A.2 S6m interface

29.3363GPPHome Subscriber Server (HSS) diameter interfaces for interworking with packet data networks and applicationsRelease 18TS

A.2.1 General

The Diameter overload control mechanism is an optional feature over the S6m interface.

It is recommended to make use of the IETF RFC 7683 [15] on the S6m interface where, when applied, the MTC-IWF shall behave as a reacting node and the HSS3GPP AAA server as a reporting node.

NOTE: There is no need to support this mechanism in the other way (overload of the MTC-IWF) as no Diameter request commands are sent by the HSS to the MTC-IWF.

A.2.2 HSS behaviour

The HSS requests traffic reduction from the MTC-IWF when it is in an overload situation, by including OC-OLR AVP in answer commands as described in IETF RFC 7683 [15].

The HSS identifies that it is in an overload situation by implementation specific means. For example, the HSS may take into account the traffic over the S6m interfaces or other interfaces, the level of usage of internal resources (CPU, memory), the access to external resources etc.

The HSS determines the specific contents of the OC-OLR AVP in overload reports and the HSS decides when to send OC-OLR AVPs by implementation specific means.

A.2.3 MTC-IWF behaviour

The MTC-IWF applies required traffic reduction received in answer commands to subsequent applicable requests, as per IETF RFC 7683 [15].

Requested traffic reduction is achieved by the MTC-IWF by implementation specific means. For example, it may implement message throttling with prioritization.

Annex B gives guidance on message prioritisation over the S6m interface.