As illustrated in the AMS protocol, a message’s initial token value is statically assigned (Section 5.2). In the proposed ASTMS scheme, the initial token assignment is made adaptive to a node’s varying interaction history in the network. The idea presented here is mathematically formulated as follows:
s/1 [ 0 . t , (3.11)
" at the node . The
Fig. 3.9. Performance comparison of AMS with Spray and Wait, and Spray and Focus.
[ c. /2. 0 . (3.12)
In above equation, the interaction rate [ depends on the fraction of recent contacts between node and destination N, whereas c is the total interaction rate of , in the whole network. The parameter is similar to the one used in the previous subsection and is considered as an upper bound to the maximum value of forwarding token. Equation (3.11) indicates that if the node more frequently interacts with the destination N, then smaller token value will be generated for the message " at node . Therefore, the initial token value is dependent on a node’s interaction frequency with a specific destination set. Based on the proposed approach, we introduce adaptive token assignment mechanism in the PRoPHET protocol. The PRoPHET protocol performs message replication if and only if the delivery predictability of the current message is comparatively higher at the neighbor node. However, the PRoPHET protocol sets no limit to the maximum number of message replicas. This may cause an increased overhead and message drop rate in the resource constrained network environments. The aforementioned problem is addressed in the proposed ASTMS scheme in the following ways: (a) by introducing adaptability in initial token assignment, (b) by setting a limit on maximum number of message replicas, and (c) by introducing adaptability in token splitting during message replication. All such enhancements depend on a source node’s interaction history with the message’s destination. Algorithm 3.1 presents the pseudo-code for the ASTMS scheme. A message created by an
application (App) is assigned the initial token value and stored in the message queue at the node (Line 1). A message with token value greater than one will be replicated, if and only if the interaction history of neighboring node is greater than the current node (Line 3 and Line 4). The token splitting is performed in Line 5, such that, a node with more frequent interactions with the message destination will get higher number of tokens. A message with token value equal to one
will be forwarded towards a neighbor with highest interaction value [ (Line 9 and Line 10). The same process will be repeated for other messages in the queue.
Fig. 3.10 indicates the improved performance of proposed scheme in comparison to the
PRoPHET protocol. The reduction in message replications by setting a limit on maximum
Algorithm 3.1. Pseudo-code for ASTMS scheme
1: " ← vww; s/1 [ 0 . t; A A ∪ " 2: for each " ∈ A do 3: if 1 then 4: if [ [ then 5: . [ //[ 9 [ 0 6: end if 7: Replicate " to j 8: else
9: Find a neighbor k with highest [ 10: Forward " to j
11: end if 12: end for
Fig. 3.10. Performance comparison of ASTMS with the PRoPHET protocol.
decrease in message copies improves the overhead, as per message transmissions are also minimized. However, the reduced overhead is at the expense of increased latency. This is because, with the decrease in message replications, the messages may have to wait longer to be delivered to the destinations.
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4. FORECAST AND RELAY: A MESSAGE ROUTING SCHEME FOR