GB/T 7617-1987 in English

《GB/T 7617-1987在电话线路上数据传输的功率电平》由339-2（工业和信息化部（通信））归口，主管部门为工业和信息化部（通信）。
本标准等效采用国际电报电话咨询委员会CCITT建议V.1（1984）《在电话线路上数据传输的功率电平》。

Scope

This standard is equivalent to the CCITT Recommendation V.2 (1984) "Power Levels for Data Transmission on Telephone Lines" of the International Telegraph and Telephone Consultative Committee. The purpose of this standard to specify the data signal level is as follows: a. In order to ensure satisfactory transmission effect and to coordinate with equipment such as signal receivers or echo suppressors, the data signal level on international circuits should be as strict as possible To control b. From the perspective of load and noise, in order to ensure the normal operation of the multi-carrier system, the average power of the data circuit and the customary value of the channel load should not be too different (-15dBm0^{-1 for each transmission direction} ). This customary value considers leaving a reasonable channel ratio P in a multi-channel system (P is the ratio of the number of channels used to transmit data to the total number of channels of the same type in a multi-channel system, such as a multi-carrier system Ratio. Its value depends on the system, generally less than 50%). In order to use a fixed power level of about -13dBm0 in each transmission direction for non-speech applications. Note: 1) In the multi-channel carrier telephone system, the distribution of the long-term average power of each channel (the customary average value is 15dBm0) has a standard deviation of about 4 dB. If the proportion of non-voice applications (including data) does not exceed the above P value, the average power of each transmission direction is -13dBmo, and it is also allowed to be used for data transmission. If in the international carrier system, the proportion of non-phone circuits is significantly higher than P (due to the development of data transmission), the power can be reduced by 2dB. C. When some authorities want to fix the signal power level of the data modulator to a specific value at the subscriber line terminal or the local telephone exchange. The relationship between these values and power levels on international circuits depends on the national transmission scheme. In any case it must be expected that there is a large range of attenuation d in the possible connection between the user and the input of the international circuit. From the considerations a~c, it is not optimal to specify only the maximum data signal level. useful form. Another consideration is to specify the nominal power at the input of international circuits, which is the average power estimated statistically from tests of many data transmission circuits