late collision,max length of cable.

[sarahr202]

Hi every body.

please consider the following scenario;

Pc1------sw1----------sw2-------pc2.

All ports are acting full duplex on Pc1,pc2 ,sw1 and sw2.

Is it possible  that late collision could occur, considering  in full duplex modem, ports  do not listen on Rx pins to detect collision?  how about if i increase the length of cable between sw1 and sw2 to 300m?  will late collision could occur? if yes then why?

802.3 ethernets based on utp, have max cable length of 100m. Is it  because the max cable length possible on utp cabling to support data rate is rated as 100m?

thanks and happy holidays to all of you.

[paolo bevilacqua]

Forget about collisions for a moment.

You cannot increase cabling length beyond specifications, simply because it will not work.

[lgijssel · Accepted solution]

You are correct: In full duplex mode there can be no collisions.

Late collisions are collisions occurring after sending the first 64 bytes of a frame.

In coaxial networks this could indicate a cable length problem but on UTP this is not the case.

Remember that all UTP networks are using separate RX and TX pairs so a true collision will never occur. Collisions are detected by looping TX signal back into RX, for compatability only. Timing on UTP networks was made identical to the 802.3 standard to allow the use of mixed media networks and the collision detection mechanism is an important part of the standard.

The 100m restriction is mainly there to allow error-free transfers; UTP is more error sensitive than coax.

When increasing the length of a UTP cable, you will worsen the signal to noise ratio and introduce a higher number of bit errors.

This is why increasing the cable length to 300m is not a good idea!

regards,

Leo

[sarahr202]

Thanks Leo.