2G and 3G session attach and detach procedures for S4-SGSN

This feature adds support to the SMF for managing attach and detach functions originating from S4-SGSN (Serving GPRS Support Node). This allows the consolidation of 2G/3G and 4G/5G network control within a single converged core. By integrating the networks, you can simplify the network management and reduce the operational costs.

Commands Introducted:

profile converged-core activated-features 2g3g —This CLI command enables S4-SGSN support for 2G and 3G RAT type in SMF.

Default Settings:Disabled - Configuration Required to Enable

Blocking UPF to handle N4 session establishment failures

This feature allows the SMF to blocklist a specific UPF node when it continuously rejects session establishment requests. The UPF may reject these requests from the SMF due to various errors, such as licensing issues.

However, without information on the issues at the UPF, the SMF might repeatedly select the same UPF, leading to an increased number of session creation failures.

By enabling this feature, the network operators can prevent the SMF from repeatedly selecting the same UPF for a defined time interval.

Commands Introduced:

• [no] activated-features upf-blocklisting [ use-alert custom_rule_name ] : This CLI is configured under converged core profile configuration mode to enable UPF blocklisting feature on SMF.

• reactivate-peer condition [blocked] attributes [frequency frequency_timer ] : This CLI is configured under the endpoint configuration mode to reactivate blocked UPF after the frequency timer is over.

Default Setting: Disabled—Configuration Required to Enable

External DHCP-based IP Address Allocation

The enterprises with large and complex 5G networks require centralized IP address allocation and management.

This feature helps achieve centralization of IPAM by allowing the SMF to allocate IPs through a DHCP server.

Commands Introduced:

• ipam dhcp : This CLI is configured under the DNN profile to indicate the IPAM as DHCP.

• dhcp : This CLI is configured under the IPAM profile to tag the address pool as DHCP.

• vlan vlan_id : This CLI is configured under the IPv4 and IPv6 modes to attach the VLAN IDs.

Default Settings: Disabled—Configuration Required to Enable

SMF includes the "3gpp-Sbi-Discovery-preferred-locality" HTTP header when communicating with the SCP. By populating this header, SMF enables more efficient NF selection based on locality during peer NF discovery, resulting in optimized network function interactions and improved service delivery.

Encode quotaManagementIndicator in the charging request

Previous Behavior: The offline converted rating group SMF did not send the quotaManagementIndicator to the CHF in charging requests.

New Behavior: The offline converted rating group SMF now sends the quotaManagementIndicator as CONVERTED_OFFLINE to the CHF in charging requests.

Explicit TEID setting in GTPv2 messages for Context Not Found scenario

Previous Behavior: SMF did not explicitly set the Tunnel Endpoint Identifier (TEID) flag to 0 in certain GTPv2 messages when sending a response with the Cause IE set to "Context Not Found (64)." This led to stale TEID values being used inadvertently.

New Behavior: SMF explicitly sets the TEID flag to 0 in the GTPv2 header for the following messages when the Cause IE is "Context Not Found (64)":

• Modify Bearer Response

• Delete Session Response

• Modify Bearer Failure Indication

• Delete Bearer Failure Indication

• Change Notification Response

This update ensures compliance with GTPv2 specifications and aligns with 3GPP standards, providing improved handling for error scenarios.

Handling of FQDN in smContextStatusUri

Previous Behavior: Receiving an FQDN in the smContextStatusUri within the N11CreateSmContextReq led to service restart, as only IPv4 and IPv6 addresses were correctly processed.

New Behavior: The system now properly decodes FQDNs in the smContextStatusUri, integrating them into the nfFqdn IE within the ServingNetworkFunctionInformation IE in ChargingDataReq. This ensures seamless handling alongside IPv4 and IPv6 addresses.

Customer Impact: Customers can now use FQDNs in the smContextStatusUri, which will be accurately processed and included in the relevant information elements, enhancing network configuration flexibility and functionality

Implement RPC limits to prevent CLI timeouts

Previous Behavior: Previously, there were no limits on the number of Remote Procedure Calls (RPCs) collected from each pod instance and included in the response, which could result in a CLI timeout.

New Behavior: The system now limits the number of RPCs received per pod instance to 50,000 and the total number of RPCs from all pod instances to 200,000. The show rpc all command displays a maximum of 200,000 lines in its output.

Interface type display for overload information

Previous Behavior: The interface type was incorrectly displayed in the output of the show overload-info peer all command. For instance, the peer type "MME" was shown as "S5" instead of its correct interface type.

New Behavior: The interface type is now correctly assigned based on the peer type:

• ePDG → "S2B"

• MME → "S11"

• SGW → "S5"

This correction aligns the command output with expected network behavior, ensuring precise representation of interface types.

Customer Impact: The update rectifies the interface type display errors in the command output, improving the clarity and accuracy of the system's overload information.

Load Control Information Calculation Update

Previous Behavior: For active and standby types of pods, such as protocol, GTPC, LI, UDP-proxy, GTPP, and Diameter, the Load Control Information (LCI) was calculated by taking the average of loads of the pods. Due to this calculation, the system did not detect overload even though the active pod was heavily loaded.

New Behavior: The Load Control Information (LCI) is now calculated by taking the maximum load among the standby and active pods. This behavior helps the system to correctly identify the overloaded active pod.

Name change for RAN Cause IE on N7 interface

Previous Behavior: In 3GPP standard releases 15.4.0 and 16.0, certain Information Elements (IEs) on the N7 interface were sent with an invalid prefix "_". The affected IEs included _5gSmCause, _5gMmCause, and _3gppPsDataOffStatus.

New Behavior: The invalid prefix "_" has been removed from the IEs on the N7 interface.

Customer Impact: Customers will observe a change in the naming of a few IEs on the N7 interface. This change ensures consistency and compliance with standard naming practices.

NF Discovery based on Preferred Locality

Previous Behavior: The 3gpp-sbi-discovery-preferred-locality header was not sent to the SCP, even if the following conditions were met:

• "locality preferred-server" was enabled under "profile nf-pair" of the respective targetNF.

• "locality client" had the same value as the configuration of "locality" under "profile smf".

New Behavior: The 3gpp-sbi-discovery-preferred-locality header is sent to the SCP when the following conditions are met:

• "locality preferred-server" is enabled under "profile nf-pair" of the respective targetNF.

• "locality client" matches the configuration of "locality" under "profile smf".

Retry-Terminate mechanism for HSMF roaming

interface pfcp  
 message N4SessionEstablishmentReq  
  cause-code pfcp-entity-in-congestion action retry-terminate max-retry 2

New Behavior: The retry-terminate mechanism is now effectively implemented for HSMF roaming scenarios. This update provides the necessary retry procedures during the UPF setup, ensuring that roaming cases are managed accurately and efficiently.

Updated Cause Code for Rejected N11 Retrieve Message during Disabled Interworking

Old behavior: Previously, during the EPS fallback scenario, if the IWK is marked as disabled the SMF rejected N11 retrieve message with a failure cause code 403 forbidden- 'UPIP_REQ_DENIED_IN_RAT'.

New behavior: With this enhancement, during the EPS fallback scenario, if the IWK is marked as disabled the SMF rejects N11 retrieve message with a failure cause code 403 forbidden with an updated cause code as "SUBSCRIPTION_DENIED".

Enhancements in UPIP Functionality to Support Roaming, Session Modification, and N16 Interface

Old Behavior: During the resource setup process at gNB, such as idle-active, N2 ho, xn ho, the SMF recalculated UPIP for existing sessions and updated the latest UPIP values to the gNB. The dynamic configuration change for UPIP under the DNN configuration was applicable for the existing sessions.

Also, previously the UPIP feature did not support roaming and session modification functionalities.

New behavior: As part of the UPIP enhancement process, the SMF decides to enable UPIP based on UDM SM data, UE data rates, and the local configuration during the 5G session create processes or handover to 5G. The SMF does not recalculate the UPIP values again during handovers, it uses the UPIP values decided during session create time. The dynamic configuration change for UPIP under the DNN configuration does not apply to the existing session.

Also, the UPIP functionality is enhanced to support roaming and UE init modification for UPIP data rate change.