SCF finds that these do not conform to the service profile, it sends to Alice's UA entity a negative response 488 Not Acceptable Here. The S-CSCF entity retrieves the destination domain name (homeB. net) from Bob's URI and forwards the INVITE request to the entity in charge of the interconnection with the domain (homeB net). 6) The homeB. net domain responds to S-CSCF entity with 100 Trying message that allows for blocking the retransmission timer of the INVITE request. 7) In the response 183 Session Progress, Bob's UA entity gives an SDP response in which it chooses a type of codec from those proposed by Alice's UA entity. Basic Procedures The 183 Session Progress response contains in the header Record Route IP addresses of entities that the subsequent requests must pass through. The 183 Session Progress response also indicates that a resource reservation is also required of Bob's side before establishing a session. a=curr:qos local none a=curr:qos remote none a=des:gos mandatory local sendrecv a=des: qos mandatory remote sendrecv 8) The S-CSCF entity forwards the 183 Session Progress response to the P-CSCF entity. The identity of the P-CSCF entity assigned to Bob's UA entity was learned during the registration (information contained in the Path header). The establishment of a dedicated bearer, assigned to voice, is coupled with the establishment of a default bearer and assigned to telephone signaling. This dedicated bearer is coupled with the default bearer assigned to telephone signaling, in that the bearer terminations are the same for both types of bearer. The establishment of the dedicated bearer is triggered by the P-CSCF entity from the analysis of telephone signaling exchanged between the terminals that want to establish a telephone call. 9) The P-CSCF entity sends to the PCRF entity the DIAMETER AAR (authenticate and authorize request) message to verify that the media settings are authorized by the EPS network and to trigger the establishment of dedicated bearer. 10) The PCRF entity consults its SPR dat