Wireless: enable power-saving mode!

Most PCMCIA wireless cards provide a "power saving" mode, and I was suspicious of just what could be done to save power this way, but it turns out to be a bona fide win. The 802.11b protocol itself designed in a kind of "polling" mechanism, so a card going into power-conservation mode wakes up periodically to listen for a "you have traffic" message from the wireless access point. This looks to be an integral part of the design, not a hack or an afterthought.

When the card sees that the WAP has traffic, it turns the radio on fulltime until all the buffered data has been received, at which time it goes back to power-saving mode. Some tests have shown a 1000% power saving, though I suspect this is only saving the power to the receiver, not the transmitter. But it's still something.

I enabled power-conservation mode on my Orinoco card, and it appears that these "Traffic Indication Map" polls happen a dozen or two times per second, and the radio is clearly off most of the time even when I have my streaming music on.

But I cannot see any performance difference - even secure shell to a remote Linux box has zero added latency: it's still totally crisp response. It may be that online gamers couldn't tolerate what I imagine are a few milliseconds of added latency, but I'm still getting <10msec ping times to my access point and cannot find a single downside to this.

Power-Conservation Mode really works.

Posted by Steve at April 06, 2003 06:41 PM | TrackBack