Part of the ISA/O3neida series@ this book discusses network systems in industrial automation and their features related to real-time and functional safety requirements. The basics of standard Ethernet are introduced@ specifying the Open System Interconnection (OSI) reference model layers and identifying Ethernet's drawbacks. Clarification on the requirements and the solutions adopted by the presented communication protocols is also addressed. Real-time capability is defined with regard to communication within safety-related systems@ underlying the strict correlation between time performances and external requirements. Finally@ the specifications of the safety profiles of five communication protocols (namely PROFIsafe@ Ethernet Powerlink Safety@ SERCOS III Safety@ EtherCAT Safety@ and Ethernet/IP Safety) are investigated.