The inter-SGSN RAU procedure is as follows:

Figure 2 Inter-SGSN RAU procedure


http://localhost:7904/pages/31185199/02/31185199/02/resources/figure/en/SGSN/fig_60_140.png

1. The MS moves from one RA to the other and sends an RAU request
   message that carries the OLD RAI, such as 4600012340001.
2. After receiving the RAU request, the SGSN initiates a domain name
   resolution request to the DNS server. The domain name to be resolved
   is converted from the RAI, such as RAC0001.LAC1234.MNC0000.MCC0460.GPRS.
3. The DNS server returns the SGSN the resolution result, which is
   the IP address of the OLD SGSN signaling plane, such as 10.161.234.254.
4. Based on the resolution result, the new SGSN requests the MS information
   from the old SGSN.
5. After receiving the request, the old SGSN sends all stored MS
   information to the new SGSN.
6. The new SGSN sends the RAU accept message to the MS and the RAU
   succeeds.

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