Abstract
One major difference between 3G cellular networks and Wireless LANs is in how packet losses are dealt with. 3G cellular networks employ selective repeat ARQ (SR-ARQ) whichmay result in packet-reordering due to local retransmissions. Wireless LANs employ stop-and-wait ARQ which may drop some packets in case the buffer overflows. While much work has been performed for TCP throughput enhancement with vertical handover between wired networks and wireless networks, little attention is paid to the vertical handover between two different wireless networks. It is expected for majority of new mobile devices to be able to connect to both 3G cellular networks and wireless LANs by being equipped with multiple wireless interfaces. If this is the case, on-going TCP transmission may move between 3G cellular networks and wireless LANs. In this paper, we propose a scheme to improve TCP throughput with vertical handoff between 3G cellular networks and wireless LANs. For this we develop an algorithm which differentiates packet-reordering from packet losses and congestion losses from wireless losses. Simulation of our algorithm using ns-2 shows significant increase in throughput as large as 80% compared to TCP-SACK. The proposed scheme is able to respond to the change of loss pattern and then improve the TCP throughput during handover.
Highlights
Vertical handover [1] refers to the process of changing interfaces for a mobile node with multiple network interfaces to move from one network to another network
Previous researches on vertical handover have addressed the handling of the difference in bandwidth-delay products between two different types of networks (e.g., 3G cellular networks and WLANs) [2,3,4]
To obtain best TCP throughput over vertical handover, we need to accurately identify these three different causes of packet loss, congestion loss, wireless loss, and packetreordering
Summary
Vertical handover [1] refers to the process of changing interfaces for a mobile node with multiple network interfaces to move from one network to another network. We consider a new problem that an ongoing TCP flow on a mobile node may experience packet losses of different natures over vertical handover depending on link layer retransmission schemes involved. The proposed scheme significantly improves any of the algorithms mentioned above for handover from WLAN to 3G cellular packet network or vice versa. We try to solve the problem of TCP throughput degradation over vertical handover between 3G cellular packet networks and Wireless LANs, while the original LD [7] is developed for TCP improvement for wired/wireless paths. Our scheme significantly improves any of the algorithms mentioned above for handover from WLAN to 3G cellular packet network or vice versa.
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