field may be provided in the header supported of the require field for indicating that this call is a test call so that the callee may return a success response message carrying the received call request message to the caller immediately according to the sipdiag in block 102 the callee receives the call request message in block 103 information of require field is obtained from the header of the call request message in block 104 it is determined whether the path information request flag is included in the require field if the path information request flag is included in the require field block 105 is performed otherwise if the path information request flag is not included in the require field block 107 is performed in block 105 the success response message in which the received call request message is included is returned to the caller in the embodiment of the invention the received call request message may be included in the message body of a 2xx message to be sent to the caller so that the caller may obtain the transmission path of the call request message according to this message in block 106 the caller obtains the transmission path of the call request message according to the received success.