Re: UDP Terminal Protocol

From	Robert Wessel <robertwessel2@yahoo.com>
Newsgroups	comp.arch.embedded
Subject	Re: UDP Terminal Protocol
Message-ID	<qs535ctbk361kav29rjd236dat22mo199e@4ax.com> (permalink)
References	<7phv4cd0dickoubm7k7rud6or7vtnft8rb@4ax.com> <o2p3bs$7fc$1@reader1.panix.com>
Organization	Forte - www.forteinc.com
Date	2016-12-14 13:28 -0600

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On Tue, 13 Dec 2016 15:16:12 +0000 (UTC), Grant Edwards
<invalid@invalid.invalid> wrote:

>On 2016-12-13, Robert Wessel <robertwessel2@yahoo.com> wrote:
>
>> OTOH, it's clear that a number of people have implemented a UDP-based
>> protocol for handling the sort of things often done with a serial
>> console attached to a device.  This has a number of advantages - you
>> can fake UPD over Ethernet with very little code, especially if you
>> define away things like fragmentation and options.  A simplified
>> TELNET-ish protocol on top of that would be pretty simple, you just
>> need some basic packet sequencing and acknowledgements.
>
>I know of people who have implemented that on top of IP rather than
>UDP.  They call it TCP. ;)

Well, yes, but the point is that TCP is a fair chunk of code, and for
this function it has to go in a spot where it's less than convenient
to update.  Hence the desire for maximum simplicity.  I used TFTP as
an example, since it solves a similar problem (and you could
certatinly trivially implemented a TCP version of TFTP), with similar
constraints.

>> IOW, something with a relationship to TELNET sort of like TFTPs
>> relationship to FTP.
>
>Just use a raw TCP connection. There's no need to implement the TELNET
>protocol at all.  The Unix command line client will skip all the
>handshaking stuff if you use a non-standard port.  Or you can use
>netcat.  Or any number of terminal emulators or COM port redirectors
>that support raw TCP connections.

Given how little TELNET actually does (or at least, needs to do), if
you have TCP, there would be no really issue implementing that.  Raw
TCP is obviously an option, but again, the incremental cost to do
actual TELNET is low.  And as I said, if you have TCP, why not just do
this with HTTP, and really make things convenient for people.

>If you're on a local Ethernet segment, just use raw UDP.  I've been
>using both those approaches for close to 20 years, and have never had
>any problems.

Yet what exactly is the protocol?  How many characters can you put in
a packet?  Any sequencing or recovery?  Acknowledgements?  Checksums
on or off?  With UDP (and a bit of consideration at the protocol
layer), you can even avoid any IP configuration requirements (at least
on a single LAN) by doing everything with broadcasts.

I've simply never implemented anything with UDP that didn't take error
handling into account - is the common practice just to assume that you
will not lose/reorder/duplicate/mangle any packing so long as you're
on a local segment?  Again, TFTP addresses those issues, at least as
they apply to its requirements.

>> OTOH, despite looking, I just don't see any standards for doing that
>> sort of thing.  Am I just missing it?  Is there a defacto standard
>> even if there's no RFC?
>
>If you want something reliable that works over WANs, use TCP: it's the
>only way you're going to dependably make anything work through a
>firewall.

Sure, no disagreement there.  And no, operation over WANs is not a
prime consideration, although it certainly wouldn't hurt if it could,
even if the user had to deal with firewall issues, or set up a relay
server of some sort.  But the scope would be within a data-center, or
perhaps campus (assuming at least real IP address assignment - without
that, local LAN).  Remember the idea here is to replace a serial
console port.

>If you're going to assume local Ethernet, you can just use UDP.

Thread

UDP Terminal Protocol Robert Wessel <robertwessel2@yahoo.com> - 2016-12-13 04:23 -0600
  Re: UDP Terminal Protocol Dimiter_Popoff <dp@tgi-sci.com> - 2016-12-13 17:10 +0200
    Re: UDP Terminal Protocol Robert Wessel <robertwessel2@yahoo.com> - 2016-12-14 13:33 -0600
  Re: UDP Terminal Protocol Grant Edwards <invalid@invalid.invalid> - 2016-12-13 15:16 +0000
    Re: UDP Terminal Protocol upsidedown@downunder.com - 2016-12-13 18:51 +0200
      Re: UDP Terminal Protocol Grant Edwards <invalid@invalid.invalid> - 2016-12-13 21:13 +0000
        Re: UDP Terminal Protocol Clifford Heath <no.spam@please.net> - 2016-12-14 09:05 +1100
      Re: UDP Terminal Protocol Rob Gaddi <rgaddi@highlandtechnology.invalid> - 2016-12-13 13:23 -0800
    Re: UDP Terminal Protocol Robert Wessel <robertwessel2@yahoo.com> - 2016-12-14 13:28 -0600
      Re: UDP Terminal Protocol Don Y <blockedofcourse@foo.invalid> - 2016-12-14 15:29 -0700
        Re: UDP Terminal Protocol Robert Wessel <robertwessel2@yahoo.com> - 2016-12-15 00:34 -0600
          Re: UDP Terminal Protocol Don Y <blockedofcourse@foo.invalid> - 2016-12-15 01:10 -0700
        Re: UDP Terminal Protocol Les Cargill <lcargill99@comcast.com> - 2016-12-15 21:52 -0600
          Re: UDP Terminal Protocol Don Y <blockedofcourse@foo.invalid> - 2016-12-15 22:00 -0700
      Re: UDP Terminal Protocol Paul Rubin <no.email@nospam.invalid> - 2016-12-14 15:22 -0800
        Re: UDP Terminal Protocol Robert Wessel <robertwessel2@yahoo.com> - 2016-12-15 00:00 -0600
      Re: UDP Terminal Protocol antispam@math.uni.wroc.pl - 2016-12-15 01:49 +0000
        Re: UDP Terminal Protocol Robert Wessel <robertwessel2@yahoo.com> - 2016-12-15 00:17 -0600
      Re: UDP Terminal Protocol Grant Edwards <invalid@invalid.invalid> - 2016-12-15 02:06 +0000
        Re: UDP Terminal Protocol Paul Rubin <no.email@nospam.invalid> - 2016-12-14 21:09 -0800
          Re: UDP Terminal Protocol Grant Edwards <invalid@invalid.invalid> - 2016-12-15 17:38 +0000
        Re: UDP Terminal Protocol Robert Wessel <robertwessel2@yahoo.com> - 2016-12-14 23:58 -0600
      Re: UDP Terminal Protocol Les Cargill <lcargill99@comcast.com> - 2016-12-15 21:49 -0600
      Re: UDP Terminal Protocol Morten Reistad <first@last.name.invalid> - 2016-12-24 16:10 +0100
        Re: UDP Terminal Protocol Grant Edwards <invalid@invalid.invalid> - 2016-12-24 18:53 +0000
          Re: UDP Terminal Protocol Theo Markettos <theom+news@chiark.greenend.org.uk> - 2016-12-25 13:45 +0000
            Re: UDP Terminal Protocol Don Y <blockedofcourse@foo.invalid> - 2016-12-25 11:44 -0700
  Re: UDP Terminal Protocol Don Y <blockedofcourse@foo.invalid> - 2016-12-13 12:53 -0700
    Re: UDP Terminal Protocol Robert Wessel <robertwessel2@yahoo.com> - 2016-12-14 14:03 -0600
      Re: UDP Terminal Protocol Don Y <blockedofcourse@foo.invalid> - 2016-12-14 15:09 -0700
        Re: UDP Terminal Protocol Robert Wessel <robertwessel2@yahoo.com> - 2016-12-15 00:50 -0600
          Re: UDP Terminal Protocol Don Y <blockedofcourse@foo.invalid> - 2016-12-15 11:01 -0700
        Re: UDP Terminal Protocol Morten Reistad <first@last.name.invalid> - 2017-01-15 16:08 +0100
      Re: UDP Terminal Protocol upsidedown@downunder.com - 2016-12-15 15:08 +0200
  Re: UDP Terminal Protocol wzab01@gmail.com - 2016-12-14 13:16 -0800
  Re: UDP Terminal Protocol upsidedown@downunder.com - 2016-12-15 12:56 +0200
    Re: UDP Terminal Protocol Don Y <blockedofcourse@foo.invalid> - 2016-12-15 11:06 -0700
      Re: UDP Terminal Protocol Robert Wessel <robertwessel2@yahoo.com> - 2016-12-26 16:34 -0600
        Re: UDP Terminal Protocol upsidedown@downunder.com - 2016-12-27 07:45 +0200
        Re: UDP Terminal Protocol Don Y <blockedofcourse@foo.invalid> - 2016-12-26 23:00 -0700
          Re: UDP Terminal Protocol Robert Wessel <robertwessel2@yahoo.com> - 2017-01-03 18:48 -0600
  Re: UDP Terminal Protocol Les Cargill <lcargill99@comcast.com> - 2016-12-15 21:42 -0600
    Re: UDP Terminal Protocol Robert Wessel <robertwessel2@yahoo.com> - 2016-12-26 17:21 -0600

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