Technique for treating channel impairments including a digital loss in transmitted signals in data communications

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). The transmitted signal representing the data may be affected by type A and/or type B robbed bit signaling occasioned by the PSTN such that the least significant bits (LSBs) of certain PCM words are “robbed” and substituted with signaling bits. In addition, the transmitted signal is attenuated because of a digital loss imposed by a switch in the PSTN. During training of a PCM modem, any occurrence of type A and/or type B robbed bit signaling is identified, and a signal level conversion table in accordance with the invention is created. Based on this table which takes into account the digital loss, the most likely transmitted PCM word is determined, given a received signal level.