zhahai@gaia.UUCP (02/02/87)
A question regarding full duplex modems and line noise (or impairment):
given a full duplex modem such as 103/212/v.22/v.22bis is there any
reason to expect that sending lots of infomation in one direction would
increase the error rate in the other direction? In each case above, the
information going each way is in a separate frequency band, where it would
normally not affect the information going the other way, given a perfect
channel. Of course, in an imperfect world, it may be possible that the
signal going one way would affect some characteristic of the communications
channel in the other direction (eg: amplitude, frequency response, phase),
given normal switched phone lines. Conceiveably, noise or impairment added
to a signal might add up to interference with the opposite direction signal
more than either alone. Or I may be way off base; my knowledge of telephone
systems and modem technology is insufficient to determine this.
To be more specific, I mean data going in the reverse direction, as opposed
to an idle line (which still has a carrier, of course). In the case of
1200/2400 bps modems, the carrier is modulated by a pseudorandom sequence
even when no characters are being sent, I understand. Nevertheless, it
seems to me (subjectively) that doing more typing on a bad connection tends
to cause more errors in the information being displayed on my terminal. I
am not sure about this, of course. This would seem to have some relevance
to full duplex data transfer protocols, thus the question. ~z~
--
Zhahai Stewart
{hao | nbires}!gaia!zhahai