PDN Connection

PDN Connection Establishment

Figure 2-3illustrates the procedure of PDN connection establishment. When the UE performs the EPS attach procedure with PDN type of Non-IP, and the subscription information corresponding to either the default APN for PDN type of Non-IP or the UE requested APN includes the Invoke SCEF Selection indicator, then the MME initiates a T6a/T6b connection toward the SCEF corresponding to the SCEF ID indicator for that APN.

Figure 2-3 PDN Connection Establishment

The MME/SGSN creates a PDN connection toward the SCEF and allocates an EPS Bearer Identity (EBI) to that PDN connection. The MME/SGSN does so by sending a Create SCEF Connection Request (User Identity, EPS Bearer Identity, SCEF ID, APN, Serving PLMN Rate Control, Serving PLMN ID, IMEISV) message toward the SCEF. If the IWK-SCEF receives the Create SCEF Connection Request message from the MME/SGSN, it forwards it toward the SCEF.

The combination of EPS Bearer Identity, APN, and User Identity allows the SCEF to uniquely identify the PDN connection to the SCEF for a given UE. If no SCS/AS has performed the NIDD Configuration procedure with the SCEF for the User Identity, then the SCEF rejects the T6a/T6b connection setup with a cause NIDD Configuration Not Available.

The SCEF saves the EPS Bearer information in its Context for the user identified using User Identity and EBI. The SCEF sends a Create SCEF Connection Response (User Identity, EPS Bearer Identity, APN, PCO) message towards the MME/SGSN confirming establishment of the PDN connection to the SCEF for the UE. If the IWK-SCEF receives the Create SCEF Connection Response message from the SCEF, it forwards it toward the MME/SGSN.

PDN Connection Update

The MME/SGSN may update certain parameters that were provided in the T6a/T6b connection establishment request by sending a connection update message to SCEF. The MME/SGSN identifies the T6a/T6b connection by the IMSI and EPS Bearer Identifier. The MME/SGSN may update these parameters by a connection update message:

• Serving PLMN
• RAT Type
• Serving PLMN Rate threshold
• Origin Host and/or Origin-Realm of the MME/SGSN

The SCEF finds the context record in its database and if found updates the parameters provided in the connection update request. The SCEF then responds with the result of the update operation to the MME/SGSN.

PDN Connection Release

The MME/SGSN releases the T6a/T6b connection(s) towards the SCEF(s) corresponding to the "SCEF ID" indicator for that APN when the UE or MME/SGSN or HSS initiates a detach procedure.

The SCEF releases the T6a/b connection(s) towards the MME/SGSN corresponding to PDN connections when an NIDD Authorization Update Request from the HSS indicates that the User is no longer authorized for NIDD, or the Granted Validity Time for the NIDD configuration provided by the HSS expires or based on a NIDD configuration deletion request from the SCS/AS.

Figure 2-4 illustrates the procedure of T6a/T6b connection release when initiated by the MME/SGSN.

Figure 2-4 MME/SGSN Initiated PDN Connection Release

Figure 2-5 illustrates the procedure of T6a/T6b connection release when initiated by the SCEF.

Figure 2-5 SCEF-Initiated PDN Connection Release