Article http over transport protocols

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Article http over transport protocols

  1. 1. Modeling the Performance of HTTP Over Several Transport Protocols
  2. 2. Modeling the Performance of HTTP Over Several Transport Protocols● Persistent-Connection HTTP● Transaction TCP● UDP-Based Request–Response Protocols
  3. 3. Modeling the Performance of HTTP Over Several Transport Protocols● Persistent-Connection HTTP ● HTTP requests and responses can be pipelined on a connection. ● Latency on subsequent requests is reduced since there is no time spent in TCPs connection opening handshake.
  4. 4. Modeling the Performance of HTTP Over Several Transport Protocols● Persistent-Connection HTTP
  5. 5. Modeling the Performance of HTTP Over Several Transport Protocols● T-TCP (RFC 1644)● The goal of T/TCP is to allow each transaction, i.e., eachrequest/response sequence, to be efficiently performed as asingle incarnation of a TCP connection.● Bypass the 3-way handshake
  6. 6. Modeling the Performance of HTTP Over Several Transport Protocols● ARDP ● ARDP’s main design goal is to provide a reliable yet light- weight communication mechanism to transport requests and responses between clients and servers. ● TCP-style flow-control ● Congestion-avoidance ● Retransmission algorithms ● ● Avoids TCP’s three-way handshake, instead randomly selecting connection identifiers
  7. 7. Modeling the Performance of HTTP Over Several Transport Protocols Network Model
  8. 8. Modeling the Performance of HTTP Over Several Transport Protocols
  9. 9. Modeling the Performance of HTTP Over Several Transport Protocols● Traffic Model ● Small page: Single 5 kB web page. ● Medium page: Single 25 kB web page. ● Large page: Single 100 kB web page. ● Small cluster: Single 6651 B page with embedded 3883 B and 1866 B images. ● Medium cluster: Single 3220 B page with three embedded images, sizes 57613 B, 2344 B, and 14190 B.8 ● Large cluster: Single 100 kB page with 10 embedded 25 kB images.
  10. 10. Modeling the Performance of HTTP Over Several Transport Protocols● Protocol Analysis ● TCP: HTTP currently runs over TCP, opening a new connection for each transaction. ● Connection caching protocols: To avoid connection setup overheads, P-HTTP and T/TCP cache connections or connection information across multiple requests. ● UDP-based request–response protocols: ARDP employs UDP to avoid TCP setup costs.
  11. 11. Modeling the Performance of HTTP Over Several Transport Protocols● Minimum Transit Times
  12. 12. Modeling the Performance of HTTP Over Several Transport Protocols● Minimum Transit Times A series of independent requests will incur only one roundtrip latency because they are pipelined. The total required time will, therefore, be:
  13. 13. Modeling the Performance of HTTP Over Several Transport Protocols Simple Model
  14. 14. Modeling the Performance of HTTP Over Several Transport Protocols● HTTP over TCP ● TCP slow start ● Performance and Discussion
  15. 15. Modeling the Performance of HTTP Over Several Transport Protocols TCP slow start
  16. 16. Modeling the Performance of HTTP Over Several Transport Protocolshttp://user.it.uu.se/~carle/Notes/43_TCP.html
  17. 17. Modeling the Performance of HTTP Over Several Transport Protocols● Performance & Discussion Cost of accessing an object via HTTP over TCP
  18. 18. Modeling the Performance of HTTP Over Several Transport Protocols● HTTP Over TCP with Connection Caching 1 2 3
  19. 19. Modeling the Performance of HTTP Over Several Transport Protocols● HTTP Over Multiple, Concurrent TCP ConnectionsMany web browsers open multiple concurrent connections to mitigateTCP start-up costs (HTTP over parallel connec- tions). We can boundtheir performance by HTTP over TCP with and without connectioncaching. Our HTTP-over-TCP model overestimates transmission timeby not considering parallelism in the concurrent slow-start of eachconnection. HTTP over connection caching underestimatestransmission time by assuming that there is no penalty for slow-startsof later requests in a cluster. A better approximation might be obtainedby treating as if it were , for concurrent connections. Completelyspecifying behavior with multiple parallel connections is an area ofcontinuing work.
  20. 20. Modeling the Performance of HTTP Over Several Transport Protocols● HTTP Over UDP-Based Protocols Time to complete a HTTP transaction over ARDP
  21. 21. Modeling the Performance of HTTP Over Several Transport Protocols● HTTP Over UDP-Based Protocols Total time to complete a series of independent HTTP requests Overhead
  22. 22. Modeling the Performance of HTTP Over Several Transport Protocols● Validation ● Methodology ● Slow Start Validation ● Model Adjustments ● Server processing time ● Request independence ● Inexact Bandwidth
  23. 23. Modeling the Performance of HTTP Over Several Transport Protocols● Protocol Discussion ● HTTP over TCP overhead is fairly low under net- working characteristics today. ● ● TCP overhead becomes significant when the band- width– delay product rises. ● ● A recent technical note by W3C has suggested that pipelining substantially reduces packet counts for persistent- connection HTTP
  24. 24. TCP Overhead
  25. 25. Connection-caching protocols
  26. 26. Modeling the Performance of HTTP Over Several Transport Protocols End

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