[guide.chat] Blue Tooth
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Bluetooth
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This article is about the electronic protocol. For the medieval King of
Denmark, see Harald I of Denmark.
File:BluetoothLogo
Bluetooth combo wordmark
Bluetooth is a proprietary open wireless technology standard for
exchanging data over short distances (using short-wavelength radio
transmissions in the ISM band from 2400-2480 MHz) from fixed and mobile
devices, creating personal area networks (PANs) with high levels of
security. Created by telecoms vendor Ericsson in 1994,[1] it was
originally conceived as a wireless alternative to RS-232 data cables. It
can connect several devices, overcoming problems of synchronization.
Bluetooth is managed by the Bluetooth Special Interest Group, which has
more than 16,000 member companies in the areas of telecommunication,
computing, networking, and consumer electronics.[2] The SIG oversees the
development of the specification, manages the qualification program, and
protects the trademarks.[3] To be marketed as a Bluetooth device, it
must be qualified to standards defined by the SIG. A network of patents
is required to implement the technology and are only licensed to those
qualifying devices; thus the protocol, whilst open, may be regarded as
proprietary.[4]
Contents [hide]
1 Name and logo
2 Implementation
2.1 Communication and connection
3 Uses
3.1 Bluetooth profiles
3.2 List of applications
3.3 Bluetooth vs. Wi-Fi (IEEE 802.11)
3.4 Devices
4 Computer requirements
4.1 Operating system support
5 Mobile phone requirements
6 Specifications and features
6.1 Bluetooth v1.0 and v1.0B
6.2 Bluetooth v1.1
6.3 Bluetooth v1.2
6.4 Bluetooth v2.0 + EDR
6.5 Bluetooth v2.1 + EDR
6.6 Bluetooth v3.0 + HS
6.6.1 Ultra-wideband
6.7 Bluetooth v4.0
7 Technical information
7.1 Bluetooth protocol stack
7.1.1 LMP
7.1.2 AVRCP
7.1.3 L2CAP
7.1.4 SDP
7.1.5 RFCOMM
7.1.6 BNEP
7.1.7 AVCTP
7.1.8 AVDTP
7.1.9 TCS
7.1.10 Adopted protocols
7.2 Baseband error correction
7.3 Setting up connections
7.4 Pairing/Bonding
7.4.1 Motivation
7.4.2 Implementation
7.4.3 Pairing mechanisms
7.4.4 Security Concerns
7.5 Air interface
8 Security
8.1 Overview
8.2 Bluejacking
8.3 History of security concerns
8.3.1 2001 - 2004
8.3.2 2005
8.3.3 2006
8.3.4 2007
9 Health concerns
10 Bluetooth Innovation World Cup marketing initiative
11 See also
12 References
13 External links
[edit]
Name and logo
File:Bluetooth
Bluetooth logo
The word "Bluetooth" is an anglicised version of the Scandinavian
Blåtand/Blåtann, the epithet of the tenth-century king Harald I of
Denmark and parts of Norway who united dissonant Danish tribes into a
single kingdom. The implication is that Bluetooth does the same with
communications protocols, uniting them into one universal standard.[5][6][7]
The Bluetooth logo is a bind rune merging the Younger Futhark runes
Runic letter ior.svg (Hagall) (?) and Runic letter berkanan.svg
(Bjarkan) (?), Harald's initials.
[edit]
Implementation
Bluetooth uses a radio technology called frequency-hopping spread
spectrum, which chops up the data being sent and transmits chunks of it
on up to 79 bands (1 MHz each; centered from 2402 to 2480 MHz) in the
range 2,400-2,483.5 MHz (allowing for guard bands). This range is in the
globally unlicensed Industrial, Scientific and Medical (ISM) 2.4 GHz
short-range radio frequency band. It usually performs 800 hops per
second, with AFH enabled. [8]
Originally Gaussian frequency-shift keying (GFSK) modulation was the
only modulation scheme available; subsequently, since the introduction
of Bluetooth 2.0+EDR, p/4-DQPSK and 8DPSK modulation may also be used
between compatible devices. Devices functioning with GFSK are said to be
operating in basic rate (BR) mode where an instantaneous data rate of 1
Mbit/s is possible. The term Enhanced Data Rate (EDR) is used to
describe p/4-DPSK and 8DPSK schemes, each giving 2 and 3 Mbit/s
respectively. The combination of these (BR and EDR) modes in Bluetooth
radio technology is classified as a "BR/EDR radio".
Bluetooth is a packet-based protocol with a master-slave structure. One
master may communicate with up to 7 slaves in a piconet; all devices
share the master's clock. Packet exchange is based on the basic clock,
defined by the master, which ticks at 312.5 µs intervals. Two clock
ticks make up a slot of 625 µs; two slots make up a slot pair of 1250
µs. In the simple case of single-slot packets the master transmits in
even slots and receives in odd slots; the slave, conversely, receives in
even slots and transmits in odd slots. Packets may be 1, 3 or 5 slots
long but in all cases the master transmit will begin in even slots and
the slave transmit in odd slots.
Bluetooth provides a secure way to connect and exchange information
between devices such as faxes, mobile phones, telephones, laptops,
personal computers, printers, Global Positioning System (GPS) receivers,
digital cameras, and video game consoles.
[edit]
Communication and connection
A master Bluetooth device can communicate with a maximum of seven
devices in a piconet (an ad-hoc computer network using Bluetooth
technology), though not all devices support this limit. The devices can
switch roles, by agreement, and the slave can become the master (for
example, a headset initiating a connection to a phone will necessarily
begin as master, as initiator of the connection; but may subsequently
prefer to be slave).
The Bluetooth Core Specification provides for the connection of two or
more piconets to form a scatternet, in which certain devices
simultaneously play the master role in one piconet and the slave role in
another.
At any given time, data can be transferred between the master and one
other device (except for the little-used broadcast mode[citation
needed]). The master chooses which slave device to address; typically,
it switches rapidly from one device to another in a round-robin fashion.
Since it is the master that chooses which slave to address, whereas a
slave is (in theory) supposed to listen in each receive slot, being a
master is a lighter burden than being a slave. Being a master of seven
slaves is possible; being a slave of more than one master is
difficult.[citation needed] The specification is vague as to required
behaviour in scatternets.
Many USB Bluetooth adapters or "dongles" are available, some of which
also include an IrDA adapter. Older (pre-2003) Bluetooth dongles,
however, have limited capabilities, offering only the Bluetooth
Enumerator and a less-powerful Bluetooth Radio incarnation.[citation
needed] Such devices can link computers with Bluetooth with a distance
of 100 meters, but they do not offer as many services as modern adapters
do.[clarification needed]
[edit]
Uses
Bluetooth is a standard wire-replacement communications protocol
primarily designed for low power consumption, with a short range
(power-class-dependent, but effective ranges vary in practice; see table
below) based on low-cost transceiver microchips in each device.[9]
Because the devices use a radio (broadcast) communications system, they
do not have to be in visual line of sight of each other, however a quasi
optical wireless path must be viable.[2]
Class
Maximum permitted power
Range
(m)
(mW)
(dBm)
Class 1
100
20
~100
Class 2
2.5
4
~10
Class 3
1
0
~5
The effective range varies due to propagation conditions, material
coverage, production sample variations, antenna configurations and
battery conditions. In most cases the effective range of class 2 devices
is extended if they connect to a class 1 transceiver, compared to a pure
class 2 network. This is accomplished by the higher sensitivity and
transmission power of Class 1 devices.[10]
Version
Data rate
Maximum application throughput
Version 1.2
1 Mbit/s
0.7 Mbit/s
Version 2.0 + EDR
3 Mbit/s
2.1 Mbit/s
Version 3.0 + HS
See Version 3.0+HS.
Version 4.0
See Version 4.0LE.
While the Bluetooth Core Specification does mandate minimums for range,
the range of the technology is application specific and is not limited.
Manufacturers may tune their implementations to the range needed to
support individual use cases.
[edit]
Bluetooth profiles
Main article: Bluetooth profile
To use Bluetooth wireless technology, a device has to be able to
interpret certain Bluetooth profiles, which are definitions of possible
applications and specify general behaviors that Bluetooth enabled
devices use to communicate with other Bluetooth devices. These profiles
include settings to parametrize and to control the communication from
start. Adherence to profiles saves the time for transmitting the
parameters anew before the bi-directional link becomes effective. There
are a wide range of Bluetooth profiles that describe many different
types of applications or use cases for devices.[11]
[edit]
List of applications
File:Product1
A typical Bluetooth mobile phone headset.
?Wireless control of and communication between a mobile phone and a
handsfree headset. This was one of the earliest applications to become
popular.
?Wireless control of and communication between a mobile phone and a
Bluetooth compatible car stereo system
?Wireless Bluetooth headset and Intercom.
?Wireless networking between PCs in a confined space and where little
bandwidth is required.
?Wireless communication with PC input and output devices, the most
common being the mouse, keyboard and printer.
?Transfer of files, contact details, calendar appointments, and
reminders between devices with OBEX.
?Replacement of previous wired RS-232 serial communications in test
equipment, GPS receivers, medical equipment, bar code scanners, and
traffic control devices.
?For controls where infrared was often used.
?For low bandwidth applications where higher USB bandwidth is not
required and cable-free connection desired.
?Sending small advertisements from Bluetooth-enabled advertising
hoardings to other, discoverable, Bluetooth devices.[12]
?Wireless bridge between two Industrial Ethernet (e.g., PROFINET) networks.
?Three seventh-generation game consoles, Nintendo's Wii[13] and Sony's
PlayStation 3 and PSP Go, use Bluetooth for their respective wireless
controllers.
?Dial-up internet access on personal computers or PDAs using a
data-capable mobile phone as a wireless modem.
?Short range transmission of health sensor data from medical devices to
mobile phone, set-top box or dedicated telehealth devices.[14]
?Allowing a DECT phone to ring and answer calls on behalf of a nearby
cell phone
?Real-time location systems (RTLS), are used to track and identify the
location of objects in real-time using "Nodes" or "tags" attached to, or
embedded in the objects tracked, and "Readers" that receive and process
the wireless signals from these tags to determine their locations[15]
?Personal security application on mobile phones for prevention of theft
or loss of items. The protected item has a Bluetooth marker (e.g. a tag)
that is in constant communication with the phone. If the connection is
broken (the marker is out of range of the phone) then an alarm is
raised. This can also be used as a man overboard alarm. A product using
this technology has been available since 2009.[16]
[edit]
Bluetooth vs. Wi-Fi (IEEE 802.11)
Bluetooth and Wi-Fi (the brand name for products using IEEE 802.11
standards) have some similar applications: setting up networks,
printing, or transferring files. Wi-Fi is intended as a replacement for
cabling for general local area network access in work areas. This
category of applications is sometimes called wireless local area
networks (WLAN). Bluetooth was intended for portable equipment and its
applications. The category of applications is outlined as the wireless
personal area network (WPAN). Bluetooth is a replacement for cabling in
a variety of personally carried applications in any setting and can also
support fixed location applications such as smart energy functionality
in the home (thermostats, etc.).
Wi-Fi is a wireless version of a common wired Ethernet network, and
requires configuration to set up shared resources, transmit files, and
to set up audio links (for example, headsets and hands-free devices).
Wi-Fi uses the same radio frequencies as Bluetooth, but with higher
power, resulting in higher bit rates and better range from the base
station. The nearest equivalents in Bluetooth are the DUN profile, which
allows devices to act as modem interfaces, and the PAN profile, which
allows for ad-hoc networking.[citation needed]
[edit]
Devices
File:Drone_4
A Bluetooth USB dongle with a 100 m range. The MacBook Pro, shown, also
has a built in Bluetooth adaptor.
Bluetooth exists in many products, such as the iPod Touch, Lego
Mindstorms NXT, PlayStation 3, PSP Go, telephones, the Nintendo Wii, and
some high definition headsets, modems, and watches.[17] The technology
is useful when transferring information between two or more devices that
are near each other in low-bandwidth situations. Bluetooth is commonly
used to transfer sound data with telephones (i.e., with a Bluetooth
headset) or byte data with hand-held computers (transferring files).
Bluetooth protocols simplify the discovery and setup of services between
devices.[18] Bluetooth devices can advertise all of the services they
provide.[19] This makes using services easier because more of the
security, network address and permission configuration can be automated
than with many other network types.[18]
[edit]
Computer requirements
File:BluetoothUSB
A typical Bluetooth USB dongle.
File:DELL_TrueMobile_350_Bluet?
An internal notebook Bluetooth card (14×36×4 mm).
A personal computer that does not have embedded Bluetooth can be used
with a Bluetooth adapter that will enable the PC to communicate with
other Bluetooth devices (such as mobile phones, mice and keyboards).
While some desktop computers and most recent laptops come with a
built-in Bluetooth radio, others will require an external one in the
form of a dongle.
Unlike its predecessor, IrDA, which requires a separate adapter for each
device, Bluetooth allows multiple devices to communicate with a computer
over a single adapter.
[edit]
Operating system support
For more details on this topic, see Bluetooth stack.
Apple has supported Bluetooth since Mac OS X v10.2 which was released in
2002.[20]
For Microsoft platforms, Windows XP Service Pack 2 and SP3 releases have
native support for Bluetooth 1.1, 2.0 and 2.0+EDR.[21] Previous versions
required users to install their Bluetooth adapter's own drivers, which
were not directly supported by Microsoft.[22] Microsoft's own Bluetooth
dongles (packaged with their Bluetooth computer devices) have no
external drivers and thus require at least Windows XP Service Pack 2.
Windows Vista RTM/SP1 with the Feature Pack for Wireless or Windows
Vista SP2 support Bluetooth 2.1+EDR.[21] Windows 7 supports Bluetooth
2.1+EDR and Extended Inquiry Response (EIR).[21]
The Windows XP and Windows Vista/Windows 7 Bluetooth stacks support the
following Bluetooth profiles natively: PAN, SPP, DUN, HID, HCRP. The
Windows XP stack can be replaced by a third party stack which may
support more profiles or newer versions of Bluetooth. The Windows
Vista/Windows 7 Bluetooth stack supports vendor-supplied additional
profiles without requiring the Microsoft stack to be replaced.[21]
Linux has two popular Bluetooth stacks, BlueZ and Affix. The BlueZ stack
is included with most Linux kernels and was originally developed by
Qualcomm.[23] The Affix stack was developed by Nokia. FreeBSD features
Bluetooth support since its 5.0 release. NetBSD features Bluetooth
support since its 4.0 release. Its Bluetooth stack has been ported to
OpenBSD as well.
[edit]
Mobile phone requirements
A Bluetooth-enabled mobile phone is able to pair with many devices. To
ensure the broadest support of feature functionality together with
legacy device support, the Open Mobile Terminal Platform (OMTP) forum
has published a recommendations paper, entitled "Bluetooth Local
Connectivity".[24]
[edit]
Specifications and features
The Bluetooth specification was developed as a cable replacement in 1994
by Jaap Haartsen and Sven Mattisson, who were working for Ericsson in
Lund, Sweden.[25] The specification is based on frequency-hopping spread
spectrum technology.
The specifications were formalized by the Bluetooth Special Interest
Group (SIG). The SIG was formally announced on May 20, 1998. Today it
has a membership of over 16,000 companies worldwide. It was established
by Ericsson, IBM, Intel, Toshiba and Nokia, and later joined by many
other companies.
All versions of the Bluetooth standards are designed for downward
compatibility. That lets the latest standard cover all older versions.
[edit]
Bluetooth v1.0 and v1.0B
Versions 1.0 and 1.0B had many problems, and manufacturers had
difficulty making their products interoperable. Versions 1.0 and 1.0B
also included mandatory Bluetooth hardware device address (BD_ADDR)
transmission in the Connecting process (rendering anonymity impossible
at the protocol level), which was a major setback for certain services
planned for use in Bluetooth environments.
[edit]
Bluetooth v1.1
?Ratified as IEEE Standard 802.15.1-2002[26]
?Many errors found in the 1.0B specifications were fixed.
?Added support for non-encrypted channels.
?Received Signal Strength Indicator (RSSI).
[edit]
Bluetooth v1.2
This version is backward compatible with 1.1 and the major enhancements
include the following:
?Faster Connection and Discovery
?Adaptive frequency-hopping spread spectrum (AFH), which improves
resistance to radio frequency interference by avoiding the use of
crowded frequencies in the hopping sequence.
?Higher transmission speeds in practice, up to 721 kbit/s,[27] than in v1.1.
?Extended Synchronous Connections (eSCO), which improve voice quality of
audio links by allowing retransmissions of corrupted packets, and may
optionally increase audio latency to provide better support for
concurrent data transfer.
?Host Controller Interface (HCI) support for three-wire UART.
?Ratified as IEEE Standard 802.15.1-2005[28]
?Introduced Flow Control and Retransmission Modes for L2CAP.
[edit]
Bluetooth v2.0 + EDR
This version of the Bluetooth Core Specification was released in 2004
and is backward compatible with the previous version 1.2. The main
difference is the introduction of an Enhanced Data Rate (EDR) for faster
data transfer. The nominal rate of EDR is about 3 Mbit/s, although the
practical data transfer rate is 2.1 Mbit/s.[27] EDR uses a combination
of GFSK and Phase Shift Keying modulation (PSK) with two variants,
p/4-DQPSK and 8DPSK.[29] EDR can provide a lower power consumption
through a reduced duty cycle.
The specification is published as "Bluetooth v2.0 + EDR" which implies
that EDR is an optional feature. Aside from EDR, there are other minor
improvements to the 2.0 specification, and products may claim compliance
to "Bluetooth v2.0" without supporting the higher data rate. At least
one commercial device states "Bluetooth v2.0 without EDR" on its data
sheet.[30]
[edit]
Bluetooth v2.1 + EDR
Bluetooth Core Specification Version 2.1 + EDR is fully backward
compatible with 1.2, and was adopted by the Bluetooth SIG on July 26,
2007.[29]
The headline feature of 2.1 is secure simple pairing (SSP): this
improves the pairing experience for Bluetooth devices, while increasing
the use and strength of security. See the section on Pairing below for
more details.[31]
2.1 allows various other improvements, including "Extended inquiry
response" (EIR), which provides more information during the inquiry
procedure to allow better filtering of devices before connection; and
sniff subrating, which reduces the power consumption in low-power mode.
[edit]
Bluetooth v3.0 + HS
Version 3.0 + HS of the Bluetooth Core Specification[29] was adopted by
the Bluetooth SIG on April 21, 2009. Bluetooth 3.0+HS supports
theoretical data transfer speeds of up to 24 Mbit/s, though not over the
Bluetooth link itself. Instead, the Bluetooth link is used for
negotiation and establishment, and the high data rate traffic is carried
over a collocated 802.11 link.
The main new feature is AMP (Alternate MAC/PHY), the addition of 802.11
as a high speed transport. The High-Speed part of the specification is
not mandatory, and hence only devices sporting the "+HS" will actually
support the Bluetooth over 802.11 high-speed data transfer. A Bluetooth
3.0 device without the "+HS" suffix will not support High Speed, and
needs to only support a feature introduced in Core Specification Version
3.0 [32] or earlier Core Specification Addendum 1.[33]
L2CAP Enhanced modes
Enhanced Retransmission Mode (ERTM) implements reliable L2CAP channel,
while Streaming Mode (SM) implements unreliable channel with no
retransmission or flow control. Introduced in Core Specification Addendum 1.
Alternate MAC/PHY
Enables the use of alternative MAC and PHYs for transporting Bluetooth
profile data. The Bluetooth radio is still used for device discovery,
initial connection and profile configuration, however when large
quantities of data need to be sent, the high speed alternate MAC PHY
802.11 (typically associated with Wi-Fi) will be used to transport the
data. This means that the proven low power connection models of
Bluetooth are used when the system is idle, and the faster radio is used
when large quantities of data need to be sent. AMP links require
enhanced L2CAP modes.
Unicast Connectionless Data
Permits service data to be sent without establishing an explicit L2CAP
channel. It is intended for use by applications that require low latency
between user action and reconnection/transmission of data. This is only
appropriate for small amounts of data.
Enhanced Power Control
Updates the power control feature to remove the open loop power control,
and also to clarify ambiguities in power control introduced by the new
modulation schemes added for EDR. Enhanced power control removes the
ambiguities by specifying the behaviour that is expected. The feature
also adds closed loop power control, meaning RSSI filtering can start as
the response is received. Additionally, a "go straight to maximum power"
request has been introduced. This is expected to deal with the headset
link loss issue typically observed when a user puts their phone into a
pocket on the opposite side to the headset.
[edit]
Ultra-wideband
The high speed (AMP) feature of Bluetooth v3.0 was originally intended
for UWB, but the WiMedia Alliance, the body responsible for the flavor
of UWB intended for Bluetooth, announced in March 2009 that it was
disbanding, and ultimately UWB was omitted from the Core v3.0
specification.[34]
On March 16, 2009, the WiMedia Alliance announced it was entering into
technology transfer agreements for the WiMedia Ultra-wideband (UWB)
specifications. WiMedia has transferred all current and future
specifications, including work on future high speed and power optimized
implementations, to the Bluetooth Special Interest Group (SIG), Wireless
USB Promoter Group and the USB Implementers Forum. After the successful
completion of the technology transfer, marketing and related
administrative items, the WiMedia Alliance will cease
operations.[35][36][37][38][39][40]
In October 2009 the Bluetooth Special Interest Group suspended
development of UWB as part of the alternative MAC/PHY, Bluetooth v3.0 +
HS solution. A small, but significant, number of former WiMedia members
had not and would not sign up to the necessary agreements for the IP
transfer. The Bluetooth SIG is now in the process of evaluating other
options for its longer term roadmap.[41]
[edit]
Bluetooth v4.0
The Bluetooth SIG completed the Bluetooth Core Specification version
4.0, which includes Classic Bluetooth, Bluetooth high speed and
Bluetooth low energy protocols. Bluetooth high speed is based on Wi-Fi,
and Classic Bluetooth consists of legacy Bluetooth protocols. This
version has been adopted as of June 30, 2010.
Bluetooth low energy (BLE), previously known as WiBree,[42] is a subset
to Bluetooth v4.0 with an entirely new protocol stack for rapid build-up
of simple links. As an alternative to the Bluetooth standard protocols
that were introduced in Bluetooth v1.0 to v3.0, it is aimed at very low
power applications running off a coin cell. Chip designs allow for two
types of implementation, dual-mode, single-mode and enhanced past
versions.[43] The provisional names Wibree and Bluetooth ULP (Ultra Low
Power) were abandoned and the BLE name was used for a while. In late
2011, new logos "Bluetooth Smart Ready" for hosts and "Bluetooth Smart"
for sensors were introduced as the general-public face of BLE.[44]
?In a single mode implementation the low energy protocol stack is
implemented solely. CSR,[45] Nordic Semiconductor[46] and Texas
Instruments[47] have released single mode Bluetooth low energy solutions.
?In a dual-mode implementation, Bluetooth low energy functionality is
integrated into an existing Classic Bluetooth controller. Currently
(2011-03) the following semiconductor companies have announced the
availability of chips meeting the standard: Atheros, CSR,
Broadcom[48][49] and Texas Instruments. The compliant architecture
shares all of Classic Bluetooth's existing radio and functionality
resulting in a negligible cost increase compared to Classic Bluetooth.
Cost-reduced single-mode chips, which enable highly integrated and
compact devices, feature a lightweight Link Layer providing ultra-low
power idle mode operation, simple device discovery, and reliable
point-to-multipoint data transfer with advanced power-save and secure
encrypted connections at the lowest possible cost.
General improvements in version 4.0 include the changes necessary to
facilitate BLE modes, as well the Generic Attribute Profile (GATT) and
Security Manager (SM) services with AES Encryption.
Core Specification Addendum 2 was unveiled in December 2011; it contains
improvements to the audio Host Controller Interface and to the High
Speed (802.11) Protocol Adaptation Layer.
[edit]
Technical information
[edit]
Bluetooth protocol stack
Main articles: Bluetooth stack and Bluetooth protocols
File:Bluetooth_protokoly
Bluetooth Protocol Stack
"Bluetooth is defined as a layer protocol architecture consisting of
core protocols, cable replacement protocols, telephony control
protocols, and adopted protocols."[50] Mandatory protocols for all
Bluetooth stacks are: LMP, L2CAP and SDP. Additionally, these protocols
are almost universally supported: HCI and RFCOMM.
[edit]
LMP
The Link Management Protocol (LMP) is used for control of the radio link
between two devices. Implemented on the controller.
[edit]
AVRCP
A/V Remote Control Profile. Commonly used in car navigation systems to
control streaming Bluetooth audio. Adopted versions 1.0, 1.3 & 1.4
[edit]
L2CAP
The Logical Link Control and Adaptation Protocol (L2CAP) Used to
multiplex multiple logical connections between two devices using
different higher level protocols. Provides segmentation and reassembly
of on-air packets.
In Basic mode, L2CAP provides packets with a payload configurable up to
64kB, with 672 bytes as the default MTU, and 48 bytes as the minimum
mandatory supported MTU.
In Retransmission and Flow Control modes, L2CAP can be configured either
for isochronous data or reliable data per channel by performing
retransmissions and CRC checks.
Bluetooth Core Specification Addendum 1 adds two additional L2CAP modes
to the core specification. These modes effectively deprecate original
Retransmission and Flow Control modes:
?Enhanced Retransmission Mode (ERTM): This mode is an improved version
of the original retransmission mode. This mode provides a reliable L2CAP
channel.
?Streaming Mode (SM): This is a very simple mode, with no retransmission
or flow control. This mode provides an unreliable L2CAP channel.
Reliability in any of these modes is optionally and/or additionally
guaranteed by the lower layer Bluetooth BDR/EDR air interface by
configuring the number of retransmissions and flush timeout (time after
which the radio will flush packets). In-order sequencing is guaranteed
by the lower layer.
Only L2CAP channels configured in ERTM or SM may be operated over AMP
logical links.
[edit]
SDP
The Service Discovery Protocol (SDP) allows a device to discover
services supported by other devices, and their associated parameters.
For example, when connecting a mobile phone to a Bluetooth headset, SDP
will be used for determining which Bluetooth profiles are supported by
the headset (Headset Profile, Hands Free Profile, Advanced Audio
Distribution Profile (A2DP) etc.) and the protocol multiplexer settings
needed to connect to each of them. Each service is identified by a
Universally Unique Identifier (UUID), with official services (Bluetooth
profiles) assigned a short form UUID (16 bits rather than the full 128).
[edit]
RFCOMM
Radio Frequency Communications (RFCOMM) is a cable replacement protocol
used to create a virtual serial data stream. RFCOMM provides for binary
data transport and emulates EIA-232 (formerly RS-232) control signals
over the Bluetooth baseband layer, i.e. it is a serial port emulation.
RFCOMM provides a simple reliable data stream to the user, similar to
TCP. It is used directly by many telephony related profiles as a carrier
for AT commands, as well as being a transport layer for OBEX over Bluetooth.
Many Bluetooth applications use RFCOMM because of its widespread support
and publicly available API on most operating systems. Additionally,
applications that used a serial port to communicate can be quickly
ported to use RFCOMM.
[edit]
BNEP
The Bluetooth Network Encapsulation Protocol (BNEP) is used for
transferring another protocol stack's data via an L2CAP channel. Its
main purpose is the transmission of IP packets in the Personal Area
Networking Profile. BNEP performs a similar function to SNAP in Wireless
LAN.
[edit]
AVCTP
The Audio/Video Control Transport Protocol (AVCTP) is used by the remote
control profile to transfer AV/C commands over an L2CAP channel. The
music control buttons on a stereo headset use this protocol to control
the music player.
[edit]
AVDTP
The Audio/Video Distribution Transport Protocol (AVDTP) is used by the
advanced audio distribution profile to stream music to stereo headsets
over an L2CAP channel. Intended to be used by video distribution profile
in the bluetooth transmission.
[edit]
TCS
The Telephony Control Protocol - Binary (TCS BIN) is the bit-oriented
protocol that defines the call control signaling for the establishment
of voice and data calls between Bluetooth devices. Additionally, "TCS
BIN defines mobility management procedures for handling groups of
Bluetooth TCS devices."
TCS-BIN is only used by the cordless telephony profile, which failed to
attract implementers. As such it is only of historical interest.
[edit]
Adopted protocols
Adopted protocols are defined by other standards-making organizations
and incorporated into Bluetooth's protocol stack, allowing Bluetooth to
create protocols only when necessary. The adopted protocols include:
Point-to-Point Protocol (PPP)
Internet standard protocol for transporting IP datagrams over a
point-to-point link.
TCP/IP/UDP
Foundation Protocols for TCP/IP protocol suite
Object Exchange Protocol (OBEX)
Session-layer protocol for the exchange of objects, providing a model
for object and operation representation
Wireless Application Environment/Wireless Application Protocol (WAE/WAP)
WAE specifies an application framework for wireless devices and WAP is
an open standard to provide mobile users access to telephony and
information services.[50]
[edit]
Baseband error correction
Depending on packet type, individual packets may be protected by error
correction, either 1/3 rate forward error correction (FEC) or 2/3 rate.
In addition, packets with CRC will be retransmitted until acknowledged
by automatic repeat request (ARQ).
[edit]
Setting up connections
Any Bluetooth device in discoverable mode will transmit the following
information on demand:
?Device name
?Device class
?List of services
?Technical information (for example: device features, manufacturer,
Bluetooth specification used, clock offset)
Any device may perform an inquiry to find other devices to connect to,
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
always responds to direct connection requests and transmits the
information shown in the list above if requested. Use of a device's
services may require pairing or acceptance by its owner, but the
connection itself can be initiated by any device and held until it goes
out of range. Some devices can be connected to only one device at a
time, and connecting to them prevents them from connecting to other
devices and appearing in inquiries until they disconnect from the other
device.
Every device has a unique 48-bit address. However, these addresses are
generally not shown in inquiries. Instead, friendly Bluetooth names are
used, which can be set by the user. This name appears 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 show only the Bluetooth
names and special programs are required to get additional information
about remote devices. This can be confusing as, for example, there could
be several phones in range named T610 (see Bluejacking).
[edit]
Pairing/Bonding
[edit]
Motivation
Many of the services offered over Bluetooth can expose private data or
allow the connecting party to control the Bluetooth device. For security
reasons it is necessary to be able to recognize specific devices and
thus enable control over which devices are allowed to connect to a given
Bluetooth device. At the same time, it is useful for Bluetooth devices
to be able to establish a connection without user intervention (for
example, as soon as they are in range).
To resolve this conflict, Bluetooth uses a process called bonding, and a
bond is created through a process called pairing. The pairing process is
triggered either by a specific request from a user to create a bond (for
example, the user explicitly requests to "Add a Bluetooth device"), or
it is triggered automatically when connecting to a service where (for
the first time) the identity of a device is required for security
purposes. These two cases are referred to as dedicated bonding and
general bonding respectively.
Pairing often involves some level of user interaction; this user
interaction is the basis for confirming the identity of the devices.
Once pairing successfully completes, a bond will have been formed
between the two devices, enabling those two devices to connect to each
other in the future without requiring the pairing process in order to
confirm the identity of the devices. When desired, the bonding
relationship can later be removed by the user.
[edit]
Implementation
File:Tecnologia_bluetooth
A typical Bluetooth pairing.
During the pairing process, the two devices involved establish a
relationship by creating a shared secret known as a link key. If a link
key is stored by both devices they are said to be paired or bonded. A
device that wants to communicate only with a bonded device can
cryptographically authenticate the identity of the other device, and so
be sure that it is the same device it previously paired with. Once a
link key has been generated, an authenticated Asynchronous
Connection-Less (ACL) link between the devices may be encrypted so that
the data that they exchange over the airwaves is protected against
eavesdropping.
Link keys can be deleted at any time by either device. If done by either
device this will implicitly remove the bonding between the devices; so
it is possible for one of the devices to have a link key stored but not
be aware that it is no longer bonded to the device associated with the
given link key.
Bluetooth services generally require either encryption or
authentication, and as such require pairing before they allow a remote
device to use the given service. Some services, such as the Object Push
Profile, elect not to explicitly require authentication or encryption so
that pairing does not interfere with the user experience associated with
the service use-cases.
[edit]
Pairing mechanisms
Pairing mechanisms have changed significantly with the introduction of
Secure Simple Pairing in Bluetooth v2.1. The following summarizes the
pairing mechanisms:
?Legacy pairing: This is the only method available in Bluetooth v2.0 and
before. Each device must enter a PIN code; pairing is only successful if
both devices enter the same PIN code. Any 16-byte UTF-8 string may be
used as a PIN code; however, not all devices may be capable of entering
all possible PIN codes.
?Limited input devices: The obvious example of this class of device is a
Bluetooth Hands-free headset, which generally have few inputs. These
devices usually have a fixed PIN, for example "0000" or "1234", that are
hard-coded into the device.
?Numeric input devices: Mobile phones are classic examples of these
devices. They allow a user to enter a numeric value up to 16 digits in
length.
?Alpha-numeric input devices: PCs and smartphones are examples of these
devices. They allow a user to enter full UTF-8 text as a PIN code. If
pairing with a less capable device the user needs to be aware of the
input limitations on the other device, there is no mechanism available
for a capable device to determine how it should limit the available
input a user may use.
?Secure Simple Pairing (SSP): This is required by Bluetooth v2.1. A
Bluetooth v2.1 device may only use legacy pairing to interoperate with a
v2.0 or earlier device. Secure Simple Pairing uses a form of public key
cryptography, and has the following modes of operation:
?Just works: As implied by the name, this method just works. No user
interaction is required; however, a device may prompt the user to
confirm the pairing process. This method is typically used by headsets
with very limited IO capabilities, and is more secure than the fixed PIN
mechanism which is typically used for legacy pairing by this set of
limited devices. This method provides no man in the middle (MITM)
protection.
?Numeric comparison: If both devices have a display and at least one can
accept a binary Yes/No user input, they may use Numeric Comparison. This
method displays a 6-digit numeric code on each device. The user should
compare the numbers to ensure they are identical. If the comparison
succeeds, the user(s) should confirm pairing on the device(s) that can
accept an input. This method provides MITM protection, assuming the user
confirms on both devices and actually performs the comparison properly.
?Passkey Entry: This method may be used between a device with a display
and a device with numeric keypad entry (such as a keyboard), or two
devices with numeric keypad entry. In the first case, the display is
used to show a 6-digit numeric code to the user, who then enters the
code on the keypad. In the second case, the user of each device enters
the same 6-digit number. Both cases provide MITM protection.
?Out of band (OOB): This method uses an external means of communication,
such as Near Field Communication (NFC) to exchange some information used
in the pairing process. Pairing is completed using the Bluetooth radio,
but requires information from the OOB mechanism. This provides only the
level of MITM protection that is present in the OOB mechanism.
SSP is considered simple for the following reasons:
?In most cases, it does not require a user to generate a passkey.
?For use-cases not requiring MITM protection, user interaction has been
eliminated.
?For numeric comparison, MITM protection can be achieved with a simple
equality comparison by the user.
?Using OOB with NFC enable pairing when devices simply get close, rather
than requiring a lengthy discovery process.
[edit]
Security Concerns
Prior to Bluetooth v2.1, encryption is not required and can be turned
off at any time. Moreover, the encryption key is only good for
approximately 23.5 hours; using a single encryption key longer than this
time allows simple XOR attacks to retrieve the encryption key.
?Turning off encryption is required for several normal operations, so it
is problematic to detect if encryption is disabled for a valid reason or
for a security attack.
?Bluetooth v2.1 addresses this in the following ways:
?Encryption is required for all non-SDP (Service Discovery Protocol)
connections
?A new Encryption Pause and Resume feature is used for all normal
operations requiring encryption to be disabled. This enables easy
identification of normal operation from security attacks.
?The encryption key is required to be refreshed before it expires.
Link keys may be stored on the device file system, not on the Bluetooth
chip itself. Many Bluetooth chip manufacturers allow link keys to be
stored on the device; however, if the device is removable this means
that the link key will move with the device.
[edit]
Air interface
The protocol operates in the license-free ISM band at 2.402-2.480
GHz.[51] To avoid interfering with other protocols that use the 2.45 GHz
band, the Bluetooth protocol divides the band into 79 channels (each 1
MHz wide) and changes channels, generally 800 times per second.
Implementations with versions 1.1 and 1.2 reach speeds of 723.1 kbit/s.
Version 2.0 implementations feature Bluetooth Enhanced Data Rate (EDR)
and reach 2.1 Mbit/s. Technically, version 2.0 devices have a higher
power consumption, but the three times faster rate reduces the
transmission times, effectively reducing power consumption to half that
of 1.x devices (assuming equal traffic load).
[edit]
Security
[edit]
Overview
See also: Mobile_security#Attacks_based_on_communication_networks
Bluetooth implements confidentiality, authentication and key derivation
with custom algorithms based on the SAFER+ block cipher. Bluetooth key
generation is generally based on a Bluetooth PIN, which must be entered
into both devices. This procedure might be modified if one of the
devices has a fixed PIN (e.g., for headsets or similar devices with a
restricted user interface). During pairing, an initialization key or
master key is generated, using the E22 algorithm.[52] The E0 stream
cipher is used for encrypting packets, granting confidentiality, and is
based on a shared cryptographic secret, namely a previously generated
link key or master key. Those keys, used for subsequent encryption of
data sent via the air interface, rely on the Bluetooth PIN, which has
been entered into one or both devices.
An overview of Bluetooth vulnerabilities exploits was published in 2007
by Andreas Becker.[53]
In September 2008, the National Institute of Standards and Technology
(NIST) published a Guide to Bluetooth Security that will serve as
reference to organizations on the security capabilities of Bluetooth and
steps for securing Bluetooth technologies effectively. While Bluetooth
has its benefits, it is susceptible to denial-of-service attacks,
eavesdropping, man-in-the-middle attacks, message modification, and
resource misappropriation. Users/organizations must evaluate their
acceptable level of risk and incorporate security into the lifecycle of
Bluetooth devices. To help mitigate risks, included in the NIST document
are security checklists with guidelines and recommendations for creating
and maintaining secure Bluetooth piconets, headsets, and smart card
readers.[54]
Bluetooth v2.1 - finalized in 2007 with consumer devices first appearing
in 2009 - makes significant changes to Bluetooth's security, including
pairing. See the #Pairing mechanisms section for more about these changes.
[edit]
Bluejacking
Main article: Bluejacking
Bluejacking is the sending of either a picture or a message from one
user to an unsuspecting user through Bluetooth wireless technology.
Common applications include short messages (e.g., "You've just been
bluejacked!"). [55] Bluejacking does not involve the removal or
alteration of any data from the device. Bluejacking can also involve
taking control of a mobile wirelessly and phoning a premium rate line,
owned by the bluejacker.
[edit]
History of security concerns
[edit]
2001 - 2004
In 2001, Jakobsson and Wetzel from Bell Laboratories discovered flaws in
the Bluetooth pairing protocol and also pointed to vulnerabilities in
the encryption scheme.[56] In 2003, Ben and Adam Laurie from A.L.
Digital Ltd. discovered that serious flaws in some poor implementations
of Bluetooth security may lead to disclosure of personal data.[57] In a
subsequent experiment, Martin Herfurt from the trifinite.group was able
to do a field-trial at the CeBIT fairgrounds, showing the importance of
the problem to the world. A new attack called BlueBug was used for this
experiment.[58] In 2004 the first purported virus using Bluetooth to
spread itself among mobile phones appeared on the Symbian OS.[59] The
virus was first described by Kaspersky Lab and requires users to confirm
the installation of unknown software before it can propagate. The virus
was written as a proof-of-concept by a group of virus writers known as
"29A" and sent to anti-virus groups. Thus, it should be regarded as a
potential (but not real) security threat to Bluetooth technology or
Symbian OS since the virus has never spread outside of this system. In
August 2004, a world-record-setting experiment (see also Bluetooth
sniping) showed that the range of Class 2 Bluetooth radios could be
extended to 1.78 km (1.11 mi) with directional antennas and signal
amplifiers.[60] This poses a potential security threat because it
enables attackers to access vulnerable Bluetooth devices from a distance
beyond expectation. The attacker must also be able to receive
information from the victim to set up a connection. No attack can be
made against a Bluetooth device unless the attacker knows its Bluetooth
address and which channels to transmit on.
[edit]
2005
In January 2005, a mobile malware worm known as Lasco.A began targeting
mobile phones using Symbian OS (Series 60 platform) using Bluetooth
enabled devices to replicate itself and spread to other devices. The
worm is self-installing and begins once the mobile user approves the
transfer of the file (velasco.sis) from another device. Once installed,
the worm begins looking for other Bluetooth enabled devices to infect.
Additionally, the worm infects other .SIS files on the device, allowing
replication to another device through use of removable media (Secure
Digital, Compact Flash, etc.). The worm can render the mobile device
unstable.[61]
In April 2005, Cambridge University security researchers published
results of their actual implementation of passive attacks against the
PIN-based pairing between commercial Bluetooth devices, confirming the
attacks to be practicably fast and the Bluetooth symmetric key
establishment method to be vulnerable. To rectify this vulnerability,
they carried out an implementation which showed that stronger,
asymmetric key establishment is feasible for certain classes of devices,
such as mobile phones.[62]
In June 2005, Yaniv Shaked and Avishai Wool published a paper describing
both passive and active methods for obtaining the PIN for a Bluetooth
link. The passive attack allows a suitably equipped attacker to
eavesdrop on communications and spoof, if the attacker was present at
the time of initial pairing. The active method makes use of a specially
constructed message that must be inserted at a specific point in the
protocol, to make the master and slave repeat the pairing process. After
that, the first method can be used to crack the PIN. This attack's major
weakness is that it requires the user of the devices under attack to
re-enter the PIN during the attack when the device prompts them to.
Also, this active attack probably requires custom hardware, since most
commercially available Bluetooth devices are not capable of the timing
necessary.[63]
In August 2005, police in Cambridgeshire, England, issued warnings about
thieves using Bluetooth enabled phones to track other devices left in
cars. Police are advising users to ensure that any mobile networking
connections are de-activated if laptops and other devices are left in
this way.[64]
[edit]
2006
In April 2006, researchers from Secure Network and F-Secure published a
report that warns of the large number of devices left in a visible
state, and issued statistics on the spread of various Bluetooth services
and the ease of spread of an eventual Bluetooth worm.[65]
[edit]
2007
In October 2007, at the Luxemburgish Hack.lu Security Conference, Kevin
Finistere and Thierry Zoller demonstrated and released a remote root
shell via Bluetooth on Mac OS X v10.3.9 and v10.4. They also
demonstrated the first Bluetooth PIN and Linkkeys cracker, which is
based on the research of Wool and Shaked.
[edit]
Health concerns
Main article: Wireless electronic devices and health
Bluetooth uses the microwave radio frequency spectrum in the 2.402 GHz
to 2.480 GHz range.[51] Maximum power output from a Bluetooth radio is
100 mW, 2.5 mW, and 1 mW for Class 1, Class 2, and Class 3 devices
respectively, which puts Class 1 at roughly the same level as mobile
phones, and the other two classes much lower.[66] Accordingly, Class 2
and Class 3 Bluetooth devices are considered less of a potential hazard
than mobile phones, and Class 1 may be comparable to that of mobile
phones : the maximum for a Class 1 is 100 mW for Bluetooth but 250 mW
for UMTS W-CDMA, 1 W for GSM1800/1900 and 2 W for GSM850/900 for instance.
[edit]
Bluetooth Innovation World Cup marketing initiative
The Bluetooth Innovation World Cup,a marketing initiative of the
Bluetooth Special Interest Group (SIG), is an international competition
encouraging the development of innovations for applications leveraging
the Bluetooth low energy wireless technology in sports, fitness and
health care products. The aim of the competition is to stimulate new
markets. The initiative will take three years, having started June 1,
2009.[67]
Bluetooth Innovation World Cup 2009
The first international Bluetooth Innovation World Cup 2009 drew more
than 250 international entries, including Nokia, Freescale
Semiconductor, Texas Instruments, Nordic Semiconductor,
STMicroelectronics and Brunel.
Bluetooth Innovator of the Year 2009
On February 8, 2010, Edward Sazonov, Physical Activity Innovations LLC,
was awarded the title of Bluetooth Innovator of the Year for 2009.
Sazonov received this recognition at a ceremony held at the Wearable
Technologies Show at ispo 2010, a trade show for sporting goods. The
award includes a cash prize of ?5,000 and a Bluetooth Qualification
Program voucher (QDID) valued at up to US$ 10,000. Sazonov's idea, The
Fit Companion, is a small, unobtrusive sensor that, when clipped-on to a
user's clothing or integrated into a shoe, provides feedback about
physical activity. The data, transmitted via Bluetooth, can help
individuals to lose weight and achieve optimal physical activity.
Intended for use in both training and daily activities like walking or
performing chores, this simple measuring device may offer a solution for
reducing obesity.
Bluetooth Innovation World Cup 2010
The Bluetooth Special Interest Group (SIG) announced the start of the
second Innovation World Cup on 1 June 2010, with a focus on applications
for the sports & fitness, health care, and home information and control
markets. The competition closed for registration on September 15, 2010.
[edit]
See also
?Bluesniping
?BlueSoleil - proprietary driver
?Continua Health Alliance
?DASH7
?Java APIs for Bluetooth
?MyriaNed
?Near Field Communication
?Tethering
?ZigBee - low-power lightweight wireless protocol in the ISM band
?RuBee - secure wireless protocol alternative
?Bluetooth wireless headsets
?Li-Fi
[edit]
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[edit]
External links
?Official website
?Bluetooth Specifications
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