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CSMA CD in Ethernet

In CSMA/CD, minimum length of packet to detect collision, L >= 2 * Tp * Bandwidth

example:Determine the maximum length of the cable (in km) for transmitting data at a rate of 500 Mbps in an Ethernet LAN with frames of size 10,000 bits. Assume the signal speed in the cable to be 2,00,000 km/s.

Tt >=2*Tp
L(length of the cable)<=(Data size*Signal speed)/(2*Bandwidth)
L<=(10,000 bits * 2 *108m/s)/(2*500*106b/s)
Hence L<=2Km.

Obaid Khan @obaidkhan
29 Dec 2016 09:59 pm

For a jamming signals if the voltage is between +15v to -15v then it will also contain the range between -5v to +5v, if the jamming signal lie in between that how will it be differentiated from the data packets?

Pritam Prasun @pritam
29 Dec 2016 10:55 pm

This was just an example. The jamming signal can also be different on the basis of frequency. 

However, +15 to -15 is not a range. It is +ve and -ve voltage of the signal.

Suman @suman08513
29 Dec 2016 11:55 pm

A doubt regd Jamming Signal:


If there is a collision in the middle of the channel (say exactly at the midpoint) who will create the Jamming signal. I mean at the mid point there is no node to generate the jamming signal.


Jamming signal is usually generated by a node to notify all the other nodes in the LAN that there a collision. If there is a collision takes place just before the receiver then the receiver generates the jamming signal to notify the sender that there is a collision.


In your video illustration you told that the collision happens at the middle then who will generate the jamming signal at the middle. There some node to generate the Jamming signal . Isn't it?

Shraddha @shraddhagami
31 Dec 2016 01:13 am

If adapter detects another transmission while trnsmitting. It aborts and send Jamming signal.(Jamming signal is nothing but have different frequency than data)

Suman @suman08513
31 Dec 2016 12:34 am

I don't think your assumption is correct Shraddhagami. Jamming Signal is to be generated by some node. If not how can it automatically be created.


But your assumption of Jamming Signal has different frequency is correct . It is to avoid the collision with data signal.

Shraddha @shraddhagami
31 Dec 2016 01:10 am

yeah Thankyou for correcting me.