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Giới thiệu về IP và ATM - Thiết kế và hiệu suất P15

QUALITY OF SERVICE AND TRAFFIC AGGREGATION In recent years there have been many different proposals (such as Integrated Services [15.1], Differentiated Services [15.2], and RSVP [15.3]) for adding quality of service (QoS) support to the current best-effort mode of operation in IP networks. In order to provide guaranteed QoS, a network must be able to anticipate traffic demands, assess its ability to supply the necessary resources, and act either to accept or reject these demands for service. This means that users must state their communications requirements in advance, in some sort of service request mechanism | Introduction to IP and ATM Design Performance With Applications Analysis Software Second Edition. J M Pitts J A Schormans Copyright 2000 John Wiley Sons Ltd ISBNs 0-471-49187-X Hardback 0-470-84166-4 Electronic 15 Resource Reservation go with the flow QUALITY OF SERVICE AND TRAFFIC AGGREGATION In recent years there have been many different proposals such as Integrated Services 15.1 Differentiated Services 15.2 and RSVP 15.3 for adding quality of service QoS support to the current best-effort mode of operation in IP networks. In order to provide guaranteed QoS a network must be able to anticipate traffic demands assess its ability to supply the necessary resources and act either to accept or reject these demands for service. This means that users must state their communications requirements in advance in some sort of service request mechanism. The details of the various proposals are outside the scope of this book but in this chapter we analyse the key queueing behaviours and performance characteristics underlying the resource assessment. To be able to predict the impact of new demands on resources the network needs to record state information. Connection-orientated technologies such as ATM record per-connection information in the network as hard state. This information must be explicitly created for the duration of the connection and removed when no longer needed. An alternative approach adopted in RSVP is soft state where per-flow information is valid for a pre-defined time interval after which it needs to be refreshed or if not it lapses. Both approaches though face the challenge of scalability. Per-flow or per-connection behaviour relates to individual customer needs. With millions of customers each one initiating many connections or flows it is important that the network can handle these efficiently whilst still providing guaranteed QoS. This is where traffic aggregation comes in. ATM technology introduces the concept of the virtual path - a bundle of virtual .