Session Management, Mobility Management, and Routing

When you turn on your GPRS handset, it registers with the SGSN of the serving GPRS
network. The network authorizes the handset and copies the user profile from the HLR
to the SGSN. It assigns a packet temporary mobile subscriber identity (P-TMSI) to the
user (GPRS attach). Detach can be handset or network initiated. After a successful
attach, the handset must apply for one or more addresses used in the PDN, for example,
an IP address. A PDP context is created for each session, for example:
 PDP type (IPv4/IPv6)
 PDP address
 Requested QoS
 Address of a GGSN serving as the access point to the PDN
The context is stored in the handset, the SGSN, and the GGSN.
Address allocation can either be static or dynamic. In static allocation, the network
operator permanently assigns a PDP address to the user. In dynamic allocation, a PDP
address is established when a PDP context is established (executed by the GGSN). This
might be used, for example, to support prepay packet traffic.
To implement routing, the SGSN encapsulates the IP packets from the handset and
examines the PDP context. The packets are routed through the intra-PLMN GPRS
backbone to the appropriate GGSN. The GGSN decapsulates the packets and delivers
them to the IP network.