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Mạng lưới Dịch vụ và Hợp đồng Nó rất hữu ích để phân biệt giữa "cao cấp" và "thấp cấp" dịch vụ. dịch vụ cao cấp là những giao diện trực tiếp với khách hàng. Cấp dưới là những dịch vụ mà khách hàng sử dụng gián tiếp và được vô hình đối với họ. Xem xét, ví dụ, mạng Internet vì nó được sử dụng bởi sinh viên và nhân viên của một đại học. Một cấp dịch vụ email; khác là trình duyệt web. Trình duyệt web sử dụng dịch vụ cấp dưới của vận tải dữ liệu Internet. | Pricing Communication Networks Economics Technology and Modelling. Costas Courcoubetis and Richard Weber Copyright 2003 John Wiley Sons Ltd. ISBN 0-470-85130-9 2 Network Services and Contracts It is useful to distinguish between higher-level and lower-level services. Higher-level services are those that interface directly with customers. Lower-level services are those that customers use indirectly and which are invisible to them. Consider for example the Internet as it is used by students and staff of a university. One higher-level service is email another is web browsing. Web browsing uses the lower-level service of Internet data transport to exchange data between users terminals and the servers where web pages reside. The quality of the higher-level web browsing service depends on the quality of the lower-level transport service. That is the speed at which web pages will be delivered to users partly depends on the quality of the network s data transport service. This will be specified in a contract between the university and the network. A transport service can be defined in many ways. It can be defined in terms of a guarantee to transport some amount of information but without any guarantee about how long this will take. It can fully specify the performance that is to be provided and do this at the start of the service. Alternatively it can respond to changing network load conditions and continuously renegotiate some qualities of the information transfer with the data source. We investigate these possibilities in this chapter. Finally we note that the provision of a service involves not only a flow of information but also a flow of value. Flow of information concerns data transport whereas flow of value concerns the benefit that is obtained. One or both parties can benefit from the flow of value. However if one party enjoys most of the value it is reasonable that he should pay for the service. For example if an information server sends a customer advertisements
