DESIRE II Slide 1

Web Replication and Caching Update

Ingrid Melve, UNINETT

http://www.desire.org/

DESIRE II project

DESIRE II Slide 2

Context IETF Web Replication and Caching WREC WG

• http://www.wrec.org/• draft-melve-taxonomy-00.txt

DESIRE II• Web searching• Web caching

DESIRE II Slide 3

Web replication and caching State of web replication and caching Deployed technology, protocols Standard concepts and terminology Replication

• Objects• Services and applications

Caching proxies• Objects

System overview Inter-cache, inter-replica Client-replica, client-proxy Network element to caching proxy

DESIRE II Slide 4

Terminology Cache: transient copies

• Sparse working set cache

Replica: persistent copies• Complete idem-potent set replication

Proxy: intermediary program that acts as both a server and a client

DESIRE II Slide 5

Distributed relationships

DESIRE II Slide 6

Distributed relationships Inter-replica

• Cooperation and communication between replica origin servers

Client to replica• Cooperation and communication between clients (user agents

& proxies) and replica origin server Client to proxy

• Configuration, cooperation and communication between user agents and a caching proxy

Inter-cache• Cooperation and communication between caching proxies

Network element to proxy cache• Cooperating and communication between caching

proxy and network elements.

DESIRE II Slide 7

Inter-Replica Replica origin servers Object replication: SOP

• demand driven• batch driven

Replication of services• CGI-scripts with consistent

performance• Interoperability of server

software

Supplied by information owner

DESIRE II Slide 8

Client to Replica Optimal replica proximity Finding an object Finding the closest copy Finding the right copy Examples

• URL redirection• DNS redirection• URN resolution• FTP mirror tracker

DESIRE II Slide 9

Client to Proxy Finding the Proxy

• Manual configuration• PAC, Proxy Auto-

Configuration script• WPAD, Web Proxy Auto-

Discovery• CARP, Cache Array

Routing Protocol

Caching proxy directives• HTTP/1.1 Cache-control

DESIRE II Slide 10

Inter-proxy communication Query for objects

• ICP, Internet Cache Protocol

• HTCP, HyperText Cache Protocol

Inform about object location in cache mesh• CacheDigest

Load balance• CARP

HTTP/1.1 have extended support for caching proxies

DESIRE II Slide 11

Network element to proxy array Redirection

• SOCKS: firewall (application)

• WCCP, Web Cache Coordination Protocol: router (network/transport)

• Proprietory protocols: switch (network/link)

Transparent redirection: hijacking web traffic

Added functionality• Load balancing • Redundancy• Fallback

DESIRE II Slide 12

Summing up Replication and caching

• Competing technologies• Complementary technlogies

Ongoing work, rapid development Replication is in its infancy Proxy caching is in puberty Proxy caching commercial products available Traffic flow is altered at the application layer Middleware development to be followed