Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!seismo!husc6!mit-eddie!genrad!decvax!ucbvax!SIMTEL20.ARPA!WANCHO From: WANCHO@SIMTEL20.ARPA Newsgroups: comp.os.cpm Subject: MEX Batch mode solved Message-ID: Date: Tue, 21-Apr-87 23:59:00 EST Article-I.D.: SIMTEL20.WANCHO.12296443207.BABYL Posted: Tue Apr 21 23:59:00 1987 Date-Received: Thu, 23-Apr-87 04:54:34 EST Sender: daemon@ucbvax.BERKELEY.EDU Distribution: world Organization: The ARPA Internet Lines: 31 At one time, I wrote out a description of the MODEM7 protocol as then implemented by the TOPS-20 version, called MODEM. Although TMODEM has replaced MODEM with many changes, the description of the protocol with respect to the timeout values used remain essentially the same. The major difference is that a multiplier of four is used instead of three for determining the timeout value for a data packet. TMODEM and MODEM before it sends the data packet as a string in a single system call rather than sending each character in the data packet with separate system calls and associated timeouts. These timeout values were empirically determined over many transfers under a variety of line conditions and delays and significantly contribute to the robustness of the protocol. Unfortunately, these values were incorporated into MODEM7 late in its life while undergoing a power struggle, and probably never made it into many of the current versions claiming to be "xmodem" compatible. In fact, many of the so-called versions of "xmodem" in the pc world are based on a very old description of the protocol that doesn't even include CRC mode, much less the MODEM7 "batch" mode. Fortunately, both MEX 1.14 and all subsequent versions of the commercial versions of MEX, MEX-PLUS and MEX-PC, do use these improved timeout values. I cannot speak for YAM and YMODEM, but I suspect they use similar values. So, those of you wishing to "improve" the timeout values should consider checking out the values given in PD:MODEM7.DOC. BTW, I must agree that the YMODEM batch method of passing filename and other information is definitely superior to the MODEM7 method. TMODEM may incorporate that option someday as well... --Frank