Results and Lessons Learned from SIP-Based OTT Voice in Private 5G SA Across Two Deployments

Over-the-top (OTT) Session Initiation Protocol (SIP)-based applications are increasingly viewed as a flexible and cost-efficient alternative to traditional IP Multimedia Subsystem (IMS) deployments. However, their performance within emerging private 5G Standalone (SA) networks remains insufficiently characterized. This paper evaluates the feasibility of deploying such services in controlled private 5G environments using two end-to-end testbeds: one built with commercial components and another based on open-source 5G software stacks. A representative open-source OTT unified communication platform is implemented on both testbeds, and extensive measurements are conducted to assess call-setup latency and media quality. Quality-of-experience (QoE) indicators, including Mean Opinion Score (MOS) values computed using the ITU-T G. 107 E-Model for audio and the G. 1070 model for video, consistently fall between 4 and 5 across all Real-time Transport Protocol (RTP) streams, demonstrating excellent perceived quality. The results further show that OTT call services achieve sub-second call-setup times while maintaining jitter and packet-loss levels well within accepted thresholds for real-time communication. These findings confirm that SIP-based OTT unified communications solutions can deliver high-performance, cost-effective communication in private 5G SA deployments, positioning them as a viable alternative to conventional IMS-based architectures.