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