Ad Hoc Nets - MAC layer

1
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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What does Bluetooth do for you?
Cable Replacement - Synchronization -
Cordless Headset
4
Example...
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Bluetooth Physical link

• Point to point link
• master - slave relationship
• radios can function as masters or slaves

• 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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Inquiry on time axis
f1
f2
Slave1
Master
Slave2
8
Piconet formation

• 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
FH/TDD
f1
f3
f4
f5
f2
f6
m
s1
s2
625 µ sec
1600 hops/sec
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Multi slot packets
FH/TDD
f1
f4
f5
f6
m
s1
s2
625 µsec
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

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Packet Types
Data/voice packets
Control packets
Voice
data
ID Null Poll FHS DM1
HV1 HV2 HV3 DV
DH1 DH3 DH5
DM1 DM3 DM5
FHS Frequency Hop Synchronization DM Data
Medium rate HV High quality Voice DV Data
Voice DH Data High rate
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Packet Format
54 bits
72 bits
0 - 2744 bits
Access code
Header
Payload
header
Data
Voice
CRC
No CRC No retries
ARQ
FEC (optional)
FEC (optional)
625 µs
master
slave
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Access Code
72 bits
Access code
Payload
Header
Purpose

• Synchronization
• DC offset compensation
• Identification
• Signaling

X
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Packet Header
54 bits
Access code
Header
Payload
Purpose

• Addressing (3)
• Packet type (4)
• Flow control (1)
• 1-bit ARQ (1)
• Sequencing (1)
• HEC (8)

16 packet types (some unused)
Broadcast packets are not ACKed
For filtering retransmitted packets
Verify header integrity
total
18 bits
Encode with 1/3 FEC to get 54 bits
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Voice Packets (HV1, HV2, HV3)
240 bits
54 bits
72 bits
366 bits
Access code
Header
30 bytes
Payload
HV1
10 bytes
1/3 FEC
20 bytes
HV2
2/3 FEC
30 bytes
HV3
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Data rate calculation DM1 and DH1
72 bits
54 bits
240 bits
366 bits
Access code
30 bytes
Header
Dir Size Freq Rate
? 17 1600/2 108.8
? 17 108.8

? 27 172.8
? 27 172.8
Payload
625 µs
1
2
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Data rate calculation DM3 and DH3
72 bits
54 bits
1626 bits
1500 bits
Access code
187 bytes
Header
Dir Size Freq Rate
? 121 1600/4 387.2
? 17 54.4

? 183 585.6
? 27 86.4
Payload
1875 µs
1
2
3
4
20
Data rate calculation DM5 and DH5
72 bits
54 bits
2870 bits
2744 bits
Access Code
343 bytes
Header
Dir Size Freq Rate
? 224 1600/6 477.8
? 17 36.3

? 339 723.2
? 27 57.6
Payload
625 µs
3125 µs
1
2
3
4
5
6
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Data Packet Types
Symmetric
Asymmetric
108.8 108.8 108.8
258.1 387.2 54.4
286.7 477.8 36.3
2/3 FEC
Symmetric
Asymmetric
172.8 172.8 172.8
390.4 585.6 86.4
433.9 723.2 57.6
No FEC
DM Data Medium rate DH Data High rate FEC
forward error correction
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Inter piconet communication
Cordless headset
Cell phone
Cell phone
Cordless headset
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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)

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Link Manager Protocol

• Setup and management
• of Baseband connections
• Piconet Management
• Link Configuration
• Security

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Piconet Management

• Attach and detach slaves
• Master-slave switch
• Establishing SCO links
• Handling of low power modes ( Sniff, Hold, Park)

Paging
req
Master
Slave
response
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Low power mode (hold)
Hold offset
Slave
Hold duration
Master
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Low power mode (Sniff)
Sniff offset
Sniff duration
Slave
Sniff period
Master

• Traffic reduced to periodic sniff slots

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Low power mode (Park)
Slave
Beacon instant
Master
Beacon interval

• Power saving keep more than 7 slaves in a
  piconet
• Give up active member address, yet maintain
  synchronization
• Communication via broadcast LMP messages

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L2CAP
Applications
L2CAP - Logical Link Control and Adaptation
Protocol
SDP
RFCOMM
Data

• L2CAP provides
• Protocol multiplexing
• Segmentation and
• Re-assembly
• Quality of service negotiation

Audio
L2CAP
Link Manager
Baseband
RF
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RFCOMM (Radio Frequency Communication)-- Serial
Port Emulation using RFCOMM
Applications
SDP
Serial Port
RFCOMM
Data

• Serial Port emulation on top of a packet oriented
  link
• Similar to HDLC (High level
• Data Link Control protocol)
• RS232
• For supporting legacy apps

Audio
L2CAP
Link Manager
Baseband
RF
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IP over Bluetooth V 1.0
Applications
SDP
GOALS
RFCOMM

• Internet access using cell phones
• Connect PDA devices laptop computers to the
  Internet via LAN access points

Data
Audio
L2CAP
Link Manager
Baseband
RF
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Inefficiency of layering

• Emulation of RS-232 over the Bluetooth radio link
  could be eliminated

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Bluetooth Networking A Layer 2 Support
IP
Ethernet-like broadcast segment
slave 3
slave 1
slave 5
slave 4
master
master
Bluetooth
slave 2
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Where is BNEP in the Bluetooth Stack?
Applications
TCP / UDP
IP
Bluetooth Network Encapsulation Protocol Host
Controller Interface
PPP
SDP
RFCOMM
L2CAP
LMP
Baseband
Bluetooth Radio
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The Bluetooth Network Encapsulation Protocol
(BNEP)

• Purpose?
• Create a Ethernet-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

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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 ?