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Article http over transport protocols

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Article   http over transport protocols Article http over transport protocols Presentation Transcript

  • Modeling the Performance of HTTP Over Several Transport Protocols
  • Modeling the Performance of HTTP Over Several Transport Protocols● Persistent-Connection HTTP● Transaction TCP● UDP-Based Request–Response Protocols
  • 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.
  • Modeling the Performance of HTTP Over Several Transport Protocols● Persistent-Connection HTTP
  • 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
  • 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
  • Modeling the Performance of HTTP Over Several Transport Protocols Network Model
  • Modeling the Performance of HTTP Over Several Transport Protocols
  • 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.
  • 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.
  • Modeling the Performance of HTTP Over Several Transport Protocols● Minimum Transit Times
  • 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:
  • Modeling the Performance of HTTP Over Several Transport Protocols Simple Model
  • Modeling the Performance of HTTP Over Several Transport Protocols● HTTP over TCP ● TCP slow start ● Performance and Discussion
  • Modeling the Performance of HTTP Over Several Transport Protocols TCP slow start
  • Modeling the Performance of HTTP Over Several Transport Protocolshttp://user.it.uu.se/~carle/Notes/43_TCP.html
  • Modeling the Performance of HTTP Over Several Transport Protocols● Performance & Discussion Cost of accessing an object via HTTP over TCP
  • Modeling the Performance of HTTP Over Several Transport Protocols● HTTP Over TCP with Connection Caching 1 2 3
  • 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.
  • Modeling the Performance of HTTP Over Several Transport Protocols● HTTP Over UDP-Based Protocols Time to complete a HTTP transaction over ARDP
  • 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
  • Modeling the Performance of HTTP Over Several Transport Protocols● Validation ● Methodology ● Slow Start Validation ● Model Adjustments ● Server processing time ● Request independence ● Inexact Bandwidth
  • 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
  • TCP Overhead
  • Connection-caching protocols
  • Modeling the Performance of HTTP Over Several Transport Protocols End