*3.1.1 Energy and lifetime*

acquisition is done by the sink node with the help of query dissemination in querybased routing. All sensor nodes are going to store the data based on the interest of nodes. Then the data are forwarded to the destination only if the sensed or received node data match with the received queries. Data descriptors are used by negotiationbased protocols for reducing redundant data relays through negotiation. QoS-based protocols mainly consider QoS metrics such as delay, throughput, bandwidth, etc., when routing the data to the base station. In coherent routing, the sensed data is transferred directly to the aggregate node. Whereas in noncoherent routing, node data processing is done locally and then is transferred to neighbor nodes. In addition, routing protocols are classified into proactive, reactive, and hybrid protocols

Continuous, event-driven, observer-initiated, and hybrid-based on application interest are the different classifications given by Tilak et al. [12] in 2002. The sensor nodes transfer their sensed data at a prespecified rate to the server in the continuous model. Only when an event occurs, the sensor nodes forward data to base station in the event-driven data model. In the observer-initiated model, the observer will give an explicit request, then only the corresponding sensor nodes respond with the results. The combination of above three approaches will be called as hybrid protocols. Based on data communication functionalities of routing protocols, Kai Han et al.

depending on path establishment between the source and destination.

*Wireless Sensor Networks - Design, Deployment and Applications*

[31], in 2013, classified the routing protocols into unicast, anycast, broadcast,

multicast, and converge-cast. One-to-one association between sensor nodes is used in unicast routing. For forwarding the sensed data, unicast routing is using one neighboring node as a relay node. In anycast routing, nodes transfer the sensed data to a potential receiver node of a group. Multicast routing is transferring the data to a selected number of neighbor nodes simultaneously in a single transmission. Broadcast routing uses a one-to-many association; in a single transmission, sensor nodes transfer the data to their all neighbor nodes simultaneously. The data are aggregated at relay nodes and forwarded toward the base station in the converge-cast mechanism. Information exchanges will be done between the pair of sensor nodes in unicast/ anycast. Whereas, multicast/broadcast is required for disseminating commands to sensor nodes, and converge-cast uses to collect the data from sensor nodes.

Routing protocols are classified as classical and swarm intelligence-based protocols by A.M. Zungeru et al. [14]. Further, each protocol is categorized into data-centric, hierarchical, location-based, network flow, and quality of service (QoS) awareness. In addition, they divided the routing protocols into proactive, reactive, and hybrid,

The energy-efficient routing protocols are classified into network structure, communication model, topology-based, and reliable routing, as presented by Pantazis et al. [15]. Network structure routing protocols are classified into flat and hierarchical protocols. Communication model routing protocols can be divided into coherent or query-based and negotiation-based or noncoherent-based protocols. Mobile agent-based or location-based routing protocols are under the category of topology-based routing protocols. Reliable routing protocols are classified as

In addition to the above, some other literature [16–20] also presented different classifications of routing protocol. However, **Figure 1** represents the overall classi-

In this section, some common design issues for data collection, such as energy,

lifetime, latency, and fault tolerance are discussed. The techniques such as

depending on the path establishment between the source and destination.

**3. Major design issues and techniques for data collection**

multipath-based or QoS-based.

**86**

fication of routing protocols in WSN.

Managing energy of the sensor nodes is the primary concern in WSN because it is the critical constraint of the sensor nodes. Saving of the node energy increases the network lifetime. Sensor node depletes much energy in two significant operations such as environment sensing and communicating sensed data to the BS. Energy consumption is stable for sensing operation because it depends on the sampling rate and does not depend on the other factors such as the topology of network or the location of the sensors. While, data forwarding process depends on them. Hence, energy conservation is feasible by designing an effective data forwarding process. Network lifetime [21] is defined as the period from the starting of the WSN operation to the time when any or a given percentage of sensor nodes die. Hence, the major objective of the data collection protocol is to gather the data with the maximum number of rounds within the lifetime of the network. The data gathering is the vital factor which considers energy saving as well as lifetime. In literature [4, 22], the authors have presented energy-efficient techniques for data collection. Rault et al. [4] have reviewed the energy-saving techniques and its classification such as radio optimization, data reduction, sleep/wake-up schemes, energyefficient routing, and battery repletion. Anastasi et al. [22] in 2009 discussed directions for energy conservation in WSNs and presented the taxonomy of energy conservation techniques such as duty cycling, data driven, and mobility-based routing.
