A Session Initiation Protocol, briefly SIP, based session setup method in a session setup process performed between terminals in a SIP based network which includes at least one or more of the terminals (UE#1; UE#2) and at least one or more network entities (P-CSCF#1, S-CSCF#1; P-CSCF#2, S-CSCF#2), the method comprising: receiving, by a terminating terminal (UE#2), a SIP INVITE message sent from an originating terminal (UE#1), which requests establishment of a session for an Internet Protocol Multimedia Subsystem service with the terminating terminal (UE#2), via at least one or more network entities (P-CSCF#1, S-CSCF#1, S-CSCF#2, P-CSCF#2), the SIP INVITE message including capability information, the capability information including at least one or more media formats that are preferred by the originating terminal (UE#1); analyzing, by the terminating terminal (UE#2), the capability information within the SIP INVITE message; determining, by the terminating terminal (UE#2), a service condition based on the analyzed capability information, the service condition indicating capability information preferred by the terminating terminal (UE#2) or capability information supported by the terminating terminal (UE#2), wherein the service condition includes a media format not included in the analyzed capability information and the step of determining the service condition further comprises: if the terminating terminal accepts at least one capability from the analyzed capability information, selecting capabilities which the terminating terminal (UE#2) prefers or can support from the analyzed capability information; and including the service condition and the selected capabilities in a SIP RESPONSE message; and if the terminating terminal rejects every capability from the analyzed capability information, including the service condition in a SIP RESPONSE message; sending (S704, S705), by the terminating terminal (UE#2), the SIP RESPONSE message to the originating terminal (UE#1) via at least one or more network entities (P-CSCF#2, S-CSCF#2, S-CSCF#1, P-CSCF#1); receiving, by the originating terminal (UE#1), the SIP RESPONSE message; analyzing, by the originating terminal (UE#1), the SIP RESPONSE message; composing a SIP RE-INVITE message by the originating terminal (UE#1) based upon the analysis; and sending, by the originating terminal (UE#1), the SIP RE-INVITE message to the terminating terminal (UE#2), wherein the SIP RE-INVITE message includes the service condition. receiving, by a terminating terminal (UE#2), a SIP INVITE message sent from an originating terminal (UE#1), which requests establishment of a session for an Internet Protocol Multimedia Subsystem service with the terminating terminal (UE#2), via at least one or more network entities (P-CSCF#1, S-CSCF#1, S-CSCF#2, P-CSCF#2), the SIP INVITE message including capability information, the capability information including at least one or more media formats that are preferred by the originating terminal (UE#1); analyzing, by the terminating terminal (UE#2), the capability information within the SIP INVITE message; determining, by the terminating terminal (UE#2), a service condition based on the analyzed capability information, the service condition indicating capability information preferred by the terminating terminal (UE#2) or capability information supported by the terminating terminal (UE#2), wherein the service condition includes a media format not included in the analyzed capability information and the step of determining the service condition further comprises: if the terminating terminal if the terminating terminal accepts at least one capability from the analyzed capability information, selecting capabilities which the terminating terminal (UE#2) prefers or can support from the analyzed capability information; and including the service condition and the selected capabilities in a SIP RESPONSE message; and if the terminating terminal selecting capabilities which the terminating terminal (UE#2) prefers or can support from the analyzed capability information; and including the service condition and the selected capabilities in a SIP RESPONSE message; and rejects every capability from the analyzed capability information, including the service condition in a SIP RESPONSE message; sending (S704, S705), by the terminating terminal (UE#2), the SIP RESPONSE message to the originating terminal (UE#1) via at least one or more network entities (P-CSCF#2, S-CSCF#2, S-CSCF#1, P-CSCF#1); receiving, by the originating terminal (UE#1), the SIP RESPONSE message; analyzing, by the originating terminal (UE#1), the SIP RESPONSE message; composing a SIP RE-INVITE message by the originating terminal (UE#1) based upon the analysis; and sending, by the originating terminal (UE#1), the SIP RE-INVITE message to the terminating terminal (UE#2), wherein the SIP RE-INVITE message includes the service condition.