The same behaviour was noticed when the handover was performed from AP-4 to AP-5 (i.e. from the slow path to the fast path). However, handover duration significantly decreased to about 1.04 seconds. The TCP disruption time takes around 2.66 seconds. TCP Packet Trace During Handover from AP-4 to AP-5 shows the TCP behaviour during a handover from AP-4 to AP-5. It can be seen that fewer timeouts and retransmissions have occurred in this experiment. The overall average handover duration and TCP disruption times are shown in Table 14-5. slow path).

The MN starts sending TCP traffic to the CN using AP-5 and moves towards AP-4. Figure 14-6 shows the time sequence number plot of the TCP connection including the handover time. We found that it takes around 4.9 seconds to handoff from AP-5 to AP-4. The TCP disruption time was found to be 10.5 seconds. As illustrated in the figure, the TCP goes through 4 consecutive timeouts and retransmissions. Because of TCP exponential backoff mechanism, TCP doubles the size of its timeout interval each consecutive timeouts. Following the handover, the TCP waits for the last timeout to elapse before starts sending data using the new care-of-address. This result demonstrate that the handover duration contribute approximately 40% of the TCP disruption time. The remaining time delay is due to TCP congestion control mechanism. The average handover duration and TCP disruption time are shown in Table 14-5.