IT351: Mobile & Wireless Computing
Wireless Personal Area Networks (WPAN)
Part-2: IEEE802.15 Bluetooth
Objectives:
– To introduce Ad Hoc networking and discuss its application domain.
– To provide a detailed study of the Bluetooth Wireless Technology including its
architecture and protocol.
Outline
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•
•
•
Motivation
History
Application and usage scenarios
Network architecture
– Piconets
– Scatternets
• Protocol stack
– Core protocols
– Cable replacement and telephony control protocols
– Profiles
• Future developments
• Wi-Fi vs. Bluetooth
Bluetooth - Motivation
• A technology that aims at ad-hoc piconets -- LAN with very
limited coverage without the need for infrastructure
• To connect small devices in close proximity (about 10 m)
• The envisaged gross data rate is 1 Mbits/s
• Both asynchronous (data) and synchronous (voice) services
• Transceiver should be very cheap
• Low power consumption chip
• Replace IrDA and solve its main problems:
– limited range – 2m for built-in interfaces
– line of sight
– usually limited to two users, only point-to-point connections are
supported
– no internet working functions
– has no MAC
– Big advantage: COST
Bluetooth
(was:
• History
– 1994: Ericsson (Mattison/Haartsen) initiated “MC-link” (multi
communicator link) project
– Renaming of the project: Bluetooth according to Harald “Blåtand” Gormsen
[son of Gorm], King of Denmark in the 10th century
– 1998: foundation of Bluetooth SIG, www.bluetooth.org
– 1999: erection of a rune stone at Ercisson/Lund ;-)
– 2001: first consumer products for mass market, spec. version 1.1 released
– 2005: 5 million chips/week
• Special Interest Group
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–
–
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Original founding members: Ericsson, Intel, IBM, Nokia, Toshiba
Added promoters: 3Com, Agere (was: Lucent), Microsoft, Motorola
> 10000 members
Common specification and certification of products
• Same time, an IEEE study group for a WPAN specifications started
IEEE802.15 – Requirements fulfilled by Bluetooth
)
History and hi-tech…
1999:
Ericsson mobile
communications AB
reste denna sten till
minne av Harald
Blåtand, som fick ge
sitt namn åt en ny
teknologi för trådlös,
mobil kommunikation.
…and the real rune stone
Located in Jelling, Denmark,
erected by King Harald “Blåtand”
in memory of his parents.
The stone has three sides – one side
showing a picture of Christ.
Inscription:
"Harald king executes these sepulchral
monuments after Gorm, his father and
Thyra, his mother. The Harald who won the
whole of Denmark and Norway and turned
the Danes to Christianity."
Btw: Blåtand means “of dark complexion”
(not having a blue tooth…)
This could be the “original” colors
of the stone.
Inscription:
“auk tani karthi kristna” (and
made the Danes Christians)
Bluetooth Was Originally a CableReplacement Technology
In the Office …
You arrive at the
office …
While in a meeting, …
When inspecting
equipment, …
On the road …
You arrive at the
airport …
You enter the airport
waiting lounge, …
You get on the rent-acar bus, …
Bluetooth - overview
•
•
Consortium: Ericsson, Intel, IBM, Nokia, Toshiba…
Scenarios:
– connection of peripheral devices
• loudspeaker, joystick, headset
– support of ad-hoc networking
• small devices, low-cost
– bridging of networks
• e.g., GSM via mobile phone - Bluetooth - laptop
•
Simple, cheap, replacement of IrDA, low range, lower data rates, low-power
– Worldwide operation: 2.4 GHz
– Available globally for unlicensed users
– Resistance to jamming and selective frequency fading:
• FHSS over 79 channels (of 1MHz each), 1600hops/s
–
–
–
–
•
Coexistence of multiple piconets: like CDMA
Links: synchronous connections and asynchronous connectionless
Interoperability: protocol stack supporting TCP/IP, OBEX, SDP
Range: 10 meters, can be extended to 100 meters
Documentation: over 1000 pages specification: www.bluetooth.com
Bluetooth
• Universal radio interface for ad-hoc wireless connectivity
• Interconnecting computer and peripherals, handheld devices,
PDAs, cell phones – replacement of IrDA
• Embedded in other devices, goal: 5€/device (already < 1€)
• Short range (10 m), low power consumption, license-free 2.45
GHz ISM
• Voice and data transmission, approx. 1 Mbit/s gross data rate
• Supports open-ended list of applications
– Data, audio, graphics, videos
One of the first modules (Ericsson).
Characteristics
• 2.4 GHz ISM band, 79 (23) RF channels, 1 MHz carrier spacing
– Channel 0: 2402 MHz … channel 78: 2480 MHz
– G-FSK modulation, 1-100 mW transmit power
• FHSS and TDD
– Frequency hopping with 1600 hops/s
– Hopping sequence in a pseudo random fashion, determined by a
master
– Time division duplex for send/receive separation
• Voice link – SCO (Synchronous Connection Oriented)
– FEC (forward error correction), no retransmission, 64 kbit/s duplex,
point-to-point, circuit switched
• Data link – ACL (Asynchronous ConnectionLess)
– Asynchronous, fast acknowledge, point-to-multipoint, up to 433.9
kbit/s symmetric or 723.2/57.6 kbit/s asymmetric, packet switched
• Topology
– Overlapping piconets (stars) forming a scatternet
Bluetooth Application Areas
• Data and voice access points
– Real-time voice and data transmissions
• Cable replacement
– Eliminates need for numerous cable attachments for
connection
• Ad hoc networking
– Device with Bluetooth radio can establish connection with
another when in range
• Developed in late 90s
– V1.2 → 1Mbps
– V2.0 → 3Mbps
– V3.0 → 24Mbps
Bluetooth Architecture
• Piconets and Scatternets
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–
–
–
Piconet is the basic unit of networking
One master device and seven slaves
Slave can only communicate with its Master
Slave can be master of another piconet
• This is called a scatternet
Piconet 1
Piconet 2
Slave Master
Master
Scatternet
Piconets and Scatternets
• Piconet
– Basic unit of Bluetooth networking
– Master and one to seven slave devices
– Master determines channel and phase
• Scatternet
– Device in one piconet may exist as master or slave in
another piconet
– Allows many devices to share same area
– Makes efficient use of bandwidth
Piconet
•
•
•
•
•
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Collection of Bluetooth devices connected in an
ad hoc fashion and synchronizes to a master
node
One unit acts as master and the others as
slaves for the lifetime of the piconet
All devices have the same network capabilities
The node establishing the piconet
automatically becomes the master
Master determines hopping pattern, slaves
have to synchronize
Each piconet has a unique hopping pattern
Participation in a piconet = synchronization to
hopping sequence
Each piconet has one master and up to 7
simultaneous slaves (> 200 could be parked)
– Parked device is an inactive device (can be
reactivated in milliseconds)
– Standby device do not participate in piconet
•
If a parked device wants to communicate and
there are 7 active slaves, then one of the
slaves has to switch to park mode
P
S
S
M
P
SB
S
P
M=Master
S=Slave
SB
P=Parked
SB=Standby
Forming a piconet
• All devices in a piconet hop together
– Master gives slaves its clock and device ID
• Hopping pattern: determined by device ID (48 bit, unique worldwide)
• Phase in hopping pattern determined by clock
• Addressing
– Active Member Address (AMA, 3 bit, 8 nodes) for all active nodes
– Parked Member Address (PMA, 8 bit, 256) for parked nodes
– SB devices do not need address
 SB
 SB
 SB 
SB
S
 SB
 SB
 SB
 SB
 SB
SB
P 
S
M
P
S
P 
SB
Scatternet
• Linking of multiple co-located piconets through the sharing of
common master or slave devices
– Devices can be slave in one piconet and master of another
– Master-slave can switch roles
• Communication between piconets
– Devices jumping back and forth between the piconets
• Overlapping piconets experience collisions. How? Hopping with
same frequency at one time slot
Piconets
P
S
(each with a
capacity of
720 kbit/s)
S
S
P
P
M
M
SB
M=Master
S=Slave
P=Parked
SB=Standby
S
P
SB
SB
S
Bluetooth Network Architecture
Piconets & Scatternets
M
S
S
S
S
S
S
S
S
S
S
M/S
S
S
S
S
S
Bluetooth Standards
• Details of various layers of Bluetooth protocol
architecture
• Bluetooth v1.1 ratified in 2002 as IEEE 802.15.1
• Bluetooth v2.0 goes to up to 3Mbps – 2004
• Bluetooth v2.1 adopted July 2007
• Wibree, an ultra low power Bluetooth technology
adopted as part of the Bluetooth specification –
2007.
• Bluetooth v3.0 adopted April 2009. up to 24Mbps
Protocol Architecture
• Bluetooth is a layered protocol architecture
– Core protocols
– Cable replacement and telephony control protocols
– Adopted protocols (using profiles)
• Core protocols
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–
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Radio
Baseband
Link manager protocol (LMP)
Logical link control and adaptation protocol (L2CAP)
Service discovery protocol (SDP)
Protocol Architecture
• Cable replacement protocol
– RFCOMM
• Telephony control protocol
– Telephony control specification – binary (TCS BIN)
• Adopted protocols
– PPP
– TCP/UDP/IP
– WAP
• Profiles
Specifications of how to support applications
Specify which parts of the total specification are mandatory,
optional, or not applicable
• No point having all functionality in all chips
Helps interoperability between vendors
Bluetooth protocol stack
audio apps. NW apps.
TCP/UDP
vCal/vCard
telephony apps.
OBEX
AT modem
commands
IP
mgmnt. apps.
TCS BIN SDP
BNEP PPP
Control
RFCOMM (serial line interface)
Audio
Logical Link Control and Adaptation Protocol (L2CAP)
Link Manager
Baseband
Radio
AT: attention sequence
OBEX: object exchange
TCS BIN: telephony control protocol specification – binary
BNEP: Bluetooth network encapsulation protocol
SDP: service discovery protocol
RFCOMM: radio frequency comm.
Host
Controller
Interface
Establishing a connection: BT – States
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•
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Standby: unconnected but awake
Inquiry: listening or wanting to connect
Page: setting up connections
Active: Connected or Transmitting
Inquiry Procedure
• Goal: aims at discovering other neighboring devices
– Potential master or inquiring node identifies devices in range that
wish to participate
– Transmits ID packet with inquiry access code
– Sends an inquiry message (packet with only the access code).
This message is sent over a subset of all possible frequencies.
– Listen for inquiry response
– Occurs in Inquiry state
• Device receives inquiry: to be discovered node:
– Enters an inquiry_scan mode
– When hearing the inquiry_message enter an inquiry_response
mode: send a Frequency Hop Sync (FHS) packet with address and
timing information
– Moves to page scan state
After discovering the neighbors and collecting
information on their address and clock, the inquiring
node can start a page routine to setup a piconet
Page Procedure
• Goal: e.g., setup a piconet after an inquiry
• Paging node (master):
– uses devices address to calculate a page frequencyhopping sequence
– Sends a page message (i.e., packet with only Device
Access Code (DAC) of paged node)
– Repeated until a response is received
– When a response is received send a FHS message to allow
the paged node to synchronize
• Paged node (slave):
– Listens on its hopping sequence
– When receiving a page message, send a page_response
and wait for the FHS of the pager
– When receiving, slave moves to connection state
Example (without security)
• A Person in a hotel wants to access her email over a
BT enabled PDA. The device will automatically carry
out the following steps
1. Inquiry
•
•
•
The device initiate an inquiry to find out access points
(Masters) within its range
All nearby access points respond with their addresses
The device picks one out of the responding devices
2. Paging
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•
The device will invoke paging procedure
It synchronizes with the access point in terms of clock,
phase and frequency hop
3. Link establishment
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The LMP will establish a link with the master
ACL link will be used (email)
Example (cont.)
4. Service discovery
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•
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The LMP will use SDP to discover what services are
available at the master (email access to the host
possible?)
Assume the service is available, else it would stop
Other available services will be presented to the user
5. L2CAP channel
•
With information obtained from SDP, an L2CAP
channel will be created to the master
6. RFCOMM channel
•
7.
An RFCOMM channel will be created over The L2CAP
channel. This emulates serial port so applications can
run without modifications
Network Protocols
•
The network protocols like TCP/IP can now send and
receive data over the link
Wi-Fi v Bluetooth
• Wi-Fi
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–
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LAN (local area)
Medium range
54Mbps (a/g)
Infrastructure
• LAN extension
– Simple connection
– Secure authentication via
WPA2 (considered safe)
– Layer 1+2 only
• Bluetooth
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–
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PAN (personal area)
Short range
1-3Mbs (v1+2)
Ad Hoc
• Cable replacement
– Complex connection
– Secure authentication via
SSP (known problems)
– Integrates (profiles)
Bluetooth versions
• Bluetooth 1.1
– also IEEE Standard 802.15.1-2002
– initial stable commercial standard
• Bluetooth 1.2
– also IEEE Standard 802.15.1-2005
– eSCO (extended SCO): higher, variable bitrates,
retransmission for SCO
– AFH (adaptive frequency hopping) to avoid interference
• Bluetooth 2.0 + EDR (2004, no more IEEE)
– EDR (enhanced date rate) of 3.0 Mbit/s for ACL and eSCO
– lower power consumption due to shorter duty cycle
• Bluetooth 2.1 + EDR (2007)
– better pairing support, e.g. using NFC
– improved security
• Bluetooth 3.0 + HS (2009)
– Bluetooth 2.1 + EDR + IEEE 802.11a/g = 54 Mbit/s