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

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

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: FOR MORE INFO...

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: text Delta Main Module imagebinary Delta database manager Sub-Delta modules

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

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

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)

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

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

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

Other resources Delta encoding IETF Internet draft – Delta-encoding research at COMPAQ (Digital) – HTTP 1.1 standard (RFC 2616) –ftp://ftp.isi.edu/in-notes/rfc2616.txtftp://ftp.isi.edu/in-notes/rfc2616.txt Apache server and Squid proxy –