Section: 8.4 Cause
Content: Cause IE is coded as depicted in Figure 8.4-1. Figure 8.4-1: Cause Cause is a variable length IE, which may have either of the following two lengths values: - If n = 2, a = 0 and the Cause IE shall be 6 octets long. Therefore, octets "a(n+1) to a(n+4)" will not be present. - If n = 6, a = 1 and the Cause IE will be 10 octets long. For PMIP based S5/S8, the SGW/MAG shall do the mapping between GTPv2 Cause IE and respective PMIPv6 IE as specified in 3GPP TS 29.275[ Proxy Mobile IPv6 (PMIPv6) based Mobility and Tunnelling protocols; Stage 3 ]  [26]. The following bits within Octet 6 indicate: - Bits 8 to 4: Spare, for future use and set to zero - Bit 1 – CS (Cause Source): If this bit is set to 1, it indicates that the corresponding error cause is originated by the remote node (i.e., the MME/SGSN to a PGW, or the PGW to an MME/SGSN). This bit is set to 0 to denote that the corresponding error cause is originated by the node sending the message. The CS should be set to 1 by the SGW when the SGW relay a response message with cause value from the MME/SGSN to the PGW or from the PGW to the MME/SGSN. For PMIP based S5/S8, the SGW shall set the CS bit to 1 when the SGW/MAG relay a response message with the cause value from the PGW/LMA to the MME/SGSN. - Bit 2 – BCE (Bearer Context IE Error): If this bit is set to 1, it indicates that the corresponding rejection cause is due to the error in the Bearer Context IE. This bit shall be discarded if the cause value is one of Acceptance cause value as given in table 8.4-1. - Bit 3 – PCE (PDN Connection IE Error): If this bit is set to 1, it indicates that the corresponding rejection cause is due to the error in the PDN Connection IE. This bit shall be discarded if the cause value is one of Acceptance cause value as given in table 8.4-1. The Cause value shall be included in a response message. In a response message, the Cause value indicates the acceptance or the rejection of the corresponding request message. The Cause value indicates the explicit reason for the rejection. If the rejection is due to a mandatory IE or a verifiable conditional IE is faulty or missing, the offending IE shall be included within an additional field "a(n+1) to a(n+4)". Only Type and Instance fields of the offending IE that caused the rejection have a meaning. The length in the Octet 8-9 and spare bits in the Octet 10 shall be set to "0". In this case, the value of "n" shall be "6". Otherwise, the value of "n" is equal to "2". The Cause may also be included in the request message. In a request message, the Cause value indicates the reason for the request. "Request accepted" is returned when the GTPv2 entity has accepted a control plane request. "Context Not Found" is used in the response message by a GTP entity when it receives a message for which it does not have context, e.g. TEID-C or EBI is not known. When "Context Not Found" is received at Bearer Context IE level, it means the bearer context is unknown in the peer. When "Context Not Found" is received at message level together with a known TEID-C in the GTPv2-C header in the response message, this indicates some bearer contexts are not known in the peer; the sender of the request message should further determine, based on the bearer context(s) included in the request message, that: - if the default bearer is unknown, this means the PDN connection is not known in the peer; - if one or more dedicated bearers are unknown, this means only those dedicated bearer contexts are not known in the peer. "Context Not Found" may be used by the PGW in the Create Session Response message during the non-3GPP to 3GPP access handover procedures, if the request corresponds to the handover of a PDN connection which does not exist in the PGW. "Context Not Found" may be used by the PGW in the Create Session Response message during the 3GPP to non-3GPP access handover procedures, if the request corresponds to the handover of a PDN connection which does not exist in the PGW. "Service not supported" is used by the GTP entity when it receives a message, which corresponds to a feature or a service which is not supported by the node. "Service denied" is used when the requested service cannot be granted. "System failure" is used by the GTP entity to indicate a generic error condition. "No resources available" is used by the GTP entity to indicate the temporary unavailability of the resource(s) to process the received request. "Semantic error in the TFT operation", "Syntactic error in the TFT operation", "Semantic errors in packet filter(s)", "Syntactic errors in packet filters(s)", "UE context without TFT already activated", "Semantic error in the TAD operation" and "Syntactic error in the TAD operation" are indications of error cases involving TFT(s)/TAD(s) as specified in clause 7.7.11 in this specification. "Missing or unknown APN" is used by the PGW when it does not support the Access Point Name, received in Create Session Request message. "Relocation failure" is used by the target MME/S4-SGSN to indicate the source MME/S4-SGSN that the relocation has failed. "Relocation failure due to NAS message redirection" is used by the new MME/S4-SGSN to indicate to the old MME/S4-SGSN that the TAU/RAU procedure is not successful due to NAS message redirection as described in 3GPP TS 23.401[ General Packet Radio Service (GPRS) enhancements for Evolved Universal Terrestrial Radio Access Network (E-UTRAN) access ]  [3], or used by the initial AMF to indicate to the old MME that the context transfer procedure is not successful due to NAS message redirection as described in clause 4.11.1.3.4 of 3GPP TS 23.502[ Procedures for the 5G System (5GS) ]  [83]. "Denied in RAT" is used by the GTP entity to indicate that the requested service is not accepted in the RAT. "Preferred PDN type not supported" is used by the PGW to indicate that the PDN type received in the Create Session Request message is not supported by the PGW for the PDN corresponding to the received Access Point Name. "Protocol type not supported" is used by the SGW to indicate that the S5/S8 protocol type requested by the MME/S4-SGSN is not supported by it. "UE not responding" is used by the MME/S4-SGSN to indicate that the UE is not responding to the request initiated by the network, e.g. Paging. "UE refuses" is used by the GTP entity to indicate that the UE, without specifying further detail, rejected the request from the network. "Unable to page UE" is used by the MME/S4-SGSN to indicate its inability to page the UE, temporarily. "User authentication failed" is used by the GTP entity to indicate that the request is rejected due to a failure in the authentication/security procedure, or because the required user authentication cannot be performed (when the UE does not support secondary DN authentication and authorization over EPC but such a procedure is mandatory due to local policies in a combined PGW-C/SMF), or is used by a combined PGW-C/SMF for an UUAA-SM during PDN connection establishment procedure as described in clause 5.2.3.3 of 3GPP TS 23.256[ Support of Uncrewed Aerial Systems (UAS) connectivity, identification and tracking; Stage 2 ]  [90] or in authorization for C2 procedure as described in clause 5.2.5.3 of 3GPP TS 23.256[ Support of Uncrewed Aerial Systems (UAS) connectivity, identification and tracking; Stage 2 ]  [90]. "APN access denied – no subscription" is used to indicate that the PGW has denied the user access to an APN because a subscription is required, but the subscriber does not have the necessary subscription. "Remote peer not responding" is used by the SGW for the messages spanning through two interfaces. This cause value is returned by the SGW to the MME/S4-SGSN or PGW in a response message where no response message is received from the PGW or MME/S4-SGSN. "Collision with network initiated request" is used by the PGW to indicate that the UE-initiated bearer resource allocation/modification request is rejected since the PGW has requested a bearer resource allocation/modification for the same service using a network-initiated procedure. "Unable to page UE due to Suspension" is used by the MME/S4-SGSN to indicate that the UE has not been paged because the bearers of the UE are in a suspended state. "APN Restriction type Incompatible with currently active PDN connection" is used by the PGW to indicate that the newly requested PDN connection has APN restriction value that is not compatible with the currently active PDN connection(s)'s APN restriction value(s). "Invalid peer" is used by the SGW to indicate that currently the UE is being managed by the different node (e.g. MME/S4-SGSN) than the node (e.g. S4-SGSN/MME) which has sent the Delete Session Request message. "Invalid Reply from remote peer" is used by the SGW for the messages spanning through two interfaces. This cause value is returned by the SGW to the MME/SGSN or PGW in a reply message where the corresponding reply message on S5/S8 or S11/S4 from the PGW or MME/SGSN is not decoded as valid. "Temporarily rejected due to handover/TAU/RAU procedure in progress" is used by the MME/S4-SGSN for the bearer related procedure initiated by the PGW. When the handover/TAU/RAU with/without SGW change and/or MME/S4-SGSN change is in progress, the MME/S4-SGSN may receive Create / Update / Delete Bearer request message for the bearer creation, modification or deletion initiated by the PGW. If the handover/TAU/RAU procedure results in the SGW and/or MME/S4-SGSN change, then the bearer related procedure cannot be handled temporarily by the MME/S4-SGSN till the handover/TAU/RAU procedure is completed. In that case the MME/S4-SGSN shall reject the bearer related procedure with this rejection cause. This cause is also used to indicate that the Downlink Data Notification message is rejected temporarily due to the mobility procedures with MME or SGSN change in progress as specified in clause 5.3.4.3 in 3GPP TS 23.401[ General Packet Radio Service (GPRS) enhancements for Evolved Universal Terrestrial Radio Access Network (E-UTRAN) access ]  [3]. The usage of "Fallback to GTPv1" is specified in clause 7.10 "Fallback to GTPv1 mechanism". In the PGW initiated bearer deactivation procedure for the default bearer, the PGW may include the Cause IE in the Delete Bearer Request with values "RAT changed from 3GPP to Non-3GPP", "Reactivation requested" or "Reactivation disallowed to APN". "APN Congestion" is used by the PGW and it indicates that the PGW has detected congestion for the requested APN and performs overload control for that APN which does not allow the PDN connection to be established. "GTP-C Entity Congestion" is used to indicate that the GTP-C entity has detected node level congestion and performs overload control at the node level, which does not allow the request to be processed. "UE already re-attached" is used by MME/S4-SGSN for the network triggered service restoration procedure as specified in 3GPP TS 23.007[ Restoration procedures ]  [17]. The MME/S4-SGSN may send the Downlink Data Notification Acknowledge or Downlink Data Notification Failure Indication with this cause as part of the network triggered service restoration procedure. "PDP connection inactivity timer expires" is used by the PGW in Delete Bearer Request(s) to indicate that all the bearer(s) for the emergency PDN connection are deleted upon the inactivity timer expiry as specified in 3GPP TS 23.203[ Policy and charging control architecture ]  [48]. "Network failure" is used by the SGSN or MME in the Delete Session Request to indicate that the message is sent due to a network problem. "QoS parameter mismatch" is used by the SGSN or MME in the Delete Session Request to indicate that the PDN connection can not be established due to a QoS parameter mismatch. "MME/SGSN refuses due to VPLMN policy" is used by the MME/SGSN in the VPLMN to indicate to the PGW in the Create Bearer Response or Update Bearer Response that it does not allow the establishment or modification of the bearer due to VPLMN operator's policy. The listed cause values for rejection response message descriptions in clause 7 are not meant to be exhaustive lists. Therefore a GTPv2 node shall use the most appropriate matching rejection response cause value that is listed in Table 8.4-1. If a Bearer Resource Command message is related to an established PDN connection for LIPA or for SIPTO at the local network, the LGW shall reject the Bearer Resource Command with the cause value of "Bearer handling not supported". "Multiple PDN connections for a given APN not allowed" is used by SGW for reply message to the MME/S4-SGSN when PMIP-based S5/S8 is used. If either SGW or PGW does not support the multiple PDN connections to the same APN function, the SGW shall reject the PDN connectivity request procedure with this rejection cause when receiving Create Session Request for additional PDN connectivity to the given APN from the same UE. As specified in clause 5.3.1.1 in 3GPP TS 23.401[ General Packet Radio Service (GPRS) enhancements for Evolved Universal Terrestrial Radio Access Network (E-UTRAN) access ]  [3] and clause 9.2.1 in 3GPP TS 23.060[ General Packet Radio Service (GPRS); Service description; Stage 2 ]  [35], the cause value "New PDN type due to network preference" indicates that the UE has requested PDN type IPv4v6 and only IPv4 or IPv6 address is allowed for the PDN based on PGW operator policy. As specified in clause 5.3.1.1 in 3GPP TS 23.401[ General Packet Radio Service (GPRS) enhancements for Evolved Universal Terrestrial Radio Access Network (E-UTRAN) access ]  [3] and clause 9.2.1 in 3GPP TS 23.060[ General Packet Radio Service (GPRS); Service description; Stage 2 ]  [35], the cause value "New PDN type due to single address bearer only" indicates that the MS has requested PDN type IPv4v6 and both IPv4 and IPv6 addressing is possible in the PDN but the Dual Address Bearer Flag of the Indication IE is set to 0 or the Indication IE is absent, or only single IP version addressing is possible in the PDN. "PGW not responding" is used by the SGW in PGW Restart Notification to indicate that the peer PGW has failed and not restarted as specified in clause 7.9.5. "UE context without TFT already activated" is used by the PGW in the Bearer Resource Failure Indication message to indicate that the PGW has received the Bearer Resource Command message without TAD IE in the secondary PDP Context Activation procedure. "Target access restricted for the subscriber" is used by the MME/SGSN in the Context Response message to indicate that the target access is prohibited for the subscriber, based on the subscription profile. "P-TMSI Signature mismatch" is used by the SGSN or MME in the Identification Response and Context Response message if the P-TMSI Signature stored in the old SGSN or MME does not match the value sent by the UE via the new SGSN or MME. "Late Overlapping Request" is used by the PGW in the Create Session Response to indicate that the incoming request collides with an existing session which has a more recent time stamp than the time stamp of the new request, as specified in clause 13.2. "Timed Out Request" is used by the SGW and PGW in the Create Session Response to indicate that the incoming request is known to have already timed out at the originating entity, as specified in clause 13.3. "UE is temporarily not reachable due to power saving" is used by the MME/SGSN in the Create/Update Bearer Response message to reject the corresponding network initiated procedures for a Delay Tolerant PDN connection and also request the PGW to hold the network initiated procedure until it receives the subsequent Modify Bearer Request message with the UASI flag indicating that the UE is available for end to end signalling. "UE not authorised by OCS or external AAA Server" is used by the PGW in the Create Session Response to reject the corresponding UE initiated procedures when the OCS or an external AAA Server on SGi did not authorise it and the support of the Cause Code was indicated by the SGSN/MME within the Create Session Request. If a Create Session Request message requests the addition of an access to a PDN connection, and NBIFOM is not supported by the MME/SGSN, SGW or TWAN, the PGW should reject the request with the cause value of "Multiple accesses to a PDN connection not allowed". This cause is also used by the PGW in the Delete Bearer Request message to initiate the removal of 3GPP access from the PDN connection due to detection of the MME/SGSN or SGW not supporting NBIFOM at the inter-PLMN mobility procedure. "Request rejected due to UE capability" is used by the MME in the Create Bearer Response to reject the request to add an EPS bearer that would exceed the UE capability (e.g. a NB-IoT UE can only support up to 2 EPS bearers). This cause value does not prevent the PGW from sending Create Bearer Request later. "S1-U Path Failure" is used by the SGW in the Create Session Response, or in the Modify Bearer Response message, or in the Modify Access Bearer Response message to report an S1-U path failure. The SGW may include this cause code in a Downlink Data Notification message and/or a Delete Bearer Request message to report the S1-U path failure. See clause 20.3 in 3GPP TS 23.007[ Restoration procedures ]  [17]. "EPS to 5GS Mobility" is used by the PGW, and it indicates that PGW initiated bearer deactivation procedure is due to EPS to 5GS mobility procedures. "5GC not allowed" is used by the source MME in the Context Response message sent to the target AMF during an EPS to 5GS idle mode mobility procedure, to indicate that the UE is not allowed for 5GC, based on the subscription profile. "PGW mismatch with network slice subscribed by the UE" is used by the PGW in the Create Session Response message during an EPS to 5GS mobility procedure, to indicate that the PGW is not serving the network slice subscribed by the UE for the APN/DNN. "Rejection due to paging restriction" is used by the MME to indicate that the UE has not been paged because the MME holds stored Paging Restriction information for the UE that restricts the Downlink Data from causing paging as specified in clause 4.3.33.6 in 3GPP TS 23.401[ General Packet Radio Service (GPRS) enhancements for Evolved Universal Terrestrial Radio Access Network (E-UTRAN) access ]  [3] or the UE has rejected the page as specified in clause 4.3.33.4 in 3GPP TS 23.401[ General Packet Radio Service (GPRS) enhancements for Evolved Universal Terrestrial Radio Access Network (E-UTRAN) access ]  [3]. Table 8.4-1: Cause values The mapping at the MME/S4-SGSN between GTP cause values received over the S11/S4 interface and the NAS cause values sent to the UE is specified in Annex C.