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