SERVICE DISCOVERY PROTOCOL
The Service Discovery Protocol (SDP) provides a means to determine which Bluetooth services are available on a particular device. A Bluetooth device may act as an SDP client querying services, an SDP server providing services, or both. A single Bluetooth device will have no more than one SDP server, but may act as a client to more than one remote device. SDP provides access only to information about services; utilization of those services must be provided via another Bluetooth or third-party protocol. In addition, SDP provides no notification mechanism to indicate that an SDP server, or any specific service, has become
available or unavailable as may occur when the services available on a device change, or when a device comes in or out of RF proximity. This would be a common occurrence in a network supporting mobile devices. The client may, of course, poll a server to detect unavailability, but other means are required to detect a server or service that has recently become available.