Section: 13.3.2 Principles
Content: The following principles shall apply if this procedure is supported, enabled by operator policy and if the PGW pertains to the same PLMN as the originating entity or if the PGW pertains to a different PLMN and operator policy in the originating entity allows to use this procedure towards this PLMN. A GTP-C entity originating a Create Session Request (i.e. MME, SGSN, TWAN or ePDG) shall include in the message the Origination Time Stamp indicating the absolute time at which the request is initiated, as specified in clause 13.2.2, and the Maximum Wait Time indicating the maximum time period to complete the processing of the request. The Maximum Wait Time, together with the Origination Time Stamp, indicates the absolute time at which the request times out at the originating entity. The MME/SGSN shall set the Maximum Wait Time to a value smaller or equal to (N3+1) x T3 set in the SGW, to avoid upstream entities continuing to process requests which would have ceased to be processed by the SGW, which could result in hanging contexts in upstream entities. NOTE 1: If the Maximum Wait Time is set to a value smaller than N3 x T3 set in the SGW, the SGW actually stops retransmitting a given GTP-C Create Session Request as soon as it receives a rejection response from the PGW due to the expiry of the Maximum Wait Time. I.e. the Maximum Wait Time actually leads to shorten the duration during which the SGW retransmits the GTP-C request. The SGW shall forward the Origination Time Stamp over the S5/S8 interface as specified in clause 13.2.2. The SGW shall also forward the Maximum Wait Time over the S5/S8 interface, if received from the MME/SGSN. Upon receipt of a request which contains the Origination Time Stamp and the Maximum Wait Time parameters, the receiving entity should check that the request has not already timed out at the originating entity. The receiving entity may perform additional similar checks during the processing of the request, e.g. upon receipt of a response from the next upstream entity. The receiving entity should reject a request that is known to have timed out with the cause 'Timed Out Request'; it may alternatively drop the request. Besides, the receiving entity should initiate the release of any session it may have successfully created towards an upstream entity, to avoid hanging sessions in the network. NOTE 2: Sending a rejection response over the last hop towards the originating node, i.e. over S11/S4 or S2a/S2b, is not useful as the request has timed out at the originated entity. In the context of this specification, the receiving entity refers to an SGW or PGW. 3GPP TS 29.212[ Policy and Charging Control (PCC); Reference points ]  [29] and 3GPP TS 29.273[ Evolved Packet System (EPS); 3GPP EPS AAA interfaces ]  [68] further specify: - the PGW requirements regarding the forwarding of the Maximum Wait Time parameter over the Gx and/or S6b interfaces, when received from the SGW or TWAN/ePDG; - the handling of the Maximum Wait Time parameter by the PCRF and 3GPP AAA Server. An originating entity which detects a NTP failure shall not insert the Origination Time Stamp and the Maximum Wait Time parameters towards other entities. A receiving entity which detects a NTP failure shall ignore the the Maximum Wait Time parameter.