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Networking over Bluetooth: overview and issues

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Title: Networking over Bluetooth: overview and issues


1
Networking over Bluetoothoverview and issues
m
s
s
s
  • Pravin Bhagwat
  • Mobile Networking Group
  • IBM T. J. Watson Research

http//www.research.ibm.com/people/p/pravin
pravinb_at_us.ibm.com
IAB Wireless Workshop Feb 29 - March 2,
2000 Sunnyvale, CA
2
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
3
Value proposition of Bluetooth
Data access point
Internet access
Cable replacement
Ad hoc networking
4
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 (gt1,500 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

5
New Applications
6
Synchronization
  • User benefits
  • Automatic synchronization of calendars, address
    books, business cards
  • Push button synchronization
  • Proximity operation


7
Cordless Headset
Cordless headset
  • User benefits
  • Multiple device access
  • Cordless phone benefits
  • Hands free operation

8
Usage scenarios examples
  • Data Access Points
  • Synchronization
  • Headset
  • Conference Table
  • Cordless Computer
  • Business Card Exchange
  • Instant Postcard
  • Computer Speakerphone

9
Bluetooth Specifications
10
Bluetooth Stack
Applications
SDP
RFCOMM
Audio
L2CAP
Link Manager
Baseband
RF
  • A hardware/software/protocol description
  • An application framework

11
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

12
Technical Overview
13
Bluetooth Radio Specification
Applications
SDP
RFCOMM
Audio
L2CAP
Link Manager
Baseband
RF
14
Radio
  • Low Cost
  • Single chip radio (minimize external components)
  • Todays 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

15
Radio
0 dBm
Tx power
Rx power _at_ 10 cm
-20
  • Allow low cost low IF
  • Trade sensitivity for integration
  • One chip radio is possible

Rx power _at_ 10m
-70
C/I 21 dB
-91
Noise floor
16
Baseband
Applications
SDP
RFCOMM
Audio
L2CAP
Link Manager
Baseband
RF
17
Connection Setup
  • Inquiry - scan protocol
  • to lean about the clock offset and device address
    of other nodes in proximity

18
Piconet formation
  • Page - scan protocol
  • to establish links with nodes in proximity

19
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

20
Piconet channel
FH/TDD
f1
f3
f4
f5
f2
f6
m
s1
s2
625 ?sec
1600 hops/sec
21
Multi slot packets
FH/TDD
f1
f4
f5
f6
m
s1
s2
625 ?sec
Data rate depends on type of packet
22
Packet Format
54 bits
72 bits
0 - 2745 bits
Access code
Header
Payload
Error correction 1/3 rate FEC 2/3 rate FEC ARQ
scheme for the data
Synchronization identification Filtering
Address Packet Type Flow control ARQ SEQN HEC
Smaller than an ATM cell ! Notice that there is
no protocol type field
23
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

24
Mixed Link Example
SCO
SCO
SCO
m
s1
s2
25
Inter piconet communication
Cordless headset
Cell phone
Cell phone
Cordless headset
26
Scatternet
27
Scatternet, scenario 2
How to schedule presence in two piconets?
Forwarding delay ?
Missed traffic?
28
Link Manager Protocol
  • Setup and Management
  • of Baseband connections
  • Piconet Management
  • Link Configuration
  • Security

Applications
SDP
RFCOMM
Audio
L2CAP
Link Manager
Baseband
RF
29
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

30
L2CAP
Logical Link Control and Adaptation Protocol
  • L2CAP provides
  • Protocol multiplexing
  • Segmentation and Re-assembly
  • Quality of service negotiation
  • Group abstraction

31
L2CAP Packet Format (CO)
16 bits
15 bits
0 - 64K bytes
DCID
Payload
Length
Minimum MTU is 48 bytes ! default is 672 bytes !
Baseband packets
32
L2CAP Packet Format (CL)
16 bits
15 bits
0 - 64K bytes
DCID
Payload
PSM
Length
Baseband packets
33
Serial Port Emulation using RFCOMM
Applications
SDP
RFCOMM
  • Serial Port emulation on top of a packet oriented
    link
  • Similar to HDLC
  • For supporting legacy apps

Audio
L2CAP
Link Manager
Baseband
RF
34
Bluetooth Service Discovery Protocol
Applications
SDP
RFCOMM
Audio
L2CAP
Link Manager
Baseband
RF
35
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

36
IP over Bluetooth V 1.0
Applications
SDP
RFCOMM
GOALS
  • Internet access using cell phones
  • Connect PDA devices laptop computers to the
    Internet via LAN access points

Audio
L2CAP
Link Manager
Baseband
RF
37
LAN access point profile
IP
Access Point
PPP
RFCOMM
L2CAP
LMP
Baseband
38
Inefficiency of layering
Palmtop
LAN access point
IP
IP
packet oriented
PPP
PPP
rfc 1662
rfc 1662
byte oriented
RFCOMM
RFCOMM
packet oriented
Bluetooth
Bluetooth
  • Emulation of RS-232 over the Bluetooth radio link
    could be eliminated

39
Terminate PPP at LAN access point
Palmtop
Access Point
IP
IP
PPP
ethernet
PPP
RFCOMM
RFCOMM
Bluetooth
Bluetooth
  • PPP server function at each access point
  • management of user name/password is an issue
  • roaming is not seamless

40
L2TP style tunneling
Palmtop
Access Point
PPP server
IP
IP
PPP
PPP
RFCOMM
RFCOMM
radio link
radio link
  • 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

41
IP over Bluetooth
Next steps
Internet connectivity for non-PC devices
IP based network connectivity
peer-to-peer connectivity
IP over wireless media
Decentralized techniques for link formulation,
naming, addressing, and routing
Investigation of the right design point
for running IP over toasters, light switches,
fire alarms
42
Research challenges
Internet
Plug-n-play applications
Resource Discovery
Routing over scatternets
Techniques for link formation
Will the current solutions for each layer work in
this environment?

43
What is different in this scenario ?
Connection oriented, low-power link technology
Small, multi-hop networks
Simple devices
Isolated network
Dynamic network
Applications ---gt services ----gt routing ----gt
link creation
44
Link Formation
The problem does not exist in most wired/wireless
networks
Low power modes require careful use of broadcast
Maintaining connectivity in absence of
application traffic seems wasteful
Hints from higher layer are needed
45
Routing over Scatternets
Nodes must co-operate to forward packets (MANET
style protocols)
x5
x1
y2
y1
Forwarding at Layer 2 or Layer 3?
Bridging or routing ?
x8
x6
x4
x2
x7
x3
What interface should be exported to the above
layer? Better coupling with the service discovery
layer is needed
46
Service discovery
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
47
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
48
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
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