Gi (application id: 1)

Gi interface is a part of the GPRS (General Packet Radio Service) network, enabling communication between the Gateway GPRS Support Node (GGSN) and external packet data networks (PDNs), such as the Internet. This interface handles the secure and efficient transmission of user data between the mobile network and external networks, allowing users to access services like the Internet from their mobile devices.

A PDP (Packet Data Protocol) Context is a logical association between a MS (Mobile Station) and PDN (Public Data Network) running across a GPRS network. The context defines aspects such as Routing, QoS (Quality of Service), Security, Billing etc.

Gi interface workflow

1. Packet Data Protocol (PDP) Context Activation
   • Activate PDP Context Request: The process starts when the terminal equipment (TE) sends a PDP Context Activate Request to the SGSN (Serving GPRS Support Node).
   • The SGSN forwards this request to the GGSN to create a PDP context.
   • Create PDP Context Request: The GGSN processes the request and establishes the PDP context, which facilitates the user's data connection to the external network (e.g., the Internet) via the Gi interface.
2. User Data Transmission
   • Once the PDP context is established, user data can be transmitted between the TE and the PDN through the GGSN, utilizing the Gi interface for data routing and transmission to external networks.
3. PDP Context Deactivation
   • Deactivate PDP Context Request: When the user decides to terminate the session, a Deactivate PDP Context Request is sent from the TE to the SGSN.
   • The SGSN forwards this request to the GGSN.
4. Delete PDP Context Request:
   • The GGSN processes the deactivation request, terminating the PDP context and stopping the user’s data session.
5. Deactivate PDP Context Accept:
   • The SGSN informs the TE that the PDP context deactivation is accepted.

Note: The AAA (Authentication, Authorization, and Accounting) processes in a GPRS network, particularly those involving the GGSN, are typically managed via interfaces like Gx (for policy control) and Gy (for online charging), not the Gi interface. The Diameter protocol may be used in these contexts, but it is separate from the primary function of the Gi interface, which focuses on user data transmission rather than direct AAA communication.
For complete technical specification of Gi interface in Diameter protocol please refer to: [3GPP TS 29.061]