10Base-T Hub network

Answered Question
Feb 18th, 2007

Hi there! I hope this all finds you in the very best of health and faith. I have a question regarding the 10Base-T Hubs which I hope someone will be able to help me with. The question is as follows:

Assuming I have a 10Base-T Hub network with say, 4 PCs attached to the hub. If PC1 sends PC2 an email, PC1's NIC will naturally loop the frame it sends (to PC2) back to its own receive pair on the NIC. So, if a collision should occur (say PC3 sends to PC4 at the same time) the incoming signal from the hub plus the looped signal on PC1's NIC lets PC1 notice that there is a collision. So, my question is, how does PC1 know when and how to take down the looped signal on PC1's NIC assuming that the frame was sent correctly to PC2? Also, is the result the same if it sent many frames at a time? Is the NIC able to keep many frames on its loopback circuitry?

Thank you all in advance for helping me out with this question.

Kind regards,

Ashraf.

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Correct Answer by scottmac about 9 years 7 months ago

If more then one device transmits, it is sensed and all transmitting devices stop transmitting (fallback) and wait for a "random" (not really random, but calculated to be psuedo-random) period of time.

The receivers are always active ... it's not like a loop is put up and taken down for every transmission.

If the NIC senses signal on the receiver, at the same time it's getting feedback through the internal looping, it calls it a collision, JAMs (sends a JAM signal to signal other stations that a collision has occurred), and falls back.

After the fallback timer expires, it will again listen, then transmit if it senses the media is quiet.

Hope this helps

Good Luck

Scott

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Correct Answer
scottmac Sun, 02/18/2007 - 13:07

If more then one device transmits, it is sensed and all transmitting devices stop transmitting (fallback) and wait for a "random" (not really random, but calculated to be psuedo-random) period of time.

The receivers are always active ... it's not like a loop is put up and taken down for every transmission.

If the NIC senses signal on the receiver, at the same time it's getting feedback through the internal looping, it calls it a collision, JAMs (sends a JAM signal to signal other stations that a collision has occurred), and falls back.

After the fallback timer expires, it will again listen, then transmit if it senses the media is quiet.

Hope this helps

Good Luck

Scott

ashraf_can2 Mon, 02/19/2007 - 00:33

Hi there! Thank you all for your replies.

gsalmon444, the answer to your question is yes. CSMA/CD algorithm basically ensures that no collisions occur or if they do that the NICs pick them up. The way they notice collisions is by having the signal the NIC sent out loop back onto its receive pair.

I hope that helps.

ashraf_can2 Mon, 02/19/2007 - 00:50

Dear Scott,

Thank you very much for your reply.

Your answer has certainly helped my understanding. I initially thought that the loop was put up and taken down for every transmission. So, I thank you very much for clarifying this particular point for me.

Wish you and all a lovely day!

Best wishes,

Ashraf.

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