| 摘要 |
In a communications arrangement, a first pulse code modulation (PCM) modem communicates data in the form of PCM words with a second PCM modem through a public switched telephone network (PSTN). Transmitted signals representing PCM words may be affected by robbed bit signaling occasioned by the PSTN such that the least significant bits (LSBs) of certain transmitted PCM words are "robbed" and substituted with signaling bits. In addition, the transmitted signals are attenuated because of a digital loss imposed by a switch in the PSTN. During training of a PCM modem, any occurrence of robbed bit signaling is identified, and a signal level conversion table is created. This table contains each transmitted PCM word and the received signal level corresponding thereto. In accordance with the invention, the digital loss is measured based on those received signal levels in the table which are free of robbed bit signaling.
|
