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IEEE

IEEE. IEEE has had the greatest impact on Layer 2 standards. IEEE divided Layer 2 into two sublayers. LLC sublayer of Layer 2. IEEE—Layers 1 & 2. IEEE 802.2.

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IEEE

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  1. IEEE • IEEE has had the greatest impact on Layer 2 standards. • IEEE divided Layer 2 into two sublayers.

  2. LLC sublayer of Layer 2 IEEE—Layers 1 & 2 IEEE 802.2 • The Logical Link Control sublayer was created to provide different Layer 1 technologies a single method of accessing the higher layers. These sample technologies include Layer 1 & the MAC sublayer of Layer 2 Ethernet 10 Base T IEEE 802.5 FDDI IEEE 802.3

  3. BASIC OF TOKEN-RING

  4. Variants IBM developed the first Token Ring network in the 1970s. It is still IBM's primary LAN technology, and is second only to Ethernet (IEEE 802.3) in terms of LAN implementation.

  5. Ring Topology

  6. Data passing • When a station has information to transmit, it seizes the token and sends data frame to the next station. • When frame reaches the destination station, the data is copied for processing. • Frame continues to circle the ring until it returns to the sending station. • Sending station removes the frame from the ring, verifies receipt, and releases the token.

  7. Token-Ring frame format

  8. Start Delimiter and End Delimiter • Startdelimiter. • Alert for the arrival of a token. • Includes an identification symbol. • Violates the encoding system to differentiate it from other frame fields. • EndDelimiter • Completes the token or data/command frame. • Contains damage indicator. • Last of logical sequence.

  9. P P P T M R R R Access control • P: Priority bits • T: Token bit • M: Monitor bit • R: Reservation bits • (this is the second field in the frame. It is one byte, or 8 bits; each bit has it’s own function.)

  10. Frame control • Only present in data/command frames. • Indicates whether frame contains data or control information. • If control, this byte specifies type of control information.

  11. Destination and Source addresses • Universal Address. • Local Administered Address. • Broadcast Address (D). • Functional Address (0x0C0000 00XXXX) (D).

  12. Data • Length limited by the maximum time a station may hold the token.

  13. Frame checksum • Frame Check Sequence. • Source fills field with calculated value dependent on frame contents. • Destination recalculates to check data integrity. • Frame is discarded if damaged.

  14. Frame status • Address recognized / frame copied indicator.

  15. Management mechanisms • Active Monitor • One station acts as centralized source of timinginformation for other stations. • Removescontinuously circulating frames by set monitor bit to 1 (i.e., ends “loops”). • Start a token, when token have been lost. • Beaconing • Detects and repairs network faults. • Initiates auto-reconfiguration.

  16. Physical topology • Physical topology : Star. • Logical topology : Ring. • IBM Token Ring network stations are connected to MSAU (Multi-Station Access Unit). • Many MSAU can be wired together to form one large ring.

  17. Multi-MSAU

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