My sincere thanks to all the staff members of the Department of Computer Science and Engineering, especially Bhrigu for helping me many times. This requires a seamless transfer of the mobile node to the best available network without interrupting the current data session.
Motivation of the Research Work
Although the tight coupling approach reduces the handover delay, the maximum achievable data rate is still limited to the data rate of the UMTS network. Most existing vertical handover mechanisms between UMTS and WiFi are based on mobile IP-based architectures [11,21,22].
Contribution of the Thesis
ISN-TCP requires freezing to maintain connection consistency during handover, but this introduces extra delay into the network. We are further working on this by extending ISN-TCP and introducing an improved TCP variant ISN-TCP-PLUS.
Organization of the Thesis
The performance of the proposed scheme was analyzed using simulation results through different QoS parameters. Vertical handover is an essential component of the fourth generation (4G) heterogeneous wireless network architecture.
UMTS and WiFi Network Architecture
Within the UMTS network, the GGSN is connected to the SGSN and the Home Location Register (HLR). Since the GGSN acts as a gateway for the UMTS network and external PDN, the mobility management functions for handover between two different networks should be integrated in the GGSN.
Multiprotocol Label Switching and Multiprotocol BGP
Within an Autonomous System (AS), routers that can send and receive BGP messages are called BGP Speakers. When using I-BGP in an AS, all BGP speakers are connected to each other, forming a complete mesh.
Vertical Handover between WiFi and UMTS: A Brief Survey
In [31], the authors propose a Mobile IPv6-based handover scheme between UMTS and WLAN to reduce handover delay incorporated in Mobile IPv4-based vertical handover. In the proposed algorithm, the first authentication and an optimized gateway are used to reduce handover delay.
TCP over Vertical Handover Framework
Assuring QoS Over Vertical Hanover Framework
In [67], the authors propose a method for signal-to-noise ratio (SINR)-based vertical transfer schemes for QoS in heterogeneous wireless networks. IEEE 802.21 Media Independent Handover (MIH) [76, 77] provides a unified framework for vertical transfer between different wireless standards.
Summary
These goals can be achieved if the traffic is switched between the two networks at some point before it enters either network. One of the interfaces is used to connect to the UMTS network, while the other is used to connect to the IEEE 802.11 network.
Proposed UMTS-WiFi Integration
The Home MSF-LER is referred to as the MN's point of attachment to the ISN. On the GGSN-3G/MSF-LER, the IP address of the MN and the Mobility Label assigned to it are stored in the MSF database. Mobile Node Registration with AP/MSF-LER: In the IEEE 802.11 network, MN sends registration requests to the AP/MSF-LER.
The procedure for setting up an "alternate" PDP context is as follows: a) The MN sends a dummy ICMP Solicitation Registration message to the GGSN-3G/MSF-LER.
Simulations
-Database - MSF-DB was changed to associate a 'set of IP addresses' with each record. During handover from UMTS to IEEE 802.11 network, data packets experience more delay in the UMTS network. Before the handover, the MN is in the UMTS network and the packets experience higher End-To-End Delay.
As shown in the graph (Figure 3.12), when the MN moves from the IEEE 802.11 network to the UMTS network, the end-to-end delay increases.
Comparison with Existing Systems
It can be noted that the layer 2 transfer delay is similar and depends only on the physical data rate for both the mobile IP-based scheme and our proposed scheme. Again, the proposed scheme reduces the number of average packet losses in the three cases of UMTS to WLAN, WLAN to WLAN and UMTS to UMTS handovers. For transfers from WLAN to UMTS, the number of average packet loss is equal to the existing schemes.
It has been observed from the simulation traces that the update time of the mobility binding at ISN is not affected if the number of MN is increased.
Discussion
The simulation results have shown that during handover from UMTS to IEEE 802.11 network, the handover duration is equal to the time required to complete the mobility binding update (≈8ms). The AAA server is responsible for authenticating and authorizing MNs requesting the mobility services provided by the ISN. As the MN keeps the mobility token with itself, this leads to various security risks (e.g. Replay Attacks).
The proposed scheme assumes that the MN is a trusted device, but the security risks arising from the storage of the Mobility Label at the MN must be addressed.
Summary
Evaluation of end-to-end TCP performance for vertical transfer using intermediate switching network. The problems of the TCP become more serious during the vertical transfer between two different wireless technologies. The performance of the WP-TCP over ISN-based framework during handover has been reported and analyzed in Section 4.1.
The further improvement of the TCP variant for the UMTS to the WLAN vertical handover, called the ISN-TCP-PLUS, is discussed in section 4.3.
Performance Evaluation of TCP for ISN Based Frame- work
This chapter further extends the analysis for UMTS-WLAN handover using the ISN framework and proposes an improved version of TCP over ISN-TCP, namely ISN-TCP-PLUS. By filtering out duplicate ACKs (DACKs) and calculating the RTT of the new network on the fly, ISN-TCP-PLUS significantly improves TCP performance during handover. Section 4.2 discusses the design of ISN-TCP with a detailed performance evaluation analysis with simulation results for WLAN to UMTS handover and vice versa using an ISN-based framework.
After the handover, CWnd is dropped due to the large amount of duplicate packet transmissions.
WP-TCP
ISN-TCP: A Naive Improvement over Conventional TCP
Both the MN and the CN store the sequence number of the first packet (SeqF M N andSeqF CN) on the new interface. After this, the MN forwards packets with the sequence number SeqL M N to SeqF M N to the CN. Likewise, the CN forwards packets with the sequence number SeqL CN to SeqF CN to the MN.
In order for TCP to easily adapt to new connection characteristics, ISN-TCP estimates the RTT and available bandwidth.
ISN TCP
ISN-TCP-PLUS: Improved TCP for ISN based Han- dover Framework
The filtering period at the transceiver layer could reach a maximum of RTO in the UMTS network (RT OU M T S). During handover from a WLAN to a UMTS network, the problem is false RTOs. The MAC layer on the MN sends a handover notification to the handover layer on the MN about the impending handover.
The transfer layer at the MN, upon receipt of the transfer message, measures the RTT between the MN and the WLAN AP (RT TM N-AP), by sending an ICMP ECHO message to the current WLAN AP.
Simulation and Analysis
ISN-TCP-PLUS
ISN -TCP-PLU S
Summary
An umbrella-like topology is considered when IEEE 802.11 networks create coverage gaps below the reach of a UMTS network. Whenever a mobile node comes under the coverage of an IEEE 802.11 WLAN network, it is preferable to switch the connection from the UMTS network to the IEEE 802.11 WLAN network. Therefore, if the QoS of the current WLAN network to which the mobile node is connected fails, it is always preferable to handover to another IEEE 802.11 WLAN, if available, than to the UMTS network.
This is because a sudden performance degradation can be observed if the mobile node is handed over to the UMTS network from an IEEE 802.11 WLAN network.
QoS based handover and Bandwidth Reservation
The mobile node sends the available network information to the MSF-LER of the current attachment point. The mobile node also sends the measured NQV value of the current network to the MSF-LER of its current attachment point. In this way, the GGSN/MSF-LER and the AP/MSF-LERs can be made aware of the current network conditions.
Let BW(m) denote the total bandwidth capacity of the network under AP/MSF-LER m, BWused(m) denote the used bandwidth, and BWavail(m) denote available bandwidth of the network under AP/MSF-LER m.
Simulation Results
The figure shows that TCP connections quickly take over the variability in the network for the proposed scheme. For the RSSI-based handover scheme, the TCP connections cannot handle the variability in the network, and the TCP congestion window frequently drops. For the proposed QoS based handover scheme, throughput for high priority nodes is maintained as the number of low priority nodes in the network increases.
The small drop in throughput for the proposed scheme is due to high contention in the network as the total number of nodes increases.
Summary
This dissertation has presented three important and meaningful contributions towards seamless vertical handover between UMTS and IEEE 802.11 networks. We studied the seamless vertical handover problem and overall, our work provided a comprehensive foundation in terms of an architectural framework, set of algorithms, and a simulated system for validating the proposed framework.
Thesis Summary
The third contribution of this thesis moves into the concept of quality of service to ensure "always the best connectivity", which becomes an essential part of the network in question and also for the users. A QoS-based vertical handover scheme between UMTS and an IEEE 802.11 WLAN based on an ISN-based framework has been proposed. Bandwidth reservation per node is based on the economic subscription of mobile nodes from the service provider.
This is because sudden performance degradation can be observed if the mobile node is handed over to the UMTS network from WLAN network.
Future Works
In Proceedings of the 5th IFIP International Conference on Wireless and Optical Communication Networks, pages 1-5, 2008. In Proceedings of the 4th International Conference on Cognitive Radio and Advanced Spectrum Management, pages. Wireless Profiled TCP Performance over Integrated Wireless LANs and Cellular Networks.IEEE Transactions on Wireless Communications June 2007.
Dhananjay Kotwal, Maushumi Barooah, and Sukumar Nandi, "Seamless Handoff between IEEE 802.11 and GPRS Networks," in the report of the 6th International Conference on Distributed Computing & Internet Technology, February 2010 (LNCS).
