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How does a 802.11 device know how long the data payload of the frame is? How does it now when the frame body ends and the FCS starts?

Hi CSC:

The length is encoded in the physical layer header by the transmitter and processed by the receiver while the frame is being received.

I hope this helps. Thanks. /criss

Thanks Criss, I got it, it's part of the PLCP header. You never seized to amaze me with your wireless knowledge.

I got a questions about the encrytion, how does a receiver know which one is being used? There is only 1 bit to indicate a protected frame in the 802.11 header, how would a receiver differentiate between WEP and CCMP as they have different headers?

Thanks

Hi CSC:

The short answer is that the cipher suite used between a pair of stations is agreed to at the outset. Any other receiver has no need to decrpyt the frame payload.

If you are interested in more detail please start another thread.

I hope this helps. Thanks. /criss