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This topic considers the various ways in which computers can be connected to each other to communicate, share data and peripherals. Four categories of network are covered in the course: 1. LAN 2. WAN 3. Internet 4. Intranet CS Topic 4 - Networks v2 1 In looking at the four categories of networks we will compare them using the following four characteristics: a. Transmission media Refers to the type of cabling or wireless method used to transfer data. b. Bandwidth Relates to the speed at which data can be transferred throughout the network. c. Geographical spread Looks at the size of the area which the network covers. d. Functions Considers what tasks the network can carry out for the users. CS Topic 4 - Networks v2 2 1. LAN 2. WAN 3. Internet http://fcit.usf.edu/network 4. Intranet a. Transmission media Fibre-optic cable, Unshielded twisted pair(UTP) cable, co-axial cable (as used in a tv aerial.) b. Bandwidth This depends on the cabling and hardware used. UTP cable allows data transfer at 10 – 100 Mbps c. Geographical spread Physical cabling is laid to connect the network. Usually one building, school, office, factory. Typically up to about two km. d. Functions Peripheral sharing, electronic mail, data sharing. CS Topic 4 - Networks v2 3 1. LAN 2. WAN 3. Internet 4. Intranet a. Transmission media Telecommunications systems covering large areas. b. Bandwidth Slower than LAN. Depends on the link used. Modem dial-up up to 56 Kbps. ADSL up to 9 Mbps, dedicated line up to 45 Mbps. c. Geographical spread WANs can cover any size of area. They use telecommunications which covers most of the earth. d. Functions Electronic mail, data sharing, conferencing. CS Topic 4 - Networks v2 4 1. LAN 2. WAN An internet is a network of networks 3. Internet 4. Intranet a. Transmission media Telecommunications systems covering large areas. b. Bandwidth Same as WAN. Depends on the link used. Modem dial-up up to 56 Kbps. ADSL up to 9 Mbps, dedicated line up to 45 Mbps. c. Geographical spread The Internet can cover any size of area. They use telecommunications which covers most of the earth. d. Functions Electronic mail, information sharing using WWW, File sharing using FTP. CS Topic 4 - Networks v2 5 1. LAN 2. WAN 3. Internet An intranet is like the internet but confined to 4. Intranet one organisation. a. Transmission media Telecommunications systems covering large areas. b. Bandwidth Slower than LAN. Depends on the link used. Modem dial-up up to 56 Kbps. ADSL up to 9 Mbps, dedicated line up to 45 Mbps. c. Geographical spread Intranet can cover any size of area using telecommunications links which cover most of the earth. East Dunbartonshire Council has its own intranet. d. Functions Electronic mail, information sharing using WWW, File sharing using FTP. CS Topic 4 - Networks v2 6 A mainframe is a very large computer which provides processing power and backing storage facilities to users working at terminals. A terminal is a monitor and keyboard with little or no processing power and no storage facility. Mainframes were popular for large scale computing ventures but many have been replaced by newer client server networks. CS Topic 4 - Networks v2 7 Mainframes offer the following facilities: High capacity input/output. Can access and store data for thousands of users simultaneously Powerful processing capability. Can process data for thousands of users simultaneously Centralised storage, processing and management of large amounts of data. Comprehensive backup, recovery and security for the system CS Topic 4 - Networks v2 8 Unlike a mainframe, a network is a collection of independent computers connected together. Each of the computers has its own processing power and backing storage capability and is capable of functioning as a standalone computer. In the Higher course we will look at two types of network: 1. Peer-to-peer network. 2. Client Server network. CS Topic 4 - Networks v2 9 In a peer-to-peer network all the computers have equal status. Each computer can choose to share its resources with the other computers. Resources include printers, backing storage devices, data files. There is no centralised backing storage as each computer stores its own data and applications. A system for backups is therefore difficult to implement. Security is difficult to maintain as resources, user names and passwords are not centrally managed. Most home networks are peer to peer. CS Topic 4 - Networks v2 10 In a Client Server network some computers are clients. People use these to access the network. A server is a computer which controls a resource that is made available to clients on the network. Resources might include applications, data files, printers, email or internet access. Backing storage is centralised and all user files are stored on a file server. It is easy to make backups on the file server. The server holds a database of all user names, passwords and access rights. Security is easy to maintain as it is centrally managed. The school network is an example of a client server network. CS Topic 4 - Networks v2 11 Advantages of a client-server network • Backing storage is centralised and all user files are stored on a file server. It is easy to make backups on the file server. • The server holds a database of all user names, passwords and access rights. Security is easy to maintain as it is centrally managed. Can allow different levels of access for different users • Easy to update software as it is done centrally • Easy to manage and control use of resources such as printers, internet. • Reports about users and computer use can be easily generated. CS Topic 4 - Networks v2 12 1. File Server 2. Print Server 3. Web Server File Server Stores users’ data files. Controls file access. Each user has access to certain files. Controls the type of access. e.g. read only, write, create Print Server Handles all printing requests from clients. Queues jobs, spools them to disk and sends to printer when printer is ready. CS Topic 4 - Networks v2 13 1. File Server 2. Print Server 3. Web Server Web Server Requests for internet access including Web pages, email and file sharing are dealt with by this server. Web Server advantages • Pages can be held locally(cached) which allows faster access to pages. • Use of the internet can be monitored more easily when all internet access goes through the web server. CS Topic 4 - Networks v2 14 The topology of a network refers to the shape of the network, how the computers are physically connected together. A node is any device which is attached to the network. e.g. a computer, printer, server, router. node A channel is the way in which data is transferred from channel one node to another. This could a cable or some form of wireless technology. Network topology diagrams must always be labelled with the words node and channel Four topologies are covered in the Higher Course. CS Topic 4 - Networks v2 15 1. Bus 2. Star 3. Ring 4. Mesh or node channel Used in LANS. All nodes are connected to a single channel. A communication from one node is seen by all the other nodes. Each node will recognise and accept communications which are addressed to it. CS Topic 4 - Networks v2 16 1. Bus 2. Star 3. Ring 4. Mesh or node channel Node Failure There is typically a mechanism to bypass a failed node so failure of one node will only affect that node. Rest of network will still function. Channel Failure A channel failure will cause the whole network to fail. CS Topic 4 - Networks v2 17 1. Bus 2. Star 3. Ring 4. Mesh node channel Used in LANS. Each node has its own channel to the central node. The whole network depends on the proper functioning of the central node. Cabling cost is high because each node has its own channel but it is easy to extend the network. CS Topic 4 - Networks v2 18 1. Bus 2. Star 3. Ring 4. Mesh node channel Node Failure A failure of one node will only affect that node. Failure of the central node will disable the entire network. Channel Failure A channel failure will only affect the outer node on that channel. CS Topic 4 - Networks v2 19 1. Bus 2. Star 3. Ring 4. Mesh node channel Used in LANS. Channels and nodes form a ring. Only one node can transmit at a time and data passes between nodes until it reaches its destination. The network has to be disrupted when a new node is added. Designing and extending the network is more difficult than with a star network. CS Topic 4 - Networks v2 20 1. Bus 2. Star 3. Ring 4. Mesh node channel Node Failure There is typically a mechanism to bypass a failed node so a failure of one node will only affect that node. Channel Failure A channel failure will disable the entire network. CS Topic 4 - Networks v2 21 1. Bus 2. Star 3. Ring 4. Mesh node channel Used in WANS. e.g. telephone grid. There are alternative channels between nodes. Several nodes can transmit at a time and data can be redirected when some channels are busy. The extra cabling makes this an expensive type of network to set up but it is very robust. CS Topic 4 - Networks v2 22 1. Bus 2. Star 3. Ring 4. Mesh node channel Node Failure The failure of one node will only affect that node. Channel Failure A channel failure will have no effect as alternative channels are available. It may, however, slow down traffic on the network. CS Topic 4 - Networks v2 23 Some nodes on a network are devices which are there to manage the flow of data. When data is sent it includes a destination address. Each node on the network has its own address to uniquely identify it. Three common devices used for managing the flow of data are: 1. Hub 2. Switch 3. Router CS Topic 4 - Networks v2 24 1. Hub 2. Switch 3. Router Nodes are connected to a hub via channels. When data is received from a node it is broadcast to all the other ports. This is inefficient as the data is intended for only one of the other nodes. Stackable hubs with 8, 16 or 24 ports can be linked to form large LANS. It may also amplify the signal if long distances are involved. CS Topic 4 - Networks v2 25 1. Hub 2. Switch 3. Router A switch is sometimes known as an intelligent hub. When data is received from a node it is examined and then sent directly to the destination known. This is more efficient than a hub as the data goes directly to the destination node. Switches are more complex than hubs and are therefore more expensive. CS Topic 4 - Networks v2 26 1. Hub How can you improve the technical performance of a network which uses a hub? 2. Switch 3. Router A Switch would be more efficient than a Hub in that it doesn’t broadcast data to all nodes on the network Higher specification cabling could improve technical performance. Faster NIC(Network Interface Cards) could also improve technical performance. CS Topic 4 - Networks v2 27 1. Hub 2. Switch 3. Router Routers connect different networks together. They control and manage the flow of data over the different networks. They connect smaller networks into larger internetworks. They connect LANS to telecommunications lines and the Internet. They cope with the differences in topologies and transmission media. CS Topic 4 - Networks v2 28 Each device on a network requires an interface to allow it to connect. A Network interface card (NIC) is usually slotted into the motherboard of the device. The NIC converts the data to and from a format that can be transmitted over the network . Wireless interface cards can also be used. These can use USB or PCMCIA cards to allow devices to connect. CS Topic 4 - Networks v2 29 Higher Bandwidth Technology is improving rapidly and improvements in bandwidth increase the rate of data transfer. Higher bandwidth allows the possibility of transferring video, graphics and audio and will allow live streaming of data. • Transmit large data files. • Play network multi-user games with high resolution graphics. • Video conferencing. CS Topic 4 - Networks v2 30 Wireless Communications Wireless communication increases flexibility of use and is becoming more popular for home, office and public spaces. • No wiring required and ability to move around. • Can be affected by electrical interference. • Easy to hack into unless firewall security is enabled. CS Topic 4 - Networks v2 31 There are many technical reasons for the increasingly widespread use of networks. These include: • Advances in computer hardware. • Network interface cards (NIC) are now built into most computers • Wireless technology makes it easier to work on a network. • Higher bandwidth and faster connection speeds make networking more attractive CS Topic 4 - Networks v2 32 • Improvements in network related software. There is a standard protocol for communication – (TCP/IP) Networking software is now built into common operating systems e.g. Windows Vista, Linux and Windows XP CS Topic 4 - Networks v2 33 The use of networks which can be local, national or even international poses legal problems for governments. Three Acts in particular are relevant for possible network misuse. Computer Misuse Act This Act makes it illegal to breach network security for any reason. “Hackers” can be fined or imprisoned for gaining access and looking at or altering data and also for introducing viruses. CS Topic 4 - Networks v2 34 Copyright, Designs & Patents Act It is very easy on a network to transfer audio, video and text at high speed. This has led to a huge increase in the unauthorised pirating of music, films and books. This Act makes it illegal to make unauthorised copies of material. Offenders can be fined or imprisoned for being involved in this activity and FAST(The Federation Against Software Theft) have had many companies and individuals prosecuted. CS Topic 4 - Networks v2 35 Data Protection Act(1998) http://www.informationcommissioner.gov.uk/ The principles of this Act also apply to network use. The Act gives individuals(Data Subjects) rights to: • gain access to their data. • seek compensation if inaccurate information causes damage. • "opt-out" of having their data used for direct marketing. • "opt-out" of fully automated decision-making about them. CS Topic 4 - Networks v2 36 Data Protection Act(1998) Organisations processing personal data ("controllers") must comply with the data protection principles. These require data to be: • Accurate. • adequate, relevant and not excessive. • processed for limited purposes. • fairly and lawfully processed. CS Topic 4 - Networks v2 37 Data Protection Act(1998) • processed in accordance with individuals' rights. • kept secure. • not kept longer than necessary. • not transferred to non-EEA (European Economic Area) countries without adequate protection. CS Topic 4 - Networks v2 38