3.1 concepts a grid that uses an economic model for managing resources is one that utilizes the real world analogy of a market economy to limit, manage and optimize the utilization of resources used. in real world markets there are many models for setting the monetary value of goods and services based on supply and demand. it has been shown that the forces of demand and supply iterate the value of a good or service towards an equilibrium value, this process is caused by the price mechanism [15]. the equilibrium value represents an idealistic value where neither demand nor supply are in excess or shortage. the price mechanism is essentially a dynamic self optimizing resource management tendency in a market economy that moves the market towards a sustainable balance between the demand and supply of a good or service. many grid projects distributed , seti home, condor pool, distributed asci supercomputer, gusto, and egrid ; have relied on the good will of the public, prizes, fun, fame or collaborative advantages in order to sustain the number of participants - who are often the largest pool of resources providers - on their grid. however without a more flexible and exchangeable reward such as real currency, the participation rate is more likely to drop [14], hence leading to reductions in grid performance and or unfair usage of the remaining resources within the system. all systems involving goals, resources, and actions can be viewed in economic terms [16]. if one considers the use of resources on a data grid on offer as various types of services then grid resource providers can be considered analogous to service suppliers and applications and ultimately grid users ; as service consumers2. in grid systems, brokers and service providers are free to choose their own private strategy, which cannot be imposed from outside. economic perspectives have already been applied to manage fair resource usage allocations in current grid brokers such as nimrod-g [14][17] and gridbus [18][34]. a data replication strategy from an economic model is proposed in [22]. in an economic grid model there are two key types of players: service providers and service consumers [14]. service consumers are users and applications that interact with their resource brokers to demand the use of resources a service ; . nodes that make their resources available for use are service providers. the motivation for service consumers in a data replication perspective with a decoupled data scheduler, for the purpose of replication, is to satisfy the requirements of a replication transfer or file transfer ; at the lowest cost within an optional constraint such as time. the motivation for service providers is to maximize the investment of their resources such as bandwidth ; so that it attracts the most amount revenue from its customers. furthermore, the two types of players are not necessarily exclusive entities. a consumer may become a provider with its idle resources in order to earn back spent credits and vice-versa. players in this system are assumed to be non-cooperative and strategic [2] without giving consideration in explicitly optimizing for the grid as a whole. however, like its analogy in the real world, market forces will implicitly guide service usage in this case bandwidth towards a balanced and sustainable global equilibrium. the medium for valuation and purchasing services can be real currency or it can be abstract grid tokens or credits as long as they can be redeemed for future services. the act of purchasing of services or transactions can be mediated through a market directory. the interaction between the mediator and players involved in the transaction are determined by a particular economic model with its associated transaction protocol. these models, discussed in the following section, will specify the process in determining the price for the use of a grid resource s ; , and transaction protocols prescribe how to trade, methods in accounting, billing and other analogous fiscal services. a complete implementation of an economic grid requires the following services [14]: a market directory for publicizing participating grid players. models of establishing the value of services so that suppliers are able to create a pricing scheme. this includes negotiation protocols for the transfer of services for credits or currency.