I

1. Introductionto Bluetooth
Bluetooth is an always-on, short-range radio hookup that resides on a microchip. It was initially
developed by Swedish mobile phone maker Ericsson in 1994 as a way to let laptop computers
make calls over a mobile phone. Since then, several thousand companies have signed on to make
Bluetooth the low-power short-range wireless standard for a wide range of devices. Industry
observers expect Bluetooth to be installed in billions of devices by 2005.
The Bluetooth standards are published by an industry consortium known as the Bluetooth SIG
(special interest group).
The concept behind Bluetooth is to provide a universal short-range wireless capability. Using the
2.4 GHz band, available globally for unlicensed low-power uses, two Bluetooth devices within 10 m
of each other can share up to 720 Kbps of capacity. Bluetooth is intended to support an open-
ended list of applications, including data (such as schedules and telephone numbers), audio,
graphics, and even video. For example, audio devices can include headsets, cordless and standard
phones, home stereos, and digital MP3 players. Following are some examples of the capabilities
that Bluetooth can provide consumers:
 Make calls from a wireless headset connected remotely to a cell phone;
 Eliminate cables linking computers to printers, keyboards, and the mouse;
 Hook up MP3 players wirelessly to other machines to download music;
 Set up home networks so that a couch potato can remotely monitor air conditioning, the oven,
and children's Internet surfing;
 Call home from a remote location to turn appliances on and off, set the alarm, and monitor
activity.
Bluetooth Applications
Bluetooth is designed to operate in an environment of many users. Up to eight devices can
communicate in a small network called a piconet. Ten of these piconets can coexist in the same
coverage range of the Bluetooth radio. To provide security, each link is encoded and protected
against eavesdropping and interference.
Bluetooth provides support for three general application areas using short-range wireless
connectivity:
 Data and voice access points - Bluetooth facilitates real-time voice and data transmissions
by providing effortless wireless connection of portable and stationary communications devices;
 Cable replacement - Bluetooth eliminates the need for numerous, often proprietary cable
attachments for connection of practically any kind of communications device. Connections are
instant and are maintained even when devices are not within line of sight. The range of each
radio is approximately 10 m, but can be extended to 100 m with an optional amplifier;
 Ad hoc networking - A device equipped with a Bluetooth radio can establish instant
connection to another Bluetooth radio as soon as it comes into range.
Bluetooth Standards Documents
The Bluetooth standards present a formidable bulk�well over 1,500 pages, divided into two
groups: core and profile. The core specifications describe the details of the various layers of the
Bluetooth protocol architecture, from the radio interface to link control. Related topics are also
covered, such as interoperability with related technologies, testing requirements, and a definition
of various Bluetooth timers and their associated values.
The profile specifications are concerned with the use of Bluetooth technology to support various
applications. Each profile specification discusses the use of the technology defined in the core
specifications to implement a particular usage model. The profile specification includes a
description of which aspects of the core specifications are mandatory, optional, and not applicable.
The purpose of a profile specification is to define a standard of interoperability, so that products

2. from different vendors that claim to support a given usage model will work together. In general
terms, profile specifications fall into one of two categories: cable replacement or wireless audio.
The cable replacement profiles provide a convenient means for logically connecting devices in
proximity to one another and for exchanging data. For example, when two devices first come
within range of one another, they can automatically query each other for a common profile. This
might then cause the end users of the device to be alerted, or cause some automatic data
exchange to take place. The wireless audio profiles are concerned with establishing short-range
voice connections.
The Bluetooth developer must wade through the many documents with a particular application in
mind. The reading list begins with coverage of some essential core specifications plus the general
access profile. This profile is one of a number of profiles that serve as a foundation for other
profiles and don't specify independently usable functionality. The general access profile specifies
how the Bluetooth baseband architecture, defined in the core specifications, is to be used between
devices that implement one or multiple profiles. Following a basic set of documents, the reading
list splits along two lines, depending on whether the reader's interest is in cable replacement or
wireless audio.
Protocol Architecture
Bluetooth is defined as a layered protocol architecture consisting of core protocols, cable
replacement and telephony control protocols, and adopted protocols.
The core protocols form a five-layer stack consisting of the following elements:
 Radio - Specifies details of the air interface, including frequency, the use of frequency
hopping, modulation scheme, and transmit power.
 Baseband - Concerned with connection establishment within a piconet, addressing, packet
format, timing, and power control.
 Link manager protocol (LMP) - Responsible for link setup between Bluetooth devices and
ongoing link management. This includes security aspects such as authentication and
encryption, plus the control and negotiation of baseband packet sizes.
 Logical link control and adaptation protocol (L2CAP) - Adapts upper-layer protocols to
the baseband layer. L2CAP provides both connectionless and connection-oriented services.
 Service discovery protocol (SDP) - Device information, services, and the characteristics of
the services can be queried to enable the establishment of a connection between two or more
Bluetooth devices.
Protocol Architecture
Bluetooth is defined as a layered protocol architecture consisting of core protocols, cable
replacement and telephony control protocols, and adopted protocols.
The core protocols form a five-layer stack consisting of the following elements:
 Radio - Specifies details of the air interface, including frequency, the use of frequency
hopping, modulation scheme, and transmit power.
 Baseband - Concerned with connection establishment within a piconet, addressing, packet
format, timing, and power control.
 Link manager protocol (LMP) - Responsible for link setup between Bluetooth devices and
ongoing link management. This includes security aspects such as authentication and
encryption, plus the control and negotiation of baseband packet sizes.
 Logical link control and adaptation protocol (L2CAP) - Adapts upper-layer protocols to
the baseband layer. L2CAP provides both connectionless and connection-oriented services.
 Service discovery protocol (SDP) - Device information, services, and the characteristics of
the services can be queried to enable the establishment of a connection between two or more
Bluetooth devices.
RFCOMM is the cable replacement protocol included in the Bluetooth specification. RFCOMM
presents a virtual serial port that is designed to make replacement of cable technologies as
transparent as possible. Serial ports are one of the most common types of communications

3. interfaces used with computing and communications devices. Hence, RFCOMM enables the
replacement of serial port cables with the minimum of modification of existing devices. RFCOMM
provides for binary data transport and emulates EIA-232 control signals over the Bluetooth
baseband layer. EIA-232 (formerly known as RS-232) is a widely used serial port interface
standard.
Bluetooth specifies a telephony control protocol. TCS BIN (telephony control specification�binary)
is a bit-oriented protocol that defines the call control signaling for the establishment of speech and
data calls between Bluetooth devices. In addition, it defines mobility-management procedures for
handling groups of Bluetooth TCS devices.
The adopted protocols are defined in specifications issued by other standards-making
organizations and incorporated into the overall Bluetooth architecture. The Bluetooth strategy is to
invent only necessary protocols and use existing standards whenever possible. These are the
adopted protocols:
 PPP - The point-to-point protocol is an Internet standard protocol for transporting IP
datagrams over a point-to-point link;
 TCP/UDP/IP - These are the foundation protocols of the TCP/IP protocol suite;
 OBEX - The object exchange protocol is a session-level protocol developed by the Infrared
Data Association (IrDA) for the exchange of objects. OBEX provides functionality similar to that
of HTTP, but in a simpler fashion. It also provides a model for representing objects and
operations. Examples of content formats transferred by OBEX are vCard and vCalendar, which
provide the format of an electronic business card and personal calendar entries and scheduling
information, respectively;
 WAE/WAP - Bluetooth incorporates the wireless application environment and the wireless
application protocol into its architecture.
Usage Models
A number of usage models are defined in Bluetooth profile documents. In essence, a usage model
is a set of protocols that implement a particular Bluetooth-based application. Each profile defines
the protocols and protocol features supporting a particular usage model. Following are the highest-
priority usage models:
 File transfer - The file transfer usage model supports the transfer of directories, files,
documents, images, and streaming media formats. This usage model also includes the
capability to browse folders on a remote device;
 Internet bridge - With this usage model, a PC is wirelessly connected to a mobile phone or
cordless modem to provide dial-up networking and fax capabilities. For dial-up networking, AT
commands are used to control the mobile phone or modem, and another protocol stack (such
as PPP over RFCOMM) is used for data transfer. For fax transfer, the fax software operates
directly over RFCOMM;
 LAN access - This usage model enables devices on a piconet to access a LAN. Once
connected, a device functions as if it were directly connected (wired) to the LAN;
 Synchronization - This model provides a device-to-device synchronization of PIM (personal
information management) information, such as phone book, calendar, message, and note
information. IrMC (Ir mobile communications) is an IrDA protocol that provides client/server
capability for transferring updated PIM information from one device to another;
 Three-in-one phone - Telephone handsets that implement this usage model may act as a
cordless phone connecting to a voice base station, as an intercom device for connecting to
other telephones, and as a cellular phone;
 Headset - The headset can act as a remote device's audio input and output interface.

4. The History of Bluetooth
A long time ago (historians differ on the exact dates, but it was sometime in the 10th Century C.E.) in a country
far, far away, (which was mostly Denmark, with a little bit of Norway added in for flavor,) there lived a Viking
king who was principally noted for converting to a foreign religion called Christianity. He was known as Harald
Bluetooth, son of Gorm the Old, and he united most of Denmark before his estranged son, Sven Forkbeard, sent
him to Valhalla and took over the family business. A little more than 1000 years later, succumbing to an attack of
Scandinavian pride, the giant Swedish telecom manufacturer Ericsson decided to honor old, weird Harald by
naming its new wireless networking standard af ter him. It convinced founding Special Interest Group co-partners
Nokia, Toshiba, IBM and Intel that Bluetooth was the right name for the thing and, together, they set off to
conquer the air.
By December 1, 1999, 3Com, Lucent, Microsoft and Motorola had joined the Promoter Group -- the folks that were
willing to spend money to hype the standard -- and in the neighborhood of 1200 other companies had joined the
SIG. (Signing up for membership costs nothing, so it isn't exactly an exclusive club.) Between them, they manged
to generate a lot of coverage about Bluetooth in the trade press.
Since the computer trade press mainly consists of English and journalism majors with no hands -on technical background, most
of whom make a living re-wording press releases, the fanfare meant very little, however. M eanwhile, actual consumers waited
for actual products actually to emerge.
A s is often the case with consortium-driven standards -- even "open" ones like Bluetooth -- that took a while. A nd, as is also
often the case, the majority of the early products were aimed not at consumers, but at developers.
While the world waited, grass -roots programmers and engineers began playing with a brand new wireless standard: an
offshoot of good, old Ethernet called 802.11b. Like Bluetooth, it used the unlicensed 2.4 - 2.48GHz portion of the radio
spectrum, so 802.11b products would work anywhere on the planet without any special license from the local authorities. A nd
it was fast -- much faster than Bluetooth's nominal 1Mbps -- and it had about 10 times the range that Bluetooth's C lass 3
devices could boast.
T ime passed and soon it was 2001, the beginning of a brand-new millenium. T he clumsy-sounding 802.11b moniker had since
been supplanted by the less-tongue-twisting name "Wi-Fi" and the cost of its hardware was plunging like a dotcom stock
option.
T he world was still waiting for Bluetooth -- and, to its SIG partners' dismay, M icrosoft announced that the initial release of its
forthcoming Windows XP would not include Bluetooth support.
M icrosoft's stated reason for omitting the V iking technology from the next release of its flagship OS was the lack of a critic al
mass of Bluetooth-enabled devices demanding Windows support. T hat basically translated to the Redmond behemoth simply
acknowledging a conspicuous worldwide lack of user demand for the namesake of Gorm the O ld's son.
T hat's not the only problem with Bluetooth, however.
The Unfaithful Servant
First of all, there's the issue of cost. T he low end of the cellular phone hardware market i s savagely price-competitive and
Bluetooth silicon is still much too expensive to be included in the "gimme" phones that entice a substantial segment of cellu lar
consumers to take the plunge. T hat creates a chicken-or-egg conundrum, since Bluetooth must become ubiquitous in order to
achieve the enconomies of scale that would make it affordable to average consumers -- but first it must universally be adopted
in order to achieve those very economies of scale.
T hen there's the question of Bluetooth's security -- or, more properly, the gaping holes therein.
A lthough some have tried to wish the problem away, others have taken a more skeptical view of the fundamental weaknesses
in Bluetooth's P IN-based generation of a device's initialization key. Juha T . V ainio of the Helsinki U niversity of T echnology's
Department of C omputer Science and Engineering quite rightly points out [4] that a 4 -digit PIN offers only 10,000 total
possible combinations -- making 4 -digit PINs highly susceptible to brute-force cracking techniques -- and the problem is further
exacerbated by the well-known user laziness factor that results in a large number of 4 -digit PINs being set to 0000.
T here's also the possibility that one Bluetooth device may use its exchange of unit keys with a second de vice and third device
to eavesdrop on their "private" conversation -- or even falsely to authenticate itself to the one, masquerading as the other.
T hat's because, when the first two devices exchange unit keys, they can "decide" to use one or the other as a shared "secret"
to generate their link key. When a third device then enters into a key exchange with the second device, and also opens a
session with the first device, it reveals its unit key to both. T he first device now knows both of the others' "secrets" -- and their

5. entirely-public 48-bit BD_ADDRs -- and it's also synched to the same master clock. Now, merely by faking one of the other
box's BD_ADDR, it can generate the public keys necessary to listen in on its two neighbors' "private" traffic. A ssumi ng that the
first device can eavesdrop on their conversations, it can also authenticate itself as either device to the other, since that
imposture requires no additional data.
T he above problem is more than simply theoretical. Bell Labs scientists M arcus J akobsson and Susanne Wetzel demonstrated
exactly that scenario in the lab, as ZDnet reported on the 8th of September, 2000.
No Expectations
A nd, of course, even the weak security Bluetooth currently offers is part and parcel of the techology's price proble m.
Encryption, decryption and key generation all require significant processor power -- especially when the encryption in question
has to take place on the fly and simultaneously be at all robust -- and that doesn't come cheap, particularly when the market is
still small.
O f course Wi-Fi has its own security issues -- I'll address them another time -- and it can be just as much of a pain in the
posterior to configure as is its Scandanavian competitor. But the distinction between the two technologies is perh aps best
illustrated by taking a look at their deployment in the real world.
O n that score, Wi-Fi wins, hands down.
O h sure, RegistryMagic (now known as V oiceFlash) and the Wall Street Holiday Inn made a big fuss last February about their
demonstration of Bluetooth for guest check-in during the Internet World Wireless conference, but a quick check of the current
Holiday Inn Wall Street Web site shows nary a mention of the thing today. P erhaps the V enetian resort/hotel/casino will be
more enthusiastic about Harald's namesake after it tries its own pilot Bluetooth demo during Fall 2001 Comdex in Las Vegas.
P erhaps not.
Now We're Getting Somewhere
M eanwhile, Wi-Fi networks are springing up like mushrooms in a cow pasture after a warm Spring rain. Starbucks now has one
in every store -- albeit with access priced to discourage all but the investment banking crowd. Likewise, airport terminals
around the country are installing 802.11b nets to capture traffic from the hordes of passengers waiting for their too-often
delayed or canceled flights.
Businesses are also discovering that Wi-Fi makes a lot of sense in office suites where rapid staff expansion -- or contraction --
causes frequent moves and changes. A nd there is also a rapidly -growing assortment of free nets, mostly built by the open
source community with pooled resources, eager to offer access to all comers.
A nd that really exemplifies the difference in my mind. T here aren't any plans for Bluetooth -based open-access-point networks
of which I'm aware. T he gear itself remains painfully scarce, prohibitively expensive and seemingly destined to wind up joining
ISDN in the M useum of Little T echologies that C ouldn't.
Which may explain why developers are turning off to Bluetooth in droves.
Bring it on home
T here are, of course, those who disagree with my gloomy assesment, including some right here on dW Wireless. Big Blue itself
is still extremely big on the technology. It offers a Bluetooth PCCard for its latest laptops and it has even gone so far as to
release a Bluetooth protocol stack for Linux, to enable the P enguin P eople to make T ux talk Viking.
T he thing is, I still can't help but think that, like Harald, the modern Bluetooth is just going to wind up teeing off so man y
people who are crucial to its survival that, again like him, it will wind up face-down in a muddy field with an arrow in its back.
T hat would leave Wi-Fi, starring as Sven Forkbeard, to inherit Harald's kingdom of the air -- and to go on to overthrow
HomeRF, in its role as Ethelred the U nready.
But that's another story altogether.
How Bluetooth works
T he number of ways to wirelessly connect an increasing number of formerly wired devices is becoming confusing. Wi -Fi,
802.11a, 802.11b, 802.11g, GPRS, IrDA and Bluetooth are just some of the terms now being used to describe different types
of wireless connectivity.
T his article explains the differences between the main types of wireless connectivity, and explains how Bluetooth can be useful
for you.

6. Different Types of Connectivity Compared
T o start off the discussion, here is a table to show the major differences between the main types of wireless connectivity an d
traditional networking.
Type Speed Range Comments
IrDA 9.6kb - 115kb (- 4Mb) < 6ft
Infra-red. T he two devices must have their
IR ports facing each other. For simple data
exchange. U ses very little power.
Wi-Fi 1M b - 54Mb see below
Wi-Fi refers to any of the three 802.11 types
of wireless service below, and to future new
subcategories yet to be released. A cts like a
regular wired network in most respects.
Either built in or available as add-on cards or
adapters for desktop computers.
802.11a 1 - 54Mb 50ft - 150ft
Not commonly used, uses different
frequency than 802.11b/g.
802.11b 1 - 11Mb 100ft - 300ft M ost common version at present.
802.11g 1 - 54Mb 120ft - 350ft
T he latest version, backwardly compatible
with 802.11b.
Bluetooth 120kb - 723kb 30ft - 300ft
C lass 3 devices (eg in most personal
computing type devices) have a short 30ft
range, high powered C lass 1 devices have
the longer range. Either built in or available
as add-on cards.
GP RS < 115kb
wherever suitable
cellphone coverage
Data service used by GSM cellphones and by
some add-on cards for laptops and pda's.
Speed typically about 30kb depending on
how many users are sharing the service on
each cell at any given time. A 2.5G service.
2.5G
variously up to about
128kb
wherever suitable
cellphone coverage
V arious compromise new types of 'always on'
data service for cell phones that are better
than nothing but not nearly as good as the
3G service that all cell phone companies are
hoping to introduce when funding and
technology allows.
3G
2M b stationary, 384kb
moving with good
signal, 144kb moving
fast/poor signal
wherever suitable
cellphone coverage
A largely futuristic technology not much
deployed (yet) in the U S which promises
amazingly fast data transfer. Sprint P CS
V ision and A T&T EDGE (100-130kb) are the
closest things to 3G in the U S at present.
M odem < 56kb not wireless
T he 'old fashioned' way to dial up from a
computer to the internet.
DSL/C able 100kb - 1.5Mb not wireless
Not wireless.'Broadband' connections to the
internet.
LA N 10M b - 100Mb not wireless
Not wireless. C ommon type of cabled
network in most offices.
So What is Bluetooth?
Bluetooth is a very simple type of wireless networking that can allow up to eight devices to be connected together in a mini -
network.

7. It is very short range in operation, and so is considered to be for 'personal' networking. With a range typically under 30ft, this
allows enough distance to perhaps communicate across your office, but not any further. T his short range is also its major
security feature - anyone wishing to eavesdrop on your Bluetooth communications would not only need special equipment but
would also need to be quite close to you.
It is a moderately slow type of networking, but it can transfer data sufficiently fast enough for most typical applications.
Bluetooth is hoped to be a very low cost type of networking, and, as it becomes more widespread, the cost of adding Bluetooth
to devices should drop down to perhaps no more than an extra $5 -10 on the selling price.
Bluetooth is designed to be compatible across a range of very different operating systems and devices, including things that
you would not normally think of as being 'computer' type items - for example, some types of headset. Bluetooth networking
can enable the headset to connect with other devices such as your phone, your M P 3 player, your computer, or your P DA.
A Bluetooth enabled headset would mean that you can leave your cellphone in your pocket or briefcase, but still receive
incoming phone calls. If your cellphone supports voice recognition for dialing out, you can even place calls as well as receive
them, while never needing to reach for your phone. T he safety benefits of this, if you're driving, are obvious.
It is probably better from a health point of view to have a very low powered headset close to y our head than it is to have a
phone that might be generating 100 or even 300 times as much radio energy close to your head.
Bluetooth can also help different devices to communicate with each other. For example, you might have a phone, a P DA, and a
computer. If all three devices have Bluetooth capabilities, then (with the appropriate software on each device) you can
probably share contact information between all three devices quickly and conveniently. A nd you can look up a phone number
on your P DA (or laptop) and then place a call direct from the laptop or P DA, without needing to touch your cellphone.
Bluetooth is not a magical solution giving universal connectivity between devices. Each device also needs to have the
appropriate software as well as the basic Bluetooth communication capability, and so sometimes the promise and theory of
what could be possible is not fully matched by the reality.
For best compatibility, devices should support the Bluetooth 1.1 standard. A new standard - 1.2, was formalized in early
November 2003 and this will quickly become the dominant standard.
Bluetooth has been slow to become accepted in the market, but now is starting to become increasingly prevalent. P rices are
falling and increasing numbers of devices are offering Bluetooth connectivity. O ver one million Bluetooth devices are now being
sold every week (although mainly outside the U S).
Bluetooth Range
M ost Bluetooth devices are described as 'Class 2'. T hese are very low power (typically 1 milliwatt - 1/1000th of a watt) and
have a range of about 10 m (33 ft).
Some devices - for example, some plug in 'dongles' that can be added to to laptop computers - are C lass 1. T hese have range
comparable to that of Wi-Fi, ie, 100 m or 330 ft.
With Bluetooth, short range is actually a benefit, because it reduces the chance of interference between your Bluetooth devices
and those belonging to other people nearby.
Devices that Use Bluetooth
A limited, but growing number of devices use Bluetooth at present. Devices that are starting to have Bluetooth connectivity
built in include:
 Digital cameras and camcorders
 P rinters
 Scanners
 C ell P hones
 P DAs
 Laptops
 Keyboards and M ice
 Headsets
 In-car handsfree kits
 GP S navigation receivers
 Home appliances (microwaves, washers, driers, refrigerators)
In addition, add on Bluetooth adapters are available for computers (eg with a U SB interface) and for P DAs (eg SD cards).
Bluetooth connections
Bluetooth is a high-speed, low-power microwave wireless link technology, designed to connect phones, laptops, P DAs and
other portable equipment together with little or no work by the user. U nlike infra -red, Bluetooth does not require line-of-sight
positioning of connected units. T he technology uses modifications of existing wireless LAN techniques but is most notabl e for
its small size and low cost. T he current prototype circuits are contained on a circuit board 0.9cm square, with a much smalle r
single chip version in development. T he cost of the device is expected to fall very fast, from $20 initially to $5 in a yea r or two.
It is envisioned that Bluetooth will be included within equipment rather than being an optional extra. When one Bluetooth
product comes within range of another, (this can be set to between 10cm and 100m) they automatically exchange address and
capability details. T hey can then establish a 1 megabit/s link (up to 2 M bps in the second generation of the technology) with
security and error correction, to use as required. T he protocols will handle both voice and data, with a very flexible networ k
topography.

8. T his technology achieves its goal by embedding tiny, inexpensive, short-range transceivers into the electronic devices that are
available today. T he radio operates on the globally-available unlicensed radio band, 2.45 GHz (meaning there will be no
hindrance for international travelers using Bluetooth-enabled equipment.), and supports data speeds of up to 721 Kbps, as well
as three voice channels. T he bluetooth modules can be either built into electronic devices or used as an adaptor. For instanc e
in a P C they can be built in as a P C card or externally attached via the U SB port.
Each device has a unique 48 -bit address from the IEEE 802 standard. C onnections can be point-to-point or multipoint. T he
maximum range is 10 meters but can be extended to 100 meters by increasing the power. Bluetooth devices are protected
from radio interference by changing their frequencies arbitrarily upto a maximum of 1600 times a second, a technique known
as frequency hopping. T hey also use three different but complimentary error correction schemes. Built -in encryption and
verification is provided.
M oreover, Bluetooth devices won't drain precious battery life. T he Bluetooth specification targets power consumption of the
device from a "hold" mode consuming 30 micro amps to the active transmitting range of 8 -30 milliamps (or less than 1/10th of
a watt). T he radio chip consumers only 0.3mA in standby mode, which is less than 3 % of the power used by a standard
mobile phone. T he chips also have excellent power-saving features, as they will automatically shift to a low-power mode as
soon as traffic volume lessens or stops.
But beyond untethering devices by replacing the cables, Bluetooth radio technology provides a universal bridge to existing data
networks, a peripheral interface, and a mechanism to form small private ad hoc groupings of connected devices away from
fixed network infrastructures. Designed to operate in a noisy radio frequency environment, the Bluetooth radio uses a fast
acknowledgment and frequency hopping scheme to make the link robust. Bluetooth radio modules avoid interference from
other signals by hopping to a new frequency after transmitting or receiving a packet. C ompared with other systems operating
in the same frequency band, the Bluetooth radio typically hops faster and uses shorter packets. T his makes the Bluetooth radio
more robust than other systems. Short packages and fast hopping also limit the impact of domestic and professional
microwave ovens. U se of Forward Error C orrection (FEC) limits the impact of random noise on long -distance links. T he
encoding is optimized for an uncoordinated environment.
Bluetooth guarantees security at the bit level. A uthentication is controlled by the user by using a 128 bit key. Radio signals can
be coded with 8 bits or anything upto 128 bits. T he Bluetooth radio transmissions will conform to the safety standards required
by the countries where the technology will be used with respect to the affects of radio transmissions on the human body.
Emissions from Bluetooth enabled devices will be no greater than emissions from industry-standard cordless phones. T he
Bluetooth module will not interfere or cause harm to public or private telecommunications network.
T he Bluetooth baseband protocol is a combination of circuit and packet switching. Slots can be reserved for synchronous
packets. Each packet is transmitted in a different hop frequency. A packet nominally covers a single slot, but can be extended
to cover up to five slots. Bluetooth can support an asynchronous data channel, up to three simultaneous synchronous voice
channels, or a channel, which simultaneously supports asynchronous data and synchronous voice. It is thus possible to transfer
the date asynchronously whilst at the same time talking synchronously at the same time. Each voice channel supports 64 kb/s
synchronous (voice) link. T he asynchronous channel can support an asymmetric link of maximally 721 kb/s in either direction
while permitting 57.6 kb/s in the return direction, or a 432.6 kb/s symmetric link.
Bluetooth Operation Modes
A n interesting aspect of the technology is the instant formation of networks once the bluetooth devices come in range to each
other. A piconet is a collection of devices connected via Bluetooth technology in an ad hoc fashion. A P iconet can be a simpl e
connection between two devices or more than two devices. M ultiple independent and non-synchronized piconets can form a
scatternet. A ny of the devices in a piconet can also be a member of another by means of time multiplexing. i.e a device can b e
a part of more than one piconet by suitably sharing the time. T he Bluetooth system supports both point-to-point and point-to-
multi-point connections. When a device is connected to another device it is a point to point connection. If it is connected to
more that one (upto 7 ) it is a point to multipoint connection. Several piconets can be established and linked together ad hoc,
where each piconet is identified by a different frequency hopping sequence. A ll users participating on the same piconet are
synchronized to this hopping sequence. If a device is connected to more than one piconet it communicates in each piconet
using a different hopping sequence. A piconet starts with two connected devices, such as a portable PC and cellular phone, an d
may grow to eight connected devices. A ll Bluetooth devices are peer units and have identical imp lementations. However, when
establishing a piconet, one unit will act as a master and the other(s) as slave(s) for the duration of the piconet connection . In a
piconet there is a master unit whose clock and hopping sequence are used to synchronize all othe r devices in the piconet. A ll
the other devices in a piconet that are not the master are slave units. A 3 -bit MAC address is used to distinguish between units
participating in the piconet. Devices synchronized to a piconet can enter power-saving modes called Sniff and hold mode, in
which device activity is lowered. A lso there can be parked units which are synchronized but do not have a M A C addresses.
T hese parked units have a 8 bit address, therefore there can be a maximum of 256 parked devices.
V oice channels use either a 64 kbps log P CM or the C ontinuous V ariable Slope Delta M odulation (CVSD) voice coding scheme,
and never retransmit voice packets. T he voice quality on the line interface should be better than or equal to the 64 kbps log
P C M. T he CVSD method was chosen for its robustness in handling dropped and damaged voice samples. Rising interference
levels are experienced as increased background noise: even at bit error rates up 4%, the C V SD coded voice is quite audible.
Bluetooth and the Internet
Bluetooth can be used to connect between a device that has internet connectivity and another device that does not, for
example, you might use Bluetooth to connect from your P DA to your laptop, and then your laptop might use Wi -Fi to connect
to a Wi-Fi router and from there you would be connected to the internet.
Sometimes when buying a P DA you may find yourself with an apparent 'either//or' choice - either buy a device with Bluetooth;
or a device with Wi-Fi capability. In such a case, it would seem at first glanc e that if you want to connect to the internet -
especially while traveling out of your office, Wi-Fi would be a better choice.

9. However, this is not quite such a clear choice. Wi-Fi 'hotspots' are few and far between. A much better approach might be to
get Bluetooth on your P DA and also on your cellphone and use Bluetooth to connect to your cellphone and then connect
through your cellphone and out to the internet from there. I use T -M obile's GPRS service - they offer unlimited connect time
and unlimited bandwidth usage for only $20/month extra on top of my regular cellphone service (and GP RS connection time
does not count against my monthly minutes - it truly is unlimited for only $20/month).
In my opinion, this is the perfect solution. GP RS coverage is much more widespread than Wi-Fi coverage, and while it is not
fast, it is adequate for simple mail sending/receiving, instant messaging, and occasional web browsing such as you're likely to
do on a P DA. A lthough I also have Wi-Fi in my laptop, these days I never use it, and indeed if I'm sitting in a Starbucks with
my laptop, I'll be connecting to the internet not through the Wi -Fi in Starbucks, but via Bluetooth and my cellphone's GPRS!
Which is better - Bluetooth or Wi-Fi
Wi-Fi is primarily used as an alternate to traditional cable based networks. It has a longer range than Bluetooth, and supports
faster data transfer speeds, and so it might seem better than Bluetooth.
But, in reality, Bluetooth and Wi-Fi have different purposes. Bluetooth is intended for limited data transfer between many
different types of devices, Wi-Fi is more focussed on faster data transfer between computers on a network.
O ne of the distinctive elements of Bluetooth is that is uses very much less power than Wi -Fi. C lass 2 devices (such as are in
P DAs, phones, headsets, etc) transmit a very low power signal (1 mW) and only transmit intermittently when in standby mode,
saving even more power. Wi-Fi, on the other hand, consumes a great deal of power, and so for any type of portable battery
operated device, Bluetooth will allow for substantially more battery life than would Wi -Fi.
If you're simply wanting to swap data between different devices in your office and elsewhere on a casual and occasional basis ,
then - assuming that the software and Bluetooth hardware is available - Bluetooth is probably a better choice for you. If you
need more range, and higher bandwidth; perhaps if you want to connect computers into your office LAN, then Wi -Fi is a better
choice for you.
Bluejacking
Bluejacking is a moderately harmless 'fun' type trick that some people have discovered. It involves sending messages from
your Bluetooth device to other people close to you with Bluetooth devices, and surprising the recipient in the process.
T he easiest way to Bluejack is to create a new phonebook contact, with the message you want to send in the name field. T hen,
in a busy place with lots of people (so that there is a chance that someone might have a Bluetooth enabled phone or P DA),
choose the option to send your new contact via Bluetooth. Y our phone or P DA will then search for all Bluetooth devices in
range, and present you with a list. C hoose whichever device you wish from the list and send it. T he recipient will get a
message asking if they wish to accept your contact, and showing the text you entered as the contact's name (eg something
like 'Bad weather today isn't it' or whatever else you wish to say).
If you're planning to enjoy Bluejacking (or T oothing, below) you'll probably want to get your eye in to guessing how fa r away
10 m/33 ft is so as to know how many people and devices might be within range.
Toothing
Harmless Bluejacking didn't take long to evolve into a more goal oriented social activity, now known as 'toothing', whereby
people communicate to other Bluetooth equipped people around them, trying to arrange casual and immediate trysts.
Summary
Bluetooth promises to be a low cost, convenient, and simple way of enabling your various computer devices to talk to each
other and to their peripherals. T he reality has yet to match the promise, but Bluetooth is becoming more widespread and
functional every day. Bluetooth is almost certainly in your future.
Bluetooth is not a competitor to Wi-Fi. It offers different functionality for different purposes.

10. How Bluetooth ShortRange Radio Systems Work-.....
If you have the normal complement of electronic equipment in your home, then you know all of the different ways that devices
connect to one another. For example:
 M any desktop computer systems have a C PU unit connected to a mouse, a keyboard, a printer and so on.
 A personal digital assistant (P DA) will normally connect to the computer with a cable and a docking cradle.
 A ny T V is normally connected to a V C R and a cable box, with a remote control for all three components.
 A cordless phone connects to its base unit with radio waves, and it may have a headset that connects to the phone with a
wire.
 In a stereo system, the C D player, tape player and record player connect to the receiver, which connects to the speaker.
T he art of connecting things is becoming more and more complex every day. O ftentimes we feel as if we need a P h.D. in
electrical engineering just to set up the electronics in our houses! We will look at a completely different way to form the
connections called Bluetooth. Bluetooth is wireless and automatic, and has a number of interesting features that should
simplify our daily lives!
The Problems
When any two devices need to talk to each other, they have to agree on a number of points before the conversation can begin.
T he first point of agreement is physical: Will they talk over wires, or through some form of wireless signals? If they use wi res,
how many are required -- 1, 2, 8, 25 or more? O nce the physical attributes are decided, several more questions arise:
 Information can be sent one bit at a time in a scheme called serial communications, or in groups of bits (usually 8 or 16
at a time) in a s cheme called parallel communications. A desktop computer uses both serial and parallel communications
to talk to different devices: M odems, mice and keyboards tend to talk through serial links, while printers tend to use
parallel links.
 A ll the parties in an electronic discussion need to know what the bits mean and whether the message they receive is the
same message that was sent. In most cases, this means developing a language of commands and responses known as a
protocol. Some types of products have a standard protocol used by virtually all companies so that the commands for one
product will tend to have the same effect on another. M odems fall into this category. O ther product types each speak their
own language, which means commands intended for one specific product will seem gibberish if received by another.
P rinters are like this, with multiple standards like PCL and P ostScript.
 C ompanies that manufacture computers, entertainment systems and other electronic devices have realized that the
incredible array of cables and connectors involved in their products makes it difficult for even expert technicians to
correctly set up a complete system on the first try. Setting up computers and home entertainment systems becomes
terrifically complicated when the pers on buying the equipment has to learn and remember all the details to connect all the
parts. In order to make home electronics more user friendly, we need some better way for all the electronic parts of our
modern life to talk to each other. T hat's where Bluetooth comes in.
Bluetooth Basics
Bluetooth is a new standard developed by a group of electronics manufacturers that will allow any sort of electronic equipmen t
-- from computers and cell phones to keyboards and headphones -- to make its own connections, without wires, cables or any
direct action from a user. Bluetooth is intended to be a standard that works at two levels:
 It provides agreement at the physical level -- Bluetooth is a radio-frequency standard.
 It also provides agreement at the next level up, where products have to agree on when bits are sent, how many will be
sent at a time and how the parties in a conversation can be sure that the message received is the same as the message
sent.
 T he companies belonging to the Bluetooth Special Interest Group, and there are more than 1,000 of them, want to let
Bluetooth's radio communications take the place of wires for connecting peripherals, telephones and computers.

11. T here are already a couple of ways to get around using wires. O ne is to carry information between components via beams of
light in the infrared spectrum. Infrared refers to light waves of a lower frequency than human eyes can receive and interpret .
Infrared is used in most television remote control systems, and with a standard call ed IrDA (Infrared Data A ssociation) it's
used to connect some computers with peripheral devices. For most of these computer and entertainment purposes, infrared is
used in a digital mode -- the signal is pulsed on and off very quickly to send data from one point to another.
Infrared communications are fairly reliable and don't cost very much to build into a device, but there are a couple of
drawbacks. First, infrared is a "line of sight" technology. For example, you have to point the remote control at the t elevision or
DV D player to make things happen. T he second drawback is that infrared is almost always a "one to one" technology. Y ou can
send data between your desktop computer and your laptop computer but not to your laptop computer and your P DA at the
same time.
T hese two qualities of infrared are actually advantageous in some regards. Because infrared transmitters and receivers have t o
be lined up with each other, interference between devices is uncommon. T he one -to-one nature of infrared communications is
useful in that you can make sure a message goes only to the intended recipient, even in a room full of infrared receivers.
T he second alternative to wires, cable synchronizing, is a little more troublesome than infrared. If you have a P alm P ilot, a
Windows C E device or a P ocket PC (a class of computer called Personal Digital Assistant, or P DA for short), you know about
synchronizing data. In synchronizing, you attach the P DA to your computer (usually with a cable), press a button and make
sure that the data on the P DA and the data on the computer match. It's a technique that makes the P DA a valuable tool for
many people, but synchronizing the P DA with the computer and making sure you have the correct cable or cradle to connect
the two can be a real hassle.
Bluetooth is intended to get around the problems that come with both infrared and cable synchronizing systems. T he hardware
vendors have developed a specification for a very small radio module to be built into computer, telephone and entertainment
equipment. From the user's point of view, there are three important features to Bluetooth:
 It's wireless. When you travel, you won't have to worry about keeping track of a briefcase full of cables to attach all your
components, and you can design your office without wondering where all the wires will go.
 It's inexpensive.
Y ou don't have to think about it. Bluetooth doesn't require you to do anything special to make it work. T he devices find one
another and strike up a conversation without any user input at all. Bluetooth communicates on a frequency of 2.45 gigahertz,
which has been set aside by international agreement for the use of industrial, scientific and medical devices (ISM). A number
of devices that you may already use take advantage of this same radio -frequency band. Baby monitors, garage-door openers
and the newest generation of cordless phones all make use of frequencies in the ISM band. M aking sure that Bluetooth and
these other devices don't interfere with one another has been a crucial part of the design process.
Avoiding Interference
O ne of the ways Bluetooth devices will avoid interfering with other systems is by sending out very weak signals of 1 milliwatt.
By comparison, the most powerful cell phones can transmit a signal of 3 watts. T he low power limits the range of a Bluetooth
device to about 10 meters, cutting the chances of interference between your computer system and your portable telephone or
television. Even with the low power, the walls in your house won't stop a Bluetooth signal, making the new standard useful fo r
controlling several devices in different rooms.
With many different Bluetooth devices in a room, you might think they'd interfere with one another, but it's unlikely that
several devices will be on the same frequency at the same time because Bluetooth uses a technique called spread-spectrum
frequency hopping. In this technique, a device will use 79 individual randomly chosen frequencies within a designated range,
changing from one to another on a regular basis. In the case of Bluetooth, the transmitters change frequencies 1,600 times
every second, meaning that more devices can make full use of a limited slice of the radio spectrum. Since every Bluetooth
transmitter uses spread-spectrum transmitting automatically, it's unlikely that two transmitters will be on the same frequency
at the same time. T his same technique minimizes the risk that portable phones or baby monitors will disrupt Bluetooth devices
since any interference on a particular frequency will last only a tiny fraction of a second.
When new Bluetooth-capable devices come within range of one another, an electronic conversation will take place to determine
whether they have data to share or whether one needs to control the other. T he user doesn't have to press a button or give a
command -- the electronic conversation happens automatically. O nce the conversation has occurred, the devices -- whether
they're part of a computer system or a stereo -- form a network. Bluetooth systems create a P ersonal-Area Network (PAN) or
"piconet" that may fill a room or may encompass no more distance than that between the cellphone on a belt-clip and the
headset you're wearing. O nce a piconet is established, the members randomly hop frequencies in unison so they stay in touch
with one another and avoid other piconets that may be operating in the same room.

12. Bluetooth compared to other wirelesstechnologies
Bluetooth technology is one solution for wireless personal area networks (WPANs). Two other technologies of
interest, namely IrDA and HomeRF, are described here. The IEEE� 802.15 standards work also addresses WPANs
and the IEEE� 802.11 working group addresses wireless LANs; this work is discussed separately in other articles.
We choose to discuss HomeRF and IrDA because they have interesting relationships with Bluetooth wireless
technology. Strictly speaking, these technologies are not limited to the WPAN domain, although they can be
considered part of it. Certainly there are other technologies that could be employed in the WPAN domain:
wearable computing devices are becoming more popular and could be considered WPANs or elements of WPANs.
IrDA is relevant for comparison to Bluetooth wireless communications because the two technologies share some
similar usage models and protocols. HomeRF, like Bluetooth wireless technology, is a relatively short -range RF
communications scheme that operates in the 2.4 gigahertz (GHz) industrial, scientific, and medical (ISM) band.
These technologies are described next, with the objective of providing a context in which Bluetooth wireless
communications as a WPAN technology can be better understood.
IrDA and Bluetooth Wireless Communication Compared
IrDA is an infrared wireless communication technology developed by the Infra red Data A ssociation. Here we compare and
contrast specific features of these technologies.
IrDA is a specific use of infrared light as a communications medium; Bluetooth technology is a specific use of radio waves as a
communications medium. Like the Bluetooth special interest group (SIG), the IrDA specifies hardware and software protocols
for wireless communication intended to promote interoperable applications.
A lthough both technologies are wireless, they use different parts of the electromagnetic spect rum with quite different signal
propagation characteristics. Because infrared uses the nonvisible infrared light spectrum, IrDA communication is blocked by
obstacles that block light (such as walls, doors, briefcases, and people). T he signal wavelength use d with Bluetooth
communication (about 12.5 cm, at its associated frequency of 2.4GHz) is three orders of magnitude greater than that of IrDA.
A t this wavelength, radio frequency (RF) communications can penetrate many of these sorts of obstacles. Recent adv ances in
infrared technology have enabled more diffuse transmission patterns, although much of the IrDA equipment in use today uses
a relatively narrowly focused beam, which usually requires that the two devices engaged in IrDA communication be aligned
with (pointed at) each other. RF transmission patterns radiate in some pattern (ideally, spherical) around the radio antenna, so
any two devices within range can communicate with each other, whether or not they are "pointed at" each other (in fact, the
second device might not be visible at all to the user of the first device, as it could be in another room behind doors and walls or
even on another floor of a building, for example).
T he initial IrDA data rate of 115 kilobits per second (Kbps) has now been enhanced to 1 megabit per second (M bps),
comparable to that of the first Bluetooth radios. T oday, IrDA can achieve data rates of up to 4M bps, with even higher rates
already specified and beginning to be implemented. Bluetooth wireless communication occurs at a raw data rate of 1M bps, with
higher speeds being investigated.
T he effective range for Bluetooth wireless communication is about 10 meters using the standard 0 dBm radio. With optional
power amplification of up to 20 dBm, range on the order of 100 meters c an be achieved. IrDA range is about 1 meter and, as
noted already, generally requires a line of sight to establish a connection.
Both Bluetooth wireless technology and IrDA communication are optimized for low power consumption and low cost. C ompared
to other RF communication technologies, Bluetooth communication consumes very little power and is projected to have very
low module costs in the foreseeable future. However, IrDA consumes significantly less power than Bluetooth technology,
because far less power is required for infrared transceivers than for RF transceivers. IrDA hardware also already is less
expensive than Bluetooth radio modules, owing largely to the maturity and wide deployment of IrDA.
T his brief discussion indicates that IrDA technology c ompares favorably to Bluetooth technology in the areas of cost, power,
and data rate. However, Bluetooth technology can add convenience and user mobility by relaxing the device alignment and line
of sight requirements of IrDA communications. T his illustrates an additional design parameter for WP A Ns: enhanced device
usability enabled by the unconscious application of communications technology. RF technologies are well suited for this aspec t
of WP A Ns, and Bluetooth wireless technology further emphasizes device usability characteristics in the profiles. A ll of these
considerations, both objective and subjective, may influence the choice of a WP A N technology for a particular application.

13. Home RF and Bluetooth Wireless Communication Compared
HomeRF is a wireless radio communications technology developed by the HomeRF working group, an industry
consortium not unlike the Bluetooth SIG (in fact, several companies participate in both groups). Like Bluetooth
wireless communications, HomeRF operates in the 2.4GHz ISM band, using radio waves for relatively short-range
voice and data communication among various types of devices. The impetus for developing the HomeRF
technology was to provide a solution for wireless in-home networks.
HomeRF and Bluetooth technologies have many parallels. Both were developed at roughly the same time, and
both operate in the unlicensed 2.4GHz ISM band for RF communications. Each one enables both voice and data
traffic; and each one is designed for relatively short-range, low-power operation. The first products using these
technologies were available by 2001.
The two technologies do have differences, though. In addition to technical differences such as packet structure
and protocol layers that are not detailed here, other characteristics distinguish them. HomeRF was designed from
the outset for home networking environments, whereas Bluetooth technology is optimized for use with WPANs
and mobile. HomeRF communication range is about 50 meters (designed to cover a typical home), which is
greater than the 10-meter range of the typical Bluetooth radio. Initially, the data rates of the two technologies
were similar at about 1Mbps; recently, HomeRF version 2.0 has specified data rates up to 10Mbps. With all other
factors being equal, higher data rates and greater range require more power consumption, so HomeRF often could
require more power, although both technologies include power-saving schemes in their respective specifications.
Like any technologies that operate in the same frequency spectrum, HomeRF and Bluetooth wireless
communications can interfere with each other. Radio frequency interference is to be expected in the unlicensed
2.4GHz ISM band. One means to mitigate RF interference is the use of frequency-hopping spread-spectrum
(FHSS), and both of these technologies use FHSS as a way to deal with undesired interference. Other techniques
also can be used to minimize the problem of RF interference among these and other RF emitters in the ISM band.
WPAN Technology Summary
Bluetooth wireless communications is one instance of a WPAN technology. Other technologies also can be used in
WPANs, and we reviewed two of these, IrDA and HomeRF.
These and other mechanisms can be employed to implement WPANs, but each is optimized for specific usage,
applications, or domains. Although in some respects, certain technologies might be viewed as competing in the
WPAN space, we believe that at least the ones discussed here are complementary to each other. Each has specific
advantages that make it particularly suitable for certain environments or applications, and we expect that
multiple WPAN technologies will exist in the foreseeable future.

14. GSM Logical & Physical Channels
- a tutorial, description, overview of GSM channels including transport and logical channels, SACCH,
SDCCH, FACCH, etc.
GSM uses a variety of channels in whichthe dataiscarried. In GSM, these channelsare separated into physical channels and logical
channels. The Physical channels are determined by the timeslot, whereas the logical channels are determined by the information
carried within the physical channel. It can be further summarised by saying that several recurring timeslots on a carrier con stitute a
physical channel. These are then used by different logical channelsto transfer information.These channelsmay either be use d for user
data (payload) or signalling to enable the system to operate correctly.
Common and dedicated channels
The channelsmay also be dividedintocommonand dedicated channels. The forward common channelsare used for paging to inform a
mobileof an incomingcall, respondingto channel requests, and broadcasting bulletinboardinformation. The returncommon ch annel is
a random access channel used by the mobile to request channel resources before timing information is conveyed by the BSS.
The dedicatedchannelsare of two main types: those used for signalling,and those used for traffic. The signalling channels are used for
maintenanceof the call and for enabling call set up, providing facilities such as handover when the call is in progress, and finally
terminating the call. The traffic channels handle the actual payload.
The following logical channels are defined in GSM:
TCHf - Full rate traffic channel.
TCH h - Half rate traffic channel.
BCCH - Broadcast Network information,e.g. for describing the current control channel structure. The BCCH is a point -to-multipoint
channel (BSS-to-MS).
SCH - Synchronisation of the MSs.
FCHMS - frequency correction.
AGCH - Acknowledge channel requests from MS and allocate a SDCCH.
PCHMS - terminating call announcement.
RACHMS - access requests, response to call announcement, location update, etc.
FACCHt - For time critical signalling over the TCH (e.g. for handover signalling). Traffic burst is stolen for a full signalling burst.
SACCHt - TCH in-band signalling, e.g. for link monitoring.
SDCCH - For signalling exchanges, e.g. during call setup, registration / location updates.
FACCHs - FACCH for the SDCCH. The SDCCH burst is stolen for a full signalling burst. Function not clear in the present version of
GSM (could be used for e.g. handover of an eight-rate channel,i.e.using a "SDCCH-like" channel for other purposes than signalling).
SACCHs - SDCCH in-band signalling, e.g. for link monitoring