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Chapter 21. Quality of Service > Mechanisms for QoS - Pg. 449

21.2 Mechanism for QoS being defined--and, in some cases, deployed--in the remit of controlled 3GPP and ETSI TISPAN multimedia networks. The approaches to QoS in IP networks are independent of the application layer--they all occur at IP level. This is a key design principle of the Internet, and has the tremendous advantage of allowing the two domains, application layer and transport layer, to evolve separately. Nevertheless, there is a need, at some point, to integrate the SIP application layer with the media transport layer, as we will see during this chapter. The first sections in the present chapter will deal with the application- independent Internet approaches for providing quality of service and policy con- trol. The last sections in this chapter will cover how to integrate the SIP layer (i.e., the control plane) with the previous approaches in an IETF-like multimedia net- work. Chapter 24 will touch upon how these concepts are used, slightly changed, in the Next Generation Networks (NGN) controlled by telecom operators. 449 21.2 Mechanisms for QoS The IETF has developed extensions to the IP architecture and the best-effort ser-