Concept
Network Check-Up (Examination and Monitoring)
When migrating an older system to a newer architecture or enhanced application environment, there is the possibility the existing system will encounter closer examinations, be expected to perform in a more detailed coordination with the larger system or be exercised in a more visible performance-sensitive manner by new applications. While an existing system may be considered stable and error free, the existing observations can sometimes be limited to the visibility offered by the earlier system. Communications problems can exist but go unnoticed (or masked) due by low level protocol retries. The typical MS/TP communications protocol setup for example can mask severe levels of communications errors with the retries not providing visibility of the issue until new dependencies on command/request latency reveals notable delays.
It is recommended that existing system MS/TP segments be examined with a BACnet communications analysis tool prior to disrupting the operation of the existing system. The objective is to capture some snapshots of the various network segments in the existing system. You can easily attach such a monitoring tool to an operating MS/TP network and capture statistics on the operation of the network for an appropriate period of time. This offers visibility into the actual performance and stability of the network targeted for migration to the new system hierarchy. An indication of high error statistics may prompt a decision for diagnostic effort on the existing network prior to the system migration, or an understanding that investigative effort will play a role in the system transition. Alternatively, the insight into actual system performance may simply be used as an indication that performance expectations for specific network segments of the system may need to be moderated. In any case, it avoids a common post-update conclusion that the problems with the system upgrade were solely a product of the new system products or installation practices.
One easily available tool is the MS/TP data capture utility known as MSTPcap. The primary purpose of the MSTPcap utility is a tool to capture BACnet MS/TP communications traffic by listening to the bus and packaging the captured traffic into data packets in a PCAP file format suitable for feeding into another tool called Wireshark. Wireshark is another very useful tool for the detailed analysis of network communications on a variety of systems. The later versions of Wireshark now include the support for decoding BACnet protocol layers.
The Schneider Electric Lessons Learned article LL#5367 provides guidance on use of the MSTPcap program for performing a network checkup. http://buildingskb.schneider-electric.com/view.php?AID=5637
MNB BACnet Devices
RS-485 Communications