Unreliable Page 1 v. The telephone company carries the signal on 2 wires only a limited distance - either to your Central Office, or to some subscriber carrier equipment near your premises. This leakage is referred to a echo , and many modems report the level of this signal in diagnostic screens. For voice calls where there are hybrids at each end, the distance between the two ends becomes a factor and can produce unwanted echo.
More delay makes the echo more noticeable.
With this in mind, as a general rule, telcos in the US place a pad whose value varies depending upon the type of call. Apparently, there is something about the way in which the pads attenuate the signal that can impair 56k PCM performance. So, it may not be practical for you to get the best pad for your 56k calls. If you have an ISP who uses the same telco office as your line is on, that ISP may give you better performance that others located further away. All rights reserved.