When a TWAN fails, all its Bearer contexts/PDN connections affected by the failure become invalid and may be deleted. TWAN storage of subscriber data is volatile. When the TWAN receives a GTP-U PDU over GTPv2 based S2a 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 TWAN should ensure as far as possible that previously used TEID values are not immediately reused after a TWAN restart, in order to avoid inconsistent TEID allocation throughout the network. When the TWAN receives a user packet with an unknown GRE Key over PMIPv6 based S2a, the TWAN shall discard the packet and optionally respond 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 a TWAN restart, the TWAN shall delete all Bearer contexts affected by the restart that it may have stored and place local TWAN restart counter value in all GTPv2 Echo requests/responses messages and PMIPv6 heartbeat responses the TWAN sends to the PGW.

The TWAN will receive the PGW restart counter in GTPv2 Echo requests/ responses and PMIPv6 heartbeat responses that the TWAN receives from the PGW. When a TWAN 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/bearer contexts associated with the peer node that fails, and may free the associated internal TWAN resources.

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

If the TWAN supports the feature, the following procedures apply. During a PDN connection establishment, the TWAN shall provide one TWAN FQ-CSID containing exactly one CSID for that particular PDN connection to the PGW. The TWAN 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 TWAN determines that the PGW supports partial failure handling by the presence of the PGW FQ-CSID in the Create Session Response for GTPv2 based S2a and/or Proxy Binding Acknowledgement message for PMIPv6 based S2a.

If the TWAN supports the feature, the following procedures apply. When a TWAN 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 TWAN shall perform the following. The TWAN may perform implementation-specific operations to clean up any residual state associated with the CSID(s). The TWAN shall send Delete PDN Connection Set Request containing all the TWAN CSIDs of the component(s) failing in TWAN FQ-CSID over the GTPv2 based S2a interface or PMIPv6 Binding Revocation Indication with G bit set message containing the equivalent TWAN FQ-CSID(s) over the PMIPv6 based S2a interface to PGW peers supporting the feature. On the GTPv2 based S2a interface, upon receiving a GTPv2 Delete PDN Connection Set Response message with Cause value "Success", the TWAN 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 S2a interface, upon receiving a successful PMIPv6 Binding Revocation Acknowledgment message with G bit set, the TWAN shall conclude that the PGW has initiated the internal deletion of the PDN connections corresponding to the CSID(s) present in the PMIPv6 Binding Revocation Indication message. The TWAN 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 TWAN supports the feature, the following procedures apply. When an TWAN receives a GTPv2 Delete PDN Connection Set Request or PMIP6 Binding Revocation Indication with G bit set message from a PGW, the TWAN shall retrieve all the PDN connections corresponding to each of the FQ-CSID(s) present in the message. The TWAN shall delete all the retrieved PDN connections, and may free the associated internal TWAN resources. As a response, the TWAN 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 S2a, if the corresponding TWAN and PGW support the partial failure feature, when the TWAN receives an FQ-CSID value of a PGW over S2a, the TWAN shall overwrite the currently stored FQ CSID value with the received value. For the removal of an existing PDN connection established over S2a, if the corresponding TWAN and PGW support the partial failure feature, a TWAN removes the corresponding PDN data as well as any relevant stored FQ-CSID value of the PGW FQ-CSID.