ices in the piconet, and to determine the characteristics of available services. Chapter Ten Services are discovered using a request/response model, where an application sends out a protocol data unit requesting information on services available on a particular L2CAP connection, and awaits a response from the target device. Service discovery can be either by searching, requesting information on a specific desired service, or by browsing, requesting information on all available services. Bluetooth in Practice A Bluetooth piconet is established by the process of device discovery and pairing between master and discovered slave devices. This process can be repeated many times to create a PAN with up to 7 active slave devices, although 255 slave devices can remain connected to the piconet in the parked state. During the pairing process, the slave device receives a frequency hop synchronisation data packet, based on the master device's 48-bit MAC address, in order to follow the frequency hopping pattern. Once this low- level connection is made, the master device establishes a service discovery protocol (SDP) connection to determine which profile will be used to communicate with the slave device. LMP is then used to configure the link according to the specific service requirements. The two devices also exchange a passphrase which may be used to generate an encryption key to ensure secure communication, depending on security settings which are discussed further in Chapter 11. An example of a Bluetooth piconet, and the associated profiles used for the various device pairings is shown in Table 10-5. If the mobile phone in the above example is then paired with a Bluetooth enabled headset, it will become the master device in a second piconet, thus forming a scatternet. The mobile phone will then time-share between the two piconets. Time slots will be allocated to it by the master device in the first piconet and it will in turn allocate time slots to the headset and any other paired devices in the second piconet. Since the fr