|
0.9 Mbps
|
|
11 Mbps
|
|
150 Mbps
|
|
19 Mbps
|
|
20/100
|
|
23 Mbps
|
|
2.4/5 GHz
|
|
2.4 GHz
|
|
2 Mbps
|
|
35/120
|
|
38/140
|
|
4.3 Mbps
|
|
54 Mbps
|
|
5 GHz
|
|
70/250
|
|
74 Mbps
|
|
802.11
|
|
802.11a
|
|
802.11b
|
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802.11 control frames are simpler than data frames. They contain a `Frame Control`, a `Duration` field and one or two addresses. The acknowledgment frames are very small. They only contain the address of the destination of the acknowledgment. There is no source address and no `Sequence Control` field in the acknowledgment frames. This is because the acknowledgment frame can easily be associated to the previous frame that it acknowledges. Indeed, each unicast data frame contains a `Duration` field that is used to reserve the transmission channel to ensure that no collision will affect the acknowledgment frame. The `Sequence Control` field is mainly used by the receiver to remove duplicate frames. Duplicate frames are detected as follows. Each data frame contains a 12 bits sequence number in the `Sequence Control` field and the `Frame Control` field contains the `Retry` bit flag that is set when a frame is transmitted. Each 802.11 receiver stores the most recent sequence number received from each source address in frames whose `Retry` bit is reset. Upon reception of a frame with the `Retry` bit set, the receiver verifies its sequence number to determine whether it is a duplicated frame or not.
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