Communicate with S5 with C# and ISO protocol

I have searched and found a lot of libraries that communicate with S7 or S5 PLCs over TCP protocol but I haven't found any C# library that communicate S5 PLCs over ISO protocol. My question is "Is it possible to connect to S5 PLC via ISO without any OPC or not?"
Thank's a lot

It's possible, but you can't create low-level ISO packets with the standard network functions from Windows, thus you'd need a library like Npcap or WinPcap. For WinPcap there is a .Net wrapper available, so you can create the packets from a C# application.

Then you need to build the packets on the low level network layer. First the ISO8073 layer, and on top I'd use the Fetch/Write protocol, as it's documented by Siemens.