LTE : What could be reason of not having the RAU "Routing Area Update" in LTE ?

Question

In LTE technology, there is a concept of tracking area update . Why a new term is defined in LTE ? and What could be reasoning behind it ?

Answer 1

Since LTE network will work with other technologies like UMTS, 2.5G . These network nodes have already been deployed, routing areas are configured and being used . If LTE use similar terminology for its own network deployment then there would be chances of conflict. That could be one of the reason not using RAU for LTE network. A new term "tracking area" is defined and network may have mapping of a tracking area to routing area .

If I thought correctly then "when a user performs combined attach to the LTE MME , tracking area to routing area mapping is used ".