ber Mapping (ENUM) within a full IPv6-enabled SIP-based architecture. As a step beyond the current state of the art, this chapter highlights issues related to migration of SIP-based conversational services to IPv6 and compli- cations to interconnect with IPv4-enabled ones. A set of operational migra- tion strategies are proposed associated with pertinent criteria to be taken into account by service providers in order to select a suitable migration scenario. This chapter does not recommend any particular IPv6 transition scenario (e.g., Tunnel Broker, Network Address Translation - Protocol Translation (NAT - PT), etc.) nor argue in favor of a given IP transport interconnec- tion mechanism in order to interconnect IPv4 and IPv6 realms. Nevertheless, this chapter assumes that one possible transport interconnection mechanism is activated to allow communication between heterogeneous realms (i.e., between IPv4-enabled and IPv6-enabled networks). Additionally, this chapter intro- duces a novel procedure to allow SIP service platform to be aware of the type of the involved peers before forwarding session establishment requests SO as to prevent from heterogeneous sessions failures and avoid invocation of adaptation functions. This procedure does not rely on "Layer 3"-related information but only on an "Application Layer"-related one. Owing to the support of this procedure, SIP proxy servers will be able to establish success- ful sessions between heterogeneous peers and optimize the invocation of ALGs modules. Moreover, a novel procedure called "blank SDP" is described within this chapter. This procedure aims at putting flexible means at the disposal of service providers to enforce their policies, especially to promote usage of IPv6 as the main transport protocol to convey traffic between SBC elements. More details about this new procedure are elaborated in this chapter. C 2009 by Taylor & Francis Group, LLC SIP Handbook: Services, Technologies, and Security 3.1.3 Chapter's Structure This chapter is structured as follows: T