RTS/CTS.

RTS/CTS in 802.11g network with no 802.11b clients

• When there is mixed mode 802.11 b and g then RTS, CTS do come in as protection mechanism.
  Are there RTS and CTS packets sent when the network only consists of 802.11g devices ?
  Also, if they are not sent, please let me know why they are not applicable.

  
  When only 802.11g devices are present, RTS/CTS frames may still be present, but they are not required.
• The original purpose of RTS/CTS was basically a way for 802.11g stations to tell 802.11b stations to be quiet. Since 802.11b stations can't understand the modulation and coding of 802.11g OFDM transmissions, the 802.11g stations have to say to 802.11b stations "please don't interrupt while I talk in a foreign language."

  The beauty of RTS/CTS is that these frames are very small and pose very low overhead to the network. So, even though they were designed to facilitate backward compatibility between 802.11b and 11g, they can be used in other ways as well. For example, if there are two client stations in a network that can't hear each other (hidden nodes), RTS/CTS can be enabled to prevent further collisions and performance degradation because the stations use these low overhead notifications that reserve the medium. The same principle can apply if there are a lot of collisions as a result of high utilization and large frames. RTS/CTS can be used to reserve the medium (small frames are less likely to experience collisions), then the larger frames can be sent, avoiding collisions. Similarly, this exchange is now useful for backward compatibility between 802.11b/g and 802.11n as well.

  For those reasons, RTS/CTS may be used even if 802.11b stations are not present. But for pure 802.11g networks, RTS/CTS is otherwise unnecessary.

  For Extreme Networks:
• Click a protection type: CTS Only or RTS CTS. The default and recommended setting is CTS Only.
  Click RTS CTS only if an 11b AP that operates on the same channel is detected in the neighborhood, or if there are many 11b-only clients in the environment. The overall throughput is reduced when Protection Mode is enabled, due to the additional overhead caused by the RTS/CTS.
  The overhead is minimized by setting Protection Type to CTS Only and Protection Rate to 11 Mbps. The overhead causes the overall throughput to be sometimes lower than if just 11b mode is used. If there are many 11b clients, it is recommended that you disable 11g support (11g clients are backward compatible with 11b APs).
  An alternate approach, although potentially a more expensive method, is to dedicate all APs on a channel for 11b (for example, disable 11g on these APs) and disable 11b on all other APs. The difficulty with this method is that the number of APs must be increased to ensure coverage separately for 11b and 11g clients.
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