Nowadays many different types of networks communicate among themselves to form heterogeneous wireless networks (HWN). Seamless vertical handover (VHO) between a Universal Mobile Telecommunications System (UMTS) and a Wireless Local Area Network (WLAN) is necessary to provide continuous internet access for mobile node (MN) as roaming across these networks is to be without interruption. To support the seamless VHO and smooth mobility in the HWN, a network layer protocol mobile IP (MIP) is exploited. MIP has several attendant issues such as hybrid routing, registration delay, data session disruption during VHO, and packet overhead. These issues occur when the data packets of the MIP are sent from a foreign agent (FA) to a home agent (HA) via a tunnel when a MN moves to a new network which will cause a triangle routing. In this paper, we propose a hybrid scheme of mobile stream control transmission protocol (mSCTP) with a bicasting mechanism or so-called Bi-mSCTP under the MIP to overcome the abovementioned triangle routing. When an MN is in the area of VHO, the proposed scheme relies on the generated mSCTP signals to allocate a new care-of-address (CoA) to the corresponding node (CN) dynamically before the link layer handover. At the same time, it inserts a bicasting flag inside the address configuration (ASCONF) data chunk to inform the CN to start the transmission over both WLAN and UMTS links. The system performances were analyzed by using the NS-2 simulation tool. The results showed that the hybrid scheme introduces approximately 1.02 and 2.64 s reduction in delay performance over both mSCTP and MIP schemes respectively. It also reduces the packet loss rate by more than 21.7 and 45% compared to mSCTP and MIP, respectively.
Key words: Seamless VHO, mSCTP, bicasting, mobile IP.
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