A policy change can be implicitly requested by the node at IP-Can session establishment time via the CCR-I command. The node supplies user identification attributes to the PCRF so that the PCRF can identify rules to be applied. However, the node does not explicitly request specific policy update, for example via Event-Trigger = RESOURCE_MODIFICATION_REQUEST.
Another way to request a policy update on the node is via the rar command in a PUSH model.
Gx policies on the node can be enforced via these three mechanisms:
Gx-based overrides
This refers to subscriber related overrides (sub/sla/aa-profile, subscriber-id, QoS, filter, category-map, and so on).
PCC rules or IP-criterion based rules
This refers to fully constructed Policy and Charging Control (PCC) rules with multiple qos/filter actions per rule and its own traffic classification.
NAS filter entry inserts via Gx
This refers to basic permits or denies entries, similar to ACL filter entries.