I'm trying to determine any limitations/recommendations for the following using an S7-1200 or 1500.

Disclaimer: I'm not the PLC programmer, I'm the .NET applications programmer. :)

I've created a service (TCP Service Application) that, like any TCP Service Application, is listening on a port. Our control engineers have successfully connected but occasionally when having multiple connections from the PLC either one is missed, or most often a packet sent is the wrong one.

Let me explain it this way - there are 5 connections created, call them A, B, C, D, and E. Often when a particular send is triggered the application receives the correct information but sometimes, especially when multiple sends are triggered, the server receives a duplicate. For example if I expected A, B, C, D, E I may instead receive A, B, D, D, and E where B was missed.

Any suggestions as to if we are encountering a limit in the PLC or if the PLC is capable I can only assume the implementation in the PLC is incorrect.

As a side note the TCP Service Application has been rigorously tested with another non-PLC implementation and it is highly unlikely to be the problem.

Thanks,

Rick 

It looks like a timing problem in PLC, but without seeing the PLC program its not possible to give any further help.

regards

I'm having the control engineer take a look again. We've been told that what we are trying to do is not possible, or at least not in the way it is being implemented, and that we need to 1) employ a type of queuing mechanism for requests or 2) use a different port for every connection.

The multiple port solution is not a good option, imagine having to create multiple instance of a web service and each instance listening on a different port. Every time we need another connection we have to select a port and install another instance. (I would have more to say about that recommendation but I would just be venting :) )

Queuing requests we are not sure about - our control engineers are most familiar with AB and just starting to work with Siemens, so they are unsure of the limitations.

To best explain imagine the PLC handling requests for multiple stations (work areas) and requests are made to a web service (it's not but the analogy holds - Simple Siemens TCP Listener). The web service is listening on a port for requests (TCP/IP, not UDP) and at any time one or more stations may make a request.

Thanks,

Rick

as Eisenpferdreiter assumed ;)

Thanks for coming back and telling that you solved the problem. 

So now you are using the multiport communication ? or are you using different ports on side of the PLC and one port as aim (your application)?