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Performance Optimizations for Wireless Wide Area Networks - Rajiv Chakravorty

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Performance Optimizations for Wireless Wide Area Networks - Rajiv Chakravorty

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  1. Performance Optimizations for Wireless Wide-Area Networks Rajiv Chakravorty Suman Banerjee Pablo Rodriguez Julian Chesterfield Ian Pratt

  2. Motivation WWAN Links: High/Variable RTT Wireless WAN (“WWAN”) BS Limited Bandwidths Link Outages Burst Losses Internet Web Servers Interference Large and Small-Scale Fading User Load Fluctuations Mobility User Experience in “WWANs” significantly User Experience in “WWANs” significantly different from the relatively stable 802.11 WLAN different from the relatively stable 802.11 WLAN

  3. Why is the Web so Slow? CNN Timeline over GPRS – Mozilla 1.4/HTTP 1.1 No. of TCP Connections ping.nnselect.com www2.cnn.com 216.39.69.0 xx.deploy.akamai xx.deploy.akamai ads.web.aol.com i2.cnn.net i2.cnn.net ads.web.aol.com i2.cnn.net www2.cnn.com Time (sec) CNN Download takes well over 3 mins… CNN Download takes well over 3 mins…

  4. Ask Why sucks? Mobile Web

  5. Three Main Contributions Benchmark— Web Browsers, Protocols and techniques over Wireless WANs  Implement & Study— Range of Optimizations at different layers of the stack and their cross-layer impact on applications  Introduce— A methodology for realistic and repeatable web experiments over WWAN

  6. Cambridge Infrastructure and Testbed

  7. Experimental Methodology We use Virtual web-hosting  Contents of some popular Web-sites change very frequently (e.g. CNN changes in minutes)  We replicate the key components of some popular Internet Web Sites in our Lab (Replicate both Volume and Structure) Virtual Web-hosting allows Web experiments Virtual Web-hosting allows Web experiments to be Repeatable and Reproducible to be Repeatable and Reproducible

  8. Cambridge Open Mobile Virtual Hosting Infrastructure Public Virtual Hosting University of Cambridge Computer Laboratory GPRS Network coms-1.srg.cl.cam.ac.uk 1 BS Altavista Mail Yahoo Go BBC Amazon Aol Sourceforge Fortunecity Cnn 2 CGSN IPSec VPN 3 Internet 4 DNS & RADIUS Controlled conditions: RSSI: -95dbm to –63dBm BER: 0-4% Client: Stationary ‘3+1’ phone coms-n.srg.cl.cam.ac.uk

  9. Content Selection  Web-sites Ranked in  100hot.com  Choice based on Content “diversity” Web Page No. of Servers Object Count Sum (KB) Avg. (KB) Mail 4 11 37KB 3.3KB Yahoo 6 16 61KB 3.8KB Amazon 3 42 92KB 2.2KB CNN 6 67 187KB 2.8KB “Diversity” = Number of Servers, Object count/size, Content types, volume and their distribution

  10. Performance Benchmarks HTTP 1.1 TCP File TCP T’put (Kbps) Website Sum (KB) HTTP T’put (Kbps) %Dgr. %Dgr. -54% -79% 5KB 18.1 MAIL 37KB 8.5 -25% -66% 50KB 29.7 YAHOO 69KB 13.8 -23% -25% -75% 100KB 30.5 AMAZON 92KB 9.6 -81% 200KB 29.9 CNN 187KB 7.6 When TCP tuned to work relatively well, why is the performance of HTTP 1.1 worse?

  11. Factoring (Under) Performance Payload DNS 196.3 TCP SS/3W Other underutilization Latency % 35.0 76.4 34.5 mail yahoo amazon cnn Payload and default HTTP 1.1 behavior Payload and default HTTP 1.1 behavior impacts web downloads over WWANs impacts web downloads over WWANs

  12. Multi-layer Optimizations  HTTP Pipelining  Content Compression  Caching/Delta Encoding Application Layer  Optimizing Browser Conn.  DNS/URL-Rewriting  Server-side `Parse-n-Push’ Session Layer Transport Layer  Link-adapted TCP Variant  Custom Transport Protocol Link Layer  Dynamic FECs (trace-driven simulations) MAR Client

  13. Proxy-based Optimizations Client Proxy (Optional) Server Proxy Server Proxy Push Push Streaming Streaming.. Client Proxy HTTP HTTP FTP… FTP App Layer Application Layer Session Layer Transport Lyr. Session Layer Transport Layer Link-Layer Web Servers Link Layer BS GGSN Internet No Proxy Mode No Proxy Mode Transparent Proxy Mode Transparent Proxy Mode Dual-Proxy Mode Dual-Proxy Mode

  14. Compression Gains Website Mail Yahoo Amazon Cnn Compression % Improvement 59% 18% 59% 41% 57% 18% 52% 12% Yahoo provides the best improvements through compression whereas CNN the least. CNN CDF Yahoo  Yahoo offers the best compression per image object size. More than 60% CNN's images objects less than 1KB size Object Sizes Compression Gains depends largely on Compression Gains depends largely on the content characteristics of websites the content characteristics of websites

  15. Tuning Browser Performance Download Latency (Normalized) HTTP-Opt. – Use of 6 TCP connections mail yahoo cnn amazon Number of Connections Optimal Connection Setting in Browsers Optimal Connection Setting in Browsers improves performance by 25 - 45% improves performance by 25 - 45%

  16. HTTP Pipelining GET 1 GET 2 Pipelined HTTP GET(s) GET 3 1 2 Response (Coalescing) 3 Website Mail Yahoo Amazon Cnn HTTP-opt. 38% 31% 43% 37% HTTP-pipe 56% 35% 49% 55% HTTP Pipelining improves utilization with HTTP Pipelining improves utilization with 5 - 20% additional gain over HTTP-opt. 5 - 20% additional gain over HTTP-opt.

  17. CHK-based Caching Improves client cache hit rates, reduces redundant data transfers and optimizes bandwidth requirements Client Proxy Server Proxy Cache objects with SHA-1 fingerprint (CHK)  URL-to-CHK mapping (offers “alias” protection) GPRS  Deltas - Send “updates” as the difference Client Cache Server Cache Caching and delta-encoding improves perf. Caching and delta-encoding improves perf. By 5 - 9% depending on the web-site By 5 - 9% depending on the web-site

  18. URL-Rewriting URL-Rewriting http://URL1  http://IP1 http://URL2  http://IP1 http://URL3  http://IP2 … IP1 = x.y.z.a IP2= x.y.z.b IP1 IP2 Internet Web Servers Proxy Cluster URL/DNS-Rewriting eliminates DNS lookups URL/DNS-Rewriting eliminates DNS lookups to provide 5 - 9% additional gain to provide 5 - 9% additional gain

  19. Transport Layer Solutions Custom Transport (UDP-GPRS) Link-Adapted TCP (TCP-WWAN) No slow-start  No TCP Transaction Cost  Credit-based Flow Control  Messages-based Protocol  NACK-based Selective Repeat for recovery No TCP slow-start  Prevent Spurious Timeouts  Enhanced Recovery  Avoid Excess Queuing Optimized Transport solutions provide further Optimized Transport solutions provide further improvements (5-14%) in performance improvements (5-14%) in performance

  20. Link Layer Optimizations GPRS supports four FEC schemes (CS1-CS4)  Most GPRS networks support static CS-2  Trace-driven Evaluation to examine how Dynamic FECs benefit Application Performance We use link-layer traces where we can infer slots received in error within RLC blocks

  21. Dynamic Link-layer FEC Impact of dynamic Link FECs on Download Latency Latency (Normalized) FEC% For a given channel condition there is an For a given channel condition there is an optimal value of FEC that minimizes latency optimal value of FEC that minimizes latency

  22. Summary of Optimizations (1) Full Compression + HTTP-opt + DNS-Rewriting + TCP-WWAN + Dynamic FECs 69% 63% Relative Contribution 53% 57% amazon yahoo mail cnn App and Session Layer Optimizations App and Session Layer Optimizations Dominate Performance Benefits (48-61%) Dominate Performance Benefits (48-61%)

  23. Summary of Optimizations (2) Transparent Proxy Opt. Dual-Proxy Opt. Website (Virtual) HTTP-Opt. (No reconf-I) HTTP-Pipelining (No reconf.-II) Client-reconf. (dual-proxy) Lat.(s) %Impr. Lat.(s) %Impr. Lat.(s) %Impr. Mail 15.7 54% 13.2 62% 12.4 64% Yahoo 11.6 67% 11.4 68% 9.9 72% Amazon 30.8 60% 27.4 64% 24.3 68% CNN 96.2 51% 65.1 67% 59.3 69% Dual-Proxy Solution provides Dual-Proxy Solution provides additional (5-18%) performance benefits additional (5-18%) performance benefits

  24. Main Observations Severe Mismatch in the performance of Default HTTP and TCP in WWANs  Standard web-browsers fail to utilize the meagre resources of WWAN links  Significant benefits can be realized from session and application layer optimizations  Proxy-based solutions are most effective in improving performance for mobile end-users

  25. Implications for 3G Links Should we expect similar benefits for 3G? Network Web CNN Page (Avg. T’put) FTP 200KB %Dgr. (Avg. T’put) GPRS 7.6 Kbps 29.9 Kbps -75% 3G-1X 35 Kbps 91 Kbps -61% 3G-UMTS 62 Kbps 178 Kbps -65% TCP and HTTP mismatch seen even TCP and HTTP mismatch seen even in CDMA 3G-1X and UMTS 3G in CDMA 3G-1X and UMTS 3G

  26. Wired dial-ups Links Are WWAN a special case of low-bandwidth high-latency links e.g. dial-ups? Web CNN Page (Avg.T’put) Network FTP 200KB (Avg.T’put) %Dgr. GPRS 7.6 Kbps 29.9 Kbps -75% Dial-up V.90 38.5 Kbps 45.8 Kbps -19% No noticeable mismatch in wired dial-ups No noticeable mismatch in wired dial-ups

  27. Virtual Web-hosting, Tools, Source Code, traces: http://www.cl.cam.ac.uk/users/rc277/wwan.html Q?

  28. Impact of Web Server FIN’ing 145 HTTP 1.0 HTTP 1.1 Nos. of TCP Connections s’forge fortune cnn aol bbc go mail yahoo amazon Altavista Benefits of HTTP 1.1 not realized due Benefits of HTTP 1.1 not realized due to explicit Web Server FIN’ing to explicit Web Server FIN’ing

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