1. doc.: IEEE 802.11-00/xxx Submission September 2003 Martin Lefkowitz, Trapeze NetworksSlide 1 Domain Signaling Martin Lefkowitz Trapeze Networks 5753 W. Las Positas Blvd, Pleasanton, CA 94588 lefko@trapezenetworks.com

2. doc.: IEEE 802.11-00/xxx Submission September 2003 Martin Lefkowitz, Trapeze NetworksSlide 2 Domain Signaling Features Domain Signaling tells the STA the Signal Strength of the AP is without the need to transmit a probe request. Domain Signaling is a way to tell the Basic Service Area; –When the next TBTT will occur for this BSS –That it is OK to transmit on this BSS at least until TBTT. Helps with 802.11h DFS mechanism Domain Signaling minimizes the amount of time required to satisfy Regulatory requirements –Configurable based on the specific site requirements

3. doc.: IEEE 802.11-00/xxx Submission September 2003 Martin Lefkowitz, Trapeze NetworksSlide 3 How does Domain Signaling work? The AP waits the maximum contention time after a packet has been sent before sending the signaling packet. –If the medium has been idle previously for the max contention period the packet may be transmitted immediately –If the medium is not idle the AP would send a packet after all other packets have been sent, and medium has been idle for max contention period.

4. doc.: IEEE 802.11-00/xxx Submission September 2003 Martin Lefkowitz, Trapeze NetworksSlide 4 How does Domain Signaling work After the Domain Signal packet has been sent an AP would wait n milliseconds before attempting to send another Domain Signaling packet. –Domain Signal Timer reduces excessive packet transmission Reduces the amount of time CCA is high. –Domain Signal Timer is configurable based on application Site administrator weighs statistically high CCA for first packet in flow vs quick access to vital BSS info.

5. doc.: IEEE 802.11-00/xxx Submission September 2003 Martin Lefkowitz, Trapeze NetworksSlide 5 Proposed Packet Structure Packet type of Management with the following structure Total Packet size of MAC Header + body + FCS 24 + 15 + 4 = 43 bytes Octets8223 MeaningTimestampNext TBTTBeacon Interval Country

6. doc.: IEEE 802.11-00/xxx Submission September 2003 Martin Lefkowitz, Trapeze NetworksSlide 6 Timing Accuracy Requirement that the Timing for the TBTT be accurate enough such that a STA may be able to schedule “Camping” on a channel to hear the beacon. –Accuracy of 2 milliseconds should be sufficient enough To allow the calculation as to when the packet actually could go out to be done in the MAC layer –After each idle time the TSF could be read. Time could be calculated to within 2ms for; Timestamp of packet Next TBTT If the packet does not go out due to other packets in the basic service area –Actual possible time of transmission is recalculated when idle is sensed.

7. doc.: IEEE 802.11-00/xxx Submission September 2003 Martin Lefkowitz, Trapeze NetworksSlide 7 Domain Signal Packet Timestamp Purpose –To allow a STA to calculate the TSF offset without receiving a beacon. Next TBTT purpose –To tell a STA when the next beacon will occur to obtain dynamic and static information not contained in the Site Report or Domain Signal Packet. –Satisfies 802.11h DFS until the next TBTT Country Purpose Satisfies 802.11h requirements of STA transmission on this channel. If the country string is the same as the country string you are currently on then all power policies of the current AP apply.

8. doc.: IEEE 802.11-00/xxx Submission September 2003 Martin Lefkowitz, Trapeze NetworksSlide 8 Max Idle Time expressed in Us IFS + CWMin time +1 slot time –802.11b (1999) 50 + 620 + 20 = 690 –802.11a (1999), 802.11g 34 + 135 + 16 = 185 –Use CWMin because if a packet already has had an error then it’s delivery status has already been compromised.

9. doc.: IEEE 802.11-00/xxx Submission September 2003 Martin Lefkowitz, Trapeze NetworksSlide 9 Max CCA High Time For Signaling packet Preamble + PHY header + PHY payload (37 bytes) –802.11b Long Preamble –192 + 172 (2Mb/s) = 364us –192 + 31.3 (11Mb/s) = 223.3us Short Preamble –96 + 172 (2Mb/s) = 268us –96 + 31.3 (11Mb/s) = 126.9us –802.11a 802.11g 24 + 6.36(54Mb/s) = 30.36us 24 + 57.19 (6Mb/s) = 81.19us

10. doc.: IEEE 802.11-00/xxx Submission September 2003 Martin Lefkowitz, Trapeze NetworksSlide 10 CCA overhead of constant Signaling 364/690 = 52% 2mbit 11b long preamble 223/690 = 32% 11mbit 11b long preamble 268/690 = 38% 2mbit 11b Short preamble 126/690 = 18% 11mbit 11b Short preamble 81/185 = 43% 6mbit 11a/g 30/185 = 16% 54mbit 11a/g

11. doc.: IEEE 802.11-00/xxx Submission September 2003 Martin Lefkowitz, Trapeze NetworksSlide 11 Percentage CCA high with Domain Signal Packet Timer Setting the Timer to send a packet every 7ms (7000us) would cause CCA to be high when BSS is quiescent: –2Mb/s 11b long preamble 364/7000 = 5.2% CCA high –11MB/s 11b long preamble 223/7000 = 3.2% CCA high –2Mb/s 11b Short preamble 268/7000 = 3.8% CCA High –11Mb/s 11b Short preamble 126/7000 = 1.8% CCA High –6Mb/s 11a/g 81/7000 = 1.0% CCA High –54Mb/s 11a/g 31/7000 = 0.4% CCA High

12. doc.: IEEE 802.11-00/xxx Submission September 2003 Martin Lefkowitz, Trapeze NetworksSlide 12 Effects of Domain Signaling on Access W/7ms DST Worst case 2mbit long preamble 802.11b –95.1% of the time no effect –5.2% packet must wait up to 340 us before contending for the medium 6mbit 802.11a/g –99% of the time no effect –1% of the time packet must wait up to 73us before contending for the network. Worst case wait on a channel to know the AP’s signal strength and whether the STA may transmit on that channel –7ms (unless there is frequency reuse with the other BSS being active)

13. doc.: IEEE 802.11-00/xxx Submission September 2003 Martin Lefkowitz, Trapeze NetworksSlide 13 Conclusion Domain Signal packets can be used to: –Reduce the wait time for 802.1d requirements –Allow the STA to schedule the reception of a beacon from an particular service area. Domain Signal Packets when used in conjunction with the Site Report can be used to: –Allow the STA to get signal strength from an AP of interest without sending a probe request, or waiting for a beacon. –Alleviate issues with TPC