I work as a project engineer of electrical equipment for substations. More and more I have to deal with the communication of these equipment with PLC and other equipments. But I really don't know much about this area. For example, we have Modbus, Profibus, IEC-61850... every now and then I have to verify if we have the components required to connect some equipment to some network. So the following questions arise: - What type of connector do I need? When do I use RS232, RS485, DB9, etc? - What type of cable do I need? When do I use fiber optic, twisted pair or whatever? I have searched and read parts of books about it, but they don't really get straight to the point. I would really appreaciate if someone could give me an introduction about it.