Connection Time out occured while invoking the web service in webMethods 6.5 version

Hi Guys, Our servers are in the DMZ zone. We created the web service in the Back end system (back-end server). And share to the client system. In the front end server, creating the native port in https and for invoking the client systems and the request is reaches to the back end system. The native port set as allow by default and access mode is put as by normal configurations. Here the problem is while invoking to the front end server (https://ipaddressoffrontendsystem:port/soap/rpc ). It is give error like, connection time out. The client application is in different system and our webMethods are location in the different Unix box. For debugging to this issue, what needs to be done? Could you please give me some idea, how any client application invokes the web service in another UNIX box? How this connectivity will occur at run time? How to verify the connectivity between the two boxes. The client application getting the time-out error. How to trace this request at network level? While we using the SOAP-UI simulator, the backend server web service is invoking successfully. While using the ip address of the back end systems. Could you please help me how to verify the above scenario? Thanks in Advance!! Regards, Srini