atus: Joined PUBLISH Status: deafen Px NOTIFY Status: P1 deafens Px FIGURE 14.13 Narrowcasting control status notification. 14.5.3 Architectural and Interface Refinement Future research includes allowing selection of multiple sources and sinks for narrowcasting commands to support arbitrary multiuser narrowcasting con- figurations. A basic challenge is that the SIP side-conference model is not rich enough to support arbitrary multiparty narrowcasting with orthogonal attributes. A related engineering issue is that MSCML is not expressive enough to convey such detailed, articulated channel crossbar control. We are also considering other conference models with multiple policy servers or media mixers. For instance, as multimedia processing becomes less of a specialized service and more of a commodity, a grid computing paradigm could be used instead of a centralized server architecture to mix and deliver media streams to distributed narrowcasting-enabled terminals. Muffle (partial deafen) and muzzle (partial mute) will enrich the narrowcasting state space [24,25]. We will also generalize policy determination in metasessions with multiple simultaneous chatspaces, in which one has presence across multiple virtual spaces, each with multiple conversants, including "multipresence," allowing designation of multiple instances of "self" [26]. 14.5.4 Convergence Besides wireline-connected workstation-based interfaces, narrowcasting might find an even more fertile platform in mobile devices. The "four-play" © 2009 by Taylor & Francis Group, LLC Narrowcasting in SIP: Articulated Privacy Control convergence of telephony, television/video, internet, and wireless is driving a proliferation of new devices and services. Mobile terminals, almost as intimate as clothing, are a kind of wearable computer, and a diversity of next-generation functionalities and form factors for smartphones is emerging, including mobile stereotelephony, inspired by cyberspatial audio [27] and augmented audio models. Meanwhile, location-based services-along 