Protocols in Bluetooth

Abstract:Protocol layers are a hierarchical model of
network or communication functions. The divisions of
the hierarchy are referred to as layers or levels, with
each layer performing a specific task. In addition,
each protocol layer obtains services from the protocol
layer below it and performs services for the protocol
layer above it. The Bluetooth system divides
communication functions into protocol layers.
The Bluetooth system consists of many existing
protocols that are directly used or have been adapted
to the specific use of the Bluetooth system. Protocols
are often divided into groups that are used for
different levels of communication (a protocol
stack). Lower level protocols (such as protocols that
are used to manage a radio link between specific
points) are only used to create, manage, and
disconnect transmission between specific points. Mid-
level protocols (such as transmission control
protocols) are used to create, manage, and disconnect
a logical connection between endpoints that may have
multiple link connections between them. High level
protocols (application layer protocols) are used
tolaunch, control, and close end-user applications.
Some of the layers associated with the Bluetooth
system include the baseband layer (physical layer),
link layer, host controller interface (HCI), logical link
control applications protocol (L2CAP), RF
Communications protocol (RFCOMM), Object
Exchange (OBEX), and service discovery.
Keywords: Bluetooth, Bluetooth stack, protocols, layers,
baseband, LMP, L2CAP, RFCOMM, Ad hoc networks,
PANs.
I.INTRODUCTION
Bluetooth is a wireless technology
standard for exchanging data over short distances
(using short-wavelength radio waves in
the ISM band from 2.4 to 2.485 GHz) from fixed
and mobile devices, building personal area
networks (PANs). Invented by telecom
vendor Ericsson in 1994, it was originally
conceived as a wireless alternative to RS-232 data
cables. It can connect several devices, overcoming
problems of synchronization.
Bluetooth is managed by the Bluetooth Special
Interest Group (SIG), which has more than 19,000
member companies in the areas of
telecommunication, computing, networking, and
consumer electronics. Bluetooth was standardized
as IEEE 802.15.1, but the standard is no longer
maintained. The SIG oversees the development of
the specification, manages the qualification
program, and protects the trademarks. To be
marketed as a Bluetooth device, it must
be qualified to standards defined by the SIG. A
network of patents is required to implement the
technology, which is licensed only for that
qualifying device.
Wireless data exchange standard Bluetooth uses a
variety of protocols. Core protocols are defined by
the trade organization Bluetooth SIG. Additional
protocols have been adopted from other standards
bodies. It an overview of the core protocols and
those adopted protocols that are widely used.
The Bluetooth protocol stack is split in two parts: a
"controller stack" containing the timing critical
radio interface, and a "host stack" dealing with high
level data. The controller stack is generally
implemented in a low cost silicon device
containing the Bluetooth radio and a
microprocessor. The host stack is generally
implemented as part of an operating system, or as
an installable package on top of an operating
system. For integrated devices such as Bluetooth
headsets, the host stack and controller stack can be
run on the same microprocessor to reduce mass
production costs; this is known as
a hostless system.
The Bluetooth technology answers the need for
short range wireless connectivity within three
areas: • Data and voice access points .
• Cable replacement
• Ad hoc networking
The Bluetooth technology specification specifies a
system solution comprising hardware, software and
interoperability requirements. The Bluetooth radio
operates in a globally available 2.4GHz ISM
Protocols In Bluetooth

band, ensuring communication compatibility
worldwide.
a. Data and voice access point :
The Bluetooth technology facilitates real time
voice and data transmission. The technology makes
it possible to connect any portable and stationary
communication device as easily as switching on the
light. You can, for instance, surf the Internet &
send e-mail on your potable PC or notebook
regardless of whether you are wirelessly connected
through a mobile phone or through a wire bound
connection (PSTN, ISDN,LSN,XDLS).
Voice channel use the Continuous Variable
Slope Delta Modulation (CVSD) coding scheme,
and never retransmit voice packets. The CVSD was
chosen for its robustness in handling dropped and
damaged samples. Rising interference levels are
experienced as increased background noise; even at
bit error rate up to 4% the CVSD coded voice is
quite audible.
b. CABLE REPLACEMENT:
The Bluetooth technology eliminates the use
for numerous often proprietary cable attachments
for connection of practically any kind of device.
Connections are instant and they are maintained
even when devices are not within line of sight. The
range of each radio is approximately 10 meters but
it can be extended around 100 meters with an
optional amplifier.
c. AD-HOC NETWORKING:
A device equipped with Bluetooth radio
establishes instant connection to another Bluetooth
radio as soon as it comes into range. Since
Bluetooth technology supports both point to point and
point to multi point connection, several piconets can be
established and linked together ad hoc. The Bluetooth
technology is best described as multiple piconet
structure.
Piconet is a connection of devices connected via
Bluetooth technology in an ad hoc fashion . A
piconet starts with two connected devices ,such as
portable PC and cellular phone and may grow into
eight connected devices. All Bluetooth devices are
peer units and have identical implementation.
However, when establishing a piconet, one unit
will act as a master and the other as a slave for the
duration of piconet connection.
Fig 1: Overview of Bluetooth.
II. Architecture of Bluetooth Protocol.
Fig 2: Architecture of Bluetooth Protocol.
a. Radio
The radio is used for specification of the air
interfaces, i.e. frequencies, modulation, and
transmit power.Bluetooth radio is a transceiver
which transmits and receives modulated electrical
signals from peer Bluetooth devices
b. Baseband
The Baseband and Link Control layer enables
the physical RF link between Bluetooth units

forming a piconet. This layer controls the Bluetooth
unit's synchronization and transmission frequency
hopping sequence. The two different link types
defined in Bluetooth, Synchronous Connection
Oriented, SCO, and Asynchronous Connectionless,
ACL, described in the section Link types, are also
managed by this layer.
The ACL links, for data, and the SCO links, mainly
for audio, can be multiplexed to use the same RF
link.
The link defines “what” of packets can be used on a
particular link. Also they fall under MAC layer.
The Bluetooth baseband technology supports two
link types:
• Synchronous connection oriented (SCO) type
(used primarily for voice)
• Asynchronous connectionless (ACL) type (used
primarily for packet data)
Different master slave pairs of the same piconet
structure can use different link types and the link
type may change arbitrarily during a session. Each
link “supports up to 16 different packet types. Four
of these are control packets and are common for
both SCO and ACL links. Both link types use a
Time Division Duplex (TDD) scheme for full
duplex transmission.
SYNCHRONOUS CONNECTIONS
ORIENTED TYPE:
The SCO link is symmetric and typically
supports time bound voice traffic. SCO packets are
transmitted over reserved intervals. Once the
connection is established, both master and slave
units may send SCO packets without being polled.
One SCO packet type allows both voice and data
transmission ; with only the data portion being
retransmitted when corrupted.
ASYNCHRONOUS
CONNECTIONLESS LINK TYPE:
The ACL link is packet oriented and supports
both, symmetric and asymmetric traffic. The master
unit controls the link bandwidth and decides how
much piconet bandwidth is given to each slave, and
the symmetry of the traffic. Slaves must be polled
before they can transmit data. The ACL link also
supports broadcast messages from the master to all
slaves in the piconet.
In order to make different hardware
implementations compatible, Bluetooth devices use
the HCI as a common interface between the
Bluetooth host (e.g. a portable PC) and the
Bluetooth core.
Higher-level protocols like the SDP, RFCOMM
(emulating a serial port connection) and the TCP
are interfaced to baseband services via the LLCAP.
Among the issues LLCAP takes care of, is
segmentation and reassemble to allow larger data
packets to be carried over a Bluetooth baseband
connection. The service discovery protocol allows
applications to find out about available services and
their characteristics when e.g. devices are moved or
switched off.
c. Audio
Audio transmissions can be performed
between one or more Bluetooth units, using many
different usage models. Audio data do not go
through the L2CAP layer (described below) but go
directly, after opening a Bluetooth link and a
straightforward set-up, between two Bluetooth
units.
d. Host Controller Interface, HCI
The Host Controller Interface, HCI, provides a
uniform interface method for accessing the
Bluetooth hardware capabilities. It contains a
command interface to the Baseband controller and
link manager and access to hardware status.
Finally, it contains control and event registers.
e. Link Manager Protocol, LMP
The Link Manager Protocol, LMP, is
responsible for link set-up between Bluetooth units.
It handles the control and negotiation of packet
sizes used when transmitting data. The Link
Manager Protocol also handles management of
power modes, power consumption, and state of a
Bluetooth unit in a piconet. Finally, this layer
handles generation, exchange and control of link
and encryption keys for authentication and
encryption.
f. Logical Link Control and Adaptation
Protocol, L2CAP
The Bluetooth logical link control and
adaptation protocol, L2CAP, is situated over the
Baseband layer and beside the Link Manager
Protocol in the Bluetooth protocol stack. The
L2CAP layer provides connection-oriented and
connectionless data services to upper layers.
The four main tasks for L2CAP are:

• Multiplexing –
L2CAP must support protocol multiplexing
since a number of protocols (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.
This and the reverse functionality, reassemble,
is performed by L2CAP.
• Quality of Service –
The establishment of an L2CAP connection
allows the exchange of information regarding
current Quality of Service for them connection
between the two Bluetooth units.
• Groups –
The L2CAP specification supports a group
abstraction that permits implementations for
mapping groups on to a piconet.
• An L2CAPimplementation must be
uncomplicated and implying low overhead
since it must be compatible with the limited
computational resources in a small Bluetooth
unit.
g. Service Discovery Protocol, SDP
The Service Discovery Protocol, SDP, defines
how a Bluetooth client's application shall act to
discover available Bluetooth servers' services and
their. Bluetooth characteristics. The protocol
defines how a client can search for a service based
on specific attributes without the client knowing
anything of the available services. The SDP
provides means for the discovery of new services
becoming available when the client enters an area
where a Bluetooth server is operating. The SDP
also provides functionality for detecting when a
service is no longer available.
• Cable replacement protocol
h. Radio Frequency Communication ,
RFCOMM
The Radio Frequency Communication
RFCOMM protocol is a serial port emulation
protocol. The protocol covers applications that
make use of the serial ports of the unit. RFCOMM
emulates RS-232 control and data signals over the
Bluetooth baseband. It provides transport
capabilities for upper level services, e.g.
OBEX that use a serial line as the transport
mechanism.
i. 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
establishment of speech and data calls between
Bluetooth units. The protocol defines the signalling
for establishment and release of calls between
Bluetooth units. As well as signalling to ease the
handling of groups of Bluetooth units. Furthermore,
TCS Binary provides functionality to exchange
signalling information unrelated to ongoing calls.
Establishment of a voice or data call in a point-to-
point configuration as well as in a point-to-
multipoint configuration is covered in this protocol
(note, after establishment, the transmission is from
point to point). The TCS Binary is based on the
ITU-T Recommendation.
Telephony Control – AT Commands
A number of AT-commands are supported for
transmitting control signals for telephony control.
These use the serial port emulation, RFCOMM, for
transmission.
j. Adopted protocols
This section describes a number of protocols
that are defined to be adopted to the Bluetooth
protocol stack. Note some of these adaptations are
at the moment incomplete.
PPP
The IETF Point-to-Point Protocol (PPP) in the
Bluetooth technology is designed to run over
RFCOMM to accomplish point-to-point
connections. PPP is a packet-oriented protocol and
must therefore use its serial mechanisms to convert
the packet data stream into a serial data streams.
TCP/UDP/IP
The TCP/UDP/IP standards are defined to
operate in Bluetooth units allowing them 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/PPP
protocol configuration is used for all Internet
Bridge usage scenarios in Bluetooth 1.0 and for
OBEX in future versions. The UDP/IP/PPP
configuration is available as transport for WAP.

OBEX Protocol
IrOBEX, shortly OBEX, is an optional
application layer protocol designed to enable units
supporting infrared communication to exchange a
wide variety of data and commands in a resource-
sensitive standardized fashion. OBEX uses a client-
server model and is independent of the transport
mechanism and transport API. The OBEX protocol
also defines a folder-listing object, which is used to
browse the contents of folders on remote device.
RFCOMM is used as the main transport layer for
OBEX.
Content formats
The formats for transmitting vCard and
vCalendar information are also defined in the
Bluetooth specification. The formats do not define
transport mechanisms but the format in which
electronic business cards and personal calendar
entries and scheduling information are transported.
vCard and vCalendar is transferred by OBEX.
Wireless Application Protocol, WAP
The Wireless Application Protocol (WAP) is a
wireless protocol specification that works across a
variety of wide-area wireless network technologies
bringing the Internet to mobile devices. Bluetooth
can be used like other wireless networks with
regard to WAP, it can be used to provide a bearer
for transporting data between the WAP Client and
its adjacent WAP Server. Furthermore, Bluetooth’s
ad hoc networking capability gives a WAP client
unique possibilities regarding mobility compared
with other WAP bearers.
The traditional form of WAP communications
involves a client device that communicates with a
Server/Proxy device using the WAP protocols.
Bluetooth is expected to provide a bearer service as
specified by the WAP architecture. The WAP
technology supports server push. If this is used
over Bluetooth, it opens new possibilities for
distributing information to handheld devices on
location basis. For example, shops can push special
price offers to a WAP client when it comes within
Bluetooth range.
CONCLUSION:
A new global standard for voice, data also the
devices are wireless so portability issue is
removed.Eliminates use of cables and need of
connecting every device with cables.Low power,
low range, low cost network device so use becomes
reasonable.Further improvements are planned to
made in Bluetooth are data rate, power reduction,
range.
Acknowledgement:
I will like to thank our Prof. for giving the chance
to explore oneself.
References:
[1].http://www.tech.plym.ac.uk/dcee/postgrad/refer
ence/BlueTooth/page2.html#architecture
[2].http://www.althos.com/tutorial/Bluetooth-
tutorial-protocol-layers.html
[3].http://www.bluetooth.com/Pages/Bluetooth-
Home.aspx
[4].http://www.palowireless.com/infotooth/tutorial.
asp
[5].http://en.wikipedia.org/wiki/Bluetooth_protocol
s
[6].http://msdn.microsoft.com/en-
us/library/ms890956.aspx
[7].http://www.thestudymaterial.com/presentation-
seminar/electronics-presentation/51-bluetooth-
technology.html?start=3
[8]http://www.scribd.com/doc/135626916/Bluetoot
h-Protocol-Stack

Protocols in Bluetooth

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Protocols in Bluetooth