Saturday, June 29, 2013
Blue Tooth
1. INTRODUCTION
The idea that resulted in the
Bluetooth technology was born in 1994. Ericsson Mobile communications initiated
a study to investigate the feasibility of a low-power, low-cost radio interface
between Mobile Phones
And their accessories. The aim was to
eliminate cables between Mobile Phones and PC cards, headsets and Desktop
devices etc.
In February 1998, five companies, Ericssion,
Nokia, IBM, Toshiba and Intel formed a Special Interest Group (SIG). The group
contained the Mix of business areas –two market leaders in Mobile Telephony, to
market leaders in Laptop computing and
a market leader in core digital – signal-processor technology. It’s important
to surround yourself with the right kind of people. That is a fact that even
old Herald knew.
In this Electronic era, the devices used by us are rapidly
growing. We are using
several wires to
supply power, to connect
user interfaces, to connect each
other. There will be no problem until we shift them from one place to another.
Bluetooth wireless technology – the technology that propels you into a new
dimension in wireless connectivity.
Bluetooth is a
new standard developed
by a group
of electronics
manufacturers, that will
allow any sort
of electronic equipment
from
Computers and cell phones to keyboards and
headphones- to make its own connections without wires, cables or any direct
action from user.
Why the name Bluetooth is given to this
technology? Answers is “Herald Bluetooth was the 10 th century Viking
King who gave name to our technology. Herald Bluetooth was king of Denmark
in the 10th century. He unified Denmark and part of Norway into a single
kingdom, and then introduced Christianity into Denmark. But he was killed in 986 during battle with
his son. Choosing this
name for this
standard indicates how important
companies from Baltic region ( nations including Denmark, Sweden,
Norway and Finland
) are to
the communications industry,
even if it says little about the way the technology works”.
2. NEED FOR BLUETOOTH
There are already a couple of ways to get
around wires. They are
1. Beams of light in the infrared spectrum.
2. Cable synchronization.
INFRARED
It is 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 communication are fairly reliable and don’t cost very much to build into a device. Reliable means interference between devices is uncommon because infrared transmitters and receivers have to be lined up with each other and we can make sure a message goes only to intended recipient, even in a room full of infrared receivers.
Drawbacks
with infrared communications are
1. Infrared is a “line of sight “technology. For example we have to point the remote control at the TELEVISION
or DVD player to make things happen.
2. Infrared is a “One –To –One”
technology. For example
we can send data
from our PC
to out LAPTOP,
but not to
both LAPTOP and PDA at the same time.
CABLE SYNCHRONIZATION
In
synchronization, we attach PDA to out computer (usually with a cable),
Press a button and make sure that the data on PDA and
the data on the computer match. Its
technique that makes the PDA a valuable tool for many people but synchronizing
the PDA with the PC and making sure we have the correct cable or cradle to
connect these two can be real hassle.
Bluetooth intended to get around the problems that come with both
Infrared and Cable synchronizing system.
3. BASICS
Wireless technology is
growing today .
We know about
WPANs, WLANS and WWANs.
·
WPANs,
such as Bluetooth Pico nets provide short-range connectivity for devices such
as Laptops, PDSs,CELL phones and even PCs in a network with small geographical
spread and support low data rates and limited ranges to achieve low cost and minimal power drain.
·
WLAN,
such as 801.11 Wireless Ethernet provides higher speed and longer range in
office buildings and homes.
·
WWANs,
such as Cellular Networks works over large area but offer much lower data rates
than WPANs and WLANs.
Bluetooth is
intended to be a standard that works at 2 levels.
1. At
physical level - Bluetooth is a radio frequency standard.
2. In
next level - 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 message
sent.
To communicate peripherals, telephones and computers “Bluetooth radio” is used instead
of wires.
From the users’
point of view, there are 3 important features in Bluetooth.
1. It is wireless. When he/she travels he won’t
have to worry about keeping track of
a brief case full of cables to attach all components.
2. It is inexpensive.
Manufacturers think that it will add about $20 per device.
3. No need to think of it. Bluetooth don’t
require doing any thing special to make it work. The devices find one another
and strike up a conversation.
When any two devices want
to talk to each other, they have to agree on
a number of points before the conversation begins.
1. The first point of agreement is physical,
will they talk over wires or through some form of wireless signal.
2. The second point is type of communication,
i.e. information can be sent one bit at a time in a scheme called Serial
Communication or in group of bits in
3. scheme called Parallel Communication. For
example, a PC uses both serial and parallel communications to talk to different
devices. Modems, mice, Keyboards are tending to use serial links, while
printers tend to use parallel links.
All
parties in a electronic conversation need to know what the bits mean and
whether the message they received is same of message that was sent. In most
cases this means developing a language of commands and responses known as
protocol. Some products have standard protocol used by virtually all companies
so that the commands for one product will tend to have the same effect on
another. Modems fall into this category. Other product types each speaks in
their own language, which means commands intended for one specific product will
seem gibberish if received by another. Printers are like this with multiple
standards like PCC and POSTSCRPT.
Computer and Entertainment
systems manufacturers realized that to setting up computers and home
entertainment systems they need more wires, so it is very difficult to setup. In order to make
home electronics friendly, we need some better way for all the electronic parts
of our modern life to talk to each other. That is where Bluetooth comes in.
4.HOW
BLUETOOTH WORKS?
4.1.
AVOIDING INTERFERENCE
Bluetooth devices sent out
very week signal of 1 milli watt. By comparison the most powerful cell phones
can transmit a signal of 3 watts. The low power limit range of Bluetooth device
to about 10 meters, cutting the chances of interferences.
With many different
Bluetooth devices in a room, they wont interfere with one another. Why because,
it is unlikely that several devices will be on the same frequency at the same time because
Bluetooth uses a technique called Frequency Hopping Spread-Spectrum (FHSS)
In this technique a device will use 79
individual randomly chosen frequencies with in a designated range, changing
from one to another on a regular basis. Transmitters changes frequencies 1600 times every
second. Since every Bluetooth transmitter uses FHSS, it is unlikely that 2
transmitters will be on the same frequency at the same time. This same
technique minimizes the risk that portable phones or baby monitors will disrupt
Bluetooth devices since any interference on
a particular frequency will lose
only a tiny fraction of a second.
FHSS is
designed to tradeoff bandwidth efficiently for reliability, integrity and
security. FHSS uses a narrow band carrier that changes frequency in a pattern
known to both transmitter and receiver.
4.2.BLUETOOTH NETWORKS
Two possible networks exist in
Bluetooth. They are:
1. Pico net.
2. Scatter
net.
When we bring Bluetooth radios with in
range of each other, an electronic conversation will take place to determine
whether they have data to share or whether one need to control one another.
Once the conversation has started the devices form a network i.e. Pico net. One
unit becomes a MASTER and other as SLAVE. The master controls all the traffic
in the Pico net. Bluetooth radios in a Pico net frequency-hop together.
Scatter
nets occur when multiple masters exists in range of each other. A master radio
may also be a slave radio on another Pico net. Each Pico net is hopping with a
different sequence sharing the same 2.4 GHz band. Because different hopping
sequences, there is very little chance that any master will hit a channel at
the same time as another master.xx
4.3. BLUETOOTH RADIO STATES
Radios in a Pico net can be in one of six
states.
1. OFF – It means initial state. There is no
connection for LMP.
2. STANDBY – Radio is waiting to join in a Piconet.
3. INQUIRE – Radio seeking other radios to
connect.
4. PAGE – Master radio asking to connect to a
specific radio.
5. CONNECTED – Radio active on a Piconet as a
master, slave or simultaneously.
6. PARK/HOLD – When there is no work for a
radio if states its position and waits for messages. This state is called Park
state. In this state it consumes least power.
Hold state consumes more power than park state. This state occurs when
they prepared to send messages. It won’t
tell to the Piconet about its state for some time.
5.EXAMPLE
If
there is an Entertainment system with Stereo, DVD player, a Satellite TV
receiver and a TV, a Cordless phone and a PC. Each of these systems uses
Bluetooth and each forms its own Piconet to talk main unit and peripherals.
The Cordless telephone has one
Bluetooth transmitter in the base and another in the handset. The manufacturer
has programmed each unit with an address that falls into a range of addresses,
it has established for a particular type of device. When the base is turned on, it sends radio signals
asking for a response from any units with an address in the range, it responds
and a tiny network is formed. Even if one of other devices receives a signal
from another system, it will ignore it since it is not corresponding to it. In
the similar way Computer and Entertainment system go through similar routines
and establishes network among them. Each Piconet hops randomly through the
available frequencies. So all of the
Piconets are completely separated from one another.
Each Piconet hops separately
so it is rarely occurred that two Piconets on same frequency, if happens
interference will be for tiny of time.
Communication may be in one (Asynchronous) or in both directions
(synchronous). Example for an asynchronous communication is speakerphone and
Synchronous communication is regular telephone handset.
6.BLUETOOTH SPECIFICATIONS
1. Devices in a Piconet share a common communication data channel.
It has total capacity of 1 Mbps. 2. In USA &Europe frequency range is 2400
– 2483.5 MHz with 79 1MHz RF channels.
3. In Japan the range is 2472 – 2497 MHz with 23 1MHz RF channels.
4. A data
channel hops 1600 times per second between 79 (or 23) RF channels.
5.Each channel is divided into time slots 625
micro seconds long.
6. A Piconet can have a master and 7 slaves.
The master transmits in even time slots and slaves in odd time slots.
7.Packets can
up to 5 time slots wide.
8.Data in a
packet can be up to 2745 bits in length
9.There may be 2 types of transfers between devices:
a. SCO (Synchronous connection oriented)
b. ACL (Asynchronous connection less)
10.In a Piconet there can be up to 3 SCO links of 64
kbps
each. To avoid timing and
collision problems, the SCO links use reserved slots setup by the master.
11. Master can support up to 3 SCO links
with 1,2 or 3 slaves.
12.
Slots not reserved for SCO links can be used for ACL links.
13. One master and slave can have single
ACL link.
14.
ACL is point-to-point or broadcast to all the slaves.
15.
ACL slaves can only transmit when requested by master.
Frequency
hops in the range 2400 – 2438.5 MHz at the rate of 1600 times per second
1,2,3
– SCO links – time slots were reserved
4,5,6,7
– ACL links – remaining slots
7.BLUETOOTH PROTOCOL STACK
The Bluetooth Special Interest Group (SIG)
has developed the Bluetooth
specification version 1.0 Draft
Foundation that allows for developing interactive services and
applications over interoperable radio modules and data communication protocols.
Different applications may run over different protocol stacks.
Nevertheless, each one of these different protocol stacks uses a common Bluetooth
data link and physical layer. This figure shows the complete Bluetooth protocol
stack as identified in the specification on top of which interoperable
applications supporting the Bluetooth usage modules are build. Not all
applications make use of all protocols shown here. Instead, applications run
over one or more vertical slices from this protocol stack.
The main principle has been to
maximize the reuse of existing protocols for different purposes at the higher
layers, instead of re-inventing the wheel once again. The protocols re-use also
helps to existing applications to work with the Bluetooth technology and to
ensure the smooth operation and interoperability of these applications. So many
applications developed can take immediate advantage of hardware and software systems.
8.BLUETOOTH PROTOCOL
ARCHITECTURE
Bluetooth
protocol stack can be divided into 4 layers according to their purpose
including the aspect whether Bluetooth SIG has been involved in specifying
these protocols.
In addition to this Host
Controller Interface (HCI), which provides access to Base band, Hardware
status, Link manager and control registers? HCI can exist above L2CAP.
Some
protocols are (RFCOMM, TCS-BIN) are also developed by Bluetooth SIG based on
other standards. Only core protocols are required by most of Bluetooth devices
while rest of the protocols is used only as needed. Other protocols enable
application to run over Bluetooth core protocols.
Since Bluetooth specification is open and additional protocols (HTTP,
FTP) can be accommodated in an interoperable fashion on top of the Bluetooth
specific transport protocols or on the top of the application oriented
protocols.
8.1. BLUETOOTH CORE PROTOCOLS
8.1.1. BASEBAND
Base band and Link control layer enable the physical RF link between
Bluetooth units forming a Pico net. This layer uses inquiry and paging
procedures to synchronize the transmission hopping frequency and clock of
different Bluetooth devices.
It provides 2 kinds of
physical links with their packets, Synchronous Connection Oriented (SCO) and
Asynchronous Connection Less (ACL), which can be transmitted in a multiplexing
manner on the same RF links. ACL packets
can contain data only, while the SCO packets can contain audio or a combination
of audio and data. FEC and CRC error
correction can be encrypted.
ARCHITECTURE OF BLUETOOTH PACKET
|
ACCESS CODE
|
POCKET HEADER
|
PAYLOAD
|
72 BITS 54 BITS 0 – 2745 BITS
Using access code slave compares data packets access code by
comparing its internal code, otherwise it rejects it.
8.1.2. AUDIO
Audio data can be transferred between one or more Bluetooth devices
making various usage models possible and audio data in SCO packets. It directly routed to and from Base band and
it does not go through L2CAP, just by
operating an audio link.
8.1.3.
LINK MANAGER PROTOCOL
It is responsible for link setup between Bluetooth devices. This includes security aspects like authentication
and encryption.
8.1.4.
L2CAP
It adapts upper layer protocols over Base band. It thought to work is parallel with LMP in
difference that L2CAP provides to the upper layer when the payload data is
never sent at LMP massages.
For Base band layer it supports SCO and
ACL packets. L2CAP permits higher-level protocols and applications to transmit
and receive L2CAP data packets up to 64 kbps lengths.
8.1.5. SDP
Discovery services are crucial part of the Bluetooth
framework. Those services provide the
basis for all the usage modules. Using
SDP, device information, services and the characteristics of services can be
queried and after that, a communication between two or more Bluetooth devices
can be established.
8.2 CABLE REPLACEMENT PROTOCOLS
8.2.1 RFCOMM
This cable replacement protocol emulates RS-232 control and data signals
over Bluetooth Base band, providing both transport capabilities for upper level
services (OBEX) that use serial line as transport mechanism.
8.3. TELEPHONY CONTROL PROTOCOL
8.3.1. TELEPHONY CONTROL – BIN
It is a bit-oriented protocol, defines the call control signaling for
the establishment of speech and data calls between Bluetooth devices.
8.3.2. TELEPHONY CONTROL – AT COMMANDS
Bluetooth SIG has developed a set
of AT commands by which a Mobile phone
and Modem can be controlled in the
multiple usage models. In
addition, the commands used for FAX services are also specified.
8.4. ADAPTED
PROTOCOLS
8.4.1. PPP
PPP is designed to run over
RFCOMM to accomplish Point-to-Point connection.
PPP – networking is the means of taking IP packets to/from the PPP layer
and placing them on the LAN.
8.4.2. TCP/UDP/IP
These
are the most widely used protocol family in the world. TCP/IP stacks have appeared on numerous
devices including printers, handheld computers and mobile handsets.
Implementation of these standards in Bluetooth devices allows for
communication with any other device connected to the Internet.
8.4.3. OBEX PROTOCOL
This is to exchange objects in a simple and
spontaneous manner. OBEX, which provides
the same basic functionality as HTTP but in a much lighter fashion, uses a
client/server model and is independent of the transport mechanism and transport
API, provided it realizes transport base.
OBEX provides model for representing objects and operations. In addition OBEX protocol defines a folder
listing objects, which is used to browse the contents of folders on remote
devices.
8.4.4. Vcard / Vcal
The specifications define the format of an
electronic business card and personal calendar entries and scheduling
information. Vcard and Vcal are bit
define any transport mechanism but only the format under which the data is
transported. SIF promote this for
exchange of personal information under these well-defined and supported
formats.
8.4.5. WAP
WAP forum builds a wireless
protocol specification that works across variety of wide-area wireless network
technologies. The goal is to bring
Internet contents and telephony services to digital Cellular phones and other
wireless terminals. The idea of reuse is
using existed upper layer protocols for WAP Application Environment (WAE). This includes WML and WTA browsers that can
interact with applications on the PC.
Building applications gateway which mediate between WAP servers and some
other applications on the PC makes it possible to implement various hidden
computing functionality, like remote control, data fetching from PC to handset.
9. BLUETOOTH USAGE MODELS
Usage
models are accompanied by a profile.
Profile defines the protocols and protocol features supporting a
particular usage model.
9.1. FILE TRANSFER MODEL
This
usage model offers the ability to transfer data objects from one device to
another. Object types includes .x1s,
.ppt, .wav,.jpg and .doc files, entire folders or directories or streaming
media formats. It also offers a
possibility to browse the contents of the folders on a remote device.
9.2. INTERNET BRIDGE
Using this model, mobile phone or cordless modem acts as modem to PC,
providing dial-up networking and fax capabilities without need for physical
connection to PC.
The dial-up networking scenario of this usage model needs a two piece
protocol stack. AT-commands are needed
to control the Mobile phone or modem and another (PPP over RFCOMM) to transfer
payload data.
The fax scenario has a similar protocol stack but PPP and the networking
protocols above PPP are not used and the application software sends a fax mail
directly over RFCOMM.
9.3. LAN ACCESS
MODEL
In this model multiple data
terminals use a LAN Access Point (LAP) as a wireless connection to a LAN. Once
connected, the DT’s operate as if it they were connected to the LAN via dial-up
networking. The DT can access all of the services provided by the LAN.
9.4. SYNCHRONIZATION MODEL
It provides a device-to-device
(phone, PDA, computer etc) synchronization of the PIM (personal information
Mgt) information, typically phonebook, calendar, message and note information.
Synchronization requires business card, calendar and task information to be
transferred and processed by computers, cellular phones and PDA utilizes a
common protocol and format.
9.5. 3 IN 1 PHONE MODEL
Telephone handsets built to this profile may connect to 3 different
service providers.
1. Telephone may act as Cordless phone connecting
to the Public Switched Telephone
Network (PSTN) at home or office. This
scenario includes making calls via a voice base station, making direct calls
between 2 terminals via a voice base station and accessing supplementary
services provided by an external network.
2. Telephones can connect directly to other
telephones for the purpose of acting as a “WALKIE-TALKIE” or handset
extension. This intercom scenario incurs
no additional charges.
3. The telephone may act as Cellular phone
connecting to the Cellular
infrastructure and incurring cellular charges.
9.6. ULTIMATE
HEADSET MODEL
The headset can be wirelessly
connected for the purpose of acting as a remote device’s audio input and output
interface. The headset increases the
users freedom of movement while maintaining call privacy.
Example is Headset used with a Cellular headset, Cordless headset, PC
for audio input and output.
The headset must be able to send AR-commands and receive result
code. This ability allows the headset to
answer incoming calls and then terminate them without physically maintaining
the telephone headset.
10. CONCLUSION
Bluetooth
wireless technology – The technology that propels you into a new dimension in
wireless connectivity.
It
is important to surround yourself with the right kind of people. Bluetooth is a
new standard developed by a group of electronics manufacturers, that will allow any sort of
electronic equipment to make it's own
connections without wires, cables or any direct action from user. It is a rapid growing technology
that makes man easy to transfer his electronic equipments from one place to another.
It is
a technology that not yet completely developed. Hope this will be achieved very
soon.
ACRONYMS
ACL
: Asynchronous
Connection Less
API
: Application
Programming Interface
CRC
: Cyclic
Redundancy Check
DT
: Data
Terminal
FEC
: Forward Error Correction
FTP
: File
Transfer Protocol
GAP
: Generic Access Profile
GOEP
:
Generic Object Exchange Profile
HCI
: Host Controller Interface
HTTP
: Hyper
Text Transfer Protocol
IP : Internet
Protocol
IrDA
: Infrared Data Association
IrMC
: Infrared
Mobile Communication
LAN
: Local Area Network
LAP
: LAN Access Point
LMP
: Link Manager Protocol
L2CAP
: Logical
Link and Control Adaptation Protocol
OBEX
: Object Exchange Protocol
PDA
: Personal
Digital Assistant
PIM
: Personnel Information Management
PPP
: Point-to-Point Protocol
PSTN
: Public Switched Telephony network
RFCOMM:
Serial
Cable Emulation Protocol
SCO
: Synchronous
Connection Oriented
SDAP
: Service Discovery Application
Protocol
SDP :
Service
Discovery Protocol
TCP
: Transmission Control Protocol
UDP
: User
Datagram Protocol
TCS-BIN
: Telephony
Control Specification-Binary
WAE
: Wireless
Application Environment
