NETWORK TOPOLOGY
Computer Network Topology
A network topology is the arrangement with which computer systems or network devices are connected to each other. Topology may define both physical and logical aspect of the network. Both logical and physical topology could be same or different in a same network. Network topology refers to the conceptual framework or architectural overview of a network. They give the idea of how the end systems, hardware inter-networking devices, connectors, cable types and other components in a network are interconnected. Physical topology gives the exact arrangement of computers and other networking devices within a network. It can be compared to the architectural layout of a building.
Logical topology describes direction of data flow and path followed by data in a network. Messages are broken into smaller units called packets for transmission on a network. Computer networks can be configured in a number of ways. Two fundamental topology in a data communication network are point-to-point and multi-point. Bus topology, Star topology, Ring topology, Mesh topology and Hybrid topology are examples of multi-point topology.
Logical topology describes direction of data flow and path followed by data in a network. Messages are broken into smaller units called packets for transmission on a network. Computer networks can be configured in a number of ways. Two fundamental topology in a data communication network are point-to-point and multi-point. Bus topology, Star topology, Ring topology, Mesh topology and Hybrid topology are examples of multi-point topology.
Point-to-Point
Point-to-point networks contains exactly two hosts such as computer, switches, routers or servers connected back to back using a single piece of cable. Often, the receiving end of one host is connected to sending end of the other and vice versa. If the hosts are connected point-to-point logically, then may have multiple intermediate devices. But the end hosts are unaware of underlying network and see each other as if they are connected directly.
In Bus topology, all devices share single communication line or cable. It is a multi-point data communication arrangement. In this topology all computers in the network share the same transmission line, called a bus. Bus topology may have problem while multiple hosts sending data at the same time. So, Bus topology either uses CSMA/CD technology or recognizes one host as Bus master to solve the issue. It is one of the simple forms of networking where a failure of a device does not affect the other devices. But failure of shared communication line can make all other devices stop functioning. Both ends of the shared channel have line terminator. The data is sent in only one direction and as soon as it reaches the extreme end, the terminator removes the data from line. In this topology, a message transmitted by one computer is received by all other computer connected to the bus. Thus, we can say that a network based on bus topology is a broadcast network. Suitable hardware interfacing devices, commonly known as taps, helps to connect computers to the common bus. A central computer is usually installed in this type of networks, to control data flow between different computers attached to the same bus.
Star Topology
Star topology is a multi-point data communication arrangement. All hosts in Star topology are connected to a central device, known as hub device, using a point-to-point connection. Hub is basically a multi-point (multi-port) repeater. Data received through one of the port is forwarded to all other computers connected to the hub. That is, there exists a point to point connection between hosts and hub. The hub device can be any of the following:
- Layer-1 device such as hub or repeater
- Layer-2 device such as switch or bridge
- Layer-3 device such as router or gateway
Loop Topology
In this type, hosts are connected via dedicated cables. There will be only one connection between any two nodes (hosts). A single line failure does not cause entire network to fail. Thus this topology is more reliable than star.Ring Topology
In Ring topology, each host machine connects to exactly two other machines, creating a circular network structure. All computers are connected in a ring fashion. The ring serves as the shared transmission medium. Each computer in the ring acts like a repeater. Data transmission is unidirectional in nature. When one host tries to communicate or send message to a host which is not adjacent to it, the data travels through all intermediate hosts. To connect one more host in the existing structure, the administrator may need only one more extra cable. Failure of any host results in failure of the whole ring. Thus, every connection in the ring is a point of failure. There are methods which employ one more backup ring.So in a classic ring topology, messages are passed from computer to computer around the ring. The direction of rotation can be clockwise or counterclockwise depending on technology. The message to circulate until it returns to source station, where it is removed. A central controlling computer is usually placed in the network to manage data flow between computers in the ring.
Mesh Topology
In Mesh topology, a host is connected to one or multiple hosts. This is a modified version of Loop topology. This topology has hosts in point-to-point connection with every other host or may also have hosts which are in point-to-point connection with few hosts only. Hosts in Mesh topology also work as relay for other hosts which do not have direct point-to-point links. Mesh technology comes into two types:- Full Mesh : All hosts have a point-to-point connection to every other host in the network. Thus for every new host n(n-1)/2 connections are required.It provides the most reliable network structure among all network topology.
- Partially Mesh : Not all hosts have point-to-point connection to every other host. Hosts connect to each other in some arbitrarily fashion. This topology exists where we need to provide reliability to some hosts out of all.
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