For the client, the context handle specifies the state within a server, and also contains binding information. If an operation has an input context handle or input/output context handle that is not NULL, it is not necessary to supply any other binding information. A context handle that has only the in attribute cannot be NULL. If an operation has in,out context handle parameters but no in context handle parameters, at least one of the in,out context handle parameters cannot be NULL. However, if the only context handle parameters in an operation are output, they carry no binding information. In this case, you must use another method to bind the client to a server.
If you specify multiple context handles in an operation, all active context handles must map to the same remote address space on the same server or the call fails. (A context handle is active while it represents context information that the server maintains for the client. It is inactive if no context has yet been created, or if the context is no longer in use.)