Transport Protocols for WSNs
Transport layer protocols in WSNs should support multiple applications, variable reliability, packet-loss recovery, and congestion control. A transport layer protocol should be generic and independent of the application. Transport protocols are quite abun
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Transport Protocols for WSNs
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4.1
Presumptions and Considerations of Transport Protocols in WSNs
Wireless sensor networks (WSNs) generally consist of one or more sinks (or basestations) and from tens to thousands of sensor nodes scattered in a physical space. With integration of information sensing, computation, and wireless communication, the sensor nodes can sense physical information, process crude information, and report them to the sink. The sink in turn queries the sensor nodes for information. WSNs have several distinctive usually recalled features: • Unique network topology. Sensor nodes are generally organized in a multihop star-tree topology that is either flat or hierarchical. The sink at the root of the tree is responsible for data collection and relaying to external networks. This topology can be dynamic due to the time varying link condition and dynamic nodes status. • Diverse applications. WSNs may be used in different environments supporting diverse applications, such as habitat monitoring, target tracking, security surveillance, industrial control, home automation. These applications may focus on different sensory data and therefore impose different requirements in terms of quality of service (QoS) and reliability. • Traffic characteristics. In WSNs, the primary traffic is in the upstream direction from the sensor nodes to the sink, although the sink may occasionally generate certain downstream traffic for the purposes of query and control. In the upstream this is a many to one type of communication. Depending on specific applications, the delivery of upstream traffic may be event driven, continuous delivery, query driven delivery, or hybrid delivery.
© Springer Science+Business Media Singapore 2016 H.M.A. Fahmy, Wireless Sensor Networks, Signals and Communication Technology, DOI 10.1007/978-981-10-0412-4_4
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4 Transport Protocols for WSNs
• Resource constraints. Sensor nodes have limited resources, specifically, low computational capability, small memory, low wireless communication bandwidth, and a limited, usually non rechargeable battery. • Small message size. Messages in sensor networks usually have a small size compared with the existing networks. As a result, there is usually no concept of segmentation in most applications in WSNs. These unique features pose distinct challenges in the design of WSNs that should meet application requirements and operate for the longest possible period of time. Typically, care should be accorded to issues such as energy conservation, reliability, and QoS. Transport protocols are used to mitigate congestion and reduce packet loss, to provide fairness in bandwidth allocation, and to guarantee end-to-end reliability. However, the traditional transport protocols that are currently used for the Internet, i.e., UDP and TCP cannot be directly implemented for WSNs. UDP has several pitfalls: • It does not provide delivery reliability that is often needed for many sensor applications. • It does not
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