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Control messages for ring maintainance in Token Bus

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• Maintaining the logical ring in the token bus network
  • Ring maintenance:

    Ring maintenance = functions to add/delete nodes to the logical ring structure in the Token bus network

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• Maintenance operations
  • Maintenance operations:

    Remove a node from the existing logical ring Add a node to the existing logical ring Recover from a node failure Node failure will break the logical ring Ring initialization Procedure to start up the token bus network

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• How is the ring maintenance operation performed ?
  • Fact:

    Nodes will exchange "control messages (frames)" with each other to perform the ring maintenance functions

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• Control messages (frames) used in ring maintenance operations
  • Control messages used to maintenance of the token bus network:

    S.Token( ): the token frame The sender S sends this S.Token( ) message to a receiver R When receiver R receives the S.Token( ) message, it set: R.predecessor = S Reason: A sender S will always send the token to its successor If the node S sends the token to node R, then: S's successor = R But also: R's predecessor = S !!! S.Set_successor( X ): The sender S sends this S.Set_successor( X ) message to a receiver R When a node R receives the S.Set_successor( X ) message, the node R will: Update its Successor variable: R.successor = X Send the token to its new successor