Re: DLT request for SDLC (BITBUS)

["Becker (ELZET80)" <Becker () elzet80 de>]

Hi Guy,

thank you for your response.

I think my request was a bit misleading and wrong formulated. I told you 
we are working on a BITBUS tracer which in reality is a SDLC tracer that 
can trace BITBUS too.

>> Is there a way to use the SDLC dissector as a DLT already?
> No, and if you were to do so, you probably wouldn't like the results, 
unless you're using SNA on the BITBUS links.
>
>> If not we would request a DLT for SDLC communication on which we 
would base our BITBUS lua dissector plugin.
>
> You should, instead, get LINKTYPE_BITBUS/DLT_BITBUS.

I don't think thats what we want as we have raw SDLC frames coming from 
our usb tracer and need to display them too.
We want to feed the data directly into Wireshark with an extcap 
component and don't want to go the detour over ethernet packets.
The payload data should not be interpreted by default (we would write a 
lua bitbus dissector for that).

Would this route be possible with a DLT like LINKTYPE_SDLC/DLT_RAWSDLC ?

Best regards
Freundliche Grüße

Paul Becker

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Am 16.01.2017 um 19:12 schrieb Guy Harris:
> On Jan 16, 2017, at 4:06 AM, Becker (ELZET80) <Becker () elzet80 de> wrote:
>
> > we are currently working on an USB tracer which captures messages from BITBUS connected devices.
> > BITBUS is based on the SDLC protocol by IBM (see: https://en.wikipedia.org/wiki/Synchronous_Data_Link_Control)
> Several protocols, including HDLC, LAPB, IEEE 802.2, etc. are, directly or indirectly, "based on the SDLC protocol".
>
> However...
>
> > We have already seen that there is a SDLC dissector implemented in Wireshark
> ...the SDLC dissector is intended to dissect IBM's SDLC, and assumes that the payload of an Information frame is SNA.
>
> According to
>
>         http://www.bitbus.org/dnl/BITBUS%20Interconnect%20Specification.PDF
>
>         1) "The BITBUS interconnect does not (and is not intended to) maintain strict SDLC compatibility"
>
> and
>
>         2) what's described by section 5.0 "MESSAGE PROTOCOL SPECIFICATION" isn't SNA.
>
> So we should not treat the BITBUS data link layer as SDLC, but as Yet Another SDLC-Based Protocol.
>
> > but as we are getting our data from our tracer tool there is no ethernet layer here.
> > Is there a way to use the SDLC dissector as a DLT already?
> No, and if you were to do so, you probably wouldn't like the results, unless you're using SNA on the BITBUS links.
>
> > If not we would request a DLT for SDLC communication on which we would base our BITBUS lua dissector plugin.
> You should, instead, get LINKTYPE_BITBUS/DLT_BITBUS.
>
> Would those packets begin with the Address field of the BITBUS header, followed by the Control field, followed by the 
> Information, with the Flag fields not included. and with bit-stuffing removed?  Would they include the FCS, or not?

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