3.2.6.3.2 TsProxyMakeTunnelCall (Opnum 3)
The TsProxyMakeTunnelCall method MUST be called with the TSG_TUNNEL_CANCEL_ASYNC_MSG_REQUEST parameter before the TsProxyCloseTunnel method is called if the previous TsProxyMakeTunnelCall has not returned. The TsProxyMakeTunnelCall method has been defined in section 3.2.6.1.3.
The TsProxyCloseTunnel method call uses a serialized context handle. If a previous call to the TsProxyMakeTunnelCall has not returned, then the RDG client cannot call TsProxyCloseTunnel, because of the serialized nature of the context handle.