Determining Mean Opinion Scores (MOS) for Variable Bit Rate Audio Streams

A network monitoring system, comprising:

• a processor;
• and
• a memory coupled to the processor, the memory configured to store program instructions executable by the processor to cause the network monitoring system to:
• receive an audio signal in a Real-time Transport Protocol (RTP) stream over a Voice-over-IP (VoIP) network, the audio signal encoded using a Variable Bit Rate (VBR) codec;
• determine that a first portion of the RTP stream corresponding to a first portion of the audio signal is transmitted with a first bit rate;
• calculate a first Mean Opinion Score (MOS) for the first portion of the audio signal based, at least in part, upon the first bit rate;
• determine that a second portion of the RTP stream corresponding to a second portion of the audio signal is transmitted with a second bit rate, the second bit rate different from the first bit rate;
• calculate a second MOS for the second portion of the audio signal based, at least in part, upon the second bit rate;
• and
• generate an average MOS for the audio signal based, at least in part, upon the first and second MOS.

A tangible electronic storage medium having program instructions stored thereon that, upon execution by a processor within a computer system, cause the computer system to:

• calculate a packet payload size distribution for an audio stream encoded with different bit rates;
• calculate Mean Opinion Scores (MOS) for each of two or more portions of the packet payload size distribution based, at least in part, upon the different bit rates;
• and
• determine an overall MOS for the audio stream based, at least in part, upon the calculated MOS and the packet payload size distribution.