Last Post: February 25, 2005:
I did a search for ripple in the learning center, didn't find your whitepaper. Could you email me a copy? thx
it's been pulled for further updating....the same info is in the CWAP study guide.
802.11b radios only understand DBPSK and DQPSK modulation using CCK coding. OFDM is foreign to them and only looks like noise. In order for the 802.11b client to recognize the 802.11g AP, it would have to be able to decode the PLCP header, then the MAC header - neither of which is possible with a CCK radio.
we are currently installing b and g together in a university multi floor bldg and are interested in more info on this situation, can you help?
So does one 802.11b device bring down the data rate of all 802.11g devices when it associates to the access point? That would sure suck.
can you inform me of how to get the news article you are referring to or from as I would like to learn more
ERP PHYs are built to detect nonERP (DSSS and HR/DSSS) PHY's in the channel and moderate the use of otherwise non-interoperable modulations with protection mechanisms. This makes the ERP PHYs much slower than without the nonERP PHY's around but still maybe twice as fast as the fastest nonERP PHYs. More importantly protection allows the ERP and nonERP PHYs to interoperate reliably, predictably, and fairly, either in the same BSS or in overlapping BSSs that share a channel.
The best known trigger for an ERP BSS to start using protection is association of a nonERP PHY into its BSS. This can be avoided by including at least one of the ERP-OFDM rates in the basic rates list of the BSS. But there are other triggers that cannot be so easily avoided. These triggers are encouraged by the standard although not required, and they all have in common detecting (directly or indirectly) a nonERP PHY communicating in the channel.
There is controversy over the effect of removing all nonERP rates from an ERP access point supported rates list. The observed result is -- no protection. Is it because protection is no longer needed or is it because protection frames (which require nonERP rates) cannot be transmitted?
Since almost no BSS administrator has absolute control of her channel we should all want to have protection poised to protect us, even at the cost of seriously degraded throughput.