09.613GPPGeneral Packet Radio Service (GPRS)Interworking between the Public Land Mobile Network (PLMN) supporting GPRS and Packet Data Networks (PDN)TS
The primary reason for the interworking between the GPRS networks is to support roaming GPRS subscribers as described in 3GPP TS 03.60 . The general model for GPRS network interworking is shown in figure 12.
Figure 12: General interworking between GPRS networks to support roaming subscribers
For roaming subscribers that have a PDP address allocated from the HPLMN a forwarding route between the HPLMN and the VPLMN is created. This route is used for both mobile terminated and mobile originated data traffic. The communication is done via the BGs (Border Gateways) as described in 3GPP TS 03.60 .
The procedures to set the link between the SGSN in the VPLMN and the GGSN in the HPLMN is described in 3GPP TS 03.60 .
The inter-PLMN link may be any packet data network or dedicated link as described in 3GPP TS 03.60 . The GPRS operators may have a dedicated inter-PLMN link to fulfil the QoS requirements of a certain protocol.
12.1 Security Agreements
Each GPRS operator may support IPsec (RFC 1825 ) and accompanying specifications for authentication (RFC 1826 ) and encryption (RFC 1827 ) as a basic set of security functionality in its border gateways. The GPRS operators may decide to use other security protocols based on bilateral agreements.
12.2 Routing protocol agreements
Each GPRS operator may support BGP (RFC 1771 ) as a basic set of routing functionality in its border gateways. The GPRS operators may decide to use other routing protocols based on bilateral agreements.
12.3 Charging agreements
Sharing the cost of the inter-PLMN link is subject to the agreement between the GPRS operators.
There may be a requirement to collect charging information in the Border Gateway (see figure 12) and this is down to the normal interconnect agreement between PLMN and PDN operators.