From: SMTP%"RELAY-INFO-VAX@CRVAX.SRI.COM" 11-MAR-1994 16:14:10.35 To: EVERHART CC: Subj: Thoughts On Establishing LAT Link From LTAnn Port To DECServer.. Date: Thu, 10 Mar 1994 23:30:15 -0500 (EST) From: "Clayton, Paul D." To: steveh@brendata.demon.co.uk CC: INFO-VAX@SRI.COM, CLAYTON@radium.xrt.upenn.edu Message-Id: <940310233015.42200b56@radium.xrt.upenn.edu> Subject: Thoughts On Establishing LAT Link From LTAnn Port To DECServer.. Steve Hanselman @ "steveh@brendata.demon.co.uk" has the following LAT problem. >I need to collect some data from a reverse LAT service. I can use set host/dte >and see the data flowing, this also proves that the port is connecting to the >right terminal server port etc. However, when we use a simple C program that >opens the devide, reads data and writes this to a file (the read is using >fgets), the connection to the LAT port is not initiated. Analyze/system shows >that the device (LTA109) has a read outstanding on it however, latcp indicates >that it is inactive, the terminal server counters do not indicate that there >has been any attempt at a remote connection. > >What are we doing wrong? > >I would have thought that the act of opening the channel to an application >port would cause the connection to be made. We have tried both queued and >non-queued port settings in LATCP. > The basic problem here is usage of LAT. And I agree that it does not appear to be 'logical' at all to me either. I ran into this some time ago when a simulator package we use was 'reconfigured' from using TX ports to LT ports off a DECserver. At the time, I had the same 'feeling' that this was going to be a 'piece of cake'. A port is a port is a port and all ports are equal. Well it AIN'T so. ;-( The ONLY SUPPORTED means to establish a usable LAT based connection from an LTA device to a terminal server port is basically the following sequence. - allocate an I/O channel to use. - Issue a IO$_TTY_PORT!IO$M_LT_CONNECT QIO to the I/O channel. - THEN, and ONLY then, use the LT port as a 'normal' TX type of port. You CAN have a LAT port established using a SET HOST/DTE command, and then get out of this and fire up your program and the link MAY still exist and be usable for some period of time. And then again, the link may be torn down before you can use it at all. And if you want to have a program that works on both TX and LT ports, then you need to do a GETDVI/SENSE command to determine which type of terminal port you have and procedd from there. I have not yet tested the case of sending the IO$_TTY_PORT!IO$M_LT_CONNECT QIO to a TX port to see what, if anything, might happen. Another thing I have run into with this setup is bandwidth abilities of the DECserver. If you have a fast baud rate coming into the DECServer, and no flow control (since it may be binary data), overall speed of the DECserver is very important. One thing we have found is that the DS700 servers can handle a cumulative data rate of several 100K bytes per second from its terminal port connections. The older models of DECServers are no where near this fast. Have fun... pdc Paul D. Clayton Address - CLAYTON@RADIUM.XRT.UPENN.EDU (USA) Disclaimer: All thoughts and statements here are my own and NOT those of my employer, and are also not based on, or contain, restricted information.