Communication services such as electronic mail, file transfer, web browsing, online chat, IP telephony and real-time video are frequently used in today''s life. To provide these services with a good quality of service, the capacities of the network links should be large enough to prevent data traffic to be delayed. The book focuses on the problem of dimensioning a link in a communication network which carries data of both consumers and a small number of corporate users. The corporate users have an access rate that is much larger than that of the consumers, but they are only active a small fraction of the time. The main goal is to develop a modeling approach to determine the capacity of the link that is required in order to achieve specific Quality-of-Service levels in terms of delays and user throughputs. In particular, impact of the presence of corporate users on the required link capacity will be examined.