W3Cache server <-> client

• checking for presence of requested data in the cache
• fetching the data from the cache

W3cache server <-> parent

• checking for presence of requested data in the parent's buffer
• fetching the requested data from the parent

W3cache server -> neighbor

• checking for presence of requested data in the neghbor's buffer
• fetching the requested data from the neighbor

W3cache server <- neighbor

• checking for presence of requested data from neighbor
• transmission of requested data to the neighbor

RED - traffic you should pay the bill for

BLUE - free traffic or the profit

• BASED ON COSTS OF SERVICE:
• materials
• energy
• administrative costs
• amortization

This model does not stimulate the development of service, because there is no need to reduce the costs. There is no possibility to fix the standards of amortization due to different hardware and software platforms used to establish the web cache.

The cost's category is only usable for cache administrators for internal purposes (cost balance).

• BASED ON PROFITS 
• traffic reduction gives measurable profit when you pay your ISP for amount of traffic (billing)
• reduced latency and response time is nonmeasurable profit for client

Profit of web cache provider is corelated with service quality. There is the need for cost reduction and increasing the hit rate

• ABONAMENT
1. profits
• non-measurable profits (changing of external/internal traffic rate, customers comfort)
• measurable profits: savings on external link's bandwidth
2. charging
• agreement between web cache provider and ISP for web cache services
• BILLING
1. profits
• measurable traffic reduction between LAN's and WAN

PROFIT = (W3C <-> customer) - (W3C <-> WAN)

2. charging
• ISP clients do not pay for traffic between the and web cache server (because it's internal in local ISP structure)
• ISP and W3C provider share the profit from traffic reduction -

W3C provider does not charge cache clients, but cooperating ISP

• before IPv6 there is no good mechanism for billing
• you could have an abonament for users will independent services (like DNS) and billing for data requested by user such as WWW objects
• you could enforce users for using web cache and charge them for WWW requests using web cache server's logs for accounting