communicating unmanaged client with managed wcf service

Question

Dear Friends
i want to developed a wcf service which can communicate from Heterogeneous/mixed client ( c++ unmanaged client & c# client) in duplex mode. currently i have tested the wcf duplex services which is working fine between c# server and C# client but unable to communicate from c++ client. i have used http binding with duplex mode for two way communication. can any one please help me out to communicate with my c++ client. its a desktop type application and service is hosted in self hosted mode  
thank in anticipation
regards
shamim