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Summary form only given. Since its initial implementation, the IP layer has provided a connectionless service and IP packets are routed hop-by-hop. The TCP/IP association provides to the users a communication service with preservation of the content but without any guarantee for the bandwidth and the delay. All applications in the past and many of them today are able to operate in this elastic mode but now with streaming video and the development of business-oriented applications, it is likely that the best effort service will have to be augmented to provide the QoS (quality of service) required by some applications. These new QoS may be related to guarantees, firm or statistical, about bandwidth or delay and will offer to the service provider an opportunity for an increase of the tariffs. We present the three approaches which are today considered to fulfil the new requirements: overprovisioning, integrated service (IntServ), and differentiated service (DiffServ). An attempt is made to identify where these different approaches may take place in the next millenium in particular, in relation with MPLS.