Proxim 7550 Manual page 48

For example, if the RTS Threshold is set to 1000 Bytes, then a
sending radio will use RTS/CTS before transmitting any packet
1000 Bytes or larger.
By default, the RTS Threshold is set to 2432 Bytes. This is
bigger than the largest Ethernet packet, so the PC Card will not
use RTS/CTS when sending any packets.
48