Section: 12.3.5.1 Definition 12.3.5.1.1 General description
Content: Within a message, one or multiple instances of the Overload Control Information (OCI) IE may be included by the same GTP-C entity. Each instance shall provide information about the overload condition to allow the receiver to apply mitigation actions which will result in an efficient alleviation of the overload condition at the sender. The GTP-C entity shall always include the full set of overload control information, i.e. all the node level and/or APN level applicable instances of the OCI IE, when signalling overload control information in a message for the first time or subsequently towards the receiver, even when only a subset of the overload control information has changed. All the instances of the OCI IE provided by a given GTP-C entity in a message shall contain the same Overload Control Sequence Number. The Overload Control Sequence Number shall be incremented whenever the overload control information is modified (see clause 12.3.5.1.2.1). When including overload control information for some APN(s), the PGW should not provide any node level Overload Control Information unless the node level information is also applicable. The receiver shall overwrite any stored overload control information of a peer with the newly received overload control information (received via one or multiple instances of OCI IE) from the same GTP-C peer entity, if the new information is more recent than the old information as indicated by the Overload Control Sequence Number, e.g. if the receiver has stored 'X' instances of the OCI IE for a peer GTP-C entity, it shall overwrite those 'X' instances with the new set of 'Y' instances received in a message from the same GTP-C peer entity, where X, Y are any integer numbers. The receiver shall consider all the parameters received in the same instance of the OCI IE in conjunction while applying the overload mitigation action. When more than one instance of the OCI IE is included, the receiver shall consider the parameters included in each instance independently, while applying the overload mitigation action. The parameters are further described in clauses 12.3.5.1.2 and 12.3.5.1.3. Overload control information may be extended with new parameters in future versions of the specification. Any new parameter will have to be categorized as: - Non-critical optional parameters: the support of these parameters is not critical for the receiver. The receiver can successfully and correctly comprehend the Overload Control Information instance, containing one or more of these parameters, by using the other parameters and ignoring the non-critical optional parameters. - Critical optional parameters: the support of these parameters is critical for the receiver to correctly comprehend the instance of the Overload Control Information containing one or more of these parameters. The sender may include one or more non-critical optional parameter(s) within any instance of Overload Control Information, without having the knowledge of the receiver's capability to support the same. However, the sender shall only include one or more critical optional parameter(s) in any instance of Overload Control Information towards a receiver, if the corresponding receiver is known to support these parameter(s). The sender may be aware of this either via signalling methods or by configuration; this will have to be defined when introducing any such new parameter in the future. Each instance of the OCI shall be associated by default to the GTP-C entity corresponding to the peer node's IP address of the PDN connection, over which the OCI IE is received, i.e. to the IP address received within the "Sender F-TEID for control plane" IE, the "PGW S5/S8/ S2a/S2b F-TEID for PMIP based interface or for GTP based Control Plane interface" IE or within the "MME/S4-SGSN Identifier" IE. Alternatively, the GW (i.e. SGW and PGW) nodes may send Overload Control Information which is associated with the GW node's identity, i.e. the FQDN or IP address of the GW node received from the HSS (for a PGW) or the DNS (for an SGW or PGW), the identity determined during the GW selection. In that case, the GW node shall provide an explicit indication that the OCI IE included in the message belongs to the GW node's identity.