Due to the fact that all services today are transmitted over the internet, they have become easier to use and more affordable. One such service is VoIP. This research focuses on the statistical analysis of VoIP user traffic with the G.711 codec and its variants (G.723, G.729). Data was provided by Intelligent Technology Partner LLC, a company offering VoIP services in Mongolia. The results of this analysis are compared with the theoretical distribution of inter-arrival time (the time between packets). Additionally, other parameters for simulation are defined based on mathematical formulas. The most influential factor in the traffic of devices connected to the internet network is the queue at the output buffer, which has been modeled using the M/D/1/∞ model, and the mathematical derivation of the model has been fully completed. Essential performance metrics, including system and queue waiting times, packet counts within the system, and their standard deviations, were obtained for environments accommodating 1 to 50 users. Simulation outcomes, derived from 1,000,000 packets, demonstrate a strong correlation with theoretical forecasts. These findings offer significant insights for enhancing VoIP system design, network planning, and prospective service advancements. The research underscores the significance of choosing the appropriate codec according to user demand to improve Quality of Service (QoS).