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Backpressure Based Adaptive Routing and Scheduling In Delay Tolerant Network

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Under high traffic conditions, this works very well, and backpressure is able to fully utilize the available network resources in a highly dynamic fashion. Under low traffic conditions, however, because many other nodes may also have a small or 0 queue size, there is inefficiency in terms of an increase in delay, as packets may loop or take a long time to make their way to the destination. This is particularly of concern in intermittent encounter-based mobile networks which are already delay-limited due to the sparse and highly dynamic network connectivity. Such networks have proposed the use of redundant transmissions to improve delay, which do not work well when the traffic load is high.

Routing protocol, such as Spray and Wait, that
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The additional transmissions incurred by BWAR due to the duplicates utilize available slots which would otherwise go idle, in order to reduce the delay. Particularly for networks that are not energy-limited, this offers a more efficient way to utilize the available bandwidth during low load conditions. In order to minimize the storage resource utilization of duplicate packets, ideally, these duplicate packets should be removed from the network whenever a copy is delivered to the destination. Since this may be difficult to implement (except in some kinds of networks with a separate control plane), we also propose and evaluate a practical timeout mechanism for automatic duplicate removal. Under high load conditions, because queues are rarely empty, duplicates are rarely created, and BWAR effectively reverts to traditional backpressure and inherits its throughput optimality property. By design, BWAR is highly robust and distributed and does not require prior knowledge of locations, mobility patterns, and load conditions.

The duplicate queues are maintained and utilized as follows:

• Original packets when transmitted are removed from the main queue; however, if the queue size is lower than a certain threshold qth, then the transmitted packet is duplicated and kept in the duplicate buffer associated with its destination if it is not full (otherwise no duplicate is created).
• Duplicate packets are not removed from the duplicate buffer when transmitted. They
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