Patrick P. Lam

Business-to-Consumer Mobile Agent-Based Internet Commerce System (MAGICS)

We present MAGICS, a mobile agent-based system for supporting business-to-consumer electronic commerce (e-commerce) or mobile commerce (m-commerce) applications. To use the system, consumers first provide their buying requirements to a proxy/agent server through a Web browser or a wireless application protocol (WAP) terminal. Having obtained the requirements, mobile agents are generated to carry out tasks for the consumers including getting offers from merchants, evaluating offers, and even completing purchases. In the case of mobile commerce, consumers can generate a mobile agent to conduct a search and evaluation in the digital marketspace before making a purchase in the physical marketplace. To make it possible to choose an offer that best satisfies the consumers requirement(s), we present a mathematical model for evaluating multiple decision factors. To test the basic functions of the mobile agent-based Internet commerce system (MAGICS), we have built a prototype system. To minimize the average cost of a product (including the cost of sending agents), we have also developed an analytical model that can determine how many agents should be sent to compare prices. Four different price distributions and some real price information are analyzed based on the model. The analysis provides valuable insights into the design of mobile agent-based shopping applications for m-commerce, in particular, and for e-commerce, in general.

Nested Network Mobility on the Multihop Cellular Network

The multihop cellular network architecture has been actively studied due to its capability to significantly increase cellular system capacity and coverage, and at the same time greatly reduce the transmission range of mobile nodes. The majority of the literature on MCN, however, is based on discussions from the physical or link layer point of view. In this article we look at the logical MCN architecture from the IP layer aspect. We believe that this aspect is critical to general deployment of Internet applications on the MCN because IP is the dominant supporting protocol for such applications. We introduce a new architecture based on the integration of nested network mobility (nested NEMO), which is a pure IP layer architecture, and MCN. We name the resulting architecture nested NEMO on MCN. We illustrate how nested NEMO on MCN operates and how it realizes the advantages provided by MCN on the IP layer. We also unveil a potential problem specific to the nested NEMO on MCN architecture: recursive IP fragmentation. A simple technique to overcome this problem is proposed.

UDP-Liter: an improved UDP protocol for real-time multimedia applications over wireless links

For wireless real-time multimedia applications, the excessive packet loss rate suffered at the receiver, especially when the packets are transported on UDP, is a major issue to resolve. The previously proposed UDP-Lite project was designed to replace traditional UDP, so that erroneous UDP payloads could be passed up to the application layer instead of being discarded. The main argument of UDP-Lite is that many real-time multimedia applications actually prefer damaged packets over lost ones because of their error resilience capabilities. The major drawback of UDP-Lite is the backward incompatibility against traditional UDP stacks in numerous UDP devices. In addition, applications have no choice but to accept UDP-Lite packets as normal ones. This paper introduces another approach, UDP-Liter, which makes use of the concept of UDP-Lite, and yet maintains 100% backward compatibility. Better yet, UDP-Liter will give applications the flexibility to handle normal packets and corrupted packets differently.

Harnessing the High Bandwidth of Multiradio Multichannel 802.11n Mesh Networks

There has been an increasing interest in deploying wireless mesh networks (WMNs) for communication and video surveillance purposes thanks to its low cost and ease of deployment. It is well known that a major drawback of WMN is multihop bandwidth degradation, which is primarily caused by contention and radio interference. The use of mesh nodes with multiple radios and channels has been regarded as a straightforward solution to the problem in the research community. However, we demonstrate in this paper through real-world experiments that such an approach cannot resolve the multihop TCP throughput degradation problem in IEEE 802.11n mesh networks. With extensive experimentation, we verify that the degradation is principally caused by the increase in TCP Round-Trip Time (RTT) when the number of hops increases. TCP throughput is fundamentally limited inversely by the RTT. We find that the multihop TCP throughput (up to five hops) when using 802.11n is no better than when using 802.11a, despite the much higher data rate 802.11n. We attempt to use multiple parallel TCP connections as a remedy to the problem, and it turns out that the wireless bandwidth can be fully utilized with a sufficient number of parallel streams. In general, our results give a key message that TCP tuning (e.g., setting the correct TCP buffers and use of parallel streams) is of paramount importance in high-bandwidth multihop wireless mesh networks that employ the latest wireless standards. These tuning techniques have to be implemented into commercial products to fully leverage the ever advancing wireless technologies to support the growing demand of multihop communications in wireless mesh networks.

Cellular universal IP for nested network mobility

In recent years, network mobility (NEMO) has been studied extensively due to its potential applications in military and public transportation. NEMO basic support protocol (NBSP), the current de facto NEMO standard based on mobile IPv6, can be readily deployed using the existing mobile IPv6 infrastructure. However, NBSPs root in mobile IPv6, such as the need of care-of address (CoA) and tunneling, results in substantial performance overhead, generally known as route sub-optimality, in nested NEMO environments. This paper tackles this problem by proposing a scheme based on cellular universal IP (CUIP) to eliminate the need for CoA and tunneling in supporting nested network mobility. Using quantitative analysis, we show that the proposed scheme outperforms the existing nested NEMO schemes by multiple folds in terms of bandwidth overhead. We also show how IP fragmentation negatively impacts route optimality, and that the proposed scheme is inherently superior to the existing schemes in this regard. More importantly, while the scalability of the existing schemes generally deteriorates with the network size, the complexity of our proposed scheme is independent of the network size and thus is far more scalable. Our results show that the proposed scheme is particularly suitable for nested NEMO networks formed by mobile routers with random and ad hoc movement patterns.

Cellular universal IP: a low delay mobility scheme based on universal IP addressing

The concept of care-of-address (CoA) is a major cause of excessive handoff delay in Mobile IPv6 for real time multimedia traffic. Many schemes eliminate the use of CoA at the micro-mobility scale, but leave the macro-mobility unsolved. This paper proposes a novel alternative IPv6 mobility scheme based on universal addressing - Cellular Universal IP (CUIP) - for real-time traffic in wireless access networks. In CUIP, a mobile node is addressed with a universal IP address regardless of its location, making CoA and tunneling unnecessary in micromobility and even macromobility handoffs. CUIP manages roaming and handoff differently - whereas explicit signaling is used for roaming, a handoff-on-the-fly route-update scheme is used during handoff to embed signaling information into the outgoing data packets to minimize handoff delay. We prove analytically that, on average, fewer than three routers need to be updated per handoff. As a result, CUIP incurs an expected network layer handoff delay on the order of milliseconds only. In addition, the support of QoS is possible. A simple security scheme is also proposed to enable mutual authentication at the network layer.

MeshFS: A Distributed File System for Cloud-based Wireless Mesh Network ☆

Abstract Wireless mesh networks have attracted considerable interest in recent years in both the academic and industrial communities. As wireless mesh routers can be interconnected through wireless links, wireless mesh networks provide greater flexibility and better cost-effectiveness. In particular, due to their ease of installation and maintenance, they can be used in different environments, especially where cable installation is difficult. Apart from providing routing service, wireless mesh networks can also be employed to provide other value-added services. Inspired by cloud computing and other distributed file systems, this paper presents the design and implementation of MeshFS, a distributed file system specifically for wireless mesh networks. A key technical challenge is to develop a lightweight software system that can be implemented over memory-limited wireless mesh network environments. With the aim of providing a lightweight distributed file system, allowing limited resources to be utilized more effectively, MeshFS integrates scattered storage resources from wireless mesh routers to provide a mountable file system interface to Unix/Linux file system with fault-tolerant capabilities and cloud computing-like storage functions.

Real-life experiments of Multi-Radio Multi-Channel wireless mesh networks: 802.11n is not any better than 802.11a!

Wireless Mesh Network (WMN) has become a popular access network architecture in the community due to its low cost and readily deployable nature. However, it is well known that multi-hop transmission in WMN is vulnerable to bandwidth degradation, primarily due to contention and radio interference. A straightforward solution to this problem is to use mesh nodes with multiple radios and channels. In this paper, we demonstrate through real-world experiments that the use of multiple radios and channels solely cannot solve the multi-hop TCP throughput degradation problem in IEEE 802.11n mesh networks. We verify that it is because the round trip time (RTT) for wireless communication path increases significantly with the number of hops, and the TCP throughput is limited inversely by the RTT. Due to this TCP throughput limitation, we also found interestingly that the multi-hop TCP throughput (up to five hops) of 802.11a is comparable to that of 802.11n. Our results give a key message that a new generation of TCP needs to be proposed and adopted so as to support the ever advancing wireless technologies and growing demand of multi-hop communications in wireless mesh networks.