eas someone else might want his or her requests to be forked sequen- tially to save sanity. Most people will want their fixed phone rung first and, if nobody answers, their mobile phone rung next. The concept of all my con- tact devices being pinged at once is an attractive one, but the concept of being pinged by all my contact devices at once is distinctly unpleasant. Besides influencing how the caller's requests are handled, a certain caller might also be interested in defining which kind of terminal he or she wants to reach. For instance, when Bob is calling Laura to talk about the opera they saw last Saturday, he does not want to reach Laura at work. He prefers to reach Laura at her private line. On the other hand, when Bob's boss calls him to talk about work-related matters, he does not want to reach Bob at his personal SIP phone. When Bob wants to speak with Laura for a long while, he does not want to reach her at her mobile SIP phone because calling this phone is more expensive than calling her fixed SIP phone. Thus, Bob wants his INVITEs to reach Laura's fixed terminal rather than her mobile one. Chapter 6 Knowing caller preferences is also useful for providing services. A user calling the tax office might speak English rather haltingly. Therefore, he wants his INVITE to reach a Spanish-speaking representative to help him with his tax declaration. Some extensions to SIP enable callers to describe how their requests should be handled and which kind of SIP UA they would like to reach. How- ever, note that the preferences of the caller have to interact with the con- figuration of the server. Thus, if a server is configured to divert incoming calls to a mobile and the caller states that he or she wants the INVITE to reach a fixed terminal, a mismatch must be resolved. In this situation, the caller would have to clarify in the request whether his or her preference for fixed terminals can be overruled or whether he or she would not accept con- nection to a mobile terminal at all. How It's Done In order to achie