BASICS OF COMPUTER NETWORKS

Network:

A network is a set of devices (often referred as nodes) connected by communicating links. A node can be computer, printer, or any other devices capable of sending and receiving data generated by other nodes on the network.

Types of connection:

A link is a communications pathway that transfers data from one device to another. For visualization purpose, it is simplest to imagine any link as line drawn between two points. For communication to occur, two devices must be connected in some way to the same link at the same time. There are two possible types of connections,

• Point-to-point
• Multi-point

Point-to-point: A point-to-point connection provides a dedicated link between two devices. The entire capacity of the link is reserved for transmission between those two devices. Most point-to-point connections use an actual length of wire or cable to connect the two ends, but other options, such as microwave or satellite links, are also possible..

Multi-point: A multi-point (also called multi-drop) connection is one in which more than two specific devices share a single link. In a multi-point environment, the capacity of the channel is shared, either spatially or temporally. If several devices can use the link simultaneously, it is a spatially shared connection. If users must take turns, it is a timeshare connection.

Physical  topology :

The term physical topology refers to the way in which a network is laid out physically. Two or more devices connect to a link; two or more links form a topology. The topology of a network is the geometric representation of the relationship of all the links and linking devices (usually called nodes) to one another. There are four basic topology possible they are,

• Mesh
• Star
• Bus
• Ring

Mesh: In a mesh topology, every device has a dedicated point-to-point link to every other device. The term dedicated means that the link carries traffic only between the two devices it connects.  A mesh offers several advantages over other network topologies. First, the use of dedicated links guarantees that each connection can carry its own data load, thus eliminating the traffic problems that can occur when links must be shared by multiple devices. Second a mesh topology is robust. If one link becomes unusable, it does not incapacitate the entire system.

Star topology: In a star topology, each device has a dedicated point-to-point link only to a central controller, usually called a hub. The devices are not directly linked to one another. Unlike a mesh topology, a star topology doesn't allow direct traffic between devices. The controller acts as an exchange; if one device wants to send data to another, it sends the data to the controller, which then relays the data to other connected device. A star topology is less expensive than a mesh topology.

Bus topology: A bus topology is multi-point. One long cable acts as a backbone to link all the devices in a network. Nodes are connected to the bus cable by drop lines and traps. A drop line is a connection running between the device and the main cable. A tap is a connector that either splices into the main cable or punctures the sheathing of a cable to create a contact with metallic core. A bus uses less cabling than a mesh or star topologies.

Ring topology: In a ring topology, each device has a dedicated point-to-point connection only with the two devices on either side of it. A signal is passed along the ring in one direction, from device to device, until it reaches its destination. Each device in the ring incorporates a repeater. When a device receives a signal intended for another device, its repeater regenerates the bits and passes them along.