Connection retention is one of the parameters influencing the Quality of Service (QOS) after the call has been set up. As the assessment of this parameter is difficult and costly, it is recommended to investigate only after information from sources such a
ITU-T E.428-1992 history
1992ITU-T E.428-1992 Connection Retention - Telephone Network and ISDN Quality of Service Network Management and Traffic Engineering (Study Group II) 4 pp