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

Responsibilities

• 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 handli

Benefits

Additional Information

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.

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