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

Skylo; Espoo; On-site; EUR 55,000 - 75,000; Full time

Benefits offered by this job

Competitive compensation packages

Occupational healthcare

Health and life insurance

Wellness and cultural benefits

Learning and development budget

Job summary

Skylo is seeking a Senior Software Engineer to enhance 5G NR-NTN protocol implementations. This role involves designing, implementing, and validating core interface protocols, focusing on PDCP, eGTP, and NGAP.

The ideal candidate has 2+ years in telecom protocol development and a Master’s or PhD in a relevant field, along with strong C++ skills. Benefits include competitive compensation, health insurance, and individual learning budgets.

Qualifications

• 2+ years of experience in wireless/telecom protocol development.
• Strong proficiency in C++ (C++14/17).
• Implementation knowledge of PDCP, eGTP, NGAP, and Xn protocols.

Responsibilities

• Design and implement C++ protocol software for 5G NR.
• Collaborate with teams to validate protocol implementations.
• Perform debugging and root-cause analysis of interface issues.

Skills

C++

Wireless Communications

Telecommunications Protocol Development

Debugging Tools

3GPP Specifications

Education

Master’s or PhD in Wireless Communications, Electrical Engineering, or Telecommunications

Tools

Wireshark

GDB

Valgrind

tcpdump

Job description

Senior Software Engineer – Protocol Stack

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 and help establish team best practices for AI‑augmented engineering.

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.

Benefits

• 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.

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.