1. 2/24/2000 Network Performance Effects on HTTP/1.1, CSS1, and PNG Luis Rivera Henrik Frystyk Nielsen : W3C James Gettys : DEC Anselm Baird-Smith: W3C

2. 2/24/2000 Luis Rivera Outline Goals HTTP 1.0 vs HTTP 1.1 »Specification »Performance Further improvements »Compression »Web content: CSS, PNB and MNG Conclusions This was two years ago, was about today?

3. 2/24/2000 Luis Rivera Paper Goals Main Goal »Present key performance differences between HTTP/1.1 and HTTP/1.0 »Stress the importance of changes in Web Content Secondary Goals »Expose the performance advantages of a well implemented HTTP/1.1 protocol »Show advantages of CSS, PNG and MNG Did I miss something?

4. 2/24/2000 Luis Rivera Problem? HTTP/1.0 »Not designed for multiple transmissions in the same request »Makes use of multiple TCP connections »Small multiple transmissions are affected by TCP slow start mechanism »Patch: “Keep-Alive” extensions don’t work with multiple proxies »Low support for compression However it is still heavily used !!!

5. 2/24/2000 Luis Rivera Solution? HTTP/1.1 »“Persistent connections” »Data compression »Ranges facilities –Partial retrieval of objects »Cache validation –“poor man’s multiplexing” Design Goals »Increase network use efficiency »Allow reliable use of caching »Improve performance perceived by end user!!!

6. 2/24/2000 Luis Rivera Implementation headaches Testbed »LAN, WAN and PPP »Jigsaw and Apache servers (SPARC platform) »Libwww robot, Netscape and Explorer (Pentium and Alpha platforms) »Microscape! Initial testing »Pipelining: Achieves better efficiency! »Persistent connections: Decreases TCP packets »BUT: Multiple connections outperforms both !!! What went wrong?

7. 2/24/2000 Luis Rivera Pipelining Maintains several outstanding requests on the same connection Tuned to produce as few small headers as possible Requests are buffered »Improves network utilization »Need to be flushed (size threshold, timer) »Flushing can take advantage of the application knowledge! Interfere with Nagle’s algorithm Can you really rely on the application knowledge?

8. 2/24/2000 Luis Rivera Performance Tuned Version Tuned HTTP/1.1 outperforms HTTP/1.0 Buffering »Reduces the number of TCP packets required »Increases packet size Pipelining »Needs to be complemented with buffering Bigger and fewer packets increase server performance!!! Look at performance tables !!!

9. 2/24/2000 Luis Rivera Compression Data, images are already compressed Could help to overcome TCP slow start effects Increases the chances to generate a new batch of request Decreases elapsed time (using zip compression) HTML tags should be lower cased for best compression This is good, but what is the cost of compressing web pages?

10. 2/24/2000 Luis Rivera Web Content Fact »HTML was not born to be used the way it is being used! »However, it has been proved flexible Changes represent »Potential web traffic reduction »Web page development could be easied Style Sheets for web page designers: CSS »Better control of page representation and layout »Saves requests by replacing images in the Unicode char set PNG and MNG for images and animation

11. 2/24/2000 Luis Rivera Conclusions HTTP/1.1+pipelining outperforms HTTP/1.0 Pipelining can significantly improve performance »Must be used with buffering and other tricks to be effective »Specially useful revalidating cached items HTTP/1.1 new techniques saves bandwidth and uses the network more efficiently Such changes could be improved further by changes in web content »For style sheets, images, animations, more?

12. 2/24/2000 Luis Rivera Discussion What about interactions between HTTP/1.1 and a hierarchy of proxy caches Performance improvements are nice but, » Will developers really care if they are achieved though heavy modification of existing technologies? »Are those performance improvements really significant to justify the change? Changes to web content make sense in an ever changing web environment !!!