SNMP to Ethernet Socket/Profibus DP

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Thread Starter

Ronald Nijssen

Hello List,

We are looking for a solution to convert SNMP into another Protocol (Ethernet/Profibus DP), not using a PC as the Gateway. A possible solution could be to have a device/card being developed since we need more than 150 units for a large project Anybody who can advise me in understanding the SNMP protocol, what kind of Data Items must I think of, how flexible is it, or might no a supplier of Protocol converters able to do the job

Thanks,
Ronald Nijssen
 
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Curt Wuollet

Are we talking about the Simple Network Management Protocol? This is somewhat confusing. The SNMP protocol I am somewhat familiar with _is_ typically on top of ethernet and loosely related to TCP/IP. That is, it is one of the Internet suite of protocols. Any SNMP compliant agent should be able to get and set SNMP parms from devices that support SNMP. Is there something I don't understand or are we talking about SNP (system ninety Protocol) or ? You would have to have an agent running on something.

I could help with an answer if I understood the question. Ask again?

Regards

cww
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Ronald Nijssen

I received several replies on my question regarding this protocol conversion We have a potential customer that has devices which support SNMP, we want to read information (data?) from these devices and use in a PLC. Given this requirement I was thinking of Industrial Networking their SNMP-OPC server and a SIMATIC WinAC SoftPLC, the issue is that the customer doesn't want to use PC's for this task. We need to connect to a (Siemens) PLC If Industrial Networking can expose SNMP information through an OPC Server than I can imagine that exposure in another form (e.g. Profibus DP) is possible as well. Therefore my question The size of the project would warrant investments, the number of places where this conversion must take place is high

I know that SNMP is a SImple Network Management Protocol, typically used in combination with active Network components. I didn't know what type of protocol concepts it supports, Data manipulation, Events, Remote Procedure Calls of such. From your reply I understand that SNMP is used to expose and manipulate Parameters of Network devices, it would still be interesting to learn if it supports events and/or Remote Procedure Calls. I also think that it is a Client Server protocol where the Network device acts as a server

Kind Regards
Ronald
 
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Curt Wuollet

You are in luck with SNMP. This is an OPEN protocol and all the information you could possibly want is in the public domain as the original RFC's. No memberships or money or permission required. (Sorry, I couldn't resist) Your problem, if understand it, is that these devices present the data as a socket on an Ethernet node, according to the standard, and you need an agent that runs on a PLC to interact. Or some way to bridge from Ethernet to another protocol that provides transport for SNMP. Since most other proto's know nothing about SNMP, you have to bidirectionally rehost the data to use another protocol or go with the first method, a PLC that really supports enough of the Internet suite of protocols to be an agent. That's gonna be tough without a PC or something open in the mix. Perhaps one of the more advanced PLC vendors has something like an ethernet coprocessor that you could write an agent on. As I recall, Siemens forbids doing anything open or standard with their "ethernet".

My approach would be an SBC running the LRP linux out of flash. And of course standard Ethernet to all the devicees. This gives you a box that speaks SNMP fluently to the devices
and is easily programmable to rehost the data. All the conversion takes place in one very capable place and the cost is minimal as the LRP Linux is very small and the SBC could be cheap and headless so you technically don't have any PC's. All the tools to do this are free, open, and available if not included. There are OSS SNMP
agents to adapt or copy. This leaves the problem of getting anything "foriegn" into a Siemens PLC. This is the kind of PITA I face all the time that other listers insist is not a problem. If there is no alternative, you can do this with a simple parallel data transfer with handshake routine. Or devise your own simple serial protocol. For GE I have spoofed the ccm protocol to load and read a few registers.

Perhaps Siemens has left a similar sliver of openness you can exploit. The Siemens guys could and perhaps, may tell you if there is a documented proto you can write to that uses serial ports or ethernet. Modbus might be an option with the Modbus code Mario wrote for our project. They make it very difficult, but there's almost always a way with an Open platform in the middle.

And before they jump on me, yes, you could probably do the same in Windows but you would need a full PC with display, no OSS SNMP agent is likely to be available as a start and wince and the tools would cost you money and you would write a lot more code and get a lot less help. Here's hoping you can find a packaged solution. If not, I can help you locate this stuff.

Hope this helps

Regards

cww
 
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