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Network topologies

Network topology refers to the way links and nodes in a network are organized to relate to each other. Topologies are classified as physical network topology, which is the means of transmitting physical signals, or logical network topology, which refers to the way data travels over the network between devices, regardless of the physical connection of the devices. Examples of logical network topology include twisted pair Ethernet, which is classified as logical bus topology, and token ring, which is classified as logical ring topology.

Examples of physical network topology include star, mesh, tree, ring, point-to-point, circular, hybrid, and bus topology networks, each of which consists of different node and link configurations. The ideal network topology depends on the size, scale, goals, and budget of each company. A network topology diagram helps visualize communication devices, which are modeled as nodes, and connections between devices, which are modeled as links between nodes.

Mesh topology

In a mesh topology, each device is connected to another device through a particular channel. In Mesh Topology, the protocols used are AHCP (Ad Hoc Configuration Protocols), DHCP (Dynamic Host Configuration Protocol), etc.

  • Suppose the number N of devices is connected to each other in a mesh topology, the total number of ports required by each device is N-1. In Figure 1, there are 5 devices connected to each other, so the total number of ports required by each device is 4. The total number of ports required=N*(N-1).
  • Suppose that a number N of devices are connected to each other in a mesh topology, then the total number of dedicated links needed to connect them is N C 2, that is, N (N-1)/2. In Figure 1, there are 5 devices connected to each other, so the total number of links needed is 5*4/2 = 10.

Advantages of this topology

  • Communication is very fast between the nodes.
  • It is robust
  • Failure is easily diagnosed. Data is reliable because is transferred between devices over dedicated channels or links.
  • Provides security and privacy.

Problems with this topology

  • Installation and configuration are difficult.
  • Cables costs are high as bulk wiring is required, making it suitable for fewer devices.
  • The maintenance cost is high.

Star topology

In star topology, all devices are connected to a single hub via cable. This hub is the central node and all other nodes are connected to the central node. The hub can be passive in nature, i.e. not a smart hub like transmission devices, at the same time the hub can be smart known as an active hub. Active hubs have repeaters in them. Coaxial cables or RJ-45 cables are used to connect computers. In star topology, many popular Ethernet LAN protocols such as CD (collision detection), CSMA (multiple access with carrier detection), etc. are used.

Advantages of this topology

  • If N devices are connected to each other in a star topology, the number of wires needed to connect them is N. Therefore, it is easy to set up.
  • Each device requires only 1 port, i.e. to connect to the hub, therefore the total number of ports needed is N.
  • If one link fails, only that link will affect and not another.
  • Easy failure identification and failure isolation.
  • Star topology is cost-effective as it uses an economical coaxial cable.

Problems with this topology

  • If the hub on which the entire topology is based fails, the entire system will collapse.
  • The installation cost is high.
  • Performance is based on the single hub.

Bus topology

Bus topology is a type of network in which each computer and network device is connected to a single cable. It is bidirectional. It is a multipoint connection and an inrobust topology because if the backbone fails, the topology fails. In the bus topology, various MAC (Media Access Control) protocols are followed by Ethernet LAN connections such as TDMA, Pure Aloha, CDMA, Slotted Aloha, etc.

Advantages of this topology

  • If N devices are connected to each other in a bus topology, then the number of cables needed to connect them is 1, known as the main cable, and N bypass lines are required.
  • Coaxial or twisted pair cables are primarily used in bus-based networks that support up to 10 Mbps.
  • The cost of cable is lower compared to other topologies, but it is used to build small networks.
  • Bus topology is a familiar technology, as installation and troubleshooting techniques are well known.

Problems with this topology

  • A bus topology is much simpler, but still requires a lot of wiring.
  • If the common cable fails, the entire system will collapse.
  • If network traffic is heavy, it increases collisions on the network. To avoid this, several protocols known as Pure Aloha, Slotted Aloha, CSMA/CD, etc. are used in the MAC layer.
  • Adding new devices to the network would slow down networks.
  • Security is very low.

Ring topology

In this topology, it forms a ring that connects devices with exactly two neighboring devices.

Multiple repeaters are used for the ring topology with a large number of nodes, because if someone wants to send some data to the last node in the ring topology with 100 nodes, the data will have to pass through 99 nodes to reach 100. node. Therefore, to prevent data loss, repeaters are used on the network.

The data flows in only one direction, that is, it is unidirectional, but it can be made bidirectional by having 2 connections between each Network Node, it is called Double Ring Topology. Ring topology, workstations use the Token Ring Passing protocol to transmit data.

The most common access method in ring topology is token passing.

Token pass: A method of network access in which a token is passed from one node to another node.

Token: It is a frame that circulates through the network.

The following operations that occur in the ring topology are:

  • A station is known as a monitoring station that assumes full responsibility for performing operations.
  • To transmit the data, the station must have the token. After the transmission is complete, the token will be released for use by other stations.
  • When no station is transmitting the data, then the token will circulate in the ring.
  • There are two types of token release techniques: early token release releases the token right after transmitting the data, and delayed token release releases the token after recognition is received from the receiver.

Advantages of this topology

  • Data transmission is high-speed.
  • The possibility of collision is minimal in this type of topology.
  • Cheap to install and expand.
  • It is less expensive than a star topology.

Problems with this topology

  • The failure of a single node in the network can cause the entire network to fail.
  • Troubleshooting is difficult in this topology.
  • Adding intermediate stations or removing stations can disrupt the entire topology.
  • Less secure.

Tree topology

This topology is the variation of the star topology. This topology has a hierarchical flow of data. Tree Topology uses protocols such as DHCP and SAC (Standard Automatic Configuration).

In this topology, the various secondary hubs are connected to the central hub that contains the repeater. This data flows from top to bottom, that is, from the central hub to the secondary and then to the devices or from the bottom up, that is, the devices to the secondary hub and then to the central hub. It is a multipoint connection and an inrobust topology because if the backbone fails, the topology fails.

Advantages of this topology

  • It allows you to connect more devices to a single central hub, reducing the distance the signal travels to reach the devices.
  • It allows the network to be isolated and also prioritized from different computers.
  • We can add new devices to the existing network.
  • Error detection and correction are very easy in a tree topology.

Problems with this topology

  • If the central hub fails, the entire system fails.
  • The cost is high due to the wiring.
  • If new devices are added, it becomes difficult to reconfigure.

Hybrid topology

This topological technology is the combination of all the various types of topologies that we have studied above. It is used when the nodes are free to take any shape. It means that they can be individual topologies, such as ring or star, or they can be a combination of several types of topologies seen above. Each individual topology uses the protocol discussed above.

This topology is a combination of all the different types of networks.

Advantages of this topology

  • This topology is very flexible.
  • The size of the network can be easily expanded by adding new devices.

Problems with this topology

  • It is a challenge to design the architecture of the Hybrid Network.
  • The hubs used in this topology are very expensive.
  • The cost of infrastructure is very high as a hybrid network requires a lot of cabling and network devices.

What is the importance of network topology?

The design of a network has a direct impact on the functionality of the network. Selecting the right topology can improve data performance and efficiency, optimize resource allocation, and reduce operational costs. Software-created network topology diagrams are important references for diagnosing network connectivity problems, investigating network slowdowns, and generally troubleshooting problems. One of the main uses of network topology is to define the configuration of various telecommunications networks, including computer networks, command-and-control radio networks, and industrial fieldbuses.