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Home » Computer Networks

What are hubs, types of hubs and their working?



Here, we are going to learn about the hubs in networking: What are hubs, hubs types, their working, CSMA/CD and Collision domain.
Submitted by Mahima Rao, on November 03, 2018

Introduction to Hubs

Hub is a network device that connects multiple ethernet devices with which they can share resources and transfer data, it works as layer 1 of the OSI model of the physical layer. It amplifies and regenerates the signal too. It has many ports in it so we also call it multi-port repeater hub port acts as a repeater of our hub and amplify the signal and tries to send it far. Hubs connect the computers to transfer data. Hubs are not intelligent, hence they can not forward data on the basis of logical and physical address.

Types of Hub

  1. Active hub
    These hubs regenerate our signals as well as amplify the signal. Active hubs need electricity to work.
  2. Passive hub
    Talking about passive hubs, it simply distributes the signal coming from the previous ports. Passive hub neither regenerates any signal nor amplifies, therefore it does not require electricity to work.
  3. Intelligence hub
    This helps the administrator to monitor network traffic, and you can configure each port on it individually, also known as a manageable hub.

Working of Hubs

When a host sends frames, the hub forwards the frames in all the ports. Hubs do not separate the type of the frame, for example, whether the frame uni-cast should be either multicast or broadcast. Hubs forward all the frames into all the ports.

Although a hub sends the frames to all the ports, a computer accepts the ones, whose MAC match matches the destination MAC address field. The rest of the frames are discarded after receiving the required information.

CSMA/CD (Carrier Sense Multiple Access with Collision Detection)

Hubs perform half duplex communication. It means either a host can send or receive data. Both works cannot be done together. Therefore frames in the hub is pretty much crashing. This happens when someone is sending a host frame, the second host is also sending the frame at the same time. It's called collision.

A technique is used to avoid a collision which is called CSMA / CD (Carrier Sense Multiple Access with Collision Detection). In this technique, before entering any host frame, checks whether the link is empty or not. If there is a signal in the link, then this host waits until the link is empty. Then this host sends its own frame.

When the collision occurs, the hosts who sent the frame detect it. The frames that were sent are destroyed then and hosts send a jam signal which shows that both hosts are about to wait. The wait time for both hosts is different. That is, if a host waits 10 seconds before sending the back frame, then the second host will wait 15 seconds so that there is no collision again.

Collision Domain

Remember, whenever the hub connected to 2 devices will send frames simultaneously then there will be a collision. Therefore all the devices connected to the hub come in the same collision domain. Hubs represent single collision domain.






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