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ATCP: TCP for Mobile Ad Hoc Networks

ATCP: TCP for Mobile Ad Hoc Networks. Speaker ：洪振捷 Adviser: ：吳和庭 教授. Outline. Introduction TCP in Mobile Ad Hoc Network ATCP Performance Conclusion. Introduction. Mobile Ad Hoc Network(MANET) - 由 多個 Mobile computing devices 所組成 ， 只要 Device 之間 的距離在彼此可通訊的範圍之內，則裝置與 裝置

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ATCP: TCP for Mobile Ad Hoc Networks

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  1. ATCP: TCP for Mobile Ad Hoc Networks Speaker：洪振捷 Adviser:：吳和庭 教授

  2. Outline • Introduction • TCP in Mobile Ad Hoc Network • ATCP • Performance • Conclusion

  3. Introduction • Mobile Ad Hoc Network(MANET) -由多個Mobile computing devices所組成，只要Device 之間的距離在彼此可通訊的範圍之內，則裝置與裝置 間可直接進行通訊，而不需要透過Access Point來傳輸 資料。

  4. TCP in MANET • TCP -在一般傳輸可靠的有線網路上，當發生buffer overflow 導致packet loss時，sender端可能會收到3個以上重 複的ACK，或者因為沒收到ACK，而發生retransmit timeout，TCP會以此作為網路發生壅塞的依據，並縮 減congestion window，降低傳送的速度。

  5. TCP in MANET (cont.) • High Bit Error Rate(High Bit Rate) -MANET是用無線電波來傳輸的，然而無線電波的傳輸 容易受到地形、環境影響，進而導致fading或者是 shadowing等干擾，使得封包在傳輸過程中受到損壞 ，稱之為 lossy channel。

  6. TCP in MANET (cont.) • Disconnection -Route recomputation： 在MANET裡，node是可以任意移動的，所以當route 裡的Intermediate node跑掉時，必須重新尋找一個 new route。

  7. TCP in MANET (cont.)

  8. TCP in MANET (cont.) • Disconnection -Network Partitions： 在MANET裡，node是可以任意移動的，所以網路拓 樸可能隨著時間改變而有所變化，在同一個partition內 的node，代表可以互相通訊；反之，如果處在不同 partition，則無法直接通訊。

  9. TCP in MANET (cont.)

  10. ATCP TCP layer ATCP layer IP layer • ATCP is called Ad Hoc TCP • ATCP是位於IPLayer和TCP Layer之間的Layer • Network State Information - ICMP “Destination Unreachable” messages - ECN (Explicit Congestion Notification) messages • 4 State - Normal, Disconnected, Loss and Congested state • Maintain TCP’s Congestion Control Behavior

  11. ATCP (cont.)

  12. ATCP (cont.) • Congested state - 假設ATCP一開始是在Normal state或者是Loss state，此時如果ATCP此時收到ECN message的話，ATCP會把state改成Congested state。

  13. ATCP (cont.) • Disconnected state -ATCP一旦收到ICMP “Destination Unreachable” messages，ATCP會進入Disconnected state，並讓TCP進入persist state。

  14. ATCP (cont.) • Loss state -當收到第三個重複的ACK時，不要馬上將第三個重複的ACK送給上層的TCP，或者當快要發生timeout的時候， ATCP進入Loss state ，並讓TCP進入persist state。

  15. Performance • 5台PCs，每一台都有兩張ethernet cards • 32-kb/s channel • 每一個實驗都有BER，都傳1MB的File • Hop-by-hop delay

  16. Performance (cont.) • Loss Case

  17. Performance (cont.) • Congestion Case

  18. Performance (cont.) • Partition Case

  19. Conclusion • ATCP的優點在於能根據High Bit Rate、Disconnection、 Network congestion 不同情況去做出適當的處理，而且沒 有更改原本congestion control的機制，在route發生變化的 時候，也能找出適合新的route的congestion window size。 • ATCP的缺點在於它都是等到發生route disconnected的 時候，才開始做route discovery的動作，這樣會浪費許多 時間。

  20. Reference • J. Liu, and S. Singh. ATCP: TCP for Mobile Ad Hoc Networks. In IEEE Journal on Selected Areas in Communications, vol. 19,pages 1300-1315, July 2001.

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