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Handover mechanisms in next generation heterogeneous wireless ...

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MULTI-INTERFACE MOBILE MODEL FOR MEDIA INDEPENDENT HANDOVER<br />

The experiment moves further to transport layers. The TCP sequence number of the non<br />

real time traffic be<strong>in</strong>g carried from the CN to the MH is used for performance<br />

evaluation. The experimental results for cross-layer trigger and non cross-layer trigger<br />

are illustrated <strong>in</strong> Figure 7.15 and Figure 7.16 respectively. For the MH with the crosslayer<br />

trigger, the <strong>in</strong>terruption of packet transmission dur<strong>in</strong>g the handover at the radio<br />

overlap area is not obvious due to the short handover delay (around 40ms). But, the<br />

TCP transmission gap <strong>in</strong> the handover at the non-radio-overlap area is noticeable<br />

because of lack of radio coverage (illustrated as handover <strong>in</strong> the non-overlap area <strong>in</strong><br />

Figure 7.15). The cross-layer trigger makes the TCP sequence curve fairly smooth. In<br />

contrast, the data transmission <strong>in</strong> non cross-layer trigger case has a longer break<strong>in</strong>g time,<br />

as demonstrated <strong>in</strong> Figure 7.16. The larger ADI can result <strong>in</strong> an excessive transmission<br />

recovery time. It is found that TCP retransmission mechanism has contributed to a TCP<br />

transmission break <strong>in</strong> handover. It is observed that the transmission break of 50s is<br />

<strong>in</strong>curred <strong>in</strong> radio overlap areas when ADI = 4s.<br />

Figure 7.15 TCP sequence number (with cross-layer trigger)<br />

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