Cabletron Systems RoamAbout Access Point Manual page 32

Transmit Rate
In most environments, Auto Rate allows the PC Card to use a higher rate for better data
throughput, yet the PC Card can still use the more reliable slower rate when transmissions
fail. A transmission can fail when the network experiences spurious noise interference.
Also use Auto Rate if you have Access Points with 11 Mbit/s PC Cards and a mix of clients
with 11 Mbit/s and 2 Mbit/s PC Cards. The Access Point can communicate with both types
of clients, but can communicate with the 11 Mbit/s clients at a higher rate than the 2 Mbit/s
clients.
Figure 2-1: Using Various Transmit Rates
Fixed Rate
A fixed rate setting prevents the PC Card from retransmitting at a lower rate after a failed
transmission. One example of why you would do this is when a microwave oven in the area
produces noise in the same frequency as the wireless network (see Figure 2-1). The
interference only occurs when the machine is in use. The interference may temporarily
disrupt communications between a client and the Access Point. After a transmission fails
more than once, the client retransmits at a lower rate. However, the interference also
prevents communication at the lower rate. Retransmitting at a lower rate does not solve the
problem and could decrease network performance. With fixed rate enabled, the client
cannot retransmit at a lower rate.
2-4 Understanding Wireless Network Characteristics