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Delta Encoding for HTTP/1.1

This project focuses on delta encoding to optimize HTTP/1.1 communication by reducing network bandwidth usage while maintaining transparency for users. It involves the development of an Apache module and modifications to the Squid proxy. The server retains multiple document versions, updates the database with changes, and the client only receives the differences between document versions. This method results in significant reductions in server load and user wait times. Configurable storage methods and algorithms enhance future scalability. For more details, visit: http://comnet.technion.ac.il/~cn33s00.

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Delta Encoding for HTTP/1.1

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  1. Delta Encoding for HTTP/1.1 Sloutsky Alexander Fink Dmitry Supervised by Lavy Libman d

  2. Project Goals • Reduce network bandwidth • Be transparent to users • Server side: • module for Apache Web Server • Client side: • modification of Squid Proxy

  3. Description • Web Server stores several versions of the same document. • Server updates DB as document changes. • Client indicates what version of document it has. • Only change between versions is sent (delta encoding) Project Home Page: http://comnet.technion.ac.il/~cn33s00 FOR MORE INFO...

  4. Details: Apache Delta module • Highly configurable module: • types of delta encoding per HTTP type • storing method of files in database • depth of database • modularity for future enchanting: Delta Main Module Delta database manager text image binary Sub-Delta modules

  5. Database: Apache Delta module • Main Database structure: • Latest version (LV) of document • Differences of previous versions (PV) to LV • Only differences are stored to save space • Storing method can be configured • Deltas Database: • For each version: • difference between LV and PV

  6. Algorithm: Apache Delta module • Receive HTTP request • If (document was changed since last time) • unpack versions of document • update main database • signal to Sub-Delta module to recalculate all deltas for this document • pack the database • Signal to Sub-delta module to select an appropriate delta

  7. Summary: Apache Delta module • Achievements: • Significantly decreases networking load on server • Reduces the time user waits for document • Payment: • Disk space (depends on database depth) • CPU cycles on document update (rare)

  8. Details: Squid Proxy • Modifying existing product • The change includes: • New field (eTag) is added to every cache entry • Support of new fields and parameters both in request and reply HTTP headers • New HTTP status (226 Delta) and its handler

  9. Algorithm: Squid Proxy • If the requested document resides in cache but needs revalidation, then: • Include Delta information in the outgoing request • If the reply is a Delta (status: 227), then: • Apply the Delta to the cached version • Save the new version and discard the old • Send the latest version to the client

  10. Technologies used • Extension to existing HTTP protocol • Transparent to non-compatible parties • Based on IETF internet draft • draft-mogul-http-delta-04.txt • Makes use of Apache module API • Client’s cache is based on squid caching mechanisms

  11. Other resources • Delta encoding IETF Internet draft • http://www.ietf.org/internet-drafts/draft-mogul-http-delta-04.txt • Delta-encoding research at COMPAQ (Digital) • http://www.research.digital.com/wrl/techreports/abstracts/97.4.html • HTTP 1.1 standard (RFC 2616) • ftp://ftp.isi.edu/in-notes/rfc2616.txt • Apache server and Squid proxy • http://www.apache.orghttp://www.squid-cache.org

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