# Monday, December 29, 2008

I've made a few references to the Silverlight Streaming Service a few times before on my website but I never quite explained what it is before. A lot of people thinks that the Silverlight Streaming service (SLS) is meant for hosting and streaming videos that are delivered via a Silverlight based video player. And thus when people go to the website they're expecting to see something like YouTube or some other video service.

But SLS is NOT JUST for hosting videos, it's meant for hosting Silverlight Applications. With Silverlight, a content creator is able to create rich interactive applications and media experiences which of course can be hosted on their own server of choice. But then, bandwidth issues come into play. Take for examples the various video podcasts/reviews/shows  and deepzoom albums I have on my site. Like any other web content I could have just hosted the files on the server itself. And that would mean that people from around the region would be able to retrieve and view the files very quickly because the server is close to them.

But... what if the viewer was from another geographical region? What if my webhost's network pipe is being throttled or consumed by someone else who is being hosted on the same server network? As an independent developer while I am able to make rich media content, I do not have the ability to host the content on some super fast, globally distributed server network.

And that's where SLS comes into the picture. As I mentioned it's not just meant for videos but entire Silverlight Applications (this includes everything on the client side ie. Your XAP file, any additional resource files, images, sounds, etc. etc. The service is not for hosting backend applications such as ASP.Net)

How SLS works is that first you upload your application files to the service and then you use the HTML tags (typically an iframe) to refer to your application. Then when a browser requests for the application, that's when the magic happens, SLS has a bunch of distribution nodes around the globe, when a request for content comes in the content is blasted via a high speed network into the distribution node closest to where the request is coming from and the content is served from that node.

This technique in theory allows most users to be able to grab the content at an efficient rate since the content will be coming from a server that's closer to the user.

There are 2 problems with this approach though, the first is a minor issue. Because the content is cached in the distribution node, any changes that you might upload (ie, replacing the XAP or an image file) might not be immediately visible to you.

The 2nd problem is much more of a headache that someone realized over at the Silverlight forums. Because the distribution nodes are given unique URLs and identifiers, if you use Isolated Storage in your Silverlight application, it's very likely that everytime a user hits the page, they'll never be able to read back their previous settings.

But other than those 2 problems, I'm happy with SLS. I'm glad that it is able to deliver my video shows on a steady bitrate. Though I do wonder what's the experience like for people outside of our region?


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