files, without a central server
• Advantages of peer-to-peer networks in a small local area network

  • Cheap to set up
  • Enables users to share resources like printers and routers
  • Not difficult to maintain
• How peer-to-peer networks are used for video on demand

  1. Thousands of people simultaneously want to download the latest episode

  2. The load is shared across hundreds of computers holding parts of the video
• Peer-to-peer networks are also used to share copyrighted material
• Peer-to-peer networking


  Impossible to trace the source of illegal downloads
• 432 non unique Web users actively searched for copyright infringing content, downloading 53 billion visits each year
• Piracy sites


  Enabled the "sharing" of copyrighted music by storing the MP3 files on users' machines
• Napster was sued for copyright infringement in 2000 but argued they were not responsible for infringement on other people's machines
• Napster lost the case and was pushed into bankruptcy, but the service has since reinvented itself on a legitimate, subscription basis
• Popcorn Time


  A decentralized peer-to-peer service for legal streaming of movies
• Popcorn Time has already been translated into 32 languages and has been described as undermining the fewer resources moviemakers have to invest in new films
• In 2013 there was a 21% drop in the 18-24 age group buying tickets to watch movies, and numbers may plummet further
• A 2011 report estimated that 1.2 million European jobs would be destroyed by 2015 in the music, publishing and photography industries because of online piracy
• The Copyright, Designs and Patents Act 1968 protects certain types of work, for a specified period of time
• Client-server model


  Data may be processed on either the client or the server, or both
• Web server request and response

  1. Client sends request message to server

  2. Server responds with requested data or HTTP response
• Client-server processing


  • Client browser sends HTTP request to web server for dynamic web page data or web resource
  • Using a web page with an online search facility such as checking availability via a booking form
• Client-side processing


  Data is processed on the client computer, rather than on the server
• Client-side processing


  • Client computer has specific software that can process information
  • To lighten the load on the server's processor
  • Can improve security by avoiding unnecessary data transfer
• JavaScript


  A client-side language frequently used to provide interactivity on a web page
• Client-side processing can also adjust styles for different platforms or screen sizes
• JavaScript validation


  Commonly used for processing data on the client side to validate data entry before it is sent to the server
• Validate function


  1. Get departure and arrival airport values

  2. Check if airport values are blank

  3. Set border color to red if blank

  4. Display alert message

  5. Return false
• JavaScript validation is A-Level only
• Client-side processing


  • Provides initial data validation
  • Provides web page interactivity
  • Manipulates user interface elements
  • Applies styles (CSS)
  • Reduces the load on the server
  • Reduces the amount of web traffic
• Server-side processing


  • Provides further validation
  • Used to query a Database
  • Updates server databases
  • Performs complex calculations
  • Encodes data to readable HTML
  • Keeps organisational data secure
• Servers often process an enormous volume of data on behalf of multiple clients
• Servers can process data much faster than a client computer
• Server-side processing uses specific languages such as SQL or PHP
• Search requests may be sent to the server where they may be applied to a database using SQL