The SMF generates a PDU session ID (pdu-session-id) upon receiving a Create Session Request from the 4G-only UE. The SMF validates if the request has the 5G-IWK indication without the PDU session ID in the Protocol Configuration option. The UDM provides the IWK indication to the SMF per DNN. The SMF does not use this indication for deciding whether the UE is 5G capable.

The SMF generates a pdu-session-id based on lbi. For the 4G Create Session Request, the SMF generates pdu-sesion-id=lbi+64 and for WiFI sessions it generates pdu-session-id=lbi+80.

The SMF allows you to configure the default NSSAI under the profile DNN, which it includes in sliceInfo IE in the Policy Create Request directed towards the PCF during session creation from 4g-only UEs. If the default slice is not configured, then SMF selects one of the configured slices. When the UE is DCNR capable, and the DCNR is enabled for the session, the SMF considers the UE capable of supporting dual connectivity. You can configure DCNR per DNN and other NFs, such as UPF.

The SGW notifies the DCNR support to PGW through the 'UPF Selection Indication Flags IE'.

DCNR-Based UPF Selection

SMF selects DCNR supported UPF for DCNR enabled session when DCNR is configured under query params. DCNR isn’t a mandatory query parameter for UPF selection. DCNR can be configured in profile network-element upf. Query parameters / Filter criteria configuration under nf-profile is enhanced to include DCNR support.

SecondaryRatData Usage Report Handling

SMF/UPF cannot differentiate usage in RAN, whether it is on NR or LTE for NSA devices while It is being tracked on eNB. SMF receives usage data ports on S5 interface in various messages, which it reports usage towards CHF.

SMF handles periodic Secondary RAT Usage Data Report from MME over S5/S8. The report is stored till it is sends out to CHF based on triggers mentioned below. SMF sends out the stored secondary RAT usage data report when any of the charging triggers are met.

UePresenceReporting Support

Presence Reporting Area is an area defined within 3GPP Packet Domain for the purposes of reporting of UE presence within that area due to policy control and/or charging reasons. In the case of E-UTRAN, a Presence Reporting Area may consist in a set of neighbor or non-neighbor Tracking Areas, or eNBs and/or cells. There are two types of Presence Reporting Areas: "UE-dedicated Presence Reporting Areas" and "Core Network pre-configured Presence Reporting Areas" that apply to an MME pool. SMF supports “Core Network pre-configured Presence Reporting Areas”.

2g/3g HO Support

During 4G to 2G/3G handover, SMF receives GTPv1 message, SMF has to drop the GTPv1 message, however, if SMF drops the request, it will delay the handover failure and subsequent attach to 2G/3G. In order to expedite the re-attach and reduce the UE service disruption, SMF supports the rejection of GTPv1 messages.

Following are the known limitations for Packet Data Unit SessionsEstablishment from 4G-Only and Option 3x Capable Devices feature:

• For PresenceAreaReporting (PRA) feature, only the PRA-ID will be sent in ‘Presence reporting area action’ IE on S5 interface, user location info won’t be sent.

• For PresenceAreaReporting (PRA) feature, only the PRA-ID will be sent in ‘repPraInfos’’ IE on N7 interface, user location info won’t be sent.

• For PRA feature, PRA Set is not supported, due to which “Additional PRA Information” sent on S5/N7 interfaces is also not supported.

• Maximum of 4 PraIds will be processed in a single PCF update message, if any PCF update has more than 4 PraIds then the other PraIds are ignored.

• PRA is applied only based on RAT from which device is connecting, not based on device type. So it is applied to both 4G and 5G devices, when connected from LTE

• SecondaryRatDataUsage Report supports only Option3 and Option3x (NR secondary RAT) UEs on S5 interface.

• SecondaryRatDataUsage Report isn’t supported on N2 interface for E-UTRAN Secondary RAT.

• PresenceAreaReporting (PRA) feature is supported only towards PCF and not towards CHF.

• Ultralow latency QCIs aren’t supported.

The Packet Data Unit Sessions Establishment from 4G-Only and Option 3x Capable Devices feature complies with the following standards:

• 3GPP TS 23.003 [2]

• 3GPP TS 24.301 [23]

• 3GPP TS 29.272 [70]

• 3GPP TS 29.274

This section describes how to configure the default NSSAI in SMF, which it includes in sliceInfo IE in the Policy Create Request message. The SMF sends this message towards the PCF during the session creation from 4G-only UEs.

To configure the default NSSAI in the SMF, use the following sample configuration:

config 
  profile dnn profile_name 
   nssai 
   sd sd_value 
   sst sst_value 
   end 

NOTES:

• profile dnn profile_name : Specifies the DNN profile name. profile_name must be an alphanumeric string.

• nssai : Enters the NSSAI configuration.

• sd sd_value : Specifies the slice descriptor (sd). The sd_value accepts a 6-digit hex string ( [0-9a-fA-F]{6} - 000000 – ffffff). For example, 1A2B3c

• sst sst_value : Specifies the slice type (sst) value. The accepted range is 0–255.

This section describes how to mark the sessions as DCNR enabled for SMF and UPF.

To enable SMF to consider the sessions as DCNR capable, use the following configuration:

configure 
  profile dnn profile_name 
    dcnr boolean_value 
    end 

NOTES:

• profile dnn profile_name – Specifies the DNN profile name.profile_name must be an alphanumeric string.

• dcnr boolean_value – Enable this command by configuring the dcnr to true. The SMF marks the session as “dcnr enabled session” only when the UE is DCNR capable, and the DCNR is configured under profile DNN.

This section describes how to enable DCNR flag in profile upf-group and link the group in upf network-element profile, also configures appropriate precedence for DCNR.

To configure the default NSSAI in the SMF, use the following configuration:

profile dnn profile_name 
upf-selection-policy  policy_name 
exit 

policy upf-selectionupf1  
precedence precedence_1 
[ dnn dcnr ] 
exit 
precedenceprecedence_2 
[ dnn ] 
exit 
exit 

profile upf-group  profile_name 
dcnr  [ true | false ] 
exit 

NOTES:

• profile dnn profile_name – Specifies the DNN profile name. profile_name must be an alphanumeric string.

This section describes configuration for storing number of Secondary RAT Usage Reports before being sent to CHF.

Use the following configuration to configure Secondary RAT Usage Report:

configure 
    profile charging profile_name 
        max-secondary-rat-reportsreport_range 
        end 

NOTES:

• max-secondary-rat-reportsreport_range Configures maximum number of secondary RAT usage reports that can be configured.report_range must be an alphanumeric string 0–50.

This section describes how to enable DCNR flag in profile upf-group and link the group in upf network-element profile, also configures appropriate precedence for DCNR.

To configure the default NSSAI in the SMF, use the following configuration:

profile dnn intershat 
upf apn intershat 
presence-reporting true 
exit 

NOTES:

• presence-reporting true – Enables presence reporting.

The SMF uses the “dcnr” label in the session gauge “smf_session_counter” and “smf_service_stats” for collecting the DCNR session count. Only when the SMF session is a DCNR supported, then the “dcnr” label value is enabled. The label doesn’t support non-dcnr sessions.

The following is a sample query to count the DCNR active SMF session:

nts{action_type="rejected",app_name="smf",cluster="smf",data_center="unknown",
failure_type="hdr_decode_failure",hdr_decode_fail_reason="",instance_id="0",interface_type="
",message_type="",reject_cause="",service_name="gtpc-ep"} 2

smf_session_counter: sum (smf_session_counters{dcnr_on="enable"}) by (dcnr)

smf_service_stats: sum (smf_session_stats{dcnr_on="enable"}) by (dcnr, status, reason)

smf_session_counters{ presence-reporting ="enable"}) by (presence-reporting)

DCNR Session Count

For DCNR, Session Count added a new label “dcnr” in the existing session gauge “smf_session_counter”. If SMF session is a DCNR session, then “dcnr” label value is “enable” otherwise it is “disable” for DCNR session.

Sample query to count DCNR active SMF sessions:

sum (smf_session_counters{dcnr_on="enable"}) by (dcnr)

For DCNR statistics added a new label “dcnr” in the existing counter “smf_service_stats”. For DCNR session this counter pegs with below labels values:

• Attempt Statistics - dcnr= “enable” and status= “attempted”

• Success Statistics – dcnr= “enable” and status= “success”

• Failure Statistics - dcnr= “enable” and status= “failures”

Sample query for DCNR statistics:

sum (smf_session_stats{dcnr_on="enable"}) by (dcnr, status, reason)

Secondary Rat Data Usage Reports

For Secondary-Rat-Data-Usage-Reports added new counter “smf_secondary_rat_usage_report_stats”

Labels for these stats include ebi, qfi, rat_type, reason, service_name, status. For this counter pegs with below labels values:

• ebi=ebi-val

• qfi=qfi-val

• rat_type=NR

• reason=success/failure

• service_name=smf-service

• status=ReceivedFromSgw/SentToChf

Sample query for DCNR statistics:

sum (smf_secondary_rat_usage_report_stats”) by (qfi, status, reason)

Presence Reporting

For Presence-Reporting Session Count added a new label “pra” in the existing session gauge “smf_session_counter”. If SMF session has presence-reporting enabled then. “presence-reporting” label value is “enable” otherwise it is “none” if presence-reporting is not enabled.

Sample query to count DCNR active SMF session:

sum (smf_session_counters{ pra ="enable"}) by (pra)

For Presence-Reporting statistics added a new label “presence-reporting” in the existing counter “smf_service_stats”. For presence-reporting session this counter pegs with below labels values.

• Attempt Statistics - pra = “enable” and status= “attempted”

• Success Statistics – pra = “enable” and status= “success”

• Failure Statistics - pra = “enable” and status= “failures”

Sample query for DCNR statistics:

sum (smf_session_stats{ pra ="enable"}) by (pra, status, reason)

The following bulk statistics are modified for release 2020.03.0:

Following new Bulk Stat is introduced to support Secondary Rat Data Usage Report in SMF schema in release 2021.01.0:

Following Stats are modified to support Secondary Rat Data Usage Report in SMF schema in release 2021.01.0: