- Effect of
a deletion:
- Suppose
initially
the (logical) ring
in the token bus network
consist of the nodes
4, 1, 0:
- After
removing the
node 1,
the logical ring will become:
- Suppose
initially
the (logical) ring
in the token bus network
consist of the nodes
4, 1, 0:
- Note:
- Node 1
can
still be connected to
the bus network
- Node 1 will
not be part of
the logical ring:
- Node 4 will not receive the token frame any more !!!
- Node 1
can
still be connected to
the bus network
- Fact:
- If a
node wants to
leave the
token bus network:
- The node initiates the node deletion protocol
- If a
node wants to
leave the
token bus network:
- Prelude to
initiating
the node deletion protocol:
- A node that wants to
leave must
first:
- Become the token holder !!!
(Because only the token holder can transmit control messages !!!)
- A node that wants to
leave must
first:
- The
node deletion
protocol:
- The "leaving" node X
sends:
X.Set_successor( X's succ ) control frame to X.predecessor
Example:
- Initial state:
Node 2 (who wants to leave) has just received the token from node 4....
- Node 2
that wants to
leave will
send:
2.SetSuccessor( 1 ) back to node 4
Graphically:
- Initial state:
- Node that receives a
Set_successor(X) message will:
- Update its successor to the node ID to X
- Send the token to its new successor node X
Example: (continued)
- Node 4 received
2.Set_successor( 1 )
will update
Successor = 1:
Notice that:
- We still need to update predecessor in the node 1 !!!
- Node 4 will
send (pass) the
token message
4.Token( )
to its new successor
node 1:
- Done:
Note:
- The ring is complete !!
- The "leaving" node X
sends:
- Note:
- Node 2
that has
left the
logical ring accomplished the
following:
- Node 2 made its successor the new token holder !!!
- Node 2
that has
left the
logical ring accomplished the
following: