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Re: Embedded Ethernet

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On 25.9.2017 г. 23:31, Robert Wessel wrote:
> On Mon, 25 Sep 2017 13:07:43 -0400, Phil Hobbs
> <pcdhSpamMeSenseless@electrooptical.net> wrote:
>
>> On 09/23/2017 08:31 AM, Dimiter_Popoff wrote:
>>> On 23.9.2017 ?. 13:32, Phil Hobbs wrote:
>>>> On 09/23/2017 06:02 AM, David Brown wrote:
>>>> ......
>>>>>
>>>>> You certainly /can/ argue that!  TCP/IP has many advantages over UDP.
>>>>> The key ones are that it saves you worrying about reinventing the
>>>>> wheel here.  With UDP, you never know if your data got transferred -
>>>>> so you need application layers to handle that.  With TCP/IP, you know
>>>>> that either the data is transferred correctly, or you end up with a
>>>>> timeout and broken connection.  It keeps it a lot simpler.
>>>>
>>>> One issue is that (iirc) TCP's 'guarantee' uses only a 16-bit checksum,
>>>> which might not be long enough for high speed data on less than stellar
>>>> connections.
>>>
>>> It is a non-issue really. The 16 bit checksum is just within tcp, but
>>> the IP layer is either embedded within Ethernet frames which have
>>> a robust enough CRC or within a PPP frame which typically has 32 bit
>>> CRC. Not sure one can encounter a situation where this would be
>>> an issue - but then it is a wide world, who knows. Certainly no
>>> issue over Ethernet though.
>>
>> Good to know, thanks.
>
>
> At least in the past, there have been cases where frames/packets have
> been damaged *inside* routers or switches.  There's a lot to be said
> for an end-to-end checksum, even if it isn't super strong.
>
> In any event, if you want a much stronger check (although not one
> providing recoverability), you can just insist on an SSL/TLS
> connection.
>
> An area where the 16-bit TCP/IP checksum clearly show itself to be
> inadequate was with some high-error-rate links without their own
> protection.  Dial-up SLIP was a good example.  PPP's checksum (when
> used on dial-up) was also too weak (but far better than the
> non-existent one on SLIP), but most of the time it got combined with
> error correcting modems underneath, and since it was a different
> checksum than TCP/IP used, the net result was better than either
> alone.
>

It has been about 15 years since I last implemented tcp/ip and ppp
but I think ppp - with 32 bit CRC as I used to have it most of the
time IIRC - was fairly robust. The phone line I had back then was
pathetic, 4 phones switched into a twisted pair by a box out in
the rain, whatever the modem I got 14400 bps max. Then again I
can't swear I never had a damaged packet but having one at 32 bit
CRC which then makes it through the tcp segment checksum seems
really unlikely. I do find the tcp checksum as it is quite adequate.
I have never done SLIP so I can't comment on that, but if it relied
solely on the modem error correction well, this may have been
insufficient.

Dimiter

======================================================
Dimiter Popoff, TGI             http://www.tgi-sci.com
======================================================
http://www.flickr.com/photos/didi_tgi/

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Embedded Ethernet pozz <pozzugno@gmail.com> - 2017-09-22 17:52 +0200
  Re: Embedded Ethernet mmm <m.colandrea@libero.it> - 2017-09-22 18:00 +0200
  Re: Embedded Ethernet David Brown <david.brown@hesbynett.no> - 2017-09-22 20:27 +0200
    Re: Embedded Ethernet pozz <pozzugno@gmail.com> - 2017-11-17 10:25 +0100
      Re: Embedded Ethernet Theo Markettos <theom+news@chiark.greenend.org.uk> - 2017-11-17 10:39 +0000
        Re: Embedded Ethernet pozz <pozzugno@gmail.com> - 2017-11-17 12:25 +0100
      Re: Embedded Ethernet "Boudewijn Dijkstra" <sp4mtr4p.boudewijn@indes.com> - 2017-11-17 11:36 +0100
        Re: Embedded Ethernet pozz <pozzugno@gmail.com> - 2017-11-17 12:54 +0100
      Re: Embedded Ethernet David Brown <david.brown@hesbynett.no> - 2017-11-17 15:23 +0100
      Re: Embedded Ethernet Mikko OH2HVJ <mikko.syrjalahti@nospam.fi> - 2017-11-18 11:29 +0200
  Re: Embedded Ethernet Joe Chisolm <jchisolm6@earthlink.net> - 2017-09-22 13:31 -0500
    Re: Embedded Ethernet pozz <pozzugno@gmail.com> - 2017-09-23 00:01 +0200
      Re: Embedded Ethernet raimond.dragomir@gmail.com - 2017-09-22 22:38 -0700
        Re: Embedded Ethernet raimond.dragomir@gmail.com - 2017-09-22 22:41 -0700
      Re: Embedded Ethernet David Brown <david.brown@hesbynett.no> - 2017-09-23 12:02 +0200
        Re: Embedded Ethernet Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-09-23 06:32 -0400
          Re: Embedded Ethernet Dimiter_Popoff <dp@tgi-sci.com> - 2017-09-23 15:31 +0300
            Re: Embedded Ethernet Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-09-25 13:07 -0400
              Re: Embedded Ethernet Robert Wessel <robertwessel2@yahoo.com> - 2017-09-25 15:31 -0500
                Re: Embedded Ethernet Dimiter_Popoff <dp@tgi-sci.com> - 2017-09-27 01:50 +0300
          Re: Embedded Ethernet Les Cargill <lcargill99@comcast.com> - 2017-09-28 20:07 -0500
        Re: Embedded Ethernet upsidedown@downunder.com - 2017-09-23 14:48 +0300
        Re: Embedded Ethernet Les Cargill <lcargill99@comcast.com> - 2017-09-28 20:06 -0500
          Re: Embedded Ethernet Joe Chisolm <jchisolm6@earthlink.net> - 2017-09-29 09:41 -0500
          Re: Embedded Ethernet upsidedown@downunder.com - 2017-09-30 18:49 +0300
        Re: Embedded Ethernet pozz <pozzugno@gmail.com> - 2017-10-12 11:26 +0200
          Re: Embedded Ethernet David Brown <david.brown@hesbynett.no> - 2017-10-12 12:46 +0200
          Re: Embedded Ethernet Joe Chisolm <jchisolm6@earthlink.net> - 2017-10-12 10:49 -0500
      Re: Embedded Ethernet Grant Edwards <invalid@invalid.invalid> - 2017-09-23 20:40 +0000
        Re: Embedded Ethernet Joe Chisolm <jchisolm6@earthlink.net> - 2017-09-23 19:24 -0500
          Re: Embedded Ethernet David Brown <david.brown@hesbynett.no> - 2017-09-24 13:28 +0200
  Re: Embedded Ethernet Les Cargill <lcargill99@comcast.com> - 2017-09-22 21:12 -0500
  Re: Embedded Ethernet Tauno Voipio <tauno.voipio@notused.fi.invalid> - 2017-09-24 11:01 +0300
  Re: Embedded Ethernet pozz <pozzugno@gmail.com> - 2017-10-16 14:10 +0200
    Re: Embedded Ethernet David Brown <david.brown@hesbynett.no> - 2017-10-16 15:10 +0200
      Re: Embedded Ethernet pozz <pozzugno@gmail.com> - 2017-10-16 17:54 +0200
        Re: Embedded Ethernet David Brown <david.brown@hesbynett.no> - 2017-10-16 23:45 +0200
          lwip/httpd: how to return dynamic data [was Re: Embedded Ethernet] pozz <pozzugno@gmail.com> - 2017-11-13 12:11 +0100
            Re: lwip/httpd: how to return dynamic data [was Re: Embedded Ethernet] David Brown <david.brown@hesbynett.no> - 2017-11-13 14:14 +0100

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