how to remove collision in LAN ?

Answer 1

Correction to the previous answer, there are no collisions in TCP/IP, but there are collisions in Ethernet, at the Data Link layer where two frames coincide on the same network segment. This does effect TCP/IP but it's not a collision, the way it manifests itself at the TCP layer is as a timeout and retransmission. In a half-duplex environment this is normal and a fact of life, this is how CSMA/CD is designed to operate. If you want to "remove" collisions on your LAN, you would need to use a switch (as opposed to a hub) and run every port directly to a PC and make sure both ends of the link are running in FULL duplex. In full duplex mode, collision detection is disabled and there will be no chance of collisions because it's just a point to point link now with dedicated transmit and receive channels.

As the previous answer mentioned, there are token passing networks that are deterministic in nature and do not have collisions, as opposed to ethernet, which is more probabilistic in nature and used CSMA/CD. It also mentioned using switches, not hubs, as explained above, every port on a switch forms its own collision domain, so run them all in full duplex (assuming the end nodes support this) and you'll be collision free.

Answer 2

TCP/IP collisions are normal and you will never get rid of all of them. There are protocols like token-ring that don't have collisions, but TCP/IP assumes there will be some.

If you are having so many that it is negatively affected a network:

1) Use switches not hubs
2) Figure out where the majority of the traffic is comming from and try to limit it.
3) Split the network into seperate nodes