Senior Software Engineer (C++ & C# / Mission-Critical Systems)

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