Section: 12.3.1 Principles of overload control
Content: The stage 2 requirements on GTP-C overload control are defined in clause 4.3.7.1a.2 of 3GPP TS 23.401[ General Packet Radio Service (GPRS) enhancements for Evolved Universal Terrestrial Radio Access Network (E-UTRAN) access ]  [3] and clause 5.3.6.1a of 3GPP TS 23.060[ General Packet Radio Service (GPRS); Service description; Stage 2 ]  [35]. The high level principles are summarized below: a) Overload control is an optional feature; b) a GTP-C entity may signal its overload to its GTP-C peers by including Overload Control Information in GTP-C signalling which provides guidance to the receiving GTP-C entity to decide actions which lead to signalling traffic mitigation towards the sender of the information; c) the Overload Control Information may provide the overload information of a GTP-C entity, e.g. a PGW, or a specific APN(s) associated with the GTP-C entity; d) an MME/S4-SGSN may signal an overload to the PGW, via the SGW. An SGW may signal an overload to the MME/S4-SGSN and to the PGW. A PGW may signal an overload to the MME/S4-SGSN, via the SGW. For non-3GPP access based interfaces, a PGW may signal an overload to the ePDG and the TWAN; the ePDG and the TWAN may signal an overload to the PGW. NOTE 1: An MME/S4-SGSN will not signal an overload to the SGW (i.e. the SGW will not perform overload control towards the MME/S4-SGSN), as this is redundant with DDN throttling (see clause 12.3.3). e) the overload control feature should continue to allow for preferential treatment of priority users (eMPS) and emergency services; f) the Overload Control Information is piggybacked in GTP control plane request or response messages such that the exchange of the Overload Control Information does not trigger extra signalling; NOTE 2: The inclusion of Overload Control Information in existing messages means that the frequency increases as the signalling load increases, thus allowing faster feedback and better regulation. g) the computation and transfer of the Overload Control Information shall not add significant additional load to the GTP-C entity itself and to its corresponding peer GTP-C entities. The calculation of Overload Control Information should not severely impact the resource utilization of the GTP-C entity, especially considering the overload situation; h) clause 4.3.7.1a.2 of 3GPP TS 23.401[ General Packet Radio Service (GPRS) enhancements for Evolved Universal Terrestrial Radio Access Network (E-UTRAN) access ]  [3] and clause 4.5 of 3GPP TS 23.402[ Architecture enhancements for non-3GPP accesses ]  [45] provides examples of various potential overload mitigation actions based on the reception of the overload related information exchanged between GTP-C entities, for 3GPP access based interfaces and non-3GPP access based interfaces, respectively. However, the exact internal processing logics of a GTP-C entity will not be standardized; i) for the inter-PLMN case, local configuration may restrict the exchange and use of Overload Control Information across PLMNs; j) the GTP-C entity may decide to send different values of Overload Control Information on inter-network (roaming) and on intra-network (non-roaming) interfaces based on local configuration, i.e. the values sent on intra-network interfaces may differ from the values sent on inter-network interfaces. However, on intra-network interfaces, the GTP-C entity should send the same values between the 3GPP and non-3GPP access based interfaces;