garvey@johnny5.uucp (Joe Garvey) (03/15/91)
It seems to me that with all the Sun accessories that live off the SCSI bus, that someone in the terminal server market should be doing something similar. I'd have loved to have a terminal server, where I had actual device files on my system to address individual serial ports. It seems to me that you could do this with psuedo-ttys and a daemon that monitored the slave side of these devices. The real problem would come when you needed so set the baud rate or handshaking mode. The actual flow of bits would be pretty simple. Why doesn't anyone do this? Is there a protocol under developement? I have seen an add for the Annex III. It claims something like this... anyone know more? -- Joe Garvey uucp: sumax!quick!johnny5!garvey J5 Research map entries are wrong for johnny5. They're Bothell, Wa. being fixed. Please use address above.
griff@Xylogics.COM (Scott Griffiths) (03/15/91)
I tried to respond to Joe Garvey directly but the mail kept bouncing so I decided to post this here. For some time now, the Xylogics family of terminal servers has provided a host based utility called rtelnet (reverse telnet). This program allows the user to specify a /dev/device_name entry for use with applications which are used to talking to /dev/tty types of devices. A data path is set up between the host and a specified port on the terminal server so these applications work without modification. The most often used applications are for printers and modems on the network (lpd, cu, tip and uucp). The utility actually works as follows. A free pty is found and reserved for use (by opening the master side). The user specified device name is linked to the corresponding slave device. Finally, a telnet connection is opened between the host and the specified terminal server port. Please let me know if you need any more information on this capability. Scott Griffiths phone: (617) 272-8140 Xylogics Annex Technical Support email: griff@xylogics.com -- Scott Griffiths phone: (617) 272-8140 Xylogics Annex Technical Support email: griff@xylogics.com
john@loverso.leom.ma.us (John Robert LoVerso) (03/16/91)
> Why doesn't anyone do this? Is there a protocol under developement?
Some terminal server vendors do let you do this. There are several ways.
The easiest involves something on the order of a user-level "reverse"
telnet daemon that runs on your host, connects to a pty pair, and makes
a telnet connection to the terminal server. This gives you a device
that you can poke random programs at. Xylogics provides source to such
a program with the software distribution that comes with the Annex.
cisco provides a similiar program via anonymous ftp access. One or
two other such programs have been posted to comp.sources in the past.
The pty approach has several hazzards, as it stretches the abilities
of the pty mechanism in various ways. However, it is a good 90% solution.
Of course, it can reek havoc with the performance of your machine - as
can anything based upon the traditional BSD telnetd/pty interaction.
Using the "in-kernel" telnetd support code can remove this performance
problem.
At least one company (Artecon) resells [Annex] terminal serves with a
SunOS device driver that does the telnet connection in the kernel and
links directly to the tty stack. This supposedly removes several of the
problems with the pty approach, but I've never used it, so I can't comment
further.
John