IPv6 offers significant advantages over IPv4. However IPv4 and IPv6
protocols are expected to coexist during a long period. Currently,
there are many IPv4/IPv6 transition/coexistence technologies, which
can be generally devided into two kinds: 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 to the IP versions of source networks
and destination networks, the IP version of transport network (the
middle part along end-to-end path) also plays an important role during
IPv4/IPv6 transition/coexistence. Therefore, we need to decide which
transition methods should be used in different typical transition
scenarios and how transition and tunneling collaborate for solving
transition/coexistence problems. This draft presents an IPv4-IPv6
transition/coexistence framework named PET (short for Prefixing,
Encapsulation and Translation), which is a network side solution. PET
includes fundamental elements needed in transition scenarios, which
provides the flexibility for network operators to decide the proper
transition technology. In addition, this draft also addresses how to
deploy PETs and analyze the advantages and disadvantages of typical
transition technologies that PET may adopt.