6.3 General on elementary ESM procedures

24.3013GPPNon-Access-Stratum (NAS) protocol for Evolved Packet System (EPS)Release 18Stage 3TS

Tools: ARFCN - Frequency Conversion for 5G NR/LTE/UMTS/GSM

6.3.1 Services provided by lower layers

Unless explicitly stated otherwise, the procedures described in the following clauses can only be executed whilst a NAS signalling exists between the UE and the MME.

6.3.2 Principles of address handling for ESM procedures

Transaction related procedures use the procedure transaction identity as address parameter in the ESM message header. When the UE or the network initiates a transaction related procedure, it shall include a valid procedure transaction identity value in the message header and set the EPS bearer identity to "no EPS bearer identity assigned". When the ProSe UE-to-network relay initiates the transaction related procedure remote UE report, it shall include a valid procedure transaction identity value in the message header and set the EPS bearer identity to a valid EPS bearer identity value.

If the response message is again a transaction related message, e.g. a PDN CONNECTIVITY REJECT, PDN DISCONNECT REJECT, BEARER RESOURCE ALLOCATION REJECT, BEARER RESOURCE MODIFICATION REJECT, ESM INFORMATION REQUEST message or ESM DUMMY MESSAGE from the network or an ESM INFORMATION RESPONSE message or ESM DUMMY MESSAGE from the UE, the sending entity shall include the procedure transaction identity value received with the request message and set the EPS bearer identity to "no EPS bearer identity assigned" (see examples in figures 6.3.2.1, 6.3.2.1a and 6.3.2.2). If the response message is the transaction related message REMOTE UE REPORT RESPONSE message from the network, the network shall include the procedure transaction identity value received with the request message and set the EPS bearer identity to the EPS bearer identity value received from the ProSe UE-to-network relay (see example in figure 6.3.2.2a).

If an ESM DUMMY MESSAGE is sent in response to a received ESM DUMMY MESSAGE, the sending entity shall include the received procedure transaction identity value in the message header and set the EPS bearer identity to "no EPS bearer identity assigned".

Figure 6.3.2.1: Transaction related procedure initiated by the UE and rejected by the network

Figure 6.3.2.1a: Transaction related procedure initiated by the UE and responded by a network initiated transaction related request

Figure 6.3.2.2: Transaction related procedure initiated by the network

Figure 6.3.2.2a: Transaction related procedure initiated by the UE

EPS bearer context related procedures use the EPS bearer identity as address parameter in the ESM message header. When the network initiates an EPS bearer context related procedure, it shall include a valid EPS bearer identity value in the message header. The procedure transaction identity value shall be set as follows:

– If the EPS bearer context related procedure was triggered by the receipt of a transaction related request message from the UE, the network shall include the procedure transaction identity value received with the transaction related request message in the message header of the EPS bearer context related request message (see example in figure 6.3.2.3).

– If the procedure was triggered network-internally, the network shall set the procedure transaction identity value in the message header of the EPS bearer context related request message to "no procedure transaction identity assigned" (see example in figure 6.3.2.4).

– If the procedure was triggered by the transport of user data via the control plane, the network shall set the procedure transaction identity value in the message header of the EPS bearer context related request message to "no procedure transaction identity assigned" (see example in figure 6.3.2.5).

In the response message of the EPS bearer context related procedure, the UE shall include the EPS bearer identity value received from the network and set the procedure transaction identity value to "no procedure transaction identity assigned".

When the UE initiates an EPS bearer context related procedure and the procedure was triggered by the transport of user data via the control plane, it shall include a valid EPS bearer identity value and set the procedure transaction identity value to "no procedure transaction identity assigned" in the message header (see example in figure 6.3.2.6).

Figure 6.3.2.3: EPS bearer context related procedure triggered by a transaction related request

Figure 6.3.2.4: EPS bearer context related procedure triggered network-internally

Figure 6.3.2.5: EPS bearer context related procedure triggered by network for the transport of user data via the control plane

Figure 6.3.2.6: EPS bearer context related procedure triggered by UE for the transport of user data via the control plane

6.3.3 Abnormal cases in the UE

The following abnormal case can be identified:

a) ESM uplink message transmission failure indication by lower layers

Unless the procedure descriptions in clause 6.6 specify a different behaviour, the following applies:

If lower layers indicate a TAI change, but the current TAI is not in the TAI list, the ESM procedure shall be aborted and re-initiated after successfully performing a tracking area updating procedure.

If lower layers indicate a TAI change, but the current TAI is still part of the TAI list, it is up to the UE implementation how the ESM procedure is re-initiated.

If lower layers indicate the TAI has not changed, it is up to the UE implementation how the ESM procedure is re-initiated.

NOTE 1: The ESM procedure can typically be re-initiated using a retransmission mechanism of the uplink message (the one that has previously failed to be transmitted) with new sequence number and message authentication code information thus avoiding to restart the whole procedure.

The case a) above does not apply to the ESM INFORMATION RESPONSE message.

NOTE 2: The ESM INFORMATION RESPONSE message cannot be subjected to a transmission failure by lower layers due to handover as no handover message can be accepted by the UE prior to reception of the ATTACH ACCEPT message (see 3GPP TS 36.331 [22]).

b) Transmission failure of the ACTIVATE DEFAULT EPS BEARER CONTEXT ACCEPT message indication from EMM sublayer when the UE received any ACTIVATE DEDICATED EPS BEARER CONTEXT REQUEST messages during the attach procedure

It is up to the UE implementation how the dedicated EPS bearer context activation procedure is re-initiated.

NOTE 3: The ESM procedure can typically be re-initiated using a retransmission mechanism of the ACTIVATE DEDICATED EPS BEARER CONTEXT ACCEPT message or ACTIVATE DEDICATED EPS BEARER CONTEXT REJECT message with new sequence number and message authentication code information thus avoiding to restart the whole procedure.

6.3.4 Abnormal cases in the network

The following abnormal case can be identified:

a) Lower layer indication of non-delivered NAS PDU due to handover

Unless the procedure descriptions in clause 6.4, 6.5 or 6.6 specify a different behaviour, the following applies:

If the downlink ESM NAS message could not be delivered due to an intra MME handover and the target TA is included in the TAI list, then upon successful completion of the intra MME handover the MME shall retransmit the ESM message. If a failure of the handover procedure is reported by the lower layer and the S1 signalling connection exists, the MME shall retransmit the downlink ESM NAS message.

b) Lower layer indication of non-delivered NAS PDU due to inter-eNodeB connected mode mobility when the transport of user data via the control plane is used

If the downlink ESM NAS message could not be delivered due to inter-eNodeB connected mode mobility and the MME is not changed, then upon successful completion of inter-eNodeB connected mode mobility the MME shall retransmit the ESM message. If a failure of inter-eNodeB connected mode mobility is reported by the lower layer and the S1 signalling connection exists, the MME shall retransmit the downlink ESM NAS message.

NOTE: If the downlink ESM NAS message could not be delivered due to inter-eNodeB connected mode mobility and the MME is changed, the retransmission of downlink ESM NAS message is not supported.

6.3.5 Handling of APN based congestion control

The network may detect and start performing the APN based congestion control when one or more APN congestion criteria as specified in 3GPP TS 23.401 [10] are met. The network may store an APN congestion back-off time on a per UE and congested APN basis. If the UE does not provide an APN for a non-emergency PDN connection, then the MME uses the APN which is used in PDN GW selection procedure as congested APN. When APN based congestion control is active, the network may reject session management requests except the modification of bearer resources requests from UEs or disconnect existing PDN connections with ESM cause value #26 "insufficient resources".

In the UE, EPS session management timers T3396 for APN based congestion control are started and stopped on a per APN basis. The APN associated with T3396 is the APN provided by the UE when the PDN connection is established. If no APN is included in the PDN CONNECTIVITY REQUEST or, when applicable, in the ESM INFORMATION RESPONSE message, then T3396 is associated with no APN. For this purpose the UE shall memorize the APN provided to the network during the PDN connection establishment. The timer T3396 associated with no APN will never be started due to any ESM procedure related to an emergency PDN connection. If the timer T3396 associated with no APN is running or is deactivated, it does not affect the ability of the UE to request an emergency PDN connection.

If timer T3396 is running or is deactivated, the UE is allowed to indicate change of the 3GPP PS data off UE status, initiate PDN disconnection procedure, initiate bearer resource modification procedure to release of bearer resources for the respective APN, and if the UE is a UE configured to use AC11 – 15 in selected PLMN, then the UE is allowed to initiate an attach procedure or any EPS session management procedure for the respective APN.

6.3.5A Handling of group specific session management congestion control

The network may detect and start performing the group specific session management congestion control when one or more group congestion criteria as specified in 3GPP TS 23.401 [10] are met. When group specific session management congestion control is active, the mechanism for APN based congestion control as specified in clause 6.3.5 shall be followed.

6.3.6 Handling of network rejection not due to APN based congestion control

The network may include a back-off timer value in an EPS session management reject message to regulate the time interval at which the UE may retry the same procedure. For ESM cause values other than #26 "insufficient resources", the network may also include the re-attempt indicator to indicate whether the UE is allowed to re-attempt the corresponding session management procedure for the same APN in A/Gb or Iu mode or N1 mode after inter-system change.

NOTE 1: If the network includes this back-off timer value, then the UE is blocked from sending another ESM request for the same procedure for the same PLMN and APN combination for the specified duration. Therefore, the operator needs to exercise caution in determining the use of this timer value.

NOTE 2: If the re-attempt indicator is not provided by the network, a UE registered in its HPLMN or in an EHPLMN (if the EHPLMN list is present) can use the configured SM_RetryAtRATChange value specified in the NAS configuration MO or in the USIM NAS_CONFIG file to derive the re-attempt indicator as specified in clauses 6.5.1.4.3, 6.5.3.4.3, and 6.5.4.4.3.

If re-attempt in A/Gb or Iu mode or N1 mode is allowed, the UE shall consider the back-off timer to be applicable only to the EPS session management in S1 mode for the rejected EPS session management procedure and the given PLMN and APN combination. If re-attempt in A/Gb and Iu mode and N1 mode is not allowed, the UE shall consider the back-off timer to be applicable to all three NAS protocols, i.e. applicable to the EPS session management in S1 mode for the rejected EPS session management procedure, to the GPRS session management in A/Gb and Iu mode for the corresponding session management procedure and the given PLMN and APN combination and to the 5GS session management in N1 mode for the corresponding session management procedure and the given PLMN and APN combination.

NOTE 3: In the present clause the terms APN and DNN are referring to the same parameter.

The APN of the PLMN and APN combination associated with the back-off timer is the APN provided by the UE when the PDN connection is established. If no APN is included in the PDN CONNECTIVITY REQUEST or, when applicable, in the ESM INFORMATION RESPONSE message, then the back-off timer is associated with the combination of the PLMN and no APN. For this purpose the UE shall memorize the APN provided to the network during the PDN connection establishment. The back-off timer associated with the combination of a PLMN with no APN will never be started due to any ESM procedure related to an emergency PDN connection. If the back-off timer associated with the combination of a PLMN with no APN is running, it does not affect the ability of the UE to request an emergency PDN connection.

The network may additionally indicate in the re-attempt indicator that a command to back-off is applicable not only for the PLMN in which the UE received the EPS session management reject message, but for each PLMN included in the equivalent PLMN list at the time when the EPS session management reject message was received.

If the back-off timer is running or is deactivated for a given PLMN and APN combination, and the UE is a UE configured to use AC11 – 15 in selected PLMN, then the UE is allowed to initiate an attach procedure or any EPS session management procedure for this PLMN and APN combination.

6.3.7 Handling of WLAN offload control

In networks that support offloading of traffic to WLAN, as specified in 3GPP TS 36.331 [22], a permission to offload is determined for the UE and the PDN connection in accordance with 3GPP TS 23.401 [10] clause 4.3.23.

6.3.8 Handling of serving PLMN rate control

Serving PLMN rate control enables the serving PLMN to protect its MME and the signalling radio bearers in the E-UTRAN from load generated by NAS messages with user data over control plane. The MME can inform the UE of any local serving PLMN rate control during the default EPS bearer context activation procedure (see clause 6.4.1). If the serving PLMN rate control is enabled, the MME shall start the serving PLMN rate control for the PDN connection when the first NAS message with user data over control plane is received over the PDN connection. The UE shall limit the rate at which it generates uplink NAS messages with user data over control plane to comply with the serving PLMN policy provided by the network. The indicated rate in a NAS procedure applies to the PDN connection the NAS procedure corresponds to, and the indicated rate is valid until the PDN connection is released.

Serving PLMN rate control is applicable for PDN connections established for control plane CIoT EPS optimization only.

Any serving PLMN rate control information provided by the network to the UE is only applicable for the PLMN which provided this information. This serving PLMN rate control information shall be discarded when the UE successfully registers to another PLMN.

NOTE: The serving PLMN can discard or delay NAS messages including user data over control plane that exceed the limit provided for serving PLMN rate control.

6.3.9 Handling of APN rate control

APN rate control controls the maximum number of uplink user data messages including uplink exception data reporting sent by the UE in a time interval for the APN in accordance with 3GPP TS 23.401 [10]. The UE shall limit the rate at which it generates uplink user data messages to comply with the APN rate control policy. The NAS shall provide the indicated rates to upper layers for enforcement. The indicated rates in a NAS procedure applies to the APN the NAS procedure corresponds to, and the indicated rates are valid until a new value is indicated or the last PDN connection using this APN is released.

If the UE supports APN rate control, the UE shall provide the support indication of APN rate control and additional APN rate control for exception data reporting to the network. If the UE indicates support of additional APN rate control for exception data reporting, the network may provide the APN rate control parameters for exception data to the UE. If the UE does not indicate support of additional APN rate control for exception data reporting, the network shall not provide the APN rate control parameters for exception data to the UE.

If an allowed indication of additional exception reports is provided with the APN rate control parameters and:

– the additional APN rate control parameters for exception data is provided and the limit for additional rate for exception data reporting is not reached; or

– the additional APN rate control parameters for exception data is not provided,

the UE is allowed to send uplink exception reports even if the limit for the APN rate control has been reached.

NOTE 1: The HPLMN can discard or delay user data that exceeds the limit provided for APN rate control.

Upon inter-system change from S1 mode to N1 mode, the UE shall store the current APN rate control status for each APN associated with PDN connection(s) to be transferred from S1 mode to N1 mode as specified in 3GPP TS 23.501 [58].

NOTE 2: How long the UE stores the current APN rate control status is implementation specific.

Upon inter-system change from N1 mode to S1 mode, the UE shall use the stored APN rate control status, if any, to comply with the APN rate control policy for an APN as specified in 3GPP TS 23.501 [58] if:

a) there is at least one PDN connection associated with this APN was transferred from N1 mode to S1 mode; and

b) the validity period of the stored APN rate control status has not expired.

After inter-system change from S1 mode to N1 mode, if all the PDU sessions associated with the same APN that was used in S1 mode are released, the UE shall delete the stored APN rate control status for this APN.

6.3.10 Handling of 3GPP PS data off

A UE, which supports 3GPP PS data off (see 3GPP TS 23.401 [10]), can be configured with up to two lists of 3GPP PS data off exempt services as specified in 3GPP TS 24.368 [15A] or in the EF_{3GPPPSDATAOFF} USIM file as specified in 3GPP TS 31.102 [17]:

– a list of 3GPP PS data off exempt services to be used in the HPLMN or EHPLMN (if the EHPLMN list is present); and

– a list of 3GPP PS data off exempt services to be used in the VPLMN.

If only the list of 3GPP PS data off exempt services to be used in the HPLMN or EHPLMN (if the EHPLMN list is present) is configured at the UE, this list shall be also used in the VPLMN.

If the UE supports 3GPP PS data off, the UE shall provide the 3GPP PS data off UE status in the protocol configuration options IE during attach, UE-requested PDN connectivity, and UE-requested bearer resource modification procedure (see clause 5.5.1, 6.5.1, and 6.5.4).

NOTE 1: The sending of the 3GPP PS data off UE status to the network happens also when the user activates or deactivates 3GPP PS data off while connected via WLAN access only, and then handover to 3GPP access occur.

The network informs the UE about the support of 3GPP PS data off during the activation of the default bearer of a PDN connection (see clause 6.4.1). If 3GPP PS data off support is not indicated in the protocol configuration options IE in the ACTIVATE DEFAULT EPS BEARER CONTEXT REQUEST message, the UE shall not indicate any change of 3GPP PS data off UE status for the PDN connection established by the default EPS bearer context activation procedure; otherwise the UE shall indicate change of the 3GPP PS data off UE status for the PDN connection by using the UE-requested bearer resource modification procedure as specified in clause 6.5.4. If the network does not provide indication of support of 3GPP PS data off during default EPS bearer context activation procedure of the PDN connection, the UE behaviour for non-exempt service requests from the network is implementation dependent.

When the 3GPP PS data off UE status is "activated":

a) the UE does not send uplink IP packets except:

– for those services indicated in the list of 3GPP PS data off exempt services to be used in the HPLMN or EHPLMN (if the EHPLMN list is present) as specified in 3GPP TS 24.368 [15A] when the UE is in its HPLMN or EHPLMN (if the EHPLMN list is present);

– for those services indicated in the list of 3GPP PS data off exempt services to be used in the HPLMN or EHPLMN (if the EHPLMN list is present) when the UE is in the VPLMN, if only the list of 3GPP PS data off exempt services to be used in the HPLMN or EHPLMN (if the EHPLMN list is present) is configured to the UE as specified in 3GPP TS 24.368 [15A];

– for those services indicated in the list of 3GPP PS data off exempt services to be used in the VPLMN when the UE is in the VPLMN, if the list of 3GPP PS data off exempt services to be used in the VPLMN is configured to the UE as specified in 3GPP TS 24.368 [15A];

– for those services indicated in the EF_{3GPPPSDATAOFF} USIM file as specified in 3GPP TS 31.102 [17];

– any uplink traffic due to procedures specified in 3GPP TS 24.229 [13D]; and

– any uplink traffic due to procedures specified in 3GPP TS 24.623 [50]; and

b) the UE does not send uplink non-IP or Ethernet user data packets.

Otherwise the UE sends uplink user data packets without restriction.

NOTE 2: If the UE supports 3GPP PS data off, uplink IP packets are filtered as specified in 3GPP TS 24.229 [13D] in L.3.1.5.

6.3.11 Handling of Reliable Data Service

If the UE supports Reliable Data Service (see 3GPP TS 24.250 [51]), the UE may request data transfer using Reliable Data Service for a PDN connection in the extended protocol configuration options IE during attach and UE-requested PDN connectivity procedures (see clause 5.5.1 and 6.5.1).

The Reliable Data Service may only be used with PDN connections for which the "Control plane only" indicator is set or with PDN connections using the control plane CIoT EPS optimization when the MME does not move such PDN connections to the user plane.

The SCEF or P-GW shall inform the UE about the acceptance of UE’s request for Reliable Data Service usage during the activation of the default bearer of a PDN connection (see clause 6.4.1) in the extended protocol configuration options IE in the ACTIVATE DEFAULT EPS BEARER CONTEXT REQUEST message.

If the SCEF or P-GW accepts the use of Reliable Data Service to transfer data for the specified PDN connection, the UE shall use this PDN connection exclusively for data transfer using Reliable Data Service; otherwise the UE shall not use this PDN connection for data transfer using Reliable Data Service.

6.3.12 Handling of Ethernet PDN type

A UE may support the Ethernet PDN type. A network may support the Ethernet PDN type.

6.3.13 Handling of Uncrewed aerial vehicle identification, authentication, and authorization

6.3.13.1 General

An EPS can support uncrewed aerial vehicle identification, authentication, and authorization (see 3GPP TS 23.256 [60]).

Before accessing EPS for UAS services, the UE supporting UAS services must have an assigned CAA-level UAV ID.

6.3.13.2 Authentication and authorization of UAV

The UE supporting UAS services may request a PDN connection for USS communication during attach and UE-requested PDN connectivity procedures (see clause 5.5.1 and 6.5.1). In the request of the PDN connection for USS communication, the UE provides CAA-level UAV ID to the network via the protocol configuration options and the network may decide to perform UUAA-SM procedure. If provided by the upper layers, a UE supporting UAS services may provide to the network the USS address via the protocol configuration options during attach and UE-requested PDN connectivity procedures so that the network may use the information to discover the USS.

After successful UUAA-SM procedure, the network may initiate the re-authentication or re-authorization procedure for the UE supporting UAS services as a part of network-initiated EPS bearer context modification procedure. If UUAA-SM fails during the re-authentication or a re-authorization procedure, or if the revocation of UUAA is initiated by the network, then the associated PDN connection for USS communication is released.

6.3.13.3 Authorization of C2 communication

The network supports C2 communication authorization for pairing of UAV and UAV-C. The pairing of UAV and UAV-C needs to be authorized by USS successfully before the user plane connectivity for C2 communication is enabled. The UE supporting UAS services may provide the network with an identification information of UAV-C to pair with, if available, via the protocol configuration options as follows:

– If the UE uses a common PDN connectivity for both USS communication and C2 communication with a UAV-C, the C2 communication with the UAV-C can be authorized using UUAA-SM procedure during the PDN connectivity procedure or during the bearer resource modification procedure. If the pairing of UAV and UAV-C is revoked, the network shall disable C2 communication for the PDN connection.

NOTE: The network can disable C2 communication for the PDN connection e.g., by removing the packet filter(s) allocated for C2 communication during EPS bearer context modification procedure as specified in clause 6.4.3 or by deactivating the EPS bearer context for C2 communication during EPS bearer context deactivation procedure as specified in clause 6.4.4.

– If the UE uses separate PDN connectivity for, respectively, USS communication and C2 communication with a UAV-C, the C2 communication with the UAV-C is authorized using UUAA-SM during the PDN connectivity procedure. If the pairing of UAV and UAV-C is revoked, the PDN connectivity or C2 communication shall be released by the network.

The authorization of UAV flight can also be performed during the C2 communication authorization procedure. The UE supporting UAS services provides flight authorization information to the network via the protocol configuration options if the flight authorization information is already available in the UE.

6.3.13.4 Void

Void.