TCP Congestion Control with ACK-Pacing for Vertical Handover


IEICE TRANSACTIONS on Communications   Vol.E90-B   No.4   pp.885-893
Publication Date: 2007/04/01
Online ISSN: 1745-1345
DOI: 10.1093/ietcom/e90-b.4.885
Print ISSN: 0916-8516
Type of Manuscript: PAPER
Category: Network
vertical handover,  TCP,  congestion control,  ACK-pacing,  

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In this paper, we discuss TCP performance in a wireless overlay network where wireless LANs and cellular networks are integrated. In the overlay network, vertical handover, where a mobile node changes its access link during a session, is one of the most important technologies. When a vertical handover occurs, throughput performance of a TCP flow is degraded due to not only packet losses during the handover, but drastic change of its bandwidth-delay product. In this paper, we propose an ACK-pacing mechanism for TCP congestion control to improve the performance degradation. The proposed system is receiver-driven, so no modification is required to the mechanism of TCP sender. In the proposed system, a TCP receiver adjusts a transmission rate of ACKs according to the relationship between bandwidth-delay products before and after a handover. Since the ACK-clocking mechanism of TCP adjusts the transmission rate of TCP segments, the TCP receiver can seamlessly adjust its congestion window size to the new bandwidth-delay product. Computer simulation results show that the proposed system can improve the TCP performance during the vertical handover.