Tomasz Janczuk has posted a sample using the HTTP polling duplex binding in Silverlight to build a pub-sub application. The HTTP polling duplex binding uses long polling to provide duplex communication over HTTP. HTTP long polling is a decently resilient and standards compliant duplex technique that uses much less bandwidth compared to traditional periodic polling while achieving much lower latency. We’ve actually had HTTP long polling in Silverlight for a while but Silverlight 3 is the first release with a decent client and proxy programming model for duplex communication, making the binding now much more usable. The corresponding server piece runs on the ordinary framework install rather than Silverlight but comes in the Silverlight SDK.