In the combined Attach process, the mobile indicates in the Attach request to the MME the
support CSFB functionality, the MME informs the MSC Server that there was an attach on the LTE network, sending a Location Update Request message, which activates the SGs association with the MSC/VLR, thus having a record also in the CS domain. Upon receiving the request, the VLR performs the Location Update procedure. After that, the identification of the MME and SGs interface connection is associated. In the attach request, the MME sends an LAI “dummy”, which is used in CS processes, to identify the location of the mobile in the LTE network. The Attach Combined is transparent to the rest of the CS network.
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