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The Token Ring network was originally developed by IBM in the 1970s. It is still IBM's primary local-area network (LAN) technology. The related IEEE 802.5 specification is almost identical to and completely compatible with IBM's Token Ring network. In fact, the IEEE 802.5 specification was modeled after IBM Token Ring, and it continues to shadow IBM's Token Ring development. The term Token Ring generally is used to refer to both IBM's Token Ring network and IEEE 802.5 networks. v TOKEN-RING NETWORK Ø A type of computer network in which all the computers are arranged (schematically) in a circle. A token, which is a special bit pattern, travels around the circle. To send a message, a computer catches the token, attaches a message to it, and then lets it continue to travel around the network. Ø (2) When capitalized, Token Ring refers to the PC network architecture developed by IBM. The IBM Token-Ring specification has been standardized by the IEEE as the IEEE 802.5 standard. A Token Ring network is a local area network (LAN) in which all computers are connected in a ring or star topology and a bit- or token-passing scheme is used in order to prevent the collision of data between two computers that want to send messages at the same time. The Token Ring protocol is the second most widely-used protocol on local area networks after Ethernet. The IBM Token Ring protocol led to a standard version, specified as IEEE 802.5. Both protocols are used and are very similar. The IEEE 802.5 Token Ring technology provides for data transfer rates of either 4 or 16 megabits per second. Very briefly, here is how it works: q Empty information frames are continuously circulated on the ring § . When a computer has a message to send, it inserts a token in an empty frame (this may consist of simply changing a 0 to a 1 in the token bit part of the frame) and inserts a message and a destination identifier in the frame. § The frame is then examined by each successive workstation. If the workstation sees that it is the destination for the message, it copies the message from the frame and changes the token back to 0. § When the frame gets back to the originator, it sees that the token has been changed to 0 and that the message has been copied and received. It removes the message from the frame. § The frame continues to circulate as an "empty" frame, ready to be taken by a workstation when it has a message to send. § The token scheme can also be used with bus topology LANs. § The standard for the Token Ring protocol is Institute of Electrical and Electronics Engineers (IEEE) 802.5. The Fiber Distributed-Data Interface (FDDI) also uses a Token Ring protocol. 802.5. The Fiber Distributed-Data Interface (FDDI) also uses a Token Ring protocol. 802.5. The Fiber Distributed-Data Interface (FDDI) also uses a Token Ring protocol. 802.5. The Fiber Distributed-Data Interface (FDDI) also uses a Token Ring protocol. 802.5. The Fiber Distributed-Data Interface (FDDI) also uses a Token Ring protocol. References: searchnetworking.techtarget.com/sDefinition/ 0,,sid7_gci213154,00.html www.webopedia.com/TERM/T/token_ring_network.html www.cisco.com/univercd/cc/td/doc/ cisintwk/ito_doc/tokenrng.htm
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Prof. Ashay Dharwadker