Section: 12.2.1 Principles of load control
Content: The stage 2 requirements on GTP-C load control solution are defined in clause 4.3.7.1a.1 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) Load Control is an optional feature; b) a GTP-C node may signal its Load Control Information to reflect the operating status of its resources, allowing the receiving GTP-C peer node to use this information to augment the existing GW selection procedures; c) the calculation of the Load Control Information is implementation dependent and its calculation and transfer shall not add significant additional load to the node itself and to its corresponding peer nodes; d) the Load Control Information may provide load information of a GTP-C node (e.g. a PGW) or, if the APN level load control feature is supported, may provide the load information about specific APN(s); e) the SGW may send its Load Control Information to the MME/S4-SGSN. The PGW may send its Load Control Information to the MME/S4-SGSN via the SGW. For non-3GPP access based interfaces, the PGW may send its Load Control Information to the ePDG and TWAN; f) the Load Control Information shall be piggybacked in GTP-C request or response messages such that the exchange of Load Control Information does not trigger extra signalling; NOTE: The inclusion of Load Control Information in existing messages means that the frequency of transmission of load control information increases as the session load increases, allowing for faster feedback and thus better regulation of the load. g) a node supporting Load Control sends Load Control Information to a peer GTP-C node based on local configuration (see clause 12.2.6); h) the format of the Load Control Information shall be specified with enough precision to guarantee a common interpretation of this information allowing interoperability between nodes of different vendors; i) for the inter-PLMN case, local configuration may restrict the exchange and use of Load Control Information across PLMNs; j) the GTP-C node may decide to send different values of Load 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 node should send the same values between the 3GPP and non-3GPP access based interfaces. k) the Load Control Information received via GTP-C signalling shall be used in conjunction with the information received from the DNS, during the node selection procedure. Refer to 3GPP TS 29.303[ Domain Name System Procedures; Stage 3 ]  [32] for further details.