• A network is a link between computer systems
• Networking is a process of linking computer systems with an aim of sharing resources
• Networks may be classified according to a wide variety of characteristics such as the medium used to transport the data, communications protocol used, scale, topology, and organizational scope.

Types of Computer Networks

• Local Area Network – A LAN connects network devices over a relatively short distance. A networked office building, school, or home usually contains a single LAN, though sometimes one building will contain a few small LANs (perhaps one per room), and occasionally a LAN will span a group of nearby buildings.
• Wide Area Networks – As the term implies, a WAN spans a large physical distance. The Internet is the largest WAN, spanning the Earth. A WAN is a geographically-dispersed collection of LANs. A network device called a router connects LANs to a WAN. In IP networking, the router maintains both a LAN address and a WAN address.
• Metropolitan Area Network – a network spanning a physical area larger than a LAN but smaller than a WAN, such as a city. A MAN is typically owned an operated by a single entity such as a government body or large corporation.
• Internet – this is a network of networks. It links web servers from different organizations hosting their information for users to access

Network Topologies

◼Network topology is the layout pattern of interconnections of the various elements (links, nodes, etc.) of a computer or biological network. Network topologies may be physical or logical.

◼Physical topology refers to the physical design of a network Including the devices, location and cable installation.

◼. Logical topology refers to how data is actually transferred in a network as opposed to its physical design.

In general physical topology relates to a core network whereas logical topology relates to basic network. Any particular network topology is determined only by the graphical mapping of the configuration of physical and/or logical connections between nodes.

Bus Topology in Computer Networking

◼In local area networks where bus topology is used, each node is connected to a single cable. Each computer or server is connected to the single bus cable. A signal from the source travels in both directions to all machines connected on the bus cable until it finds the intended recipient. If the machine address does not match the intended address for the data, the machine ignores the data.

Alternatively, if the data matches the machine address, the data is accepted. Since the bus topology consists of only one wire, it is rather inexpensive to implement when compared to other topologies.

However, the low cost of implementing the technology is offset by the high cost of managing the network. Additionally, since only one cable is utilized, it can be the single point of failure. If the network cable is terminated on both ends and when without termination data transfer stop and when cable breaks, the entire network will be down.

Star Network Topology in Computer Networking

◼In local area networks with a star topology, each network host is connected to a central hub with a point-to-point connection.

The network does not necessarily have to resemble a star to be classified as a star network, but all of the nodes on the network must be connected to one central device. All traffic that traverses the network passes through the central hub.

The hub acts as a signal repeater. The star topology is considered the easiest topology to design and implement. An advantage of the star topology is the simplicity of adding additional nodes.

The primary disadvantage of the star topology is that the hub represents a single point of failure.

Ring Network Topology

◼A network topology that is set up in a circular fashion in which data travels around the ring in one direction and each device on the right acts as a repeater to keep the signal strong as it travels. Each device incorporates a receiver for the incoming signal and a transmitter to send the data on to the next device in the ring. The network is dependent on the ability of the signal to travel around the ring.

Network Components

◼A network card, network adapter, or NIC (network interface card) is a piece of computer hardware designed to allow computers to physically access a networking medium. It provides a low-level addressing system through the use of MAC addresses.

◼A repeater is an electronic device that receives a signal, cleans it of unnecessary noise, regenerates it, and retransmits it at a higher power level, or to the other side of an obstruction, so that the signal can cover longer distances without degradation.

◼A network bridge connects multiple network segments and broadcasts to all ports except the port on which the broadcast was received. However, bridges do not promiscuously copy traffic to all ports, as hubs do.Once the bridge associates a port and an address, it will send traffic for that address to that port only. Bridges learn the association of ports and addresses by examining the source address of frames that it sees on various ports. Once a frame arrives through a port, its source address is stored and the bridge assumes that MAC address is associated with that port.

◼A network switch is a device that forwards and filters  chunks of data communication)between ports (connected cables) based on the MAC addresses in the packets.A switch is distinct from a hub in that it only forwards the frames to the ports involved in the communication rather than all ports connected.

◼A router is an internetworking device that forwards packets between networks by processing information found in the datagram or packet. Routers use routing tables to determine what interface to forward packets

◼A firewall is an important aspect of a network with respect to security. It typically rejects access requests from unsafe sources while allowing actions from recognized ones. The vital role firewalls play in network security grows in parallel with the constant increase in ‘cyber’ attacks for the purpose of stealing/corrupting data, planting viruses, etc.

◼Modem  _  Helps users to access internet connections and provide better platforms for accessing various forms of data.

Modes of Data Transmission

◼A simplex connection is a connection in which the data flows in only one direction, from the transmitter to the receiver. This type of connection is useful if the data do not need to flow in both directions (for example, from your computer to the printer or from the mouse to your computer…).

◼A half-duplex connection (sometimes called an alternating connection or semi-duplex) is a connection in which the data flows in one direction or the other, but not both at the same time. With this type of connection, each end of the connection transmits in turn. This type of connection makes it possible to have bidirectional communications using the full capacity of the line.

A full-duplex connection is a connection in which the data flow in both directions simultaneously. Each end of the line can thus transmit and receive at the same time, which means that the bandwidth is divided in two for each direction of data transmission if the same transmission medium is used for both directions of transmission