Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!uunet!seismo!rutgers!sri-spam!ames!ucbcad!ucbvax!SIMTEL20.ARPA!WANCHO From: WANCHO@SIMTEL20.ARPA ("Frank J. Wancho") Newsgroups: comp.protocols.tcp-ip Subject: TAC "noise" Message-ID: Date: Tue, 4-Aug-87 16:28:00 EDT Article-I.D.: SIMTEL20.WANCHO.12323875172.BABYL Posted: Tue Aug 4 16:28:00 1987 Date-Received: Thu, 6-Aug-87 04:43:26 EDT Sender: daemon@ucbvax.BERKELEY.EDU Distribution: world Organization: The ARPA Internet Lines: 42 This one has got me stumped, and I'd appreciate it if this message was redirected to a more appropriate forum if there is one. We have noticed this "noise" problem on and off for quite some time and are now realizing that perhaps what we and our users are seeing is not line noise but something else. In general, when a user calls to complain about seeing "noise" from a TAC connection, we naturally assume the problem is caused by line noise in the phone circuit between the user and the TAC port modem. However, it has turned out that we have not been asking the right question in determining the noise characteristic. The question is: are you seeing "noise" when there is supposed to be no activity on the line, or are you seeing it as garbage only when the remote host is sending a long string of characters. If the answer is yes to the former, the problem is probably a "bad" circuit. However, if the answer is yes to the latter, then we have a whole new problem, or so it seems. I've seen the latter problem only at 2400bps. Others have reported the problem at 1200, and some even at 300. With the rumored eventual upgrade to 9600bps dialup TAC access, I am concerned that there may be an underlying basic TAC-to-modem interface problem that needs to be found and fixed before higher speeds become commonly available and useable. The characteristic of this form of "noise" is that the first several lines of expected output appear OK, then garbage (noise). This is consistently repeatable. We have empirically ruled out several possible causes, including real line noise, and noise caused by level settings in the modems themselves. It seems one possibility remains: that there is a "slight" speed mismatch between what the TAC outputs and what the modem expects and bits eventually get shifted... There is one further complication that makes things harder to track: it appears that the TAC software *may* have been undergoing "minor" changes during this time without the version number changing in the TAC herald. Thus, it is somewhat difficult to pinpoint when this problem started to occur relative to TAC version. I suggest that followups to this message be made privately amongst interested parties unless there is some general interest in this subject on this list. The only reason for bringing this up here is that I have several high level users wanting answers *now* and I can't evade the queries for much longer... --Frank