RAU
procedure will happen in the following two case:
-MS entered a new Route Area
-Periodic RAU ( after
periodic timer expires)
Inter-SGSN
RAU
-The new SGSN find the old
SGSN from the old RAI
-Old SGSN stop downlink
signaling, transfer MM context and PDP context to new SGSN
-Tunnelling N-PDU to the new
SGSN
-Update PDP context and
subscriber data
