Token-ring

Token ring local area network (LAN) technology is a protocol which resides at the data link layer (DLL) of the OSI model. It used a special three-byte frame called a token that travels around the ring. Token-possession grants the possessor permission to transmit on the medium. Token ring frames travel completely around the loop. Initially used only in IBM computers, it was eventually standardized with protocol IEEE 802.5. ... The token scheme can also be used with bus topology LANs. ... Stations on a token ring LAN are logically organized in a ring topology with data being transmitted sequentially from one ring station to the next with a control token circulating around the ring controlling access. This token passing mechanism is shared by ARCNET, token bus, 100VG-AnyLAN(802.12) and FDDI, and has theoretical advantages over the stochastic CSMA/CD of Ethernet. Physically, a token ring network is wired as a star, with 'MAUs' and arms out to each station and the loop going out-and-back through each. Cabling is generally IBM "Type-1" shielded twisted pair, with unique hermaphroditic connectors, commonly referred to as IBM data connectors in formal writing or colloquially as Boy George connectors. The connectors have the disadvantage of being quite bulky, requiring at least 3 x 3 cm panel space, and being relatively fragile. Connectors at the computer were usually DE-9 female. [Token ring. Wikipedia]