Introduction to HTTP2
- 1. HTTP/2 Sudarshan Pant Mokpo National University
- 2. History of HTTP HTTP/0.9 1991 HTTP/1.0 HTTP/1.1 1996 1999 HTTP/2 2015
- 3. Limitations of HTTP/1.1 Simple and text based. Concurrent Connection Limit Head-of-line blocking Unable to use TCP at it’s full capability Latency
- 4. Limitations of HTTP/1.1 HTTP/1.1 RFC states that there should be only 2 concurrent connections per server/proxy. Maximum Concurrent connections supported by browsers: Chrome: 6 IE: 8 Firefox: 6 Opera: 6 Safari: 4
- 5. Optimization with HTTP/1.1 ■ HTTP/1.1 defines Pipelining but most Browsers do not implement it. ■ Pipelining -> Multiple requests can be sent concurrently but still the responses are sent in the same order as the requests are made. PIPELINING
- 6. Optimization with HTTP/1.1 ■ Use multiple sub-domains to get more connections ■ For example : sub-1.example.com, sub-2.example.com, sub-3.example.com etc. ■ Complicates architecture DOMAIN SHARDING
- 7. Optimization with HTTP/1.1 ■ Combine resources into a single larger resource ■ Example, bundling of CSS and javascript,use of image sprites. ■ Inlining:Requests are reduced by using inline styles in HTML instead of writing in separate files. CONCATENATION AND INLINING
- 8. More problems… ■ Complexity in Web design and maintenance increases. ■ Increased resource consumption. ■ Reduces cacheability of resources. ■ Duplicate resources
- 9. SPDY ■ Experimental protocol, developed at Google and announced in mid-2009 with goals. - Target a 50% reduction in page load time(PLT) - Avoid the need for any changes to content by website authors. - Minimize deployment complexity. - Avoid change in network infrastructure - Implement in partnership with open-source community.
- 10. SPDY Make more efficient use of the underlying TCP connection by introducing a new binary framing layer to enable request and response multiplexing, prioritization, and header compression.
- 11. HTTP and SPDY evolution HTTP/0.9 1991 HTTP/1.0 HTTP/1.1 1996 1999 HTTP/2 Approved 2015 SPDY Implemented 2012 End of SPDY 2016 ■ July 2012 – development of SPDY announced publicly by group of developers at Google. ■ All Major browsers started implementing SPDY which started in the path of standardization. ■ February 2015, Google announced removal of support for SPDY ■ February 2016, Google announced that Chrome will no longer support SPDY after May 15, 2016 HTTP/2 first draft 2012 SPIDY Development 2009
- 12. Beginning of HTTP/2.0 ■ March 2012 : Call for Proposal for HTTP/2 ■ November 2012: First Draft of HTTP/2 (Based on SPDY) ■ August 2014: HTTP/2 draft-17 and HPACL draft-12 are published ■ February2015: IESG approved HTTP/2 and HPACK drafts ■ May 2015: RFC 7540 (HTTP/2) and RFC 7541 (HPACK) are published.
- 13. New in HTTP/2 ■ Reduce latency by introducing Header Field Compression ■ Allow multiple concurrent exchanges on the same connection. ■ Server Push
- 14. Protocol Overview Supports all core features of HTTP/1.1 ■ HTTP/2 uses the same “http” and “https” URI schemes as HTTP/1.1 ■ HTTP/2 uses same default port numbers as HTTP/1.1 (80 for http and 443 for https) ■ HTTP Semantics, such as verbs, methods, and headers are unaffected.
- 15. Binary Framing Layer HTTP 1.1 POST /upload HTTP/1.1 Host: www.example.com Content-Type: application/json Content-Length:15 {“msg”:”hello”} DATA frame HEADERS frame
- 16. Streams, messages and frames •Stream: A bidirectional flow of bytes within an established connection, which may carry one or more messages. •Message: A complete sequence of frames that map to a logical request or response message. •Frame: The smallest unit of communication in HTTP/2, each containing a frame header, which at a minimum identifies the stream to which the frame belongs.
- 17. Connection
- 18. Request and Response Multiplexing HTTP/2.2 enables full multiplexing by allowing the client and server to break down HTTP messages into independent frames, interleave them and them reassemble them on the other end. https://developers.google.com/web/fundamentals/performance/http2/
- 19. Stream prioritization • Each stream may be assigned an integer weight between 1-256 • Each stream may be given an explicit dependency on another stream. https://developers.google.com/web/fundamentals/performance/http2/
- 20. One connection per origin • No Longer needs multiple connections • Single connection is established between client and server and multiple streams are exchanged between them. • Reduces the memory and processing footprint along the full connection path. • Reduces Network latency.
- 21. Flow control • A mechanism to prevent the sender from overwhelming the receiver with data • Each receiver may choose to set any window size that it desires for each stream and the entire connection. • Window size is defined in SETTINGS frame when connection is established • Default size is 65,535 bytes. Max is (2^31 -1) bytes • Can be maintained using WINDOW_UPDATE frame.
- 22. Server Push • In addition to the response to the original request, the server can push additional resources to the client, without the client having to request each one explicitly. • Push resources can be: Ø Cached by the client Ø Reused across different pages Ø Multiplexed alongside other resources Ø Prioritized by the server Ø Declined by the client
- 23. Server Push Image Source: https://developers.google.com/web/fundamentals/performance/http2/
- 24. Header Compression • HPACK header compression reduces size of HTTP/2 header • Compressed using Huffman encoding, resulting in an average 30% reduction. • Frequently used headers can be encoded as variable length integer, opposed to re-sending the whole header every time. • Faster content delivery due to smaller headers.
- 25. Thank you