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Network topology is the arrangement of the various elements such as links, nodes, etc. of a computer. Distances between nodes, physical interconnections, transmission rates, and/or signal types may differ between two networks, yet their topologies may be identical. It is the topological structure of a network, and may either be physical or logical.

 

Categories of network topology

Network topology can be classified into two.

  • Physical topology refers to the placement of the network’s various components, including device location and cable installation. The physical topology of a network is determined by the capabilities of the network access devices and media, the level of control or fault tolerance desired, and the cost associated with cabling or telecommunications circuits.
  • Logical topology refers to how data flows within a network, regardless of its physical design. The logical topology, in contrast, is the way that the signals act on the network media, or the way that the data passes through the network from one device to the next without regard to the physical interconnection of the devices.

 

Different Types of Computer Network Topologies

A) Bus Topology: Bus Topology is the simplest of network topologies. In this type of topology, all the nodes (computers as well as servers) are connected to the single cable (called bus), by the help of interface connectors. This central cable is the backbone of the network and is known as Bus (thus the name). Every workstation communicates with the other device through this Bus. Computers on a bus topology network communicate by addressing data to a particular computer and sending out that data on the cable as electronic signals. Network data in the form of electronic signals is sent to all the computers on the network. Computers on a bus either transmit data to other computers on the network or listen for data from other computers on the network. They are not responsible for moving data from one computer to the next. Consequently, if one computer fails, it does not affect the rest of the network. Because the data, or electronic signal, is sent to the entire network, it travels from one end of the cable to the other.

A signal from the source is broadcast and it travels to all workstations connected to bus cable.

 

Advantages (benefits) of Linear Bus Topology

  1. Easy to implement and extend.
  2. Well suited for temporary networks (quick setup).
  3. Typically the cheapest topology to implement.
  4. Faster than a ring network.
  5. If any node on the bus network fails, the bus its self is not effected.
  6. Requires less cable than a Star network.
  7. It is easy to set-up and extend bus network.
  8. Cable length required for this topology is the least compared to other networks.

 

Disadvantages (Drawbacks) of Linear Bus Topology

  1. Difficult to administer/troubleshoot: It is difficult to detect and troubleshoot fault at individual station.
  2. Limited cable length and number of stations.
  3. A cable break can disable the entire network.
  4. Maintenance costs may be higher in the long run.
  5. Performance degrades as additional computers are added or on heavy traffic.
  6. Low security (all computers on the bus can see all data transmissions).
  7. One virus in the network will affect all of them (but not as badly as a star or ring network).
  8. Proper termination is required.(loop must be in closed path).
  9. There is a limit on central cable length and number of nodes that can be connected.
  10. Security is very low because all the computers receive the sent signal from the source.
  11. Dependency on central cable in this topology has its disadvantages. If the main cable (i.e. bus ) encounters some problem, whole network breaks down.
  12. It is not suitable for networks with heavy traffic.

 

B) Ring Topology: A ring network is a topology of computer networks where each node is connected to two other nodes, so as to create a ring. The ring topology connects computers on a single circle of cable.

In Ring Topology, all the nodes are connected to each-other in such a way that they make a closed loop. Each workstation is connected to two other components on either side, and it communicates with these two adjacent neighbors. Data travel around the network, in one direction.

The signals travel around the loop in one direction and pass through each computer, which can act as a repeater to boost the signal and send it on to the next computer. One method of transmitting data around a ring is called token passing. A token is a special series of bits that travels around a token-ring network. Each network has only one token. The token is passed from computer to computer until it gets to a computer that has data to send. The sending computer modifies the token, puts an electronic address on the data, and sends it around the ring.

 

Advantages of Ring Topology

  1. This type of network topology is very organized. Each node gets to send the data when it receives an empty token. This helps to reduces chances of collision. Also in ring topology all the traffic flows in only one direction at very high speed.
  2. Even when the load on the network increases, its performance is better than that of Bus topology.
  3. There is no need for network server to control the connectivity between workstations.
  4. Additional components do not affect the performance of network.
  5. Each computer has equal access to resources.

 

Disadvantages of Ring Topology

  1. Each packet of data must pass through all the computers between source and destination. This makes it slower than Star topology.
  2. If one workstation or port goes down, the entire network gets affected.
  3. Network is highly dependent on the wire which connects different components.
  4. Network cards are expensive as compared to Ethernet cards and hubs.

 

C) Star Topology: Star Topology is the most common type of network topology that is used in homes and offices. In the Star Topology there is a central connection point called the hub which is a computer hub or sometimes just a switch. In a Star Network the best advantage is when there is a failure in cable then only one computer might get affected and not the entire network.

The Star Network Topology typically needs more cable to be networked than the usual Bus topology. A common cable that is used in Star Network is the UTP or the unshielded twisted pair cable. Another common cable that is used in star networks is the RJ45 or the Ethernet cables.

In a Star Network the entire network is dependant on the hub so if the entire network is not working then there could be a problem with the hub. This feature makes it easy to troubleshoot by offering a single point for error connection ad at the same time the dependency is also very high on that single point.

In Star topology, all the components of network are connected to the central device called”hub” which may be a hub, a router or a switch.

 

Advantages of Star Topology

  1. A Star Network Topology is very easy to manage because of its simplicity in functionality.
  2. The Star Topology is very simple in format so it is very easy to expand on the Star Topology.
  3. As compared to Bus topology it gives far much better performance, signals don’t necessarily get transmitted to all the workstations. A sent signal reaches the intended destination after passing through no more than 3-4 devices and 2-3 links. Performance of the network is dependent on the capacity of central hub.
  4. Easy to connect new nodes or devices. In star topology new nodes can be added easily without affecting rest of the network. Similarly components can also be removed easily.
  5. Centralized management. It helps in monitoring the network.
  6. Failure of one node or link doesn’t affect the rest of network. At the same time its easy to detect the failure and troubleshoot it.

 

Disadvantages of Star Topology

  1. Too much dependency on central device has its own drawbacks. If it fails whole network goes down.
  2. The use of hub, a router or a switch as central device increases the overall cost of the network.
  3. Performance and as well number of nodes which can be added in such topology is depended’on capacity of central device.

 

D) Mesh Topology: In a mesh topology, each computer on network has redundant data paths. The mesh topology provides fault tolerance-if a wire, hub, switch, or other component fails, data can travel along an alternate path. A diagram of a mesh network looks like a fishing net. A mesh topology is most often used in large backbone networks in which failure of a single switch or router can result in a large portion of the network going down.

 

E) Tree or Expanded Star: A tree topology combines characteristics of linear bus and star topologies. It consists of groups of star-configured workstations connected to a linear bus backbone cable. Tree topologies allow for the expansion of an existing network, and enable schools to configure a network to meet their needs.

 

Advantages of a Tree Topology

  1. Point-to-point wiring for individual segments.
  2. Supported by several hardware and software venders.

 

Disadvantages of a Tree Topology

  1. Overall length of each segment is limited by the type of cabling used.
  2. If the backbone line breaks, the entire segment goes down.
  3. More difficult to configure and wire than other topologies.

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