Improving Distributed TCP                Caching for Wireless                Sensor NetworksAhmed Ayadi, Patrick Maillé an...
Outline        TCP over wireless sensor networks        Distributed TCP Caching        Enhanced Distributed TCP Caching...
Wireless Sensor Networks3   TELECOM Bretagne   Improving Distributed TCP Caching
Reliable transport protocol for WSNs      The WSNs are fault-tolerant networks      The number of sensor network applica...
Problems of TCP deployment in WSNs        High error rate in wireless networks (interferences,         congestion, collis...
TCP end-to-end recovery      1     2     3      4       5       6      7       8       9        10                       T...
Distributed TCP Caching (DTC)      A DTC node saves the received TCP-DATA segment if       the cache buffer is empty or u...
Distributed TCP Caching      1       2   3    4     5      6        7        8     9            10          1          2  ...
Limits of DTC        DTC does not take into account TCP-ACK losses,        A DTC node can loss the cached,        DTC d...
Enhanced Distributed TCP Caching         New version of DTC for CSMA-CA networks (e.g. IEEE          802.11 and IEEE 802....
Disable unnecessary retransmissions       1     2     3    4     5      6       7       8       9        10               ...
Cache memory managementDTC                                     TCP‐DATA
2
                                        TCP‐DATA...
Cache memory managementEDTC                                    TCP‐DATA
1
              Node 1                     Node 2 ...
TCP ACK losses detection                      DTC                                                  EDTCNode1             N...
Simulation parameters     Parameters                          Value     MAC layer                           IEEE 802.11b R...
Consumed Energy & Transfer Duration• DTC with the new cachemanagement (DTC-CM) andDTC with smoothed RTO (DTC-SRTO) reduce ...
DTC vs EDTC with different BER     •  EDTC is more energy efficient than DTC and TCP in     low-lossy networks and high-lo...
TCP Congestion Windows     • The increase of the TCP window does not increase     significantly the TCP throughput,     • ...
Maximum Link Layer Attempts     • The increase of the maximum link layer attempt     reduces the end-to-end TCP retransmis...
Conclusion and Perspectives         EDTC is more energy-efficient than DTC and TCP,         EDTC increases the chance of...
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Improving Distributed TCP Caching for Wireless Sensor Networks

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Improving Distributed TCP Caching for Wireless Sensor Networks

  1. 1. Improving Distributed TCP Caching for Wireless Sensor NetworksAhmed Ayadi, Patrick Maillé and David RosInstitut Telecom / Telecom BretagneMedHocNet Workshop, June 25, Juan les Pins 2010
  2. 2. Outline   TCP over wireless sensor networks   Distributed TCP Caching   Enhanced Distributed TCP Caching •  Cache memory management •  Disable unnecessary retransmissions •  TCP acknowledgment loss detection   Simulation results   Conclusion and Perspectives2 TELECOM Bretagne Improving Distributed TCP Caching
  3. 3. Wireless Sensor Networks3 TELECOM Bretagne Improving Distributed TCP Caching
  4. 4. Reliable transport protocol for WSNs   The WSNs are fault-tolerant networks   The number of sensor network applications grows, so there is a need to build more powerful hardware capable of reprogramming or re-tasking sensors.   New military and hearth applications are sensitive to losses.   All these tasks require reliable data transport from the sink to wireless node and vice versa.   The most deployed reliable transport protocol model in the Internet is TCP/IP.   Running TCP/IP in the sensor network makes it possible to connect the sensor network directly to IP- based network infrastructures without proxies.4 TELECOM Bretagne Improving Distributed TCP Caching
  5. 5. Problems of TCP deployment in WSNs   High error rate in wireless networks (interferences, congestion, collisions, etc),   End-to-end retransmission of lost packets,   Length of TCP header (20-60 bytes),   The number of TCP acknowledgements.5 TELECOM Bretagne Improving Distributed TCP Caching
  6. 6. TCP end-to-end recovery 1 2 3 4 5 6 7 8 9 10 TCP-DATA N TCP-DATA N+1 TCP-DATA N+2 ACK N TCP-DATA N6 TELECOM Bretagne Improving Distributed TCP Caching
  7. 7. Distributed TCP Caching (DTC)   A DTC node saves the received TCP-DATA segment if the cache buffer is empty or unlocked.   A DTC locks a segment if a link layer acknowledgement is not received.   DTC uses TCP-SACK to detect packet loss.   A DTC node measures the round-trip timer (RTT) to the receiver and sets a retransmission time out (RTO) to 1.5 x RTT.   A DTC node retransmits a cached segments after a RTO if it does not receive a TCP-ACK or TCP-SACK.7 TELECOM Bretagne Improving Distributed TCP Caching
  8. 8. Distributed TCP Caching 1 2 3 4 5 6 7 8 9 10 1 2 3 ACK1(SACK(3)‫‏‬ ACK1(SACK(2,3)‫‏‬ 2 1 ACK48 TELECOM Bretagne Improving Distributed TCP Caching
  9. 9. Limits of DTC   DTC does not take into account TCP-ACK losses,   A DTC node can loss the cached,   DTC does not smooth the RTT value in intermediate nodes,9 TELECOM Bretagne Improving Distributed TCP Caching
  10. 10. Enhanced Distributed TCP Caching   New version of DTC for CSMA-CA networks (e.g. IEEE 802.11 and IEEE 802.15.4),   A EDTC node detects TCP-ACK losses and deletes already acknowledged TCP segment,   EDTC disables retransmission of already retransmitted segments,   An EDTC node locks received TCP DATA segments and unlocks them after receiving a LL-ACK,   EDTC computes smoothed RTO with Paxson and Allman algorithm.10 TELECOM Bretagne Improving Distributed TCP Caching
  11. 11. Disable unnecessary retransmissions 1 2 3 4 5 6 7 8 9 10 TCP-DATA N TCP-DATA N TCP-DATA N TCP-ACK N+111 TELECOM Bretagne Improving Distributed TCP Caching
  12. 12. Cache memory managementDTC TCP‐DATA
2
 TCP‐DATA
1
 Node 1 Node 2 Node 3 TCP‐DATA
1
 TCP‐DATA
2
 TCP‐DATA
1
 12 TELECOM Bretagne Improving Distributed TCP Caching
  13. 13. Cache memory managementEDTC TCP‐DATA
1
 Node 1 Node 2 Node 3 TCP‐DATA
1
 TCP‐DATA
2
 TCP‐DATA
1
 13 TELECOM Bretagne Improving Distributed TCP Caching
  14. 14. TCP ACK losses detection DTC EDTCNode1 Node 2 Node 3 Node 1 Node 2 Node 3 TCP‐DATA
2
 TCP‐DATA
2
 TCP‐DATA
2
 TCP‐DATA
2
 TCP‐ACK
3
 TCP‐ACK
3
 TCP‐DATA
2
 TCP‐DATA
2
 TCP‐DATA
2
 TCP‐ACK
3
 14 TELECOM Bretagne Improving Distributed TCP Caching
  15. 15. Simulation parameters Parameters Value MAC layer IEEE 802.11b RTS/CTS disabled PHY bitrate 1Mbps Propagation model FreeSpace Model (PathLoss = 3) Distance between wireless nodes 200 meters Routing protocol AODV Transferred data size 50kBytes TCP MSS 100 Bytes TCP advertised window 200 Bytes15 TELECOM Bretagne Improving Distributed TCP Caching
  16. 16. Consumed Energy & Transfer Duration• DTC with the new cachemanagement (DTC-CM) andDTC with smoothed RTO (DTC-SRTO) reduce better theconsumed energy than DTC• EDTC combines the twoschemes and gives the bestresults• EDTC reduces the transferduration and increases thethroughput of the TCPconnection.16 TELECOM Bretagne Improving Distributed TCP Caching
  17. 17. DTC vs EDTC with different BER •  EDTC is more energy efficient than DTC and TCP in low-lossy networks and high-lossy networks.17 TELECOM Bretagne Improving Distributed TCP Caching
  18. 18. TCP Congestion Windows • The increase of the TCP window does not increase significantly the TCP throughput, • The use of short TCP window reduces the congestion and the interference between TCP-ACK and TCP-DATA messages,18 TELECOM Bretagne Improving Distributed TCP Caching
  19. 19. Maximum Link Layer Attempts • The increase of the maximum link layer attempt reduces the end-to-end TCP retransmissions,19 TELECOM Bretagne Improving Distributed TCP Caching
  20. 20. Conclusion and Perspectives   EDTC is more energy-efficient than DTC and TCP,   EDTC increases the chance of TCP to be the reliable transport protocol for WSNs,   Compress the TCP header,   Reduce the number of TCP acknowledgements,   Adapt the TCP maximum segment size depending on the loss rate.20 TELECOM Bretagne Improving Distributed TCP Caching

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