53 an sip network server 5 c of wlan home net domain transmits a call to physical sip user agents currently registered as alice wlan home net 53 through forking since there are three sip user agents currently registered as alice wlan home net 52 tel 82421238282 54 alice laptop home1 net 55 and tel 82161231005 57 the call can be respectively transmitted to these three sip user agents in this manner improved personal mobility can be provided while call setup can be carried out only when the communication peer knows the logical sip identifier allocated to the user in the prior art the peer can be provided with an optimal communication state irrespective of the sip network service or terminal the user uses if the peer knows the user 39 s global sip identifier that is his her lifelong number in the present invention fig6 shows an sip request message processing procedure in an sip network server 5 a included in the global domain for providing personal mobility in the sip based multimedia communication system according to an embodiment of the present invention referring to fig6 when the sip network server 5 a included in the global domain receives an sip message from a communication user the sip.