In considering "connection quality", it is important to recognize that the "user" must already have a complete end-to-end connection, i.e. a distant end answer signal has been received before the connection quality can be assessed. “Connection quality” does not include call set-up delays, etc.
ITU-T E.432 SPANISH-1992 Referenced Document
ITU-T G.821 Error performance of an international digital connection operating at a bit rate below the primary rate and forming part of an Integrated Services Digital Network SERIES G: TRANSMISSION SYSTEMS AND MEDIA DIGITAL SYSTEMS AND NETWORKS Digital networks Quali*， 2024-04-19 Update
ITU-T G.921 DIGITAL SECTIONS BASED ON THE 2048 kbit/s HIERARCHY