mycroes
commented
3 years ago Is it possible to have multiple connections to the same PLC with Sally7, assuming of course that some limit on maximum number of connections imposed by the PLC is not reached? Is it possible by just opening multiple connections, or would that require adding some form of "connection number" before/while establishing the connection? (I know that the DeltaLogic AGLINK has such a concept, but am not sure if that is just internally in their library or if it is related to the S7 protocol).
It's possible, but you need to have the connections defined and loaded into the PLC. You can add additional S7 connections in the network topology in TIA portal between the PLC and a PC station. The IP address needs to match for the PLC to accept the connections using the supplied TSAP's. I might have a small instructional movie from one of our PLC developers somewhere, let me know if you can't figure this out.
The second part / the reason why I am asking is: A single PLC connection with S7NetPlus/Sally7 still needs to be synchronized, even when used with async/await. To truly increase the bandwidth of accessing data I would either have access multiple data items at the same time, or use multiple connections to the same plc concurrently.
I did some lab testing where I would get something like a 3% improvment (IIRC) when using multiple connections, with a PLC nearby the PC. However I've recently been thinking about a multitude of changes. For one, if multiple requests would be used then there's less impact of higher network latency. At some point network latency might actually be even more than the actual request handling duration, so on slower networks that could have huge impact. The other thing is combining read actions, which results in larger requests and thus also benefits from concurrent requests.
The first option with reading/writing multiple data items unfortunately does not fit at all in the existing software I have, and only solves scenarios where you can read multiple date items in a correlated fashion. For performing multiple independent actions on the same PLC, multiple connections would still be preferable.
I don't follow, maybe you could provide a bit more detail or a concrete example. I do think that it doesn't matter much whether you're using multiple connections or concurrent requests; except for the fact that concurrent requests requires a single connection only so there's less configuration there.
So to get to the point: My idea would be to have a pool of available, established connections. A worker grabs a connection, perform a read/write, and gives the connection back into the pool. Some other worker ensured that connections are initially established / re-established. Alternatively, the pool could contain virtual connection handles and the normal workers are also responsible for establishing the connection itself, besides using it for read/write.
What do you think about that idea? What .NET collections and other mechanisms would you recommend for getting something like that to work?
Honestly, I'm not sure. I never did pooling in that way. I'm trying to figure out what synchronization primitives to apply to concurrent requests, it's something I intend to add sooner rather than later. When I add it I'll probably migrate it to S7NetPlus as well.
What you could do is push all the connections to a ConcurrentQueue or BlockingCollection, take a connection, perform some action, add it back to the queue. However, both only have a sync API, so I'm not entirely sure if this is the way to go because there's a fair change you go through all your connections faster than any of them has finished it's request.
Anyway, I intend to address this inside the libraries, it still has to materialize though....
scamille
SmackyPappelroy
This is more of a 2 part question, the first being about Sally7:
Is it possible to have multiple connections to the same PLC with Sally7, assuming of course that some limit on maximum number of connections imposed by the PLC is not reached? Is it possible by just opening multiple connections, or would that require adding some form of "connection number" before/while establishing the connection? (I know that the DeltaLogic AGLINK has such a concept, but am not sure if that is just internally in their library or if it is related to the S7 protocol).
The second part / the reason why I am asking is: A single PLC connection with S7NetPlus/Sally7 still needs to be synchronized, even when used with async/await. To truly increase the bandwidth of accessing data I would either have access multiple data items at the same time, or use multiple connections to the same plc concurrently.
The first option with reading/writing multiple data items unfortunately does not fit at all in the existing software I have, and only solves scenarios where you can read multiple date items in a correlated fashion. For performing multiple independent actions on the same PLC, multiple connections would still be preferable.
So to get to the point: My idea would be to have a pool of available, established connections. A worker grabs a connection, perform a read/write, and gives the connection back into the pool. Some other worker ensured that connections are initially established / re-established. Alternatively, the pool could contain virtual connection handles and the normal workers are also responsible for establishing the connection itself, besides using it for read/write.
What do you think about that idea? What .NET collections and other mechanisms would you recommend for getting something like that to work?