ITU-T E.161-2001
可用于增加电话网接入的电话和其他装置的数字、字母和符号的安排 E系列:整体网络操作 电话服务
Arrangement of Digits Letters and Symbols on Telephones and Other Devices that can be Used for Gaining Access to a Telephone Network Series E: Overall Network Operation Telephone Service Service Operation and Human Factors International Operation - Number