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RE: [bacnet-ip-wg] Add. AI PPR2 Draft5 has been uploaded

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  • Buddy Lott
    All, It just occurred to me that there was a proposed ( or approved?) change to the standard that added a LARGER frame to MS/TP network. This has me wondering:
    Message 1 of 9 , Jan 5, 2012

      All,

       

      It just occurred to me that there was a proposed ( or approved?) change to the standard that added a LARGER frame to MS/TP network. This has me wondering:

       

      The cause of an Inverted network is a Lower-NPDU-Sized network being used to connect two ( or more)  Larger-NPDU-Sized networks. The largest NPDU sizes are for Ethernet and IP.   Of smaller NPDU size networks:

                  ZigBee seems intended for low bandwidth and low power uses which ( to me) would excluded connecting two larger NPDU networks.

                  ArcNet & LonTalk I have never seen in action, but I wonder if they are really being used to connect larger NPDU sized networks.

                  MS/TP looks like it might get larger data frame sizes which would solve this problem.

                  PTP, which is the first “reasonable” (IMHO) cause of an inverted network, could also benefit from the larger data frame sizes which would fix this problem.

       

       

      Another suggestion/thought would be Network Layer “segmentation” for messages that are going from router-to-router ( i.e. The message came into one router and is going to another router for more routing). This would not need to be as robust as the Application Layer Segmentation, but good enough to handle a message going between two routers.

       

       


      From: Coleman Brumley [mailto:bacnet_cb@...]
      Sent: Wednesday, January 04, 2012 4:57 PM
      To: bacnet-ip-wg@yahoogroups.com
      Subject: RE: [bacnet-ip-wg] Add. AI PPR2 Draft5 has been uploaded

       

       

      Buddy,

       

      Thank you for the feedback. 

       

      Up until this point, we have been avoiding modifying existing services or Network Layer messages as much as possible.  Your suggestion is a good one, and we've discussed similar approaches in the teleconferences.  We've also discussed modifying the I-Am-Router-To-Network message so that it contains the max-apdu-length-accepted for the next hop router to that network.

       

      We also agreed that in order to move this much needed addendum forward, that we would consider modifications to existing network layer messages as a separate proposal. 

       

      Having said all that, draft 6 will have new language with how max-apdu-length-accepted is handled in the Device object in the case of multi-port devices but it will not address deprecating or modifying existing services. 

       

      Regards,

      Coleman

       

       

      From: bacnet-ip-wg@yahoogroups.com [mailto: bacnet-ip-wg@yahoogroups.com ] On Behalf Of Buddy Lott
      Sent: Wednesday, January 04, 2012 4:43 PM
      To: bacnet-ip-wg@yahoogroups.com
      Subject: RE: [bacnet-ip-wg] Add. AI PPR2 Draft5 has been uploaded

       

       

      All.

       

      I have not read the proposal but after reading this chain I am curious why the Reject-Message-To-Network with a reason code of 4 ( message is too long) was not “adjusted” to include the “legal” size of message going to that DNET.

       

      In principle (without much detailed thought):

      1)       Intervening routers could store this information and stop messages that were too “big” much earlier.

      2)       Since the DNET would have a size associated with it (instead of just the device), 1 reject message could adjust all traffic coming to/from a network. Potential reducing congestion.

      3)       This could also allow vendors to modify their routers to “adjust” I-AM messages at the edges versus all the way thru the network (all though it could be done anywhere).

      4)       This could also handle situations where an I-AM was NOT sent before attempting communication.

       

      I suppose another proposal ( which has probably been made and discarded) would be to  have a network layer “request-path-size” message that could be used to determine the maximum size between 2 devices.

       

      Thanks,

       

       


      From: Carl Neilson [mailto:cneilson@...]
      Sent: Wednesday, January 04, 2012 11:29 AM
      To: bacnet-ip-wg@yahoogroups.com
      Subject: RE: [bacnet-ip-wg] Add. AI PPR2 Draft5 has been uploaded

       

       

      1) Is not solved for the reasons I indicated.

       

      2) Has no impact on this as it will be that way anyway.

       

      3) I disagree that global broadcasts are bad (and this would be the root of the disagreement).

       

      4) 1+3 make 4 moot. (they also make 4, but that is math not BACnet :)

       

      Carl

       

       

      From: bacnet-ip-wg@yahoogroups.com [mailto: bacnet-ip-wg@yahoogroups.com ] On Behalf Of Hartman, John
      Sent: Wednesday, January 04, 2012 8:25 AM
      To: bacnet-ip-wg@yahoogroups.com
      Subject: RE: [bacnet-ip-wg] Add. AI PPR2 Draft5 has been uploaded

       

       

      And my reasons for WANTING I-Am to contain a useful maxAPDU are

       

      1)      I-Am is (or was intended to be) the way clients determine how or if they need to segment of limit their requests.  Why not make it work?

      2)      Simple devices are generally single-port, so these issues apply only to routers or other multi-port devices, which by definition have greater capability

      3)      Global broadcast of I-Am should be deprecated, if not forbidden.  It makes sense for the relatively few routers on a site to broadcast I-Am-Router at startup.  It is a bad idea for 10000 MS/TP VAV boxes to do so.

      4)      Absent global broadcast, the logic of “which max APDU” goes in the incoming Who-Is handler, just like it would go into the incoming Read Property handler if we use the wildcard port instance

       

       

       

      From: bacnet-ip-wg@yahoogroups.com [mailto:bacnet-ip-wg@yahoogroups.com] On Behalf Of Carl Neilson
      Sent: Wednesday, January 04, 2012 10:15 AM
      To: bacnet-ip-wg@yahoogroups.com
      Subject: RE: [bacnet-ip-wg] Add. AI PPR2 Draft5 has been uploaded

       

       

      Coleman et al,

       

      I am uncomfortable with the decision to have IAms reflect the MaxAPDU size by port, a switch in the position from the teleconference two meetings ago. I hope that I can have the opportunity to argue the opposite position.

       

      My reasons for not agreeing are:

       

      1) The problem violates the network vs application layer separations in a manner far beyond simple knowledge transfer. When a device globally broadcasts its IAms, the application layer generates the IAm and passes it to the network layer, the network layer then has to modify the IAm for each port it is sent out. This requires that the network layer inspect every packet that is sent, and adjust the packet contents accordingly.

       

      This is unlike any other layer violation we have considered to date. To date, we have passed information through the layer API: does the service expect a response; the port was the service received on; indications of errors; security information; etc.

       

      2) The perceived problem only impacts inverted networks. In all other cases, either the PDU size will be accurate or will be limited by the directly attached network of the client.

       

      3) The problem is not solved for non-routers or distant routers. The inverted network issue will still exist for non-routers, and for routers not directly attached to the small intervening network.

       

      Carl

       

       

      From: bacnet-ip-wg@yahoogroups.com [mailto:bacnet-ip-wg@yahoogroups.com] On Behalf Of Coleman Brumley
      Sent: Tuesday, January 03, 2012 7:27 PM
      To: bacnet-ip-wg@yahoogroups.com
      Subject: [bacnet-ip-wg] Add. AI PPR2 Draft5 has been uploaded

       

       

      IP-WG,

       

      Please check the Yahoo group for the latest draft. 

       

      Please note that I did not reinstate the draft 2 max-apdu-length-accepted changes, and we will revisit that discussion during the teleconference.  It's my hope that other than editorial changes, that there won't be many other discussion points. 

       

      Regards,

      Coleman

       



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