Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!watmath!clyde!rutgers!ames!ucbcad!ucbvax!decvax!tektronix!reed!nscpdc!atelabs!cds From: cds@atelabs.UUCP Newsgroups: comp.dcom.modems Subject: Re: Hayes command set oversight/problem Message-ID: <200@atelabs.UUCP> Date: Fri, 20-Feb-87 20:05:05 EST Article-I.D.: atelabs.200 Posted: Fri Feb 20 20:05:05 1987 Date-Received: Sat, 21-Feb-87 20:31:42 EST References: <871@basser.oz> <1408@cbmvax.cbmvax.cbm.UUCP> <533@viper.UUCP> <658@uw-warp.UUCP> Reply-To: cds@atelabs.UUCP (David Shanks) Organization: AT&E Laboratories, Beaverton, OR Lines: 48 In article <658@uw-warp.UUCP> dennis@uw-warp.UUCP (Dennis Gentry) writes: >The Scenario: >------------- >The poster that started this whole discussion described a scenario >where an escape sequence of "+++" is sent through modem A to a remote >computer through modem B. This would get modem A into command mode as >desired, but supposedly when the remote computer echoed the "+++" back >to modem B, modem B would go off into the neutral zone (command mode, >actually), leaving you with a "hung" connection. > >The Way It Should Work: >----------------------- >It seems to me like the best design solution to this problem would be >to have the modem NOT SEND the "+++" if it had seen the 1 second delay >before you typed the "+++". Then if it got another delay, it could >return you to command mode without even letting the remote system know >that you had done ANYTHING. If it didn't get the delay, meaning that >you didn't want to go to command modem, then it could go ahead and >"catch up" by sending the "+++". This might be the way it actually >works with a real live Hayes modem. Fortunately real Hayes modems do not work this way. In fact, they can't work this way without undesirable side effects. The Hayes spec (and I use that term loosly) says that when the modem sees an escape sequence on its DTE data stream it will drop into command mode. The escape sequence is a pause, followed by three '+' characters with no characters in between, followed by a 1 second pause. The first pause length is controlled by a register in the modem. Suppose that, after a suitable pause, the DTE sends a single '+' character to the modem. If Hayes follows the suggestion made above then the modem cannot transmit this character until at least one more character comes from the DTE, possibly two (if the next character is also a '+'). I don't believe that this is a desirable "feature." I might want to send a single '+' and wait for the remote computer to respond. Yes, I know that I can change the escape character to something else, but I might want to send any character by itself. A better solution would be to provide a configuration option which, if turned on, would tell the modem to ignore all escape codes. Unfortunately, Hayes modems (at least model 1200) do not have such a feature. We simply have to live with them the way they are or get a different brand of modem which doesn't have the problem. -- Dave Shanks ..!tektronix!tessi!atelabs!cds AT&E Laboratories cds@atelabs.UUCP 1400 NW Compton Suite 300 (503) 690-2000 Beaverton, OR 97006