One of the main challenges of WSN is reliable data transport. Reliable data delivery and congestion control are the two major functions in transport layer. Depending on the direction of data flow of data flow of the applications, the data transport can be classified into sensors-to-sink and sink-to-sensors. In this part I am going to give a brief over view of reliable data transport protocols.
PSFQ: This protocol guarantees reliable data delivery from sink-to-sensors. It comprises of three components: pump operation, fetch operation and report operation. It guarantees the reliability by fast fetching packets from neighboring nodes after a packet sequence gap is detected. It also deals with hop-by-hop loss recovery. Main drawback of PSFQ is use of in-sequence forwarding for message delivery to accomplish the pump slowly operation and this results in wastage of precious bandwidth.
RMST: Its primary goal is the delivery of large pieces of data to all subscribed sinks. RMST is NACK-based; it places responsibility for loss detection at the receivers (which can be intermediate nodes as well as the actual sinks). Missing fragments requests are uni cast from the sink to source. Caches in intermediate nodes allow for fast recovery. This scheme lacks in congestion control and energy efficiency.
GARUDA: Uses core-recovery idea to implement reliable downstream data delivery. Some nodes in the network play the role as loss recovery servers, and other non-core nodes need to have one-hop connection with at least one core nodes. GARUDA works in two-stage recovery. GARUDA's design is not optimized for very large messages and therefore it does not use features such as pipe lining which are critical fore reduced data propagation latency in large networks.
They did a good job of summarizing the protocols.
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