Computer Network Topology

The computer network is one of the wonderful things in our world. With that we have conquered over many limitations. in fact you are reading this blog-post through a computer network. But computer network requires many things to work and requires topological arrangements which we call network topology. Here I have tried to give you some basic ideas about the network topology.

Computer network topology is a very important thing in networking. But before going to this we need to know about three important things. And they are :

  1. Computer Network,
  2. Node and
  3. Hub or switches.

Computer Network:- A computer network is a group of computer systems and other computing hardware devices that are linked together through communication channels to facilitate communication and resource-sharing among a wide range of users.Networks are commonly categorized based on their characteristics. The ARPANET (1967), developed by the ARPA (Advanced Research Projects Agency) of U.S Ministry of  Defence was the first well-established computer network.

Node:-  Node is an active electronic device that is attached to a network, and is capable of sending receiving or forwarding information over communications channels. A node may be a computer, printer, Bluetooth, modem, router, cell phone, workstation, server, satellites etc.

Hub or Switches :- The word “Hub” means central part or most active place. In computer networking, “Hub” is a device for connecting multiple devices together and making them act as a single network segment. To connect more than two computers in a networking system a hub is used. Different types of hubs are found and they can transmit 10 mega bites to 100 mega bites per second according to network design. It’s also a part of a node.A hub can be both active or passive.In figure-1 we have a sample of the hub.

Fig. 1: Hub

Now we can talk about what is a Network Topology,

The term network topology refers to the way in which nodes of a network are linked together. There are two basic categories of network topology.

  1. Physical topology and
  2. Logical topology.

Physical topology: Physical topology refers to the layout of cables, computers and other peripherals.  Bus, ring, star, mesh topology etc are the example of this type of topology.

Logical topology: It is the method used to pass information the information between the computers. PAN, LAN, WAN, HAN, MAN are the examples of logical topology.

LAN is the only networking system that includes both the physical and logical topology.

Here we will only talk about the physical topology and its aspects.

The factors for choosing one topology should be:

  1. The desired performance of the system,
  2. The desired reliability of the entire system,
  3. Size of the system,
  4. Cost of the components,
  5. Expand-ability of the system and
  6. Availability of the system.

Although the number of possible network topology is seemingly limitless, the most popular topologies are

  1. Bus topology,
  2. Ring topology,
  3. Star topology,
  4. Mesh topology,
  5. Hybrid topology.

Bus topology:

In this kind of arrangement, all the nodes like computers are attached to the same communication line (cable). Any computer can send any information to a definite computer, which can be fixed when it is sent. All the computers under network receive the information but only definite one accepts it and the others just regret it. A computer must wait until the bus (line) is free. When the signal reaches the end

of the wire, it bounces back and travels back up the wire. when a signal echoes back and forth along an unterminated bus, it is called “ranging”. To stop ranging two terminators are used in this type of topology. In figure-2 we have shown the diagram for the bus topology.

Advantages of Bus topology:

  1. It’s simple, reliable in a small network, it’s easy to use and understand.
  2. It requires the least amount of cable to connect and less expensive.
  3. The failure of any node does not affect the others.
  4. It’s easy to extend.

Disadvantages of  Bus topology:

  1. All computers in the network should good communication and decision making capability.
  2. Heavy network traffic can slow down the network.
  3. If the communication line fails, the entire communication will collapse.

Fig. 2: Bus Topology

Ring topology:

In this arrangement, every computer is connected to the next computer in the ring and each retransmits what it receives from the previous computer. There is an absence of controlling or master computer. A computer receives information from its two adjacent computers. The only decision a computer has to take is whether the data is for its own use. If it is addressed to it, it utilizes it or just pass it to another computer.The necessary diagram is shown in the figure-3.

Advantages of Ring topology:

  1. Ring network works well though it has no master computer or controlling computer.
  2. It is more reliable than the bus topology.

 

Disadvantages of  Ring topology:

  1. In a ring network, communication delay is directly proportional to the number nodes present.
  2. Addition of new node like computer is not so easy and it increases communication delay.
  3. The ring network requires more complicated software than the bus and star topology.
  4. Disturbance or failure of one computer can affect the whole network.

Fig. 3: Ring Topology

Star topology:

In star topology the multiple computers are connected to a central computer or a hub or a switch. This thing controls the whole network. Hub is the mostly used device. Each computer under the star network communicates with the central hub, that re sends the message either to all computers or only to the destination computer. Hub can be active or passive in the star network. We can easily expand the network by adding another star hub. The pictorial representation of star topology is given below in figure-4.

Advantages of Star topology:

  1. It’s relatively easy to modify and add new computers to a star network.
  2. Hub or centre of a star network is a good place to find the problem in a network easily.
  3. Huge network can be made in this arrangement and it doesn’t have any network disturbance.
  4. Failure of one computer does not bring down the whole network.

Disadvantages of Star topology:

  1. When the hub goes down, the total network goes down.
  2. It definitely requires more cables than the others.
  3. Because of having extra components, it is relatively expensive than the others.

FIg. 4: Star Topology

Mesh topology:

In this topology a computer is connected to one or two or more than two computers. This topology may have computers having “Point to Point” connections to all computers or with some of computers. Computers in the topology also work as relays for those which do not have direct point to point links. The diagram for mesh topology  is shown in figure-5

(Point to point connection means direct dedicated link)

Mesh topology can have two types, and they are:

  1. Full mesh: It has point to point connections to each It’s the most reliable structure among the all topologies.
  2. Partially mesh: It doesn’t provide point to point connections to all the computers.

Advantages of Mesh topology:

  1. This type of network is very reliable. If a connection fails, the whole network system still continues
  2. Each computer of the network need not have routing capability.
  3. Communication is very fast between two nodes.
  4. Easy to troubleshoot.

Disadvantages of  Mesh topology:

  1. It’s one of the most expensive arrangements of network.
  2. It’s very difficult to understand and use.
  3. It’s very difficult to install this kind of network system, and it’s also difficult to reconfigure.

Fig. 5: Mesh Topology

Hybrid topology:

Different network topologies have their own advantages and limitations. In reality a pure star, ring or completely connected network is hardly used. In the place of these topologies, Hybrid topology is used. It’s the combination of two or more different network topologies. The size of it depends on the needs. In some cases, the hybrid network may have components of star, ring and completely connected networks. The arrangement should be like figure-6

Advantages of Hybrid topology:

  1. It’s the most reliable network system. It can be expanded as much as needed. Internet is the best example of hybrid topology.
  2. Failure of any node doesn’t affect the whole arrangement.

Disadvantages of Hybrid topology:

  1. It’s one of the most expensive network systems which requires a huge number of cable connections.
  2. Presence of a large number of nodes like computers can make the network a little bit slower.

Fig. 6: Hybrid topology

Beside all of these we can include the following topologies:

  1. Tree topology,
  2. Point to Point or Peer to Peer topology,
  3. Line topology,
  4. Daisy chain topology

Fig. 7a: Tree topology

Fig. 7b: Peer to Peer Topology

Fig. 7c: Daisy Chain Topology

So that’s all for today.

Hope you have got some ideas about network topologies. All  the images are collected from several websites. If you have any question or opinion on this topic please leave it in the comment section.

Thank you.

Comments

Md. Abdullah Al Zaman (Proyash)

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