 service platform, and for whom no backward constraints are to be considered, the task is similar to the introduction of new IPv4-enabled SIP services since there is no risk regarding the impact on the stability of the already offered services at least for the enforcement of IPv6 SIP support objective. For a VoIP service provider that already offers an IPv4-enabled SIP-based telephony service, there are sensitive precautions to be taken into account before modifying the existent service platform and the risk of disturb- ing the service offerings that a number of customers have paid for is critical. This category of service providers should clearly identify the risks related to the evolution of the deployed service offerings and evaluate the Quality of the Service (QoS) that will be perceived by their customers. What follows are a set of pertinent indicators that should be taken into account in order to guide the IPv6 migration operations: - The celerity of introduction of IPv6 in operational networks: Service providers should evaluate if there will be a massive migration to IPv6 or only a partial migration. They should evaluate if the coverage will be global or only reduced to a limited set of IP network providers' domains. This input will facilitate the phasing of the service migration operations and also the dimensioning of traffic matrix in terms of calls to be supported in both IPv4 and IPv6. - Constraints on the IP connectivity service provider to service provider inter- face: Service providers should identify their needs regarding specific informa- tion to be carried at the control plane and if IP network providers should provide service providers with pertinent information for the correct behavior of their conversational service offerings. In addition, service providers should decide where to put the complexity of the migration solution(s) and examine if it is possible to maintain the service layer working independently of the type of IP connectivity protocol. - The risk on the stability of IPv4-enabled se