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Community Member

Half and Full duplex


Can some one explain me how a half duplex and full duplex works with the pin desciption. I have the following question

1. Does a half duplex have a Tx and Rx wire. Does it need one pair of wire?

2. For full duplex does it need 2 pairs of wires


Re: Half and Full duplex


Both Half & Full Dulpex requires 2 pairs of wires for sending & receiving data. Basically Half Duplex detects collisions, where as full duplex doesn't. When you hav 1000Mbps all 4 pairs will be used, where as in 10/100Mbps only 2 pairs are used.

Hope this helps.

Community Member

Re: Half and Full duplex


can u please explain how the 2 pair of wires are used in both half and full duplex. DO u have any link which explains the pins used

Community Member

Re: Half and Full duplex


I think you are asking about 10/100Base-Tx ( twisted pair cable) pin outs.

We need to review how the technology evolved to understand the difference better.

For 10/100base-tx the standard itself specifies a separate pair for transmit and receive.

Whereas In earlier technologies like 10base5,10base2, which are co-ax based there is no way to implement a full-duplex link, as you dont have a separate pair of wires to do the simultaneous transmission.

So when those standards where there, the ethernet NIcs and the relevant circuitary were designed to run on only half-duplex. There is no possibility to run full-duplex.

As the later 10/100base-tx standard have specified a separate pair for transmit/receive, this opens up a possiblity to trasmit and receive simultaneously.

To accomplish the same full-duplex logic was built in to the circuitary of the 10/100Base-tx NICs.

Now the nic know that there exists a separate path for transmit and receive and it can do simulateneous data transfer on both direction. When these NIC runs on full-duplex, the Collision detection logic is disabled in the circuitary.

When the same NIcs run on half-duplex in 10/100base-tx media, they still use the separate pairs for transmit receive

Pins 1,2 used for transmit.

Pins 3,6 used for receive.

But only one action can be performed at any time. Collision detection logic is activated in the circuitary when running on half-duplex mode.

The circuitary locks the operation to happen in only one direction.

When the NIC is transmitting data, if it receives any data, it detects it as a collision.

Hope this clarifies your query.


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