Impact of NI-PSP on network traffic?

[ThinkG]

Hi,

We are planning a large-scale automation project and are looking to widely use Shared Variables.  What concerns should we have about the impact on network traffic?  Should the LabVIEW-based systems exist on their own subnet?  Are there any special network switch hardware that is recommended?  For instance, Rockwell Automation systems use UDP and recommend switches capable of IGMP Snooping.  Are any such network hardware features recommeded for a system based on LabVIEW Shared Variables?  Thank you.


Chris White
ThinkG Consulting LLC

[Doug M]

Chris,
I am not aware of any recommended out of the ordinary network hardware for use with NI-PSP.  There have been issues on machines that have more than one network interface enabled, and this is not a supported configuration, as noted in the LabVIEW DSC Readme:

"Network-published shared variables do not function properly if multiple network adapters are enabled on the same computer."

NI-PSP is built on UDP and any firewalls that block certain UDP ports can be a problem.  How external network traffic affects NI-PSP and vice versa is a pretty arbitrary question that obviously depends on how much external traffic you have and how much NI-PSP traffic you have, which depends on the number of shared variables, the number of subscribers and publishers, and the update rates of these variables, as well as whether variables are bound to I/O servers.  UDP is a lossy protocol so extremely heavy traffic could cause some packets to be missed. 

Hope this answers your questions!

[ThinkG]

Doug,

Thanks for the info.  We were not aware of the dual network card issue.  I'm curious about your comment:  "UDP is a lossy protocol so extremely heavy traffic could cause some packets to be missed."  According to the link below, "Unlike the UDP protocol, however, the NI-PSP protocol guarantees delivery by implementing an additional layer of functionality on top of the raw UDP protocol."  I'm guessing that by your comment, the "additional layer of functionality" starts to breakdown under extremely heavy traffic conditions.

http://zone.ni.com/devzone%5Cconceptd.nsf/webmain/5B4C3CC1B2AD10BA862570F2007569EF?opendocument&node=dz00000_us


Chris White
ThinkG Consulting LLC

[Doug M]

Chris,

Good catch, I had forgotten about that, so NI-PSP is not lossy. Probably the best resource for information on the shared variable is the Shared Variable White Paper.  It contains a ton of great info on shared variable specifics and considerations.