Automated Techniques for Distributing up-to-date Content

P. Rodriguez



We    introduce SPREAD -    a  new scalable  architecture for  distributing up-to-date Web    content   that simultaneously  employs    three different mechanisms: client validation, server invalidation, and replication.

SPREAD   is built using  a network  of  Layer-4  proxies that self-configure themselves to form scalable distribution hierarchies that connect the origin servers of content providers to clients. Proxies within SPREAD locally decide the best technique to  keep  documents up-to-date  (client-validation,  replication, or server-invalidation) based on  the  document's popularity  and   modification frequency. Requests  and subscriptions  propagate from edge proxies  to the origin server through a chain of intermediate proxies. Invalidations and replications travel in the opposite direction. SPREAD's network  of proxies automatically reconfigures when proxies go down or come up, or when new ones are added.

The  ability to spontaneously   form caching hierarchies is   based  on a  modified Transparent Proxying mechanism, called Translucent Proxying, that sanitizes Transparent  Proxying. Current day  transparent proxies require all packets of  a proxied TCP  connection to go  through them.  Since routes may change during  a  connection, their   use  is  limited  to  the access   points of single-homed clients  and    networks.  Translucent  proxying is   a   more sophisticated proxying mechanism that does not suffer from this limitation, and therefore allows proxies to be placed anywhere in the network.

[P. Rodriguez]