The PROFIBUS OLMs (Optical Link Module) allow optical PROFIBUS networks to be configured in bus, star or redundant ring topologies, e. road tunnels or traffic control systems. It detects all PROFIBUS data rates from 9. 6 kbit/s up to 12 Mbit/s automatically including 45,45. familiar advantages of optical transmission technology, the modules can be integrated into existing PROFIBUS field bus networks. 1 Introduction Every module has two (OLM P11, G11), three (OLM P12, G12), or four (OLM. The Siemens OLM V4.