Planning an IP Network for Voice and Data

Users have certain quality expectations for telephone communication. When they are talking to a customer through a VOIP link, for instance, they might insist on toll-quality voice. This means that they want it to sound to them and to the customer as though they are on an ordinary TDM telephone link.

The quality of a call can be measured using one of several call quality metric calculations. The most commonly used system is the Mean Opinion Score (MOS). The MOS score of a call is between 1 (for unusable) and 5 (for excellent). VOIP calls that are working properly fall between 3.5 and 4.2 MOS. A score of 4.0 is defined as toll quality. Other systems for quality measurement are R-factor, PSQM, PESQ, and PAMS. These other systems produce scores for a call that can be mapped to MOS for comparison.