Mobile Voice Core Expert

Strength. Care. Growth

Did you know that A1 Bulgaria is working on international projects as well?

Our wide portfolio has long past the telecom services, and we are now offering digital solutions to millions of corporate, public, and private customers.

State-of-the-art technology, the latest innovations, and extremely talented professionals in various areas help us deliver the best-in-class products, services, and customer experience.

You’ll know A1 Bulgaria is the right place for you if you are driven by:

• Opportunities to learn and build your career.
• Meaningful work in a stable and fast-paced company.
• Diversity of people, projects, and platforms.
• A supportive, fun, and inspiring place to work.

Would you like to join us?

Georgi Kodjaivanov is looking for a new team member.

Your daily routine would include:

• Design, deploy, operate, and optimize IMS & VoLTE/VoWiFi/VoNR voice core platforms for all A1 OpCos.
• Manage and optimize core elements, including P‑CSCF, I‑CSCF, S‑CSCF, SBC, TAS, MRF, and MGW.
• Ensure stability, performance, and high availability of voice services 24×7.
• Troubleshoot complex SIP/Diameter signaling flows and perform root-cause analysis.
• Support device testing, interoperability testing, regulatory feature validation (e.g., lawful interception, emergency call routing), and new service introduction.
• Implement automation for configuration management, alarms, KPIs, and routine operational tasks.
• Develop scripts and tools to improve core network reliability and operational speed.
• Collaborate closely with vendors on upgrades, migrations, capacity expansion, and deployment of new features.
• Contribute to the transformation toward cloud-native IMS and Voice over 5G (VoNR).

We’ll know you can make it if you have:

• Strong expertise in 3GPP standards, IMS, VoLTE, VoWiFi, and SIP signaling.
• Deep knowledge of Diameter, RTP/RTCP, and other telecom signaling protocols.
• Familiarity with EPC and 5GC voice architecture and features, such as SRVCC and SMS over IP.
• Experience analyzing packet captures using tools like Wireshark and vendor-specific trace tools.
• Practical experience with automation tools, e.g., Ansible; Terraform is a plus.
• Scripting skills in Python, Bash, or similar languages.
• Ability to automate repetitive operational tasks and build dashboards or monitoring tools.
• Hands-on experience with virtualized core networks (VMware, KVM).
• Understanding of cloud-native architectures, containerization (Docker), and Kubernetes.
• Familiarity with CI/CD pipelines, microservices, and Git-based workflows is an advantage.

Nice to Have:

• Experience with 5G SA VoNR (IMS over 5GC).
• Knowledge of CSFB, OMR, and supplementary services.
• Hands-on experience with vendor platforms, such as Ericsson, Nokia, Mavenir, and Oracle SBC.
• Exposure to observability and monitoring stacks, including Prometheus, Grafana, and ELK.
• Experience building internal tools or APIs to support network operations.

Our gratitude for the job done will be eternal, but we’ll also offer you:

• Innovative technologies and platforms to “play” with;
• Modern working environment for your comfort;
• Friendly, ambitious, and motivated teammates to support each other;
• Thousands of online and in-person learning opportunities to grow;
• Challenging assignments and career development opportunities in multinational environment;
• Attractive remuneration package;
• Flexible working schedule and opportunity for home office;
• Numerous additional goodies, including, but not limited to free A1 services, discounts, health insurance and services, sports center, childcare, team and family events, etc.