Your mission
Are you passionate about writing clean, high-quality code and building reliable software solutions? We are looking for a Senior C++ & C# Developer to join our growing development team in Budapest, working for a multinational leader in the telecommunications sector. In this role, you’ll contribute to cutting-edge projects that power secure and efficient communication systems across the Globe.
Your profile
Role Overview
We are looking for a strong engineering talent with solid C++ foundations who is also open to working in C#/.NET. Our Core Communication System (CCS) is implemented in C++ and runs in Linux-based environments. Currently, this domain is owned by a single senior engineer — we are looking for someone who can grow into this system, learn its architecture deeply, and gradually take ownership.
When C++-focused development is not the primary priority, the role actively contributes to our C#/.NET-based backend services within our broader digital services and microservices ecosystem.
This role is ideal for an engineer who enjoys low-level systems thinking (C++) as well as modern backend development (C#) and wants to operate across platform boundaries.
Product & Platform Context
1. Core Communication System (C++ / Linux / Embedded-like environments)
- Telephony (PSTN) and VoIP systems
- Supervision, lawful interception, recording
- Device management & hardware integrations
- Build systems (CMake), Debian/Ubuntu environments
2. Digital Services Ecosystem (C# / .NET / Microservices)
- Distributed backend services
- Financial systems (wallets, billing, invoicing)
- APIs and integrations
- Azure-first cloud transformation (hybrid environment)
Key Responsibilities
- Contribute to the evolution and stabilization of our C++-based Core Communication System
- Gradually learn and take ownership of complex C++ modules running in Linux environments
- Collaborate on architecture decisions across C++ and C# domains
- Design and implement backend services using C# / .NET
- Contribute to microservices architecture and domain-driven design initiatives
- Integrate APIs and external systems
- Participate in CI/CD and DevOps improvements
- Ensure high reliability, performance, and security standards
- Support modernization efforts across legacy and distributed systems
- Collaborate closely with DevOps, QA, Product and other engineering teams
Required Qualifications & Experience
Core Engineering Foundation
- 4+ years of professional software engineering experience
- Strong computer science fundamentals (algorithms, data structures, system design)
- Ability to independently design and implement complex modules
- Strong analytical and problem-solving skills
C++ Domain
- Solid experience in modern C++ development
- Experience working in Linux environments (Debian/Ubuntu)
- Familiarity with CMake or similar build systems
- Understanding of system-level programming concepts, performance, memory management
- Openness to deeply understand and evolve an existing complex system
C# / .NET Domain
- Experience with C# and .NET (ASP.NET Core or similar)
- Experience building APIs and backend services
- Understanding of service-oriented or microservices architectures
- Database design experience (relational preferred)
Engineering Mindset
- Strong ownership mentality
- Curiosity toward modern technologies and AI-assisted development
- Comfortable working in hybrid (cloud + on-prem) environments
- English proficiency (written and spoken)
Advantages
- Experience with VoIP technologies (SIP, RTP)
- Experience with Qt framework or embedded Linux
- Experience with Azure cloud services
- Exposure to financial or billing systems
- Experience with DevOps automation tools
- Knowledge of Domain-Driven Design
- Experience working in regulated or mission-critical environments
Why us?
- Work on mission-critical systems with real societal impact
- Own and evolve a strategically important C++ platform
- Contribute to a modern C# microservices ecosystem
- Join a high-ambition engineering transformation
- Shape the future of secure communication platform
- Professional challenges, inspiring diverse tasks
- Structured development process
- Multiculture environment
- Home office days
- Relaxed atmosphere, steady, supportive international team
- Easily accessible modern office with good infrastructure
- Complimentary coffee, fruit and snacks
About us
Telio is a medium-sized, internationally active, rapidly growing company in the field of telecommunications and IT services in the prison sector. As the European market leader, we have been providing communications solutions for prisons and their inmates worldwide for over 25 years. With more than 270 employees, we are active in 23 countries and develop, install and operate communication and media systems that make an important contribution to resocialization in prisons as well as in correctional facilities.
