RAU (Routing Area Update) is a procedure in mobile networks that allows a mobile device to update its location information when it moves from one routing area to another. A routing area is a geographical area that is served by a specific group of base stations or cells in a mobile network. When a mobile device moves out of its current routing area and enters a new one, it needs to inform the network about its new location so that the network can route incoming calls, messages, and data to the appropriate location.
Here is a detailed explanation of the RAU procedure:
- Movement Detection: When a mobile device moves from one routing area to another, it continuously monitors the signal strength and quality of the neighboring cells. It detects that the signal from the current serving cell is becoming weak and the signal from a new cell is getting stronger. This triggers the mobile device to initiate the RAU procedure.
- RAU Request: The mobile device sends a Routing Area Update (RAU) request message to the serving base station. This message contains information such as the mobile device's identity (IMSI or International Mobile Subscriber Identity), the identity of the new routing area, and other relevant information required for updating the location.
- Authentication and Security: The serving base station validates the identity of the mobile device by checking its IMSI against the subscriber database. It also performs authentication and encryption procedures to ensure the security of the signaling messages.
- Update Location in the Network: After successful authentication, the serving base station updates the location of the mobile device in the network. This involves updating the Visitor Location Register (VLR) and Home Location Register (HLR) databases with the new routing area information. The VLR maintains temporary subscriber information, while the HLR stores permanent subscriber information.
- Notification to Neighboring Cells: The serving base station informs the neighboring base stations and the Mobile Switching Center (MSC) about the location update. This ensures that incoming calls, messages, or data destined for the mobile device are correctly routed to the new routing area.
- Update of Paging Areas: The MSC updates the list of paging areas for the mobile device. Paging areas are smaller subdivisions within a routing area. By updating the paging areas, the network can efficiently locate the mobile device when there is an incoming call or message.
- Acknowledgment and Handover: The serving base station sends a Routing Area Update Accept message to the mobile device, acknowledging the successful location update. If the new routing area is served by a different base station or cell, a handover procedure may be initiated to transfer the ongoing communication from the old cell to the new cell seamlessly.
- Service Resumption: Once the mobile device receives the RAU Accept message, it resumes normal operation in the new routing area. It can receive and make calls, send and receive messages, and access data services without any disruption.
Overall, the RAU procedure ensures that the mobile network maintains accurate location information for each mobile device, enabling efficient call and message routing as users move across different routing areas.