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SPDY protocol

Explore the experimental SPDY protocol by Google for efficient web content delivery with minimal latency. Learn about its features, benefits, and innovative functionalities like server push and hints. Discover how SPDY enhances the traditional HTTP protocol and speeds up webpage loading times.

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SPDY protocol

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  1. SPDY protocol By Jory Cohen Made for CISC856, Spring 2010 Thanks to Dr. Amer, Mike Belshe(Google), Jon Leighton

  2. What is SPDY? • Experimental protocol being researched by Google and the UD PEL • Application-layer protocol for transporting content over the web, designed specifically for minimal latency

  3. Why SPDY? • HTTP is inefficient • Single request per connection • Browsers now open 6connections per domain for concurrency • Only clients can initiate requests • Header size – 200 bytes to over 2 KB • Redundant headers • Optional data compression

  4. What does SPDY offer? • Multiplexed requests • No limit to number of requests over SPDY connection • Prioritized requests • Compressed headers and data • Server push and server hint • Only changes way data is written to network • SPDY keeps cookies, encoding negotiations, etc. same as HTTP

  5. Which layer is SPDY?

  6. Some SPDY features • Streams can be bi-directional • SPDY allows for unlimited concurrent streams over a single TCP connection • Fewer network connections need to be made, and fewer, but more densely packed, packets are issued

  7. SPDY benefits • The client can request as many items as the clientwants from the server, and assign a priority to each request • SPDY compresses request and response HTTP headers, resulting in fewer TCP PDUs and fewer bytes transmitted

  8. Server Push • Server pushes to the client before something is requested • Valuable for visiting a webpage, server knows everything that should be requested • Reduces the client’s processing time before being able to send out subsequent requests • Server must open multiple streams

  9. Server Push Example Client Server Stream 1 HTTP Get request Response for HTTP Get Stream 1 Server push Stream 2 Server push Stream 4 Server push Stream 6 Server push Stream 8

  10. Server hint • Server tells client that itwill probably ask for certain resources • Client can request resources due to server hint much faster than without • Client can also make decision to ignore hint given by the server • Has similar benefit to server push, reduces processing time necessary at client before new requests are sent to the server

  11. Server Hint Example Client Server HTTP Get request Stream 1 Response for HTTP Get Stream 1 Server hints to client Stream 2 Client request based on hint Stream 3 Client request based on hint Stream 5 Client request based on hint Stream 7 Client request based on hint Stream 9 Server responses Streams 3,5,7,9

  12. Stream IDs and connections • Connections started by the client must be odd • Connections started by the server must be even • Stream number 99 can be initiated before stream number 2 • No steam ID of 0 • Stream must be set to be unidirectional in SYN_STREAM, default would be bi-directional

  13. Example • Client sends SYN_STREAM to open connection • Client can begin sending data or requests for data without waiting for response • After client is done sending, clientsets the FLAG_FIN flag and connection is half closed

  14. Client Server Stream ID = 1 SYN_STREAM Data or Requests Stream ID = 3 SYN_STREAM Data or Requests SYN_STREAM Stream ID = 2 Data or Requests Stream ID = 1 SYN_REPLY SYN_REPLY Stream 3 & Data Stream 1

  15. Connection termination • Normal termination • Both sides have sent FLAG_FIN • Abrupt termination • One side sends RST_STREAM • TCP connection teardown • Both sides must realize that the connection was abnormally terminated

  16. Client Server Stream 3 Data + FLAG_FIN Data reply for Stream 3 Data reply for Stream 3 Data reply for Stream 3 Data reply for Stream 3 Data reply for Stream 3 + FLAG_FIN

  17. Compression 4244 bytes on wire, 9978 total bytes uncompressed. 42% of bytes without compression. 861 bytes on the wire, 2299 total bytes uncompressed. 37% of bytes without compression.

  18. Interesting SPDY PDUs • NOOP • Receiver does nothing, ignores PDU • PING • Used to test RTT, takes priority over data • GOAWAY • Used for graceful termination • Contains a last good stream number • HEADERS • Used to send additional headers that would not fit in a previous PDU • WINDOW_UPDATE • Used for per stream flow control in SPDY

  19. Interesting SPDY PDUs (cont’d) • SETTINGS • Used to communicate ID/value pairs • Upload bandwidth • Download bandwidth • Round trip time • Maximum concurrent streams • Current CWND • Persistence of previous settings

  20. Download of 25 websites with 1% constant packet loss. Download was run 10 times for each site and average page load time is reported. [1]

  21. Download of 25 websites with 1% constant packet loss. Download was run 10 times for each site and average page load time is reported.[1]

  22. Download of 25 websites with 1% constant packet loss. Download was run 10 times for each site and average page load time is reported.[1]

  23. Google and PEL work • SPDY enabled Chrome browser with Flip-in-mem server • SPDY “plug-in” for wireshark • Use SCTP with SPDY

  24. References • SPDY protocol specification http://www.chromium.org/spdy/spdy-protocol/spdy-protocol-draft2 • SPDY white paper http://www.chromium.org/spdy/spdy-whitepaper [1] • SPDY homepage with other resources http://www.chromium.org/spdy/

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