Ayub Qaisar, Ngadi Asri, Rashid Sulma, Habib Hafiz Adnan
Department of Computer Science, University of Engineering and Technology Taxila, Rawalpindi, Pakistan.
Department of Computer Science University Technologi Malaysia, Johor Bahru, johor, Malaysia.
PLoS One. 2018 Feb 13;13(2):e0191580. doi: 10.1371/journal.pone.0191580. eCollection 2018.
Delay Tolerant Network (DTN) multi-copy routing protocols are privileged to create and transmit multiple copies of each message that causes congestion and some messages are dropped. This process is known as reactive drop because messages were dropped re-actively to overcome buffer overflows. The existing reactive buffer management policies apply a single metric to drop source, relay and destine messages. Hereby, selection to drop a message is dubious because each message as source, relay or destine may have consumed dissimilar magnitude of network resources. Similarly, DTN has included time to live (ttl) parameter which defines lifetime of message. Hence, when ttl expires then message is automatically destroyed from relay nodes. However, time-to-live (ttl) is not applicable on messages reached at their destinations. Moreover, nodes keep replicating messages till ttl expires even-though large number of messages has already been dispersed. In this paper, we have proposed Priority Queue Based Reactive Buffer Management Policy (PQB-R) for DTN under City Based Environments. The PQB-R classifies buffered messages into source, relay and destine queues. Moreover, separate drop metric has been applied on individual queue. The experiment results prove that proposed PQB-R has reduced number of messages transmissions, message drop and increases delivery ratio.
延迟容忍网络（DTN）多副本路由协议有特权创建并传输每条消息的多个副本，这会导致拥塞且一些消息会被丢弃。这个过程被称为反应式丢弃，因为消息是为了克服缓冲区溢出而被主动丢弃的。现有的反应式缓冲区管理策略应用单一指标来丢弃源消息、中继消息和目的消息。因此，选择丢弃一条消息是值得怀疑的，因为每条作为源、中继或目的的消息可能消耗了不同数量的网络资源。同样，DTN包含定义消息生命周期的生存时间（ttl）参数。因此，当ttl过期时，消息会从中继节点自动销毁。然而，生存时间（ttl）不适用于到达目的地的消息。此外，即使大量消息已经被分散，节点仍会不断复制消息直到ttl过期。在本文中，我们针对基于城市环境的DTN提出了基于优先级队列的反应式缓冲区管理策略（PQB-R）。PQB-R将缓冲的消息分类到源队列、中继队列和目的队列中。此外，对每个队列应用了单独的丢弃指标。实验结果证明，所提出的PQB-R减少了消息传输数量、消息丢弃数量并提高了交付率。
