*3.1.2 Latency*

Latency is the period from the time unit that the data generation at the sensor node started to the time unit that data reception was completed at the base station. It is one of the main concerns for time significant applications such as military and medical health-care monitoring. Attaining low latency is a vital concern because of the following reasons:


To deal with the above issues, there is a need for low-latency protocols. Literature [23, 24] presents recent survey works on low-latency routing protocols. Srivathsan and Iyengar [23] have reviewed some key mechanisms to reduce the latency in single-hop and multi-hop wireless sensor networks; such mechanisms are sampling time, propagation time, processing time, scheduling, use of directional antennas, MAC protocols, sleep/wake-up cycles, predictions, use of dual-frequency radios, etc. A review on energy-efficient and low-latency routing protocols for WSNs without dominating the other design factors is presented by Bagyalakshmi et al. [24].

accuracy of the aggregated data that have been received by it and also cannot

Network coding is the same as the aggregation technique. In this technique, the nodes collect the data from neighbor nodes and combine them together by applying mathematical operations; then it transmits data to the BS. This technique improves the network throughput, reliability, energy efficiency, and scalability; it is also resilient to attacks and eavesdropping. Network traffic in broadcast scenarios can be reduced by combining several packets as a single packet rather than sending sepa-

For energy conservation, duty cycling is one of the important techniques in WSNs. In duty cycling, the radio transceiver mode of sensor node is changing between active and sleep. This technique requires cooperative coordination between nodes for communication. Nodes want to communicate with each other and the nodes will shift from sleep mode to wake-up mode. A node must wait for its neighbor nodes to awake for communication. Sleep latency is increased due to this. Multi-hop broadcasting is complex in this technique because all the neighboring

Transmitting or receiving signals with one or more directions at a time with greater power is done with directional antennas. This technique improves the performance with respect to throughput by increasing the transmission range. With the help of directional antennas, bandwidth reusability is also possible. However, transmission power calculations and optimal antenna pattern selection overhead is more in these directional antennas. Also, directional antennas are more exposed to

Sink mobility is one of the energy-efficient technique, where mobility is introduced with sink nodes. The mobile sink nodes collect the data from sensor nodes with single-hop while moving in a specified path and then forward the same to the BS. This scheme reduces the workload of nodes which are placed nearer to the sink nodes and it increases the network lifetime. With the help of sink mobility, so many sparse networks can be connected and communicated which in turn provides scalability of the network. Reliability will be improved because of single-hop communication between the mobile sink and sensor nodes. However, trajectory path maintenance is a critical part of sink node while moving. Mobile collector needs a proper synchronization mechanism with sensor nodes, otherwise this causes packet

When compared to layered approaches, cross-layered approach in WSN is energy efficient. The protocol stack is considered as a single system instead of individual layers in the cross-layered approach. For interaction among the protocol

restore the data.

rate packets.

*3.2.4 Duty cycling*

nodes are not active at the same time.

hidden and exposed terminal problems.

*3.2.5 Directional antennas*

*3.2.6 Sink mobility*

loss while data gathering.

*3.2.7 Cross-layered approach*

**89**

*3.2.3 Network coding*

*Data Collection Protocols in Wireless Sensor Networks DOI: http://dx.doi.org/10.5772/intechopen.93659*

#### *3.1.3 Fault tolerance*

Fault tolerance [25] enhances the availability, reliability, and dependability of the system by ensuring the usage availability of the system without any disruption in the presence of faults. In WSN, fault tolerance is also a demanding issue due to the sensor nodes more vulnerable to failure because of energy depletions, desynchronization, communication link errors, etc., which are provoked owing to hardware and software failures, environmental conditions, etc. Hence, fault management in WSN must be administered with additional care. Initial review works on fault-tolerant routing schemes are present in literature [21, 25–28]. Yu et al. [26] have explained issues in the fault management of WSN. Three phases called fault diagnosis, fault detection, and fault recovery for supervising faults have been proposed. In fault detection phase, an unexpected failure should be identified by the system. Literature [26–28] explains various fault detection techniques. In fault diagnosis phase, comprehensive description or model has been determined to distinguish various faults in WSNs [21] or fault recovery action. In the fault recovery phase, the sensor network is redesigned from failures or fault nodes to enhance the network performance. Fault recovery techniques have been dealt by literature [25].

#### **3.2 Major techniques used for data collection design issues**

The major techniques utilized for attaining energy saving, low latency, long lifetime, and fault tolerance in WSNs are discussed in this section.

#### *3.2.1 Cluster architecture*

Cluster-based architecture is a foremost technique for effective energy conservation. In this mechanism, the network is partitioned into clusters, where the cluster head (CH) is a leader to manage the members of each cluster. Every member sensor node transmits the sensed data to their corresponding CH; then, CHs communicate the collected data to the BS. This technique avoids flooding, routing loops, and multiple routes; hence, reduced network traffic and low latency are attained. The major advantage of cluster-based architecture is that it needs less transmission power because of small communication ranges within the cluster. The CH uses the fusion mechanism to minimize the size of the transmission data. CH selection is performed in a rotation basis to balance the energy consumption in the network and improve the network lifetime. However, in cluster-based routing protocols, cluster head selection plays a critical role. Further, clustering algorithms do not consider the location of the base station, which creates a hot spot problem in multi-hop wireless sensor networks.

#### *3.2.2 Data aggregation*

Data aggregation is one of the significant methods applied to aggregate the raw data evolved from multiple sources. In data aggregation schemes, nodes receive the data, reduce the amount of data by employing data aggregation techniques, and then transmit the data to the BS. The average or minimum amount of received data are merely forwarded by the received node. This reduces the network traffic and hence low latency is achieved. However, the base station (sink) cannot ensure the

accuracy of the aggregated data that have been received by it and also cannot restore the data.
