rvice offerings: Service provi- ders should evaluate the impact of the migration operations on the (already C 2009 by Taylor & Francis Group, LLC SIP and IPv6 deployed) IPv4-enabled service offerings and that there is no interference with these services in terms of technical constraints and other critical aspects such as billing, numbering, etc. - Manageability of the deployed interworking solution: Service providers should evaluate the complexity of the management operations and required mainte- nance tasks. The solution design should take into consideration reducing the cost of maintenance operations and simplifying engineering procedures owing to the support of automatic means dedicated to configuration and monitoring of the SIP-based VoIP service. Based on the aforementioned indicators and in order to kick off SIP IPv6 migration operations, several options may be envisaged by service providers. These options are described below: - If the new platform will serve only IPv6-capable customers or both. By "new platform" we mean the new changes made in the context of the IPv6 introduc- tion operations. This could enclose new (physical) elements or new functions that should be supported by the already deployed physical entities. Service providers should clearly decide if the new platform will serve only IPv6 cus- tomers or if it is designed also for IPv4 ones. This clarification is useful to help the solution designer and could guide the dimensioning of the SIP-based VoIP service platform (including both IPv4 and IPv6 traffic matrix). - If the new platform should include means to ease the final migration to a pure IPv6 connectivity. In other words, this aims at preparing the final transition (i.e., only IPv6 is supported by all customers) SO that the same problems found in the current stage are not encountered. The shifting to a situation, where only pure IPv6-enabled customers are present, should be achieved with no major (technical) difficulties. Specifically, service providers can opt for distinct strategies to o