Supported Platforms
Gx-Plus for Provisioning Subscribers Overview
Gx-Plus is a Diameter-based application that extends the capability of the Gx interface. The 3rd Generation Partnership Project (3GPP) defined Gx as the online policy interface between the Policy Control and Charging Rules Function (PCRF) and the Policy and Charging Enforcement Function (PCEF), to provide control over policy and flow-based charges for subscribers. The PCRF is a centralized policy decision point that deploys business policy rules to allocate broadband network resources and manages flow-based charges for subscribers and services. The router functions as the PCEF in this environment.
Gx-Plus provides provisioning, activation, and deactivation of services; threshold triggers for service statistics processing; service accounting; subscriber session termination; fault recovery; and event (subscriber login and logout) notifications. The terminology typically used for PCRFs varies slightly from standard Junos OS terminology. The terms listed in Table 1 are interchangeable.
Table 1: Differences Between Gx-Plus and Junos OS Terminology
Gx-Plus | Junos OS |
|---|---|
policy | service |
rule | service |
rule install or installation | service activation or instantiation |
rule uninstall | service deactivation |
usage monitoring | service accounting |
Gx-Plus enables the router acting as a PCEF to exchange Diameter Credit-Control Application (DCCA) messages with a PCRF residing on a server to request credit authorization and service provisioning for authenticated subscribers. When an application requests AAA to activate a subscriber’s session, the router sends a Credit-Control-Request (CCR) message to determine whether the subscriber has credit for the desired services and to request provisioning of those services from the PCRF policy manager.
The PCRF responds with a Credit-Control-Answer (CCA) message that indicates success or failure for credit authorization. If the subscriber has sufficient credit for the requested services, credit is authorized. If the subscriber has insufficient credit for the services, credit authorization fails.
The CCA can include services to be activated for the subscriber. If the response times out, the subscriber is logged in but only default services—if present—are activated for the subscriber. The router interprets the omission of the Result-Code AVP from the CCA as a provisioning authorization failure and does not allow the subscriber to log in.
When a subscriber client application, such as DHCP, sends a subscriber logout notice to AAA, the router in turn sends a CCR message to the PCRF to request subscriber termination. The PCRF acknowledges the logout with a CCA message.
Different Diameter message types exchanged by the router and the PCRF contain different sets of attribute-value pairs (AVPs). If data for an AVP is not available for a request to the PCRF, that AVP is omitted from the message. If the PCRF subsequently has insufficient information to decide on the request, it may deny the request.
Gx-Plus establishes sessions that correspond to IPv4 DHCP sessions on dual-stack IPv6/IPv4 or IPv4-only subscriber interfaces, depending on the access profile. By default, IPv6 information is not communicated to the PCRF. You must explicitly configure Gx-Plus to include IPv6 information. When you do so, Gx-Plus can establish sessions that correspond to DHCPv6 sessions on IPv6-enabled subscriber interfaces and on dual-stack IPv6/IPv4-enabled interfaces.
For dual-stack DHCP subscribers (DHCPv4 and DHCPv6 on the same VLAN), each DHCP session is treated as a separate Gx-Plus session. However, only a single Gx-Plus session exists for dual-stack PPP sessions.
Gx-Plus includes the following fault tolerance and recovery capabilities:
- Unlimited retries of unacknowledged provisioning requests
- Unlimited retries of logout requests
- Router event notification
- Router discovery
 | Note: More than one Diameter-based application (function), such as Gx-Plus or JSRC, can run on a router simultaneously. |
