As an introduction in computer networking, topology refers to the layout of connected devices while a network topology is the arrangement of a network, including its nodes and connecting lines. There are two ways of defining network geometry which is the physical topology and the logical topology. The physical topology refers that, a way in which a network is laid out physically and it will include the devices, installation and location. Logical topology refers that how data transmissions in a network as opposed to its design and also refers to the nature of the paths the signals follow from node to node.
Network topologies are categorized into the following basic type which is bus, ring, star, tree and mesh. More complex networks can be constructed as hybrids of two or more of the above basic topologies such as combination of star topology and ring topology or between bus topology and star topology. Every single type of network topologies has their own advantages and disadvantages that need to consider before choosing the best topology pattern at our deployment environment based on several factors.
The first network topology that I want to discuss is a bus topology. Bus topology uses one main cable to which all nodes are directly connected. The main cable acts as a backbone for the network. The backbone functions as a shared communication medium that devices attach or tap into with an interface connector. One of the computers in the network typically acts as the computer server. A device wanting to communicate with another device on the network sends a broadcast message onto the wire that all other devices see, but only the intended recipient actually accepts and processes the message. However, there are advantages and disadvantages of this network topology. The first advantage of bus topology is that it is easy to connect a computer or peripheral device. The second advantage is that the cable requirements are relatively small so it’s resulting in lower cost. There are a lot of disadvantages of this network topology which is difficult to administer, limited cable length and number of stations. If the main cable breakdowns, the entire network goes down. For these reasons, this type of topology is not used for large networks, such as those covering an entire building. This type of network also difficult to identify the problem if the entire network shutdown and low security which is all computers on the bus can see all data transmissions. Last but not least, the maintenance costs may be higher in the long run.
The second network topology is ring topology. The network contains of dedicated point to point connection and a set of repeaters in a closed loop. A signal is passed along the ring in one direction, from device to device, until it reaches its destination. It may be clock wise or anti clock wise. When a device receives a signal intend for another device, its repeater generates the bits and passes them along. As with the bus and tree, data are transmitted in frames. As a frame circulates past all the other stations, the destination station recognize its address and copies the frame into a local buffer as it goes by. The frame continues to circulate until it returns to the source station, where it is removed. These topologies are used in school campuses and some office buildings. The first advantage of this topology is the transmission of data is relatively simple as packets travel in one direction only so that data is quickly transferred. Secondly, transmitting network is not affected by high traffic or by adding more nodes, as only the nodes having tokens can transmit data. The best advantage of ring topology is cheap to install and expand so that affordable to deployment environment. However, data packets must pass through every computer between the senders and recipient therefore this makes it slower. If any of the nodes fail then the ring is broken and data cannot be transmitted successfully. It is difficult to troubleshoot the ring. Because all stations are wired together, to add a station we must shut down the network temporarily. In order for all computers to communicate with each other, all computers must be turned on. All these factors contribute to disadvantages of ring topology.
The third network topology is a star topology, each station is directly connected to a common node called hub. Unlike a mesh technology, the devices are not directly linked to one another. A star topology does not allow direct traffic between devices. The controller act as an exchange, like if one device wants to send to another, it sends the data to the controller, which then relays the data to the connected device. In a star, each device needs only one link and one I/O port to connect it to any number of others. The star topology is used in local area networks (LAN) and sometimes high speed LAN often uses a star topology with central hub. Star topology is very popular because the startup costs are low. It is also easy to add new nodes to the network. The network is robust in the sense that if one connection between a computer and the hub fails, the other connections remain intact. Failure of one node or link doesn’t affect the rest of network. At the same time it’s easy to detect the failure and troubleshoot it. Similarly components can also be removed easily. But the major disadvantage of this network topology is that if the central hub fails, all computers connected to that hub would be disconnected. A major disadvantage of this network topology is that if the central hub fails, all computers connected to that hub would be disconnected. The use of hub, a router or a switch as central device increases the overall cost of the network. Performance and as well number of nodes which can be added in such topology is depended on capacity of central device. More software is required to run the network proficiently.
The forth network topology is tree topology. Tree topology is the simplification of the bus topology. It integrates the multiple star topologies together on to a bus. The transmission medium is a branching cable with no closed loops. The tree layout begins at a point known as the head end. The branches in turn may have additional branches to allow quite complex layouts. A transmission from any station propagates throughout the medium and can be received by all other stations. This topology will allow for the expansion of an existing network. The advantage of tree topology is well supported by the hardware and software vendors. Point to point wirings for each and every segment of the network. It is the best topology for the branched networks. However, it is more costly because more hubs are required to install the network. Tree topology is entirely depends upon the backbone line, if it fails then the entire network would fail. It is very difficult to configure and wire than other network topologies. In a tree topology, the length of network depends on the type of cable being used.
The fifth network topology is mesh topology. Mesh topology presents the concept of routes. Unlike each of the previous topologies, messages sent on a mesh network can take any of several possible paths from source to destination. Recall that even in a ring, although two cable paths exist, messages can only travel in one direction. Some WANs, most notably the Internet, employ mesh routing. A mesh network in which every device connects to every other is called a full mesh. Partial mesh networks also exist in which some devices connect only indirectly to others. The advantages of mesh to topology are it can handle heavy traffic, as there are dedicated paths between any two network nodes. The arrangement of the network nodes is such that it is possible to transmit data from one node to many other nodes at the same time. The failure of a single node does not cause the entire network to fail as there are alternate paths for data transmission. Point-to-point contact between every pair of nodes makes it easy to identify faults. However, factors that contribute to disadvantages of this network are installation and reconnection is difficult. Large amounts of cabling and the number of I/O ports requisite. Sheer bulk of the wiring can be greater than the available space can accommodate. The hardware required to connect each link can be prohibitively expensive.
The last network is hybrid topology. The hybrid topology is the combination of multiple topologies, used for constructing a single large topology. The hybrid topology is formed when two different network topologies are interconnected. If two ring topologies are connected then the resultant topology is not the hybrid topology. On the other hand, if the ring topology is connected to the bus topology then the resulting topology is called the hybrid topology. This topology generally combines the features of the two topologies and is therefore more effective and efficient than the individual topologies. The Advantages of hybrid topology are more effective as it uses multiple topologies. The hybrid topology contains the best and efficient features of the combined topologies from which it is constructed. However, it also has their own disadvantage which is relatively more complex than the other topologies. The hybrid topology is also difficult to install and configure.
After knowing the advantages and disadvantages all the network topology, selecting an appropriate topology for our deployment environment depends upon several factors which is available hardware resources, application invocation patterns, types of business processes that you plan to implement (interruptible versus non-interruptible), how heavily we intend to use the Common Event Infrastructure (CEI), individual scalability requirements, administrative effort involved.
As a conclusion, computer networks have had a profound effect on the way that we communicate with each other. The first computer network was created to allow for a spread communications network that lets a person do automatic rerouting. The original job of this type of system was to allow government researchers and military leaders to continue monitoring the possibility of danger from the enemy. Below are some effects that computer networks have had on communications. Some people believe that the Internet and email have perorated the English language and the way that we communicate as people because it has become so impersonal. However, others believe that it has caused the way that we communicate to become broader, and that it has done more good than bad. One argument for computer networking is that it has caused the art of letter writing to be reborn because it now takes us less time to write it. The art of writing letters has resulted in more spontaneous letters being sent because it takes almost less than a second for information to travel across the world.
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