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159RE: [bacnet-oswg] CLB-013 - Network Port Object

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  • Coleman Brumley
    May 26, 2011
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      Carl,

       

      Thanks for the feedback.  The first 3 points are cut and dried and will be addressed prior to Montreal. 

       

      As far as the 4th point...

       

      I loathe to re-open this can of worms because it's going to be a big discussion no matter how we slice it.

       

      The following is from an email from David Fisher on 7-Sep-2010.  I believe this points to the requirement of a single home for devices in clause 5.1. 

       

      For those of you wanting to know where the standard defines this binding idea it is

      described in detail at the end of 5.1 (since the first 1995 standard):

      A "BACnetDevice" is any device, real or virtual, that supports digital communication

      using the BACnet protocol. Each BACnet Device contains exactly one Device Object,

      as defined in 12.10. A BACnet Device is uniquely located by an NSAP, which consists

      of a network number and a MAC address.

       

      But, as Bill Swan points out on 20-Jan-2011:

       

      The phrase says “located” and not “homed.”  A multi-homed router can still be uniquely

      “located” (found) at a single address by some other device, no matter where that

      device is in the system.  Two devices in different locations have different NSAPs for

      the target device in their tables, but the system still works.

       

      As you pointed out, also on 20-Jan-2011:

       

      In post meeting discussions, Bill and I agreed that the issue has little impact on

      real interoperability as shown by numerous real-world installations that show no ill effects

       

      I agree with your point about interoperability.  It shouldn't matter one way or another to the rest of the network whether the binding looks like it's a routed address or not -- assuming the routing information is correct. 

       

      Frankly, I don't care either way and I really don't want to hold this proposal up because of this ages long argument. 

       

      So, how about a "straw poll" for one of the following 2 options:

       

      1) The property is marked as required currently.  How about if we just make it optional?  Then those who use the "single homed" approach can  use it, and those who use the "multi homed" approach won't. 

      2) Remove it entirely.  I can make an argument for this, because how is it used anyway?  What's the use case for this property? 

       

      - Coleman

       

      From: bacnet-oswg@yahoogroups.com [mailto:bacnet-oswg@yahoogroups.com] On Behalf Of Carl Neilson
      Sent: Wednesday, May 25, 2011 6:23 PM
      To: bacnet-oswg@yahoogroups.com; bacnet-ip-wg@yahoogroups.com
      Subject: [bacnet-oswg] CLB-013 - Network Port Object

       

       

      BACneteers,

       

      I have received a few comments on the Network Port object from a developer at Delta Controls and would like to share those comments before Montreal:

       

      - NetworkPort.MAC_Address is defined as type BACnetMACAddress.  The BACnetMACAddress is defined as a Sequence with only one field, a mac-address octet string.  It would be cleaner if NetworkPort.MAC_Address were defined as an octet string type directly, skipping the extra sequence tagging.

       

      - NetworkPort.BACnet_IP_Subnet_Mask is defined as type BACnetHostAddress.  An IPv4 subnet mask can never be specified by DNS hostname so a base octet string would be a more appropriate type than BACnetHostAddress.

       

      - NetworkPort.BACnet_IP_Default_Gateway is defined as type BACnetHostAddress.  A default gateway isn’t defined by DNS hostname so a base octet string would probably be more appropriate.

       

      - Dev.Home-Port – It is not clear why devices have to be single homed.

       

      There has been a comment in CLB-013 since revision 11 indicating that the need for a Home network be reviewed with respect to the requirements for Network Security and that if it is to remain in the document that a definition of a home port be added. At this point I am not convinced that the standard, including network security, requires single homed devices. This should be evaluated before Montreal and removed if we cannot find the requirement in the existing standard.

       

      Carl

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