Bluetooth Technology
Bluetooth is a wireless technology standard for exchanging data over short distances (using short-wavelength UHF radio waves in the ISM band from 2.4 to 2.485 GHz)from fixed and mobile devices, and building personal area networks (PANs). Invented by telecom vendor Ericsson in 1994, 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 (SIG), which has more than 25,000 member companies in the areas of telecommunication, computing, Networking, and consumer electronics. The IEEE standardized Bluetooth as IEEE 802.15.1, but no longer maintains the standard. The Bluetooth SIG oversees development of the specification, manages the qualification program, and protects the trademarks. A manufacturer must make a device meet Bluetooth SIG standards to market it as a Bluetooth device. A network of patents apply to the technology, which are licensed to individual qualifying devices.
The Origin of Bluetooth
The development of the "short-link" radio technology, later named Bluetooth, was initiated in 1989 by Dr. Nils Rydbeck CTO at Ericsson Mobile in Lund and Dr. Johan
Ullman. The purpose was to develop wireless headsets, according to two inventions by Johan Ullman, SE 8902098-6, issued 1989-06-12 and SE 9202239, issued 1992-07-24.
Nils Rydbeck tasked Tord Wingren with specifying and Jaap Haartsen and Sven Mattisson with developing. Both were working for Ericsson in Lund, Sweden. The
specification is based on frequency-hopping spread spectrum technology
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
reach this maximum. The devices can switch roles, by agreement, and the slave can become the master (for example, a headset initiating a connection to a phone
necessarily begins as master as initiator of the connection—but may subsequently operate as 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.) 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. The specification is vague as to required behavior in scatternets.
Many USB Bluetooth adapters or "dongles" are available, some of which also include an IrDA adapter.
Uses
Class
Max. permitted power
Typ. range
(m)
(mW)
(dBm)
1
100
20
~100
2
2.5
4
~10
3
1
0
~1
Bluetooth is a standard wire-replacement communications protocol primarily designed for low-power consumption, with a short range based on low-cost transceiver
microchips in each device. 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.[6] Range is power-class-dependent, but effective ranges vary in practice; see the table on the right.
Officially Class 3 radios have a range of up to 1 metre (3 ft), Class 2, most commonly found in mobile devices, 10 metres (33 ft), and Class 1, primarily for
industrial use cases,100 metres (300 ft). Bluetooth Marketing qualifies that Class 1 range is in most cases 20–30 metres (66–98 ft), and Class 2 range 5–10 metres
(16–33 ft).
Version
Data rate
Max. application throughput
1.2
1 Mbit/s
>80 kbit/s
2.0 + EDR
3 Mbit/s
>80 kbit/s
3.0 + HS
24 Mbit/s
See Version 3.0 + HS
4.0
24 Mbit/s
See Version 4.0 LE
The effective range varies due to propagation conditions, material coverage, production sample variations, antenna configurations and battery conditions. Most
Bluetooth applications are for indoor conditions, where attenuation of walls and signal fading due to signal reflections make the range far lower than specified line-
of-sight ranges of the Bluetooth products. Most Bluetooth applications are battery powered Class 2 devices, with little difference in range whether the other end of
the link is a Class 1 or Class 2 device as the lower powered device tends to set the range limit. In some cases the effective range of the data link can be extended
when a Class 2 device is connecting to a Class 1 transceiver with both higher sensitivity and transmission power than a typical Class 2 device. Mostly however the
Class 1 devices have a similar sensitivity to Class 2 devices. Connecting two Class 1 devices with both high sensitivity and high power can allow ranges far in excess
of the typical 100m, depending on the throughput required by the application. Some such devices allow open field ranges of up to 1 km and beyond between two similar
devices without exceeding legal emission limits.
The Bluetooth Core Specification mandates a range of not less than 10 metres (33 ft), but there is no upper limit on actual range. Manufacturers' implementations can
be tuned to provide the range needed for each case.
Bluetooth profiles
Main article: Bluetooth profile
To use Bluetooth wireless technology, a device must be able to interpret certain Bluetooth profiles, which are definitions of possible applications and specify general
behaviours 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.
List of applications
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 control of and communication with tablets and speakers such as iOS and Android devices.
Wireless Bluetooth headset and Intercom. Idiomatically, a headset is sometimes called "a Bluetooth".
Bluetooth vs. Wi-Fi
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 high speed 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 also works for fixed location
applications such as smart energy functionality in the home (thermostats, etc.).
Wi-Fi and Bluetooth are to some extent complementary in their applications and usage. Wi-Fi is usually access point-centered, with an asymmetrical client-server
connection with all traffic routed through the access point, while Bluetooth is usually symmetrical, between two Bluetooth devices. Bluetooth serves well in simple
applications where two devices need to connect with minimal configuration like a button press, as in headsets and remote controls, while Wi-Fi suits better in
applications where some degree of client configuration is possible and high speeds are required, especially for network access through an access node. However,
Bluetooth access points do exist and ad-hoc connections are possible with Wi-Fi though not as simply as with Bluetooth. Wi-Fi Direct was recently developed to add a
more Bluetooth-like ad-hoc functionality to Wi-Fi.
Devices
A Bluetooth USB dongle with a 100 m range.
Bluetooth exists in many products, such as telephones, tablets, media players, robotics systems, handheld, laptops and console gaming equipment, and some high
definition headsets, modems, and watches. 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. Bluetooth devices can advertise all of the services they provide. This makes using
services easier, because more of the security, network address and permission configuration can be automated than with many other network types.
Computer requirements
A typical Bluetooth USB dongle.
An internal notebook Bluetooth card (14×36×4 mm).
A personal computer that does not have embedded Bluetooth can use a Bluetooth adapter that enables the PC to communicate with Bluetooth devices. While some desktop
computers and most recent laptops come with a built-in Bluetooth radio, others require an external adapter, typically in the form of a small USB "dongle."
Unlike its predecessor, IrDA, which requires a separate adapter for each device, Bluetooth lets multiple devices communicate with a computer over a single adapter.
Operating system implementation
For more details on this topic, see Bluetooth stack.
Apple products have worked with Bluetooth since Mac OS X v10.2, which was released in 2002.
For Microsoft platforms, Windows XP Service Pack 2 and SP3 releases work natively with Bluetooth v1.1, v2.0 and v2.0+EDR. Previous versions required users to install
their Bluetooth adapter's own drivers, which were not directly supported by Microsoft. 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
work with Bluetooth v2.1+EDR. Windows 7 works with Bluetooth v2.1+EDR and Extended Inquiry Response (EIR).
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 that supports more profiles or newer Bluetooth versions. The Windows Vista/Windows 7 Bluetooth stack supports vendor-supplied
additional profiles without requiring that the Microsoft stack be replaced.
Linux has two popular Bluetooth stacks, BlueZ and Affix. The BlueZ stack is included with most Linux kernels and was originally developed by Qualcomm. The Affix stack
was developed by Nokia. FreeBSD features Bluetooth since its v5.0 release. NetBSD features Bluetooth since its v4.0 release. Its Bluetooth stack has been ported to
OpenBSD as well.
Specifications and features
The specifications were formalized by the Bluetooth Special Interest Group (SIG). The SIG was formally announced on 20 May 1998. Today it has a membership of over
20,000 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 support downward compatibility. That lets the latest standard cover all older versions.
The Bluetooth Core Specification Working Group (CSWG) produces mainly 4 kinds of specifications
The Bluetooth Core Specification, release cycle is typically a few years in between
Core Specification Addendum (CSA), release cycle can be as tight as a few times per year
Core Specification Supplements (CSS), can be released very quickly
Errata
Bluetooth v1.0 and v1.0B
Versions 1.0 and 1.0B[citation needed] 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.
Bluetooth v1.1
Ratified as IEEE Standard 802.15.1–2002
Many errors found in the v1.0B specifications were fixed.
Added possibility of non-encrypted channels.
Received Signal Strength Indicator (RSSI).
Bluetooth v1.2
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, 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 concurrent data transfer.
Host Controller Interface (HCI) operation with three-wire UART.
Ratified as IEEE Standard 802.15.1–2005
Introduced Flow Control and Retransmission Modes for L2CAP.
Bluetooth v2.0 + EDR
This version of the Bluetooth Core Specification was released in 2004. 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. EDR uses a combination of GFSK and Phase Shift Keying modulation
(PSK) with two variants, p/4-DQPSK and 8DPSK. 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, the v2.0 specification contains other minor
improvements, 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.
Bluetooth v2.1 + EDR
Bluetooth Core Specification Version 2.1 + EDR was adopted by the Bluetooth SIG on 26 July 2007.
The headline feature of v2.1 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.
Version 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.
Bluetooth v3.0 + HS
Version 3.0 + HS of the Bluetooth Core Specification was adopted by the Bluetooth SIG on 21 April 2009. Bluetooth v3.0 + HS provides 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 colocated 802.11 link.
The main new feature is AMP (Alternative 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 that display the "+HS" logo actually support Bluetooth over 802.11 high-speed data transfer. A Bluetooth v3.0 device without the "+HS" suffix is
only required to support features introduced in Core Specification Version 3.0 or earlier Core Specification Addendum 1.
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.
Alternative 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 must be sent, the high speed alternative MAC PHY 802.11 (typically associated with Wi-Fi) transports the
data. This means that Bluetooth uses proven low power connection models when the system is idle, and the faster radio when it must send large quantities of data. AMP
links require enhanced L2CAP modes.
Unicast Connectionless Data
Permits sending service data 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.
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.
On 16 March 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 successful completion of the technology transfer, marketing, and related administrative items,
the WiMedia Alliance ceased operations.
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.
Bluetooth v4.0
See also: Bluetooth low energy
The Bluetooth SIG completed the Bluetooth Core Specification version 4.0 (called Bluetooth Smart) and has been adopted as of 30 June 2010. It 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.
Bluetooth low energy, previously known as Wibree, is a subset of 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. 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.
In a single-mode implementation, only the low energy protocol stack is implemented. STMicroelectronics, AMICCOM, CSR, Nordic Semiconductor and Texas Instruments have
released single mode Bluetooth low energy solutions.
In a dual-mode implementation, Bluetooth Smart functionality is integrated into an existing Classic Bluetooth controller. As of March 2011, the following semiconductor
companies have announced the availability of chips meeting the standard: Qualcomm-Atheros, CSR, Broadcom 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.
Core Specification Addendum 3 revision 2 has an adoption date of 24 July 2012.
Core Specification Addendum 4 has an adoption date of 12 February 2013.
Bluetooth v4.1
The Bluetooth SIG announced formal adoption of the Bluetooth v4.1 specification on 4 December 2013. This specification is an incremental software update to Bluetooth
Specification v4.0, and not a hardware update. The update incorporates Bluetooth Core Specification Addenda (CSA 1, 2, 3 & 4) and adds new features that improve
consumer usability. These include increased co-existence support for LTE, bulk data exchange rates—and aid developer innovation by allowing devices to support multiple
roles simultaneously.
New features of this specification include:
Mobile Wireless Service Coexistence Signaling
Train Nudging and Generalized Interlaced Scanning
Low Duty Cycle Directed Advertising
L2CAP Connection Oriented and Dedicated Channels with Credit Based Flow Control
Dual Mode and Topology
LE Link Layer Topology
802.11n PAL
Audio Architecture Updates for Wide Band Speech
Fast Data Advertising Interval
Limited Discovery Time
Notice that some features were already available in a Core Specification Addendum (CSA) before the release of v4.1.
Bluetooth v4.2
Bluetooth v4.2 was released on December 2, 2014. It Introduces some key features for IoT. Some features, such as Data Length Extension, require a hardware update. But
some older Bluetooth hardware may receive some Bluetooth v4.2 features, such as privacy updates via firmware.
The major areas of improvement are:
LE Data Packet Length Extension
LE Secure Connections
Link Layer Privacy
Link Layer Extended Scanner Filter Policies
IP connectivity for Bluetooth Smart devices to become available soon after the introduction of BT v4.2 via the new Internet Protocol Support Profile (IPSP).
IPSP adds an IPv6 connection option for Bluetooth Smart, to support connected home and other IoT implementations.
Technical information
Bluetooth protocol stack
Bluetooth Protocol Stack
Bluetooth is defined as a layer protocol architecture consisting of core protocols, cable replacement protocols, telephony control protocols, and adopted protocols.
Mandatory protocols for all Bluetooth stacks are: LMP, L2CAP and SDP. In addition, devices that communicate with Bluetooth almost universally can use these protocols:
HCI and RFCOMM.
LMP
The Link Management Protocol (LMP) is used for set-up and control of the radio link between two devices. Implemented on the controller.
L2CAP
The Logical Link Control and Adaptation Protocol (L2CAP) is 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 64 kB, 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 flushes 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.
SDP
The Service Discovery Protocol (SDP) allows a device to discover services offered by other devices, and their associated parameters. For example, when you use a mobile
phone with a Bluetooth headset, the phone uses SDP to determine which Bluetooth profiles the headset can use (Headset Profile, Hands Free Profile, Advanced Audio
Distribution Profile (A2DP) etc.) and the protocol multiplexer settings needed for the phone to connect to the headset using 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).
RFCOMM
Radio Frequency Communications (RFCOMM) is a cable replacement protocol used to generate 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.
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.
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.
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 for video distribution profile in the Bluetooth transmission.
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.
Adopted protocols
Adopted protocols are defined by other standards-making organizations and incorporated into Bluetooth’s protocol stack, allowing Bluetooth to code 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.
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).
Setting up connections
Any Bluetooth device in discoverable mode transmits 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 cellular phones have the Bluetooth name set to the manufacturer and model of the phone by default. Most cellular 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 cellular phones in
range named T610 (see Bluejacking).
Pairing and bonding
Motivation
Many services offered over Bluetooth can expose private data or let a connecting party control the Bluetooth device. Security reasons make it necessary to recognize
specific devices, and thus enable control over which devices can 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 in range).
To resolve this conflict, Bluetooth uses a process called bonding, and a bond is generated through a process called pairing. The pairing process is triggered either by
a specific request from a user to generate 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 confirms the identity of the devices. When pairing successfully completes, a bond forms
between the two devices, enabling those two devices to connect to each other in the future without repeating the pairing process to confirm device identities. When
desired, the user can remove the bonding relationship.
Implementation
During pairing, the two devices establish a relationship by creating a shared secret known as a link key. If both devices store the same link key, 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, ensuring it is the
same device it previously paired with. Once a link key is generated, an authenticated Asynchronous Connection-Less (ACL) link between the devices may be encrypted to
protect exchanged data against eavesdropping. Users can delete link keys from either device, which removes the bond between the devices—so it is possible for one
device to have a stored link key for a device it is no longer paired with.
Bluetooth services generally require either encryption or authentication and as such require pairing before they let a remote device connect. 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.
Pairing mechanisms
Pairing mechanisms 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 must 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, although 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 some types can help protect against man in the middle, or MITM attacks. SSP has the following
authentication mechanisms:
Just works: As the name implies, this method just works, with no user interaction. 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 this limited set of devices uses for legacy pairing. 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 of these 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 can be eliminated.
For numeric comparison, MITM protection can be achieved with a simple equality comparison by the user.
Using OOB with NFC enables pairing when devices simply get close, rather than requiring a lengthy discovery process.
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 that require that encryption be disabled. This enables easy identification of normal
operation from security attacks.
The encryption key must 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 let link keys be stored on the device—however,
if the device is removable, this means that the link key moves with the device.
Air interface
The protocol operates in the license-free ISM band at 2.402–2.480 GHz. 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 1600 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; this comes with a concomitant higher power consumption. In
some cases, the higher data rate is expected to offset this increased drain.
Security
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. 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.
In September 2008, the National Institute of Standards and Technology (NIST) published a Guide to Bluetooth Security as a reference for organizations. It describes
Bluetooth security capabilities and how to secure 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 and 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.
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.
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!". Bluejacking does not involve the removal or alteration of any data from the device. Bluejacking can also involve
taking control of a mobile device wirelessly and phoning a premium rate line, owned by the bluejacker. Security advances have alleviated this issue.
Bluetooth is a wireless technology standard for exchanging data over short distances (using short-wavelength UHF radio waves in the ISM band from 2.4 to 2.485 GHz)
from fixed and mobile devices, and building personal area networks (PANs). Invented by telecom vendor Ericsson in 1994, 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 (SIG), which has more than 25,000 member companies in the areas of telecommunication, computing,
networking, and consumer electronics. The IEEE standardized Bluetooth as IEEE 802.15.1, but no longer maintains the standard. The Bluetooth SIG oversees development of
the specification, manages the qualification program, and protects the trademarks. A manufacturer must make a device meet Bluetooth SIG standards to market it as a
Bluetooth device. A network of patents apply to the technology, which are licensed to individual qualifying devices.
The Origin of Bluetooth
The development of the "short-link" radio technology, later named Bluetooth, was initiated in 1989 by Dr. Nils Rydbeck CTO at Ericsson Mobile in Lund and Dr. Johan
Ullman. The purpose was to develop wireless headsets, according to two inventions by Johan Ullman, SE 8902098-6, issued 1989-06-12 and SE 9202239, issued 1992-07-24.
Nils Rydbeck tasked Tord Wingren with specifying and Jaap Haartsen and Sven Mattisson with developing. Both were working for Ericsson in Lund, Sweden. The
specification is based on frequency-hopping spread spectrum technology
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
reach this maximum. The devices can switch roles, by agreement, and the slave can become the master (for example, a headset initiating a connection to a phone
necessarily begins as master as initiator of the connection—but may subsequently operate as 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.) 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. The specification is vague as to required behavior in scatternets.
Many USB Bluetooth adapters or "dongles" are available, some of which also include an IrDA adapter.
Uses
Class
Max. permitted power
Typ. range
(m)
(mW)
(dBm)
1
100
20
~100
2
2.5
4
~10
3
1
0
~1
Bluetooth is a standard wire-replacement communications protocol primarily designed for low-power consumption, with a short range based on low-cost transceiver
microchips in each device. 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.[6] Range is power-class-dependent, but effective ranges vary in practice; see the table on the right.
Officially Class 3 radios have a range of up to 1 metre (3 ft), Class 2, most commonly found in mobile devices, 10 metres (33 ft), and Class 1, primarily for
industrial use cases,100 metres (300 ft). Bluetooth Marketing qualifies that Class 1 range is in most cases 20–30 metres (66–98 ft), and Class 2 range 5–10 metres
(16–33 ft).
Version
Data rate
Max. application throughput
1.2
1 Mbit/s
>80 kbit/s
2.0 + EDR
3 Mbit/s
>80 kbit/s
3.0 + HS
24 Mbit/s
See Version 3.0 + HS
4.0
24 Mbit/s
See Version 4.0 LE
The effective range varies due to propagation conditions, material coverage, production sample variations, antenna configurations and battery conditions. Most
Bluetooth applications are for indoor conditions, where attenuation of walls and signal fading due to signal reflections make the range far lower than specified line-
of-sight ranges of the Bluetooth products. Most Bluetooth applications are battery powered Class 2 devices, with little difference in range whether the other end of
the link is a Class 1 or Class 2 device as the lower powered device tends to set the range limit. In some cases the effective range of the data link can be extended
when a Class 2 device is connecting to a Class 1 transceiver with both higher sensitivity and transmission power than a typical Class 2 device. Mostly however the
Class 1 devices have a similar sensitivity to Class 2 devices. Connecting two Class 1 devices with both high sensitivity and high power can allow ranges far in excess
of the typical 100m, depending on the throughput required by the application. Some such devices allow open field ranges of up to 1 km and beyond between two similar
devices without exceeding legal emission limits.
The Bluetooth Core Specification mandates a range of not less than 10 metres (33 ft), but there is no upper limit on actual range. Manufacturers' implementations can
be tuned to provide the range needed for each case.
Bluetooth profiles
Main article: Bluetooth profile
To use Bluetooth wireless technology, a device must be able to interpret certain Bluetooth profiles, which are definitions of possible applications and specify general
behaviours 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.
List of applications
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 control of and communication with tablets and speakers such as iOS and Android devices.
Wireless Bluetooth headset and Intercom. Idiomatically, a headset is sometimes called "a Bluetooth".
Bluetooth vs. Wi-Fi
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 high speed 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 also works for fixed location
applications such as smart energy functionality in the home (thermostats, etc.).
Wi-Fi and Bluetooth are to some extent complementary in their applications and usage. Wi-Fi is usually access point-centered, with an asymmetrical client-server
connection with all traffic routed through the access point, while Bluetooth is usually symmetrical, between two Bluetooth devices. Bluetooth serves well in simple
applications where two devices need to connect with minimal configuration like a button press, as in headsets and remote controls, while Wi-Fi suits better in
applications where some degree of client configuration is possible and high speeds are required, especially for network access through an access node. However,
Bluetooth access points do exist and ad-hoc connections are possible with Wi-Fi though not as simply as with Bluetooth. Wi-Fi Direct was recently developed to add a
more Bluetooth-like ad-hoc functionality to Wi-Fi.
Devices
A Bluetooth USB dongle with a 100 m range.
Bluetooth exists in many products, such as telephones, tablets, media players, robotics systems, handheld, laptops and console gaming equipment, and some high
definition headsets, modems, and watches. 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. Bluetooth devices can advertise all of the services they provide. This makes using
services easier, because more of the security, network address and permission configuration can be automated than with many other network types.
Computer requirements
A typical Bluetooth USB dongle.
An internal notebook Bluetooth card (14×36×4 mm).
A personal computer that does not have embedded Bluetooth can use a Bluetooth adapter that enables the PC to communicate with Bluetooth devices. While some desktop
computers and most recent laptops come with a built-in Bluetooth radio, others require an external adapter, typically in the form of a small USB "dongle."
Unlike its predecessor, IrDA, which requires a separate adapter for each device, Bluetooth lets multiple devices communicate with a computer over a single adapter.
Operating system implementation
For more details on this topic, see Bluetooth stack.
Apple products have worked with Bluetooth since Mac OS X v10.2, which was released in 2002.
For Microsoft platforms, Windows XP Service Pack 2 and SP3 releases work natively with Bluetooth v1.1, v2.0 and v2.0+EDR. Previous versions required users to install
their Bluetooth adapter's own drivers, which were not directly supported by Microsoft. 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
work with Bluetooth v2.1+EDR. Windows 7 works with Bluetooth v2.1+EDR and Extended Inquiry Response (EIR).
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 that supports more profiles or newer Bluetooth versions. The Windows Vista/Windows 7 Bluetooth stack supports vendor-supplied
additional profiles without requiring that the Microsoft stack be replaced.
Linux has two popular Bluetooth stacks, BlueZ and Affix. The BlueZ stack is included with most Linux kernels and was originally developed by Qualcomm. The Affix stack
was developed by Nokia. FreeBSD features Bluetooth since its v5.0 release. NetBSD features Bluetooth since its v4.0 release. Its Bluetooth stack has been ported to
OpenBSD as well.
Specifications and features
The specifications were formalized by the Bluetooth Special Interest Group (SIG). The SIG was formally announced on 20 May 1998. Today it has a membership of over
20,000 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 support downward compatibility. That lets the latest standard cover all older versions.
The Bluetooth Core Specification Working Group (CSWG) produces mainly 4 kinds of specifications
The Bluetooth Core Specification, release cycle is typically a few years in between
Core Specification Addendum (CSA), release cycle can be as tight as a few times per year
Core Specification Supplements (CSS), can be released very quickly
Errata
Bluetooth v1.0 and v1.0B
Versions 1.0 and 1.0B[citation needed] 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.
Bluetooth v1.1
Ratified as IEEE Standard 802.15.1–2002
Many errors found in the v1.0B specifications were fixed.
Added possibility of non-encrypted channels.
Received Signal Strength Indicator (RSSI).
Bluetooth v1.2
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, 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 concurrent data transfer.
Host Controller Interface (HCI) operation with three-wire UART.
Ratified as IEEE Standard 802.15.1–2005
Introduced Flow Control and Retransmission Modes for L2CAP.
Bluetooth v2.0 + EDR
This version of the Bluetooth Core Specification was released in 2004. 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. EDR uses a combination of GFSK and Phase Shift Keying modulation
(PSK) with two variants, p/4-DQPSK and 8DPSK. 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, the v2.0 specification contains other minor
improvements, 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.
Bluetooth v2.1 + EDR
Bluetooth Core Specification Version 2.1 + EDR was adopted by the Bluetooth SIG on 26 July 2007.
The headline feature of v2.1 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.
Version 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.
Bluetooth v3.0 + HS
Version 3.0 + HS of the Bluetooth Core Specification was adopted by the Bluetooth SIG on 21 April 2009. Bluetooth v3.0 + HS provides 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 colocated 802.11 link.
The main new feature is AMP (Alternative 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 that display the "+HS" logo actually support Bluetooth over 802.11 high-speed data transfer. A Bluetooth v3.0 device without the "+HS" suffix is
only required to support features introduced in Core Specification Version 3.0 or earlier Core Specification Addendum 1.
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.
Alternative 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 must be sent, the high speed alternative MAC PHY 802.11 (typically associated with Wi-Fi) transports the
data. This means that Bluetooth uses proven low power connection models when the system is idle, and the faster radio when it must send large quantities of data. AMP
links require enhanced L2CAP modes.
Unicast Connectionless Data
Permits sending service data 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.
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.
On 16 March 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 successful completion of the technology transfer, marketing, and related administrative items,
the WiMedia Alliance ceased operations.
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.
Bluetooth v4.0
See also: Bluetooth low energy
The Bluetooth SIG completed the Bluetooth Core Specification version 4.0 (called Bluetooth Smart) and has been adopted as of 30 June 2010. It 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.
Bluetooth low energy, previously known as Wibree, is a subset of 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. 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.
In a single-mode implementation, only the low energy protocol stack is implemented. STMicroelectronics, AMICCOM, CSR, Nordic Semiconductor and Texas Instruments have
released single mode Bluetooth low energy solutions.
In a dual-mode implementation, Bluetooth Smart functionality is integrated into an existing Classic Bluetooth controller. As of March 2011, the following semiconductor
companies have announced the availability of chips meeting the standard: Qualcomm-Atheros, CSR, Broadcom 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.
Core Specification Addendum 3 revision 2 has an adoption date of 24 July 2012.
Core Specification Addendum 4 has an adoption date of 12 February 2013.
Bluetooth v4.1
The Bluetooth SIG announced formal adoption of the Bluetooth v4.1 specification on 4 December 2013. This specification is an incremental software update to Bluetooth
Specification v4.0, and not a hardware update. The update incorporates Bluetooth Core Specification Addenda (CSA 1, 2, 3 & 4) and adds new features that improve
consumer usability. These include increased co-existence support for LTE, bulk data exchange rates—and aid developer innovation by allowing devices to support multiple
roles simultaneously.
New features of this specification include:
Mobile Wireless Service Coexistence Signaling
Train Nudging and Generalized Interlaced Scanning
Low Duty Cycle Directed Advertising
L2CAP Connection Oriented and Dedicated Channels with Credit Based Flow Control
Dual Mode and Topology
LE Link Layer Topology
802.11n PAL
Audio Architecture Updates for Wide Band Speech
Fast Data Advertising Interval
Limited Discovery Time
Notice that some features were already available in a Core Specification Addendum (CSA) before the release of v4.1.
Bluetooth v4.2
Bluetooth v4.2 was released on December 2, 2014. It Introduces some key features for IoT. Some features, such as Data Length Extension, require a hardware update. But
some older Bluetooth hardware may receive some Bluetooth v4.2 features, such as privacy updates via firmware.
The major areas of improvement are:
LE Data Packet Length Extension
LE Secure Connections
Link Layer Privacy
Link Layer Extended Scanner Filter Policies
IP connectivity for Bluetooth Smart devices to become available soon after the introduction of BT v4.2 via the new Internet Protocol Support Profile (IPSP).
IPSP adds an IPv6 connection option for Bluetooth Smart, to support connected home and other IoT implementations.
Technical information
Bluetooth protocol stack
Bluetooth Protocol Stack
Bluetooth is defined as a layer protocol architecture consisting of core protocols, cable replacement protocols, telephony control protocols, and adopted protocols.
Mandatory protocols for all Bluetooth stacks are: LMP, L2CAP and SDP. In addition, devices that communicate with Bluetooth almost universally can use these protocols:
HCI and RFCOMM.
LMP
The Link Management Protocol (LMP) is used for set-up and control of the radio link between two devices. Implemented on the controller.
L2CAP
The Logical Link Control and Adaptation Protocol (L2CAP) is 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 64 kB, 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 flushes 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.
SDP
The Service Discovery Protocol (SDP) allows a device to discover services offered by other devices, and their associated parameters. For example, when you use a mobile
phone with a Bluetooth headset, the phone uses SDP to determine which Bluetooth profiles the headset can use (Headset Profile, Hands Free Profile, Advanced Audio
Distribution Profile (A2DP) etc.) and the protocol multiplexer settings needed for the phone to connect to the headset using 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).
RFCOMM
Radio Frequency Communications (RFCOMM) is a cable replacement protocol used to generate 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.
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.
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.
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 for video distribution profile in the Bluetooth transmission.
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.
Adopted protocols
Adopted protocols are defined by other standards-making organizations and incorporated into Bluetooth’s protocol stack, allowing Bluetooth to code 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.
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).
Setting up connections
Any Bluetooth device in discoverable mode transmits 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 cellular phones have the Bluetooth name set to the manufacturer and model of the phone by default. Most cellular 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 cellular phones in
range named T610 (see Bluejacking).
Pairing and bonding
Motivation
Many services offered over Bluetooth can expose private data or let a connecting party control the Bluetooth device. Security reasons make it necessary to recognize
specific devices, and thus enable control over which devices can 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 in range).
To resolve this conflict, Bluetooth uses a process called bonding, and a bond is generated through a process called pairing. The pairing process is triggered either by
a specific request from a user to generate 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 confirms the identity of the devices. When pairing successfully completes, a bond forms
between the two devices, enabling those two devices to connect to each other in the future without repeating the pairing process to confirm device identities. When
desired, the user can remove the bonding relationship.
Implementation
During pairing, the two devices establish a relationship by creating a shared secret known as a link key. If both devices store the same link key, 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, ensuring it is the
same device it previously paired with. Once a link key is generated, an authenticated Asynchronous Connection-Less (ACL) link between the devices may be encrypted to
protect exchanged data against eavesdropping. Users can delete link keys from either device, which removes the bond between the devices—so it is possible for one
device to have a stored link key for a device it is no longer paired with.
Bluetooth services generally require either encryption or authentication and as such require pairing before they let a remote device connect. 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.
Pairing mechanisms
Pairing mechanisms 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 must 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, although 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 some types can help protect against man in the middle, or MITM attacks. SSP has the following
authentication mechanisms:
Just works: As the name implies, this method just works, with no user interaction. 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 this limited set of devices uses for legacy pairing. 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 of these 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 can be eliminated.
For numeric comparison, MITM protection can be achieved with a simple equality comparison by the user.
Using OOB with NFC enables pairing when devices simply get close, rather than requiring a lengthy discovery process.
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 that require that encryption be disabled. This enables easy identification of normal
operation from security attacks.
The encryption key must 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 let link keys be stored on the device—however,
if the device is removable, this means that the link key moves with the device.
Air interface
The protocol operates in the license-free ISM band at 2.402–2.480 GHz. 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 1600 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; this comes with a concomitant higher power consumption. In
some cases, the higher data rate is expected to offset this increased drain.
Security
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. 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.
In September 2008, the National Institute of Standards and Technology (NIST) published a Guide to Bluetooth Security as a reference for organizations. It describes
Bluetooth security capabilities and how to secure 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 and 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.
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.
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!". Bluejacking does not involve the removal or alteration of any data from the device. Bluejacking can also involve
taking control of a mobile device wirelessly and phoning a premium rate line, owned by the bluejacker. Security advances have alleviated this issue.
Samsung insists that the battery life of Samsung Galaxy TabPro S is 10 hours long from the 39.5Whr, 5200 mAh battery capacity. It’s a relatively tiny battery for a 12-inch tablet with such a high resolution and 4GB of RAM. So I really want to see this tested out. Charging time is 2.5 hours. What is certain however is that the Samsung Galaxy TabPro S is now the thinnest and lightest 12-inch Windows 10 2-in-1 tablet at the start of 2016. But only marginally lighter, because while the thickness is an impressive 6.3 mm, the weight is 693 grams for the Wi-Fi model. That makes it the lightest 12-inch Windows 10 tablet on the market, but the Surface Book is actually even more impressive, with its 13.5-inch screen and weight of 726 grams.
Samsung insists that the battery life of Samsung Galaxy TabPro S is 10 hours long from the 39.5Whr, 5200 mAh battery capacity. It’s a relatively tiny battery for a 12-inch tablet with such a high resolution and 4GB of RAM. So I really want to see this tested out. Charging time is 2.5 hours. What is certain however is that the Samsung Galaxy TabPro S is now the thinnest and lightest 12-inch Windows 10 2-in-1 tablet at the start of 2016. But only marginally lighter, because while the thickness is an impressive 6.3 mm, the weight is 693 grams for the Wi-Fi model. That makes it the lightest 12-inch Windows 10 tablet on the market, but the Surface Book is actually even more impressive, with its 13.5-inch screen and weight of 726 grams.
