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Stéphane Boyera, Luc Ottavj

W3C-LA Web Mirroring Activity. Stéphane Boyera, Luc Ottavj. Plan. Web Mirroring Keywords Underlying Problems of Mirroring Experimental Protocol Hardware Software Results Conclusion. Web Mirroring Keywords. Transparency for the user Homogeneity between mirrors Independence

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Stéphane Boyera, Luc Ottavj

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  1. W3C-LA Web Mirroring Activity Stéphane Boyera, Luc Ottavj Stéphane Boyera, Luc Ottavj

  2. Plan • Web Mirroring Keywords • Underlying Problems of Mirroring • Experimental Protocol • Hardware • Software • Results • Conclusion Stéphane Boyera, Luc Ottavj

  3. Web Mirroring Keywords • Transparency for the user • Homogeneity between mirrors • Independence • Fault Tolerance and flexibility Stéphane Boyera, Luc Ottavj

  4. Underlying Problems of Mirroring • Building the package to send • Defining the periodicity of update • Broadcasting the update • Recovering local or global failures Stéphane Boyera, Luc Ottavj

  5. Periodicity of updates • True Real Time : • Initiative of mirroring given to the user • Simulated Real Time : • Initiative to the system • Short periodicity : ~30mn - 1 hour • Differed mirroring : • Initiative to the system • Periodicity : ~daily Stéphane Boyera, Luc Ottavj

  6. How is an update processed ? • Classical mirroring systems : rdist, ftp, … • A master server contact each mirror one by one • Drawbacks : the more numerous the mirrors the more decreased the perf. of the overall system • Reliable Multicast technology • Advantage : not affected by the number of mirrors • Drawbacks : no standard available but products Stéphane Boyera, Luc Ottavj

  7. The Underlying Network • Internet : actually not reliable • Satellite transmission : • Dedicated Bandwidth • Private Network • Well fitted for the multicast technology • Covering the whole continent Stéphane Boyera, Luc Ottavj

  8. Experimental Protocol • Building of update : endless rough process finding files to broadcast (~20mn) • Periodicity : Simulated Real Time • Broadcast : • using multicast through Internet • using multicast through Satellite • using unicast/TCP through Internet Stéphane Boyera, Luc Ottavj

  9. Hardware • On the Master Site (Sophia) • One master server housing files and being both multicast sources and unicast server • One Internet Multicast Router • One Satellite Router (Uplink) • On Mirror Sites • One Multicast router for both Internet and Satellite multicast groups • One server receiving the update by the three ways Stéphane Boyera, Luc Ottavj

  10. Software • Unicast / TCP : RSYNC • Free software • Implementing a gdiff algorithm • Multicast : Starburst Communication Mftp product Stéphane Boyera, Luc Ottavj

  11. Results • Period : 02/26/1998 to 05/11/1998 • Effective Working Days : 53 • Measures : 3653 • Transfers : 1218 (0,95 Transfer/hour) • Files : 16284 • Bytes : 0.54 GBytes (W3C site : 1.6 GBytes) • Average Update Size : 442 KBytes Stéphane Boyera, Luc Ottavj

  12. Rsync Results • Time used : 280975 s • Number of failures : 97 / 4872 • Average time to transmit : 231 s • Average Bandwidth : 15.3 Kbits/s Stéphane Boyera, Luc Ottavj

  13. Mftp Internet Results • Time Used : 39620 s • Number of Failures : 692 / 4872 • Average Time to transmit : 33 s • Average Bandwidth : 109 Kbits/s Stéphane Boyera, Luc Ottavj

  14. Mftp Satellite Results • Time Used : 22414 s • Number of Failures : 469 / 4872 • Average Time to transmit : 18 s • Average Bandwidth : 196 Kbits/s Stéphane Boyera, Luc Ottavj

  15. Conclusion • Mftp through Internet : Not Usable • Rsync : Surprisingly good • The most reliable solution • Can fit with the actual need (servers and files change rate) • Not performant • Weak supervision needed • Few Hardware Stéphane Boyera, Luc Ottavj

  16. Conclusion (2) • Mftp + Satellite : not fully operational • High performance • Good Scalability : • if number of servers increases • if traffic of the W3C site increases • if internet connectivity decreased • Accurate supervision needed • Low Reliability : • Operational Vs Experimental Uplink • Hardware problems with Comatlas card • Price ?? Stéphane Boyera, Luc Ottavj

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