Senior Manual QA Engineer (VoIP / Voice / Real-Time Communications)

Since 2007, MMDSmart has been a leading supplier in cloud communications, delivering IT products to businesses in over 100 countries. The company focuses on Messaging and Voice solutions to empower client communications.

• 5+ years of software testing experience, with at least 2+ years in VoIP / Voice / real-time communication systems.
• Strong hands-on understanding of SIP protocol (call flows, registrations, INVITE flows, SDP, RTP).
• Practical experience analyzing SIP/RTP traffic.
• Experience testing call center / CCaaS systems (IVR flows; ACD / call routing logic; call recording; agent states & call lifecycle).
• Familiarity with WebRTC technologies and real-time communication challenges.
• Deep understanding of voice quality metrics (latency, jitter, packet loss, echo, MOS).
• Solid knowledge of TCP/IP networking, NAT, firewalls, ports, STUN/TURN.
• Experience working in Linux environments and reading server logs.
• Basic scripting skills in Python, JavaScript, or TypeScript for test tooling and log analysis.
• Experience with REST API testing (Postman, curl, or similar).
• Understanding of RTP media flow vs SIP signaling.
• Ability to debug one-way audio, no audio, delayed media, early media.
• Experience testing systems dependent on timing, network conditions, and concurrency.
• Understanding telephony behavior differences from web applications (stateful, event-driven, race conditions).

Nice to have:

• Experience with test automation using Playwright or similar.
• Experience with API automation frameworks (pytest, REST Assured, etc.).
• Familiarity with performance/load tools (k6, JMeter, Locust).
• Experience simulating SIP traffic using SIPp.
• Experience working with PBX / SBC / softswitches (Asterisk, FreeSWITCH, Zoiper, etc.).
• Experience testing under network impairment (packet loss/delay simulation).

• Analyze business requirements and technical specifications for web interfaces and backend, proactively challenging architectural assumptions.
• Act as a "Voice System Investigator" performing deep-dive analysis of complex call flows and media streams using packet captures (PCAPs) and server logs to identify root causes of signaling and audio defects.
• Design and execute advanced test strategies covering the entire communication lifecycle, ensuring integration between WebRTC components, IVR logic, ACD routing, and call recording systems.
• Investigate intersections of web application states and real-time media, debugging UI/UX synchronization with agent states, call control race conditions, and WebRTC connectivity issues.
• Simulate network impairments (latency, jitter, packet loss) and use voice quality metrics (MOS) to ensure system resilience under sub-optimal conditions.
• Drive quality improvements within an Agile environment, participate in architectural reviews and brainstorming sessions to advocate for testability and system stability.
• Mentor the team and improve QA processes, sharing expertise in troubleshooting stateful, event-driven systems and refining estimation and testing methodologies.
• Maintain technical documentation and Root Cause Analysis (RCA) reports for complex bugs.

Equal opportunity employer committed to diversity and inclusion. Medical Insurance and Sport Card perks are available only for employees located in Bulgaria.