## 5 Analysis of Prominent Clustering Routing Protocols in WSNs
### Data-Transmission Based Clustering Routing Protocols
#### 5.2.3. Apteen  
The Adaptive Threshold sensitive Energy Efficient sensor Network protocol (APTEEN) [28], introduced by [PERSON] and [PERSON], is an extension to TEEN and aims at both transmitting periodic data and reacting to time critical events. APTEEN, on the other hand, is a hybrid protocol that changes the periodicity or threshold values used in TEEN according to the requirement of users and the type of the application. APTEEN is based on a query system which allows three types of queries: historical, on-time, and persistent which can be used in a hybrid network. Moreover, QoS requirements are introduced for the on-time queries and minimum delay is achieved by a TDMA schedule with a special time slot assignment manner.  
In APTEEN, CHs broadcast the following four parameters: (1) Attributes (A)--this is a set of physical parameters which the user is interested in obtaining data about; (2) Thresholds--this parameter consists of the hard threshold (HT) and soft threshold (ST). HT is a particular value of an attribute beyond which a node can be triggered to transmit data. ST is a small change in the value of an attribute which can trigger a node to transmit data again; (3) Schedule--this is a TDMA schedule, assigning a slot to each node; (4) Count time (CT)--it is the maximum time period between two successive reports sent by a node. It can be a multiple of the TDMA schedule length and it accounts for the proactive component.  
The distinctive feature of APTEEN is to switch between proactive and reactive modes to transmit data. All nodes sense the environment continuously, but only those nodes which sense a data value at or beyond the hard threshold permit transmitting. Once a node senses a value at or beyond the hard threshold, it transmits data. If a node does not send data for a time period equal to the count time, it must sense and transmit the data again. In APTEEN, each CH aggregates the data from the MNs within its cluster and transmits the aggregated data to the BS. During the process of data aggregation, it is assumed that the data received from the corresponding MNs are sufficiently correlated, thus it reduces a large amount of redundancy of the data to be transmitted to the BS. Moreover, a modified TDMA schedule is used to implement the hybrid network by assigning each node in the cluster a transmission slot. Additionally, APTEEN offers a lot of flexibility by allowing the user to set the CT interval and the threshold values for energy consumption can be controlled by changing the CT as well as the threshold values.  
The characters and advantages of APTEEN include: (1) APTEEN combines both proactive policies, which is alike that of LEACH, and reactive policies, which is alike that of TEEN. Accordingly it is suitable in both proactive and reactive applications; (2) It embodies a lot of flexibility by setting the count-time interval, and the threshold values for the energy consumption can be adjusted by changing the count time as well as the threshold values.  
The main disadvantages of APTEEN are as follows: (1) There exist additional complexity required to implement the threshold functions and the count time; (2) Actually, both TEEN and APTEEN share the same drawbacks of additional overhead and complexity of cluster construction in multiple levels, implementing threshold-based functions, and dealing with attribute-based naming of queries--APTEEN more than TEEN [74].