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Domain Signaling. Martin Lefkowitz Trapeze Networks 5753 W. Las Positas Blvd, Pleasanton, CA 94588 [email protected] Domain Signaling Features. Domain Signaling tells the STA the Signal Strength of the AP is without the need to transmit a probe request.

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Domain Signaling

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Domain signaling l.jpg

Domain Signaling

Martin Lefkowitz

Trapeze Networks

5753 W. Las Positas Blvd,

Pleasanton, CA 94588

[email protected]

Martin Lefkowitz, Trapeze Networks


Domain signaling features l.jpg

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

Martin Lefkowitz, Trapeze Networks


How does domain signaling work l.jpg

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.

Martin Lefkowitz, Trapeze Networks


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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.

Martin Lefkowitz, Trapeze Networks


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Packet type of Management with the following structure

Total Packet size of

MAC Header + body + FCS

24 + 15 + 4 = 43 bytes

Proposed Packet Structure

Martin Lefkowitz, Trapeze Networks


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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.

Martin Lefkowitz, Trapeze Networks


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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.

Martin Lefkowitz, Trapeze Networks


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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.

Martin Lefkowitz, Trapeze Networks


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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

Martin Lefkowitz, Trapeze Networks


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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

Martin Lefkowitz, Trapeze Networks


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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

Martin Lefkowitz, Trapeze Networks


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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)

Martin Lefkowitz, Trapeze Networks


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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

Martin Lefkowitz, Trapeze Networks


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