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 advocate the use of redundant transmissions, to make additional copies of the communicated information in the network. The replication of the content makes it faster for the destination to access a copy. However, as the additional replication always increases the network load, these protocols, which are not throughput-optimal to, suffers additional congestion. Hence wemove to an adaptive redundancy technique for backpressure routing, that yields the beneﬁts of replication to reduce delay under low load conditions, while at the same time preserving the performance and beneﬁts of traditional backpressure routing under high trafﬁc conditions. This technique, which we refer to as backpressure with adaptive redundancy (BWAR), essentially creates copies of packets in a new duplicate buffer upon an encounter, when the transmitter’s queue occupancy is low. These duplicate packets are transmitted only when the original queue is empty.
This mechanism can dramatically improve delay of backpressure during lowload conditions due to two reasons:
(1) Due tothe existence of multiple copies of the same packets at multiple nodes, the destination is more likely to encounter a massage intended for it.
(2) This way, the algorithm builds up gradients towards the destinations faster and reduces packet looping.
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...