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Performance and Robustness Testing of Wireless Web Servers Guangwei Bai Kehinde Oladosu

Performance and Robustness Testing of Wireless Web Servers Guangwei Bai Kehinde Oladosu Carey Williamson. 1. Introduction and Motivation. Observation : the same wireless technology that allows a Web client to be mobile also allows Web servers to be mobile

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Performance and Robustness Testing of Wireless Web Servers Guangwei Bai Kehinde Oladosu

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  1. Performance and Robustness Testing of Wireless Web Servers Guangwei Bai Kehinde Oladosu Carey Williamson TeleSim Research Group

  2. 1. Introduction and Motivation • Observation: the same wireless technology that allows a Web client to be mobile also allows Web servers to be mobile • Idea: portable, short-lived, ad hoc networks • Possible applications: • classroom area networks, seminars • press conferences, media events • sporting events, gaming, exhibitions • conferences and trade shows • disaster recovery sites, field work, etc. TeleSim Research Group

  3. Background: Portable Networks • Assumptions: the characteristics of a portable short-lived network are: • set it up when needed; tear down after • only needed for minutes or hours • when may not be known a priori • where may not be known a priori • no existing infrastructure of any kind • general Internet access notavailable • general Internet access not required • pre-defined content; target audience • 1-100 users; mobile; limited bw needed TeleSim Research Group

  4. 2. Objectives • to assess feasibility of portable networks • to benchmark the performance capabilities and limitations of an Apache Web server in a wireless adhoc network • to identify the performance bottlenecks • to understand impacts of different factors • number of clients • Web object size • persistent connections • transmit power (energy consumption) • wireless channel conditions TeleSim Research Group

  5. 3. Experimental Setup • Compaq Notebooks (1.2GHz Pentium III, 128MB RAM, • 512 KB L2 cache, Cisco Aironet 350 network cards) • RedHat Linux 7.3, httperf, Apache 1.3.23, SnifferPro 4.6 • Network: 11 Mbps IEEE 802.11b wireless LAN, ad hoc mode TeleSim Research Group

  6. Experimental Setup (Cont’d) • IEEE 802.11b: a standard for wireless LANs • Carrier Sense Multiple Access with Collision Avoidance • (CSMA/CA), up to 11 Mbps data rate at physical layer • adhoc mode • frames are addressed directly from sender to receiver • httperf • Web benchmarking software tool developed at HP Labs • Web server: Apache (version 1.3.23) • Process-based, flexible, powerful, HTTP/1.1-compliant • SnifferPro 4.6 • real-time capture, recording all wireless channel activity, • enabling protocol analysis at MAC, IP, TCP and HTTP layers TeleSim Research Group

  7. Factor Levels Number of Clients 1, 2, 4 HTTP Transaction Rate (per-client) 10, 20, 30, …, 160 HTTP Transfer Size (KB) 1, 2, 4, 8, …, 100 Persistent Connections no, yes HTTP Requests per Connection 1, 5, 10, 15, …, 60 Transmit Power (mW) 1, 5, 20, 30, 50, 100 Client-Server Distance (m) 1, 10, 100 4. Experimental Design • Impacts of different factors on wireless Web server • performance (one-factor-at-a-time) Experimental Factors and Levels • Performance metrics • HTTP transaction rate, throughput, response time, error rate • at Application Layer, • TCP connection duration at Network Layer • Transmit queue behaviour at Link Layer,

  8. 5. Measurement Results and Analyses - Expt 1: Request Rate - Expt 2: Transfer Size - Expt 3: Number of Clients - Expt 4: Persistent Connections - Expt 5: Transmit Power - Expt 6: Wireless Channel TeleSim Research Group

  9. Experiment 1: Request Rate • Purpose: to determine the range of feasible and sustainable • loads for the wireless Web server • Design: • Number of Clients: 1 • HTTP transaction rate: 10, 20, …, 160 req/sec • HTTP transfer size: 1 KB (fixed) • Persistent connections: no • Transmit power: 100 mW • Client-server distance: 1 meter (on same desk) TeleSim Research Group

  10. Wireless Web Performance at Application Layer • Main observation: • As the offered load increases: • linear increase  instability  lower plateau • Peak throughput < 1 Mbps for 1 KB transfers TeleSim Research Group

  11. Transmit Queue Behaviour for Experiment 1 • Main observation: Wireless LAN is the bottleneck • Packet drops occur from link-layer queue (client side) • Even before they get on the wireless LAN!!! • Reason: • No flow control / backpressure mechanism • Note: default queue size is 100 in the Linux kernel TeleSim Research Group

  12. Wireless Web Performance at Application Layer (Cont’d) • Main observation: • the response time is about 9 ms at low load, increase • significantly to over 2 sec at high load (>85 req/sec) • failures occur frequently under overload TeleSim Research Group

  13. Measurement at Network Layer Overload: 100 req/sec Queue buildup,Packet drops, Retransmissions,TCP resets Low load: 10 req/sec Stable performance Mean: 9.7ms High load: 80 req/sec More variability, some spikes, slight skew Medium load: 50 req/sec Greater variation, 2 spikes Mean: 10ms TeleSim Research Group

  14. Experiment 2: Transfer Size • Purpose: to study impact of HTTP response size • Design: • Number of Clients: 1 • HTTP transaction rate: 10 req/sec (fixed) • HTTP transfer size (KB): 1, 2, 4, 8, … • Persistent connections: no • Transmit power: 100 mW • Client-server distance: 1 meter (on same desk) TeleSim Research Group

  15. Measurement at Network Layer General observation: as HTTP transfer size increases, mean TCP connection duration increases, as does the variance of distribution. TeleSim Research Group

  16. Light load: 8 KB Duration: 24 msec Throughput: 2.8 Mbps Overload: 64 KB Duration: >100 msec Throughput: 4.1 Mbps Medium load: 32 KB Duration: 67 msec Throughput: 3.9 Mbps Measurement at Network Layer TeleSim Research Group

  17. Experiment 3: Number of Clients • Purpose: to study impact of high load generated by • multiple clients • Design: • Number of Clients: 2, 3, 4 • HTTP transaction rate: 10, 20, …, 160 req/sec • HTTP transfer size: 1 KB (fixed) • Persistent connections: no • Transmit power: 100 mW • Client-server distance: 1 meter (on same desk) TeleSim Research Group

  18. Wireless Web Performance at Application Layer (4 Clients)

  19. Wireless Web Performance at Application Layer (4 Clients) • Main observation: • 4 clients share network and server resources equally • 30% higher aggregate throughput (110 conns/sec) • bottleneck is now at server network card (drops!!) TeleSim Research Group

  20. Wireless Web Performance at Application Layer (2 or 3 Clients) TeleSim Research Group

  21. Wireless Web Performance at Application Layer (2 or 3 Clients) Main observation: unfairness problem at high loads: one client obtained a higher proportion of the throughput at expense of another (don’t know why?) TeleSim Research Group

  22. Experiment 4: Persistent Connections • Persistent Connections: • Multiple HTTP transactions can be sent on the • same TCP connection. • amortize overhead of TCP connection processing • reduce memory consumption for TCP state • Purpose of this experiment: to study impact of • persistent connection on wireless Web performance • Design: • Number of Clients: 1 and 2 • HTTP transaction rate: 10 req/sec (fixed) • HTTP transfer size: 1 KB (fixed) • Persistent connections: yes • Transmit power: 100 mW • Client-server distance: 1 meter (on same desk) TeleSim Research Group

  23. Achieved Throughput for Experiment with Persistent Connections • Main observation: • Peak throughput: 3.22 Mbps, 3.5x improvement • over non-persistent connections (0.9 Mbps), • two clients share the server and network resources • equally TeleSim Research Group

  24. Experiment 5: Transmit Power • Energy consumption- an important issue for mobile • Clients and Server. • Purpose: to see what transmit power is required for • acceptable performance in classroom setting • Design: • Number of Clients: 1 • HTTP transaction rate: 10 req/sec (fixed) • HTTP transfer size: 1 KB (fixed) • Persistent connections: no • Transmit power: 1, 5, 20, 100 mW • Client-server distance: 10 meter (same floor) TeleSim Research Group

  25. Measurement at Network Layer • General observation: • If transmit power<10 mW: • MAC-layer retransmits • rightward skew • unacceptable perf. • If transmit power20 mW: • acceptable performance TeleSim Research Group

  26. Experiment 6: Wireless Channel Characteristics • Wireless Internet is characterized by limited • bandwidth, high error rates, and interference. • Purpose: to study the impact of the wireless channel • characteristics on wireless Web performance • Design: • Number of Clients: 1 • HTTP transaction rate: 10 req/sec (fixed) • HTTP transfer size: 1 KB (fixed) • Persistent connection: no • Transmit power: 100 mW • Client-server distance: 1m, 10m, 100m TeleSim Research Group

  27. Measurement at Network Layer (100m scenario) Low load: 10 req/sec Significant skew to the tail of the distribution, Some periodicity (why?) Medium load: 50 req/sec Significant skew to the tail of the distribution TeleSim Research Group

  28. 6. Summary and Conclusions • What we did: wireless Web server, portable nw • Application-layer measurements (httperf) • Network-layer measurements (Wireless Sniffer) • Our results show: • Server capability:100 conn/sec for non-persistent • HTTP with throughputs up to 4 Mbps (adequate?) • Bottleneck: at wireless network interface • Some “network thrashing” for large HTTP transfers • when the network utilization is high (aborts, resets) • Effect of wireless channel on performance at • TCP and HTTP-level (MAC-layer retransmits) • Power consumption issue for mobile client and server TeleSim Research Group

  29. 7. Future Work • Explaining the anomalies (fairness, periodicity) • Better system instrumentation (Linux) • More realistic Web workloads • Larger WLAN testing (classroom scenario) • Repeat experiments with IEEE 802.11a (55 Mbps) • Kenny’s M.Sc. Thesis... • Another paper? TeleSim Research Group

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