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Bob Mandeville bob@iometrix

Bob Mandeville bob@iometrix

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Bob Mandeville bob@iometrix

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  1. Wireless Performance Prediction(WPP) - Approaches to the Issue Bob Mandeville bob@iometrix.com Bob Mandeville, Iometrics

  2. IETF (BMWG) Based on two-step approach to definitions: Terminology document (all relevant functional characteristcs are defined) Methodology document This method is most appropriate for performance testing ATM Forum, Metro Ethernet Forum Based on ratified standards documents Each test definition is referenced to standards source text This method is most appropriate for conformance testing Two Approaches to CreatingTesting Standards Bob Mandeville, Iometrics

  3. IETF BMWG Test Standards Templates • Terminology Definition Template: • Term to be defined. (e.g., Latency) • Definition: The specific definition for the term. Discussion: A brief discussion about the term, it's application and any restrictions on measurement procedures. • Measurement units: The units used to report measurements of this term, if applicable. • Issues: List of issues or conditions that effect this term. • See Also: List of other terms that are relevant to the discussion of this term. • Methodology Definition Template: • Objectives • Setup parameters • Procedures • Measurements • Reporting formats Bob Mandeville, Iometrics

  4. Conformance OrientedTest Methods Template 1/2 Bob Mandeville, Iometrics

  5. Conformance OrientedTest Methods Template 2/2 Bob Mandeville, Iometrics

  6. Sample List of 802.11 Terms to be Defined by Category: Bob Mandeville, Iometrics

  7. Standardized Approach A sample application - Roaming Bob Mandeville, Iometrics

  8. Sample Application to a Key VariableRoaming Performance • Roaming Test • A practical example which shows poor performance related to a lack of test standards definitions • To roam a 802.11 a/b/g device will: • disassociate from one AP • search for a stronger RF signal from another AP • then associate and authenticate with that A • resume normal data transmission • Roaming can fail due to: • transient RF conditions • the time that APs and devices take to complete the four step roaming process Bob Mandeville, Iometrics

  9. Test Configuration Bob Mandeville, Iometrics

  10. Test Procedure • Roaming Test recorded: Total Roaming Time = Decision Time + Switch Over Time • The Decision Time is the time it took the NIC to stop attempting to transmit packets to AP 1 after the attenuation of the RF signal • The Switch Over Time is the time it took the NIC to complete its association with AP2 after it stopped attempting to transmit packets to AP 1 • During the Decision Time cards recognized the signal attenuation and invoked proprietary algorithms to adapt their rates to slower speeds. • Switch Over Time ends when the NIC receives the AP’s acknowledgement to its association request. • This time should only be recorded as valid if data traffic from the NIC to the AP successfully resumes transmission after association. Bob Mandeville, Iometrics

  11. Test Results Bob Mandeville, Iometrics

  12. Bob Mandeville, Iometrics

  13. Test Conclusions • Need to break out Decision Time and Switch over Time • Switch Over Times are as low as 60 milliseconds and averages a little over 700 milliseconds over all the combinations excepting two outliers which took over 8 seconds. • In the majority Decision Time is the largest contributor to the overall Roaming Times. • Packet traces show that most implementations of the rate adaptation algorithms maintain transmission at the lowest 1 Mbps rate for several seconds after loss of RF signal has been detected. • These algorithms will need to be revisited to deliver quality roaming. • Test standards for measuring roaming times can make a significant contribution by aligning all vendors and users on a common set of definitions • This applies to roaming but also to a large number of other undefined terms Bob Mandeville, Iometrics

  14. Thank you Bob Mandeville, Iometrics