21 Overload control

29.1653GPPInter-IMS Network to Network Interface (NNI)Release 18TS

21.1 General

Based on inter-operator agreement, overload control may be supported over the II-NNI.

The overload control defines two optional mechanisms:

– a feedback based mechanism;

– and a load filter mechanism.

The support of either one of the mechanism is based on operator agreements.

If a mechanism is supported, the related procedures from the 3GPP TS 24.229 [5] shall be applied with the requirements in the relevant clause below.

Based on regional/national requirements and inter-operator agreement, Multimedia Priority Service (MPS), as specified in 3GPP TS 22.153 [187], shall be exempted from SIP overload controls across II-NNI up to the point where further exemption would cause network instability.

21.2 Feedback based mechanism

The procedures in 3GPP TS 24.229 [5] shall be applied and the capabilities below shall be provided at the II-NNI.

The feedback based mechanism, defined in IETF RFC 7339 [165], requires no additional support at the II-NNI as it is supported using header field parameters within existing header fields supported at the II-NNI.

NOTE: An algorithm will need to be selected. The IETF RFC 7339 [165] also defines the default algorithm for usage of the feedback based mechanism in the IM CN subsystem. Additional algorithms are either already defined, e.g. the rate-based scheme defined in IETF RFC 7415 [166], or can also be defined in the future.

21.3 The load filter mechanism

The procedures in 3GPP TS 24.229 [5] shall be applied and the capabilities below shall be provided at the II-NNI.

A SUBSCRIBE request containing the Event header field "load-control" and, optionally, an Accept header field containing the "application/load-control+xml" MIME type as defined in IETF RFC 7200 [167] shall be supported on the II-NNI.

NOTE: The addresses to targets that can be supervised need to form part of the service level agreement.

A NOTIFY request containing the "application/load-control+xml" MIME body defined in IETF RFC 7200 [167] shall be supported on the II-NNI.