Title of the thesis:



[pic]

Figure 7.64 CWND – 10Mb – 10ms – DSDV – Tahoe – 80 KM/H

[pic]

Figure 7.65 CWND – 10Mb – 5ms – DSDV – Reno – 60 KM/H

[pic]

Figure 7.66 CWND – 10Mb – 5ms – DSDV – Reno – 80 KM/H

[pic]

Figure 7.67 CWND – 10Mb – 5ms – DSDV – Newreno – 60 KM/H

[pic]

Figure 7.68 CWND – 10Mb – 10ms – DSDV – Newreno – 80 KM/H

[pic]

Figure 7.69 CWND – 10Mb – 5ms – DSDV – Fack – 60 KM/H

[pic]

Figure 7.70 CWND – 10Mb – 10ms – DSDV – Fack – 80 KM/H

[pic]

Figure 7.71 CWND – 10Mb – 5ms – DSDV – Sack – 60 KM/H

[pic]

Figure 7.72 CWND – 10Mb – 10ms – DSDV – Sack – 80 KM/H

[pic]

Figure 7.73 CWND – 10Mb – 2ms – DSDV – Vegas – 60 KM/H

[pic]

Figure 7.74 CWND – 10Mb – 10ms – DSDV – Vegas – 80 KM/H

Let us now focus on Round Trip Time behavior of the communication at different speeds for the MN. To demonstrate the impact of the MN’s speed on the RTT, we are inserting below the RTT graphs at the following conditions:

- 10 Mb – 5 ms - 60 KM/H

- 10 Mb – 5 ms - 80 KM/H

For each flavor of the TCP (Figure 7.75 to Figure 7.86). The reader can confirm some improvements when the MN is moving at the speed of 60 KM/H because the RTT becomes more stable.

[pic]

Figure 7.75 RTT – 10Mb – 5ms – DSDV – Tahoe – 60 KM/H

[pic]

Figure 7.76 RTT – 10Mb – 5ms – DSDV – Tahoe – 80 KM/H

[pic]

Figure 7.77 RTT – 10Mb – 5ms – DSDV – Reno – 60 KM/H

[pic]

Figure 7.78 RTT – 10Mb – 5ms – DSDV – Reno – 80 KM/H

[pic]

Figure 7.79 RTT – 10Mb – 5ms – DSDV – Newreno – 60 KM/H

[pic]

Figure 7.80 RTT – 10Mb – 5ms – DSDV – Newreno – 80 KM/H

[pic]

Figure 7.81 RTT – 10Mb – 5ms – DSDV – Fack – 60 KM/H

[pic]

Figure 7.82 RTT – 10Mb – 5ms – DSDV – Fack – 80 KM/H

[pic]

Figure 7.83 RTT – 10Mb – 5ms – DSDV – Sack – 60 KM/H

[pic]

Figure 7.84 RTT – 10Mb – 5ms – DSDV – Sack – 80 KM/H

[pic]

Figure 7.85 RTT – 10Mb – 5ms – DSDV – Vegas – 60 KM/H

[pic]

Figure 7.86 RTT – 10Mb – 5ms – DSDV – Vegas – 80 KM/H

CHAPTER 8

CONCLUSION AND FUTURE WORK

8.1 Conclusion

Wireless networks present a challenge for an efficient data transport. Researchers have been and are still working in order to find a way to improve the wireless network at the transport level of the Internet stack. Proposals have been made, but each one of them presents some limitations:

- Snoop performs badly when long or frequent disconnections are common.

- Indirect TCP (I-TCP) violates TCP semantics. The sender can receive an ACK for a packet even before it gets to the receiver. What if it gets lost after that or the base station crashes? Moreover, I-TCP does not handle handoff.

- Explicit Congestion Notification (ECN) and Explicit Lost Notification (ELN) sound efficient, but are difficult to implement.

- Fast retransmit accommodates only losses due to the handoff and not those on wireless link.

- New Transport Control Protocols for the wireless (Wireless TCP, Wave and Wait protocol, TCP-Probing) have not been implemented yet.

Mobility changes important assumptions on which the wired network operates, suffering from delays and losses that are not related to congestion. Reliable transport protocols that will be able to differentiate motion-related packet losses from congestion-related packet-losses do not exist yet. The situation suggested an in depth study of the behavior of all the transport control protocols available on the network simulator NS-2 in order to understand how they work on the wireless network using a mobile host.

No such approach has been taken so far. We performed our simulation on a topology where a correspondent fixed host is communicating with a mobile host.

TCP Tahoe, Reno, Newreno, Vegas, Fack and Sack have been involved, using different bandwidth values for the communication (1 Mb, 5.5 Mb and 10 Mb). Diverse values have been considered to simulate the congestion level on the link layer (2 ms, 5 ms and 10 ms). We also considered many speeds for the mobile node, but only three were kept for our analysis in this thesis (40 KM/H, 60 KM/H and 80 KM/H). Surprisingly, the results were unpredictable most of the time. This leads us to really understand that there is a deep difference between the wireless network and the wired network as far as TCP is concerned.

Researchers cannot presume that the more efficient a TCP flavor is on the wired network, the least worst it will be on the wireless network. Moreover, we found that it is not always true contrary to scientists assumptions, that the less congested the connection, the more packets are received by the mobile node from a fixed correspondent host. Fortunately, a proposition can emerge from our research in order to maximize a throughput of a communication on a wireless link with a mobile host. It appears that, from now until the time a good TCP is found for a wireless network using a mobile node, three TCP flavors can be used: Tahoe, Fack and Sack. Reno, Newreno and Vegas should not be selected. When the mobile node decides to perform such communication, its speed should be set and maintained at 60 KM/H. If the mobile host is moving during the network communication either at 40 KM/H or at 80 KM/H, it will receive few packets from its correspondent, and even be disconnected. In a zone where the line is too congested, TCP Tahoe and Fack are more advisable. We hope a publication of a paper on the results of this thesis will prompt another approach in the solution search.

8.2 Future work

In this thesis, we have performed our simulation using one fixed host communicating with one mobile host. In order to confirm the results of this thesis, the future work could be to perform the same tests using a mobile host communicating with another mobile host.

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