QoS : Quality of Cloud Services

Quality of Services (QoS)  depicts a considerable level of performance expected of a service provider in terms of the utility derived from the cloud service being provided to a cloud service consumer.

The utility derived is fundamental and highly dependent on the type of cloud service and application, the business objectives and regulatory requirements of the cloud service consumers.

Quality of cloud services depicts the level of minimum expected satisfaction derived from the use of cloud services (including the platform, application or infrastructure) based on reliability, performance, availability, and compliance with customers’ business requirements provisioned by a cloud service provider or broker.

Cloud QoS can be evaluated along with performance utility features, economic, security and quality assurance dimensions.

Performance quality evaluation measures of the cloud services are summarized and presented below.

Communication

Description

This measures the quality of the efficiency of the connection and data transfer between internal service instances, different cloud services, or between the external consumer and the cloud.

Metrics
  • Packet loss frequency
  • Connection error rate
  • MPI transfer bit/byte speed
  • MPI transfer delay

Computation

Description

This represents the computing task and/ or data processing in the cloud.

Metrics
  • CPU load (%)
  • Benchmark OP (FLOP) Rate
  • Instance efficiency (% CPU peak)

Memory

Description

This defines the efficiency in the rate of use of temporary stored information contained in slow-accessed hard disk drive.

Metrics
  • Mean hit time (s)
  • Memory bit/byte speed (MB/s, GB/s)

Time

Description

This specifies the time taken to run a project to completion without violating quality requirement constraints.

Metrics
  • Computation time
  • Communication time

Cost

Description

This is the total cost associated with the use of a cloud service. It is evaluated to reflect the economic benefits of adopting cloud to drive business objectives over a period of time.

Metrics
  • Total cost ($)
  • FLOP cost (cent/FLOP, $/GFLOP)
  • Supported users on a fixed budget
  • Component resource cost ($)
  • Price/performance ratio
  • Cost over a fixed time ($/year)

Cloud (rapid) elasticity

Description

This quality attribute describes the degree of on-demand flexibility of a cloud service to workload changes via dynamic provisioning (scaling-up) and de-provisioning (scaling-down) of public cloud infrastructure resources on a pay-as-you-grow or pay-per-user model. It also significantly typifies the speed of responses used to adjust workload.

Metrics
  • Boot time (second)
  • Suspend time (second)
  • Delete time (second)
  • Provision (or deployment ) time (second)
  • Total acquisition time (second)

Data security

Description

This attribute refers to a consolidated set of technologies, policies, controls and systems employed to protect data, applications components and other infrastructure of cloud systems.

Metrics
  • Is SSL applicable
  • Communication latency over SSL
  • Auditability

Authentication

Description

This attribute is responsible for the verification and management of valid identities of both users and devices on the cloud.

Metrics
  • Meaning
  • Sensitivity
  • Effectiveness
  • Confidentiality

Availability

Description

This phenomenal attribute depicts the ability to access cloud services, data and tools anytime and anywhere.

Metrics
  • Flexibility
  • Accuracy
  • Response time

Scalability

Description

This depicts the ability to enhance the resizable computing power of the service provider’s system by adding more workload without affecting the system’s performance.

Metrics
  • Average of assigned resources among the requested resources

Reliability

Description

This is a critical measure of the system’s capability to continuously provision a service with an acceptable degree of efficiency without malfunctioning.

Metrics
  • Service constancy
  • Accuracy of service
  • Fault tolerance
  • Maturity
  • Recoverability

Efficiency

Description

This is a measure of the performance level derived from the use of the least amount of resources to provide a service relative to energy, time, cost expended, and level of resource utilization with the highest utility after the service runs into completion.

Metrics
  • Utilization of resource
  • Ratio of waiting time
  • Time behavior

Reusability

Description

This measures the degree to which a resource, a component, an application or a system may be reused in a number of other programs or applications.

Metrics
  • Readability
  • Coverage of variability
  • Publicity

Composability

Description

This refers to a measure of interoperability characteristics.

Metrics
  • Service Modularity
  • Service interoperability

Adaptability

Description

This measures the capacity of a solution, an application, a service or a system to be modified for new utilization by other services, applications or systems.

Metrics
  • Completeness of variant set
  • Coverage of variability

Usability

Description

This is the potential degree to which a service could be used by particular consumers to meet their business objectives based on ease-of-use and consistency.

Metrics
  • Operability
  • Attractiveness
  • Learn ability

Modifiability

Description

This depicts the ease with which a cloud service and /or associated component(s) can be modified to improve performance, correct errors or adapt to a changed and different environment rapidly and cost-effectively.

Metrics
  • Mean Time to Change (MTTC)

Sustainability

Description

This depicts the environmental effect of the cloud service employed. It measures how well the needs of a customer are satisfied and how the social and environmental performance of the entire cloud service has been significantly improved.

Metrics
  • Data Center Performance per Energy (DPPE) parameter
  • Power Usage Efficiency (PUE)