Page 2 Lecture Notes in Computer Science 2865 Edited by G. Goos ...

74 R. Shah and N.C. Hutchinson3.1 The Source NodeWhen a node X is unable to find a route to node Y or has lost the route tonode Y, it buffers the message M meant for Y and requests the neighbour list ofall of its neighbours. After the neighbour list is received from all its neighbours,node X selects the neighbouring node Z that has most neighbours that are notneighbours of X and adds it to its picked set. It then eliminates all of thoseneighbouring nodes that are also the neighbours of Z by putting them in theeliminated set. Node X repeats the same selection and elimination process withthe neighbouring nodes set after removing node Z and those nodes that werejust added to the eliminated set. The process ends when all the neighbouringnodes of X are either in the picked or in the eliminated set. The algorithm canbe described in set notation as follows:neigh(X) = neighbour list of node Npicked(X) = emptyeliminated(X) = emptywhile(neigh(X) is not empty)Select a node Z : Z ∈ neigh(X)and ∀ M ( M ∈ neigh(X) and M ≠ Z|neighbour list of node Z - neighbour list of X| ≥|neighbour list of node M - neighbour list of X| )picked(X) = picked(X) ⋃ {Z}eliminated(X) = eliminated(X) ⋃{M : M ∈ neigh(X) and M ∈ neighbour list of node Z}neigh(X) = neigh(X) - picked(X) - eliminated(X)endwhileAfter this process completes, the nodes in the picked set are sent the messageM and the eliminated set in a HOLD control message. Each application message,M is uniquely identified by the tuple:A HOLD message sent by node X consists of the following fields:The message-type field indicates that its a HOLD message. The nodes inthe eliminated set are sent a NACK for message M which they buffer in theirNAKMSG queue. Node X and the nodes in the picked set buffer message M intheir HOLDMSG queue.3.2 Other Selected NodesWhen a node R receives a HOLD control message from another node S, it startsa similar selection process to select other nodes to hold the application messageM. Like the original source node, node R requests the neighbour list from all of