Byung Ho Rhee

Improving TCP Performance over WiMAX Networks Using Cross-Layer Design

With the rapid growth of wireless technologies, the task of providing efficient connectivity is still a challenge. Since almost wireless network poses many problems, including limited bandwidth, coping with bandwidth fluctuations, and lost or corrupted data, lots of studies have been done and many solutions proposed. The IEEE 802.16 WiMAX is a standard for the wireless broadband access networks and recognized as one of the strongest contenders. However, it also has some lossy wireless link problem.On the other hand, Transmission Control Protocol (TCP) is the most commonly used transport protocol on the Internet. But regular TCP is not suitable for wireless networks because packet losses will occur more often due to unreliable wireless links than due to congestion.In this paper, we study the performance when TCP is used on the wireless network and propose cross-layer design to improving TCP performance on wireless network, specifically, over the IEEE 802.16 WiMAX. The key feature in our proposal is that we use the feedback information about channel state to adaptively control packet size, packet amount, and retransmission decision between sender and receiver. And the Sender which send TCP packet adopts cross-layer architecture to improving TCP performance. The cross-layer design is a new paradigm to provide better performance gain. Preliminary simulations were provided and the result shows the performance enhancements of TCP connection over the WiMAX networks.

Seamless Connection for Mobile P2P and Conventional Wireless Network

Recently, with the expansion and advent of the wireless Internet such as WiFi, mobile WiMax, and mobile peer-to-peer (P2P) voice over IP (VoIP) communication through P2P overlay network in all-IP area has been deeply investigated as a research area. When the connected peer terminal leaves hot spot of all-IP area, it will be lost the communication session. In this paper, we propose seamless voice connection over P2P mobile VoIP and conventional wireless network. In this case, the concept of vertical handoff is not the handoff of IP layer but that of session layer to create new VoIP session in latency before the previous session ends. We have two kind of wireless communication network; one is all-IP and the other is CDMA cellular and assumes that the mobile node has the functionality to communicate with each other network. We certain the dynamically adjusted trigger method is better than the fixed trigger in the success of new call setup processing and the decrease of unnecessary signaling in cellular network. We think that this work is able to achieve seamless and low-cost communication between P2P VoIP and cellular network.

A New Approach Network Selection with MIH between WLAN and WMAN

The hybrid networks of WLAN and WMAN can provide high data rate and enhanced multimedia services, but there are many challenges to obtain handover decision based dynamic QoS information. IEEE 802.21 aims at providing a framework that defines Media Independent Handover (MIH) mechanism that supports seamless handover across hetero geneous networks. In this paper, we propose a new approach network selection algorithm using MIH between WLAN and WMAN. Our simulation results give the best network selection with QoS between WLAN and WMAN.

Performance Enhancement Technique for TCP over Mobile Ad Hoc Networks

Ad hoc networks are wireless networks of mobile nodes, self-organizing systems formed by co-operating nodes within communication range of each other that form temporary networks in which the topology rapidly changes result from the movement of mobile nodes. This frequent topology may lead to sudden packet losses and delays. So, the current implementation of TCP for the Internet is not efficient when used for mobile ad hoc networks. This is because TCP dose not show a satisfactory performance in mobile ad hoc networks due to a high BER (bit error rate) and node mobility. Base TCP-Vegas does not recognize the distinction between congestion and packet losses because of transmission errors, which are current in mobile ad hoc networks. In particular, when a route is re-established it requires to be set CWND in accordance with the new route characteristic. In this paper, we propose a method to improve the TCP performance over mobile ad hoc network using new additional new module to TCP-Vegas. With this module sender node distinguishes between congestion and transmission errors it effectively adjusts the TCPs CWND and transmission rate. Simulation results using OPNET show that the proposed scheme increase TCP throughput compared with those of general TCP

Congestion control algorithm of ANDSF priority in heterogeneous networks

In Heterogeneous networks applied ANDSF, UEs select the access network based on priority provided by ANDSF. The congestion network has the lower priority, need to recover the lower priority when congestion is over. In this paper, introduce the recovery method of the lower priority to the default priority based on time value. As a result, the network is able to provide a better QoS with UE, also expected to load balancing of networks.