GTPP Interface Overview
This section provides information on GTPP interface between Charging Gateway Function (CGF) and Cisco Systems' licensed products running on the ASR 5500 core platforms, including the GGSN, P-GW, S-GW, and SGSN in General Packet Radio Service (GPRS), Universal Mobile Telecommunications System (UMTS) data networks, 3GPP2 evolved High Rate Packet Data (eHRPD) and Long Term Evolution-System Architecture Evolution (LTE-SAE) wireless data networks.
The Ga is the reference point from Charging Data Function (CDF) to the CGF, which is intended for the transport of CDRs. The CDF could either be GGSN, P-GW, S-GW, or any other similar products.
By definition, dealing with CDRs only implies that Ga is solely related to offline charging.
The following figure depicts the position of the Ga reference point within the overall 3GPP offline charging architecture.
As illustrated in the above figure, the CDF in each network domain, service or subsystem is relevant for the network side of the Ga reference point. Different mappings of the ubiquitous offline charging functions, CDF and CGF, onto physical implementations are possible.
The transport protocol associated to the Ga reference point, providing functions for transfer of CDRs from CDF to CGF, is GTPP.
Each CDF will have an O&M; configurable address list of CGFs (Charging Gateways) to which it can send its CDRs. The list will be organized in CGF address priority order. If the primary CGF is not available (for example, out of service), then the CDF will send the CDRs to the secondary CGF and so on.
Each CDR generating function will only send the records to the CGF(s) of the same PLMN, not to CGF(s) located in other PLMNs.
Each CGF in the PLMN will know the other CGFs' network addresses (for example, for redundancy reasons, to be able to recommend another CGF address). This is achieved by O&M; configuration facilities that will enable each CGF to have a configurable list of peer CGF addresses.
The GTPP charging support is currently available for the following core multimedia gateway products:
- Evolved Packet Data Gateway (ePDG)
Gateway GPRS Support Node (GGSN)
IP Services Gateway (IPSG)
Packet Data Gateway/Tunnel Termination Gateway (PDG/TTG)
Packet Data Network (PDN) Gateway (P-GW)
Serving Gateway (S-GW)
Serving GPRS Support Node (SGSN)
S2a Mobility Over GTP (SaMOG) Gateway
CDR Transport by GTPP
GTPP has been designed to deliver the CDR(s) from the CDF to the CGF(s). This protocol is required if the CGF resides outside the CDFs. It utilizes some aspects of GTPP, which is used for packet data tunneling in the backbone network.
GTPP operates on the Ga interface and does not imply the use of any specific backbone network.
GTPP performs the following functions:
CDR transfer between the CDF and the CGF
Redirection of CDRs to another CGF
Advertise to peers about its CDR transfer capability (for example, after a period of service downtime)
Prevents duplicate CDRs that might arise during redundancy operations. If so configured, the CDR duplication prevention function may also be carried out by marking potentially duplicated CDR packets, and, delegating the final duplicate deletion task to a CGF or the Billing Domain (instead of handling the possible duplicates solely by GTPP messaging).