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Re: UDP Terminal Protocol

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On 2016-12-14, Robert Wessel <robertwessel2@yahoo.com> wrote:
> 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,

By the time you do "packet sequencing and acknowledgements" for both
target and host side, test it, revisit the bad protocol design
decisions, and then re-implement it for both sides you've spent more
time than you would have just doing a simple TCP implementation.

And in the end you've got something that's non-standard, non-portable,
probably still doesn't work right, and for which Wireshark doesn't
have a packet dissector.

Don't underestimate the importance of that last one.

>>> IOW, something with a relationship to TELNET sort of like TFTPs
>>> relationship to FTP.

What features of TELNET do you need?

>>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.

In my experinece the incremental value of Telnet is negative, since
various Telnet clients behave it vastly different and bizarre ways.

YMMV.

> And as I said, if you have TCP, why not just do this with HTTP, and
> really make things convenient for people.

OK.

>>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?  

Um... UDP.

> How many characters can you put in a packet?

UDP says 65536 bytes per datagram.  UDP will fragment that and
reassemble it.  If you want to do a stripped-down UDP iplimentation,
limit it to about 1200.

> Any sequencing or recovery?

Nope.

> Acknowledgements?

Nope.

> Checksums on or off?

For a local Ethernte segment, you let the MAC layer worry about that.

> 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.

Some IP stacks won't receive UDP broadcast packets with a
non-reachable source IP.

> 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?

Unless your Ethernet segment is pretty heavily loaded, I find you can
ignore all that.

If you can't, then you need the equivalent of TCP.

-- 
Grant

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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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