For optimizing Internet access resources, a method and system for billing network access capacities shared across Internet service providers is disclosed. A Client Service Provider (CSP) may rent access on Points Of Presence belonging to a Master Service Provider (MSP) while maintaining a constant security level and providing connection accounting. When a CSP's subscriber sends an access request to a MSP, the MSP analyzes the subscriber's realm and checks the capacities allocated to the subscriber's CSP. If connection is allowed, the MSP sends an authentication request to the CSP. If the subscriber is authenticated, the MSP launches an accounting process based on the subscriber's realm while the CSP may launch an accounting process associated with the subscriber identifier. The cost of rented Points Of Presence capacity is based on total connection time and on the number of simultaneous connections established by the MSP for the CSP, combined with predetermined thresholds.