nation of private data. We assume that the end-user consents for C 2009 by Taylor & Francis Group, LLC SIP Handbook: Services, Technologies, and Security the collection and manipulation of his/her private data, and has authorized specific legal entities for these purposes. Scalability. This is an important criterion, since VoIP networks grow fast. Scalability should be considered when authentication is involved, since PKI and CA might need to establish complex cross-certification chains, or when reputations and assertions are used. Adoption. This parameter corresponds to the success of the anti-SPIT coun- termeasure, and depends on the effort it takes for an end-user, or a provider, to begin using it. Availability. It denotes the increase in the availability of network, computing, memory, or human resources when preventing, detecting or handling SPIT countermeasures apply. More specifically, in the description of VoIP SEAL mechanism [21], it is mentioned that the particular mechanism is intrusive for the end-user, as there is an interactive part requiring user's feedback. In our analysis, we do not estimate how intrusive this mechanism is or not, but we emphasize that there are information in the description of the mechanism that could help someone value accordingly the particular criterion, namely human interfer- ence. Finally, regarding the vulnerabilities criterion we must emphasize that we only focus on the vulnerabilities considerations that the authors take into account, whether these are few or many. 19.6.2 Compliance of SPIT Mechanisms to Assessment Criteria Table 19.6 presents which mechanisms takes into account the SPIT identifi- cation criteria we defined. For this purpose we only took into consideration an abstract description of each mechanism. Furthermore, we do not consider whether the mechanisms meet the criteria well or not, but we rather pro- vide the mere existence of each criterion in the mechanisms' description. For example, in the description of reputation/charging mechanism, the use of blac