bitting-douglas@cs.yale.edu (Douglas Bitting) (06/20/91)
In article <56721@nigel.ee.udel.edu> johnston@minnie.me.udel.edu writes: >I have a similar question. I just got a Teleport ADB modem which >supports MNP 4 and 5. I notice an improvement when reading text >or news, but when I'm downloading I see little differnce in throughput. This is MNP5's downfall. MNP5 tries to compress the data to be transmitted on the fly. However, the one thing it doesn't do (which is very important) is check to see if it is actually doing any good. The reason why this is important is that many of the files you will download are already compressed. What happens when you try to compress them again? Not much... that is why you see no improvement in these cases. In fact, MNP5 can actually slow down transmission dramatically if it is trying to compress pre-compressed files. v.42bis (which is a protocal found in some/many 9600 bps modems and a few 2400 bps modems) is a better protocol. It can achieve 4:1 compression (ideally... that is, this rarely happens) as opposed to 2:1 for MNP5 (which is also an ideal statistic). Furthermore, it checks to see if it is actually doing any good. If it isn't, it stops trying to compress the file being transmitted. Anyway, modem protocols are a rather tricky subject which I don't pretend to know anything about. These are just the two compression/error correction protocols I do know about... Hope that this clarifies why MNP5 isn't always improving your throughput. > >-- Bill (johnston@minnie.me.udel.edu) --Doug -- Doug Bitting | "And we know that in all things God works PO Box 3043 Yale Station | for the good of those who love him..." New Haven, CT 06520 | --Romans 8:28 bitting@cs.yale.edu +------------------------------------------