When a customer purchases service plan, Billing creates a subscription. Depending on service plan configuration, the customer becomes either reseller or end-user. Subscription may be considered as a services contract between the vendor and the customer. Subscription provides information on the service plan that the customer has subscribed to, vendor's and customer's personal and billing contacts, as well as technical and service provisioning terms information. The customer can enroll for multiple subscriptions. The subscription is valid within a period of time called subscription period.
When you start reading this chapter we assume that all necessary service plans are properly configured. Namely, subscription periods, resource rates, allowed upgrades and downgrades are all set up and service plans themselves are ready for sales.