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A Bidirectional Multi-channel MAC Protocol for Multihop Wireless Ad Hoc Networks

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A Bidirectional Multi-channel MAC Protocol for Multihop Wireless Ad Hoc Networks Tianbo Kuang and Carey Williamson University of Calgary Multi-Hop Wireless Ad Hoc ... – PowerPoint PPT presentation

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Title: A Bidirectional Multi-channel MAC Protocol for Multihop Wireless Ad Hoc Networks


1
A Bidirectional Multi-channel MAC Protocol for
Multihop Wireless Ad Hoc Networks
  • Tianbo Kuang and Carey Williamson
  • University of Calgary

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Multi-Hop Wireless Ad Hoc Networks
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Multi-Hop Wireless Ad Hoc Networks
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Multi-Hop Wireless Ad Hoc Networks
(Assume ideal world)
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Multi-Hop Wireless Ad Hoc Networks
(Reality check)
Problem 1 node A cant use both of these links
at the same time - shared wireless
channel - transmit or receive, but not
both
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Multi-Hop Wireless Ad Hoc Networks
Problem 2 cant use both of these links at same
time - range overlap at A -
hidden node problem - exposed node
problem
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Multi-Hop Wireless Ad Hoc Networks
Problem 3 LOTS of contention for the channel -
in steady state, all want to send - need RTS/CTS
to resolve contention
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RTS Request-To-Send CTS Clear-To-Send
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Multi-Hop Wireless Ad Hoc Networks
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RTS
CTS
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Multi-Hop Wireless Ad Hoc Networks
RTS
CTS
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Multi-Hop Wireless Ad Hoc Networks
Problem 4 TCP uses ACKS to indicate reliable
data delivery - bidirectional traffic (DATA,
ACKS) - even more contention!!!
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TCP ACK
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A Bidirectional Multi-channel MAC Protocol for
Multihop Wireless Ad Hoc Networks
  • Tianbo Kuang and Carey Williamson
  • University of Calgary

53
Agenda
  • Problems of TCP over 802.11 MAC in
    multi-hop wireless ad hoc networks
  • Proposed Solution Bi-MCMAC
  • Performance Evaluation
  • Fairness
  • Throughput
  • Response Time
  • Conclusion

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Proposed Bi-MCMAC Protocol
  • Idea 1 Use multiple channels (e.g., 4) on each
    wireless link, with 1 channel for control, and
    the others for data (suggested in literature
    previously, but not specifically for TCP
    problem)
  • Idea 2 Extend the RTS/CTS to make bidirectional
    channel reservations (this handles DATA/ACK
    common case)

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Multi-Hop Wireless Ad Hoc Networks
Problem 2 cant use both of these links at same
time - range overlap at A -
hidden node problem - exposed node
problem
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Idea 1 Multi-Channel MAC Protocols
- Sender transmits RTS on control channel,
indicating candidate set of channels to use - CTS
reply indicates channel to use (if any) - Sender
and receiver tune to that channel for the
duration of that packet transmission
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A big win! - Confines contention to control
channel only - Reduces hidden node/exposed node
problems - Shortens the contention distance (3
to 2) - Significantly improves throughput
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Multi-Channel MAC Protocols
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Multi-Channel MAC Protocols
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Multi-Channel MAC Protocols
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Multi-Channel MAC Protocols
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Multi-Channel MAC Protocols
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Multi-Channel MAC Protocols
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Multi-Channel MAC Protocols
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Multi-Channel MAC Protocols
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Multi-Channel MAC Protocols
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Idea 2 Bidirectional Reservations
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Old way RTS CTS DATA 3 (ack) RTS CTS ACK 1
(ack)
B
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Our new way RTS CTS CRN DATA 3 ACK 1 (ack)
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25 less overhead in common case of TCP DATA/ACK
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Performance Evaluation
  • Simulation using ns-2 network simulator
  • Three protocols
  • 802.11 MAC, MCMAC, Bi-MCMAC
  • Static ad hoc networks
  • Performance metrics
  • Fairness
  • Throughput (FTP-like bulk data transfer
    applications)
  • Response Time (Web-like applications)

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Performance Evaluation
Channel Capacity 1 Mbps
Number of Channels 4
Propagation Model Two-ray ground
Transmission Range 250 m
Transport Protocol TCP NewReno
TCP Delayed ACK Enabled
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Fairness Example
MCMAC
802.11 MAC
Bi-MCMAC
Total 736 kbps
Total 1406 kbps
Total 1528 kbps
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Throughput
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Throughput Results
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Throughput (contd)
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Throughput (contd)
Random Topology
Grid Topology
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Response Time

Client
Server
Single Web object

Clients
Servers
Multiple Web objects
75
Response Time (contd)
76
Conclusions
  • Bi-MCMAC protocol was proposed to improve TCP
    performance on multi-hop wireless ad hoc
    networks.
  • Simulation results show 50 to 180 improvement
    in throughput.
  • Significant improvements on fairness and transfer
    delay are also achieved.
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