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For my presentation I put together an application that highlights some of the coolest web services features available in Silverlight 4 Beta. The app is intended to be used by travel agents and helps with their day-to-day work: it displays (fake) real-time price information for flight tickets, it can pull up real-time information about the status of a flight, it supports a chat feature so travel agents can talk to each other, and it supports sharing a set of tasks from Sharepoint.

As you may know, when accessing any service located in a domain different from the one in which the Silverlight application itself is hosted, Silverlight will check for a cross domain file being in place. Cross-domain policies prevent Silverlight applications to connect with services that are not in the same domain. However, a service can opt-in to be connected to if at the root of the domain, a cross-domain policy file has been deployed. Silverlight will check for its existence (the file should be named clientaccesspolicy.xml or crossdomain.xml, which is the cross-domain file of Flash) and if found, Silverlight will connect in a cross-domain manner.

Jeff Prosise examines one of the most useful but yet little-known new features of Silverlight 3 - the client networking stack.

In Silverlight 3, networking is still performed using the browser’s HTTP stack by default. But the new client stack allows you to bypass the browser and do your networking through the operating system. The table below lists important differences between the browser stack and the client stack. With the client stack, for example, SOAP faults can be handled properly since the operating system doesn't alter HTTP response codes. And with the client stack, you can use additional HTTP commands such as PUT and DELETE because while browsers may not expose that capability, operating systems do.

In this article Andrea Boschin demonstrates how to avoid flooding in a Polling Duplex Service.

Returning on the PollingDuplex argument, today I would like to illustrate a tecnique I used to avoid the flooding in my Polling Duplex service. The problem come from the fact that my server retain a list of connected clients and is unable to detect the disconnection in a short time. After a while the notification from the server to the disconnected client will timeout so the server handle the timeout and remove the client from its list. But if for some reason a client Register itself multiple times the server notification list will grow and this may become a problem causing the service to slow down its response time.

This web application has a desktop, a taskbar with notification icons and a start menu, floating windows that can be resized, maximized, or minimized. It resembles a client OS and takes advantage of the new Silverlight 3 Out-Of-Browser and Networking APIs.

Mike Ormond has posted the demos for Part 2 of the “Catching Up on Rich Clients” - Slide Overview, DLR Console, Networking and Data, and three demos about Deep Zoom.