Echo Algorithm
From CasGroup
(New page: A typical example for a total algorithm is the echo algorithm, which has been discovered by Ernest J.H. Chang in 1982. == Echo Algorithm == The echo algorithms consis...) |
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A typical example for a [[Total Algorithm|total algorithm]] is the echo algorithm, which has been discovered by Ernest J.H. Chang in 1982. | A typical example for a [[Total Algorithm|total algorithm]] is the echo algorithm, which has been discovered by Ernest J.H. Chang in 1982. | ||
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travels from the border of system back to the initiator and can be used to collect information from the system. | travels from the border of system back to the initiator and can be used to collect information from the system. | ||
During the propagation of the first explorer wave, a spanning tree is constructed which consists of all the predecessor | During the propagation of the first explorer wave, a spanning tree is constructed which consists of all the predecessor | ||
| - | nodes stored in the parameter | + | nodes stored in the parameter "pred" at each node. The echo wave travels back along this spanning tree to the initiator. |
If it reaches the initiator, the algorithm is terminated. | If it reaches the initiator, the algorithm is terminated. | ||
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N = 0; | N = 0; | ||
| - | The parameter | + | The parameter "Engaged" shows if the explorer wave has already visited the node, |
and the echo counter N contains the number of echos the node has received. | and the echo counter N contains the number of echos the node has received. | ||
The initiator starts like this | The initiator starts like this | ||
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Send Explorer-Msg to all Neighbors; | Send Explorer-Msg to all Neighbors; | ||
| - | If a process receives a Message from process p it reacts like the following piece of code: each node which is visited for the first time by an explorer message will propagate itself explorer messages to all its neighbors and waits for responses ( | + | If a process receives a Message from process p it reacts like the following piece of code: each node which is visited for the first time by an explorer message will propagate itself explorer messages to all its neighbors and waits for responses ("echos") from the neightbors. If all neighbors have responded, the node sends itself an echo-message to its predecessor. |
IF NOT Engaged THEN | IF NOT Engaged THEN | ||
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ELSE finished; | ELSE finished; | ||
| - | The '''message extinction principle''' says that if two explorer messages hit each other on a single link, then both extinguish each other. They are received, but have no effect, because both sender nodes are already marked as | + | The '''message extinction principle''' says that if two explorer messages hit each other on a single link, then both extinguish each other. They are received, but have no effect, because both sender nodes are already marked as "engaged". |
== Articles == | == Articles == | ||
