Section: 12.3.6 Propagating the MME/S4-SGSN identity to the PGW
Content: When the Overload Control feature is supported by the MME/S4-SGSN and the SGW, and it is also activated for the PLMN to which the PGW belongs (see clause 12.3.11), the following shall apply: - The MME/S4-SGSN shall include the MME/S4-SGSN identity towards the SGW during: - the PDN connection establishment, any mobility with an MME/S4-SGSN change or any SGW change procedures; - the dedicated bearer activation procedure, PGW initiated bearer modification procedure and PGW initiated bearer deactivation procedure as per the conditions specified in the corresponding messages. - The SGW shall forward the MME/S4-SGSN identifier to the PGW if it is received in the Create/Update/Delete Bearer Response messages. When it is received in other GTP-C messages, the SGW shall store the received MME/S4-SGSN identity and shall include the currently serving MME/S4-SGSN's identity in subsequent Modify Bearer Request messages which are sent over the S5/S8 interface, whenever there is signalling over the S5/S8 interface. NOTE: This allows updating of the PGW with the identity of the new MME/S4-SGSN during inter-MME/SGSN mobility scenarios as early as possible and without generating extra signalling over the S5/S8 interface. Inter-MME/inter-SGSN intra SGW mobility scenarios not requiring to send any S5/S8 signalling could result in the PGW not being updated with the currently serving MME/S4-SGSN's identity, for a given subscriber, until subsequent S5/S8 signalling takes place for the same PDN connection. However, considering these scenarios are not so frequent and considering that several features anyway require S5/S8 signalling during these scenarios (e.g. for user location reporting), the PGW will most often get the identity of the currently serving MME/S4-SGSN. Hence the risk that the PGW wrongly throttles PGW initiated signalling for that PDN connection, if the old MME/S4-SGSN is in overload, is low. - The PGW shall store the currently serving MME/S4-SGSN identity, received from the SGW, to be able to reduce the PGW initiated signalling messages for the PDN connections during an overload situation at the serving MME/S4-SGSN.