VoIP need not be “toll quality”

Public Switched Telephony System (PSTN) uses a fixed sampling rate, typically 8k Hz and coding to 8 bits, this results in 64 kbps voice coding

However, VoIP is not limited to using this coding and could have higher or lower data rates depending on the CODEC(s) used, the available bandwidth between the end points, and the user’s preference(s).

One of the interesting possibilities which VoIP offers is quality which is:

better that “toll grade” telephony or
worse than “toll grade” telephony (but perhaps still acceptable)

This is unlike the fixed quality of traditional phone systems.

To assess the quality of a call, see standards such as ITU-T’s Methods for Subjective Determination of Transmission Quality, Recommendation P.80.

Slide Notes

CCITT, Methods for Subjective Determination of Transmission Quality, CCITT, Recommendation P.80, 1998, A later version of the standard is ITU-T Recommendation P.80, March 1993, Section 7: Subjective Opinion Tests, paragraph 3.1.2.3 Silence (gap) characteristics, http://starlet.deltatel.ru/ccitt/1988/ascii/5_1_06.txt Links to an external site.

ITU-T, Methods for Subjective Determination of Transmission Quality, ITU-T, Recommendation P.80, March 1993.

Transcript

[slide90] As we said, voice didn't need to always be toll quality.