Gy is between Online Charging System (OCS) and PCEF. In most cases PCEF is based inside PDN GW (Packed Data Network Gateway) or just short PGW. Gy interface allows online credit control for service data flow based charging.

Credit Control (Gy//Ro) Application ( 4 ) The Gy interface is used for online charging between the OCS and the PDN Gateway (PGW), while the Ro interface is between the OCS and the IMS Call Session Control Function (CSCF). The two interfaces are functionally equivalent.

Gx interface enables signaling of PCC decisions, negotiation of IP-CAN bearer establishment mode and termination of Gx session . Gy. It is online charging reference point. Gy lies between PCEF (Policy Control Enforcement Function) and OCS (Online Charging Function).

AVP Code (4-bytes) The AVP Code, combined with the Vendor-Id field, identifies the attribute uniquely. AVP numbers 256 and above are used for Diameter, which are allocated by IANA. AVP numbers 1 through 255 are reserved for backward compatibility with RADIUS, without setting the Vendor-Id. field.

Online charging system (OCS) is a system allowing a communications service provider to charge their customers, in real time, based on service usage.

Gy interface is between the PCEF and OCS. It uses Diameter over TCP, UDP, SCTP transport protocol.

Quota holding indicates the number of seconds for which the quota granted by the OCS, is held by the gateway when no traffic is received for that rating group.

The Gx interface connects the PCRF with policy enforcement points. These are found in the packet core of 3G and 4G networks. The serving GPRS support node (SGSN), gateway GPRS support node (GGSN), and PDN Gateway are all considered as enforcement points, supported by the Gx interface.

Gx interface. A Gx interface (as specified in 3GPP 29.212) is a standard interface based on the Diameter protocol that allows exchange of policy control and charging rules between a PCRF and a Policy and Charging Enforcement Function (PCEF) entity in a Telco network.

The capabilities exchange message sequence, CER/CEA, is standard Diameter messaging used as a means of correlating client capabilities with server services. The CER message is used to discover peer’s identity and exchange capabilities, including applications supported, vendor-Id and device addressing information.

An Online Charging System (OCS) can be thought of as the heart of a telecommunication network architecture; all the transactions within the system are linked with and processed by the OCS, such as the subscriber’s account balance and charging transactions.

The charging application specification is given in diameter standard 4006 . The following section describes call flow GTP and Diameter messages for charging over the Gy interface. Gy uses two messages over Diameter protocol, Credit control request (CCR), and Credit Control Answer (CCA).

The Gx application is defined as a vendor specific Diameter application, where the vendor is 3GPP and the Application-ID for Gx application is 16777238. The vendor identifier assigned to 3GPP by IANA is 10415. When a Diameter protocol defined over the Gx interface, the node (PCEF) acts as a Diameter Client and the PCRF acts as a Diameter server.

Gy uses two messages over Diameter protocol, Credit control request (CCR), and Credit Control Answer (CCA). For accessing the data, a data session is created, update, and terminated for a device. The following are the details for Gy messages. GGSN or PGW sends this message to the OCS.

Included at command level or embedded within [3GPP – 873] Service-Information / [3GPP – 874] PS-Information grouped AVPs when configured ( gy include-avp ps-information ). The IPv6 prefix of the SLAAC subscriber host that triggered the creation of the Diameter Gy session.