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[nitin]

nitin

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hi,i have come to one problem in my reaserch which i am not able to understand (as explained in paper).Can we proof that there exist no(at some situation) edge symmetry in undirected graph?Like consider there are n number of sensor nodes.these nodes are connected through undirected edges.if u-->v i.e. node v is neighbor of u and node u can transmit data to v.but v can not transmit data to node u,but u is neigbhor of v .
(you can consider the concept of transmission radius)

[sri]

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hi,i have come to one problem in my reaserch which i am not able to understand (as explained in paper).Can we proof that there exist no(at some situation) edge symmetry in undirected graph?Like consider there are n number of sensor nodes.these nodes are connected through undirected edges.if u-->v i.e. node v is neighbor of u and node u can transmit data to v.but v can not transmit data to node u,but u is neigbhor of v .
(you can consider the concept of transmission radius)

An undirected graph representation is a model for the sensor network. You can represent a wireless sensor network as an undirected graph if communication is symmetric in the first place (i.e. if A can speak to B, then B can also speak to A).

In reality though communication need not always be symmetric because of physical constraints (a part of the bandwidth getting attenuated due to hurdles or atmospheric conditions) and variations in transmission power among the nodes.

[nitin]

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thanks sir, i got some  picture of the situation. But if in realty this happens that there is an  undirected edge between A to B  and A can send data to B but B can not due to some transmission power issues.then how B can ACK back to A that data has been recieved. Because if A does not get ACK then after some time it may again send the data and keep on sending and thus wasting BW  as well as energy of its own.

[aditya]

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The graph being directed or undirected is just a model. A model does not represent the reality completely. So, an undirected model can not be used to represent the problem which you are stating. You either need add another layer of modelling to make the error transparent to the graph or you have to model the whole thing as a directed graph. Anyway, these are problems which are very basic in sensor networks and distributed systems. A good survey of those will answer your question more thoroughly.