2.8 GPRS Mobility Management and Session Management (GMM/SM)
Apart from forwarding data packets between GPRS subscribers and the Internet, the GPRS network is also responsible for the mobility management of the subscribers and the session management to control the individual connections between subscribers and the Internet. For this purpose, signaling messages and signaling flows have been defined that are part of the GMM/SM protocol.
2.8.1 Mobility Management Tasks
Before a connection to the Internet can be established, the user has to first connect to the network. This is similar to attaching to the circuit-switched part of the network. When a subscriber wants to attach, the network usually starts an authentication procedure, which is similar to the GSM authentication procedure. If successful, the SGSN sends a location update message to the HLR to update the location information of that subscriber in the network's database. The HLR acknowledges this operation by sending an ‘insert subscriber data’ message back to the SGSN. As the name of the message suggests, it not only acknowledges the location update but also returns the subscription information of the user to the SGSN so that no further communication with the HLR is necessary as long as the subscriber does not change the location. The SGSN, subsequently, will send an attach accept message to the subscriber. The attach procedure is complete when the subscriber returns an attach complete message to the SGSN. Figure 2.28 shows ...