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MOS measures subjective call quality for a call. MOS scores range from 1 for unacceptable to 5 for excellent.
VOIP calls often are in the 3.5 to 4.2 range.
The ITU P.861 (PSQM) and P.862 standards explain how to calculate MOS scores.
The methods used require a test call in order to make the measurements. Kurittu and Mattila debate the practicality of P.862 for VoIP in an AES paper titled "Practical Issues in Objective Speech Quality Assessment with ITU-T P.862". I can't vouch for it because I couldn't find it online for free, but there may be a few similarities with Takahashi, Hideaki, and Kitawaki's Perceptual QoS Assessment Technologies for VoIP.
ITU P.563 calculates call quality passively and calculates an R Factor that can be used to estimate a MOS score.
Using the PESQ and PAMS call quality measurement methods requires a license from Psytechnics a spinoff from British Telecom.
Newer versions of Cisco IOS has built-in tools for measuring call quality metrics including estimated MOS scores for test calls. A detailed description of their methods is in this document: Service Assurance Agent (SAA) VoIP Proactive Monitoring
For products to measure call quality see: How To Debug and Troubleshoot VOIP
- Passive voice quality analysis based on voice quality impairments detection. The technology implements innovative approach for receiving MOS scores of call records and deliver information on the voice quality impairments that caused the quality loss.
- Recommended VoIP Call Quality Metrics
- AQuA - Audio Quality Analyzer - a VoIP friendly technology providing perceptual voice quality assessment for end-to-end testing
- NIQA - Non-Intrusive Quality Analyzer - a VoIP friendly technology providing perceptual voice quality assessment for single-ended testing
- SoliCall Improving Audio Quality in VoIP Networks
- VOIP Troubleshooter
- Related ITU standards
- State of the Art Voice Quality Testing - whitepaper by Opticom GmbH that offers a good summary
- Asterisk soundfile "call-quality-menu.gsm"
- Recqual - Recqual (Real Call Quality) is an Asterisk based call quality tool that analyzes the round trip audio path.
- VoIP Spear — Web site that monitors your Internet connection 24×7x365 and shows you what your VoIP QoS is.
- http://www.voipmonitor.org — VoIPmonitor is open source live network packet sniffer which analyze SIP and RTP protocol.
- http://tools.voxygen.co.uk — Skype Connect Test Tool utilises a JAVA SIP applet to take real-time QoS measurements.
- http://www.imsloader.com — IMSLoader allows to sniff the network packet and analyse SIP session, allows also traffic generation
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