MME supports temporary buffering of single MT Data Request received from SCEF while UE is in idle mode. The request is buffered till UE is paged and an MT Data Answer is sent upon paging success/failure.

The following functionality for temporary buffering is applicable on a UE basis.

• MT Data Request is buffered while UE is being paged till the corresponding MT Data Answer is sent.

• A single MT Data Request will be buffered per SCEF PDN.

• The subsequent MT Data Request for the PDN will not be buffered and immediately rejected with experimental result code DIAMETER_ERROR_UNABLE_TO_COMPLY (5012).

• Sends buffered non-IP payload to UE and MT Data Answer with success result code (2001) to SCEF, upon paging success.

• Sends MT Data Answer with experimental result code DIAMETER_ERROR_USER_TEMPORARILY_UNREACHABLE (5653) upon paging failure. MME also sends MT Data Answer with this result code due to expiry of SCEF wait time prior to paging completion.

• Sends Connection Management Request (CMR) with Connection-Action AVP set to Connection Update and CMR-Flags AVP set to 1, once UE comes to connected mode. MT Data Answer was previously sent with experimental result code DIAMETER_ERROR_USER_TEMPORARILY_UNREACHABLE (5653), so that SCEF can send buffered data to MME once UE is reachable.

• MT Data Request is not buffered if UE cannot be paged due to PSM/eDRX.

  MT Data Answer with cause code DIAMETER_ERROR_USER_TEMPORARILY_UNREACHABLE (5653) will be sent followed by CMR when UE comes to connected mode.

• Statistics are supported for MT Data Request buffered, MT Data Answer sent for buffered requests and MT Data Answer dropped for buffered requests.

The Buffering Non-IP Data from SCEF feature is enabled by default.

Connection Release when UE in Idle Mode : In this StarOS 21.20.26 release, MME supports the Connection Release (CMR - Connection Management Request) received from SCEF when UE in the Idle mode.

Without PDN support, if Connection Release is requested from SCEF for the last PDN in the UE Idle mode, MME initiates:

• Paging when ppf flag was TRUE

• Detach with Re-Attach required towards UE after successful completion of paging.

Before the implementation of Packet Data Network (PDN) Disconnect or Detach procedure in a network, MME followed the below process after receiving the permanent failure code:

1. The User Equipment (UE) connects to the network with Non-IP Data Delivery (NIDD) option and establishes T6a connection.

2. UE tries Mobile Originated (MO) NIDD whenever a Session DB on the SCEF gets cleared.

3. UE sends Non-Access Stratum (NAS) “MO REQUEST” with the data and receives NAS_SERVICE_ACCEPT.

4. The MME sends Diameter “MO-Data-Request” over T6A and receives “DIAMETER_ERROR_INVALID_EPS_BEARER (5651)” or “DIAMETER_ERROR_USER_UNKNOWN”.

However, there was data loss. This data loss was because of the lack of PDN Disconnect or Detach procedure initiation from MME towards the UE. UE may assume that it is T6a connected and retry MO NIDD indefinitely.

In StarOS 21.19 and later releases, the MME supports PDN Disconnect or Detach procedure towards the UE when it receives a MO Data Answer message with Permanent Failure Result-Code/Experimental-Result from SCEF. If the permanent failure is different from DIAMETER_ERROR_ INVALID_EPS_BEARER and from DIAMETER_ERROR_USER_UNKNOWN, then MME also initiates the "Connection Management by MME/SGSN" procedure to release the T6a connection between the MME and the SCEF.

The UE indicates in the ESM connection request (for example: in the Attach or PDN Connectivity Request) that a Non-IP PDN type is used. The subscription information has a default APN for PDN Type Non-IP, which the MME uses for the first received Non-IP connectivity request unless the UE has included an APN in the request. The MME then initiates a T6a connection towards the SCEF corresponding to the SCEF ID indicator for that APN.

At each PDN connectivity request, the MME decides which delivery mechanism (SCEF based delivery or SGi based delivery) is used for delivering the Non-IP data between RAN and AS. An indication associated with the used APN determines if SCEF based delivery or SGi based delivery shall be used.

When the MME decides to use SCEF based delivery mechanism for Non-IP data, a PDN connection is established towards the selected SCEF. Such a PDN Connection is also known as an "SCEF Connection".

The Non-IP Data Delivery over SCEF feature has the following limitations:

• In release 21.1.V0 (N5.1): MME does not support buffering of data.

  In 21.3 and later releases: MME supports temporary buffering of single MT Data Request received from SCEF while UE is in idle mode. Buffering of multiple MT Data Request messages per SCEF PDN for a UE is not supported.

• Non-IP data in-sequence delivery cannot be guaranteed and data PDUs may be lost requiring higher protocol layers to ensure guaranteed delivery when needed.

• Currently, only Connection Establishment, Connection Release, MO data transfer, MT data transfer with connected mode is supported.

  In StarOS 21.20.26 release, paging on MT data request and paging on Connection Release from SCEF for the UE in IDLE mode, is supported.

• For Control Plane IoT Optimized UEs, both Inter-MME and Intra-MME handovers are not supported.

The Non-IP Data Delivery over SCEF feature complies with the following standards:

• 3GPP TS 24.301 Non-Access-Stratum (NAS) protocol for Evolved Packet System (EPS); Stage 3.

• 3GPP TS 23.401 General Packet Radio Service (GPRS) enhancements for Evolved Universal Terrestrial Radio Access Network (E-UTRAN) access.

• 3GPP TS 23.682 Architecture enhancements to facilitate communications with packet data networks and applications.

• 3GPP TS 29.128 Mobility Management Entity (MME) and Serving GPRS Support Node (SGSN) interfaces for interworking with packet data networks and applications.

• 3GPP TS 29.274 3GPP Evolved Packet System (EPS); Evolved General Packet Radio Service (GPRS) Tunnelling Protocol for Control plane (GTPv2-C); Stage 3.

• 3GPP TS 29.272 Evolved Packet System (EPS); Mobility Management Entity (MME) and Serving GPRS Support Node (SGSN) related interfaces based on Diameter protocol.

The following CLI command configures SCEF-service:

configure 
   context context_name 
      scef-service service_name 
         [ no ] diameter endpoint endpoint_name 
         [ default ] diameter dictionary standard 
         end 

Notes:

• The prefix no disables the configuration.

• The prefix default assigns or restores the default vale for the selected parameters.

• The scef-service command is used to create and configure an SCEF Peer Service to communicate with SCEF peers.

• The service_name variable identifies the scef-service. The service name is a string with range 1 to 63 characters.

• The diameter command configures the Diameter interface (T6a-interface).

• The dictionary standard command configures the standard dictionary to be used for T6a interface.

• The endpoint endpoint_name command configures the diameter endpoint.

Note	It is recommended to not remove a diameter endpoint when there are active calls on the system. Adhere to the 'Method of Procedure' to remove an endpoint, otherwise the system behavior would be undefined.

The following CLI configuration associates the SCEF-service to an MME-service:

configure 
   context context_name 
      mme-service service_name 
         [ no ] scef-service service_name 
         end 

Notes:

• The no command prefix disables/disassociates the scef-service configuration.

• The scef-service command associates SCEF with its MME peer.

• The service_name identifies the name of the SCEF service that will be used by the MME service. It is a string of range from 1 to 63.

The following CLI configuration associates SCEF-service to the Call-Control-Profile.

configure 
   call-control-profile profile_name 
      [ remove ] scef-service service_name 
      end 

Notes:

• The no command prefix disables/disassociates the scef-service configuration.

• The scef-service command associates SCEF with the call-control-profile.

• The service_name identifies the name of the SCEF service. It is a string of range from 1 to 63.

The following CLI configures/overrides PDN Type indicator in APN profile.

configure 
   apn-profile profile_name 
      pdn-type { ip | non-ip { sgi | t6a [ scef-id scef_id [ scef-realm realm_name ] ] } } 
      remove pdn-type 
      end 

Notes:

• The remove command prefix removes the pdn-type configuration.

• The pdn-type command identifies the Cellular IoT PDN type.

• The ip keyword identifies the Cellular IoT PDN type as IP PDN.

• The non-ip keyword identifies the Cellular IoT PDN type as Non-IP PDN.

• The t6a keyword identifies the Cellular IoT Non-IP PDN delivery path type as T6a

• The scef-id scef-id-string is an optional keyword, which specifies the SCEF identifier at the T6a interface. The SCEF identifier is a string of length 1 up to 63 characters.

• The scef-realm realm-name is an optional keyword, which specifies the SCEF Diameter realm. The realm_name is string of length 1 up to 127 characters.

Use the following configuration in the APN Profile Configuration mode to configure the SCEF wait time value in APN Profile.

configure 
   apn-profile profile_name 
      [ remove ] ciot scef wait-time wait_time 
      end 

Notes:

• ciot : Configures the parameters related to Cellular IoT features.

• scef : Configures the SCEF specific parameters.

• wait-time wait_time : Specifies the wait time in seconds, before which MME is expected to send MT Data Answer (TDA) to SCEF in response to the MT Data Request (TDR) message. wait_time is an integer ranging from 1 to 100.

• The SCEF wait time configuration at MME overrides the value of SCEF wait time received in MT Data Request. MME will respond with MT Data Answer within the configured SCEF wait time value irrespective of the presence or absence of SCEF Wait Time AVP in MT Data Request sent by SCEF.

• This command is disabled by default.

This section provides information regarding show commands and/or their outputs in support of this feature.