We know Silverlight needs a limit range of Port number 4502 ~ 4534, and Port 943 for security policy.
But in Silverlight 4, the security policy file can be downloaded via either TCP port 943 or HTTP (port 80);
so here we found 2 great samples for using port 943 and not using port 943:
1: In this page, check the last 2 links: Pushing Data to a Silverlight Client with Socket I and II, this is for using Port 943;
2: Silverlight 4: Silverlight 4 RC – Socket Security Changes