Networking over Bluetooth: overview and issues
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Transcript of Networking over Bluetooth: overview and issues
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Networking over Bluetooth:overview and issues
Pravin BhagwatMobile Networking Group
IBM T. J. Watson Research
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http://www.research.ibm.com/people/p/pravin
IAB Wireless WorkshopFeb 29 - March 2, 2000
Sunnyvale, CA
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Bluetooth
A cable replacement technology 1 Mb/s symbol rate Range 10+ meters
Single chip radio + baseband at low power & low price point
Why not use Wireless LANs?- power- cost
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Value proposition of Bluetooth
Cordlessheadset
Cell phone
mouse
Cable replacement
Ad hoc networking
Data accesspoint
Internet access
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Bluetooth working group history
February 1998: The Bluetooth SIG is formed promoter company group: Ericsson, IBM, Intel, Nokia,
Toshiba
May 1998: The Bluetooth SIG goes “public” July 1999: 1.0A spec (>1,500 pages) is published December 1999: ver. 1.0B is released December 1999: The promoter group increases to 9
3Com, Lucent, Microsoft, Motorola
February 2000: There are 1,500+ adopters adopters "enjoy" royalty free use of the Bluetooth
technology products must pass Bluetooth certification
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New Applications
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Synchronization
User benefits Automatic synchronization of
calendars, address books, business cards
Push button synchronization Proximity operation
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Cordless Headset
User benefits Multiple device access Cordless phone benefits Hand’s free operation
Cordlessheadset
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Usage scenarios examples
Data Access Points Synchronization Headset Conference Table Cordless Computer Business Card Exchange Instant Postcard Computer Speakerphone
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Bluetooth Specifications
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RF
Baseband
AudioLink Manager
L2CAP
Data Con
trol
Bluetooth Stack
A hardware/software/protocol description An application framework
RFCOMMSDPIP
Applications
Single chip with RS-232,USB, or PC card interface
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Interoperability & Profiles
A profile represents a default solution for a usage model
Vertical slice through the protocol stack Basis for interoperability and logo requirements Each Bluetooth device supports one or more
profiles
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TechnicalOverview
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RF
Baseband
AudioLink Manager
L2CAP
Data Con
trol
Bluetooth Radio Specification
RFCOMMSDPIP
Applications
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Radio
Low Cost Single chip radio (minimize external components) Today’s technology Time divison duplex
Low Power Standby modes Sniff, Hold, Park Low voltage RF
Robust Operation Fast frequency hopping 1600 hops/sec Strong interference protection
Fast ARQ Robust access code Forward header correction
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Radio
Allow low cost low IF Trade sensitivity for integration One chip radio is possible
0 dBm
-20
-70
-91
Tx power
Rx power @ 10 cm
Rx power @ 10m
Noise floorC/I = 21 dB
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RF
Baseband
AudioLink Manager
L2CAP
Data Con
trol
Baseband
RFCOMMSDPIP
Applications
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Connection Setup
Inquiry - scan protocol to lean about the clock offset
and device address of other nodes in proximity
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Piconet formation
Master
Active Slave
Parked Slave
Standby
Page - scan protocol to establish links with
nodes in proximity
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Addressing
Bluetooth device address (BD_ADDR) 48 bit IEEE MAC address
Active Member address (AM_ADDR) 3 bits active slave address all zero broadcast address
Parked Member address (PM_ADDR) 8 bit parked slave address
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Piconet channel
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625 sec
f1 f2 f3 f4
1600 hops/sec
f5 f6
FH/TDD
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Multi slot packets
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FH/TDD
Data rate depends on type of packet
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Packet Format
Access code
Header Payload
72 bits 54 bits 0 - 2745 bits
Synchronizationidentification
Filtering
AddressPacket TypeFlow controlARQSEQNHEC
Error correction1/3 rate FEC2/3 rate FEC
ARQ scheme for the data
Smaller than an ATM cell !Notice that there is no protocol type field
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Physical Link Types
Synchronous Connection Oriented (SCO) Link slot reservation at fixed intervals
No ARQ, No CRC FEC (optional) 64 Kbps
Asynchronous Connection-less (ACL) Link Polling access method ARQ, CRC FEC (optional) Symmetric data rate 108 - 433 Kbps Asymmetric data rate up to 723 Kbps
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Mixed Link Example
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SCO SCO SCOACL ACL ACLACL ACL ACL
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Inter piconet communication
Cell phone Cordlessheadset
Cordless
headset
Cell phone
Cordlessheadset
Cell phone
mouse
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Scatternet
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Scatternet, scenario 2
How to schedule presence in two piconets?
Forwarding delay ?
Missed traffic?
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RF
Baseband
AudioLink Manager
L2CAP
Data Con
trol
Link Manager Protocol
RFCOMMSDPIP
Applications Setup and Management of Baseband connections
• Piconet Management• Link Configuration• Security
LMP
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Link Manager Protocol
Piconet Management Attach and detach slaves Master-slave switch Establishing SCO and ACL links Handling of low power modes ( Sniff, Hold, Park)
Link Configuration packet type negotiation power control
Security functions Authentication Encryption
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L2CAP
RF
Baseband
AudioLink Manager
L2CAP
Data
RFCOMMSDPIP
Applications Logical Link Control andAdaptation Protocol
• L2CAP provides• Protocol multiplexing• Segmentation and Re-assembly• Quality of service negotiation• Group abstraction
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L2CAP Packet Format (CO)
Length DCID Payload
15 bits 16 bits 0 - 64K bytes
Baseband packets Minimum MTU is 48 bytes !default is 672 bytes !
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L2CAP Packet Format (CL)
Length DCID Payload
15 bits 16 bits 0 - 64K bytes
Baseband packets
PSM
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RF
Baseband
AudioLink Manager
L2CAP
Data
Serial Port Emulation using RFCOMM
RFCOMMSDPIP
Applications
Serial Port emulation on top of a packet oriented link• Similar to HDLC• For supporting legacy apps
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RF
Baseband
AudioLink Manager
L2CAP
Data
Bluetooth Service Discovery Protocol
RFCOMMSDPIP
Applications
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Example usage of SDP
Establish L2CAP connection to remote device Query for services
search for specific class of service, or browse for services
Retrieve attributes that detail how to connect to the service Establish a separate (non-SDP) connection to user the service
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RF
Baseband
AudioLink Manager
L2CAP
Data
RFCOMMSDPIP
Applications
GOALS
IP over Bluetooth V 1.0
Internet access using cell phones Connect PDA devices & laptop
computers to the Internet via LAN access points
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LAN access point profile
SecurityAuthenticationAccess control
Efficiencyheader and data compression
Auto-configurationLower barrier for deployment
Why use PPP?
Access Point
Baseband
LMP
L2CAP
RFCOMM
PPP
IP
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Inefficiency of layering
Emulation of RS-232 over the Bluetooth radio link could be eliminated
Bluetooth
RFCOMM
rfc 1662
PPP
IP
Bluetooth
RFCOMM
rfc 1662
PPP
IP
Palmtop LAN access point
packet oriented
packet oriented
byte oriented
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Terminate PPP at LAN access point
PPP server function at each access point management of user name/password is an issue roaming is not seamless
Bluetooth
RFCOMM
PPP
IP
Bluetooth
RFCOMM
PPP
IP
ethernet
Palmtop Access Point
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L2TP style tunneling
Tunneling PPP traffic from access points to the PPP server 1) centralized management of user name/password 2) reduction of processing and state maintenance at each access
point 3) seamless roaming
radio link
RFCOMM
PPP
IP
Palmtop Access Point
radio link
RFCOMM
PPP
IP
ethernet
IP
UDP
ethernet
IP
UDP
PPP server
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IP over Bluetooth
IP based network connectivity
peer-to-peer connectivity
Internet connectivity for non-PC devices
IP over wireless media
Decentralized techniquesfor link formulation, naming, addressing, and routing
Investigation of the rightdesign point forrunning IP overtoasters, light switches,& fire alarms
Next steps
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Research challenges
Techniques for link formation
Routing over scatternets
Resource Discovery
Plug-n-play applications
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cell phone Palmpilot
cable modem
PC
keyboard mouse
head set
Cordless base
Internet
Will the current solutions for each layerwork in this environment?
cell phone Palmpilot
cable modem
PC
keyboard mouse
head set
Cordless base
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What is different in this scenario ?
Dynamic network
Isolated network
Simple devices
Small, multi-hop networks
Connection oriented, low-power link technology
Applications ---> services ----> routing ----> link creation
cell phone Palmpilot
cable modem
PC
keyboard mouse
head set
cordless bases
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Link Formation
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Low power modes require
careful use of broadcast
Proximity Link
The problem does not exist
in most wired/wireless networks
Maintaining connectivity in absence of application traffic seems wasteful
Hints from higher layer are needed
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Routing over Scatternets
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Nodes must co-operate to forward
packets (MANET style protocols)
Forwarding at Layer 2 or Layer 3?
Bridging or routing ?
What interface should be exported to the above layer?
Better coupling with the service discovery layer is needed
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Service discovery
cell phone Palmpilot
cable modem
PC
keyboard mouse
head set
cordless bases
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Need solutions for address allocation,
name resolution, service discovery
Existing solutions in the Internet
depend on infrastructure
Judicious use of Multicast/broadcast
is needed
These goals are similar to what Zero-conf WG is already
working on
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Point to ponder
Will Zero-conf on top of MANET
on top of scatternet construction
algorithm solve our problem?
Layered and simple, but potential
inefficiencies
Cross-layer optimizations are
worth considering
Zero-conf
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MANET
Scatternet formation
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Final Remarks
• Zero-conf and Bluetooth can benefit from each other
• Similarly, MANET and Bluetooth can also benefit from each other
• A new working group in IETF for IP over Bluetooth ?
• Multi-hop wireless networks will force us to re-evaluate our assumptions about network layering. Should IRTF start looking into those issues?
http://www.research.ibm.com/people/p/pravin