ad hoc nets - mac layer part ii – tdma and polling - bluetooth
TRANSCRIPT
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Ad Hoc Nets - MAC layer
Part II – TDMA and Polling
- Bluetooth
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Bluetooth• Bluetooth Piconet: a polling/TDMA scheme• Bluetooth working group history
– February 1998: The Bluetooth SIG is formed– promoter company group: Ericsson, IBM, Intel,
Nokia, Toshiba– + 3Com, Lucent, Microsoft, Motorola
• Where does the name come from?– To honor a 10th century king Bluetooth in Denmark
who united that country and established Christianity
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Personal Ad-hoc Networks
Cable Replacement
- Synchronization - Cordless Headset
Landline
Data/Voice Access Points
What does Bluetooth do for you?
…and combinations!
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Example...
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Bluetooth Physical link
• Point to point link– master - slave relationship– radios can function as
masters or slavesm s
ss
m
s
• Piconet– Master can connect to 7 slaves– Each piconet has max capacity =1 Mbps ~ 10 - 100 Meter– hopping pattern is determined
by the master
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Connection Setup
• Inquiry - scan protocol– to learn about the clock offset and device
address of other nodes in proximity
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Piconet formation
Master
Active Slave
Parked Slave-Connected-Not in Pico
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 MAC protocol : Polling
m
s1
s2
625 µ sec
f1 f2 f3 f4
1600 hops/sec
f5 f6FH/TDD
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Multi slot packets
m
s1
s2
625 µsec
f1 f4 f5 f6
FH/TDD
Data rate depends on type of packet
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Physical Link Types
• Synchronous Connection Oriented (SCO) Link – slot reservation at fixed intervals
• Asynchronous Connection-less (ACL) Link– Polling access method
m
s1
s2
SCO SCO SCOSCO SCO SCOACL ACL ACLACL ACL ACLSCO SCO SCO
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Packet Types
Controlpackets
Data/voicepackets
ID*NullPollFHSDM1
Voice data
HV1HV2HV3DV
DM1DM3DM5
DH1DH3DH5
FHS – Frequency Hop SynchronizationDM – Data Medium rateHV – High quality VoiceDV – Data VoiceDH – Data High rate
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Packet Format
72 bits 54 bits 0 - 2744 bitsAccess code
Header Payload
DataVoice CRC
No CRCNo retries
625 µs
master
slave
header
ARQ
FEC (optional) FEC (optional)
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Packet Header
• Addressing (3)• Packet type (4)• Flow control (1)• 1-bit ARQ (1)• Sequencing (1)• HEC (8)
Access code Header Payload
54 bits
Purpose
Encode with 1/3 FEC to get 54 bits
Broadcast packets are not ACKed
For filtering retransmitted packets
18 bitstotal
ss
m
s
16 packet types (some unused)
Max 7 active slaves
Verify header integrity
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Inter piconet communication
Cell phone Cordlessheadset
Cordless
headset
Cell phone
Cordlessheadset
Cell phone
mouse
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Scatternet- Gateway node participates in more than one piconet
on a time-division basis
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Scatternet, scenario 2
How to schedule presence in two piconets?
Forwarding delay ?
Missed traffic?
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Baseband: Summary
• TDD, frequency hopping physical layer• Device inquiry and paging• Two types of links: SCO and ACL links• Multiple packet types (multiple data rates
with and without FEC)
Baseband Baseband
L2CAPL2CAPLMPLMP
Physical
Data link
Device 2Device 1
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Link Manager Protocol
Setup and management of Baseband connections
• Piconet Management• Link Configuration• Security
LMP
RF
Baseband
AudioLink Manager
L2CAP
Data Con
trol
SDP RFCOMM
IP
Applications
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Piconet Management• Attach and detach slaves• Master-slave switch• Establishing SCO links• Handling of low power modes ( Sniff, Hold, Park)
req
response
Paging
Master
Slaves
s
m
s
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L2CAP
L2CAP - Logical Link Control and Adaptation Protocol
L2CAP provides• Protocol multiplexing• Segmentation and Re-assembly• Quality of service negotiationRF
Baseband
AudioLink Manager
L2CAP
Data
SDP RFCOMM
IP
Applications
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RFCOMM (Radio Frequency Communication)-- Serial Port Emulation using RFCOMM
Serial Port emulation on top of a packet oriented link• Similar to HDLC (High level Data Link Control protocol)
• RS232• For supporting legacy apps
RF
Baseband
AudioLink Manager
L2CAP
Data
SDP RFCOMM
IP
Applications
Serial Port
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GOALS
IP over Bluetooth V 1.0
• Internet access using cell phones
• Connect PDA devices & laptop computers to the Internet via LAN access pointsRF
Baseband
AudioLink Manager
L2CAP
Data
SDP RFCOMM
IP
Applications
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Inefficiency of layering
• Emulation of RS-232 over the Bluetooth radio link could be eliminated
L2CAP
RFCOMM
rfc 1662
PPP
IP
L2CAP
RFCOMM
rfc 1662
PPP
IP
Palmtop LAN access point
packet oriented
packet oriented
byte oriented
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master
slave 1
slave 2
slave 3
masterslave 4 slave 5
Bluetooth
IPIP
Ethernet-like Ethernet-like broadcast broadcast segmentsegment
Bluetooth Networking: A Layer 2 Support
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Where is BNEP in the Bluetooth Stack?
Bluetooth Radio
Baseband
LMP
L2CAP
Bluetooth Network Encapsulation Protocol
Host Controller Interface
RFCOMM
PPP
IP
TCP / UDP
SDP
Applications
BNEP
IP
TCP / UDP
Applications
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The Bluetooth Network Encapsulation Protocol (BNEP)
Purpose? Create a Ethernet-likeEthernet-like broadcast environment for
IP in a Bluetooth Scatternet, hiding Bluetooth specifics (e.g. notion of piconet/scatternet forming and maintenance) from IP and above
Features:• Clear division between Bluetooth spec and IP • IP and IP networking applications will work as
usual (DHCP, ARP)• Easy to apply zeroconf protocols• across scatternets
– Ad-hoc L2 routing, handle loop-free broadcast
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BNEP Overhead
• Type: 7 bit Bluetooth value identifies the type of BNEP header contained in this packet
• 1 bit extension flag that indicates if one or more extension headers follow the BNEP Header before the data payload.
• 1M of Data transfer– Additional ~0.2% Overhead– Additional Bluetooth Transmission time: 11
mSec
0 4 8 12 16 20 24 28 31
Extension Headeror BNEP Payload ...
BNEP Type =0x02
Networking Protocol TypeE
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Bluetooth Personal Area Networks - Ad Hoc and extend to Mesh
• PANs extend the Internet to the user personal domain• 3G (2.5G) networks will give Internet access to PANs• PANs will generate more traffic than a single device• Utilize an aggregate of access networks (WLAN, 3G, DSL)
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IP Bluetooth Networking - Conclusions
Bluetooth IP networking opens up new possibilities ---- Mesh networks
• Enables spontaneous Ad Hoc networking – Between people,– Between machines,
• Mainly small, short range ad-hoc networks– Solves your “personal problems”...– Limited complexity and security risks
• The enabler for PANs! – Gives a natural extension of Internet into the PAN
via 3G– Enables stepwise upgrading of devices -- not tied to
one multimedia terminal!– Makes use of the 3G bandwidth immediately
• QoS ~ Bluetooth ?