# Sink-Type-Dependent Data-Gathering Frameworks in Wireless Sensor Networks: A Comparative Study
## 3 Qualitative Comparison
### Optimization Criteria and Evaluation Parameters
However, IoJHR and CTP consider the minimization of the number of hops in their data-gathering process. Clustering minimizes the number of hops compared to the traditional gathering of data from sensor nodes to sink nodes when the source node is far removed from the sink node. Consideration of the proximity of a neighbor node in the design of a data-gathering technique helps to reduce energy consumption for data transmission from one sensor node to another. PEGASIS, HEED, CPDC, and NDCMC protocols consider the neighboring node proximity while performing clustering or CH selection in their data-gathering schemes, whereas CTP considers the proximity of the neighbor nodes for forwarding the data packet. A node is assumed to be dead when it loses power and cannot participate in sensing or data transmission. The transmission distance mentioned in Table 3 refers to the distance required for the transmission of data from the source node to the sink. The energy consumption increases with increasing distance, particularly in the case of a mobile sink when the sink has to travel to the sensor nodes for data gathering. All the reviewed protocols, except for the TEEN and EPMS protocols, consider the data transmission distance for their data-gathering schemes. The investigated data-gathering protocols evaluate their performance by considering different parameters, of which energy efficiency is the most important evaluation parameter as energy consumption remains one of the most critical problems. All of the investigated protocols--evaluated by means of energy consumption--demonstrated that their methods exhibited better energy efficiency than the protocols to which they were compared. Consideration and evaluation of network lifetime are necessary when designing a data-gathering protocol--the network lifetime can be calculated using the data transmission duration or round until all nodes are alive or the first sensor node in the network dies. Apart from CTP and UEWDC, all the investigated protocols consider network lifetime, and the validation is done by comparing with other existing protocols. Network lifetime using different numbers of nodes was also analyzed. In a WSN environment, where critical and emergency data gathering is required, latency is an important issue that needs to be taken into account. The CTP considers reducing the topology repair latency when the route is repaired after detecting an inconsistency in the network. This latency plays a role for reducing the overall data-gathering latency in the network. The IoJHR protocol evaluates the data-gathering latency with respect to a different number of nodes, comparing it with other protocols. The EPMS protocol has shown that the average data delivery latency decreases when the speed of the mobile sink increases. NDCMC performs a trade-off between power saving and data-gathering latency by adjusting the cluster radius. The packet delivery ratio is the total number of packets sent until the end of a simulation round. The IoJHR protocol evaluated the delivery ratio with 100, 200, and 300 nodes in the network and compared it with other protocols. The EPMS protocol compared its packet delivery ratio over an increasing number of rounds and compared it with other data-gathering schemes. The IoJHR protocol evaluated the number of dead nodes in a network with respect to a different number of nodes. It was shown that the IoJHR protocol had a minimum number of dead nodes compared to other protocols. The NDCMC protocol defines a node as a dead node when its residual energy is less than a threshold. Subsequently, the number of dead nodes was evaluated by increasing the number of simulation rounds, the number of simulation rounds being a parameter that defines the network lifetime. The PEGASIS protocol appraised the number of rounds until 1%, 20%, 50%, and 100% of the nodes in the network were dead.