Enabling rapid wireless system composition through layer-2 discovery

Although small mobile computers have processors whose capabilities are increasing, often they still are resource constrained in terms of performing many common computing tasks. Composition is a technique that overcomes this limitation by wirelessly connecting several nearby devices together to share their resources to create a logical platform that is better suited to a given task. However, current standards for ad hoc wireless networks were not designed for this goal, and currently, wireless computers cannot discover services on other devices without first making layer- 3 network connections between them. This requires users to engage in a lengthy and repetitive sequential connection process to find these services on the various computers and is a barrier for effective use. In this article, we quantify the layer-3 discovery overhead for both WiFi and Bluetooth and propose a mechanism to address this problem enabling users to rapidly form ad hoc compositions using a layer-2 service discovery mechanism. To achieve this result, we propose extensions to existing wireless standards by adding service information to beacons that typically are used for device discovery. An architecture is described that also enables legacy service information to be aggregated with additional service descriptions specific to composition and further encoded in layer-2 wireless beacons. Finally, we present measurements of layer-2 discovery implemented using the nascent UWB wireless standard, demonstrating its efficacy for composable systems.

Composition and Service Discovery

Sharing resources between devices through wireless services is a key building block of a composition system. For example, users may want to move content between their mp3 players and their home entertainment systems; or from various recording devices (such as cameras, camcorders, or camera phones) to a home PC. Existing network file system protocols such as Samba can provide this capability. Users also might wish to make use of a larger display than is available on their mobile device. Service solutions such as virtual network computing (VNC) and Remote Desktop Protocol (RDP) are available for this purpose. In fact, sharing resources in general can be achieved by using existing network services or designing new ones; and all these services typically are advertised at the IP layer — layer-3 in the open systems interconnection (OSI) model. However, in existing wireless standards, there are no mechanisms to advertise these services before a link-layer (layer-2) connection is established. Thus, layer-2 service advertisement and discovery is an essential ingredient of a wireless system that supports dynamic composition.