Same Channel on Different WLANs and RTS/CTS

Hi
I have 2 questions about physical layer of wireless lan.
1-) Many WLANs(SSID) use same channel for communication, that means they use same frequency, what prevents the collisions between different wlans but same channel?( I am asking about RF signal collision)
2-) Do rts and cts valid for just one wlan that computer which is generated, belongs to or do rts/cts synchronize all different wlans that use same frequency.
Thanks.

1.) Congestion Avoidance. Before the client transmits, it listens to for energy on the frequency it is transmitting on. If it hears energy, it backs off for a time. Then listens again.
http://en.wikipedia.org/wiki/Carrier_sense_multiple_access_with_collision_avoidance take a look at the diagram on the left
2.) RTS/CTS client sends the RTS, then the AP will send the CTS.
http://en.wikipedia.org/wiki/IEEE_802.11_RTS/CTS
HTH,
Steve

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Date: 2008-12-11 14:24:37 -0800 (Thu, 11 Dec 2008)
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Same Channel on Different WLANs and RTS/CTS

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