Bluetooth Networking

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REPORT ON

BLUETOOTH® NETWORKING

SUBMITTED BY

SUBASH PANDEY

(ICE 2010/11)

TECHNISCHE HOCHSCHULE MITTELHESSEN

SUBMITTED TO

PROF. DR. FRIEDRICH KLEIN

1st JUNE 2011

FRIEDBERG

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ABSTRACT

This report is focused on Bluetooth focusing on its Networking technology . It also gives brief

overview on Bluetooth's History , its technical features, its core protocols such as Radio Frequency,

Linking Protocol. It also describes Bluetooth profiles, Connection methods. Security Problems andcomparison to competing technology is also made here. And its future relevancy is discussed in brief.

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1 Introduction

The concept of Bluetooth originated when it was thought that a common wireless link was needed toconnect the mobile devices such as Mobile Phone, ,Laptop, netbook etc to data communication

interface and getting rid of company specific cable connection and configuration . An obvious solutionwas to get rid of the cables and use short-range wireless links to facilitate on-demand connectivity

among devices. So in 1998 five major companies ( Ericsson, Nokia, IBM, Toshiba, and Intel) formed a

group to create a license free technology for PAN( Personal Area Network) connectivity . To date thisgroup has about 14000 members.

Bluetooth is a technology named after a 10th-century king of Denmark, Harald Blåtand (Bluetooth)who brought warring Viking tribes under a common rule as in the same way Bluetooth brought all

mobile devices under one communication profile. The logo for Bluetooth is based on Runes

surrounding the legend of Harald Bluetooth

The Bluetooth specifications define a radio frequency (RF) wireless communication interface and the

associated set of communication protocols and usage profiles.

The specifications of Bluetooth such as link speed, communication range, and transmit power level are

chosen in such format so that they can support low-cost, power-efficient, single-chip implementations

of the current technology.

Key features are robustness, low power, and low cost. Many features of the core specification are

optional, allowing product differentiation. The Bluetooth core system consists of an RF transceiver,

baseband, and protocol stack. The system offers services that enable the connection of devices and theexchange of a variety of classes of data between these devices. The current specification running is

Bluetooth version 4.0, released on June 30, 2010 .

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2 History

The Bluetooth specification was developed as a cable replacement in 1994 by Jaap Haartsen and Sven

Mattisson, who were working for Ericsson in Lund, Sweden. The specification is based on frequency-hopping spread spectrum technology.

The specifications were formalized by the Bluetooth Special Interest Group (SIG). The SIG was

formally announced on May 20, 1998. It was established by Ericsson, IBM, Intel, Toshiba and Nokia,and later joined by many other companies. Today it has a membership of over 14,000 companies

worldwide.

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3 Air Interface

3.1 Frequency

Bluetooth operates in the unlicensed ISM band at 2.4 GHz. The system employs a frequency hoptransceiver to combat interference and fading and RF operation uses a shaped, binary FM modulation

to minimize transceiver complexity. The symbol rate is 1 Megasymbol per second (Ms/s) supportingthe bit rate of 1 Megabit per second (Mb/s).

3.2 Piconet and Scatternet

A bluetooth network is called a piconet. The initiating device is called a master and the connecteddevice is called the slave. Being an adhoc connection normally the connection is terminated after the

current task has been completed. The majority of Bluetooth applications will be point-to-point

applications .A master can have simultaneous connections (point-to-multipoint) to up to seven slaves.

a) Point-to-point

b)Point to multipointc) Scatternet

Fig: Types of Bluetoth Network Connection

One device can also be connected in two or more piconets. The set-up is called scatternet. A device can

act as master to only one piconet . The role of master/slave is not fixed and can be changed during

connections.

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3.3 Frequency-hopping

Bluetooth uses frequency-hopping as the method to transmit packets between the users. In frequency-

hopping every packet is transmitted on a different frequency. With a fast hop rate of 1600 hops per

second interference is kept at minimum.

Fig: Frequency-hopping

The minimum slot time is 625 micro seconds but three to five slots can be combined so that switching

time can be reduced but this may also reduce the robustness of the packets and in a crowdedenvironment the long packets may be lost more easily.

Data is transmitted in packets. Each packet contains three things ,the access code, the header, and the payload .The size of the access code and the header are fixed. The payload ranges from 0 to 2745 bits

per packet. The control packets may also consist of the access code only, or of the access code and

header only.

Three methods are used for ensuring reliable data transfer in crowded environments. In the Forward

Error Correction (FEC) scheme, additional check bits are added in the packet header or the payload. Inthe Automatic Repeat Request (ARQ) scheme, the data payload is retransmitted until the recipient

sends an acknowledgment. Acknowledgement information is included in the header of the return

Fig : Bluetooth Packet

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5 Connection Establishment

Before any connections are made, all units are in standby mode. A unit in a standby mode wakes up

every 1.28 seconds to listen to page/inquiry messages. Each time a unit wakes up, it listens on one of

the 32 defined hop frequencies. The connection to a desired device is made by a “page” message.

When paging, the master must know the slave’s Bluetooth address and system clock to calculate the proper access code and the wake-up sequence phase. That information will be provided in the inquiry

process which is needed when master does not the Bluetooth address of the slave.

In inquiry, the master sends an inquiry access code, and other devices respond with their identity and

system clock. After that, the connection can be made with any of those devices using the paging procedure described earlier.

After “page” message the connection is made. In connection state, the Bluetooth unit can be in severalmodes of operation. Sniff , hold, and park modes are used to save power or to free the capacity of a

piconet. These modes are explained in more details below.

Active mode: In the active mode, the Bluetooth unit actively participates on the channel.

Sniff mode: In the sniff mode, the duty cycle of the slave’s listen activity can be reduced. This means

that the master can only start transmission in specified time slots.

Hold mode: While in connection state, the ACL link to a slave can be put in a hold (possible SCO links

are still supported). In hold mode, the slave can do other things, such as scanning, paging, inquiring, or attending another piconet .

Park mode: If a slave does not need to participate in the piconet but still wants to remain synchronized

to the channel (to participate in the piconet again later), it can enter the park mode. It gives up its activemember address. Park mode is useful if there are more than seven devices that occasionally need to

participate in the same piconet. The parked slave wakes up regularly to listen to the channel in order to

re-synchronize and to check for broadcast messages sent by the master.

Fig: Steps of Bluetooth connection

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6 Profiles

To use Bluetooth technology the device must interpret certain “Profiles” which are basically definitions

and protocols needed by the Bluetooth devices to communicate with each other. There are wide range

of Bluetooth profiles which explain the diverse functionality in which we can use the Bluetooth

technology. These profiles are defined and adopted by Bluetooth SIG.

Main Profiles needed for generic connections are

General Access Profile ( GAP): This profile is required by all usage models and defines how

Bluetooth devices and connect to one another, as well as defines security protocols. All Bluetooth

devices must conform to at least the GAP to ensure basic interoperability between devices.

Service Discovery Application Profile (SDAP):The SDAP uses parts of the GAP to define the

discovery of services for Bluetooth devices.

Serial Port Profile(SPP): This profile defines how to set up and connect virtual serial ports between

two devicesThis serial cable emulation can then be used for tasks such as data transfer and printing.

Generic Object Exchange Profile (GOEP): GOEP is dependent on the Serial Port Profile and is used

by applications to handle object exchanges. This capability is then used, in turn, by other profiles to

perform such functions as Object Push, File Transfer, and Synchronization .

Object Push: This profile is used for the exchange of small objects, such as electronic calling cards.

File Transfer: This profile is used to transfer files between two Bluetooth devices.

Synchronization: This profile is used to synchronize calendars and address information between

devices.

There are many other profiles such as Advanced Audio Distribution Profile (A2DP) for audio transfer.

Basic Imaging Profile (BIP) for image handling between the device. And many more.

At a maximum, each profile specification contains information on the following topics:

Dependencies on other formats

Suggested user interface formats

Specific parts of the Bluetooth protocol stack used by the profile. To perform its task, each profile uses particular options and parameters at each layer of the stack. This may include an

outline of the required service record, if appropriate.

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7 Security

The following are the security components which make up the Bluetooth Technology

Bluetooth Device Address 48-bit addressAuthentication Key 128-bit random number

Encryption Key 8-128 bits in lengthRandom Number 128-bit random number

7.1 Levels of Security

Devices :

1. Trusted unrestricted access

2. Not Trusted restricted access

Services:1. Require authentication and authorization

2. Authentication only

3. Open to all devices

7.2 Connection and Encryption

If two devices wish to communicate, a random number must be sent from one device to the other. The

receiving device must also have knowledge of the PIN of the sender. With these two sets of

information, a link key is generated (as above) on both devices. The sender would then have to enter intheir PIN on device B manually or by a key exchange mechanism.

To verify if the link keys are equal the sender must generate another random number and encrypts theBluetooth Device Address (of the receiver) using the link key and the random number to produce a

signed response authentication result (SRES). The sender sends the new random number and encrypts

it to also produce a SRES. If these two are equal, then a connection is established.

7.3 Security Concern

While bluetooth has its benefits it also has some security concerns where an unauthorized user or

device might eavesdrop , cause denial of service or modify the incoming message. To minimize these

risks users/manufacturers can evaluate and then incorporate the security features needed as explainedabove.

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8 Comparison

Bluetooth was basically designed to replace the RS 232 serial cable and is therefore basically limited to

WPAN( wireless personal area network ) where as WIFI is basically used as wireless replacement for

LAN with ethernet connection . Wi-Fi uses the same radio frequencies as Bluetooth, but with higher

power, resulting in a faster connection and better range from the base station but this increases the power consumption which is not desirable according to the blueprint of bluetooth technology.

There may be some loss of packets when these are used concurrently but Bluetooth radio can detect

some frequencies as“undesirable” (due to interference) and not use them in a hopping sequence . If same device such as netbook uses both WPAN and WLAN network then some exchange of message

can take place between the competing network to mitigate the loss of packets.

9 Future of Bluetooth

Use of Broadcast channel using pulling method where mobile phones or devices pull information from

information points instead of pushing of information which is the current form .

There is also going to be improvement in QoS enabling better quality of videos and sounds being

transferred.

This all developments plus the current technology of Bluetooth will secure its survival . But on the

other side there could emerge a technology that would make Bluetooth obsolete.

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10 Conclusion

Based on this report I can conclude that Bluetooth is an essential part of Wireless Personal Area

Network . With the backing it gets from the companies that started it and vast members of SIG it is still

a powerful player in Wireless Technology . But to keep it relevant in future more development and

research towards its security issues must be done.

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Appendix

AcronymsACL - Asynchronous Connection-LessARQ – Automatic Repeat RequestCSMA- Carrier Sense Multiple Access

DSSS- Direct Sequence Spread Spectrum

FEC – Forward Error Correction

FHSS - Frequency Hopping Spread SpectrumIEEE - Institute of Electrical & Electronic Engineers

ISM - Industrial, Scientific, Medical

LAN - Local Area Network Mbps - Megabits per second

OFDM- Orthogonal Frequency Divison Multiplexing

PAN - Personal Area Network PHY - Physical (Layer)

PIN – Personal Identification Number

POS - Personal Operating Space

QoS - Quality of ServiceSCO - Synchronous Connection Oriented

SDP - Service Discovery Protocol

SIG - Special Interest GroupUSB – Universal Serial Bus

WLAN - Wireless LAN

WPAN- Wireless PAN

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References

[1] Bluetooth SIG http://www.bluetooth.com

[2]Bluetooth specifications http://www.bluetooth.com/developer/specification/specification.asp[3] Wikipedia http:/ /www.en.wikipedia.org/bluetooth

[4 ]Bluetooth Technology Review Forum Nokia Version 1.0; April 4, 2003

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Bluetooth Networking