NETWORK TOPOLIG9.1 # STATEMENT AND EXPLAINED THE TOPOLOGY IN COMPUTER NETWORK
Network topology is a physical layout of the computer network and it defines how the computers, devices, cables, etc are connected to each other. The topology description of a network can also include or imply the nature of the data flow through the network. The topologies can be either physical or logical.
Physical topologies describe how the cables are run.
Logical topologies describe how the network messages travel.
v Bus topology A bus is the simplest physical topology. It consists of a single cable that runs to every workstation. This topology uses the least amount of cabling, but also covers the shortest amount of distance. Each computer shares the same data and address path. With a logical bus topology, messages pass through the trunk, and each workstation checks to see if the message is addressed to itself. If the address of the message matches the workstation’s address, the network adapter copies the message to the card’s on-board memory. It is difficult to add a workstation have to completely reroute the cable and possibly run two additional lengths of it. If any one of the cables breaks, the entire network is disrupted. Therefore, it is very expensive to maintain.
v Star topology A physical star topology branches each network device off a central device called a hub, making it very easy to add a new workstation. Also, if any workstation goes down it does not affect the entire network. (But, as you might expect, if the central device goes down, the entire network goes down). Some types of Ethernet and ARCNet use a physical star topology. Figure 8.7 gives an example of the organization of the star network. Star topologies are easy to install. A cable is run from each workstation to the hub. The hub is placed in a central location in the office. Star topology are more expensive to install than bus networks, because there are several more cables that need to be installed, plus the cost of the hubs that are needed.
v Ring topology Each computer connects to two other computers, joining them in a circle creating a unidirectional path where messages move workstation to workstation. Each entity participating in the ring reads a message, then regenerates it and hands it to its neighbor on a different network cable. The ring makes it difficult to add new computers. Unlike a star topology network, the ring topology network will go down if one entity is removed from the ring. Physical ring topology systems don’t exist much anymore, mainly because the hardware involved was fairly expensive and the fault tolerance was very low.
v Mesh topology The mesh topology is the simplest logical topology in terms of data flow, but it is the most complex in terms of physical design. In this physical topology, each device is connected to every other device. This topology is rarely found in LANs, mainly because of the complexity of the cabling. If there are x computers, there will be (x × (x–1)) ÷ 2 cables in the network. For example, if you have five computers in a mesh network, it will use 5 × (5 – 1) ÷ 2, which equals 10 cables. This complexity is compounded when you add another workstation.
With a logical mesh topology, however, there will always be a way of getting the data from source to destination. It may not be able to take the direct route, but it can take an alternate, indirect route. It is for this reason that the mesh topology is still found in WANs to connect multiple sites across WAN links. It uses devices called routers to search multiple routes through the mesh and determine the best path. However, the mesh topology does become inefficient with five or more entities.
v 2 Tier Network topology It s a modified version of the basic star topology. Instead of a single concentrator router, two or more routers are used to eliminates single points of failure, traffic bottlenecks and scalability issues, as well as improving overall throughput and ease of management. This rectifies the basic vulnerability of the star topology without compromising its efficiency or scalability. xample - The 2-tier Architecture is based on a client-server machine. In this type of architecture, the applications on client-side interact directly with the database present at the server-side. This interaction between client and server uses Application Program Interface like Open Database Connectivity (ODBC) and Java Database Connectivity (JDBC).
# Distinguish between network topologies
|
Topology |
Advantages |
Disadvantages |
|
Bus |
Cheap. Easy to install. |
Difficult to reconfigure. Break in bus disables entire network.
|
|
Star |
Cheap. Easy to install. Easy to reconfigure. Fault tolerant.
|
More expensive than bus |
|
Ring |
Efficient. Easy to install.
|
Reconfiguration difficult. Very expensive. |
|
Mesh |
Simplest. Most fault tolerant. |
Reconfiguration extremely difficult. Extremely expensive. Very complex.
|
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