D.1 Message prioritisation over S6a/d

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

This clause describes possible behaviours of the MME/SGSN regarding message prioritisation as guidance and for an informative purpose when Diameter overload control is applied over S6a/d.

When the HSS is overloaded, the MME/SGSN will receive overload reports from the HSS requesting a reduction of the requests sent by the MME/SGSN. The following and not exhaustive considerations may be taken into account for the MME/SGSN throttling decisions:

– Prioritisation of requests related to priority traffic (e.g. MPS as identified by the MME/SGSN through access procedures, emergency)

– Identification of the procedures that can be deferred (e.g. UE reachable notification, purge after a long inactivity time), so to avoid to drop non deferrable procedures;

– Prioritisation of certain types of requests (i.e. between AIR, ULR, PUR, NOR) according to the context of their use, in particular:

– Higher prioritisation of ULR commands when used in relation with mobility management (e.g. handover) for an attached user, so to avoid the interruption of the service for the user;

– Lower prioritisation of AIR and ULR commands when related to an initial attach, so to avoid the attachment of new users;

– Skipping of optional authentication (e.g. in TAU procedures).

Annex E (normative):
Diameter message priority mechanism