Network Layer Mobility: An Architecture and Survey

In this article we explore various network layer concepts that play a crucial role in the design of mobile networking systems. We show that mobility is essentially an address translation problem and is best resolved at the network layer. We describe services that must be supported at the network layer to carry out the task of address translation. Using these service primitives as building blocks, we describe a network-layer architecture which enables smooth integration of mobile end systems within the existing Internet. A summary of some of the key Mobile IP proposals is presented, and it is shown that each proposal can be viewed as a special case of the architecture outlined in this article

Investigations on the control of cell behaviour and the cell cycle

Little work has been done previously on cells grown as sail-sheets. This thesis describes the morphology, behaviour and movement of chick heart fibroblasts (CHFs) in sail-sheets and the effects of mechanical tension on actin content and the cell cycle of these cells. Abercrombie et ad. (1970 a) quantified the measurements on the features of movement of CHFs on glass coverslips (or, conventional cultures). Since the sail-sheet cultures appeared to resemble more closely the in vivo situation than the conventional cultures, it seemed appropriate that the features of cell movement in sail-sheets be studied and compared with those in conventional cultures. The work presented in this thesis suggests that CHFs in sail-sheets do exhibit such features as described for conventional cultures (Abercrombie et al., 1970 a) but at a relatively lower speed. Mechanical tension occurs within and between cells during embryogenesis, wound healing and in the repetitive contractile processes performed by various muscles of the body. Curtis and Seehar (1978) found that short-term tensing of sail-sheets with a low frequency oscillator shortened the duration of the cell cycle in CHFs. This thesis investigates whether tensing of sail-sheets for longer durations and at much lower frequencies produces any different effects than those found by Curtis and Seehar (1978). The work from these experiments suggested that on the whole, tension causes a reduction in the duration of the cell cycle. The effects of tension in a rectangular cell sheet differ from corners, edges and centres perhaps because of local stress concentration. The hypothesis that the effect of tension on the cell cycle may be due to its effect on the microfilaments was investigated. Results were inconclusive

On-line Banking Systems: Are they sustainable?

Although the trend for on-line banking has increased in recent years, the customers have not shown enthusiastic participation in the past and in present. Since the sustainability of a bank supporting on-line-banking service depends on what capacity it can attract new customers, retain already existing customers and how well can it extend its services to the current and future customer base. This investigation is focused on examining if there is any significant difference among the factors namely the transactional security, information design, navigational design, visual design, web site trust, web site satisfaction and e-loyalty over sustainability of on-line banking for different banks in USA and in India. An already available questionnaire with 23 questions classified under seven different factors mentioned above was circulated among 91 and 93 participants from USA and India who had a good experience on on-line banking. The results of the survey were analyzed using MANOVA and ANOVA. Results from the survey indicated that transaction security in on-line banking system was a concern among on-line bankers in India. But none of the factors were significant for on-line bankers in USA

Writing an Efficient Device Driver for a Multimedia Teleconferencing System

Modern high speed networks, such as ATM, can provide the bandwidth and the QoS guarantees to demanding real-time multimedia applications. However, overall performance of a networked multimedia application will greatly depend on the in-host data movement. Analyzing the characteristics and requirements of those applications, we came to several conclusions about the operation of the multimedia devices' drivers. We applied these conclusions in the design and implementation of a device driver for a multimedia teleconferencing system, based on IBM RS/6000 servers, running the AIX 3.2 operating system. Tracing the complete in-host data path, we found that though our device driver minimized the movement of data between the teleconferencing card and user main memory, the UDP/IP stack proved to be a cause of delay in the movement of data between user main memory and the network interface. (Also cross-referenced as UMIACS-TR-96-18

Parallel and Distributed Simulation of Discrete Event Systems

The achievements attained in accelerating the simulation of the dynamics of complex discrete event systems using parallel or distributed multiprocessing environments are comprehensively presented. While parallel discrete event simulation (DES) governs the evolution of the system over simulated time in an iterative SIMD way, distributed DES tries to spatially decompose the event structure underlying the system, and executes event occurrences in spatial subregions by logical processes (LPs) usually assigned to different (physical) processing elements. Synchronization protocols are necessary in this approach to avoid timing inconsistencies and to guarantee the preservation of event causalities across LPs. Included in the survey are discussions on the sources and levels of parallelism, synchronous vs. asynchronous simulation and principles of LP simulation. In the context of conservative LP simulation (Chandy/Misra/Bryant) deadlock avoidance and deadlock detection/recovery strategies, Conservative Time Windows and the Carrier Nullmessage protocol are presented. Related to optimistic LP simulation (Time Warp), Optimistic Time Windows, memory management, GVT computation, probabilistic optimism control and adaptive schemes are investigated. (Also cross-referenced as UMIACS-TR-94-100

Multiprocessor Priority Ceiling Based Protocols

We study resource synchronization in multiprocessor hard real-time systems. Specifically, we propose a multiprocessor resource control protocol which allows a job to simultaneously lock multiple global resources, removing a restriction from previous protocols. Allowing nested critical sections may permit a finer granularity of synchronization, increasing parallelism and throughput. All the protocols discussed belong to the class of priority inheritance protocols and rely in some fashion on priority ceilings for global semaphores. We consider both static and dynamic priorities, building upon the multiprocessor priority ceiling protocol (MPCP) proposed by Rajkumar et al. and the dynamic priority ceiling protocol (DPCP) proposed by Chen and Lin. The extended protocols prevent deadlock and transitive blocking. We derive bounds for worse case blocking time, and describe sufficient conditions to guarantee that m sets of periodic tasks can be scheduled on an rn multiprocessor system. Performance comparisons of these protocols with MPCP shows that the proposed protocols increase schedulability. (Also cross-referenced as UMIACS-TR-94-42

Measuring NFS Performance in Wireless Networks

Technological trends suggest that soon communication networks will consist of a high speed wired backbone with numerous wireless Local Area Networks. Mobile computing and wireless subnetworks are increasingly in demand. Mobile routing solutions provide wireless LANs with seamless connectivity to backbone wired systems. However, these solutions do not provide acceptable performance. Wireless networks have distinct transmission characteristics which present challenges to achieving efficient performance. Performance over wireless links is limited by high error rates, mobility, and low bandwidth. We have studied the performance of TCP and NFS over a wireless network. The prevalence of these protocols means that mobile hosts will frequently use them when communicating with stationary hosts. Measurements have been collected to determine the response of these protocols in the presence of various error patterns. These measurements show that NFS and TCP performance suffer extreme degradation due to these wireless link characteristics. Unexpectedly, NFS performance is not better than an TCP FTP file transfer. NFS performance over wireless links is limited by large packet sizes, long retransmission timeouts, and slow response to losses. Our goal is to understand the effects of wireless communication on these protocols and improve performance without requiring changes to the current network Infrastructure. (Also cross-referenced as UMIACS-TR-95-125

Network Layer Mobility: an Architecture and Survey

In this paper we explore various network layer concepts that pertain to the design of mobile networking systems. We show that mobility is essentially an {\em address translation} problem and is best resolved at the network layer. We have identified the fundamental services that must be supported at the network layer to carry out the task of address translation. Using these service primitives as building blocks, we propose a network layer architecture which enables smooth integration of mobile end systems within the existing Internet. The architecture is modularized into well-defined logical components. In this paper our objective is not to propose {\em a specific scheme} for supporting mobility, rather it is to highlight and analyze the essential aspects of supporting mobile end-systems, as well as to better understand the trade-off between various design alternatives. (Also cross-referenced as UMIACS-TR-95-117

Carry-Over Round Robin: A Simple Cell Scheduling Mechaniasm for ATM Networks

We propose a simple cell scheduling mechanism for ATM networks. The proposed mechanism, named Carry-Over Round Robin (CORR), is an extension of weighted round robin scheduling. We show that albeit its simplicity, CORR achieves tight bounds on end-to-end delay and near perfect fairness. Using a variety of video traffic traces we show that CORR often outperforms some of the more complex scheduling disciplines such as Packet-by-Packet Generalized Processor Sharing (PGPS). (Also cross-referenced as UMIACS-TR-96-45