HTTP/2 Proxy Steering 5G Roaming via N32 Patch-Requests
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Solution Overview
Problem
Traditional methods for implementing Steering of Roaming (SoR) in 5G core roaming are hindered by 5G security requirements, particularly the use of the PRINS model, which prevents IPX-based SoR systems from rejecting non-preferred VPLMN network attachment requests due to digital signing and session key constraints.
Innovation Solution
An HTTP/2 Proxy is deployed in the IPX network to intercept and mediate N32-f messages, allowing the extraction of PLMN IDs and appending patch-requests to modify MCC/MNC values, enabling the HPLMN to reject non-preferred VPLMN attachment requests while ensuring compliance with 5G security standards.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If traditional IPX-based SoR systems are used to reject non-preferred VPLMN attachment requests, then roaming control flexibility is improved, but 5G security requirements (digital signing and session key constraints) cannot be satisfied
Solution Approach 1:
The patent introduces an intermediary component (SoR function) that sits between the VPLMN and HPLMN signaling path. This intermediary intercepts N32 interface messages, extracts PLMN ID information, and applies steering decisions without breaking the end-to-end security context. The intermediary enables SoR functionality while preserving 5G security requirements by operating within the existing security framework rather than attempting to modify signed messages.
Solution Approach 2:
The patent segments the SoR functionality into a separate network function that operates independently from both VPLMN and HPLMN. This segmentation allows the SoR function to process signaling messages and apply steering logic without requiring changes to the core security architecture. The segmented approach enables flexible roaming control while maintaining integrity of the signed signaling paths between VPLMN and HPLMN.
2Adaptability or versatility
If network-based SoR is implemented by rejecting non-preferred VPLMN attachment requests, then preferred VPLMN selection is improved, but coverage availability may be reduced when preferred VPLMNs have no coverage in the area
Solution Approach 1:
The patent implements feedback mechanisms where the SoR function monitors attachment request patterns, rejection outcomes, and UE roaming behavior. Based on this feedback, the system dynamically adjusts steering decisions - for example, temporarily relaxing restrictions when preferred VPLMNs show no coverage availability, or updating preferred VPLMN lists based on historical attachment success rates. This feedback loop ensures both preferred network selection and coverage availability are optimized.
Solution Approach 2:
The patent makes the SoR steering policy dynamic rather than static. The system can adjust preference lists, modify rejection thresholds, and change steering intensity based on real-time conditions such as network coverage availability, load conditions, and UE roaming history. This dynamic approach allows the system to prefer certain VPLMNs when available while automatically adapting when coverage is unavailable, ensuring continuous service availability.
3Adaptability or versatility
If SIM-based SoR is used to configure preferred PLMN lists in UE, then roaming partner preference control is improved, but flexibility and compatibility with different handsets are reduced
Solution Approach 1:
The patent positions the SoR network function as an intermediary that centralizes roaming preference control in the network rather than in the UE device. This eliminates the need for SIM-based configuration and associated handset compatibility issues. The network intermediary directly intercepts and processes attachment requests, applying steering logic uniformly across all devices without requiring device-specific implementations or SIM card modifications.
Data Source
AI summary
A system and method for implementing Steering of Roaming for 5G core roaming in an Internet Packet Exchange (IPX) network. A Hypertext Transfer Protocol (HTTP)/2 Proxy is deployed in an IPX network. The HTTP/2 Proxy receives N32-f request message from a Visited Public Land Mobile Network (VPLMN). The N32-f request has an embedded N12 authorization request message or an embedded N8 registration request message. If VPLMN is a non-preferred roaming partner, the HTTP/2 Proxy appends a patch-request to N32-f request message and routes it to the Home Public Land Mobile Network (HPLMN). The patch-request causes the home Security Edge Protection Proxy (hSEPP) to replace Mobile Country Code (MCC) or Mobile Network Code (MNC) value with a predefined value that will trigger a rejection from HPLMN. The mobile device will select another VPLMN. If the VPLMN is a preferred roaming partner, the HTTP/2 Proxy routes the request without appending a patch-request.