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RE: [bacnet-mstpwg] STK-030 MSTP-Zero-Config proposal

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  • Hartman, John
    Let s see if I understand this correctly: Carl Father of the Network Port Object Neilson is concerned about a datalink using application layer data? :) The
    Message 1 of 2 , Jul 24, 2013
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      Let's see if I understand this correctly: Carl "Father of the Network Port Object" Neilson is concerned about a datalink using application layer data? :)

      The NPO lets you read and change MAC addresses. It lets you read and set BDTs (actually, it becomes the ONLY way to set BDTs).
      So the DATA itself doesn't seem to be a problem.

      Was Carl perhaps referring to the TAGGING of the data? To date, BACnet datalinks and network layer haven't used clause 20-style tagging. But given that ZeroConfigurationUniqueData contains a pair of strings which might be in various character sets and lengths, clause 20-style tagging seems to be the best option.

      In an implementation, I would imagine initialization code tagging up the ZeroConfigurationUniqueData and passing it as a bag of bytes to the MS/TP datalink. The MS/TP code just stuffs the bytes into Test frames - it doesn't need to parse or build the string.

      So from the average node's point of view, I don't see a problem - except perhaps that Serial_Number is an optional property.



      -----Original Message-----
      From: bacnet-mstpwg@yahoogroups.com [mailto:bacnet-mstpwg@yahoogroups.com] On Behalf Of SKarg
      Sent: Monday, July 15, 2013 3:24 PM
      To: bacnet-mstpwg@yahoogroups.com
      Subject: [bacnet-mstpwg] STK-030 MSTP-Zero-Config proposal

      Hello MS/TP working group!

      At the recent SSPC-135 BACnet meeting in Denver, the committee discussed STK-030 MSTP-Zero-Config proposal[1] during the plenary. Carl asked about the "ZeroConfigurationUniqueData" variable, and why the MS/TP datalink layer was using application layer data. As defined in STK-030-9:

      ZeroConfigurationUniqueData: A series of four or more octets that uniquely identify this node. The octets shall be derived from the BACnet Device object Vendor_Identifier property, the Model_Name property, and the Serial_Number property for nodes that have a BACnet Application layer. The order and encoding of the data are defined in Clause 21.

      ZeroConfigurationUniqueData::= SEQUENCE {
      vendorID Unsigned,
      modelName CharacterString,
      serialNumber CharacterString
      }

      In my original proposal, the ZeroConfigurationUniqueData was not explicitly defined, and only referenced in sentences such as "with a unique sequence (i.e. vendor identifier and serial number) of one or more octets in the Data portion of the frame".

      It doesn't really matter what data is appended to the Test Request frame since a station will be checking for its own data when and if it receives the Test Response frame.

      Should the proposal continue specifying the application layer data, should it allow alternate data for non-BACnet applications using MS/TP, or should the unique data be vague as in the original proposal?

      Best Regards,

      Steve
      [1] http://tech.groups.yahoo.com/group/bacnet-mstpwg/files/STK-030-9-MSTP-Zero-Config.doc




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