## 1 Introduction  
Progress in Telecommunications and Networking is fostering the development of high-speed and ubiquitous networks, both wired and wireless (_i.e._ heterogeneous configurations), characterized by an unprecedented degree of transport capacity and flexibility. Open-service framework concepts will enable the provisioning of a wide spectrum of services merging voice and data features. It offers potential benefits to shareholders by enabling application services to make better use of network functions (and thereby retain more of the services' value-add within the network). The lack of access and location transparency as well as of re-configurability and adaptability capabilities has proven to be a major shortcoming for the evolution towards a universal 4G mobile wireless network [1]. Therefore, the future trend is going to provide the transmission rates required by most potential users, but the practical question arises of what type of services can be provided, as well as when and where [2]. Moreover, streaming of multimedia content to different receivers across heterogeneous networks is a challenge in the current Internet [3]. There exists a clear trend for the convergence of IP protocol to wireless, that is, what we now call wireless IP, leading to the Wireless Internet [4].  
Addressing some of these issues, this paper proposes a cooperative processing of multimedia content (namely, double boomerang approach) for dynamic QoS management, exploiting the tracing watermarking technique recently introduced in [5]. More specifically, we employed the transmitted video-sequences to monitor the QoS in a videoconference call: the video-sequence of every active user travels on the communication link one time as video (transparent mode), one time as watermark (hidden mode). Therefore, every video-sequence of each user involved in the communication describes a boomerang trajectory. Moreover, real-time video transmission is very sensitive to burst errors caused by the time varying signal strength received from the wireless channels. Even one bit error might cause severe degradation in video quality. Therefore, it is obligatory for the video encoder to protect the video data from the channel errors by using error control techniques such as forward error correction (FEC) and the automatic repeat request (ARQ). Our watermarking technique can also be used for quality control (such as in the outer loop power control in UMTS environment) and to implement error control approaches, e.g. FEC or the ARQ with piggybacking or the Hybrid ARQ, such as in classical UMTS applications. In such a way, the advantages of distributing the management process allow: (i) an easier and more precise localization of the cause of QoS problems, (ii) a better knowledge of local situations, (iii) a lower complexity for a single QoS agent (_i.e._ the user equipment) and (iv) an increase in possible actions. Moreover, the basic idea of using a two-way spread spectrum communication (called double boomerang transmission system) was exploited in [6] for the purpose of sharing data and positioning information in vehicular networks. The remainder of this paper is organized as follows. Section 2 is about the state of the art of the QoS techniques used in wireless networks. In the first half of Section 3, the principles of the tracing watermarking approach are briefly summarized, while the cooperative QoS assessment, obtained exploiting the tracing watermarking technique, is detailed in the second half of the Section. Our numerical results and comparisons are outlined in Section 4, and finally, our conclusions are depicted in Section 5. A future work Section is developed in Section 6.