k and white lists requires the existence of a way to identify and han- dle users, either by SIP URI, IP address or even domain of origin. However, as something like that is not explicitly mentioned, we put the appropriate negative value in the table. Furthermore, the table can be used as a refer- ence to choose the appropriate mechanism for anti-SPIT mechanisms in a given context. For example the call and message patterns might be highly cost demanding, in terms of data gathering and analysis, and thus mecha- nisms that focus on, and better fulfill the other criteria might be of prefer- ence. Finally, the table can be read as a concentrated area of further research directions regarding anti-SPIT countermeasures. Some of the questions that one can answer using the table include how can a particular mechanism con- tribute in terms of prevention, detection or handling of SPIT, and which combinations of techniques should someone use in order to fight SPIT more effectively, etc. © 2009 by Taylor & Francis Group, LLC TABLE 19.6 Compliance of SPIT Mechanisms to Identification Criteria SPIT identification criteria Caller/ Call and message Calls/messages callee origin patterns relationship Caller Caller Number Sequential Dialed/ Large White/ Anti-SPIT Caller Calls answered number of of SIP black mechanisms address domain message calls duration numbers calls errors message lists Anti-SPIT Entity Reputation/ Charging DAPES Biometrics RFC 4474 SIP SAML VoIP Seal © 2009 by Taylor & Francis Group, LLC SIP Handbook: Services, Technologies, and Security Finally it must be mentioned, that although many mechanisms check the content of the SIP messages, for example the headers FROM, VIA, etc, none of them check the appropriate the messages' bodies and reason phrases for car- rying the actual SPIT message. This explains why the corresponding column in the table has only negative values. 19.7 Anti-SPIT Mechanisms and Legal Issues Protection of individual rights has-or should have-an impact on the choice and design, implementation as 