Networks What is a network? A computer network is a system that connects two or more computing devices for transmitting and sharing information. What are the uses of a network? An example that could be used could be that of a doctor’s surgery where the following uses could be applied: - The receptionist will record appointments and will advise the doctor whenever a patient is waiting. - The doctor will use the network to call up details of previous visits from the same patient. This information could be shared with other doctors who work at the same practice. - Prescription and charging details can be entered by the doctor and then accessed by the receptionist. Purpose of a network: Modern networks have developed to carry voice, music, video streams, text, and graphics between different devices such as computer systems, smartphones, tablets, etc. It can be classified as single purpose and multipurpose network. Single Purpose - A laptop can exchange data with a printer. - Bluetooth connection with the laptop. Multipurpose -Employees can send emails to each other and they can access the internet. Advantages of Network: • • • • • Sharing devices such as printers saves money. Software licenses are likely to be cheaper than buying several standalone licences. Files can easily be shared between users. Network users can communicate by email and instant messenger. Security is good - users cannot see other users' files unlike on stand-alone machines. • Data is easy to backup as all the data is stored on the file server. Disadvantages of Network: • Purchasing the network cabling and file servers can be expensive. • Managing a large network is complicated, requires training and a network manager usually needs to be employed. • If the file server breaks down the files on the file server become inaccessible. Email might still work if it is on a separate server. The computers can still be used but are isolated. • Viruses can spread to other computers throughout a computer network. • There is a danger of hacking, particularly with wide area networks. Security procedures are needed to prevent such abuse, ex. a firewall. Network Devices: Hub – Network connection point for devices on a single network. Data arriving at a hub is copied and send to all the devices on the network. Switch – Network connection point for devices on a single network. It can identify and sends the data to the appropriate receiver. Networks connected with a switch are faster than Hub network. Router – More sophisticated than hub and switch. Its use is to join multiple networks and serve as an intermediary between these networks so that data can be exchanged effectively and efficiently between network devices of those networks. For example, a router is used to connect a home network to the Internet. Hub Switch Router Wired communication: • A wired network employs wires to link devices to the Internet or another network, such as laptops or desktop PCs. • Wired networks use physical cables, such as copper wire, twisted pair, or fiber optic cables, to transmit data between devices. • Wired networks are more secure than wireless networks because data is transmitted over physical cables, which are harder to tamper with to intercept messages. • Wired networks offer higher speed, stability, and security, but they also require more infrastructure, maintenance, and cost than wireless network. Copper Cable (metal conductors) - It is the most common kind of cabling in computer networks. Coaxial cable- It consists of two copper conductors. It was used in computer networks, as well as to carry TV signals. Low cost of installation. Unshielded Twisted Pair Cable (UTP) - Very popular in LANs. Easy to install. Prone to electrical interference. Used in telephone networks. Very secure. Shielded Twisted Pair Cable - More difficult to install. Reduced interference. Fiber Optic Cable - Optical fiber carries a beam of light. Very expensive. Offers higher speed. Extremely secure. Used for data transmission and telephone lines. Ethernet Cable Jack Fibre Optic cable Patch Panel Wireless communication: • Wireless networks use radio waves or infrared signals to transmit data between devices, such as laptops, smartphones, or tablets, and wireless access points, which are connected to a wired network. • Wireless networks offer mobility, scalability, and ease of installation, but they also suffer from interference, lower bandwidth than wired networks. • Wireless networks are less secure than wired networks because they use air as a medium to send radio waves or infrared waves, which can be intercepted by unauthorized users. Cellular Data – Use microwave radio signals for data transmission. Use cellular towers to transmit data between devices. Radio wave signals offer high bandwidth but lower than cables. 2G, 3G, 4G and 5G are different generations of cellular networks. For optimum results no buildings and other structures should be between the transmitter and the received. Weather conditions affect the performance. Less secure than wired communication. Satellites – Use microwave signals. Bluetooth – Use microwave radio to exchange data. They transmit at very low power levels. What is a server? A server can either be a computer system or a software application that provides a service to the other computer systems connected to the same network. For example – a server can provide the ability to the rest of the computers on the network to store and to share files, taking the role of a file server. What is a client? A client can either be a computer system or a software application that requests a service from a server connected to the same network. For example – an email client software application can request from an email server software application to fetch any emails that may have been received. Web browser software application access website in the web server. Here, web browser is the client and Web server is the server. Network Types: PAN is a personal area network. This is usually two devices (or a small number) in proximity connected for a specific purpose, for example connecting a mobile phone to a television to view images or connecting a laptop to a printer. LAN is a local area network. This is multiple devices connected over a small geographical area (usually defined as a single building or under a mile). The hardware (infrastructure) is owned by the network owner, so it does not use external cabling or the internet. Examples include a home network of devices, or a school on a single site. LAN Wired connection LAN Wired and Wireless WAN is a wide area network. This is multiple devices connected over a large geographical area (usually defined as multiple buildings). Some of the hardware is not owned by the specific individual or company but may instead be provided by a utility company. Examples include a multi-campus university, local government, or a nationwide store. Speed of data transmission across a network: Bandwidth – Amount of data that can be transmitted within a certain amount of time. Measured in bps (bits per second), kbps (Kilobits per second), Mbps (Megabits per second) and Gbps (Gigabits per second). Transmission Distance – how far data can be sent using the transmission method. Interference – It is caused when something interrupts the transmission of a signal. This could be a physical obstruction such as walls or other radio waves. Factors that affect speed of data transmission: • Bandwidth of the network • Data transfer rate of storage devices • Interferences. Errors in data transmission may occur due to various factors, including: • Interference from other electrical devices • Objects in the way • A fault in the transmission media, such as damaged cable, power loss. Network Topologies: Network Topology is the schematic description of a network arrangement, connecting various nodes (devices means sender and receiver) through lines of connection. Bus Topology - Bus topology is a network type in which every computer and network device is connected to single cable. When it has exactly two endpoints, then it is called Linear Bus topology. Features Advantages -It transmits data only in one - It is cost effective. -Cable required is least direction. compared to another -Every device is connected network topology. to a single cable. -Used in small networks. -It is easy to understand. -Easy to expand joining two cables together. Ring Topology - It forms a ring as each computer is connected to another computer, with the last one connected to the first. Exactly two neighbours for each device. Disadvantages - Cables fails then whole network fails. - If network traffic is heavy or nodes are more the performance of the network decreases. - Cable has a limited length. - It is slower than the ring topology. Features -The transmission is unidirectional, but it can be made bidirectional - Data is transferred in a sequential manner that is bit by bit. Data transmitted, has to pass through each node of the network, till the destination node. Advantages - Transmitting network is not affected by high traffic - Cheap to install and expand Disadvantages - Adding or deleting the computers disturbs the network activity. - Failure of one computer disturbs the whole network. Star Topology - All the computers are connected to a single hub through a cable. This hub is the central node, and all other nodes are connected to the central node. Features - Every node has its own dedicated connection to the hub. - Can be used with twisted pair, Optical Fibre or coaxial cable. Advantages - Fast performance with few nodes and low network traffic. - Hub can be upgraded easily. - Easy to identify failure computer. - Easy to setup and modify. - Only that node is affected which has failed, rest of the nodes can work smoothly. Disadvantages - Cost of installation is high. - Expensive to use. - If the hub fails then the whole network is stopped because all the nodes depend on the hub. - Performance is based on the hub that is it depends on its capacity Tree Topology - It has a root node, and all other nodes are connected to it forming a hierarchy. It is also called hierarchical topology. It should at least have three levels to the hierarchy. Features - Ideal if workstations are located in groups. - Used in Wide Area Network. Advantages - Extension of bus and star topologies. - Expansion of nodes is possible and easy. - Easily managed and maintained. - Error detection is easily done. Disadvantages - Heavily cabled. - Costly. - If more nodes are added maintenance is difficult. - Central hub fails, network fails. Mesh Topology – In mesh topology each device is connected to every other device on the network through a dedicated point-to-point link. When we say dedicated, it means that the link only carries data for the two connected devices only. Features - Fully connected. - Robust. - Not flexible. Advantages - Each connection can carry its own data load. - It is robust. - Fault is diagnosed easily. - Provides security and privacy. Disadvantages - Installation and configuration are difficult. - Cabling cost is more. - Bulk wiring is required. Hybrid Topology - It is two different types of topologies which is a mixture of two or more topologies. For example, if in an office in one department ring topology is used and, in another star, topology is used, connecting these topologies will result in Hybrid Topology (ring topology and star topology). Features - It is a combination of two or topologies - Inherits the advantages and disadvantages of the topologies included Advantages Disadvantages - Reliable as Error detecting - Complex in design. and troubleshooting is easy. - Costly. - Effective. - Scalable as size can be increased easily. - Flexible.
