bluetooth handout

www.ausystem.com

Whitepaper

BluetoothTM

Bluetooth White Paper 1.1, AU-System, January 2000 1

Summary

The number of computing and telecommunications devices is increasing andconsequently, the focus on how to connect them to each other. The usual solutionis to connect the devices with a cable to make file transfer and synchronisationpossible. File transfer is required so that the user is able to type a document in, forinstance, a PDA and move it later to the PC. There is also a need for synchronisa-tion of events in the calendars of the various devices. The solution to theserequirements has been to connect the devices with a cable, or sometimes toconnect them using infrared light.

The cable solution is often complicated since it may require a cable specific to thedevices being connected as well as configuration software. The infrared solutioneliminates the cable, but requires line of sight. To solve these problems a newtechnology, Bluetooth, has been developed. Bluetooth provides the means for ashort-range radio link solution. It is the result of a co-operative effort among anumber of companies all working for a cheap, simple, and low power-consumingsolution with broad market support.

With Bluetooth, users will be able to connect a wide range of computing andtelecommunications devices easily and simply, without the need for connectingcables. The technology defines how units can communicate up to 10 meters fromeach other. It also defines how certain applications should be mapped onto thehardware to be compatible with Bluetooth. If this is achieved, the concept ensuresthat devices can operate with other Bluetooth applications and devices regardlessof manufacturer. The concept can also act as a way to avoid cable solutions.Furthermore, it can also be used to enable communication between several units,such as small radio LANs. This results in a multitude of possible future userscenarios.

The strength of the Bluetooth concept is that Bluetooth chips can be made verysmall; they are cheap and they are low power-consuming. Furthermore, there issupport for the technique from a vast variety of companies. It is supported notonly in the PC and mobile phone industries, but also in several other industries aswell.


Introduction

This Bluetooth white paper aims to give a good overview of the Bluetoothconcept. It strives to cover technical aspects, regarding hardware, software andBluetooth applications. It also deals with marketing aspects in relation tocompeting techniques. Furthermore, it describes some of the companies behindBluetooth and some of their motives.

The document begins with an introduction where the Bluetooth background andthe Bluetooth standardisation organisation are described. What benefits andpossibilities the technology can provide to users are handled in the sectionBluetooth – Cable replacement, and more. This section also gives a view of themarketing position that the Bluetooth technology enters. The Bluetooth protocollayers and their configuration is described in the section Bluetooth architecture. ItA section describing the Bluetooth air interface follows it. Competing techniquesand the strengths with the Bluetooth concept is then handled in the section WhyBluetooth − Technical aspects. Finally, a brief look at the near Bluetooth future isdone in the last section.

BackgroundBluetooth technology and standards provide the means for the replacement ofcable that connects one device to another with a universal short-range radio link.The technology was initially developed for replacing cables, but has now evolvedinto not only being a cable replacement technique but also a technique toestablish connection between several units. For instance, it shows how to createsmall radio LANs.

A study was initiated at Ericsson Mobile Communications in 1994 to find a lowpower and low cost radio interface between mobile phones and their accessories.The requirements regarding price, capacity and size were set so that the newtechnique would have the potential to outdo all cable solutions between mobiledevices. Initially a suitable radio interface with a corresponding frequency rangehad to be specified. A number of criteria for the concept were defined regardingsize, capacity and global uniformity. The radio unit should be so small andconsume such low power that it could be fitted into portable devices with theirlimitations. The concept had to handle both speech and data and finally thetechnique had to work all around the world.

The study soon showed that a short-range radio link solution was feasible. Whendesigners at Ericsson had started to work on a transceiver chip, Ericsson soonrealised that they needed companions to develop the technique. The associatesstrove not only to improve the technical solutions but also to get a solid and broadmarket support in the business areas of PC hardware, portable computers andmobile phones. Fear for a market situation with a multitude of non-standard cablesolutions, where one cable is designed specifically for one pair of devices, wasone of the motives that made competing companies join the project.

Ericsson Mobile Communications, Intel, IBM, Toshiba and Nokia Mobile Phonesformed a Special Interest Group (SIG) in 1998. This group represented thediverse market support that was needed to generate good support for the new


technology. In May of the same year, the Bluetooth consortium announced itselfglobally. The intention of the Bluetooth SIG is to form a de facto standard for theair interface and the software that controls it. The purpose is to achieveinteroperability between different devices from different producers of portablecomputers, mobile phones and other devices.

The name Bluetooth comes from a Danish Viking and King, Harald Blåtand(Bluetooth in English), who lived in the latter part of the 10th century. HaraldBlåtand united and controlled Denmark and Norway.

Bluetooth SIGIn February 1998, the Bluetooth Special Interest Group, SIG, was founded. At thestart, it consisted of the five companies mentioned above. Today more than 1300companies have joined the SIG to work for an open standard for the Bluetoothconcept. By signing a zero cost agreement, companies can join the SIG andqualify for a royalty-free licence to build products based on the Bluetoothtechnology.

To avoid different interpretations of the Bluetooth standard regarding how aspecific type of application should be mapped to Bluetooth, the SIG has defined anumber of user models and protocol profiles. These are described in more detailin the section entitled Bluetooth Usage Models and Profiles.

The SIG also works with a Qualification Process. This process defines criteria forBluetooth product qualification that ensures that products that pass this processmeet the Bluetooth specification.


Bluetooth – Cable replacement, and more

Why Bluetooth −−−− Marketing aspectsThe removal of the cable connections between the mobile phone and itsaccessories was the origin of the Bluetooth concept. A computer connected to akeyboard, a mouse, a pair of loudspeakers, a PDA and so on, is a situation wherea cordless solution would be useful. The need for different devices to be placedbeside each other can also be eliminated. Instead, the location of devices issuddenly only limited by where to get the power supply.

Another motive for the Bluetooth technology is the problems with connecting andconfiguring mobile devices. To connect a new device a cable is needed, oftenspecific to the brand of the device. When the physical connection is established acomplicated configuration of the connection often follows. With existing cablereplacement techniques, the security of the data transmission is insufficient.These difficulties are also addressed in the development of the Bluetoothtechnique.

The introduction of the Nokia Communicator 9000 has also been described as anevent that increased interest in Bluetooth development. The Communicatorreduced the complexity of connecting a mobile phone with a computer bybuilding a two-in-one unit to solve the problem. It showed that one of thesimplest ways to run data traffic via GSM was to buy a Communicator and not tobuy a GSM Data interface card with cables matching both the phone and theportable computer. The combination of two devices in one was seen as a threat tothe major manufacturers of portable PCs [1]. What if people started to buycommunicators from mobile phone manufacturers instead of portable PCs fromIBM or Toshiba? Furthermore, the introduction of Communicators "would impactsales of central processors for chip supplier Intel which dominates the PC marketbut doesn't have a competitive product for the likes of intelligent phones orhandheld PCs" [1]. Hence, a development where the strong market position forportable PCs is maintained, is essential for the PC industry.

Other motives for a new cable replacement technique are [2]:

• The number of users of portable PCs is increasing. This implies a largermarket for cordless connection of devices.

• The constant shrinking of portable PCs has led to solutions where devices,e.g. CD-ROM drives, are external and need to be connected smoothly to thePC.

• "Mobile computers now rival desktop systems in performance" [2]. The needfor a stationary PC at the office and a portable PC for travelling is decreasing.

The Bluetooth technique provides a solution to the problems described above.The solution eliminates the annoying cable and its limitations regardingflexibility (often specific for a brand or pair of devices) and range. But, Bluetoothimplies more than that. The technique provides the means for connecting severalunits to each other such as setting up small radio LANs between any types of


Bluetooth devices. A number of user scenarios are described. They highlightmore possibilities that reach far beyond just an elimination of the point-to-pointcable.

Bluetooth −−−− The future is nowAlex, sales and marketing manager at Sysau Inc., is working on an importantdocument on a PC. Sysau Inc. is a software consultant company outside London.In Alex's office, there are no cables except for the power supply to the electronicdevices. Telephone, keyboard, loudspeakers, PC screen, and the PC itself, are allinterfaced through Bluetooth. The removal of signalling cables has led to newways of furnishing an office, as the CPU no longer needs to be next to thekeyboard and monitor. When Mr Miller calls, Alex answers with the Bluetoothheadset by tapping the answer button on the headset. Mr Miller is one of theorganisers of an exhibition in New York. He asks if Alex can speak at theexhibition and present Sysau's view of new small LAN techniques. Whenchecking the calendar, Alex notices that this is at the same time as a meeting sheis scheduled to attend at the same exhibition. Still, Alex agrees to do the presenta-tion and while heading to the travel agent, which is a few doors down the hall, thechairman of the meeting calls to remind Alex of some of the items that will bediscussed at the meeting. During the call, the travel agent has finalised the airreservation and Alex instructs the travel agent to send the ticket later on as an"electronic ticket". After finishing the work and checking that the presentation isin order, Alex pockets the computer and heads for the car.

While driving, the e-ticket to New York arrives on Alex's smartphone. WhenAlex arrives at Heathrow's parking garage, her credit card ID is transmitted viaBluetooth to the parking system. Naturally, Alex will pay wirelessly with theWAP browser and wireless-PKI services in the smartphone when parking the carat Heathrow, and renting a car in New York.. At the check-in counter, identi-fication and check-in is done via Bluetooth. After check-in, Alex strolls to thebusiness lounge. The doors open automatically when the Bluetooth equipment inthe lounge doors detects Alex's electronic boarding pass. In order to get a map ofthe exhibition area, Alex connects to the Internet through the lounge LAN usingBluetooth.

On the plane, Alex and an old friend are seated apart from each other, so theystart chatting using their portable PCs. They talk about a computer game thatAlex has not tried and after sending the game to Alex, they start playing. After abland aeroplane dinner, Alex writes an e-mail to send home. It will be transmittedwhen the plane has landed and Alex's smartphone can be switched on again.

At the exhibition area, Alex finds hall two, where the speakers have congregated.The organiser gives Alex and the other speakers a password that enables them touse the main video projector. As usual, the speakers use cordless Bluetoothmicrophones for their presentations and the convention goes as planned.Afterwards, Alex meets with Mr Scott and four others participating in a jointventure. She and the others exchange vCards via their smartphones usingBluetooth. Everyone attending the meeting is using the new Bluetooth techniquewhere all participants form a network with their PCs so that they can work on thesame document at the same time. After some minor discussions, they finish theirwork with the Multimedia over Bluetooth specification and Alex can dash for theplane back home.


An Introduction to the Bluetooth air interfaceTo meet the requirements for the air interface a frequency band between 2.400and 2.500 GHz was selected. Thus, the requirements regarding operating worldwide, support for both data and speech and the limitations regarding physicalcharacteristics (size and power consumption) were covered. This radio frequencyband is the Industrial-Scientific-Medical, ISM band and ranges in Europe and theUSA from 2.400 to 2.4835 GHz (in France and Spain only parts of this range areavailable). As a result, Bluetooth devices must be able to act in the range from2.400 to 2.500 GHz and be able to select a segment in the ISM band within whichthey can act. The ISM band is open to any radio system. Cordless telephones,garage door openers and microwave ovens operate in this band, where microwaveovens are the strongest source of interference.

Bluetooth units connect to each other forming a so-called piconet, consisting ofup to eight active Bluetooth units. This and the way interference due to otherunits acting in the ISM band is handled, is described in the section on TheBluetooth air interface.


Bluetooth architecture overview

This section describes the Bluetooth architecture. The complete protocol stackcomprises, as seen in Figure 1, of both Bluetooth specific protocols and non-Bluetooth specific protocols. In the figure, non-Bluetooth specific protocols areshaded.

WAE

WAP

UDP TCP

IP

PPP

RFCOMM

vCard/vCalendar

OBEX

AT-Commands SDP TCS

L2CAP

LMP

Baseband

Audio

HCI

Figure 1 The Bluetooth Protocol Stack

The Bluetooth architecture strategyA number of profiles have been defined by the Bluetooth standardisationorganisation. These profiles have been developed in order to describe how imple-mentations of user models are to be accomplished. The user models describe anumber of user scenarios where Bluetooth performs the radio transmission. Theseprofiles specify how applications and devices shall be mapped onto the Bluetoothconcept.

A profile defines a selection of messages and procedures from the Bluetoothspecifications and gives an unambiguous description of the air interface forspecified services and use cases. A profile can be described as a vertical slicethrough the protocol stack. It defines options in each protocol that are mandatoryfor the profile. It also defines parameter ranges for each protocol. The profileconcept is used to decrease the risk of interoperability problems between differentmanufacturers' products.

The profile defined for exchanging of vCard information is illustrated in Figure 2,where an application, vCard, is defined to operate over a certain subset (OBEX,


RFCOMM and so on) of the Bluetooth protocol stack. Some of the user modelsand their profiles are described in section Bluetooth Usage Models and Profiles.

vCARD

SDP

L2CAP

Base Band

LMP

RFCOMM TCS Binary

OBEX

HCI

Figure 2 The Object Push Profile

There are four general profiles defined, on which some of the highest prioritiseduser models and their profiles are directly based on. These four models are; theGeneric Access Profile (GAP), the Serial Port Profile, the Service DiscoveryApplication Profile (SDAP) and the Generic Object Exchange Profile (GOEP).

Protocols such as OBEX and UDP have been included in the protocolarchitecture to facilitate the adaptation of applications using such existingprotocols. This gives for instance a number of existing applications supportingUDP an interface to the Bluetooth technology.

Bluetooth Usage Models and ProfilesIn this section, four general profiles GAP, the Serial Port Profile, SDAP andGOEP are defined. A number of usage models are identified by the BluetoothSIG as fundamental, and are therefore, highlighted in the Bluetooth documenta-tion. Some of these user models and their relative profiles are also described inthis section. Note that for every user model there is one or more correspondingprofiles. The Bluetooth profiles and how they are related is illustrated in Figure 3.


Generic Access Profile

Serial Port ProfileGeneric ObjectExchange Profile

Service DiscoveryProfile

Dial up Network-ing Profile

Fax Profile

Headset Profile

LAN AccessProfile

File TransferProfile

Object PushProfile

SynchronisationProfile

TCS Binary profiles

CordlessTelephony Profile Intercom Profile

Figure 3 The Bluetooth Profiles

The four general Bluetooth profiles

The four profiles described in this section form the basis for the user models andtheir profiles. The profiles also provide the foundation for future user models andprofiles.

Generic Access Profile, GAP

The Generic Access Profile, GAP, defines how two Bluetooth units discover andestablish a connection with each other. GAP handles discovery and establishmentbetween units that are unconnected. The profile defines operations that aregeneric and can be used by profiles referring to GAP and by devicesimplementing multiple profiles.

GAP ensures that any two Bluetooth units, regardless of manufacturer andapplication, can exchange information via Bluetooth in order to discover whattype of applications the units support. Bluetooth units not conforming to anyother Bluetooth profile must conform to GAP to ensure basic interoperability andco-existence [3].

Service Discovery Application Profile, SDAP

The Service Discovery Application Profile, SDAP, defines the investigation ofservices available to a Bluetooth unit. The profile handles the search for knownand specific services as well as a general service search.

SDAP involves an application, the Service Discovery User Application, which isrequired in a Bluetooth unit for locating services. This application interfaces theService Discovery Protocol that sends and receives service inquiries to and fromother Bluetooth units. Hence, SDAP describes an application that interfaces witha specific Bluetooth protocol to take full advantage of it for the direct benefit ofthe end-user.


The SDAP is dependent on the GAP, i.e. SDAP re-uses parts of the GAP [4].

Serial Port Profile

The Serial Port Profile defines how to set-up virtual serial ports on two devicesand connecting these with Bluetooth. Using this profile provides the Bluetoothunits with an emulation of a serial cable using RS232 control signalling (RS232is a common interface standard for data communications equipment). The profileensures that data rates up to 128 kbit/s can be used.

The Serial Port Profile is dependent on the GAP, i.e. just as SDAP, Serial PortProfile re-uses parts of the GAP [5].

Generic Object Exchange Profile, GOEP

The Generic Object Exchange Profile, GOEP, defines the set of protocols andprocedures to be used by applications handling object exchanges. A number ofusage models, described in the section Bluetooth Usage Models, are based on thisprofile, e.g. File Transfer and Synchronisation. Typical Bluetooth units using thisprofile are notebook PCs, PDAs, mobile phones and smart phones.

Applications using the GOEP assume that links and channels are established, asdefined by the GAP. The GOEP describes the procedure for pushing data fromone Bluetooth unit to another. The profile also describes how to pull data betweenunits.

The GOEP is dependent on the Serial Port Profile [6].

Bluetooth Usage Models

In this section a number of Bluetooth usage models are described. For each usagemodel there is one or more corresponding profiles defining protocol layers andfunctions to be used. The profiles are not described in detail in this document, formore information refer to the Bluetooth standardisation documents.

File Transfer

The File Transfer usage model offers the capability to transfer data objects fromone Bluetooth device to another. Files, entire folders, directories and streamingmedia formats are supported in this usage model. The model also offers thepossibility of browsing the contents of the folders on a remote device.Furthermore, push and exchange operations are covered in this usage model, e.g.business card exchange using the vCard format. The File Transfer model is basedon GOEP.

Internet Bridge

The Internet Bridge usage model describes how a mobile phone or cordlessmodem provides a PC with dial-up networking capabilities without the need forphysical connection to the PC. This networking scenario requires a two-pieceprotocol stack, one for AT-commands to control the mobile phone and anotherstack to transfer payload data.


LAN Access

The LAN Access usage model is similar to the Internet Bridge user model. Thedifference is that the LAN Access usage model does not use the protocols for AT-commands. The usage model describes how data terminals use a LAN accesspoint as a wireless connection to a Local Area Network. When connected, thedata terminals operate as if it they were connected to the LAN via dial-upnetworking.

Synchronisation

The synchronisation usage model provides the means for automaticsynchronisation between for instance a desktop PC, a portable PC, a mobilephone and a notebook. The synchronisation requires business card, calendar andtask information to be transferred and processed by computers, cellular phonesand PDAs utilising a common protocol and format.

Three-in-One Phone

The Three-in-One Phone usage model describes how a telephone handset mayconnect to three different service providers. The telephone may act as a cordlesstelephone connecting to the public switched telephone network at home, chargedat a fixed line charge. This scenario includes making calls via a voice basestation, and making direct calls between two terminals via the base station. Thetelephone can also connect directly to other telephones acting as a “walkie-talkie”or handset extension i.e. no charging needed. Finally, the telephone may act as acellular telephone connecting to the cellular infrastructure. The cordless andintercom scenarios use the same protocol stack.

Ultimate Headset

The Ultimate Headset usage model defines how a Bluetooth equipped wirelessheadset can be connected, to act as a remote unit’s audio input and outputinterface. The unit is probably a mobile phone or a PC for audio input and output.As for the Internet Bridge user model, this model requires a two-piece protocolstack; one for AT-commands to control the mobile phone and another stack totransfer payload data, i.e. speech. The AT-commands control the telephoneregarding for instance answering and terminating calls.

Bluetooth core protocols

Baseband

The Baseband and Link Control layer enables the physical RF link betweenBluetooth units forming a piconet. This layer controls the Bluetooth unit'ssynchronisation and transmission frequency hopping sequence. The two differentlink types defined in Bluetooth, Synchronous Connection Oriented, SCO, andAsynchronous Connectionless, ACL, described in the section Link types, are alsomanaged by this layer.

The ACL links, for data, and the SCO links, mainly for audio, can be multiplexedto use the same RF link [7].


Audio

Audio transmissions can be performed between one or more Bluetooth units,using many different usage models. Audio data do not go through the L2CAPlayer (described below) but go directly, after opening a Bluetooth link and astraightforward set-up, between two Bluetooth units.

Host Controller Interface, HCI

The Host Controller Interface, HCI, provides a uniform interface method foraccessing the Bluetooth hardware capabilities. It contains a command interface tothe Baseband controller and link manager and access to hardware status. Finally,it contains control and event registers [8].

Link Manager Protocol, LMP

The Link Manager Protocol, LMP, is responsible for link set-up betweenBluetooth units. It handles the control and negotiation of packet sizes used whentransmitting data. The Link Manager Protocol also handles management of powermodes, power consumption, and state of a Bluetooth unit in a piconet. Finally,this layer handles generation, exchange and control of link and encryption keysfor authentication and encryption [9].

Logical Link Control and Adaptation Protocol, L2CAP

The Bluetooth logical link control and adaptation protocol, L2CAP, is situatedover the Baseband layer and beside the Link Manager Protocol in the Bluetoothprotocol stack. The L2CAP layer provides connection-oriented andconnectionless data services to upper layers.

The four main tasks for L2CAP are:

• Multiplexing – L2CAP must support protocol multiplexing since a number ofprotocols (e.g. SDP, RFCOMM and TCS Binary) can operate over L2CAP.

• Segmentation and Reassembly – Data packets exceeding the MaximumTransmission Unit, MTU, must be segmented before being transmitted. Thisand the reverse functionality, reassemble, is performed by L2CAP.

• Quality of Service – The establishment of an L2CAP connection allows theexchange of information regarding current Quality of Service for theconnection between the two Bluetooth units.

• Groups – The L2CAP specification supports a group abstraction that permitsimplementations for mapping groups on to a piconet.

An L2CAP implementation must be uncomplicated and implying low overheadsince it must be compatible with the limited computational resources in a smallBluetooth unit [10].

Service Discovery Protocol, SDP

The Service Discovery Protocol, SDP, defines how a Bluetooth client'sapplication shall act to discover available Bluetooth servers' services and their


characteristics. The protocol defines how a client can search for a service basedon specific attributes without the client knowing anything of the availableservices. The SDP provides means for the discovery of new services becomingavailable when the client enters an area where a Bluetooth server is operating.The SDP also provides functionality for detecting when a service is no longeravailable [11].

Cable replacement protocol

RFCOMM

The RFCOMM protocol is a serial port emulation protocol. The protocol coversapplications that make use of the serial ports of the unit. RFCOMM emulates RS-232 control and data signals over the Bluetooth baseband. It provides transportcapabilities for upper level services, e.g. OBEX that use a serial line as thetransport mechanism.

Telephony control protocol

Telephony Control – Binary

The Telephony Control protocol – Binary, TCS Binary or TCS BIN, is a bit-oriented protocol, which defines the call control signalling for the establishmentof speech and data calls between Bluetooth units. The protocol defines thesignalling for establishment and release of calls between Bluetooth units. As wellas signalling to ease the handling of groups of Bluetooth units. Furthermore, TCSBinary provides functionality to exchange signalling information unrelated toongoing calls.

Establishment of a voice or data call in a point-to-point configuration as well asin a point-to-multipoint configuration is covered in this protocol (note, afterestablishment, the transmission is from point to point). The TCS Binary is basedon the ITU-T Recommendation Q.931.

Telephony Control – AT Commands

A number of AT-commands are supported for transmitting control signals fortelephony control. These use the serial port emulation, RFCOMM, fortransmission.

Adopted protocolsThis section describes a number of protocols that are defined to be adopted to theBluetooth protocol stack. Note some of these adaptations are at the momentincomplete.

PPP

The IETF Point-to-Point Protocol (PPP) in the Bluetooth technology is designedto run over RFCOMM to accomplish point-to-point connections. PPP is a packet-oriented protocol and must therefore use its serial mechanisms to convert thepacket data stream into a serial data stream.


TCP/UDP/IP

The TCP/UDP/IP standards are defined to operate in Bluetooth units allowingthem to communicate with other units connected, for instance, to the Internet.Hence, the Bluetooth unit can act as a bridge to the Internet. The TCP/IP/PPPprotocol configuration is used for all Internet Bridge usage scenarios in Bluetooth1.0 and for OBEX in future versions. The UDP/IP/PPP configuration is availableas transport for WAP.

OBEX Protocol

IrOBEX, shortly OBEX, is an optional application layer protocol designed toenable units supporting infrared communication to exchange a wide variety ofdata and commands in a resource-sensitive standardised fashion. OBEX uses aclient-server model and is independent of the transport mechanism and transportAPI. The OBEX protocol also defines a folder-listing object, which is used tobrowse the contents of folders on remote device. RFCOMM is used as the maintransport layer for OBEX

Content formats

The formats for transmitting vCard and vCalendar information are also defined inthe Bluetooth specification. The formats do not define transport mechanisms butthe format in which electronic business cards and personal calendar entries andscheduling information are transported. vCard and vCalendar is transferred byOBEX.

Wireless Application Protocol, WAP

The Wireless Application Protocol (WAP) is a wireless protocol specificationthat works across a variety of wide-area wireless network technologies bringingthe Internet to mobile devices. Bluetooth can be used like other wireless networkswith regard to WAP, it can be used to provide a bearer for transporting databetween the WAP Client and its adjacent WAP Server. Furthermore, Bluetooth’sad hoc networking capability gives a WAP client unique possibilities regardingmobility compared with other WAP bearers.

The traditional form of WAP communications involves a client device thatcommunicates with a Server/Proxy device using the WAP protocols. Bluetooth isexpected to provide a bearer service as specified by the WAP architecture.

The WAP technology supports server push. If this is used over Bluetooth, itopens new possibilities for distributing information to handheld devices onlocation basis. For example, shops can push special price offers to a WAP clientwhen it comes within Bluetooth range.


The Bluetooth air interface

This section describes the Bluetooth air interface. It is a continuation of theintroduction to the air interface and is based on [12].

The Frequency Hopping techniqueInterference is avoided by using a frequency-hop, FH, spread spectrumtechnology. This technology is well suited for low-power, low-cost radioimplementations and is used in some wireless LAN products. The mainadvantage with Bluetooth's choice of parameters is the high hop rate, 1600 hopsper second, instead of just a few hops per second. The shorter packet length in theBluetooth technology is another benefit.

The frequency band in FH systems is divided into a number of hop channels.Every hop channel is just a fraction of the total frequency band. In Bluetooth onechannel is used in 625 µs (one slot) followed by a hop in a pseudo-random orderto another channel for another 625 µs transmission, repeated constantly. In thisway the hopping spreads the Bluetooth traffic over the entire ISM band and asystem with good interference protection is achieved. If one of the transmissionsis jammed by, for instance, a microwave oven, the probability of interference onthe next hop channel is very low. Error correction algorithms are used to correctthe fault caused by jammed transmissions.

t

625 µ s 625 µs

fn

fn+1

fn +2f

Figure 4 Frequency hop per time division

Modulation/Transmission and packet definitionA Gaussian shaped binary FSK modulation is used to reduce the transceivercomplexity in Bluetooth units. Full duplex transmission capability is achieved byusing time division duplex, subsequent slots are used for transmitting andreceiving. The Bluetooth baseband protocol is a combination of circuit and packetswitching. Reservation of slots can be done for synchronous packets. One packettypically uses one slot, but a multi-slot method is also defined in the Bluetoothspecifications. Multi-slot packets can cover three or five slots. Packets are alwayssent on one single hop channel. That means that when multi-slot packets aretransmitted the hopping frequency is reduced and there is no hop until the wholepacket is sent. This is illustrated in Figure 5. The channel using the white packet


starts the illustrated sequence with a multi-slot packet covering three slots. Notethat the hopping channel after the multi-slot packet is the same (compare withFigure 4) as if there had not been a multi-slot packet.

t

625 µ s 625 µs

fn

fn+1

fn +2f

Figure 5 Mulit-slot packet

Bluetooth networkingWhen Bluetooth units are communicating, one unit is master and the rest of theunits act as slaves. The master unit's system clock and the master identity are thecentral parts in the frequency hop technology. The hop channel is determined bythe hop sequence and by the phase in this sequence. The identity of the masterdetermines the sequence and the master unit's system clock determines the phase.In the slave unit, an offset may be added to its system clock to create a copy ofthe master's clock. In this way every unit in the Bluetooth connection holdssynchronised clocks and the master identity, that uniquely identifies theconnection. Hops synchronised with the master can therefore be achieved asdescribed in Figure 6. 79 hop carriers have been defined for the Bluetoothtechnology except for France and Spain where 23 hop carriers have been defined,because the ISM-band is narrower there.

Slaveclock

+

Sequence

Phase

Hop selection

Hop

Offset

Master identity

Figure 6 The hop selection

The Bluetooth packets have a fixed format. A 72-bit access code comes first inthe packet. The access code is based on the master's identity and the master'ssystem clock, i.e. it provides the means for the synchronisation. This code isunique for the channel and used by all packets transmitting on a specific channel.A 54-bit header follows the access code. This header contains error correction,retransmission and flow control information. The error correction information can


be used for correcting faults in the payload and in the header itself. Finally comesthe payload field with anything between zero and 2,745 bits, i.e. up to 340 bytes.

t

625 µs

fn

fn+1

fn +2f

Accesscode

Packetheader Payload

72 bits 54 bits 0-2745 bits

Figure 7 The Bluetooth packet format

Radio parametersBluetooth units operate on the ISM band, at 2.45 GHz. The transmitting power isbetween 1 and 100 mW. The radio-frequency transmitters are very small.Ericsson's 1 mW Bluetooth radio module is only 10.2x14x1.6 mm. The lowpower consumption implies that a Bluetooth unit can operate on the power from asmall battery for a long time (months). These hardware characteristics make itpossible to fit a Bluetooth unit in many electrical devices. The maximumBluetooth range is 10 m, with a possibility to extend it to 100 m.

The maximum bit rate is 1 Mbit/s. Maximum effective payload is lower becausethe different protocol layers require data payload for signalling to theircorresponding layers in the unit with which the device is communicating.Estimates have indicated data transfer rates up to 721 kbit/s.

Link typesTwo types of link have been defined, Asynchronous Connectionless, ACL, andSynchronous Connection Oriented, SCO. When two Bluetooth unitscommunicate a piconet is established (capable of handling up to eight Bluetoothdevices). One device in the piconet always has the master role. Different master-slave pairs in the same piconet can use different link types. The link type may bechanged during a session. The SCO links support symmetrical, circuit-switched,point-to-point connections and are therefore primarily used for voice traffic. Twoconsecutive time slots, up and down, at fixed intervals are reserved for a SCOlink. The data rate for SCO links is 64 kbit/s.

ACL links are defined for bursty data transmission, i.e. packet data primarily.They support symmetrical and asymmetrical, packet-switched, point-to-multipoint connections. Multi-slot packets use the ACL link type and can reachthe maximum data rate 721 kbit/s in one direction and 57.6 kbit/s in the otherdirection if no error correction is used. The master unit controls the ACL linkbandwidth and decides how much of the bandwidth in a piconet a slave can use.The master also controls the symmetry of the traffic. Broadcast messages aresupported in the ACL link, i.e. from the master to all slaves in the piconet.


Data packets are protected by an Automatic Retransmission Query, ARQ,scheme. This scheme implies that at every packet reception an error check isdone. If an error is detected, the receiving unit indicates this in the return packet;thus lost or faulty packets only cause a one-slot delay. In this way, retransmissionis in this way selective, only faulty packets are retransmitted.

Since retransmission is not optimal for voice transmissions due to itsvulnerability for delays, a voice-encoding scheme is used. This scheme is highlyresistant to bit errors. The errors that cannot be corrected result in an increasingbackground noise.

Piconet and ScatternetAny two Bluetooth devices that come within range of each other can set up a so-called ad hoc connection. When such a connection is established a piconet isformed. There is always a master unit in a piconet and the rest of the units act asslaves. Up to eight active units can form a piconet, which is defined by thechannel these units share. The number of devices in a piconet is actuallyunlimited even though you can have only eight active devices at any givenmoment. There is no difference in hardware or software between a master and aslave, hence any unit can be master. The unit that establishes the piconet becomesthe master unit. The roles in a piconet can change but there can never be morethan one master.

The master unit controls all traffic in the piconet. It allocates capacity for SCOlinks and handles a polling scheme for ACL links. Slave units may only send inthe slave-to-master slot after being addressed in the preceding master-to-slaveslot. If the master does not have any information to send in the master-to-slaveslot, a packet with access code and header only is sent. That is, every slave unit isaddressed in a specific order, and polling scheme, and may only send upon beingaddressed. In this way, packet collisions between sending slave units areeliminated.

Establishing network connections

Before a unit has joined a piconet it is in standby mode. In this mode, anunconnected unit periodically wakes up and listens for messages every 1.28seconds. Paging messages are transmitted on 32 of the 79 (16 of 23 for Spain andFrance) hop carriers which are defined as wake-up carriers (the unit's identitydetermines which of the hop carriers it is). A connection is made by a pagemessage if the address is already known, or by an inquiry message followed by asubsequent page message if the address is unknown.

The wake-up sequence is transmitted by the master over the 32 (or 16 for Spainand France, below is the 32 hop carrier system described) wake up carriers.Initially, the 16 first hop carriers are used, if there is no response, the rest of thecarriers are used. The slave's system clock determines the phase in the wake-upsequence. The slave listens for 18 slots on the wake-up carrier and compares theincoming signal with the access code derived from its own identity. If there is amatch, the unit invokes a connection-set-up procedure and enters Connectedmode. The master unit must know the slave's identity and its system clock. This isrequired to calculate the proper access code and the wake-up sequence and topredict the wake-up sequence phase. To keep track of the slaves' system clocks, apaging procedure is defined for the master unit. It defines how identities are


transmitted between master and slave units and how the slaves' current systemclocks are distributed to the master.

To connect units with an unknown address an inquiry signal is transmittedinitially. This signal is used to inform the master unit of the slave's identity withintransmission range. The paging unit on the inquiry wake-up carriers sends aninquiry access code. Units receiving this message respond with their identity andsystem clock. The inquiry message is typically used for finding Bluetoothdevices, including public printers, fax machines and similar devices with anunknown address.

Power saving modes

Three different power saving modes have been defined, Hold, Sniff and Park.They can be used if there is no data transmission ongoing in the piconet. A slavecan either demand to be put in Hold mode or be put in Hold by the master unit. InHold mode only an internal timer is running. Data transfer restarts instantly whenunits make the transition out of Hold mode. The mode is used when connectingseveral piconets or managing a low power device such as a temperature sensor. Inthe Sniff mode, a slave device listens to the piconet at reduced rate, therebyreducing its duty cycle. In the Park mode a unit remains synchronised in thepiconet but does not participate in the traffic [13].

Scatternet

To optimise the use of the available spectrum, several piconets can exist in thesame area. This is called scatternet. Within one scatternet all units share the samefrequency range but each piconet uses different hop sequences and transmits ondifferent 1 MHz hop channels. Thus, a way to optimise the data transmissioncapability is to keep the piconets small (i.e. few units). All piconets share the 80MHz band, where each piconet uses 1 MHz, thus, as long as the piconets pickdifferent hop frequencies, no sharing of 1 MHz hop channels occurs.

Consequently, if a mobile user wants to connect a number of Bluetooth units tohis mobile phone, the best way to get high data transmission capacity is to formas many piconets as possible in one scatternet. Every connection is using apiconet's maximum capacity (721 kbit/s). The laws of probability imply that thenumber of collision resulting in retransmission is so low that up to 8 piconets arepossible in one scatternet.

Bluetooth securityIntroducing the Bluetooth technology as a cable replacement technique exposesthe need for security functionality in the wireless solution. By replacing the cableand introducing radio signals there is a need for the Bluetooth device to havebuilt-in security to prevent eavesdropping and falsifying the message originator.Therefore, functionality for authentication and encryption has been added to theBluetooth technology. Authentication is used to prevent unwanted access to dataand to prevent falsifying of the message originator. Encryption is used to preventeavesdropping. These two techniques combined with the frequency hoppingtechnique and the limited transmission range for a Bluetooth unit, usually 10 m,give the technology higher protection against eavesdropping.


Since the need for security is dependent on what kind of application is executed,three levels of security are defined in the Bluetooth concept.

1. Non-secure; This mode bypasses functionality for authentication and encrypt-ion.

2. Service-level security; Security procedures are not initiated until L2CAPchannel establishment.

3. Link-level security; Security procedures are initiated before the link set-up atthe LMP level is completed.

Service-level security

In the Service-level security mode, it is suggested to introduce a SecurityManager that controls the access to services and units. This security modeprovides the possibility to define trust levels for the services and units usedrespectively. The access is restricted according to the defined trust levels.

Link-level security

The Link-level security mode is based on the concept of link keys. These keys aresecret 128 bit random numbers stored individually for each pair of devices in aBluetooth connection. Each time two Bluetooth units communicate, the link keyis used for authentication and encryption.


Why Bluetooth −−−− Technical aspects

Competing techniquesThere are a number of competitors to the Bluetooth technology. However, there isno obvious single competitor in all the market segments in which the Bluetoothtechnology can operate.

IrDA

The main competitor in the cable replacement market segment is IrDA. IrDA isan infrared interface standard providing wireless solutions between, for instance,mobile phones and PDAs. The technique is well known in the market but has hadproblems because some IrDA manufacturers have made implementationsincompatible with standard implementations. The maximum payload in the IrDAtechnology exceeds the maximum Bluetooth payload. The two maindisadvantages with IrDA are that it is limited to point-to-point connections (onlytwo parties in a connection) and its need for line of sight (since it is based oninfrared light).

Implementations based on IEEE 802.11

The main competitors in the market segment for wireless LAN are theimplementations based on the IEEE 802.11 standard. Some of theseimplementations also use the frequency hopping technology. The maindifferences between Bluetooth and these implementations are:

• Implementations based on IEEE 802.11 have higher transmission capacity

• The number of simultaneous users is higher for IEEE 802.11-based systems

• The Bluetooth hardware size is considerably smaller

• The five Euro unit is 10 to 20 times cheaper than an IEEE 802.11 unit

• The number of frequency hops is considerably higher for Bluetooth than foran IEEE 802.11 implementation

Ultra-Wideband Radio, UWB

Ultra-Wideband Radio, UWB, is a new radio technology. The concept is similarto radar. Short pulses are transmitted in a broad frequency range. The informationis modulated by the pulses' time and frequency. The technique is not fullydeveloped but might be a threat to the Bluetooth concept since its superiority incapacity and power consumption. UWB prototypes indicate payloads up to 1.25Mbit/s with 70 meters range at just 0.5 mW power consumption.

Home RF

Home RF is a technique developed by a consortium with, among others,Microsoft, Intel, HP, Motorola and Compaq. The technique is developed from the


DECT concept and operates in the 2.4 GHz frequency band (the same asBluetooth). The intention has been to develop a technique for the home market.There are many similarities with Bluetooth, price per unit, range, transmittingpower etc. The major differences are that Home RF can handle up to 127 unitsper net and it uses just 50 frequency hops per second. The figures for Bluetoothare 8 and 1600 respectively.

Bluetooth strengthsThe Bluetooth concept offers several benefits compared with other techniques.The main advantages of Bluetooth are:

• The minimal hardware dimensions

• The low price on Bluetooth components

• The low power consumption for Bluetooth connections

The advantages make it possible to introduce support for Bluetooth in many typesof devices at a low price. The diversity in product offerings (mobile phones,PDAs, computers, computer hardware, notebooks etc) from companies in theBluetooth SIG and their broad support for the technique creates a unique marketposition. Both hardware and device manufacturers will work for the introductionof Bluetooth in many different devices.

The capabilities provided by Bluetooth, approximately 720 kbit/s, can be used forcable replacement and several other applications such as speech, LAN and so on,as described in the use cases, described in the section entitled Bluetooth UsageModels. Figure 8 indicates in what areas the Bluetooth concept can be used.Defining of specific user models and corresponding profiles combined with thefour general profiles will most likely lead to a market situation where applicationscovered by the user models will use the defined user models and their profiles.Furthermore, it is likely that new applications will use the standard profiles andthereby avoid interoperability problems between different manufacturers.

Figure 8 Data transmission requirements


The close Bluetooth future

It is estimated that before year 2002, Bluetooth will be a built-in feature in morethan 100 million mobile phones and in several million other communicationdevices, ranging from headsets and portable PC's to desktop computers andnotebooks. The first Bluetooth products will probably be basic cable replacementproducts. However, when the Bluetooth chips have entered the mass market andchips are found in a multitude of devices, several new markets will open forBluetooth solutions. A few Software Development Kits (SDK) have now beenintroduced on the market. More competition on the SDK market and lower priceson Bluetooth chips will make manufacturers of electronic equipment easy toconvince to insert Bluetooth support in their devices. The Bluetooth hardwaredimensions and its uniform method for building applications will ensure aBluetooth market with matching implementations regardless of brand and whatcountry the product is designed for.


References

[1] "Bluetooth − the gap between perception and reality"Mobile Europe, September 1999 , p 14-17

[2] "Bluetooth Technology:The Convergence of Computing and Communications",Intel Corporation,http://www.gsmdata.com/cannes99/cannespaper.htm

[3] Generic Access Profile Specification, www.bluetooth.com

[4] Service Discovery Application Profile Specification,www.bluetooth.com

[5] Serial Port Profile Specification, www.bluetooth.com

[6] Generic Object Exchange Profile Specification,www.bluetooth.com

[7] Baseband Specification, www.bluetooth.com

[8] Host Controller Interface, Functional Specification,www.bluetooth.com

[9] Link Manager Protocol, Specification, www.bluetooth.com

[10] Logical Link Control and Adaptation Protocol Specification,www.bluetooth.com

[11] Service Discovery Protocol, Specification, www.bluetooth.com

[12] "Bluetooth − The universal radio interface for ad hoc, wirelessconnectivity",Ericsson Review No. 3, 1998

[13] Bluetooth overview, www.bluetooth.com

http://www.gsmdata.com/cannes99/cannespaper.htm

http://www.bluetooth.com/











Abbreviations

Abbreviationor Acronym

Meaning

ACL Asynchronous ConnectionLessAPI Application Programming InterfaceARQ Automatic Retransmission QueryAT-commands ATtention commandsFSK Frequency Shift KeyingGAP Generic Access ProfileGOEP Generic Object Exchange ProfileFH Frequency-HopHCI Host Controller InterfaceIETF Internet Engineering Task ForceIP Internet ProtocolIrDA Infrared Data AssociationISM Industrial-Scientific-MedicalLAN Local Area NetworkLMP Link Manager ProtocolL2CAP Logical Link and Control Adaptation ProtocolOBEX Object Exchange ProtocolPDA Personal Digital AssistantPPP Point-to-Point ProtocolRF Radio FrequencyRFCOMM Serial Cable Emulation ProtocolSCO Synchronous Connection-OrientedSDAP Service Discovery Application ProfileSDP Service Discovery ProtocolSIG Special Interest GroupTCP Transport Control ProtocolTCS Binary Telephony Control Specification – BinaryUDP User Datagram ProtocolWAE Wireless Application EnvironmentWAP Wireless Application Protocol

bluetooth handout

Documents