This IEEE Standards product is part of the 802 family on LAN/MAN. This amendment to Local and Metropolitan Area Network standard, ISO/IEC 8802-5 : 1998, is part of a family of local area network (LAN) standards dealing with the physical and data link layers as defined by the ISO/IEC Open Systems Interconnection Basic Reference Model. The requirements for dedicated token ring (DTR) operation are specified, including the changes and additions to the Medium Access Control (MAC) layer to provide for an additional full-duplex mode of operation (switching), and for interconnection of shared LAN segments to switch ports. Also specified are the characteristics of a fibre optic interface for connecting a 4 Mbit/s or 16 Mbit/s token ring station to the trunk coupling unit (TCU) of a token ring, including station, port, and channel requirements. Fibre optic trunk signaling recommendations are also made.