The quality of VoIP (Voice over Internet Protocol) communications is a crucial element in ensuring an optimal user experience. For instance, consider the use of VoIP in call centers, which are increasingly adopting this solution due to its cost-effectiveness and high scalability.
One of the most widely used standards for measuring the perceived quality of VoIP calls is the Mean Opinion Score (MOS). This index, which typically ranges from 1 (poor quality) to 5 (excellent quality), is obtained through subjective and objective methods to evaluate clarity, latency, and other parameters that impact the performance of a VoIP network.
What the MOS (Mean Opinion Score) Measures and How It Works
The MOS is an indicator that reflects the perceived quality of a VoIP call based on several technical parameters:
- Latency: the delay in data transmission between two endpoints.
- Packet Loss: the loss of data packets during transmission.
- Jitter: the variation in the arrival time of packets, which can disrupt the smoothness of the conversation.
- Codecs used: VoIP codecs influence the compression and decompression of voice data, directly affecting quality.
How to Evaluate VoIP Using the MOS
The evaluation of MOS can be conducted in two main ways:
- Subjective method: involves users listening to voice recordings and assigning a score based on perceived quality.
- Objective method: uses algorithms and software tools to calculate MOS based on technical parameters.
How to Calculate MOS
The most common formula for calculating MOS objectively is derived from the E-Model, standardized by ITU-T in recommendation G.107. MOS is calculated from the R score, which ranges from 0 to 100, using the following equation:
[ MOS = 1 + 0.035R + 7 \times 10^{-6} R(R – 60)(100 – R) ]
Where:
– R is the transmission rating factor that accounts for variables like delay, packet loss, and jitter.
A higher R score indicates better perceived quality. For example:
– R > 90 corresponds to a MOS of about 4.5 (excellent quality).
– R between 70 and 90 corresponds to a MOS between 3.5 and 4.4 (acceptable quality).
– R < 60 indicates poor quality.
Tools for Automatically Measuring MOS
Nowadays, numerous tools are available to analyze MOS and VoIP traffic without complex calculations. Among the most common are:
- Wireshark: a network analyzer that monitors VoIP traffic and calculates metrics like jitter, latency, and packet loss.
- VoIPmonitor: specifically designed for VoIP networks, it offers detailed analyses of call quality based on MOS.
- SIPp: an open-source tool for testing VoIP network performance, useful for simulating SIP calls and measuring quality.
- PESQ (Perceptual Evaluation of Speech Quality): an advanced model for evaluating speech quality in VoIP scenarios.
The Importance of Choosing a Reliable VoIP Provider
To ensure high-quality VoIP traffic, it is also essential to rely on a reliable VoIP provider that guarantees consistent and superior service quality.
A good provider not only offers robust infrastructures optimized to minimize latency, jitter, and packet loss but also provides dedicated technical support to quickly resolve any issues.
Additionally, quality providers implement advanced Quality of Service (QoS) policies and use efficient codecs to balance audio quality and bandwidth usage. Opting for a professional provider ensures a superior user experience, reducing disruptions and issues that could compromise business communications.
MOS and VoIP Traffic Management
For those managing large volumes of VoIP traffic, monitoring MOS is critical to ensuring optimal communication quality. A low MOS score requires immediate interventions, such as router and server configuration optimization to reduce latency.
The adoption of high-efficiency codecs, such as G.729 or G.711, can improve the balance between audio quality and bandwidth usage. Implementing Quality of Service (QoS) policies is equally important to prioritize VoIP traffic over other data types and minimize packet loss.
Limitations and Considerations of MOS
Despite its utility, MOS has some limitations. For example, it does not account for users’ personal preferences or hardware variations, such as the use of different-quality headsets or speakers.
Moreover, MOS may not fully capture the impact of occasional issues, such as sudden jitter spikes or network congestion. For this reason, combining MOS with other network metrics is recommended to achieve a more comprehensive performance overview.