Talk:Web Science/Part1: Foundations of the web/Ethernet/Collision detection

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Resources[edit source]

Although you base your graphics on Wikimedia-Uploads, you might want to consider uploading and linking your modified graphics below the video as well. --144.76.104.179 (discuss) 18:06, 23 October 2013 (UTC)

Thanks for your hint. I have just fixed this and included the file below the video. you can also find the file at File:CSMACD-Algorithm.svg --Renepick (discusscontribs) 14:44, 24 October 2013 (UTC)


How long do we listen if some other station is transmitting?[edit source]

How long do we listen if some other station is transmiting? --oleamm (discusscontribs) 16:12, 27 October 2013 (UTC)

you listen until no one is sending. And yes this could mean if the network is under heavy traffic that you never can start transmitting. Nowerdays douplexed cables and packet switching have been introduced to fight these problems. But I am pretty sure you have been to a place where the WIFI was just not usable. since too many people have been there. Remember Air of wifi is a shared medium and wifi operates on ethernet --Renepick (discusscontribs) 16:28, 27 October 2013 (UTC)

How can we detect if some other station is transmitting?[edit source]

Only if we receive 1 (high voltage on a wire)? What if other station is transmitting several 0s one by one it means we will assume there is no data transfer right now? --oleamm (discusscontribs) 16:12, 27 October 2013 (UTC)

When a new ethernet frame arrives you will read the preamble and header in any case (independent if the frame is for you or not). this will give you the length of the frame. so your network card will know for how long the wire is occupied. (this is at least how I would implement this) Also saying a 1 is high voltage and 0 is low is kind of oversimplification. If you want to know more you could have a look at Manchester Code which I think is being used by ethernet --Renepick (discusscontribs) 16:28, 27 October 2013 (UTC)

I guess there is an error in the diagram.[edit source]

In the moment when collision occurs, we need to wait. In the video you are talking about "slot waiting time". As I understood, each machine wait for 512 cycles * rand(16). Then starts from the beginning. But in the picture File:CSMACD-Algorithm.svg, we have "wait one clock signal", instead of "wait 512 clock signals (1 slot)". --oleamm (discusscontribs) 16:12, 27 October 2013 (UTC)

Yes you are right. Of course it has to be "wait one slot time" (as it is in the video). I think we uploaded an old version of the file. You could download the file correct the error and upload a new version. But don't forget to purge the file --Renepick (discusscontribs) 16:28, 27 October 2013 (UTC)
I've changed this string, corrected a mistake, added some padding and split some texts in two (else Webkit will sometimes render the text wrong). Sadly, I just fail at replacing it on commons. Under File History it says: »You cannot overwrite this file.«. I'm logged in on commons. --Onse (discusscontribs) 20:02, 27 October 2013 (UTC)
that is weired why would wiki commons disallow other people to override existing files? I never had problems like this but maybe your account has to have some uploads before you can exchange existing content. Following article i have now included the current template Could you please try again and if it is still not possible send me the new version of the file via mail (you find my address on my blog) and I will re upload it and also mention you as another author. --Renepick (discusscontribs) 20:27, 27 October 2013 (UTC)
After long trying, searching and so on, I found out, that my account is "too new" to overwrite pictures. For overwriting, my account would probably have to be autoconfirmed. An error message told me, I should upload the new version and ask on the help desk for someone to move it. We'll see if that works. --Onse (discusscontribs) 23:00, 27 October 2013 (UTC)
I am sorry that there was so much trouble for new students to use the page --Renepick (discusscontribs) 22:45, 10 September 2014 (UTC)

When the network starts retransmitting data[edit source]

I am confused that when the network starts retransmitting data . When the number of wait is 0, it will go to Attempt++. Does the network starts retransmitting data at this time? And the video says normally, the max attempt number is 20. What does it mean? What can be transmitted for 20 times?----Yuan 11:05, 28 October 2013 (UTC)

After the Attempt++, we check if someone else is currently transmitting (so we are back at "Is some other station transmitting?"). At that point, we do exactly the same as we did in the first round. The max attempt number of 20 means that when we try to transmit a frame but detect a collision 20 times in a row, we will give up (see "no transmission possible" in the bottom right in the diagram). --Mkrnr (discusscontribs) 17:35, 28 October 2013 (UTC)

Software used for presentation (collision detection)[edit source]

I would like to know what kind of software(or programming library) was used for creating the presentation. Awesome presentation!

this was done by user:rob-nowman using final cut pro. unfortunately this video was marked as video spam in the corresponding wikipedia article. --Renepick (discusscontribs) 22:47, 10 September 2014 (UTC)
Yes, I was using FCPX and "Motion", but there might be better tools for this task - it was a lot of work! :-) --Rob Nowman (discusscontribs) 07:15, 11 September 2014 (UTC)

Doesnt collision detection and transmission happen in parallel?[edit source]

I am just wondering about the consistency of what you said about packet size and cable length and network media full occupancy. arent the collision detection and transmission at the same time in parallel? If a collision is detected on receive wire then it stops transmission on transmit wire on cat-5 cable? --99.244.138.7 (discuss) 15:51, 30 January 2016 (UTC)

I mean with continuous transmission (not waiting after each bit) the media full occupancy will happen too --99.244.138.7 (discuss) 15:54, 30 January 2016 (UTC)