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Computer networks Fundamentals of Information Technology Session 6 Slide 2 Computer networks A computer network is a group of interconnected computers This can involve as few as two computers. At the other extreme it can involve millions of computers (e.g. the Internet) Computers in a network are generally connected for a purpose Share data (e.g. files, multimedia) Provide access to resources (e.g. web pages, applications) Provide services (e.g. processing, printing, communications) Slide 3 Network types There are two main types of computer network in use : Peer-to-peer (P2P) Client-server Slide 4 Peer-to-peer In a P2P network, the relationship between computers is one of equality All machines are essentially the same in terms of what they do The point is simply to provide access to files P2P networks are commonly used for file-sharing and internet telephony Examples of P2P networks are Napster, Gnutella, etc. Slide 5 Client-server In client-server networks, one type of machine (the server) is used by another (the client) to provide data or services. This is done through a series of requests and responses sent over a network Slide 6 Client-server In client-server networks, different types of server are used to provide different types of services to users: File server Application server Web server Print server Mail server Slide 7 File Server File servers provide a location for the shared storage of files so that they can be accessed by multiple workstations in the network To the user the network appears transparent. Files appear to be stored on his her computer File servers usually have a back-up server in case of problems with the main server Slide 8 Application server Application servers store whole applications or major components of applications and make these available to client machines Again, to the user the network appears transparent. The applications he/she uses appear to be installed on his/her computer Use of an application server makes updating software easier, as it is done centrally on the server, not on individual clients Slide 9 Web server Web servers provide a location for online resources (e.g. web pages, multimedia) They control access to these resources from users on the Web or company intranet Slide 10 Print server Print servers provide access to networked printers, manage the print queue and direct print jobs Slide 11 Mail server Mail servers control the flow of email in and out of an organisation and to and from internal client computers Slide 12 Advantages of client-server networks Access, resources and security are all controlled centrally at server level All data is stored in a central repository and usually backed-up File-management and version control is easier, as files are stored in one central location Utilities (e.g. anti-virus) are installed at server level Data is workstation independent, which means if one workstation goes down, data can be accessed through a different workstation Applications (where there is an application server) can be updated centrally, at server level Slide 13 Network scale Local Area Network (LAN) Covers a small geographical area. Used for networks in small and medium companies, schools, colleges, hospitals, etc. Wide Area Network (WAN) Covers a wider geographical area. Used to connect LANs together Slide 14 Network software Clients must run an operating system that allows networking (e.g. Windows XP) Servers require specialist server software (e.g. Microsoft Server 2003, Apache, Novell Netware). This software controls and monitors: Access Security Resources Performance Slide 15 Network hardware client and server Any typical desktop or notebook computer can act as a client in a network Any computer can act as a server, but it must have the processing power and storage capacity needed for the task Typical servers have multiple processors (up to 32 in some cases), multiple hard-drives and extensive RAM Server computers must be robust and reliable because of the central role they play in maintaining a network Thus, failsafe strategies, such as multiple power supply options are often built in Slide 16 Data transmission So that data can be moved between networks, universal standards (protocols) for data transmission have been implemented The de-facto standard is Transmission Control Protocol/Internet Protocol (TCP/IP) The TCP part of TCP/IP relates to the rules of how data should be sent The IP part relates to where it should be sent. Each computer has its own unique IP address (e.g. 193.61.29.155 ). This enables data to be routed to its correct destination You can find your own unique IP address at: http://www.ip-adress.com/ Slide 17 Data transmission Sending a message across a network involves several steps: 1.The message is decomposed into a number of smaller packets using the TCP protocol 2.Each packet is addressed with the recipient IP address 3.The packets are sent to the clients network/mail server 4. The clients network/mail server sends the packets onto the recipients PC 5.The packets are reassembled into the original message Slide 18 Virtual Private Network (VPN) A VPN is an extension of a private network across a public network (usually the Internet) VPNs use "virtual" connections routed through the Internet from the company's private network to the remote site or employee VPNs use encryption and tunnelling to ensure that only authorized users can access the network and that the data cannot be intercepted VPNs require special VPN software to be installed on the remote computer to deal with authorisation encryption and decryption Slide 19 Virtual Private Network (VPN) Slide 20 FIT Session 6 Activities Now do Activity 6 Computer Networks