Building a Passive Ethernet Hub

Figure 1 

The circuit illustrates the operation behind the design of a passive ethernet hub in connection to the signals being received and transmitted.

• Ethernet Hub – also known as concentrator, is a small rectangular box, used to connect two or more computers and other devices in for the purpose of data exchange and connection sharing in a local area network; classified as layer 1 devices
• Passive Hub – does not amplify the electrical signal of incoming packets before broadcasting what they are supposed to be passing along

This diagram works in a half duplex mode which provides communication in both directions, but only one direction at a time. Under normal operation, each port is constantly sensing any traffic through its receiving pair of wire, pins 3 & 6. As long as it can sense that data is being processed, it will not start sending data. The significance of this operation is to avoid collision where two ports are sending data at the same time, and due to this phenomenon, data will be discarded. When this issue is resolved by both computers, they will start to transmit at random amount of time. The circuit employs the method known as Carrier Sense Multiple Access / Collision Detecion (CSMA/CD) wherein it allows the devices to take turns using the signal carrier line. In this operation, the hub’s primary task is to allow each port to check the signal level of the line to determine whether someone is already using it. The device waits for a few seconds if it is in use, or it transmits otherwise.

Ethernet hubs are found in many home and small business networks because of their low cost. Passive hubs are normally used to organize and physically maintain cables from a single source. Passive hubs can be used together with active or intelligent hubs.

Source:www.zen22142.zen.co.uk/Circuits/Interface/pethhub.htm