Presentation on theme: "WPP Study Group Tutorial Group created at Vancouver meeting to create test definitions and methods for 802.11 Presentations today will cover WPP from several."— Presentation transcript:
WPP Study Group Tutorial Group created at Vancouver meeting to create test definitions and methods for 802.11 Presentations today will cover WPP from several points of view –Large user –IC vendor –Testing community
Agenda Bob Mandeville: Iometrix Don Berry: Microsoft Mike Wilhoyte: Texas Instruments Kevin Karcz: UNH-IOL Jason A. Trachewsky: Broadcom Fanny Mlinarsky: Azimuth Systems Round Table Discussion and Q&A
802.11 Requirements for Testing Standards Bob Mandeville firstname.lastname@example.org
WPP What is the need for 802.11 metrics What problems will they help solve? Who will the primary users be? How do we go about creating new metrics for wireless?
Two Approaches to Creating Testing Standards IETF (BMWG) –Based on two-step approach to definitions: Terminology document (all relevant functional characteristics 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
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
Conformance Oriented Test Methods Template 1/2 Test Name Name derived from reference document Test Definition ID A punctuated alphanumeric string assigned to each defined requirement and test procedure couple using the following convention: one to three letter abbreviated source document name. section number - paragraph number in the section from which requirement is derived. This number always figures as the last number of an ID. Ethernet Services Model=M; Ethernet Services Definitions=S; Traffic and Performance Parameters for SLSs=T. Example: M.6.1-4 Reference Document Source Reference document and section (and paragraph when useful for clarity) Test Type Functional, Conformance, Interoperability or Performance Test Status Normative, optional, additional Requirement Description Brief description of the service requirement that the device must or should satisfy Description of DUT/SUT Type of Ethernet frame forwarding Device Under Test (DUT). Common designations used in this document are: CE Device (Customer Equipment Device); UNI Device (User Network Interface Device); MEN Device (Metro Ethernet Network Device). A UNI device may be considered as a kind of MEN border device.
Conformance Oriented Test Methods Template 2/2 Test Object Succinct description of test purpose Test Bed Configuration Succinct description of test bed configuration Test Procedure Succinct description of the test procedure with mention of the test stimulus and expected output Units Units can be time units, rates and counts in integers such as milliseconds, frames per second and numbers of frames transmitted or received. For the most part units used are defined in RFCs 2285, 2544, 2889 Variables Variables such as frame length, test duration, numbers of interfaces under test must be described Results Description of the textual, numerical and/or graphical format in which to display test results Remarks Description of any particular observations that might effect the test result
Sample List of 802.11 Terms to be Defined by Category:
Requirements for Testing Standards 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: 1.disassociate from one AP 2.search for a stronger RF signal from another AP 3.then associate and authenticate with that A 4.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
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 APs 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.
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
Challenges of Operating an Enterprise WLAN Don Berry Senior Wireless Network Engineer Microsoft Information Technology
Microsofts Current WLAN Network –4495 Access Points –1 AP per 3500 sq/ft –~15 Million sq/ft covered in 79 countries –70,000 users –500,000+ 802.1x authentications per day – EAP-TLS –Supports 5.5 and 11Mbps only
Wireless Service Challenge What is Wireless Service? How is it measured? What factors impact Wireless Service? How do you improve Wireless Service?
Wireless Service and Support Service Goals –Make Wireless service equivalent to wired –Offer unique mobile services Operational Goals –Reduce operational costs –Minimize support personal
How can WPP Help? Produce criteria that reflect the client experience Offer information that can compare different environments – Enterprise, SOHO, home
Desired Outcome of WPP: A Perspective From a Si Provider Mike Wilhoyte Texas Instruments
Key Issues We Face Relevant to WPP Supporting Customers w/ Custom Test Fixtures –Are often uncontrolled and therefore repeatability is questionable –May introduce unintentional impairments and therefore dont effectively isolate the feature under test –May unintentionally push beyond the boundary of the specification –May stress the system beyond what any user or evaluator will do –May overlook other critical areas of system performance The complexity of the specification has grown since the days of 11b and more than ever, performance is setup dependent –Are tests really apples-to-apples?
These Issues Result in: Confusion over unexpected test results Resource drain
A Real Example: Customer ACI Test Fixture RF Shield Room – non Anechoic AP DUTSMIQ People Observing the Results AP Over 30 Active APs TCP/IP Test: Plot TCP/IP throughput with increasing levels of interference from the SMIQ
Issues With This ACI Test Fixture Metal walls in shield room producing multipath making the test results depend even more on the position of the laptop (in a fade?) People (2.4 GHz RF absorbers) in the room Over 30 APs active which may couple into the RF front-end (even though its cabled) of the test AP SMIQ produces a non-realistic signal since the carrier is always present even though it may be triggered externally –There are ways around this The test AP is not isolated from the interference and its behavior will affect the test result of the DUT –Rx performance in the same interference –Deferral behavior in the Tx (CCA) is affected –Rate adjustment behavior Can you imagine trying to repeat any test result from this fixture in YOUR lab?
A Better ACI Test Fixture Testing the STA AP STA out PA DUT AP Attenuator 30 dB 20 dB Anechoic Chamber 1 Anechoic Chamber 2 in clp 30 dB Interfering network swept on channels 1-11 Anechoic Chamber 4 Channel 6 PA isolates interfering network and is not affected by traffic in chambers 3,4 clp out in Anechoic Chamber 3 Atten pad
A Better ACI Test Fixture Testing a Network (AP+STA) AP STA out PA DUT AP Attenuator 30 dB 20 dB Anechoic Chamber 1 Anechoic Chamber 2 in clp 30 dB Interfering network swept on channels 1-11 Anechoic Chamber 3 Channel 6 PA isolates interfering network and is not affected by traffic in chamber 3
Desirable Outcomes of WPP Develop a minimal set of test metrics that are relevant to key performance parameters such as: –Robustness –Throughput/Capacity –Range Develop a Set of Test Best Practices that: –Produce repeatable results –Achieve the right balance between complexity and cost –The industry will use
UNH-IOL perspective on WLAN Performance testing Kevin Karcz March 15, 2004
A Quick Background UNH-IOL Wireless Consortium primarily has focused on interoperability and conformance tests for 802.11, not performance testing Have generated traffic loads to observe a DUTs behavior under stress, but not specifically to measure throughput or related parameters. However, QoS is inherently about providing performance while sharing limited resources –Optimization of: Throughput, Range, Delay & Jitter –Constrained by: User resources: CPU load, DC power Community resources: Available spectrum, aggregate users –
Examples of performance tests PHY layer –Multi-path fading channel emulation using a Spirent SR5500 fader. What fading models should be used? MAC layer –Throughput varies with Traffic Generator used –CPU load differs significantly for between different vendors. Much greater than CPU load for a typical Ethernet device.
Clear methods of testing are needed… As we start measuring more performance metrics Can each layer of the network be measured independently? Which metrics need to look at the interaction of multiple layers? Hassle of real world scenario testing vs. a PHY test mode? –Black box testing requires DUT to authenticate and associate with test equipment and interact at the MAC layer, not just the PHY layer.
Some gray areas of testing Throughput –Is throughput measured as a MAC layer payload? At IP layer? TCP or UDP layer? –One DUT may have better PER measurements at the PHY layer than a 2 nd DUT, but may get worse throughput if its rate selection algorithm is poor. –Difficult to maintain consistency in an open (uncontrolled) environment Can throughput be measured in a cabled environment without an antenna? What if the DUT has a phased array antenna? What if the device is mini-PCI and inherently has no antenna? Range test –What if a higher TX level causes higher adjacent channel interference and brings the aggregate throughput down for a neighboring BSS? Power consumption –Is this just the DC power drain at the cardbus card interface? –Should CPU load be included if the DUT implements much of its MAC functionality on a host PC? Roaming –Quickest time: 1 STA, 2 APs on same channel –More realistic: AP reboots, Multiple STAs roam to new AP on new Channel
Why WPP role is important to UNH-IOL? Open standards are desired for the basis of test suite development Defining test parameters and standardization of Test Scenarios makes comparison of Apples to Apples easier IEEE focuses on the technical content Our interest is the testing, not determining how results are utilized
Why WPP should define the tests UNH-IOL follows IEEE PICS for test cases More detailed info for test results –Cases: PDA/laptop/AP weight test results differently
Example criteria weighting Through put Delay & Jitter DC power Roaming time Laptop+++ + AP++ N/A VoIP phone 0+++++
Comments on Wireless LAN Performance Testing And Prediction Jason A. Trachewsky Broadcom Corporation email@example.com
Topics Test Categories for WPPTest Categories for WPP Some Test Configurations
Test Categories for WPP Deciding what parameters are to be considered is the challenge. How do we transform user perception of performance into a set of repeatably- measurable quantities? –Throughput and Range (what environments?) –Frame latency –Visibility of APs
Test Categories for WPP How do we transform user perception of performance into a set of repeatably- measurable quantities? –Delays in association/authentication –Host CPU utilization –Ability to roam without loss of connections –Etc.
Test Categories for WPP Basic PHY/RF Measurements –Transmitter Parameter Measurements TX EVM or Frame Error Rate (FER) with Golden/Calibrated Receiver Carrier suppression Carrier frequency settling
Test Categories for WPP –Receiver Parameter Measurements RX FER vs. input power –Flat channel (controlled through cabled/shielded environment) –Controlled frequency-selective channels (known multipath power-delay profile) –Antenna measurements cable/feed losses (S11 and S21) gain vs. azimuth and elevation angle One can easily take a great receiver design and blow away all gains with a bad antenna or lossy feed!
Test Categories for WPP MAC Layer Measurements –rate adjustment behavior specific parameters? test conditions? –association and roaming behavior specific parameters? test conditions? –frame latency –layer-2 throughput with encryption –host CPU cycles consumed?
Test Categories for WPP Layer-4 Measurements –UDP frame loss rate and latency vs. received power flat or frequency-selective channels? –TCP throughput vs. received power flat or frequency-selective channels?
Test Categories for WPP Open-air Measurements –Open-air measurements are always subject to imperfectly-known time-varying multipath power-delay profiles. There is substantial variation at 2.4 and 5.5 GHz over 10s of msec.
Test Categories for WPP –We have established that frequency-selectivity due to multipath can result in higher-loss channels having higher capacity than lower- loss channels. The capacity of the channel can vary rapidly. This is a more significant problem for systems like 802.11a and 802.11g which include a large number of possible rates to better approach the practical capacity. (The problem wont get easier for future WLAN standards.)
Test Categories for WPP Open-air Measurements –What can we do? Try to perform as many measurements as possible with cable networks. Perform open-air measurements in an area in which the distance between transmitter and receiver is small compared with the distance between either transmitter or receiver and any other object. I.e., strong LOS. –Helpful but not sufficient, as even small reflections affect channel capacity.
Test Categories for WPP Open-air Measurements –What can we do? Give up and perform a large ensemble of measurements and gather statistics.
Channel Measurement Block Diagram Scope provides 10Mhz reference clk for all systems 3 long interconnect cables connect tx and rx side Filt module includes LNA Scope rx Filt 10 Mhz clk linux controller DC PWR 10/100 hub ARB tx0 ARB tx1 ARB tx2 ARB tx3 10 Mhz clk ARB txctl I / Q 10/100 hub gpib ethernet UPS ethernet trigger
Time- and Frequency-Selective Fading > 10-dB change in received signal power in some bins over 60 msec.
Topics Test Categories for WPP Some Test ConfigurationsSome Test Configurations
System Block Diagram –Main boardtest system –Transmit test system boardtest system Transmit Test Filter Mux Microwave Spectrum Analyzer controller (attenmach) GPIB or DIO line ethernet RF cable GPIB
Boardtest System DUTmux-2 power meter attenREFcoupler mux-3 mux-6 SA 5V,12V,GND controller (attenmach) GPIB or DIO line Ethernet RF cable GPIB
RF Loop Block Diagram Split / Combine 6-dB Loss Split / Combine 6-dB Loss Golden Node DUT ATTEN Does WPP specify RF test fixtures? Does WPP specify fading channel emulators (no!) or a set of fading channel profiles (maybe!).
Multipath Channel 2 Example fixed multipath channel power-delay profile.
Comments on Wireless LAN Performance Testing And Prediction Fanny Mlinarsky Azimuth Systems firstname.lastname@example.org
Ethernet vs. WiFi Wired test metrics RFC 2285,2544,2889 Wireless test metrics
Security Security Test Metrics Offered Load Packet Size # of Clients % of Power Save Clients % Load Of Assoc/ De-assoc/ Re-assoc Encryption RTS/CTSFragmentation Authentication Packet forwarding Roaming Rate adaptation Behavioral Behavioral WEP TKIP AES EAP-TLS EAP-TTLS PEAP LEAP QoS QoS
Forwarding Rate Measurement Open air Controlled RF
Controlled Test Environment If measurements are not repeatable then the test is invalid Open air creates unpredictable test conditions due to interference and multipath Shielded and cabled test environment may be necessary for some measurements
Summary The IT managers question: How well do mobile computing solutions perform in the enterprise? The dilemma: Standard wired benchmarking techniques wont give the right answer Verifying function and performance in the inherently unstable wireless space calls for a new methods & metrics The answer: New methods to test and measure every aspect of wireless protocols Wireless metrics outnumber traditional Ethernet metrics 5:1