Improved TCP Performance during the Upward Vertical Handover Using an IEEE 802.21 MIHF Framework
In Upward Vertical Handover(UVHO) from a fast WLAN link to a slow 3G cellular link, the TCP sender may encounter precocious timeout since the RTT of the 3G link is too large for the RTO(Retransmission Time Out) which is tuned to the small RTT of the WLAN. Although IEEE 802.21 MIHF framework provides the vertical handover procedure, it does not deliver RTT of the new link since this does not belong to static information to be delivered by IEEE 802.21 MIHF. Conventional TCP such as TCP Reno, even with IEEE 802.21 MIHF, may encounter timeout after UVHO, degrading TCP throughput considerably during UVHO. In this article, we propose a modified TCP scheme in which we estimate the RTT of the new link using timeout instant, the ACK traveling through the new link just after UVHO and the old RTT. We also estimate appropriate CWND size for the new link. Simulation results show that our proposed scheme improves TCP performance during the UVHO compared with previous schemes as well as TCP Reno.
KeywordsUpward Vertical Handover TCP Congestion Control Congestion Window IEEE 802.21 MIHF
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