Project PDA

A Bluetooth device playing the role of the "master" can communicate with up to 7 devices playing the role of the "slave". This network "group of up to 8 devices" (1 master + 7 slaves) is called a piconet.

A piconet is an ad-hoc computer network of devices using Bluetooth technology protocols to allow one master device to interconnect with up to seven active slave devices (because a three-bit MAC address is used). Up to 255 further slave devices can be inactive, or parked, which the master device can bring into active status at any time.

At any given time, data can be transferred between the master and 1 slave; but the master switches rapidly from slave to slave in a round-robin fashion. (Simultaneous transmission from the master to multiple slaves is possible, but not used much in practice). Either device may switch the master/slave role at any time.

Bluetooth specification allows connecting 2 or more piconets together to form a scatternet, with some devices acting as a bridge by simultaneously playing the master role in one piconet and the slave role in another piconet. These devices have yet to come, though are supposed to appear in 2007.

Setting up connections

Any Bluetooth device will transmit the following sets of information on demand:

• Device Name
• Device Class
• List of services
• Technical information eg: device features, manufacturer, Bluetooth specification, clock offset

Anything may perform an "inquiry" to find other devices to which to connect, and any device can be configured to respond to such inquiries. However, if the device trying to connect knows the address of the device it will always respond to direct connection requests and will transmit the information shown in the list above if requested for it. Use of the device's services however may require pairing or its owner to accept but the connection itself can be started by any device and be held until it goes out of range. Some devices can only be connected to one device at a time and connecting to them will prevent them from connecting to other devices and showing up in inquiries until they disconnect the other device.

Every device has a unique 48-bit address. However, these addresses are generally not shown in inquiries and instead friendly "Bluetooth names" are used which can be set by the user, and will appear when another user scans for devices and in lists of paired devices.

Most phones have the Bluetooth name set to the manufacturer and model of the phone by default. Most phones and laptops will only show the Bluetooth names and special programs that are required to get additional information about remote devices. This can get confusing as, for example, there could be several phones in range named "T610" (see "Bluejacking").

Pairing

Pairs of devices may establish a trusted relationship by learning (by user input) a shared secret known as a "passkey". A device that wants to communicate only with a trusted device can cryptographically authenticate the identity of the other device. Trusted devices may also encrypt the data that they exchange over the air so that no one can listen in. The encryption can however be turned off and passkeys are stored on the device's file system and not the Bluetooth chip itself. Since the Bluetooth address is permanent, a pairing will be preserved even if the Bluetooth name is changed. Pairs can be deleted at any time by either device. Devices will generally require pairing or will prompt the owner before it allows a remote device to use any or most of its services. Some devices such as Sony Ericsson phones will usually accept OBEX business cards and notes without any pairing or prompts.

Certain printers and access points will allow any device to use its services by default much like unsecured Wi-Fi networks.