CSCD 439/539 Wireless Networks and Security Lecture 7 Bluetooth

Fall 2007

I am King Harold BluetoothI am King Harold Bluetooth who unified warringwho unified warring Viking Tribes in the Viking Tribes in the 10th Century. In the 21st 10th Century. In the 21st Century a wireless Bluetooth Century a wireless Bluetooth network is named after menetwork is named after me

Who is Bluetooth?

• Harald Blaatand “Bluetooth” II– King of Denmark 940-981 AC– Harald Bluetooth was first

Christian king of Denmark– He united Denmark under his

rule in the mid-900's– Similarly, Bluetooth seeks to

unite personal computing devices wirelessly

How did Bluetooth start?

• In 1994 – need for low power consumption wireless devices to substitute for cable

• Ericsson – driving force behind Bluetooth– Pre-Cell phone– 1998, Ericsson, Nokia, IBM, Toshiba, Intel

formed the Bluetooth Special Interest Group (SIG)

– 1999 – Release of Bluetooth protocol– 2002 – IEEE adopted Bluetooth standard,

802.15 working group

Bluetooth Vision• Vision of Bluetooth

– Personal connectivity space• Bubble that follows you around• Connect personal devices anytime one enters

bubble sphere• Connectivity is spontaneous, accommodate

devices of diverse power and capacity– Laptops, phones, PDA’s, cameras …

• Users don’t even need to be aware of Bluetooth connection

Bluetooth Vision

• Idea is …– Connections will be done seamlessly without

need for installations and software drivers– Devices can discover other Bluetooth-enabled

devices• Determine its capabilities and applications,

and establish connections for data exchange

• User doesn’t need to be highly skilled

Bluetooth ApplicationsMore prevalent applications of Bluetooth include:• Wireless communication between a mobile phone and a

hands-free headset or car kit • Wireless communications with PC input and output

devices, the most common being the mouse, keyboard and printer

• For controls where infrared was traditionally used• Sending small advertisements from Bluetooth enabled

advertising hoardings to other, discoverable, Bluetooth devices

• Seventh-generation game consoles– Nintendo Wii, Sony PlayStation 3– Use Bluetooth for their wireless controllers

• Receiving commercial advertisements ("spam") via a kiosk, e.g. at a movie theatre or lobby

What does Bluetooth do for you?

Personal Ad-hoc Personal Ad-hoc NetworksNetworks

Cable Cable ReplacementReplacement

Landline

Data/Voice Data/Voice Access PointsAccess Points

Ultimate Headset

Cordless Computer

General Description• Bluetooth operates in unlicensed Industrial

Scientific Medical (ISM) band at 2.4 GHz– Which ensures worldwide communication

compatibility– ISM band is open to anyone, systems operating on

this band must deal with unpredictable sources of interference,

– Microwave ovens, baby monitors and 802.11 wireless networks

• Reduce interference, Bluetooth uses Frequency Hopping Spread Spectrum (FHSS) technology

Frequency Hopping Spread Spectrum (FHSS)

• Works like this …– During a connection, radio transceivers hop from one

channel to another– One packet is sent on a channel, two devices then

retune their frequencies (hop) to send the next packet on a different channel.

• So, if one frequency channel is blocked, limited disturbance to the Bluetooth communication

– Allows several Bluetooth networks to run concurrently without interrupting one other

– Link rate: 1 Mbps, but with overhead, this reduces to 721 kbps

– Range for Bluetooth: • 10m, can reach up to 100m depending on the power class of

the device

Adaptive Frequency Hopping (AFH)

• Bluetooth version 2.0 + EDR uses an enhanced technology called: Adaptive Frequency Hopping (AFH)

– AFH allows Bluetooth devices to measure quality of wireless signal

– Determines if there are bad channels present on specific frequencies due to interference from other wireless devices.

– If bad channels present on a specific frequency, Bluetooth device will adjust its hopping sequence to avoid them

– As a result, the Bluetooth connection is stronger, faster, and more reliable

Definitions - Piconet

• A network of devices connected in an ad hoc fashion using Bluetooth technology– A piconet is formed when at least two devices,

such as a portable PC and a cellular phone, connect

• Can support up to eight devices• When piconet is formed, one device acts as the

master while the others act as slaves • A piconet is sometimes called a PAN

– Personal Area Network

Definitions - Scatternet

• Scatternet is …– A group of independent and non-

synchronized piconets that share at least one common Bluetooth device

– Bluetooth devices must have point-to-multipoint capability to engage in scatternet communication

– There may be a maximum of 10 fully loaded piconets in a scatternet

– Scatternet is a more recent use of Bluetooth

Piconets

• Two or more Bluetooth units sharing the same channel form a piconet– Slaves in a piconet can only have links to the master– Slaves cannot directly transmit data to one another– Master acts as a switch for the piconet and all traffic

must pass through master– Any device can be either a master or a slave within a

piconet and they can change roles at any point in a connection when a slave wants to take over a master's role

Piconets• Every Bluetooth device has its own clock and

can be uniquely identified by its Bluetooth device address– Slaves in a piconet use master's Bluetooth device

address and clock to determine the frequency hopping sequence

– Slaves synchronize with master's clock for duration of the connection

– Master also controls when devices transmit data, since slaves can only transmit when scheduled by a master

– Master controls how total available bandwidth is distributed among the slaves

Scatternets• A set of two or more interconnected

piconets form scatternets (More recent development)– A Bluetooth unit can be a slave in two or more

piconets, but it can be a master in only one– Devices that participate in two or more

piconets may act as gateways, forwarding traffic from one piconet to another

Scatternets and Piconets

Bluetooth Protocols

• Bluetooth protocols contain standard procedures for connections and data exchange between Bluetooth devices– Bluetooth protocol stack (See next slide)

Bluetooth Protocol Stack

The Radio is the interface between the on-air channel medium and the Baseband

The Baseband layer is responsible for channel coding and decoding

Digitizes signals received by the radio for passing up the stack and it formats the data it receives from the Link Controller for transmission over the channel

The Link Controller is responsible for establishing and maintaining links between Bluetooth units

Link Manager Protocol (LMP) handles piconet management and link configuration. It also includes link security

Bluetooth Protocol StackHost Controller Interface (HCI) defines uniform methods for accessing and controlling lower layers of the protocol stack, namely baseband and the link manager

Logical Link Control and Adaptation Protocol (L2CAP) provides connection-oriented and connectionless data services to the other higher level protocol layers

Service Discovery Protocol (SDP) defines procedures for discovering services of other devices as well as determining the characteristics of those services.

RFCOMM protocoldefines a transport protocol for emulatingRS-232 serial ports.

Bluetooth Protocol Stack• Telephony Control Protocol

Specification (TCS) defines call control signaling for establishing speech and data calls between Bluetooth devices, provides them with telephony services

• Object Exchange Protocol (OBEX) is for object data exchange over infrared (IR) links

• Wireless Application Protocol (WAP) includes interoperability requirements for Bluetooth

Connecting with Bluetooth

• Say we want a laptop connecting wirelessly to a mobile phone to use dial-up networking.– Process is shown in following slide– First, Bluetooth device looks for devices that it might connect to

• Step 1 - the Inquiry Process. • Inquiring device, A, sends out an inquiry packet or repeated inquiry

packets and waits to receive responses back• Discoverable devices in range respond to an inquiry by sending a

Frequency Hop Synchronization (FHS) packet, which contains all the information device A needs to connect to the responding device, including the Bluetooth device's address, page scan modes, and clock offset

• All devices that respond to the inquiry are reported to the host controller of device A.

• List of all devices discovered is presented to the user - is application-dependent

Connecting with Bluetooth

Step 1

Connecting with Bluetooth

• At this point, A knows which devices are in range, but it doesn’t know which devices support dial-up – Step 2 - Using information retrieved from inquiry, A

now attempts to connect to different devices that responded to its inquiry in order to find out what services they support

– Depending on the application, device A may either 1) Establish links to all devices that responded to its inquiry

and get information about their services and later on reconnect with one that supports dial-up networking; or

2) Upon seeing that a device supports dial-up networking, directly proceed to setting up a connection with that device without finding out the services from the rest of the devices in the list.

In following slide, second option is adopted.

Connecting with Bluetooth

Step 2

Connecting with Bluetooth

• Step 2 continued– Device A wants to find out services of a device, so, device A

sends out paging packets– Connectable device will respond and a baseband link can be

established between the two devices– Following that, a L2CAP connection will be established before

they can exchange service information. Information exchange is handled by Service Discovery Protocol

– Device B responds, “I have dial-up networking service”– RFCOMM connection can then be established across the

already existing L2CAP link– After this, a dial-up networking connection can then be

established on top of the RFCOMM connection– Laptop can then start using the cell phone to access the phone

network without any cables being needed for connections

Example Bluetooth Networks

• In a modern living room,– An entertainment system with a stereo, a DVD

player, a satellite TV receiver and a television, plus a cordless telephone and a personal computer

– Each system uses Bluetooth, and each forms its own piconet to talk between the main unit and peripheral

Example Bluetooth Networks

• Cordless telephone has one Bluetooth transmitter in the base and another in the handset.

• 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 base is first turned on– Sends radio signals asking for a response from any units with an

address in a particular range– Since handset has an address in range, it responds, and a tiny

network is formed

• Even if one of these devices should receive a signal from another system, it will ignore it since it’s not from within the network

Example Bluetooth Networks

• Computer and entertainment system go through similar routines, establishing networks among addresses in ranges established by manufacturers.

• Once the networks are established, the systems begin talking among themselves

• Each piconet hops randomly through the available frequencies, so all of the piconets are completely separated from one another

Bluetooth Profiles

• Bluetooth enabled devices must use and understand certain Bluetooth "profiles" in order to use Bluetooth technology to connect to one another– These profiles define the possible applications that a

Bluetooth enabled device can support.

• In order for one Bluetooth device to connect to another– Both devices must share at least one of the same

Bluetooth profiles

Bluetooth Profiles

• Bluetooth profiles define possible applications and describe how Bluetooth technology is to be used for each specific device

– For example• File Transfer profile is used to define how devices like a PDA

will use Bluetooth Technology to transfer files to other devices like another PDA, cell phone, or computer

– When a Bluetooth device is developed• Manufacturer assigns (In accordance with the Bluetooth

SIG's requirements) specific Bluetooth profiles for that device to use in order to establish applications which will work with other Bluetooth devices

Bluetooth Challenges• Two challenges faced by Bluetooth include: Scheduling

algorithms for scatternets and interference with other wireless technologies

• The first issue concerns the development of effective scheduling algorithms for Bluetooth scatternets– As discussed previously, a Bluetooth unit can only be active in

one piconet but it can be a member in a number of piconets– Hence, a unit that participates in multiple piconets needs to

divide its time among the different piconets– To schedule communication with such units, their availability in

other piconets needs to be taken into consideration• This then becomes a scatternet-wide coordination problem

which can easily become a bottleneck in scatternet organization

Bluetooth Challenges• Second issue is interference problems with

IEEE 802.11 wireless networks– Because both IEEE 802.11 and Bluetooth wireless

networks operate on the same frequency band, it is expected that some interference will occur when these two networks are present in the same environment

– Simulations and experiments have shown that significant packet losses and access delays do occur

• Some co-existence mechanism may need to be developed to reduce the performance degradation when these two technologies are present in one area

802.11 vs. Bluetooth

• Where interference issues occur interesting to look at intersections in 802.11b wireless local area network (WLAN) technology and Bluetooth– Could we just use 802.11b in place of Bluetooth?

• Although IEEE 802.11b was originally designed for providing network access, can also operate in ad hoc mode– Possible to form ad hoc personal area networks

(PANs) which is where Bluetooth shines– Because widespread use of IEEE 802.11b standard

even in small handheld devices, • Concern that this technology might surpass Bluetooth in

terms of usage and acceptance even in PANs.

802.11 vs. Bluetooth

Bluetooth IEEE 802.11b

Media Access Control Based on controlling unit Random-access-

Master oriented

Neighbor Discovery Standardized discovery No defined way to

using INQUIRY process discover unknown

devices (may use

broadcasting

Multihop PAN's Involves scatternets Straightforward

interconnected piconets no piconet

architecture,

all nodes are peers

Summary• Bluetooth is a global, RF-based (ISM band: 2.4GHz),

short-range, connectivity technology & solution for portable, personal devices– it is not just a radio

– create piconets on-the-fly (appr. 1Mbps)• piconets may overlap in time and space for high aggregate bandwidth

• The Bluetooth spec comprises– a HW & SW protocol specification

– usage case scenario profiles and interoperability requirements

• 1999 Discover Magazine Awards finalist• To learn more: http://www.bluetooth.com

• Holiday on Monday!!!• Take-home Midterm

– Due: Wed. November 14