From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: To: BlueZ mailing list Message-ID: <20040622171857.GA8829@bougret.hpl.hp.com> Reply-To: jt@hpl.hp.com Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii From: Jean Tourrilhes Subject: [Bluez-devel] Re: inquiry scan mode and page scan mode questions Sender: bluez-devel-admin@lists.sourceforge.net Errors-To: bluez-devel-admin@lists.sourceforge.net List-Unsubscribe: , List-Id: List-Post: List-Help: List-Subscribe: , List-Archive: Date: Tue, 22 Jun 2004 10:18:57 -0700 Albert Huang wrote : > > My immediate goal is to understand why 10.24 s is the recommended > duration for an inquiry, and to see if it's possible to decrease the > average time to discover a bluetooth device. Ha, ha ! Inquiry is one of the greatest pain of BlueTooth. Everybody wants to decrease this time, but unfortunately there is not much wiggle room. One of the idea is that if you do periodic inquiry, it would be nice to do shorter Inquiry more often so as not to degrade your latency. Not possible. I don't want to go into details, but just to give you general pointers. The killer is the backoff, in 10.7.4 it specifies that the node doing Inquiry scan has to wait between 0 and 1023 slots before sending an Inquiry response. Then, you have interference, collision, time shift and all kind of nastiness over the channel. If the Inquiry and Inquiry scan happen to be on the same frequency at the same time, it's not guaranteed to go through. In practical term, a one-shot Inquiry need to be 6.4 s to have a good probability of detection at close range. If you do periodic Inquiry, you can go down to 3.84 s, but expect a few periods before the node is discovered. Those are from one of my unpublished paper. Have fun... Jean ------------------------------------------------------- This SF.Net email sponsored by Black Hat Briefings & Training. Attend Black Hat Briefings & Training, Las Vegas July 24-29 - digital self defense, top technical experts, no vendor pitches, unmatched networking opportunities. Visit www.blackhat.com _______________________________________________ Bluez-devel mailing list Bluez-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/bluez-devel