piet@cwi.nl (Piet Beertema) (06/03/88)
Recently we got a set of 4.0 EPROMs for our Trailblazers (TB+) for testing purposes (Telebit doesn't officially export 4.0 outside the USA yet). Works great indeed within the country (Holland). But real problems appeared when I tried to set up a transatlantic link (to uunet) with it: in at least 8 out of 10 attempts it failed to get a good connection! However, once I got a good connection, it stayed good. The symptoms were that in first instance a connection was made (I got the CONNECT message), but response was *extremely* slow (taking half a minute to echo the login name). So I tried it with the speaker on all the time (ATM2); that revealed what was going on: once the connection was made, instead of getting the rapid on/off "noise" you normally end up with, the modem would enter a series of retrains and renegotiate sequences, often ending in the connection being dropped altogether. I've tried the same with other Trailblazers that still have the 3.0 firmware and found that there was almost NO problem at all when setting up a transatlantic link, even though the remote site (uunet) has the 4.0 firmware. Playing with the register settings gave no improvement whatsoever with 4.0-to-4.0; specifically setting echo suppressor compensation (S121=1) didn't help. Now, since Telebit doesn't export 4.0 yet, I have no site in Europe to test it with. But I also don't have any idea yet whether this problem shows up only when I try to set up a link to the USA and not the other way around. I would expect the problem to show up in both directions, since I suspect that the cause of the problems is some sort of interference between the modem's line turnaround timing and the delays experienced on the transatlantic lines. If you have other ideas & suggestions, please let me know. If anyone over there would be willing to do a test and let me know the results, I would greatly appreciate it. For that purpose I've temporarily (for one week) set up a special number: +31 20 5924154 with a Trailblazer (with 4.0) on it. I'm not inviting hackers, so the modem is not connected to any system. All I'm interested in is to know what happens when someone (with 4.0!) tries to set up a connection from the USA (do ATM2 before dialing!) to that modem, i.e. if you succeed in getting the normal "on/off noise sequence", characteristic of a good connection, (almost) right away. Thanks in advance, -- Piet Beertema, CWI, Amsterdam (piet@cwi.nl)