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Protocol Stack for Wireless Sensor Networks (WSNs)

The protocol stack for WSNs consists of five protocol layers:

  1. Physical layer
  2. Data link layer
  3. Network layer
  4. Transport layer
  5. Application layer

The application layer contains a variety of application – layer protocols to generate various sensor network applications.

The transport layer is responsible for reliable data delivery required by the application layer.

The network layer is responsible for routing the data from the transport layer.

The data link layer is primarily responsible for data stream multiplexing, data frame transmission and reception, medium access, and error control.

The physical layer is responsible for signal transmission and reception over a physical communication medium, including frequency generation, signal modulation, transmission and reception, data encryption, and so on.

On the other hand, the protocol stack can be divided into a group of management planes across each layer, including power, connection, and task management planes. The power management plane is responsible for managing the power level of a sensor node for sensing, processing, and transmission and reception, which can be implemented by employing efficient power management mechanisms at different protocol layers. For example, at the MAC layer, a sensor node can turn off its transceiver when there is no data to transmit and receive.

At the network layer, a sensor node may select a neighbor node with the most residual energy as its next hop to the sink. The connection management plane is responsible for the confi guration and reconfi guration of sensor nodes to establish and maintain the connectivity of a network in the case of node deployment and topology change due to node addition, node failure, node movement, and so on. The task management plane is responsible for task distribution among sensor nodes in a sensing region in order to improve energy efficiency and prolong network lifetime. Since sensor nodes are usually densely deployed in a sensing region and are redundant for performing a sensing task, not all sensor nodes in the sensing region are required to perform the same sensing task. Therefore, a task management mechanism can be used to perform task distribution among multiple sensors.

1.  Application Layer

The application layer includes a variety of application – layer protocols that perform various sensor network applications, such as query dissemination, node localization, time synchronization, and network security. For example, the sensor management protocol (SMP) is an application – layer management protocol that provides software operations to perform a variety of tasks, for example, exchanging location – related data, synchronizing sensor nodes, moving sensor nodes, scheduling sensor nodes, and querying the status of sensor nodes.

2. Transport Layer

In general, the transport layer is responsible for reliable end – to – end data delivery between sensor nodes and the sink(s). Due to the energy, computation, and storage constraints of sensor nodes, traditional transport protocols cannot be applied directly to sensor networks without modifi cation. For example, the conventional end – to – end retransmission – based error control and the window – based congestion control mechanisms used in the transport control protocol (TCP) cannot be used for sensor networks directly because they are not effi cient in resource utilization.

3. Network Layer

The network layer is responsible for routing the data sensed by source sensor nodes to the data sink(s). In a sensor network, sensor nodes are deployed in a sensing region to observe a phenomenon of interest. The observed phenomenon or data need to be transmitted to the data sink. In general, a source node can transmit the sensed data to the sink either directly via single – hop long – range wireless communication or via multihop short – range wireless communication. However, long – range wireless communication is costly in terms of both energy consumption and implementation complexity for sensor nodes. In contrast, multihop short – range communication can not only signifi cantly reduce the energy consumption of sensor nodes, but also effectively reduce the signal propagation and channel fading effects inherent in long – range wireless communication, and is therefore preferred. Since sensor nodes are densely deployed and neighbor nodes are close to each other, it is possible to use multihop short – range communication
in sensor networks. In this case, to send the sensed data to the sink, a source node must employ a routing protocol to select an energy- efficient multihop path from the node itself to the sink.

4. Data Link Layer

The data link layer is responsible for data stream multiplexing, data frame creation and detection, medium access, and error control in order to provide reliable point – to – point and point – to – multipoint transmissions. One of the most important functions of the data link layer is medium access control (MAC). The primary objective of MAC is to fairly and effi ciently share the shared communication
resources or medium among multiple sensor nodes in order to achieve good network performance in terms of energy consumption, network throughput, and delivery latency.

5. Phisycal Layer

The physical layer is responsible for converting bit streams from the data link layer to signals that are suitable for transmission over the communication medium. For this purpose, it must deal with various related issues, for example, transmission medium and frequency selection, carrier frequency generation, signal modulation and detection, and data encryption. In addition, it must also deal with the design of the underlying hardware, and various electrical and mechanical interfaces.

Source : WIRELESS SENSOR NETWORKS  A Networking Perspective Book, Edited by Jun Zheng, Abbas Jamalipour

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