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									                        WHAT IS BLUE TOOTH
P.MANASA                                              A.LAVANYA
III B.Tech (E.C.E A)                                  III B.Tech (E.C.E A)
JNTU NO: 06341A0450                                   JNTU NO: 06341A0404
Phno: 9393166988                                      phno: 9849493766
Emai id:pakkimanasa@gmail.com




SUMMARY:-
Bluetooth is a standard for short range,
low power, low cost wireless                  into open standards to ensure rapid
communication       that     uses     radio   acceptance and compatibility in the
technology.      Although        originally   market place. The resulting Bluetooth
envisioned as a cable-replacement             specification,    developed     by    the
technology by Ericsson (a major cell          Bluetooth SIG, is open and freely
phone manufacturer) in 1994, embedded         available at the official Bluetooth
Bluetooth capability is becoming              website Www.bluetooth.org. Bluetooth
widespread in numerous types of               technology is already supported by over
devices. They include intelligent devices     2100 companies around the world. The
(PDAs, cell phones, PCs), data                Wireless Personal Area Network
peripherals (mice, keyboards, joysticks,      (WPAN) technology, based on the
cameras, digital pens, printers, LAN          Bluetooth Specification, is now an IEEE
access points), audio peripherals             standard under the denomination of
(headsets, speakers, stereo receivers),       802.15 WPANs. In 2003, Cahners In-
and embedded applications(automobile          Stat estimated that Bluetooth-enabled
power locks, grocery store updates,           equipment shipments would climb to
industrial systems, MIDI musical              just fewer than 1 billion units by
instruments).Ericsson joined forces with      2005.The Bluetooth specification define
Intel Corporation, International Business     how Bluetooth devices will group
Machines Corporation (IBM), Nokia             themselves for the purposes of
Corporation, and Toshiba Corporation to       communication. A Bluetooth Wireless
form the Bluetooth Special Interest           Personal Area Network (BT-WPAN)
Group (SIG) in early 1998. 3Com               consists of piconets. Each piconet is a
Corporation, Lucent/Agere Technologies        cluster of up to eight Bluetooth devices.
Inc., Microsoft       Corporation and         One device is designated as the master,
Motorola Inc. joined the group in late        and the others are the slaves. Two
1999. Joint work by the SIG members           piconets can be connected through a
allowed the Bluetooth vision to evolve        common Bluetooth device (a gateway or
bridge) to form a scatternet. These          Interface (HCI) are included in the
interconnected piconets within the           Transport Protocol group. These
scatternet form a backbone for the           protocols support both asynchronous and
Mobile Area Network (MANET), and             synchronous transmission. All the
can enable devices which are not directly    protocols in this group are required to
communicating with each other, or            support       communications      between
which are out of range of another device,    Bluetooth devices. The Middleware
to exchange data through several hops in     Protocol group includes third-party and
the scatternet.Current implementations       industry-standard protocols, as well as
of Bluetooth depend primarily on simple      Bluetooth SIGdeveloped protocols.
point-to point data links between            These protocols allow existing and new
Bluetooth devices within direct range of     applications to operate over Bluetooth
each other. However, the Bluetooth           links. Industry standard protocols
specification defines not only a point-to-   include Point-to-Point Protocol (PPP),
point link (connectivity) solution, but      Internet Protocol (IP), Transmission
also a solution for more complex             Control Protocol (TCP), wireless
networking topologies. Therefore, the        application protocols (WAP), and object
goal is to form Bluetooth scatter nets       exchange (OBEX) protocols, adopted
that provide effective and efficient         from      Infrared    Data     Association
communication over multiple hops with        (IrDA).Bluetooth           SIG-developed
acceptable response times and power          protocols include 1) a serial port
consumption so that end-to-end solutions     emulator (RFCOMM) that enables
can be deployed. This article presents an    legacy applications to operate seamlessly
overview of Bluetooth communication.         over Bluetooth transport protocols, 2) a
The Bluetooth protocol stack:                packet based telephony control signaling
The Bluetooth specification divides the      protocol (TCS) for managing telephony
Bluetooth protocol stack into three          operations, and 3) a service discovery
logical groups. They are the Transport       protocol (SDP) that allows devices to
Protocol group, the Middleware Protocol      obtain information about each other’s
group and the Application group, as          available services. Reuse of existing
shown in Fig. 1. The Transport group         protocols and seamless interfacing to
protocols allow Bluetooth devices to         existing applications was a high priority
locate each other, and to manage             in the development of the Bluetooth
physical and logical links with higher       specifications, as shown in Fig. 2.The
layer protocols and applications. Please     Application group consists of actual
note that the use of the word “transport”    applications that use Bluetooth links.
in the Transport protocol group does not     They can include legacy applications as
indicate that it coincides with the          well as Bluetooth-aware applications. A
Transport layer of the Open systems          brief discussion of the layers in the
Interconnection Reference Model (OSI)        Transport group follows. Radio layer.
model.      Rather,    these    protocols    The specification of the Radio layer is
correspond to the Data-Link and              primarily concerned with the design of
Physical layers of the OSI model. The        the Bluetooth transceivers, discussed in
Radio, Base band, Link Manager,              detail later. Base band layer. These layer
Logical Link Control and Adaptation          define show Bluetooth devices search
(L2CAP) layers and the Host Controller       for and connect to other devices. The
                                            general data, bandwidth reservation for
                                            audio traffic, authentication using
                                            challenge response methods, and trust
                                            relationships       between       devices,
                                            encryption of data and control of power
                                            usage. Power usage control includes the
                                            negotiation of low power activity modes
                                            and the determination of transmission
                                            power levels.L2CAP layer. The Logical
                                            Link Control and Adaptation Protocol
                                            (L2CAP) layer provides the interface
master and slave roles that a device may    between the higher-layer protocols and
assume are defined here, as are the         the lower-layer transport protocols.
frequency-hopping sequences used by         L2CAP supports multiplexing of several
devices. The devices use a time division    higher layer protocols, such as RFComm
duplexing (TDD), packet-based polling       and SDP. This allows multiple protocols
scheme to share the air-interface. The      and applications to share the air
master and slave each communicate only      interfaces L2CAP is also responsible for
in their pre-assigned time slots. Also,     packet segmentation and reassembly,
defined here are the types of packets,      and for maintaining the negotiated
packet processing procedures and the        service level between devices.HCI
strategies for error detection and          layers.      The      Host      Controller
correction,       signal      scrambling    Interface(HCI) layer defines a standard
(whitening),      encryption,      packet   interface for upper level applications to
transmission and retransmissions. The       access the lower layers of the stack. This
Base band layer supports two types of       layer is not a required part of the
links: Synchronous Connection-Oriented      specification. Its purpose is to enable
(SCO) and Asynchronous Connection-          interoperability among devices and the
Less (ACL). SCO links are characterized     use of existing higher level protocols and
by a periodic, single-slot packet           applications.
assignment, and are primarily used for      Communication
voice transmissions that require fast,      A Bluetooth transceiver is a frequency
consistent data transfer. A device that     hopping spread-spectrum (FHSS) device
has established a SCO link has, in          that uses the unlicensed (worldwide) 2.4
essence, reserved certain time slots for    GHz ISM (Industrial, Scientific,
its use. Its data packets are treated as    Medical) frequency band. In most
priority packets, and will be serviced      countries, there are 79 channels
before any ACL packets. A device with       available; however, some countries
an ACL link can send variable length        allow the use of only 23 channels. The
packets of 1, 3 or 5 time-slot lengths.     nominal bandwidth for each channel is
But it has no time slots reserved for it.   1MHz. FCC part 15.247 regulations
Link Manager layer. This layer              restrict the maximum allowed peak
implements the Link Manager Protocol        power output to 1 watt and require that
(LMP), which manages the properties of      at least 75 of the 79 channels be used in
the air interface link between devices.     a pseudorandom manner. A device can
LMP manages bandwidth allocation for        not operate on a given channel for longer
than 0.4 seconds within any 30-second         of data, and may be protected by a 1/3
period. These limits (or restrictions)        rate FEC (simple bit repetition, for SCO
were put into place to minimize the           packets only), a 2/3 rate FEC (which is a
amount of interference in the ISM band,       (15,10) shortened Hamming code
which is also used by 802.11 b/g              capable of correcting all one-bit errors
devices, Home RF devices, portable            and detecting all two-bit errors), or a 3/3/
phones and microwave ovens. When              rate (no FEC). For SCO connections,
connected to other Bluetooth devices, a       packets must be exactly one time-slot in
Bluetooth     device hops         (changes    length. For ACL links, packets may be 1,
frequencies) at the rate of 1600 times per    3, or 5 time slots in length. Bluetooth
second for typical use, with a residence      uses polling-based packet transmission.
time of 625 sec. When in inquiry or           All communication between devices
page mode, it hops at 3200 hops per           takes place between a master and a
second with a residence time of 312.5         slave, using time-division duplex (TDD),
sec .A Bluetooth transceiver uses all 79      with     no    direct    slave-to     slave
channels, and hops pseudo-randomly            communication. The master will poll
across all channels at a rate of 1600Hops     each active slave to determine if it has
per second for standard transmissions. It     data to transmit. The slave may only
has a range of approximately 10 meters,       transmit data when it has been polled.
although ranges up to 100 meters can be       Also, it must send its data in the time
achieved with amplifiers. Because the         slot immediately following the one in
transceiver has an extremely small            which it was polled. The master
footprint, it is easily embedded into         transmits only in even numbered time
physical devices, making it a truly           slots, while the slaves transmit only in
ubiquitous radio link. The Bluetooth          odd-numbered time slots. In each time
specification     uses    time     division   slot, a different frequency channel f is
duplexing (TDD) and time division             used (a hop in the hopping sequence).
multiple access (TDMA) for device             The piconet
communication. A single time slot is 625      The Bluetooth specification defines a
    sec in length, representing the length    piconet as an ad-hoc, spontaneous
of a single-slot packet. At the Base band     clustering of Bluetooth devices. In it,
layer, a packet consists of an access         one device holds the role of master,
code, a header, and the payload, as           while the rest of the devices are slaves.
shown in Fig. 3. The access code              While there is no limit to the total
contains the piconet address (to filter out   number of slaves in a piconet, a
messages from other piconets) and is          maximum of seven slaves can be active
usually 72 bits in length. The header         in a piconet at any given point in time. If
contains link control data, encoded with      there are more than seven slaves, the rest
a forward error-correcting code (FEC)         of the slaves must be “parked.” The
with a 1/3 rate for high reliability. Such    maximum number of “parked” slaves is
code is a repetition code and thus every      255 per piconet with direct addressing
bit in the header is transmitted three        via a parked slave address as defined by
times. The header is usually 18 bits in       the SIG; however, indirect addressing of
length, and includes the active member        parked slaves by their specific Bluetooth
address for a currently active slave. The     device address is also permitted,
payload can contain from 0 to 2745 bits
effectively allowing any number of           and clock information in order for the
parked slaves.                               slave to join the master’s piconet.
                                             Bluetooth devices each have a unique
                                             Global ID used to create a hopping
                                             pattern. The master radio shares its
                                             Global ID and clock offset with each
                                             slave in its piconet, providing the offset
                                             into the hopping pattern. A slave must be
                                             able to recreate the frequency-hopping
                                             sequence of the piconet it has joined,
                                             must know which frequency to use at
                                             which time, and must synchronize itself
                                             with the master’s clock. The slave
                                             device does not actually adjust its own
                                             clock. Rather it tracks the amount of
                                             clock drift between its clock and the
                                             master’s, and adjusts its transmission
                                             schedule accordingly. A Bluetooth
                                             bridge device (or gateway) interconnects
                                             two or more piconets for multi-hop
                                             communication.           The         bridge
                                             communicates with all the piconets
 To reactivate a parked slave, the master    connected to it by aligning itself with the
must first place a currently active slave    clocking of each piconet when it is ready
into a parked state. When two Bluetooth      to communicate. However, it can only
devices enter into communication range,      communicate with one piconet at a time.
they will attempt to communicate with        Because the bridge incurs addition an
each other.                                  overhead shifting from one clocking to
If no piconet is available at that time, a   another to communicate with each
negotiation process will ensue. One          connected piconet, it has the potential to
device will become the master (usually       become a bottleneck. A bridge device
the device which initiated the               may be a slave in all of the piconets to
communication) and the other will            which it is connected, or it may be a
become a slave. Any Bluetooth device         master in one piconet and a slave in the
can function within a piconet as a           others. The interconnection of two or
master, a slave or a bridge. These roles     more piconets via bridge devices results
are temporary and exist only as long as      in the formation of a Bluetooth scatter
the piconet itself exists. The master        net. A Bluetooth device can be in one of
device selects the frequency, the            The following states: standby, inquiry,
frequency-hopping sequence, the timing       page, connected, transmit, hold, park or
(when the hops will actually occur) and      sniff, as shown in Fig. 4. A device is in
the polling order of the slaves. The         Standby mode when it is powered on but
master is also responsible for instructing   has not yet joined a piconet. It enters the
the slave devices to switch to different     Inquiry state when it sends out requests
device states for periods of inactivity. A   to find other devices to which it might
master and slave must exchange address       connect. A master of an existing piconet
may also be in a Page state, sending out      enable many types of devices to
messages looking for devices that it can      communicate; and
invite to join its Pico net.          When    4) Bluetooth uses an unregulated
successful communication is made              frequency band available anywhere in
between the master and the new device,        the world.
the new device assumes the slave role,        To fully realize the Bluetooth vision,
enters the connected state, and receives      full networking of multiple Bluetooth
an active address. While connected, the       A device is required. This leads to the
slave can transmit data when the master       Investigation of Bluetooth scatters nets,
polls it. During the transmission of its      Which      must      address    scatternet
data, the slave is in a Transmit state. At    formation?
the end of its transmission, it returns to    and reconfiguration, scheduling,
the connected state. The Sniff state is a     and routing issues.
low-power consumption state in which
the slave “sleeps” for a pre-determined
number of time slots. It wakes up at its
appointed       time     slot    for   data
transmission. It then returns to the
inactive state until its next designated
Sniff time slot arrives. The Hold state is
another low-power state in which the
slave is not active for a predetermined
amount of time. However, there is no
data transfer within the Hold state. When
a slave device has no data to send or
receive, the master may instruct the
slave to enter the Park state. When it
enters a Park state, the slave relinquishes
its active address in the Pico net. The
address will then be given to another
slave that the master is reactivating from
Park state.
CONCLUSION:
Bluetooth         wireless       technology
encompasses several key points that
facilitate its widespread adoption:
1) It is an open specification that is
publicly available and royalty free;
2) Its short-range wireless capability
allows        peripheral      devices    to
communicate over a single air-interface,
replacing cables that use connectors with
a multitude of shapes, sizes and numbers
of pins;
3) Bluetooth supports both voices and
data, making it an ideal technology to

								
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