Tsinghua University Tsinghua University Tsinghua University Tsinghua University Tsinghua University IPv6 offers significant advantages over IPv4, however it will take a long time to replace IPv4 with IPv6. Therefore, these two protocols are expected to coexist during the transition period. Currently, there are many transition technologies, such as translation and tunneling. In some typical transition scenarios, both tunneling and translation are needed. However, either translation or tunneling has limitation and application scope. In addition, besides IP version of source, middle and destination network, the network property (a regular edge network or a backbone) has key impact on system performance. Therefore, we need to decide which transition method should be used in some typical transition scenarios and how transition and tunneling collaborate for solving transition problems. This draft presents an IPv4-IPv6 transition framework, which is a network side transition solution. It introduces a toolbox named PET (short for Prefixing, encapsulation and translation) to solve IPv4- IPv6 transition. PET includes fundamental elements needed in transition scenarios, which provides the flexibility for network to decide the proper transition methods. In addition, this draft also addresses how to deploy PETs and analyze the advantages and disadvantages of all transition methods that PET may adopt.