Section: 13.2.2 Principles
Content: The following principles shall apply if this procedure is supported and enabled by operator policy. 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. The SGW shall forward this parameter over the S5/S8 interface, if it is received from the MME/SGSN. Upon receipt of a session establishment request which collides with an existing session context, the PGW shall accept the new session establishment request only if it contains a more recent time stamp than the time stamp stored for the existing session. An incoming session request shall be considered as more recent than an existing session and be accepted if no Origination Time Stamp information was provided for at least one of the two sessions. The PGW shall reject an incoming request whose time stamp is less recent than the time stamp of the existing session with the cause 'Late Overlapping Request'. 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 Origination Time Stamp parameter over the Gx and/or S6b interfaces, when received from the SGW or TWAN/ePDG; - the handling of the Origination Time Stamp parameter by the PCRF and 3GPP AAA Server for an incoming request colliding with an existing session context. An originating entity which detects a NTP failure shall not include the Origination Time Stamp towards other entities.