WCF/WF - How to maintain same sessionid in WCF in Silverlight application

HI,

   I create a wcf service for polling, that is binded with PollingDuplexHttpBinding i push the data to client using using Sessionid and Channel in  OperationContract. I want the sessionId and Channel should be same. but when ever a request come to server, immeditly the Sessionid get changed why?. To maintain the same sessionid till i signout what i have to use?. is PollingDuplexHttpBinding binding support to maintain session, because am using Silveright appllication for that wsHttpBinding doesn't support.

try this link
http://forums.silverlight.net/forums/p/16645/319918.aspx