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I was asked to prototype something with the Duplex Polling feature of Silverlight 3 for some new Silverlight applications we're working on for eggheadcafe.com. So, like any good developer, the first thing I did was set out not to have to reinvent the wheel. I found several good examples of duplex on the web, but the one that best suited my needs was the "Duplex End to End Sample". This is a well-written simple chat service that also sends out a fake random stock price update using the "Push to all clients" model.

Many people ask question why polling duplex session shutdown after 10 minutes in spite of polling duplex InactivityTimeout value is more than hour.

In private email Christopher Scrosati (Silverlight WS Team) told me that I've also should configure ReciveTimout.

Alexey Zakharov has a short post in which he shows you one way to increase amount of Silverlight duplex clients.

Amount of silverlight polling duplex clients is defined by MaxConcurrentSessions throttling property. Default value is 10. To increase it you should programmatically add ServiceThrottlingBehavior.

Nigel Sampson is explaining about the use of duplex services in Silverlight.

I'm currently working on a project that requires the use of duplex services to report progress on a long running event (I'll go more into the actual event in a later post). The reference material I started with was "How to: Build a Duplex Service" and "How to: Access a Duplex Service with the Channel Model", building the service itself its a relatively simple affair with a slight learning experience as I hadn't really used the Message class from WCF before.

Note: This article is submitted by Thomas Holloway for Silverlight Contest: Write and Win.Thanks a lot, Thomas! Hello All, Please drop a comment if you like it.

Overview
Alright, so now that we know what a simple messenger looks like with WCF callbacks, what does it take to put one together in Silverlight? For starters, Silverlight does not have the same capabilities as the full WCF framework. WCF callbacks in Silverlight must be done through HTTP Polling and therefore we don’t really have a truly bi-directional environment. Instead, we must manually setup the message asynchronous message architecture with a few special classes in a new System.ServiceModel.PollingDuplex library.

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