Token Ring (TR)

station when it sees the frame and subsequently can be used by the AM to identify a frame that is endlessly circling the ring.The R bits are Reservation bits used by a station to reserve the token for a future transmission.

• Frame Control (FC): A field of one octet establishing whether the frame is a control frame or a data frame. If the frame is a control frame, the FC field identifies the specific type.

• Destination Address (DA): A field of two or six octets identifying the MAC address of the target node.

• Source Address (SA): A field of two or six octets identifying the Medium Access Control (MAC) address of the originating node.

• Data: A field of variable length containing up to 4,048 octets of payload.

• Frame Check Sequence (FCS): A field of four octets containing a cyclic redundancy check (CRC) for use by the receiving node for error control.

• End Delimiter (ED): A field of one octet that variously denotes the ending of the token.The bit pattern JK1JK1IE intentionally violates the Manchester coding scheme used elsewhere in the frame, thereby firmly establishing its identity. ( Note: J indicates the intentional violation of a 1 bit, and K

indicates the intentional violation of a 0 bit.The I bit is an Intermediate frame bit, and the E bit is an Error detection bit.)

• Frame Status (FS): A field of one octet terminating the frame.

Each downstream station examines the destination address to see if the frame is addressed to it. If so, it copies the data. If not, it passes the frame to the next downstream station. If a station wishes to reserve the token for the next opportunity and has a priority level that meets or exceeds that of the data frame, as set by the transmission station, it sets the priority bits.When the next token is generated, it includes the priority level of the reserving station. Any station that raises the priority level of a frame must reinstate the original priority level once it completes its transmission.

Token Ring is a sophisticated technology that offers excellent congestion control and, therefore, excellent throughput. As it also is complicated and expensive to administer, it has been overwhelmed by the simpler, less expensive, and much faster Ethernet (802.3). See also 802.3, bandwidth, beaconing, bit, CRC, deterministic, domain, downstream, error control, Ethernet, frame, IEEE, LAN, MAC, Manchester coding, node, non-deterministic, octet, overhead, Physical Layer, ring topology, star topology, throughput, and token passing.

• Class C ATM traffic
• Class C cable
• Class C IP address
• CLASS (Custom Local Access Signaling Services)
• Class D ATM traffic
• Class D ATM traffic
• Class D cable
• Class D IP address
• Class D IP address
• Class E cable
• Class E IP address
• Class F cable
• Classical IP over ATM (Classical Internet Protocol over Asynchronous Transfer Mode)
• Classless Inter-Domain Routing (CIDR)
• class of service (CoS)
• Class X ATM traffic
• clear channel
• clear to send (CTS)
• CLEC (Competitive Local Exchange Carrier)
• CLID (Calling Line IDentification)
• client
• client mesh
• client/server
• Clipper Chip
• CLNP (ConnectionLess Network Protocol)