Senior Software Engineer – NR-NTN Protocols (L3 & L4 / Core Interfaces)

The world still has coverage blind spots. You could help eliminate them at Skylo. Skylo has pioneered a standards-based approach to satellite connectivity. We connect smartphones and IoT devices directly to satellites. No special hardware, no entirely new networks. Just billions of existing devices, suddenly reachable anywhere on Earth. We're not building toward this future. We're already in it. Our direct-to-device service is live on millions of activated devices across five continents, covering more than 72 million square kilometers, in partnership with leading satellite operators, mobile network operators, Tier-1 chipset makers, and OEMs worldwide. And we're just getting started. At the heart of it all is Skylo's commercial NTN vRAN: a 3GPP standards-based, cloud-native platform that seamlessly bridges terrestrial and satellite networks. It's the infrastructure that makes true anywhere, anytime connectivity possible. When you join Skylo, you'll work at the intersection of three markets reshaping how the world stays connected: mass-market consumer devices, automotive, and industrial IoT. Enabling people outdoors and critical workflows in the world's most remote places. This is a rare chance to work on technology that matters, at a company that's already proving it works This role is based in Espoo, Finland, one of Skylo's core engineering hubs and fastest-growing sites. You'll work onsite three days a week as part of a team that's scaling quickly. How You Will Impact Skylo We are seeking a highly skilled Senior Software Engineer to join our Protocol Stack team, focused on the development and optimization of 5G NR-NTN upper-layer and core interface protocol implementations. In this role, you will design, implement, and validate PDCP, eGTP, Xn interface, NGAP (N2), and N2/N3 reference point software that runs on Skylo's NTN vRAN and core integration platform, working closely with our Core Network, MNO integration, and systems teams to deliver production-grade NTN connectivity. What You’ll Do Design, develop, and maintain C++ implementations of 5G NR upper-layer and core interface protocols: PDCP, eGTP-U/C, Xn Application Protocol (XnAP), NGAP (N2 interface), and N3 user-plane tunnelling. Implement NTN-specific PDCP adaptations : extended PDCP sequence number space, reordering timer adjustments for long propagation delay, lossless handover support, and PDCP status reporting enhancements. Develop and maintain eGTP-U tunnelling for N3 user-plane: GTP-U path management, echo/error indication handling, end-marker procedures, and QoS flow-to-DRB mapping for NTN deployments. Implement Xn interface procedures (XnAP): Xn Setup, UE Context Retrieval, handover preparation and resource release, NG-RAN node configuration update, and Xn-U user-plane tunnel management. Implement and maintain NGAP procedures over the N2 interface : Initial UE Message, UE Context Setup/Modification/Release, Handover Preparation/Resource Allocation/Notification, Paging, and AMF Configuration Update. Develop NTN-aware N2/N3 signalling enhancements: handling of NTN-specific IEs in NGAP, satellite ephemeris-related AMF interactions, and NTN QoS handling across the N3 reference point. Collaborate with Core Network and MNO integration teams to validate NGAP procedures against AMF implementations (commercial and lab) in live MNO environments. Integrate and validate Xn/N2/N3 interfaces end-to-end across gNB-CU-CP, gNB-CU-UP, and core network elements in a disaggregated vRAN architecture. Perform debugging, root-cause analysis, and performance tuning of interface-layer issues using packet capture and protocol analysis tools (Wireshark, tcpdump, custom dissectors). Collaborate with systems engineers to translate 3GPP Rel-17/18 NR-NTN specifications (TS 38.413, TS 38.423, TS 29.281, TS 38.323) into software requirements and detailed designs. Participate in code reviews, architecture discussions, and contribute to technical documentation and design specifications. Actively use AI coding assistants (Claude, Cursor, Codex) throughout the development lifecycle — from spec interpretation and boilerplate generation to test automation and code review — and help establish team best practices for AI-augmented engineering. Sound Like You? What You Bring: 2+ years of hands-on software engineering experience in wireless/telecom protocol development, with specific depth in upper-layer and core interface protocols Master's or PhD degree in Wireless Communications, Electrical Engineering, Telecommunications, or a closely related field.. Strong proficiency in C++ (C++14/17) with demonstrated experience writing production-grade near-real-time protocol software. Deep, implementation-level knowledge of PDCP : integrity protection, ciphering, header compression (ROHC), sequence number management, and lossless/lossy handover procedures. Strong understanding of eGTP (GTP-U and GTP-C): tunnel management, path failure detection, bearer/QoS flow handling, and N3 interface operation in a 5G SA core. Solid understanding of Xn interface (XnAP TS 38.423) : Xn Setup, handover signalling, UE context transfer, and NG-RAN node management procedures. Strong understanding of NGAP (TS 38.413) : full N2 procedure set including UE context management, handover signalling, paging, error handling, and AMF/gNB interactions. Experience with Linux kernel/user-space debugging tools: GDB, Valgrind, perf, tcpdump, Wireshark (with custom dissectors), and system log analysis. Proficiency in production-grade protocol software : ASN.1/PER message encoding/decoding, state machine design, and multi-threaded protocol engines. Ability to read and independently derive software requirements from 3GPP specifications . What We Offer This is a once-in-a-lifetime opportunity to help build and run the world's first commercial, live direct-to-device satellite network. You'll work alongside a world-class team spanning software, hardware, chipsets, telecom, satellite, and network virtualization, some of the most sought-after expertise in the industry. And you'll do it inside a culture that's open, transparent, and inclusive, shaped by the best of Silicon Valley, Nordic, and South Asian ways of working. With employees working across three continents, Skylo is proud to be an equal opportunity employer dedicated to building an inclusive and diverse workforce. Our worldwide and inclusive culture encourages a flexible approach to work, and we also offer an attractive range benefits such as: Competitive compensation packages Occupational Healthcare and Health and Life Insurance E-passi including, wellness, culture, lunch and commuting benefit Phone & Internet allowance Individual learning & development budget for further personal and professional development Ready To Join Us? Apply now and a member of our recruiting team will be in touch. We review applications on an ongoing basis, so we encourage you to apply early. Our process includes an initial call with a recruiter, a take-home assignment, and two interviews with different team members. Still have questions? Teea Kuusimurto, our Senior Recruiter, has answers. Say hello at [email protected]. EEO Statement Skylo is an equal-opportunity employer and we celebrate diversity. We do not discriminate on the basis of race, religion, color, ancestry, national origin, caste, sex, sexual orientation, parent or caregiver status, political affiliation, gender, gender identity or expression, age, disability, medical condition, pregnancy, genetic makeup, marital status, or military service consistent with applicable federal, state, and local laws. We are also committed to providing reasonable accommodations for qualified individuals with disabilities and disabled veterans in our job application procedures. Please let us know if you need assistance or accommodation due to a disability.