wtm@neoucom.UUCP (Bill Mayhew) (12/09/89)
One thing to keep in mind is that if you dial into the Unix PC On Board Modem set for MNP, the MNP modem will freak out because the On Board Modem echoes back the MNP negotiation string beause of the way [uu]getty works. Microcomm thoughtfully made the negotiation handshake the same for both directions, so the caller modem thinks that the Unix PC OBM is MNP-capable when, in fact, it is not. The result is a lock-up that can only be broken by hanging up and restting the remote modem to disable MNP. Keen, huh? This MNP feature/bug, of course, is not necessarily unique to the Unix PC. In general, I've not been terribly excited by MNP. It turns out that any line that has even a modest amount of noise reults in so many retransmits of packets that the throughput drops to the tens of buad range. I haven't had a whole lot of success by switching to short MNP packets. PEP mode modems deal with noise much better than QPSK modems. My experince has been that shopping for a modem wiht adaptive equalization circuitry is money better spent than buying MNP. Adaptive EQ and MNP features aren't aways features that occur as a pair. It is possible to implement MNP with software on the host system. I use Mirror III with the MNP A-I (Add-In) kit on my laptop, and it works quite well with the plain vanilla Hayes-compatible internal modem. Total cost for Mirror and MNP A-I was less than $100. With regards to the Trailblazer, its MNP is sort of strange. It's like MNP level 3-1/2. Not all of the Level 4 MNP features are implemented. Bill