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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. 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

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  1. Exploiting Path Diversity In The Link Layer In Wireless Ad Hoc Networks Shweta Jain, Samir Das. WoWMoM 2005

  2. Overview • Introduction • Description of IEEE 802.11 • Description of Anycast protocol • Performance results: Analytical, Test Bed and Simulation results • Conclusion WoWMoM 2005

  3. 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

  4. 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

  5. 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

  6. 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

  7. IEEE 802.11 Control Handshake WoWMoM 2005

  8. 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

  9. 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

  10. Protocol Details WoWMoM 2005

  11. 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

  12. Performance Results Analytical Model Test Bed using Berkeley Motes Simulation results WoWMoM 2005

  13. 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

  14. Test Bed WoWMoM 2005

  15. Simulation results Static Grid Scenario WoWMoM 2005

  16. Simulation results Static Random Scenario WoWMoM 2005

  17. Simulation results Random Mobile Scenario WoWMoM 2005

  18. 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

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