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Steel-Belted Radius Carrier extends RADIUS functionality to 3GPP implementation on the scale required by Internet Service Providers and carriers. 3GPP support facilitates the management of mobile sessions and their associated resources through communication with a Gateway GPRS Support Node (GGSN). The 3GPP support in Steel-Belted Radius Carrier is based on the specifications given in the Interworking between the Public Land Mobile Network (PLMN) supporting Packet Based Services and Packet Data Networks (PDN) documentation (TS 29.061), which is available at

Within the 3G network, the AAA server (Steel-Belted Radius Carrier) interfaces with only one type of RADIUS client device, called a Gateway GPRS Support Node (GGSN). The GPRS network consists of a GGSN and a Serving GPRS Support Node (SGSN). The SGSN is responsible for detecting mobile stations (MS) in its serving area, data packet transmissions to and from the MS, and monitoring the location of MS in its serving area. The GGSN serves as a gateway between the GPRS network and external Packet Data Networks (PDN) such as the Internet or private data networks.

Data Connection Process

Data Connection Process

Establishing a data connection between an MS and PDN is a two-phase process:

  1. GPRS attach procedure

  2. PDP context activation

The GPRS attach procedure creates a logical link between the MS and the SGSN. This procedure includes user authentication (identity verification) and authorization to access GPRS services. After the attach procedure is complete, the MS is ready to establish the data session.

To transmit or receive GPRS data, the MS must activate a Packet Data Protocol (PDP) context. The PDP context is a set of parameters of all the information required for establishing an end-to-end connection such as PDP type (for example, IP), PDP address (IPv4 or IPv6), Quality of Service (QoS) parameters, and Network Service Access Point Identifier (NSAPI). After the PDP context is activated, a point-to-point tunnel is established between the SGSN and the GGSN allowing for data transmission between the MS and the requested application.

A single MS might require multiple sessions, using multiple PDP contexts on a single GGSN. Multiple PDP contexts enable the MS to simultaneously access multiple applications. However, each application may require a different set of transmission parameters. For example, an e-mail application might require different QoS parameters than a Multimedia Messaging Service (MMS) application, which uses images, audio, video, and rich text.

Steel-Belted Radius Carrier supports the ability to differentiate between these sessions by using a concatenation of the value of the User-Name attribute with the one-character NSAPI (network service access point identifier) value.

Accounting Process

Accounting Process

The 3GPP specification enables GGSN to generate multiple Accounting Start/Stop pairs for a given session. When 3GPP is enabled, the Steel-Belted Radius Carrier server expects the GGSN to send the 3GPP-Session-Stop-Indicator attribute as needed in Accounting Stop requests.

  • When a GGSN sends an Accounting Stop request that includes a 3GPP-Session-Stop-Indicator attribute (regardless of its value), the GGSN notifies the AAA server to delete the session.

  • When a GGSN sends an Accounting Stop request that does not include a 3GPP-Session-Stop-Indicator attribute in the request, the Steel-Belted Radius Carrier server marks the session as dormant and does not free any of its allocated resources (for example, IP address).

This type of Accounting Stop request is typically followed by an Accounting Start that marks the session as being active again.