COMPUTER NETWORKS

This article explains the basics of computer network. A computer network can be simply defined as the interconnection of two or more independent computers. Applications of computer networks are found everywhere. They are used in our homes, schools, colleges, railway stations, offices and business. They help us to send an email, to watch a live sports event at our computer to book rail/air tickets to do chatting with our friends. The unit explains uses of computer networks, a client/server network, peertopeer network architecture, network topology, OSI & TCP/IP models and some useful application of computer networks.

Here we discuss the methods to create a network. A network may consists of multiple computers connected using some type of interface, each having one or more interface devices such as a Network Interface Card (NIC) and/or a serial device. Usually networks are categorized in two main categories which are: server based and peertopeer.

Next important thing which we know is Topology. Network Topology is the study of the arrangement or mapping of the elements (links, nodes, etc.) of a network. It studies the physical and logical interconnection between the nodes. Topologies can be physical or logical. There are various kinds of topologies like Star, Bus, Tree, Ring and mesh topology. Factors like money, length of cable, future growth of network and cable type need to be considered for selecting a network.

Bus topology is a linear topology in which all the computers are connected by a single length of cable with a terminator at each end. It is a simple, reliable, and in daily used small sized local area network. It requires least amount of cable to connect computer together and is therefore less expensive than other cabling arrangements.

Ring topology is also known as circular topology. In this topology, each node is connected to two and only two neighbouring nodes. It is an orderly network where every device has access to the token and the opportunity to transmit. Network adapter cards and Multi Access Units used in this topology are much more expensive than Ethernet cards and hubs. In star topology each computer on a network communicates with a central hub that resends the message either to all the computers or only to the destination computer. We can use several types of cable to implement a star network like ATM. It is expensive to install as it require more cable. 

Tree topology topologies integrate multiple star topologies together onto a bus. In its simplest form, only hub devices connect directly to the tree bus and each hub functions as the "root" of a tree of devices. It required pointtopoint wiring for individual segments but if the backbone line breaks, the entire segment goes down.

In a Mesh topology, each of the computers and network devices are interconnected with one another allowing for most transmissions to be distributed, even if one of the connections go down the network remain intact. Data travels by hopping from one node to another and then reaches the destination. It provides redundant paths between devices and hence it is more reliable and stable. With the hybrid topology, two or more topologies are combined to form a complete network.

We know the basic classification of networks where each of the networks is categorized as LAN, WAN & MAN. LAN is a group of computers located in the same room, on the same floor or in the same building that are connected to form a single network. Each computer connected to a LAN can be configured to be able to access the other connected computers’ hard drives, as if they were installed internally. A LAN comprises of different communication devices across the network such as repeater, router, hub, switch etc. LAN’s are private networks, not subject to tariffs or other regulatory controls.

Metropolitan area networks, or MANs, are large computer network usually spanning a city. They typically use wireless infrastructure or Optical fiber connections to link their sites. A MAN is optimized for a larger geographical area than a LAN, ranging from several blocks of buildings to entire cities. Some technologies used for implementing LAN are ATM, FDDI, and SMDS. MAN typically use wireless infrastructure or Optical fiber connections to link their sites.

Wide Area Network (WAN) is a computer network that covers a broad area (i.e., any network whose communications links cross metropolitan, regional, or national boundaries). The largest and most wellknown example of a WAN is the Internet.

WANs are used to connect LANs and other types of networks together, so that users and computers in one location can communicate with users and computers in other locations. Communication medium used are communication circuits which are connected by routers. In WAN, Hosts are typically connected (or close to) the routers.