Trustworthy accounting of resource consumption in the Cloud


Santosh Shrivastava,
School of Computing Science,
Newcastle University, UK


Abstract of current work

The services offered by Internet Data Centers involve the provision of 
storage, bandwidth and computational resources. A common business model 
is to charge consumers on a pay-per-use basis where they periodically 
pay for the resources they have consumed (as opposed to a fixed charge 
for service provision). Central to the pay-per-use model is the issue of 
accountability for the consumed resources: who performs the measurement 
and decides how much resource has been consumed –– the provider, the 
consumer, a trusted third party (TTP), or some combination of them?

Traditional utility providers such as water, gas and electricity 
services use provider-side accounting based on metering devices that 
have a certain degree of tamper-resistance and are deployed in the 
consumer’s premises. Provider-side accounting is also widely used by 
phone services and Internet-based utility providers like Amazon. 
However, in contrast to traditional utilities, the infrastructure 
responsible for measuring resource consumption is deployed at the 
provider. The distinguishing feature of provider-side accounting is that 
it is unilateral.  Provider-side accounting is acceptable when the 
consumer has good reason to trust the provider not to accidentally or 
maliciously overcharge. However, we contend that there will be a class 
of applications, or of relationships between consumer and provider, 
where this assumption does not hold and where other models are needed. 
Unilateral consumer-side accounting can be implemented but we do not 
discuss it here because it is not representative of practical 
applications –– it is very unlikely that a provider would simply accept 
accounts unilaterally computed by a consumer.

Unilateral accounting by a TTP on behalf of both consumer and provider 
would be more practical than consumer-side accounting, but here we 
consider a hitherto unexplored alternative of bilateral accounting of 
resource consumption. We develop a new model in which the consumer and 
provider independently measure resource consumption, compare their 
outcomes and agree on a mutually trusted outcome. The problem of 
achieving mutual trust in accounting for resource consumption is 
currently neglected but is becoming important as users increasingly rely 
on utility (or cloud) computing for their needs. We explore the 
technical issues in bilateral accounting and develop a model that is 
abstract and general enough to apply to the different types of resources 
that are being offered on a utility basis [1].

Our work so far has indicated that the success of bilateral accounting 
to a large extent will depend on two factors: the quality of accounting 
data consumers can collect and the availability of a relatively simple 
comparison and conflict resolution protocol (CCRP) to enable production 
of mutually agreed outcomes. Service providers can help consumers by 
providing (i) suitable service interfaces to enable consumer side 
metering, and (ii) a reference model  (e.g., an accounting model) to 
enable consumers to estimate resource consumption and associated 
charges. Further, sometimes there is also a need for a consumer 
(provider) to collect metering data directly at the provider’s 
(consumer’s) premises, so suitable metering techniques will need to be 
developed. CCRP procedures will also need to be developed and agreed as 
a part of the service level agreement.

To ground our approach in current practice, we will use storage 
consumption as an example and, in particular, use Amazon’s S3 as a case 
study for bilateral accounting.


[1] Carlos Molina-Jimenez, Nick Cook and Santosh Shrivastava, “On the 
Feasibility of Bilaterally Agreed Accounting of Resource Consumption”, 
International Workshop on Enabling Service Business Ecosystems 
(ESBE’08), December 2008, Sydeny, Springer, LNCS 5472, pp. 270–283, 2009.