ve this functionality, three new headers and new Contact header parameters were defined [draft-ietf-sip-caller- prefs]. The new headers are Accept-Contact, Reject-Contact, and Request- Disposition. New parameters for Contact headers describe the user's terminal. Figure 6-12 demonstrates the usage of these new headers and parame- ters. Bob sends a REGISTER to his server stating that he is available at Bob's Bob's Figure 6-12 mobile fixed Laura uses new SIP headers to indicate Laura Proxy terminal terminal (1) REGISTER her preferences. Contact: Bob@131.160.1.112; mobility="fixed"; class="business" (2)200 OK (3) REGISTER Contact: :BBob.Johnson@mobile.com; mobility="mobile"; class="personal" (4) 200 OK (5) INVITE Accept-Contact: *;mobility="fixed" (6) INVITE Reject-Contact: *;mobility="mobile" Accept-Contact: *;mobility="fixed" Request-Disposition: no-fork Reject-Contact: *;mobility="mobile" Request-Disposition: no-fork Extending SIP: The SIP Toolkit SIP:Bob@131.160.1.112 and specifying that this is a fixed terminal used for business. Therefore, the Contact header of his REGISTER looks like the following: Contact: ip:Bob@131.160.1.112; mobility="fixed"; class= "business" Bob sends a second REGISTER saying that he is also available at SIP:Bob.Johnson@mobile.com. He specifies that this is a mobile terminal used for personal matters. The Contact header of this REGISTER looks like the following: Contact: sip:Bob.Johnson@mobile.com mobility="mobile"; class= "personal" Now Laura wants to call Bob. She sends an INVITE containing her pref- erences. Today she has to reach Bob on a fixed terminal and does not want under any circumstances to reach Bob on his mobile. To express these pref- erences, Laura uses the Accept-Contact and Reject-Contact headers. Accept-Contact: * ; mobility="fixed Reject-Contact: * ; mobility="mobile" The * is a wild card. These headers together mean that Laura agrees to reach any fixed address while she refuses any mobile address. Laura also adds a Request-Disposition header to her INVITE to prevent h