It is widely understood that most system downtime is acounted for by programming errors and administration time. However, a growing body of work has indicated an increasing cause of downtime may stem from transient errors in computer system hardware due to external factors, such as cosmic rays. This work indicates that moving to denser semiconductor technologies at lower voltages has the potential to increase these transient errors. In this paper, we investigate the susceptibility of commodity operating systems and applications on commodity PC processors to these soft-errors and we introduce ideas regarding the improved recovery from these transient errors in software. Our results indicate that, for the Linux kernel and a Java virtual machine running sample workloads, many errors are not activated, mostly due to overwriting. In addition, given current and upcoming microprocessor support, our results indicate that those errors activated, which would normally lead to system reboot, need not be fatal to the system if software knowledge is used for simple software recovery. Together, they indicate the benefits of simple memory soft error recovery handling in commodity processors and software.

Mobile IPv6 provides comprehensive mobility management for the IPv6 protocol. Yet, it has been known for some time that the default mobile IPv6 protocol for handover between subnets can result in packet drops, which cause a user-perceptible deterioration in a real time traffic. Recent work has defined several new algorithms for Mobile IPv6 handover. These algorithms consist of two components: preconfiguring the care of address when it is known, and establishing a source route-based tunnel between the old access router and the new so that the mobile node can continue to receive its traffic on the new link under its old care of address. In this paper, we present measurements of the fast Mobile IPv6 (FMIPv6) handover algorithms on a handover emulator. While the algorithms can reduce the number of packet drops, some amount of buffering helps smooth handover. In addition, algorithms differ in their ability to reduce handover packet drops, depending on the wireless link characteristics.

The main problems with using existing firewall approaches in wireless and mobile environments are these methods cannot prevent internal attacks and at the same time preserve wireless bandwidth, have little or no packet filtering capability for mobile users, and inconvenient for service providers and end users to change firewall policies dynamically. We propose mobile firewall architecture to solve these problems. The paper presents the design and implementation of the mobile firewall, and shows the packet-filtering performance results and the maintenance cost in the mobile firewall.

We investigate fast IP handoffs in wireless LAN networks. As a simple mobile-controlled approach, we introduce Mobile Initiated Tunneling Handoff protocol for IPv4 (MITHv4). Our experimental results show, that MITHv4 can achieve optimized low latency and low loss IP handoffs in wireless LAN networks. Furthermore, MITHv4 significantly reduces the link layer trigger requirements and substantial access network support to synchronize link layer and IP layer handoffs that Fast Mobile IPv4 (FMIPv4) protocols heavily rely on. These benefits of MITHv4 are crucial for wireless LAN networks where the required link layer triggers for FMIPv4 are-not feasible due to limited access network control.

Mobile IP is focused on providing transparent connectivity to mobile nodes in an IP based network environment. While transparent mobility support is essential for compatibility with applications that are geared towards fixed network environment, it is a handicap for applications that can potentially benefit from mobility awareness. In this paper, we present Mobile IP API which is an interface between the applications and the mobility management module at mobile terminals and their correspondent nodes. Our main focus is basic Mobile IP API which primarily enables reading of mobility information for applications on mobile nodes and correspondent nodes. We present usage scenarios, design, and implementation of the API. We are also currently pursuing standardization of Mobile IP API through the IETF.

It is widely understood that most downtime is accounted for by programming errors and administration time. However, recent work has indicated an increasing cause of downtime may stem from transient hardware errors caused by external factors, such as cosmic rays. Moving to denser semiconductor technol- ogies at lower voltages will cause an increase in transient errors. We investigate the trends in transient errors and the susceptibility of operating systems and applications to them, and we introduce ideas regarding software transient error recoverability. We believe that if transient errors become a prominent prob- lem, that it will be possible to improve commodity system availability with simple software recovery. Results indicate that in the Linux kernel and a Java virtual machine few errors need to be fatal. We also propose two recovery examples which we believe indicate that it is possible to increase error detec- tion and recovery without the cost of a fail-over cluster.

It is a common belief that most of computer system failures nowadays stem from programming errors. Computer systems are becoming more complex and harder to maintain and administer, making software errors an even more common case, while contemporary computer architectures are optimized for price and performance and not for availability. In this paper, we raise a case for an increasing relevance of memory hardware soft-errors. In particular with the introduction of 64-bit processors, memory scaling is significantly increased, resulting in higher probability for memory errors. At the same time, due to the ubiquitous use of computers, such as at higher altitudes, environmental conditions impact errors (terrestrial cosmic rays). Finally, in shared memory systems, the failure of one node's memory can take the whole machine down. Current commodity systems do not tolerate memory errors, neither commodity hardware (processors, memories, interconnects) nor software (operating systems, applications, application environments). At the same time, users expect increased reliability. We present the problems of such errors and some solutions for memory error recovery at the processor, operating system and programming model level.