This section is divided into two main parts - GPRS scenarios, and scenarios with the IP Multimedia Subsystem (IMS). The first part - GPRS scenarios - concentrates on scenarios with a User Equipment (UE) connecting to services in the Internet, e.g., mail, web. The second part - IMS scenarios - then describes how an IMS capable UE can connect to other SIP-capable nodes in the Internet using the IMS services.

1.  GPRS Scenarios
               This section describes the scenarios that might occur when a GPRS UE  contacts services, or nodes outside the GPRS network, e.g., web-  server in the Internet.
              Transition scenarios of the GPRS internal interfaces are outside of  the scope of this document.  The following scenarios are described here. In all of the scenarios,  the UE is part of a network where there is at least one router of the  same IP version, i.e., GGSN, and it is connecting to a node in a  different network.
              The scenarios here apply also for PDP Context type Point-to-Point  Protocol (PPP) where PPP is terminated at the GGSN. On the other  hand, where the PPP PDP Context is terminated e.g., at an external  ISP, the environment is the same as for general ISP cases.

Brief Description of the 3GPP Network Environment

               This section describes the most important concepts of the 3GPP environment for understanding the transition scenarios. The first part of the description gives a brief overview to the GPRS network as such. The second part concentrates on the IP Multimedia Core Network Subsystem (IMS).

1.  GPRS Architecture Basics
             This section gives an overview to the most important concepts of the  3GPP packet architecture. For more detailed description, please see
   [1].   From the point of view of this document, the most relevant 3GPP  architectural elements are the User Equipment (UE), and the Gateway
   GPRS Support Node (GGSN). A simplified picture of the architecture  is shown in Figure 1.   The UE is the mobile phone. It can either be an integrated device comprising a combined GPRS part, and the IP stack, or it might be a  separate GPRS device, and separate equipment with the IP stack, e.g.,    a laptop.
            The GGSN serves as an anchor-point for the GPRS mobility management. It also serves as the default router for the UE.  The Peer node mentioned in the picture refers to a node with which  the UE is communicating.

Session Control in the IP Multimedia Subsystem

 

              The IP Multimedia Subsystem (IMS) defined by 3GPP provides an enabling architecture that is access independent. This is central in the move towards convergence. Now each access type is being 'enabled' to work with a multimedia IMS core, be it DSL, WLAN, GPRS or emerging technologies, such as WiMAX.
 

IP Multimedia Subsystem

 

             The IP Multimedia Subsystem (IMS) is an architectural framework for delivering internet protocol (IP) multimedia to mobile users. It was originally designed by the wireless standards body 3rd Generation Partnership Project (3GPP), and is part of the vision for evolving mobile networks beyond GSM. Its original formulation (3GPP R5) represented an approach to delivering "Internet services" over GPRS. This vision was later updated by 3GPP, 3GPP2 and TISPAN by requiring support of networks other than GPRS, such as Wireless LAN, CDMA2000 and fixed line.