Wireless Networks - MAC layer

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Wireless Networks - MAC layer

• - Bluetooth

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What is Bluetooth?

• Cable replacement technology primarily
• Bluetooth wireless technology is an open
  specification for a low-cost, low-power,
  short-range radio technology for ad-hoc wireless
  communication of voice and data anywhere in the
  world.
• 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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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
• Bluetooth uses a frequency-hopping scheme in the
  unlicensed band at 2.4 GHz.
• The major goal is to allow relatively cheap
  electronic devices to communicate directly in an
  ad-hoc fashion, Moreover, the Bluetooth equipped
  devices can also form networks such a network of
  personal devices is often referred to as a
  personal area network (PAN).

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What does Bluetooth do for you?
Cable Replacement - Synchronization -
Cordless Headset
It is reported that more than two billion
Bluetooth-ready devices were shipped during 2012
over 50 millions every day.
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Example...
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Bluetooth Technical Features

• 2.4 GHz ISM Open Band
• Globally free available frequency
• 79 channels (2400-2483.5 MHz ISM band)
• Frequency Hopping Time Division Duplex (1600
  hops/second typically)
• 10-100 Meter Range
• Class I 100 meter (300 feet)
• Class II 20 meter (60 feet)
• Class III 10 meter (30 feet)
• Link Rate 1 Mbps
• Simultaneous Voice/Data Capable
• SCO (Synchronous connection oriented) for voice
• ACL (Asynchronous connectionless link) for data

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Frequency Hopping
1Mhz
79
83.5 Mhz

• Divide Frequency band into 1 MHz hop
• channels
• Radio hops from one channel to another in a
• pseudo-random manner as dictated by a hop
  sequence

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Frequency Hopping Map

• Wireless channel is divided into time slots of
  625µs
• Frequency hopping sequence is defined by a
  pseudorandom number generator known to both
  transmitter and receiver
• Packet transmission is aligned with the start of
  time slot

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Bluetooth Network Topology

• PICONET Bluetooth LAN
• Collection of devices connected in an ad hoc
  fashion
• One unit acts as master and the others as slaves
  for the lifetime of the piconet
• Master device that initiates a data exchange
• Slave device that responds to the master
• Master determines hopping pattern, slaves
  have to
  synchronize
• There is one only one pattern in one piconet
• 1600hops/sec
• Devices in a piconet are synchronized to the same
  clock defined by master

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Bluetooth Network Topology

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

Assigning address If (node -gt node
address0) MASTER else SLAVE

• Piconet
• Master can connect to 7 slaves
• hopping pattern is determined by the master

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Connection Setup

• Inquiry(????)
• Master ?????????,????????????????????????????(48b)
  ???

• Inquiry scan(????)
• Slave??????????????????,????????,?????????????????
  ?

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Connection Setup

• Page (??)
• Master ??????????????,????????,
  ???????????slaver???????

• Page scan(????)
• Slaver ?????????????????,?????????,
  Slaver????1.28s???????????????????????

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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 used for timing synchronization,
offset compensation, paging, and inquiry
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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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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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
Not implemented in COTS equipment
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Scatternet, scenario 2
How to schedule presence in two piconets?
Forwarding delay ?
Missed traffic?
Not implemented in COTS equipment
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Bluetooth Protocol Stack

• Composed of protocols to allow Bluetooth
  devices to locate each other and to create,
  configure and manage both physical and logical
  links that allow higher layer protocols and
  applications to pass data through these transport
  protocols

Transport Protocol Group
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Bluetooth Protocol Stack

Middleware Protocol Group

• Additional transport protocols to allow
  existing and new applications to operate over
  Bluetooth. Packet based telephony control
  signaling protocol also present. Also includes
  Service Discovery Protocol.

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Bluetooth Protocol Stack
Application Group

• Consists of Bluetooth aware as well as un-aware
  applications.

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Link Manager Protocol

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

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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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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
• Sharing 3G traffic in current mobile internet????
• 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 ?