5G SA roaming is not yet mainstream, and roaming agreements take time to be negotiated and implemented. Prior to this, the mobile operator needs to be confident that the customer experience when roaming in a brand new technology will be good from day one, to minimize delay to revenue and to avoid complex troubleshooting across multiple networks and interconnect points. However, there is a lot of new network infrastructure in the 5G SA Roaming and Security service that must be validated in advance of commercial launch.
Understanding 5G Roaming Architecture
5G SA roaming connectivity is established through a complex sequence of interactions between the Home PLMN and the Visited PLMN via the N32c and N32f interfaces prior to connectivity being established between the home UPF and visited UPF via the N9 interface. The N32-c Handshake service is used over N32 between the Security Edge Protection Proxies (SEPPs) in different PLMNs for performing the initial handshake. N32f facilitates secure communication between SEPPs located in different PLMNs.
Given the possibility that the HPLMN and VPLMN components are from different vendors, and the HPLMN operator's limited control over the VPLMN environment, it is critical to test interoperability of these new control plane mechanisms early and frequently.
It therefore makes a lot of sense to test the interworking of the hSEPP and its associated network functions against a standards-compliant VPLMN infrastructure, so that the HPMN can have maximum confidence that their network is indeed ready for 5G SA roaming.
Testing hSEPP Infrastructure
Using advanced packet core emulation, it is possible to pre-test your SEPP configuration against a fully emulated VPLMN infrastructure.
In the diagram above, the whole of the vSEPP infrastructure (in blue) is emulated to 3GPP standards (ref1), whereas the real hSEPP (in grey) can be compliance tested by emulating the various HPLMN network functions (In blue). The emulated NFs run all the control plane traffic across the multiple interfaces to establish a secure link between the HPLMN and the VPLMN. Any exceptions will be clearly identified, and a detailed analysis will be provided for troubleshooting purposes. Full emulation of the NFs other capabilities is not required; it is only necessary to emulate the interface control traffic associated with roaming for the purposes of testing the H&V PLMNs.
If testing indicates an issue not within the hSEPP itself but in the associated surrounding NFs, then further tests can be run by testing each real NF by surrounding it with emulated control plane traffic to isolate the NF at fault.
Testing the VPLMN
If, once the operator is confident their HPLMN is compliant and initial tests to a roaming partner identify issues, it is also possible to use an emulated HSEPP and DN or a full emulated HPLMN to enable deep analysis of traffic sent to the VPLMN and the responses received. This assists the roaming partner in the debugging process on the N32 and N9 interfaces.
Summary
Being prepared for 5G SA Roaming will enable the operator to earn revenue from day one by going live with confidence, and will assist any potential partner to iron out issues more quickly. Experience shows that most of the interworking and interoperability issues when introducing a new technology in roaming are found within the first 12 months. By its very nature, Roaming is a highly distributed service that relies on multiple vendors and interconnect points. Being able to methodically isolate technical issues to establish a root cause is critical to achieve confidence that 5G SA roaming is indeed ready for prime time. If the above topic is of interest, then contact us today to explore more.
Ref 1: GSMA NG113.12 Roaming Guidelines Jan 2025 https://www.gsma.com/newsroom/wp-content/uploads/NG.113-v12.0.pdf
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