Section: 4.11.5.9 Network Slice Admission Control
Content: Support of NSAC in conjunction with interworking with EPC is described in clause 5.15.11.5 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2]. If EPS counting is required for a network slice, the SMF+PGW-C performs NSACF discovery that supports controlling the maximum number of PDU sessions per network slice as described in clause 6.3.22 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2] and in clause 5.2.7.3.2. If non-Hierarchical NSAC or Centralized NSAC architecture is deployed at the network, the following impacts are applicable to clause 4.2.11.4 (Number of PDU Sessions per network slice availability check and update procedure): - The SMF+PGW-C invokes this procedure to perform network slice availability check on the number of PDU Sessions and update for S-NSSAI associated with the PDN connection during PDN connection establishment and PDN connection release. In this case the SMF in figure 4.2.11.4-1 is replaced with SMF+PGW-C. - Step 3: The NSACF determines whether or not to accept the request as described in clause 5.15.11.5 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2]. If Hierarchical NSAC architecture is deployed at the network, the following impacts are applicable to clause 4.2.11.4a: - The SMF+PGW-C invokes this procedure to perform network slice availability check on the number of PDU Sessions and update for S-NSSAI associated with the PDN connection during PDN connection establishment. In this case the SMF in figure 4.2.11.4a-1 is replaced with SMF+PGW-C. - Step 8: The NSACF determines whether or not to accept the request as described in clause 5.15.11.5 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2]. When the local maximum number is reached, the NSACF may interact with the Primary NSACF before it returns the response back to the SMF+PGW-C as defined in clause 4.2.11.4a. The SMF+PGW-C performs NSACF discovery that supports controlling the maximum number of UEs per network slice as described in clause 6.3.22 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2] and in clause 5.2.7.3.2. If non-Hierarchical NSAC or Centralized NSAC architecture is deployed at the network, the following impacts are applicable to clause 4.2.11.2 (Number of UEs per network slice availability check and update procedure): - The SMF+PGW-C invokes this procedure to perform network slice availability check on the number of UEs and update for S-NSSAI associated with the PDN connection during PDN connection establishment. In this case the AMF in figure 4.2.11.2-1 is replaced with SMF+PGW-C. - Step 2: The SMF+PGW-C includes in the message the S-NSSAI, identity of SMF+PGW-C, UE ID and update flag. In a centralized NSAC architecture, the SMF+PGW-C additionally includes the NSAC service area if available. - Step 3: The AMF ID is replaced by the SMF + PGW-C ID. - Step 3: The NSACF determines whether or not to accept the request as described in clause 5.15.11.5 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2]. If Hierarchical NSAC architecture is deployed at the network, the following impacts are applicable to clause 4.2.11.2a: - The SMF+PGW-C invokes perform network slice availability check on the number of UEs and update for S-NSSAI associated with the PDN connection during PDN connection establishment. In this case the AMF in figure 4.2.11.2a-1 is replaced with SMF+PGW-C. - Step 2: The SMF+PGW-C includes in the message the S-NSSAI, identity of SMF+PGW-C, UE ID and update flag. - Step 3: The AMF ID is replaced by the SMF + PGW-C ID. - Step 8: The NSACF determines whether or not to accept the request as described in clause 5.15.11.5 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2]. When the local maximum number is reached the NSACF may interact with the Primary NSACF before it returns the response back to the SMF+PGW-C as defined in clause 4.2.11.2a. The SMF+PGW-C shall continue the PDN Connection Establishment procedure only when the Network Slice subject to NSAC is available based on both numbers of PDU Sessions and number of UEs.