S-NSSAI Validation Against the UDM Subscription S-NSSAI
The SMF uses the Single Network Slice Selection Assistance information (S-NSSAI) from UDM subscription response to reselect the subscriber policy. The SMF matches the S-NSSAI based on the Slice or Service Type (SST) and Slice Differentiator (SD) parameters.
The S-NSSAI subscription selection is based on the following criteria:
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If both the parameters match, then SMF selects the S-NSSAI subscription with both SST and SD matched (fully matched).
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If only SST matches and SD is unavailable in either the requested S-NSSAI or in UDM subscription S-NSSAI, then SMF selects the subscription with SST only matched (partially matched).
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If the requested S-NSSAI partially matches with the SMF local configuration S-NSSAI (allowed snssai under SMF profile), then the local configuration S-NSSAI is used for validating with the UDM subscription response. This criteria is applicable for the 5G call.
The following table lists the validation criteria for selecting subscription from UDM N10 subscription.
Serving RAT |
Selected S-NSSAI before N10 Subscription |
S-NSSAI in Subscription |
Final S-NSSAI after N10 Subscription |
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5G |
Requested S-NSSAI that is received in Create message |
Single S-NSSAI in subscription |
Subscribed S-NSSAI, which matches with requested S-NSSAI. |
5G |
Requested S-NSSAI that is received in Create message |
Multiple S-NSSAI in subscription |
Subscribed S-NSSAI, which matches with requested S-NSSAI. |
4G or Wi-Fi |
Requested S-NSSAI (default S-NSSAI configured under DNN profile. If the default S-NSSAI isn't available, then one of the allowed S-NSSAIs available under SMF profile is selected). |
Single S-NSSAI in subscription |
Subscribed S-NSSAI, which matches with the requested S-NSSAI or the requested DNN or APN available in the Create Session Request (CSR). |
4G or Wi-Fi |
Requested S-NSSAI (default S-NSSAI configured under DNN profile. If the default S-NSSAI isn't available, then one of the allowed S-NSSAIs available under SMF profile is selected) |
Multiple S-NSSAI in subscription |
Subscribed S-NSSAI, which matches with the requested S-NSSAI or the requested DNN or APN available in the Create Session Request (CSR). |
The following table provides details on SMF and UDM behavior based on the availability of the query parameters in the N10 Subscription Request message.
Configuration |
URI Parameters in N10 Subscription |
UDM Behavior |
SMF N10 Subscription Response Handling |
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Default or no configuration |
PLMN, Selected SNSSAI, DNN |
UDM uses requested PLMN and sends subscription that matches the S-NSSAI and DNN. |
SMF selects the S-NSSAI subscription that matches the requested S-NSSAI and selects the DNN configuration that matches with the requested DNN from the selected subscription. |
Skip PLMN |
Selected S-NSSAI, DNN |
UDM uses home PLMN and sends subscription that matches the S-NSSAI and DNN. |
SMF selects S-NSSAI subscription that matches with the requested S-NSSAI and selects the DNN configuration that matches the requested DNN from selected subscription. |
Skip S-NSSAI |
PLMN, DNN |
UDM uses requested PLMN and responds with the S-NSSAI subscriptions that match DNN. |
SMF selects S-NSSAI subscription that matches with requested S-NSSAI and selects the DNN configuration that matches with the requested DNN from the selected subscription. |
Skip DNN |
Selected S-NSSAI, PLMN |
UDM uses the requested PLMN and sends S-NSSAI subscriptions that match S-NSSAI. |
SMF selects S-NSSAI subscription that matches with requested S-NSSAI and selects the DNN configuration that matches with the requested DNN from selected subscription. |
Skip PLMN, S-NSSAI |
DNN |
UDM uses home PLMN and sends all the S-NSSAI subscriptions that match DNN. |
SMF selects S-NSSAI subscription that matches with requested S-NSSAI and selects the DNN configuration that matches with the requested DNN from selected subscription. |
Skip PLMN, DNN |
S-NSSAI |
UDM uses home PLMN and sends S-NSSAI subscriptions matching S-NSSAI. |
SMF selects S-NSSAI subscription that matches with requested S-NSSAI and selects the DNN configuration that matches with the requested DNN from selected subscription. |
Skip S-NSSAI, DNN |
PLMN |
UDM uses requested PLMN and sends all the S-NSSAI subscriptions. |
SMF selects S-NSSAI subscription that matches with requested S-NSSAI and selects the DNN configuration that matches with the requested DNN from selected subscription. |
Skip PLMN, S-NSSAI, DNN |
None |
UDM uses home PLMN and sends all the S-NSSAI subscriptions. |
SMF selects S-NSSAI subscription that matches with requested S-NSSAI and selects the DNN configuration that matches with the requested DNN from selected subscription. |