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Bluetooth Hotspot: Extending the Communication
Range between Bluetooth Devices
Madhu Kanojia, Swati Garje
Lokmanya Tilak College of Engineering,
Navi Mumbai, Maharashtra
[email protected]
Lokmanya Tilak College of Engineering,
Navi Mumbai, Maharashtra
[email protected]
Abstract: Bluetooth is a wireless technology standard for exchanging data over short distances from fixed and mobile devices and
building personal area network (PANs).Bluetooth is a wireless communication protocol, since it’s a communication protocol, you can
use Bluetooth to communicate to other Bluetooth enabled devices. Bluetooth has a client server architecture; the one that initiates the
connection is the client, and the one who receives the connection is the server.
Keywords: Ad hoc, Bluetooth, piconet, scatternet, Hotspot, Internet, GPRS or Wi-Fi facility.
1. Introduction
Bluetooth (Ericsson trademark) takes its name from Harald
Blatland (Bluetooth), a Danish king born in AD 908 who
united his country under Christianity. An Ericsson-led
consortium, including IBM, Intel, Nokia, and Toshiba, have
developed the technology. A second group, the Bluetooth
Special Interest Group (SIG) was then formed to promote the
technology and comprised 1371 member companies in early
January 2000 [12].
Ad hoc networks today are based primarily on Bluetooth
technology. Bluetooth is an open standard for short-range
digital radio. It is touted as a low –cost, low –power, and low
profile technology that provide a mechanism for creating
small wireless networks on an Ad hoc basis. Bluetooth
is considered a wireless PAN technology that offers
fast and reliable transmission for both voice and data
[3].
Untethered Bluetooth devices will eliminate the need for
cables and provide a bridge to existing networks [1].A
broadband hotspot is one application where Bluetooth has a
value in providing internet access to mobile users.
Consumers owning a Bluetooth enabled mobile phone can
easily access a Bluetooth hotspot to browse the internet
without having to carry a PDA or laptop [3].A distinguishing
feature of Bluetooth networks is the master-slave relationship
maintained between the network devices.Upto eight
Bluetooth devices may be networked together in a masterslave relationship called piconet. As shown in Fig 1 In
piconet one device is designated as the master of the network
with upto seven slaves connected directly to the network [1].
Figure 1: Piconet and Scatternet
2. Bluetooth Protocol Stack
The protocol stack makes up the core portion of the
Bluetooth implementation [3]. As shown in figure 2 the
connection devices can exchange data and interact with one
another through various applications. The protocol
architecture of the bluetooth consists of following in a
bluetooth protocol stack:
 Core protocols consisting 5 layer protocol stack viz.
radio, baseband, link manager protocol, and logical
link control and adaptation protocol, service
discovery protocol.
 Cable
replacement
protocol
,RFCOMM
 Telephony
Control
Protocols
 Adopted protocols viz. PPP, TCP/UDP/IP, OBEX
and WAE/WAP [5].
2.1
Core Lower Layers
2.1.1 Radio
This layer deals with the conversion of data into radio
frequency (RF) signals for transmission through the air
[4].Data is broken up into very small packets and transmitted
usually one packet per frequency jump or slot [1]. Bluetooth
operates in the 2.4 GHz Industrial, Scientific and Medical
(ISM) radio-frequency band, which is license-free for lowpower transmissions in most of the world [3]
2.1.2 Baseband/Link Controller
Addressing scheme, packet frame format, timing and power
control algorithms required for establishing connection
between bluetooth devices within piconet defined in this part
of protocol specification [3].The baseband layers role is to
properly format data for transmission to and from the radio
module and perform basic error control[1].The link
controller is responsible for encoding and decoding of
Bluetooth packets from the data payload and parameters
related to the physical channel, logical transport and logical
link[4].
2.1.3 Link Manager
The link manager is responsible for the creation,
modification, and release of logical links as well as the
update of parameters related to physical link between devices
[4]. This protocol also includes authentication and encryption
specifications [5].
2.2 Host Controller Interface(HCI)
The HCI provides a command interface to the baseband link
controller and link manager, and access to hardware status
and control registers [6].The host controller driver should be
independent of the underlying transport technology [4].
2.3
Core Upper Layers
2.3.1 Logical Link Control and Adaptation
The Logical link control and adaptation protocol
acts as
the middle manager between applications and the bluetooth
link controller [3].L2CAP passes packets either to the Host
controller Interface(HCI),or in a Host-less system,L2CAP
passes packets directly to the Link manager[7].
2.3.2 Service Discovery Protocol
Service related queries including device information can be
taken care at this protocol so that connection can be
established between bluetooth devices [5]. SDP consists of
servers and clients components, where the requesting devices
are a client and the requested device the server. A single
Bluetooth device can perform both roles of a SDP-server and
–client [3].
2.4 Non-Core Upper Layers
2.4.1 RFCOMM
The RFCOMM protocol provides emulation of serial ports
over the L2CAP protocol. RFCOMM is only concerned with
the connection between the devices in the direct connect
case, or between the device and a modem in the network case
[8].
2.4.2 OBEX
Object Exchange (OBEX) is a widely used protocol for
simple file transfers between mobile devices. Its main use is
in infrared communication, where it is used for generic file
transfers between notebooks or PDAs, and for sending
business cards or calendar entries between cellular phones
and other devices with Personal Information Manager (PIM)
application. The OBEX client is used to push and/or pull
objects from the OBEX server [8].
2.4.3 Bluetooth Network Encapsulation Protocol (BNEP)
The Bluetooth Network Encapsulation Protocol (BNEP) sits
on top of L2CAP and allows standard network protocols such
as TCP, IPv4 and IPv6 to be transported across Bluetooth
links. BNEP provides this encapsulation by replacing the
Ethernet header, with a BNEP header and sends this header
and the data across the L2CAP layer [3].
2.5 Audio
Audio transmission can be performed between one or more
bluetooth units, using many different usage models. Audio
data do not go through the L2CAP layer but go directly, after
opening a bluetooth link and a straightforward setup between
two bluetooth units [9].
2.6 Finding a Device
Before a device is able to make a connection to another
device, it needs to discover that device. For device discovery,
the three states are inquiry, inquiry scan and inquiry
response [3].
Figure 2: Bluetooth protocol stack
2.6.1 Inquiry State
The inquiry state is entered when a device attempts to
discover all other devices within range. In this state the
searching device repeatedly transmits inquiry message on a
set of different frequencies [3].
2.6.2 Inquiry Scan Display
For a Bluetooth device to be discoverable, it has to answer
inquiry messages from other devices. This is done by
entering an optional inquiry scan state. A device which is
discoverable does this periodically (at least every 2.56
seconds) and listens for an extended time compared to the
inquiry state. If a device does not want to be located it can be
set to be non-discoverable and therefore will not enter the
inquiry scan state [3].
2.6.3 Inquiry Response State
When a device receives a valid inquiry message it will then
enter the inquire response state and respond with a frequency
hopping synchronisation (FHS) packet [1].
3. Need
As the number of bluetooth products increases each year, it is
important to develop applications and services to take full
advantage of their potential and capabilities. A broadband
hotspot is one application where Bluetooth has a value in
providing Internet access to mobile users. Consumers owning
a Bluetooth enabled mobile phone can easily access a
Bluetooth hotspot to browse the Internet without having to
carry a PDA or a laptop [10].
sitting in front of the PC if the acquired slave information
indicates that the user’s bluetooth device is specified as an
authentication key [11].
Figure 3. Inquiry Method
5.2
Communication Link Method
A communication link is data transmission connection
between a master and slave for sending and receiving data
packets. The master sets up a communication link to a slave
by using slave information when the master establishes a
connection with the slave, and it controls data transmission to
confirm whether the slave can communicate with it[11].
4. Basic Steps
Steps to be followed in Bluetooth hotspot are:
• Connectivity
• Authentication and security
• Data transfer
The process starts with connectivity process in which
Bluetooth server sending a message of pairing to all the
discoverable mobile devices in its range. The devices
receiving the message need to send an appropriate response
to the server back to complete the authentication. Now the
connection link is established and the data/ file transfer can
take place [10].
5. Connectivity
Identification and authorization are the two important steps
for having trusted connection between two Bluetooth
devices. Connectivity is the first step for establishing any
Connection [11].
Figure 4. Communication link Method
6.
Eavesdropping is the act of secretly listening to the private
conversation of others without their consent [11].
6.2
•
Inquiry method (Inquiry function of Bluetooth)
• Communication link method (Monitoring communication
link)
5.1 Inquiry Method
The Bluetooth device of the PC (master) gets the slave
information of surrounding Bluetooth devices by running the
inquiry function regularly. The PC then judges that the user is
Security
When a user sends data over a wireless network, he has a
reasonable expectation that such data is not easily readable
by unauthorized persons. Unlike a wired network, which
requires a physical intrusion, wireless data packets can be
received by anyone nearby with an appropriate receiver,
potentially outside the physical security barriers of an
organization. There are basically two main security issues in
wireless technology which are needed to be considered for
trust building between two devices [11].
Eavesdropping
False authentication
Bluetooth technology provides a method for authenticating
devices .Device authentication is provided using a shared
secret between the two devices. The common secret key is
called a link key. There are two types of link keys. Unit keys
and combination keys [11].A device using a unit key uses the
same secret for all of its connections. Combination keys are
link keys that are unique to a particular pair of devices. The
combination key is only used to protect the communication
between these two devices [11].Authentication is performed
with a challenge response Scheme utilizing the E1 algorithm.
The scheme operates as follows:
The verifier issues a 128 bit long challenge. The claimant
then applies E1 using the challenge, its 48-bit bluetooth
address, and the current link key. He then returns the 32 most
significant bits of the128 bit result. The verifier confirms the
response, in which case the authentication has succeeded
[11].
7.
Data Transfer
Data is transferred using packets .To transfer data, a link
needs to be established between the devices.
Between two (or more) Bluetooth devices two types of links
can be established, namely:
8.2.1 Masquerading
This requires designing a system where each hotspot is able
to masquerade as other bluetooth devices and therefore able
to advertise itself as a device that is located at other hotspots.
As shown in the Figure 6 where bluetooth device A is
communicating with bluetooth device B via the hotspots.
Each Bluetooth device thinks that it is communicating
directly with each other but in fact are communicating with
the respective hotspot which is masquerading as the distant
device.
• Synchronous Connection-Oriented (SCO) link
The SCO link is typically used for time-bounded data, such
as voice.
• Asynchronous Connectionless Link (ACL)
The ACL link works as a traditional packet switched
network. Packets are transmitted only when necessary.
8.
Proposed Bluetooth Hotspot
In this section we propose a bluetooth hotspot and examine
two different implementation approaches.
8.1 BlueSpot
BlueSpot, the software components of the proposed
Bluetooth hotspot are introduced, as well as the connection
framework between these components and other hotspots.
Bluetooth devices that are out of radio range to communicate
with each other we envision setting up a collection of devices
that would be connected together by an IP network as shown
in Figure 4 and would act as what has been called Bluetooth
hotspots. These Bluetooth Hotspots would allow Bluetooth
devices that are distant from each other but within range of a
hotspot to be able to communicate with each other via the
hotspots.
Figure 6: Using masquerading to create communications
8.2.2 Using Service Proxying
The second method was to examine Bluetooth’s SDP and the
feasibility of using SDP to provide facilities to discover
remote devices and make possible the setting up of
communication links between devices.
Figure7: Using Service Discovery to create communications
As shown in figure 7 a user (Device A) within the range of
hotspot (Hotspot X) is able to query that hotspot for all the
services that it offers. The hotspot will then return a
list(“service available”) of what other devices (device B) are
within range of other distant hotspot(Hotspot Y) and what
services they can offer to allow for communication with a
distant device [1].
Figure 5: Bluetooth Hotspot
8.2 Different Approaches
The functionality of extending the reach of Bluetooth
Communication can be implemented at different layers in the
Bluetooth protocol stack. These could be broken down into
two primary implementation approaches:
 Hotspots masquerade as other remote bluetooth devices,
 Hotspots offer or otherwise proxy the services offered
by other devices
8.3 Bluetooth Hotspot
The bluetooth hotspot is made up of three separate
interlinked components.
Figure 9: Advertising a services
Figure 8: Bluetooth hotspot components
8.3.1
Management Component:
Manages the other software components that make up the
hotspot as well as detects when bluetooth devices come
within range and leave. The main role of the management
component is to supervise such as start and stop the different
applications. It periodically scans for the local bluetooth
devices that have entered range and detecting as if previously
detected device is not communicating and inform to service
device component about new device.
8.3.2
Using a proxyed service
Service Database Component:
Collects, stores and advertises services that are detected by
all the Bluetooth hotspots within a network. When it is
notified of a new bluetooth device it will acquire a list of all
the services that that device is advertising via its SDP server.
If the services have transport application available then it can
added to an internal database and all the other remote
database are notified about the device. Then the local and
remote databases will start the transport.
8.3.3 Transport Component:
This makes the connection between hotspot and bluetooth
devices. It transports the bluetooth communications between
the two bluetooth devices via bluetooth hotspots over an IP
network.
8.4
8.4.2
Figure 10: Using a proxyed service
1. A bluetooth device B browses the SDP server on
Hotspot Y.
2. The transport component then connect to its peer and
start transmitting the data received from device B1.
3. A bluetooth device B browses the SDP server on
Hotspot Y2.
4. Using the above information it then connect to the
transport component and transport component is
then connect to its peer and start transmitting the
data it receives from device B.
Connection Framework
The two jobs that a bluetooth hotspot performs are the
advertising of services from remote devices and the
facilitating of communication between two devices.
8.4.1 Advertising a service
The steps for advertising a service are:
Bluetooth hotspot X detects bluetooth device A.
1. The management component informs the local
service database component(SDC) of the new
device within range
2. The SDC queries the SDP server on the bluetooth
device and finds out what services it is able to
facilitate.
3. The SDC then starts the transport component for
services.
9. Bluetooth vs. Infrared
Infrared
Infrared technology is what most TV remotes use. The
distance an infrared signal can travel varies based on the
strength of the remote, but is usually less than 50 feet for
household electronics. In order for an infrared signal to be
detected, there must be a direct line of sight between the
transmitter (Remote) and the receiver (TV).If there is a wall
on large object between them, the signal will not pass
through it.
Bluetooth
Bluetooth uses a radio frequency, which allows transmission
through walls and other objects. The standard range of
bluetooth device is upto 30 ft. which makes it ideal for
syncing PDAs with computers, using wireless cell phone
headsets, and enabling hands free cell phone use inside
Bluetooth-enabled automobiles.
While Bluetooth is well on its way to replacing infrared in
many different areas, the technology is not meant to be used
for wireless networking. Instead, Wi-Fi technology, which
has a larger range and higher bandwidth than Bluetooth, is
the standard that most wireless networking equipment uses
[13].
Conclusion
Bluetooth is a wireless radio specification designed to
replace the cables as the medium for data and voices signals
between electronic devices. With the use of internet so
rampant in these days the access of internet must be
simplified and made common. Bluetooth Hotspot is the
perfect way to realize this need. Bluetooth Hotspot already
exists for use in computers and in laptops. But to carry
around a laptop everywhere to access free internet on mobile
phone is a lot of effort. Also a Bluetooth dongle should be
used. That is why Bluetooth Hotspot will be of a great help.
The Bluetooth specification seeks to simplify communication
between electronic devices by automating the connection
process. In this paper we explained Bluetooth protocol stack
and its different layers, then moving on to how Bluetooth
networks are formed and devices are located. The proposed
idea in this paper is to develop Bluetooth hotspot and
examine two different implementation
Approaches. BlueSpot, the software components of the
Proposed Bluetooth hotspot are introduced, as well as the
connection framework between these components and other
Hotspot.
Aacknowledgement
We would like to thank our guide, Prof. Anil Chhangani for
his guidance and support, which has helped us, complete this
research paper successfully.
References
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