Communication systems that use different physical layer (PHY) protocols can coexist on a communication medium (e.g., a powerline medium) by using an Inter-PHY Protocol (IPP). The different protocols may use different signal modulation schemes but still may have some features in common. The IPP includes a resource sharing mechanism that regulates access to the communication medium by devices functioning as communication devices (for example, devices communicating over a power line). A subset of devices that communicate among each other form a logical network that shares the medium with other logical networks that use either the same PHY protocol or a different PHY protocol.