# Toward a Trust Evaluation Mechanism in the Social Internet of Things
## 4 REK Trust Evaluation Model in the SIoT
### Knowledge TI Evaluation Model
#### 4.2.2 User Recruitment in Mobile Crowd-Sensing Use-Case
It shows how much a user uses his smart device for social applications and is ready to fulfil an assign task which is essential to consider for user recruitment. The Availability can be calculated based on both time spending on social network application and amount of data consumed [44; 45]. This TA belongs to the _Ability dimension_. * _Transmission Capability_: It is required to be reliable, fast, and secure when fulfilling important tasks in traffic incident reports; thus this indicator is essential for reflecting the capability of a smart device to transmit data in real-time or nearly real-time as well as in a secure and privacy manner without compromise. Therefore, this indicator includes several TAs in Ability dimension mentioned in Section 4.2.1 such as Reliability, Confidentiality and Integrity. For simplicity, we specify the level of the Transmission Capability based on some information: _signal strength_, _signal-to-interference-plus-noise-ratio_ (_SIRN_), and the _communication technology_ in use (_WiFi_, _LTE_, _3G_, _WiMax_, and _Bluetooth_). For example, Transmission Capability is _high_ when the user is using 4_G LTE_ for data transmission with high signal strength (_4G LTE Signal \(\geq-\)50 dBm_) and _high LTE_ _SIRN (LTE SIRN \(\geq\) 12.5)_ whereas it is _low_ when 3\(G\) is used with _low_ 3\(G\) _SIRN (3G SIRN \(\leq-\)5)_. * _Cooperativeness_: This TA represents the degree of a user cooperates with crowd-sensing tasks, thus, high cooperativeness indicates more opportunities that the user is willing to accomplish an assigned sensing task, and vice versa. This TA belongs to the _Benevolence dimension_. Cooperativeness can be simply calculated by using Equation (1): \[Cooperativeness(i)=Frequency(i)\times\frac{|Number\ of\ tasks\ involved|}{|Number\ of\ tasks\ requested|}\] (1) where \(Frequency(i)\) indicates how frequently the user \(i\) has involved in the crowd-sensing campaign. It is calculated based on Equation (2) \[Frequency(i)=\frac{|Number\ of\ sensing\ tasks\ involved|}{|sampling\ period\ of\ time|}\] (2) The numbers of tasks requested is the number of times the MCS Tasking server has requested the user to participate in a sensing task; and the number of tasks involved is the number of times the user has accepted to involve in sensing tasks that the MCS has requested. The number of tasks canceled is the number of times the user cancels a sensing task when it has already accepted to involve in the sensing task. The number of requested, involved, and canceled sensing tasks of the user \(i\) is kept track and managed by the MCS Tasking Server. * _Honesty:_ This TA represents the degree of keeping promise once a sensing task is already assigned to a user. High honesty means that the user is not going to cancel a task once it is assigned due to any cause whatsoever. This TA belongs to the _Integrity dimension_ and it is simply measured by the Equation (3). \[Honesty(i)=1-\frac{|Number\ of\ tasks\ canceled|}{|Number\ of\ tasks\ involved|}\] (3) An aggregation mechanism for inferring the direct trust Knowledge TI will be prototyped in Section 4.5.