| Communication and connection | | | | however be turned off and passkeys are stored |
| A Bluetooth device playing the role of the | | | | on the device's file system and not the Bluetooth |
| "master" can communicate with up to seven | | | | chip itself. Since the Bluetooth address is |
| devices playing the role of the "slave". This | | | | permanent, a pairing will be preserved even if the |
| network "group of up to 8 devices" (one master | | | | Bluetooth name is changed. Pairs can be deleted |
| and seven slaves) is called a piconet. | | | | at any time by either device. Devices will generally |
| A piconet is an ad-hoc computer network of | | | | require pairing or will prompt the owner before it |
| devices using Bluetooth technology protocols to | | | | allows a remote device to use any or most of its |
| allow one master device to interconnect with up | | | | services. Some devices such as Sony Ericsson |
| to seven active slave devices. Up to 255 further | | | | phones will usually accept OBEX business cards |
| slave devices can be inactive, or parked, which | | | | and notes without any pairing or prompts. Certain |
| the master device can bring into active status at | | | | printers and access points will allow any device to |
| anytime. | | | | use its services by default much like unsecured |
| At any given time, data can be transferred | | | | Wi-Fi networks. Pairing algorithms are sometimes |
| between the master and one slave; but the | | | | manufacturer-specific for transmitters and |
| master switches rapidly from slave to slave in a | | | | receivers used in applications such as music and |
| round-robin fashion. (Simultaneous transmission | | | | entertainment. |
| from the master to multiple slaves is possible, but | | | | Air interface |
| not used much in practice.) Either device may | | | | The protocol operates in the license-free ISM |
| switch to the master or slave role at any time. | | | | band at 2.45 GHz. In order to avoid interfering |
| Bluetooth specification allows connecting two or | | | | with other protocols which use the 2.45 GHz |
| more piconets together to form a scatternet, | | | | band, the Bluetooth protocol divides the band into |
| with some devices acting as a bridge by | | | | 79 channels (each 1 MHz wide) and changes |
| simultaneously playing the master role in one | | | | channels up to 1600 times per second. |
| piconet and the slave role in another piconet. | | | | Implementations with versions 1.1 and 1.2 reach |
| These devices have yet to come, though are | | | | speeds of 723.1 kbit/s. Version 2.0 |
| supposed to appear in 2007. | | | | implementations feature Bluetooth Enhanced Data |
| Setting up connections | | | | Rate (EDR), and thus reach 2.1 Mbit/s. Technically |
| Anything may perform an "inquiry" to find other | | | | version 2.0 devices have a higher power |
| devices to which to connect, and any device can | | | | consumption, but the three times faster rate |
| be configured to respond to such inquiries. | | | | reduces the transmission times, effectively |
| However, if the device trying to connect knows | | | | reducing power consumption to half that of 1.x |
| the address of the device it will always respond | | | | devices (assuming equal traffic load). |
| to direct connection requests and will transmit the | | | | Bluetooth differs from Wi-Fi in that the latter |
| information shown in the list above if requested | | | | provides higher throughput and covers greater |
| for it. Use of the device's services however may | | | | distances but requires more expensive hardware |
| require pairing or its owner to accept but the | | | | and higher power consumption. They use the |
| connection itself can be started by any device | | | | same frequency range, but employ different |
| and be held until it goes out of range. Some | | | | multiplexing schemes. While Bluetooth is a cable |
| devices can only be connected to one device at a | | | | replacement for a variety of applications, Wi-Fi is |
| time and connecting to them will prevent them | | | | a cable replacement only for local area network |
| from connecting to other devices and showing up | | | | access. Bluetooth is often thought of as wireless |
| in inquiries until they disconnect the other device. | | | | USB whereas Wi-Fi is wireless Ethernet, both |
| Every device has a unique 48-bit address. | | | | operating at much lower bandwidth than the cable |
| However, these addresses are generally not | | | | systems they are trying to replace. However, this |
| shown in inquiries and instead friendly "Bluetooth | | | | analogy is not entirely accurate since any |
| names" are used which can be set by the user, | | | | Bluetooth device can, in theory, host (be a |
| and will appear when another user scans for | | | | master to) any other Bluetooth device something |
| devices and in lists of paired devices. | | | | that is not universial to USB devices. |
| Most phones have the Bluetooth name set to the | | | | Many USB Bluetooth adapters are available, some |
| manufacturer and model of the phone by default. | | | | of which also include an IrDA adapter. |
| Most phones and laptops will only show the | | | | Older (pre-2003) Bluetooth adapters, however, |
| Bluetooth names and special programs that are | | | | have limited services, offering only the Bluetooth |
| required to get additional information about | | | | Enumerator and a less-powerful Bluetooth Radio |
| remote devices. This can get confusing as, for | | | | incarnation. Such devices are able to link |
| example, there could be several phones in range | | | | computers via Bluetooth, but they unfortunately |
| named "T610" (see "Bluejacking"). | | | | do not offer much in the way of the twelve or |
| Pairing | | | | more services that modern adapters are able to |
| Pairs of devices may establish a trusted | | | | use. |
| relationship by learning (by user input) a shared | | | | Security |
| secret known as a "passkey". A device that | | | | Bluetooth uses the SAFER+ algorithm for |
| wants to communicate only with a trusted device | | | | authentication and key generation. The initialisation |
| can cryptographically authenticate the identity of | | | | key and master key are generated using the E22 |
| the other device. Trusted devices may also | | | | algorithm. The E0 stream cipher is used for |
| encrypt the data that they exchange over the air | | | | encrypting packets. This makes eavesdropping on |
| so that no one can listen in. The encryption can | | | | Bluetooth-enabled devices more difficult. |