ion sent from a mobile client to LBS is indistinguish- able from the location information of at least k - 1 other mobile clients [20]. The location perturbation is an effective technique for supporting location k-anonymity and dealing with location privacy breaches exemplified by the location inference attack scenarios. If the location information sent by each mobile client is perturbed by replacing the position of the mobile client with a coarser grained spatial range such that there are k - 1 other mobile clients within that range k > 1, then the adversary will have uncertainty in match- ing the mobile client to a known location-identity association or an external observation of the location-identity binding. This uncertainty increases with the increasing value of k, providing a higher degree of privacy for mobile clients. Proposals for Anonymity in SIP In the original specification of SIP the anonymity feature was juvenilely sup- ported. To enable anonymity, the UAC should use in the "From" header field C 2009 by Taylor & Francis Group, LLC SIP Handbook: Services, Technologies, and Security the display name "Anonymous", along with a syntactically correct, but other- wise meaningless URI (e.g., sip:an@anonymous.user). Additionally, tunneling encryption is suggested for anonymity. This is achieved by encrypting the header fields, and producing an outer new "From" header field that includes the "Anonymous" value in the display name subfield. This end-to-end encryp- tion is not immune to location tracing attacks, since statistical analysis of sniffed data might prove the identities of the communicating parties. A more recent draft RFC discussed privacy issues in SIP [21]. This RFC introduces guidelines for the creation of messages that do not reveal personal identity information, and a new "privacy service" logical role for intermedi- aries is defined to answer some privacy requirements. Additionally, an Internet draft proposal suggested the extension of the SIP that enables parties in an SIP session to be identif