Cloudware Economics - Guide to Cloud Computing for Business and Technology Managers - page 295

privacy policies, and so on, all of which must be described. It is thus obvious
that the QoS offered by a cloud service is becoming the highest priority for
service providers and their customers.
Delivering QoS on the Internet is a critical and significant chal-
lenge because of its dynamic and unpredictable nature.
Applications with very different characteristics and require-
ments compete for all kinds of network resources. Changes in
traffic patterns, securing mission-critical business transactions, and
the effects of infrastructure failures, low performance of Web proto-
cols, and reliability issues over the Web create a need for Internet QoS
standards. Often, unresolved QoS issues cause critical transactional
applications to suffer from unacceptable levels of performance
degradation.
Traditionally, QoS is measured by the degree to which applications, sys-
tems, networks, and all other elements of the IT infrastructure support
availability of services at a required level of performance under all access
and load conditions. While traditional QoS metrics apply, the character-
istics of cloud services environments bring both greater availability of
applications and increased complexity in terms of accessing and managing
services and thus impose specific and intense demands on organizations,
which QoS must address. In the cloud services' context, QoS can be viewed
as providing assurance on a set of quantitative characteristics. These can
be defined on the basis of important functional and nonfunctional service
quality properties that include implementation and deployment issues as
well as other important service characteristics such as service metering
and cost, performance metrics (e.g., response time), security requirements,
(transactional) integrity, reliability, scalability, and availability. These char-
acteristics are necessary requirements to understand the overall behavior
of a service so that other applications and services can bind to it and exe-
cute it as part of a business process.
The key elements for supporting QoS in a cloud services environment are
summarized in the following:
1. Availability : Availability is the absence of service downtimes.
Availability represents the probability that a service is available.
Larger values mean that the service is always ready to use while
smaller values indicate unpredictability over whether the service
will be available at a particular time. Also associated with availabil-
ity is time to repair (TTR). TTR represents the time it takes to repair
a service that has failed. Ideally, smaller values of TTR are desirable.