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Beginner

Can Collisions occur when using Twisted pair cable

Hi All,

I have a question which may sound a little bit silly. If the sending and the recieving pairs are different how can collisions occurs even in a half duplex setup.

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VIP Mentor

Can Collisions occur when using Twisted pair cable

When you are running half-duplex, the system has to assume the worst-case. And that is that on the other end of the cable you have a hub attached. When your system sees incoming data while still sending data out (or short after while inside the collision-window) the system has to assume that there was a collision also if everything was transmitted fine.

To make sure that you don't face any problems with that, control your duplex-settings. And keep in mind that we have 2012, auto-negotiation works (most of teh time).

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Beginner

Can Collisions occur when using Twisted pair cable

Hi karsten, Thanks a lot for the quick response.

I understand with the switched based networks we have full duplex and this problem does not occuer any more. I was just trying to understand the concept. I always thought that the collision was a problem with the coaxial cables, because the same cable was used to send and recieve the data and collison on the wire is understandable in that case. But when we have seperate cabled how will the data colloid.
From your answer i understand that the layer 2 software is not sure if the underlying is a coaxial or a twisted pair hence if the sender recieves a data within the collision windows it assumes that the data has colloided.


It just seems to be a bit of grey area hence the confusion.

VIP Mentor

Can Collisions occur when using Twisted pair cable

Your local system will probably know which the local media-type is. But when running in half-duplex, the system has no clue what happens behind the end of the cable. *There* anyhing could be attached from thinnet, to yellow cable. At least in theory.

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Participant

Can Collisions occur when using Twisted pair cable

The easiest way to understand this is the nature of half duplex is one-way at a time communications.  Like old walkie-talkies or CB radios are half duplex connections.  Full duplex connections are like modern phone calls where you can have traffic in both directions without collisions. 

On half duplex links, the errors come from the traffic trying send and receive at the same time on that link, thus causing a collisions. 

I hope this helps with understanding the collisions and errors with ethernet duplexing issues.

Thanks and Cheers!

Kimberly

Please remember to rate helpful posts.

Thanks and Cheers! Kimberly Please remember to rate helpful posts.
Beginner

Re: Can Collisions occur when using Twisted pair cable

Thank you for your answer. I understand how full duplex and half duplex works but my concern is with Twisted pair we have 2 seperate pairs of cables 1 for sending and 1 for recieving. Even if we are operating in half duplex mode the nodes are not going to send the data on the same wire. So if the wires are different where is the chance of collison.

I was reading a bit in this book today Ethernet - The Definitive Guide. page 226

A twisted-pair transceiver, for example, detects a collision by the simultaneous occurrence of a

signal on both the transmit and receive wire pairs. An excessive amount of signal crosstalk can result

in the generation of spurious or

What i understand from the statement is that the collision is not detected on the wire but insted colission is, getting a signal on both the sender and reviever cable at the same time.

phantom collisions being detected on the twisted-pair segment

VIP Mentor

Re: Can Collisions occur when using Twisted pair cable

For traditional Ethernet, you always have to look at the whole system and not only at the local link. Remember the 5-4-3-rule. Although on the TP-link can't be a physical collision, behind the next repeater can be a real collision.

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