Ethernet HUB and its function

Ques: What is Ethernet HUB and its function?

Ans: In the term of devices, NIC was discussed in previous article. And we have known how to connect if we have two computers. We have to just plug the Ethernet cable into NIC port on both computers then install the LAN driver and game over. Computers are physically connected. Like this, look below :

But what will happen if you have more than two computers. Just assume you have 6 computers and you have to connect them. The point-to-point network will not work for multiple systems. We need a central device. All Computers will be connected with central device and data will be transmitted via central device. Hub, Bridge, Switch can used as central device. In this article we will discuss about only Ethernet HUB.

Ethernet Hub is central device where you can connect multiple computers. When any signal received by any port of hub, it copies the signal and forwards to its all active port. This is known as broadcasting. In other words, forwards the traffic to all active ports except receiving port is known as broadcasting. Actually HUB doesn't have examining capability where to send packet because it does not know anything about addressing (IP or mac etc). It mostly operates on raw bits, thus, receiving any data is rebroadcasted to all active ports. Therefore, On the basis of this knowledge we can say that hub is physical layer device.

Hub is designed on bus architecture, it means, only receiving or sending can be performed simultaneously. In plain English Hub is half-duplex device. Due to Half duplex and broadcasting nature hub and connected hubs create a single collision domain. It means all the devices (hubs and computers) connected with hubs come under a single collision domain. In one collision domain only one type of transmission (receiving or sending) can be done at a time. If two devices send data at a same time within a collision domain they will collide. Hub is also participate in collision detection using CSMA/CD (discussed later). The larger the collision domain, the more chances for colliding the data.

Hub has multiple I/O (Input/Output) ports. This device is form a multiple repeater. Generally Hub supports 10 Mbps but some supports 100 Mbps. Broadcasting shares the available bandwidth.

The port using in hub is generally RJ-45 (your modern NIC port) but it might be come with BNC or AUI port to make connectivity with 10Base2 and 10Base5 network segment. Availability of low price switches is main reason that hub is not seen in modern network and ofcourse it has some disadvantage such as large collision domain, sharing bandwidth, always broadcast etc.

Summery of Hub:

• It is physical layer device
• It has maximum 8 ports.
• Multiple devices can be connected.
• It is half duplex device
• It always broadcast
• It is form of multi-port repeater
• Hub and connected device create a single broadcast domain
• Hub and connected device create a single collision domain
• It detects collision using CSMA/CD
• Easy to install and easy to troubleshoot
• Redundancy is not supported.
• Low speed.