An Architectural Framework for Seamless Hand-off between UMTS and WLAN Network

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In recent years, Cellular wireless technologies like GPRS, UMTS, CDMA and Wireless Local Area Network (WLAN) technologies like IEEE 802.11 have seen a quantum leap in their growth. Cellular technologies can provide data services over a wide area, but with lower data rates. WLAN technologies offer higher data rates, but over smaller areas, popularly known as Spots The demand for an ubiquitous data service can be fulfilled, if it is possible for the end-user to seamlessly roam between these heterogeneous technologies. In this thesis, a novel architectural framework is proposed consisting of an intra-ISP network called Switching Network which is fused between UMTS and WLAN networks as well as data (Internet) services for providing seamless mobility without affecting user activities. The ISN uses MPLS and Multiprotocol-BGP to switch the data traffic between UMTS to IEEE 802.11 networks, as per the movements of the user. The ISN is integrated with the UMTS network at the GGSN-3G and at the Access Point for IEEE 802.11 network respectively. The Mobile Node considered, is a high end device (e.g. PDA or Smart Phone) which is equipped with two interfaces, one for UMTS and the other for WiFi and can use both the interfaces simultaneously. The simulation result shows the improved performance of the ISN based framework over existing schemes. Most of the traffic in today networks use the Transmission Control Protocol (TCP) as the transport layer protocol for reliable end-to-end packet delivery. However, TCP considers packet loss to be the result of network congestion which makes it unsuitable for mobile wireless communication, where sporadic and temporary packet losses are usually due to fading, shadowing, hand-off and other radio effects. During the vertical handoff between different wireless technologies, the problem of end-to-end connection and reliability management for TCP becomes more severe. This thesis also evaluates the performance of TCP over the proposed ISN based framework. The improved TCP scheme uses a cross layer interaction between the network and the transport layer to estimate TCP retransmit timeout and congestion window during handover. Simulation results establishes effectiveness of the proposed scheme. Ensuring Quality of Service(QoS) for the mobile users during vertical handover between IEEE 802.11 and UMTS is another key requirement for seamless mobility and transfer of existing connections from one network to another. The QoS assurance criteria for existing connections can be affected by fluctuations of data rates when a user moves from the high speed WLAN network to the low speed UMTS network, even in the presence of another WLAN network in its vicinity. This can happen if the alternate WLAN network is highly loaded. Therefore handover from a high speed network to a low speed network should be avoided, whenever possible. The final contribution of this thesis proposes a QoS based handover procedure that prioritizes the existing connection over the new connections, so that rate fluctuations due to handover can be avoided if there exist another WLAN network in the range of the mobile user. Whenever the possibility of handover is detected, a pre-handover bandwidth reservation technique is used to reserve bandwidth at the alternate WLAN networks to avoid QoS degradation. The proposed scheme is implemented in Qualnet network simulator and...
Supervisor: Sukumar Nandi