GOST R 56087.4-2014 有关电信服务质量的国家标准体系. 本地长距离国际电话通信的服务质量. 电话呼叫质量指数的标准值"
System of national standards for quality of telecommunication services. Quality of services of local, long-distance and international telephone communication. Normative values for quality indices of telephone calls