On Fri, Mar 24, 2006 at 12:38:40PM -0500, Dan Williams wrote: > However, the problem with active scanning is that you have to power up > the transmit components of the radio, while passive scanning, even > though it takes a bit longer, doesn't necessarily require that. Active > scanning takes more power.
For some class of devices, that is certainly correct. For other classes, it does not really matter much (e.g., my laptop has large enough battery for me not to care about active scan). > So what I'm arguing for here is that drivers should _default_ to passive > scanning when given a scan request with no scan type information. But > they should be able to do so when they get a request for an active scan > using IW_SCAN_TYPE_ACTIVE. Drivers should default to using less power, > and more only when the app requests so. Is battery use more important than accuracy of results and the amount of time needed to perform the operation? > It's somewhat unfortunate that wireless.h defines ACTIVE scan type as 0 > since then, that's what non-WE-18 apps would inadvertently set. And > apps that are power-aware would be setting that bit anyway. Most > drivers that are FullMAC do passive scanning without sending probe > requests, AFAIK, and so do OK here. Please note that this field is in struct iw_scan_req and non-WE-18 apps do not know about that in the first place. In other words, it does not really matter what the value of IW_SCAN_TYPE_ACTIVE is.. The only open question I see here is what should happen if struct iw_scan_req is not included and my current understanding is that the driver is allowed to do either active or passive scanning based on its default and I just happen to think that the default would more likely be active scanning unless somehow (driver specific parameter) it has been modified to do something else. Have you actually observed that FullMAC drivers are using passive scanning (i.e., used a wireless sniffer to see what they are doing)? Most drivers I've looked at at this level are sending out probe request frames.. -- Jouni Malinen PGP id EFC895FA - To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
