CompuServe Messages

Jason, That's what V.32bis is, a full-duplex, 14.4kbps link. The HST protocol does not provide error correction. Before USR retrofitted the modems with V.42 and V.42bis, they used MNP level 4 for error correction and level 5 for data compression. The V.42 compatible modems will fall back to MNP if it connects with one that only supports MNP. And yes, V.42 does offer a speed increase, the same as MNP level 4 does. It reformats the data into packets and strips the start and stop bits for each byte in the process. So, by removing two bits in ten, you have a gross performance increase of 20%. But, since you have to factor in packet and handshake overhead, the gain is cut down to about 15-17%. That's why you get about 1650cps on a 14.4kbps link, the error correction provides the extra throughput (so long as it's a clean connection). V.42bis provides data compression, the same as MNP level 5, but without the performance penalty that the latter gives you when transfering an already compressed file. -jack