The RTS / CTS mechanism is invoked when the packet size crosses the RTS threshold. And in general you would wish to use RTS / CTS only when transmitting data packets and not control packets. Therefore, when running any experiment, users must

a. Configure the application such that the packet size is greater than the RTS Threshold. Note that fragmentation occurs in the IP layer. Hence its best to keep packet size between 500 to 1460 and keep the RTS threshold below this value

b. Disable TCP. Since TCP ACK's will be below RTS / CTS threshold

c. Enabling RTS / CTS  in MANET is not a good idea because DSR / AODV control packets such as RREQ, RREP etc will be below RTS / CTS Threshold.

b. Even if the RTS mechanism is enabled you can have "collisions". These would be RTS - RTS and RTS - CTS collisions. These collisions can be analyzed in the packet trace file.