# A Trusted Multi-Cloud Brokerage System for Validating Cloud Services Using Ranking Heuristics
## 2 Literature Review
### Extraction of Service Trust Factors from Multi-Cloud Environment
#### 3.1.1 Identification of Trust Factors and Feedback  
In this paper, 13 service trust factors with respect to the available cloud services are considered for validation and verification process. From each cloud service provider's side, we have attained the values for the trust factors. In addition to that, the ICB enables the cloud user to post feedback for the consumed services. The obtained feedback can be utilized for the determination of service trust factors. The service trust factors which are considered in the proposed model are presented below. _Service Response Time (\(p_{1}\))_  
Service response time (SRT) indicates the service availability, which is measured from the response time of the service provider. In IaaS, it is measured as how quickly the service is available to the user. The service response time is calculated by  
\[\text{SRT}=\sum_{x}{{}^{t_{x}}/N} \tag{1}\]  
where \(x\) is user id, \(t_{x}\) is the time between user \(x\)'s request time and the time at which the service becomes available, and N is total number of service requests. The service response time failure (SRTF) is calculated by  
\[\text{SRTF}=\
icefrac{{ns}}{{N}} \tag{2}\]  
Figure 1: Proposed work for validation and verification of multi-cloud services. where _ns_ is the number of times the service provider was not able to provide the service within the maximum response time. _Sustainability (p2)_  
The environmental impact of cloud service provisioning is referenced by the term'sustainability' and is measured by the average carbon footprint or energy efficiency of cloud services. The carbon footprint or energy efficiency is calculated by carbon calculators such as the PUE (Power Usage Efficiency) calculator. \[\text{Sustainability}=\frac{Number\ of\ essential\ features\ provided\ by\ provider}\text{s\ services}{Number\ of\ essential\ features\ required\ by\ the\ customer} \tag{3}\]  
_Suitability (p3)_  
Suitability is the proportion of essential features required by the customer that are actually provided by the cloud service. It is defined as follows:  
\[\text{Suitability}=\frac{|Essential\ Features\ Provided\cap Essential\ Features\ Required|}{|Essential\ Features\ Required|} \tag{4}\]  
_Accuracy (p4)_  
Accuracy indicates the degree of proximity to the user's actual values when using a service compared to the expected values. Also, the frequency of success in fulfilling the promised SLA in terms of storage, computing, and network is considered. The accuracy is calculated by  
\[\text{Accuracy}=\sum_{\alpha}\frac{s_{x}}{n} \tag{5}\]  
where \(n\) is the number of previous users and _sx_ is the number of times the cloud provider successfully satisfied the promised values for user \(x\) over service time T.  
_Transparency (p5)_  
Transparency is an important feature in cloud services which directs the range to which users' usability is not affected by any changes in services. The usability is measured by  
\[\text{Usability}=\frac{Number\ of\ time\ services\ not\ affected}{Number\ of\ time\ changes\ in\ services} \tag{6}\]  
_Interoperability (p6)_  
The ability of the services to interact with other services is denoted as interoperability and is calculated by  
\[\text{Interoperability}=\frac{Number\ of\ platforms\ offered\ by\ the\ provider}{Number\ of\ platforms\ required\ by\ customers\ for\ interoperability} \tag{7}\]  
_Availability (p7)_  
Availability is measured by the percentage of time a customer accesses the services.