When an ePDG fails, all its Bearer contexts/PDN connections affected by the failure become invalid and may be deleted. ePDG storage of subscriber data is volatile. When the ePDG receives a GTP-U PDU over GTPv2 based S2b for which no Bearer context exists, it shall discard the GTP-U PDU and return a GTP error indication to the originating node (i.e. the PGW). The ePDG should ensure as far as possible that previously used TEID values are not immediately reused after an ePDG restart, in order to avoid inconsistent TEID allocation throughout the network. When the ePDG receives a user packet with an unknown GRE Key over PMIPv6 based S2b, the ePDG shall discard the packet and optionally response back with an ICMP message, as specified in Section 8.2 of RFC 2473 and Section 8.3 of RFC 2473 for the node unreachable error case.

After an ePDG restart, the ePDG shall delete all MM Bearer contexts affected by the restart that it may have stored. During or immediately after an ePDG Restart the ePDG shall place local ePDG restart counter value in all GTPv2 Echo requests/responses messages and PMIPv6 heartbeat responses the ePDG sends to the PGW.

The ePDG will receive the PGW restart counter in GTPv2 Echo requests/ responses and PMIPv6 heartbeat responses that the ePDG receives from the PGW. When an ePDG detects that a peer PGW has restarted (see clause 18 "GTP-C based restart procedures" and clause 19 "PMIPv6 based restart procedures") it shall delete all PDN connection table data/MM bearer contexts associated with the peer node that fails, free any internal ePDG resources associated with those PDN connections and initiate the release of the corresponding SWu instances (i.e. IKEv2 tunnels).

See clause 23. The partial failure feature is optional for ePDG. If the ePDG does not support the feature then partial failure handling does not apply to that specific PDN connection.

If the ePDG supports the feature, the following procedures apply. During a PDN connection establishment, the ePDG shall provide one ePDG FQ-CSID containing exactly one CSID for that particular PDN connection to the PGW. The ePDG shall store the Node-ID and CSID from the FQ-CSID provided by the PGW for that particular PDN connection in its PDN Connection table. The ePDG determines that the PGW supports partial failure handling by the presence of the PGW FQ-CSID in the Create Session Response for GTPv2 based S2b and/or Proxy Binding Acknowledgement message for PMIPv6 based S2b.

If the ePDG supports the feature, the following procedures apply. When an ePDG detects that it has undergone a partial failure, it shall verify that one or more corresponding CSID(s) are present for the component undergoing a partial fault. If there is no such CSID, then the following does not apply. When one or more CSIDs are currently assigned, the ePDG shall perform the following. The ePDG may perform implementation-specific operations to clean up any residual state associated with the CSID(s). The ePDG shall send Delete PDN Connection Set Request containing all the ePDG CSIDs of the component(s) failing in ePDG FQ-CSID over the GTPv2 based S2b interface or PMIPv6 Binding Revocation Indication with G bit set message containing the equivalent ePDG FQ-CSID(s) over the PMIPv6 based S2b interface to PGW peers supporting the feature. On the GTPv2 based S2b interface, upon receiving a GTPv2 Delete PDN Connection Set Response message with Cause value "Success", the ePDG shall conclude that the PGW has initiated the internal deletion of the PDN connections corresponding to the FQ-CSID(s) present in the GTPv2 Delete PDN Connection Set Request message. Similarly, on the PMIPv6 based S2b interface, upon receiving a successful PMIP6 Binding Revocation Acknowledgment message with G bit set, the ePDG shall conclude that the PGW has initiated the internal deletion of the PDN connections corresponding to the CSID(s) present in the PMIP6 Binding Revocation Indication message. The ePDG is not required to perform any further recovery actions towards PGW peers for PDN connections in the connection set identified by the PGW FQ-CSID(s).

If the ePDG supports the feature, the following procedures apply. When an ePDG receives a GTPv2 Delete PDN Connection Set Request or PMIP6 Binding Revocation Indication with G bit set message from a PGW, the ePDG shall retrieve all the PDN connections corresponding to each of the FQ-CSID(s) present in the message. The ePDG shall delete all the retrieved PDN connections, free the associated internal resources and initiate the release of the corresponding SWu instances (i.e. IKEv2 tunnels). Other implementation-specific actions may be performed. As a response, the ePDG shall send a GTPv2 Delete PDN Connection Set Response message with an appropriate Cause value or a PMIPv6 Binding Revocation Acknowledgment message with G bit set to the PGW.

For the modification of an existing PDN connection established over 2b, if the corresponding ePDG and PGW support the partial failure feature, when the ePDG receives an FQ-CSID value of a PGW over S2b, the ePDG shall overwrite the currently stored FQ CSID value with the received value. For the removal of an existing PDN connection established over S2b, if the corresponding ePDG and PGW support the partial failure feature, an ePDG removes the corresponding PDN data as well as any relevant stored FQ-CSID value of the PGW FQ-CSID.