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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.
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