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Exploiting Path Diversity In The Link Layer In Wireless Ad Hoc Networks. Shweta Jain, Samir Das. Overview . Introduction Description of IEEE 802.11 Description of Anycast protocol Performance results: Analytical, Test Bed and Simulation results Conclusion. Introduction.

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exploiting path diversity in the link layer in wireless ad hoc networks

Exploiting Path Diversity In The Link Layer In Wireless Ad Hoc Networks

Shweta Jain, Samir Das.

WoWMoM 2005

overview
Overview
  • Introduction
  • Description of IEEE 802.11
  • Description of Anycast protocol
  • Performance results: Analytical, Test Bed and Simulation results
  • Conclusion

WoWMoM 2005

introduction
Introduction
  • Received signal strength in a wireless network varies at a rapid rate and the variations are transient.
  • We develop a MAC protocol that extends IEEE 802.11 to combat channel fluctuation by exploiting availability of multiple paths from multi-path routing
  • We demonstrate the benefit of using path diversity in different wireless Ad-hoc network scenarios through an analytical model and computer based simulation experiments

WoWMoM 2005

motivation
Motivation
  • Fading and interference levels affect the SINR at the receiver.
  • Significant changes in fading and interference levels might cause transient loss of link between two nodes.
  • Such changes might last long enough for routing and transport protocols to react by failing the route or bringing down the offered load.
  • There is a need to incorporate mechanisms that can withstand such link losses at shorter time scale.
  • Lower layers have more knowledge about the channel conditions and thus can be exploited to adapt to short term changes.

WoWMoM 2005

features
Features
  • Multi-path routing concept can be utilized at the MAC layer to provide resistance to short term physical layer variations.
  • Routing layer provides multiple link options to the MAC layer .
  • Simple variations in the RTS frames used in IEEE 802.11 to enable Anycasting.
  • MAC layer exploits this path diversity to produce better packet delivery fraction
  • Analytical, simulation and Test bed results prove the benefit of exploiting path diversity at the link layer

WoWMoM 2005

ieee 802 11 rts cts handshake
IEEE 802.11 RTS/CTS Handshake

Algorithm:

  • Tx: After CSMA/CA send RTS frame to the intended receiver
  • Rx: If ready to receive send CTS frame else do nothing
  • Tx: If CTS received correctly send DATA else back-off and try again (max 7 tries)
  • Rx: If DATA received correctly send ACK else do nothing
  • Tx: If ACK received backoff (successful transmission) else backoff and retry (max 4 tries)

WoWMoM 2005

anycast mac our approach
Anycast MAC—Our Approach
  • Tx: After CSMA/CA send RTS frames to some available next hops in the route (max 4, min 1). The RTS frame carries IP addresses of the next hops.
  • To avoid collision between CTS from different receivers, the CTSs are ordered in time based upon the order in which the IP addresses appear in the RTS frame.
  • Rx1: If ready to receive send CTS frame else do nothing
  • Rx2-4: If RTS received but DATA not heard until timeout send CTS. This time out is set to (2n-1)xSIFS + nxCTS_TIME where n = position of the IP Address in the RTS frame.

WoWMoM 2005

anycast mac our approach contd
Anycast MAC—Our Approach --contd
  • Tx: If CTS received correctly from any receiver send DATA to that receiver else back-off and try again (max 6 retries). This timeout is set to 2NxSIFS + NxCTS_TIME where N = number of next hop receivers.
  • The DATA and ACK procedure is unaltered.
    • Rx: If DATA received correctly send ACK else do nothing
    • Tx: If ACK received backoff (successful transmission) else backoff and retry (max 4 tries).

WoWMoM 2005

protocol details
Protocol Details

WoWMoM 2005

comments
Comments
  • In the absence of multiple paths Anycast reduces to IEEE 802.11
  • Anycast extends the idea of multiple paths to the MAC layer
  • It can act as an aid for enhancing the network performance which use multi-path routing

WoWMoM 2005

performance results

Performance Results

Analytical Model

Test Bed using Berkeley Motes

Simulation results

WoWMoM 2005

analytical model

p = Prob of loss at each link

B(L) = # of paths through boundary nodes at i+j =L

NB(L)= #of paths through non boundary at i+j=L

Analytical Model

WoWMoM 2005

test bed
Test Bed

WoWMoM 2005

simulation results
Simulation results

Static Grid Scenario

WoWMoM 2005

simulation results16
Simulation results

Static Random Scenario

WoWMoM 2005

simulation results17
Simulation results

Random Mobile Scenario

WoWMoM 2005

conclusion
Conclusion
  • Anycast is a simple enhancement of IEEE 802.11.
  • This protocol utilizes multi-path routing to achieve resilience against multi-path effect.
  • Anycast performs significantly better than IEEE 802.11 if multiple paths are available at each hop.
  • Analytical, Experimental and simulation results corroborate the above conclusion.

WoWMoM 2005