Navigating SMSF Redundancy in 5GC

With the emergence of 5G, there's a push for new services like IoT, V2X, and VR. This puts added strain on networks, as these services require networks capable of handling large amounts of data and providing online services no matter the location. The reliability and uninterrupted functionality of services are now crucial due to the growing use of mobile services by individuals and businesses. However, the cloud-based network functions are not as sturdy as the traditional network elements due to changes in the network structure – the introduction of off-the-shelf hardware and a virtualization layer. This makes ensuring the availability of services on 5G Core Network Functions (5GC NFs) both urgent and more complex than on conventional network elements. To address these challenges, the 5GC redundancy solution tackles the issue by setting up NFs in different configurations such as active/standby pairs, active-active pairs, or pools across data centers in various locations.

The redundancy network setup for 5GC spans both cloud-based Network Functions (NFs) and traditional Network Elements (NEs). This encompasses a range of components like NSSF, NRF, PCF/PCRF, AUSF/HLR/HSS/UDM, IWF, SMSF, SMF/PGW-C, AMF, and unified UPF/PGW-U. Control-plane NFs are positioned centrally, while user-plane NFs are strategically placed at varying distances from users to fulfill different bandwidth and latency demands. For instance, the unified UPF/PGW-U can be stationed in a regional data center for internet access, or it can be situated closer to users, even at the network edge, to enhance access to local networks like campuses.

Redundancy in 5GC

The 5G Core (5GC) has the capability to implement redundancy using three methods: active/standby, active-active, or based on pools.

Active-Standby: A pair of Network Functions (NFs) are set up in different data centers, operating in an active/standby configuration. In this arrangement, only the active NF handles service processing, while the standby NF remains ready as a backup. The two NFs communicate by sending heartbeat messages to assess each other's operational status and ensure data synchronization for consistency. If the active NF encounters a malfunction, the standby NF proceeds with the control of the services.

Active-Active: A duo of Network Functions (NFs) is positioned in distinct data centers, functioning as an active-active duo. In this setup, both NFs are engaged in service processing at all times. While certain NFs establish data backup connections with their corresponding counterparts, others do not. Should one of the NFs experience a malfunction, the other NF seamlessly proceeds with the responsibility of service provision.

Network Pool: Network Functions (NFs) are organized into a pool configuration. While operational, all the NFs participate in service processing. In the event that one of the NFs encounters a malfunction, the remaining NFs step in to continue the service operation.

SMSF Redundancy

The SMSC and IPSM-GW employ heartbeat detection on the SCTP layer to verify the availability of the connection to the SMSFs. Should the connection prove to be defective, the SMSC and IPSM-GW transition to an alternate link. In the event that all links leading to the SMSF are impaired, the SMSC and IPSM-GW switch their connection to the alternative SMSF.

The AMF uses either a ping method or subscribes to the NRF to stay updated about the status of the SMSF. If it identifies that one SMSF is not functioning properly, the AMF redirects service requests to the operational SMSF. However, the second SMSF can't proceed with the control of services until it re-registers with the UDM.