HLR / HSS / UDM Architect

The HLR / HSS / UDR / UDM Mobile Core Engineer will analyze, design, implement, and verify the configuration and integration of subscriber data management nodes, networks, and systems across our 2G through 5G infrastructure. Your scope of work includes introduction, upgrade, expansion, functionality, and capacity scenarios spanning legacy HLR environments through modern cloud-native UDM and UDR deployments. You will be a key contributor to the convergence of subscriber databases as OXIO evolves its MVNO platform toward 5G standalone architecture — and your work will directly shape the reliability and scalability of the networks our partners depend on.

Key responsibilities :

• As part of the mobile core team, you will own the subscriber data management platform across our network generations. Your responsibilities include:

• Manage and operate HLR, HSS, UDR, and UDM nodes across 2G, 3G, 4G, and 5G core domains, ensuring high availability and data integrity for subscriber profiles.

• Design and maintain subscriber provisioning workflows, including IMSI/MSISDN management, service profiles, and roaming configurations.

• Implement and verify MAP, Diameter (S6a, S6d, Cx, Sh, Zh), and HTTP/2-based (N8, Nudm) interfaces connecting subscriber data nodes to MSC, MME, AMF, SGSN, and other core elements.

• Use and build dashboards to monitor subscriber node KPIs, quickly surface abnormal conditions, and identify patterns before they become outages.

• Own incident management for the subscriber data domain: follow communications procedures for internal escalation and external vendor coordination, ensuring SLAs are met.

• Perform maintenance, security audits, patching, and emergency response for HLR/HSS/UDM/UDR platforms.

• Undertake fault handling and corrective actions at node, service, and infrastructure level, including protocol trace analysis (Wireshark/tcpdump) on Diameter, MAP, and HTTP/2 signaling.

• Lead and contribute to project activities: E2E introduction of new subscriber management nodes, capacity expansions, software upgrades, and feature activations.

• Support MVNO onboarding by configuring subscriber data repositories, IMSI ranges, and roaming agreements in HLR/HSS/UDM/UDR systems.

• Participate in 7x24 on-call rotation, including shift monitoring, babysitting activities during maintenance windows, and emergency response.

• Provide, implement, and verify improvements to processes and work instructions; drive automation of repetitive provisioning and audit tasks.

• Collaborate with IMS, RAN, and transport teams to resolve cross-domain subscriber authentication and registration issues.

Key Qualifications

At least 10 years of experience in core network engineering with a focus on subscriber data management in mobile networks.

Education & Background

• BSc degree in Telecommunications, Computer Science, or equivalent; post-graduate studies are a plus.

• 10+ years of core telecommunications network experience, with a minimum of 5 years hands-on with HLR, HSS, UDR, or UDM platforms.

Technical — Subscriber Data Management

• Deep operational knowledge of HLR platforms (e.g., Ericsson HLR, Nokia FlexiISN, Huawei HLR9820) and their MAP/TCAP/SCCP signaling stacks.

• Hands-on experience with HSS platforms and Diameter-based interfaces: S6a, S6d, Cx, Sh, Zh — including Diameter routing agent (DRA) configuration and troubleshooting.

• Practical experience with 5G UDM and UDR, including cloud-native deployments (containerized/Kubernetes-based NFs) and HTTP/2 SBI interfaces (N8, Nudm_SubscriberDataManagement, Nudr_DataRepository).

• Solid understanding of subscriber profile structures: EPS subscription data, 5GS subscription, IMS subscription (Cx/Sh), CAMEL service data, and operator-determined barring.

• Experience with IMSI/MSISDN range management, number portability (NP/MNP) integration, and SIM/eSIM provisioning workflows.

Technical — Protocols & Standards

• Strong knowledge of SS7 stack: MAP (Mobile Application Part), TCAP, SCCP, MTP — including MAP operations for location update, authentication, subscriber info retrieval, and SMS routing.

• Diameter protocol expertise: peer configuration, routing, AVP manipulation, error handling, and Diameter watchdog/transport management.

• Familiarity with 3GPP standards governing subscriber data: TS 23.008, TS 29.272 (S6a), TS 29.328/29.329 (Sh), TS 29.503/29.504 (UDM/UDR SBI), TS 23.502 (5G procedures).

• Understanding of roaming architecture, IR.21 data, IREG testing, and GSMA interconnect requirements relevant to subscriber data exchange.

Technical — Network & Systems

• Working knowledge of 2G (HLR/AuC/VLR), 3G (HSS/HLR), 4G (MME/HSS/EPC), and 5G SA (AMF/SMF/UDM/UDR/AUSF/UDSF) core architectures and their subscriber data flows.

• Comfortable with Linux/Unix-based systems — able to navigate shells, interpret logs, manage processes, and perform basic system administration on telecom NF hosts.

• Hands-on with Wireshark, tcpdump, and vendor-specific trace tools for deep analysis of MAP, Diameter, and HTTP/2 subscriber signaling.

• Experience with high-availability configurations for subscriber databases: active/standby, geo-redundancy, and database replication/synchronization.

Soft Skills & Ways of Working

• Strong written and verbal communication skills in English — able to produce clear incident reports, change request documentation, and runbooks.

• Able to work under pressure during high-severity incidents while maintaining methodical troubleshooting discipline.

• Effective at interacting with external vendors, MVNO partners, and cross-functional internal teams.

• Adaptable and comfortable driving change in a fast-moving MVNO environment.

• Ready to work on morning/afternoon shifts and participate in on-call rotation.

Nice to Have

• 2+ years of scripting experience (Python, Bash) for automation of provisioning, audit, and reconciliation tasks on HLR/HSS/UDM/UDR systems.

• Experience with AUSF, UDSF, or PCF in 5G SA environments.

• Familiarity with cloud-native telecom platforms (OpenShift, Kubernetes) and Helm-based NF lifecycle management.

• Exposure to OSS/BSS integration for subscriber data, including provisioning APIs and mediation layer design.

• Knowledge of eSIM (GSMA SGP.02 / SGP.22) and its interaction with subscriber data repositories.

• Experience with MVNO/MVNE operating models and multi-tenant subscriber data isolation.

OXIO is committed to fostering a diverse, equitable, and inclusive workplace where all employees feel valued and empowered. We believe that diversity in all its forms drives innovation and creativity, and we strive to create an environment that reflects and celebrates the unique backgrounds, perspectives, and talents of our employees. We do not discriminate against any employee or applicant for employment based on race, color, religion, sex (including pregnancy, gender identity, and sexual orientation), national origin, age, disability, genetic information, veteran status, or any other characteristic protected by applicable federal, state, or local law. We are dedicated to providing a work environment free from discrimination and harassment. We committed to ensuring that all qualified applicants have an equal opportunity to apply for job openings. If you need assistance or an accommodation due to a disability, please contact us at hr@oxio.io for more information.