Routing optimization in DMM

This draft proposes a PMIP-based routing optimization method in distributed anchor architecture. The anchor of the mobile node is able to communicate with the anchor of corresponding node directly using optimized routing. In this draft, there are two modes for the setup of routing optimization: the direct mode and the relay mode. The difference between them lies in that whether the routing optimization is set up directly or under the assistance of a third anchor. The situation that Communication Node(CN) is a fixed terminal or a content server is also considered and 3 solutions are provided correspondingly. The method proposed in this draft can reduce the delay and save signaling overhead in the current scheme.