My WCF client and server exchange objects whose types are defined on a class library shared by both, the server and the client. These objects implement custom serialization via ISerializable. However, my custom serialization is not being used. DataContractSerializer is being used, instead. How do I force my custom serialization to be used?

The reason why I need to use my own serialization is because I do trasfer some big object graphs and my serialization algorithm does a good job in compressing/speeding up things.