Path: utzoo!attcan!uunet!tektronix!reed!omen!caf
From: caf@omen.UUCP (Chuck Forsberg WA7KGX)
Newsgroups: comp.protocols.misc
Subject: Re:  About Protocols for File Transfer
Message-ID: <690@omen.UUCP>
Date: 9 Jun 88 12:49:03 GMT
References: <8806061401.AA04016@hcx9.ucf.edu>
Reply-To: caf@omen.UUCP (Chuck Forsberg WA7KGX)
Organization: Omen Technology Inc, Portland Oregon
Lines: 40

In article <8806061401.AA04016@hcx9.ucf.edu> goldfarb%hcx9@ucf.CSNET ("Benjamin I. Goldfarb") writes:
:>There isn't much of an upper bound on the number of extra
:>characters that might be inserted into the stream.  Would you
:>believe several hours' worth of "UUUUUUUUUUUUUUUU" at 1200
:>bps?  (I enhanced error recovery procedures after that one.)
:>That's one modem's rendition of dial tone.
: ------ --- ------- --------- -- ---- ----
:
:OH YEAH?  More likely the "UUUUUUUUUUU" was an erroneously
:initiated test mode in the modem in question.  Racal-Vadics are
:notorious for this but the feature can be disabled by either
:a dip switch or a strap option.  A stream of ASCII U's makes for a
:good digital test because U is 01010101, so a stream of them
:creates a nice, big, fat square wave on a scope.
:
:Sorry to be so picky, but I never saw a modem "render" a 
:dial tone.
:
:			Ben Goldfarb
:			University of Central Florida
:			goldfarb@ucf-cs.ucf.edu
:			{decvax,peora,uflorida,codas}!ucf-cs!goldfarb

Come to think of it, the dialtone rendition might not have
been a string of U's, typically seen when one of the loopback
modes is activated.  However, the point still stands, the
modem would emit a stream of characters if a caller
disconnected in just the right way, without any dead time
between loss of carrier and the onset of dial tone.  This
was on a stepper switch, the "precision" dial tone on DTMF
lines would be less likely to do this.

I didn't mention, however, several other ways that a large
number of characters may be "invented" by the modem or other
parts of the transmission medium, including buffer pointer
errors and scramblers losing sync.

So, yes, I have seen a modem "render" a dial tone.  More to
the point, the observation of the effect of that and related
impairments remains valid in respect to protocol discussions.