The term Gx interface (or simply Gx) refers to the implementation of the Gx reference point on the node. Gx reference points are defined in the 3GPP 29.212 document.
The ESM subscriber is a host or a collection of hosts instantiated on the Broadband Network Gateway. The ESM subscriber represents a household or a business entity for which various services with committed Service Level Agreements (SLA) can be delivered.
AA Subscriber is a representation of ESM subscriber in MS-ISA for the purpose of managing its traffic based on applications (Layer 7 awareness). An AA subscriber has no concepts of ESM hosts.
BNG refers to the network element on which a Gx interface is implemented and policy rules are enforced (PCEF).
Flow
A flow in Gx context represents traffic matching criteria (traffic classification or traffic identification) based on any combination of the following fields:
source IP address
destination IP address
source port or port ranges
destination port or port ranges
protocol field
DSCP bits
A Gx flow is defined in the Flow-Information AVP:
Flow-Information ::= < AVP Header: 1058 > 3GPP 29.212 §5.3.53
[ Flow-Description ] 3GPP 29.214 §5.3.8
[ ToS-Traffic-Class ] 3GPP 29.212 §5.3.15
[ Flow-Direction ] 3GPP 29.212 §5.3.65
*[ AVP ]
Gx flows are similar to dynamically created filter or ip-criteria (QoS) entries and are inserted within the entry range configured for the base filter/qos-policy.
IP criterion
These fields are used in IPv4/v6 packet header used as a match criterion. The supported fields are DSCP bits and 5 tuple. This is part of traffic classification (or traffic identification) within the PCC rule or within the static qos-policy/filter entry.
Gx policy rule
There are three types of Gx policy rules supported:
Gx based overrides
subscriber-related overrides (sub/sla/aa-profile, subscriber-id, QoS, filter, category-map, and so on).
NAS filter entry inserts via Gx
Basic permit/deny entries, similar to ACL filter entries
PCC rules or IP-criterion based rules which are fully constructed Policy and Charging Control (PCC) rules with multiple QoS/filter actions per rule and its own traffic classification
PCC rule represents a single or a set of IP based classifiers (DSCP bits or 5 tuple) associated with a single or multiple actions.
For example:
Each PCC rule can be removed via Gx from the node by referencing its name (Charging-Rule-Name AVP).
The PCC rule can contain a combination of QoS and IPv4/v6 filter actions as they pertain to the node.
PCC Rule Classifier
A flow-based (5 tuple) or a DSCP classifier defined in the Flow-Information AVP within the PCC Rule. There can be a single classifier or multiple classifiers (Flow-Information AVPs) within a single PCC rule. A PCC classifier (Flow-Information AVP) corresponds to an entry (match criteria) within the filter/ip-criteria definition.
CAM entry
A single entry in the CAM that counts toward the CAM scaling limit. For example a match condition within ip-criteria in a filter or qos-policy can evaluate into a single CAM entry or into multiple entries (where port-ranges are configured in the classifier, or where matching against UDP and TCP protocols are enabled simultaneously).
Subscriber Host Policy
A collection of PCC rules (classifiers and actions), Gx overrides, NAS filter inserts and statically configured rules (CLI defined QoS or filter) that are together applied to the subscriber host.