I am sitting here thinking about how might be implemented the RSSI and RSSI trigger features for IEEE 802.11. For those that are not familiar:
- RSSI is the received signal strength
- RSSI trigger is an indication that is pass upwards through the stack when certain RSSI threshold has been crossed.
In both cases, it does not make sense to say that a target interface receives a signal of a certain strength without specifying the source. Naturally, if there are multiple sources, there are mutliple transmitters, at different distances, so the RSSI at the target will be different for each transmitting source.
I am wondering if this is the reason why so few adapters support the RSSI trigger feature (in software at least on Windows) . To make it work, target adapter would have to keep track of the MAC addresses of old frames. When a new frame is received, the received signal strength calculated during the reception of that particular frame would have to be compared to that caculated during reception of other prior frames with the same MAC address. For infrastructure mode, the MAC address is often that of the access point and is narrow-sense stationary. However, for ad-hoc mode, the *very first* reception of a frame that appears "out of the blue" has a MAC address that could not possibly be compared with a previous MAC address, as there were none. Then what? If I were the engineer prescribing what should be done in this situation, I would force a trigger. But at present, it seems that the adapter drive writers do nothing at all, which, as I have stated in a previous post, is extremely perplexing/frustrating.
I would like to know if anyone has ever used or seen this feature in software, and if not, whether they expect any of the driver writers to support it in the near future.
Reference:
-Le Chaud Lapin-