Presentation on theme: "Doc.: IEEE 11-03-0691-01-000k Submission September 2003 Martin Lefkowitz, Trapeze NetworksSlide 1 Directed Probe Request With No Response Option Martin."— Presentation transcript:
doc.: IEEE k Submission September 2003 Martin Lefkowitz, Trapeze NetworksSlide 1 Directed Probe Request With No Response Option Martin Lefkowitz Trapeze Networks, 5753 W. Las Positas Blvd., Pleasanton, CA
doc.: IEEE k Submission September 2003 Martin Lefkowitz, Trapeze NetworksSlide 2 Directed Probe Request/No Response The Directed Probe Request With the No Response Option set (DPWNR) is a mechanism whereby a STA can receive Signal Strength information based on the Ack for a unicast to a targeted AP. –STA already knows this is an AP of interest.
doc.: IEEE k Submission September 2003 Martin Lefkowitz, Trapeze NetworksSlide 3 DPWNR Advantages The needed dynamic information is gained in 1 frame exchange. –Max sized probe request packet Plus protocol overhead b 2mbit long Preamble DIFS + CWMIN (Last Slot) + Preamble + Phy Header + Max Size Probe Reqest Payload + No Response Option + SIFS + ACK= = 1332 us –While this calculation is very approximate and changes due to medium access rules, it’s clear that the needed signal strength information can occur in as little as a millisecond on an idle channel. It currently takes on average 10-16ms to perform a full probe on a channel (according to An Empirical Analysis of the IEEE MAC Layer Handoff Process) Reduces Overhead on medium caused by scanning. –AP’s do not respond to STA’s. Reduces Mismatch between AP an STA’s Scanning Algorithm whereby a STA may already be off the channel before the AP responds causing upwards of 40ms of retries on the medium.
doc.: IEEE k Submission September 2003 Martin Lefkowitz, Trapeze NetworksSlide 4 How does the STA find out about an AP of interest? From a previous Full Passive or Active scan of the channel From the Site Report From a combination of the two. –The site report does not contain needed information for a STA, or an application running on the STA to make a roaming decision. Site Reports along with DPWNR do not replace the need for beacon, or probe response, reception. Currently an application has no way of knowing that it’s service is supported on another AP
doc.: IEEE k Submission September 2003 Martin Lefkowitz, Trapeze NetworksSlide 5 Changes needed to Current Specification Clarification of clause on scanning procedure. –Make it clear that directed probe requests are OK –Possible inclusion of informative note defining behavior of directed probe request with no Response Add Information, or Request Element, in clause 7, that Instructs the AP not to respond to the probe request. Add an indication in the Site Report and Beacon that tell inform the STA of this capability. –STA’s should not use this on AP’s that do not support this option because the AP will attempt to send the unicast probe response frame to a STA that is not present on the medium. –This mechanism should be optional.
doc.: IEEE k Submission September 2003 Martin Lefkowitz, Trapeze NetworksSlide 6 Conclusion Directed Probe Requests with No Response Option can be a valuable tool to gain needed signal strength information for a STA that wishes to perform a smoothing algorithm to get a more accurate representation of the environment while reducing the amount of signaling overhead required to do this. –Could also be a valuable tool for a STA that has a weak signal but is transmitting a lot of data.