E.2 S6a/S6d interfaces

29.2723GPPEvolved Packet System (EPS)Mobility Management Entity (MME) and Serving GPRS Support Node (SGSN) related interfaces based on Diameter protocolRelease 17TS

E.2.1 General

The Diameter message priority mechanism is an optional feature.

It is recommended to make use of IETF  RFC 7944 [57] over the S6a/S6d interfaces of an operator network when the overload control defined in Annex C is applied on these S6a/d interfaces.

E.2.2 HSS, CSS, EIR behaviour

When the HSS, the CSS or the EIR supports the Diameter message priority mechanism, the HSS, the CSS, or the EIR shall comply with IETF RFC 7944 [57].

The HSS or the CSS sending a request shall determine the required priority according to its policies. When priority is required, the HSS or the CSS shall include the DRMP AVP indicating the required priority level in the request it sends, and shall prioritise the request according to the required priority level.

When the HSS or the CSS receives the corresponding response, the HSS or the CSS shall prioritise the received response according to the priority level received within the DRMP AVP if present in the response, otherwise according to the priority level of the corresponding request.

When the HSS, the CSS, or the EIR receives a request, it shall handle the request according to the received DRMP AVP priority level. For the response, the HSS, the CSS, or the EIR may modify the priority level received in the DRMP AVP according to its policies and shall handle the response according to the required priority level. If the required priority level is different from the priority level received in the request, the HSS, the CSS, or the EIR shall include the DRMP AVP in the response.If:

– the HSS, the CSS or the EIR supports using the Diameter message priority mechanism for DSCP marking purposes,

– the transport network utilizes DSCP marking, and

– message-dependant DSCP marking is possible for the protocol stack transporting Diameter,

then the HSS, the CSS or the EIR shall set the DSCP marking for transport of the request or response according to the required priority level.

When not-explicitly requested, the inclusion and priority value of the DRMP AVP in Diameter messages are implementation specific.

E.2.3 MME/SGSN behaviour

When the MME/SGSN supports the Diameter message priority mechanism, the MME/SGSN shall comply with IETF RFC 7944 [57].

The MME/SGSN sending a request shall determine the required priority according to its policies. When priority is required, the MME/SGSN shall include the DRMP AVP indicating the required priority level in the request it sends, and shall prioritise the requests according to the required priority level.

When the MME/SGSN receives the corresponding response, it shall prioritise the received response according to the priority level received within the DRMP AVP if present in the response, otherwise according to the priority level of the corresponding request.

When the MME/SGSN receives a request, it shall handle the request according to the received DRMP AVP priority level. For the response, it may modify the priority level received in the DRMP AVP according to its policies and shall handle the response according to the required priority level. If the required priority level is different from the priority level received in the request, it shall include the DRMP AVP in the response.

If:

– the MME/SGSN supports using the Diameter message priority mechanism for DSCP marking purposes,

– the transport network utilizes DSCP marking, and

– message-dependant DSCP marking is possible for the protocol stack transporting Diameter,

then the MME/SGSN shall set the DSCP marking for transport of the request or response according to the required priority level.

Diameter requests related to high priority traffic (e.g. MPS as identified by the MME/SGSN via the RRC Establishment Cause IE set to the highPriorityAccess value as per 3GPP TS 36.413 [19] or through subscription information in the MPS-Priority AVP, emergency) shall contain a DRMP AVP with a high priority of which the level value is operator dependent.

When not-explicitly requested, the inclusion and priority value of the DRMP AVP in Diameter messages are implementation specific.

Annex F (normative):
Diameter load control mechanism