Hannu Kari

Proposed operation of GSM packet radio networks

The standardization of the GSM General Packet Radio Service (GPRS) is progressing in European Telecommunications Standards Institute (ETSI). This paper describes the proposed architecture, signaling and protocols for the GPRS network. Also, the network layer interworking, mobility management, service establishment/management, as well as link layer issues are discussed here.

Ad Hoc Routing Protocol Performance in a Realistic Environment

Multiple wireless devices jointly create and maintain ad hoc networks; their employment is favored to happen in a variety of environments with distinct topological characteristics. Diversified environmental conditions are expected to vary network performance. In fact, obstacles, buildings and/or mountains may act as either barriers, or source of noise for the radio signals. Nevertheless, most of the previous performance evaluation studies based on simulation, neglected this consideration; they used simulation models that were too simplistic, and too narrow (i.e. idealistic) in their scopes. With this paper we propose a new, complete and realistic Urban Mobility Model (UMM). It models realistically users motion, and radio signals propagation in a citylike scenario. Our aim is to study the effects of realistic network simulation on routing performance. The results prove that a realistic scenario with roads and buildings has a significant impact on routing.

A security architecture for wireless ad hoc networks

An ad hoc network is a collection of nodes that do not need to rely on a predefined infrastructure to keep the network connected. The current trend in military ad hoc networking is to deploy technologies based on open standards that are widely used in the civilian environment. However, the military environment places heavier demands on networking and security solutions than the civilian environment. In this paper we present a model for a security architecture for wireless ad hoc networks that operate in a hostile environment. We especially focus on handling incomplete trust management to protect the network from attacks stemming from within the network.

Detection of defective media in disks

The authors present new improved methods for detecting latent sector faults in a disk subsystem as caused by media deterioration of the disk magnetic storage material. Usually, sectors in a disk are accessed using uneven patterns causing some of the sectors to be accessed only seldom. In case of media deterioration on the rarely accessed sectors, a latent disk fault may remain undetected for a long time. To detect latent sector faults, a disk is scanned through periodically. An adaptive algorithm is proposed to utilize the idle time for the disk for scanning commonly used disks that comply with SCSI-II interface standards.

Distributing incomplete trust in wireless ad hoc networks

The main objective is to present a method for distributing information regarding the trustworthiness of other nodes in the network. The process of managing incomplete trust in ad hoc networks is described. A protocol for distributing incomplete trust as rumors in an ad hoc network is described. The protocol is adapted to the CAM architecture, which is implemented in all network nodes. The CAM architecture provides the protocols and applications with an interface, through which they may store and retrieve values from a common database. The Rumor protocol thus uses this interface to retrieve trust values from the common database and broadcast them to the environment and to update trust values received from the environment.

Ad hoc routing protocol's performance: a realistic simulation based study

Multiple wireless devices jointly create and maintain ad hoc networks; their employment is favored to happen in a variety of environments with distinct topological characteristics. Diversified environmental conditions are expected to vary network performance. In fact, obstacles, buildings and/or mountains may act as either barriers, or source of noise for the radio signals. Nevertheless, most of the previous performance evaluation studies based on simulation, neglected this consideration; they used simulation models that were too simplistic, and too narrow (i.e. idealistic) in their scopes. With this paper we propose a new, complete and realistic Urban Mobility Model (UMM). It models realistically users motion, and radio signals propagation in a city-like scenario. Our aim is to study the effects of realistic network simulation on routing performance. The results prove that a realistic scenario with roads and buildings has a significant impact on routing.

An architecture for context aware management

Military networks are subject to frequent changes due to hostile activities, movement of forces, weather conditions, terrain, etc. In order to function optimally, the network nodes must be able to rapidly adapt to the changes in the environment. Traditionally, this has been done by tailoring applications and protocols to exchange information. However, such solutions suffer from several disadvantages, e.g. due to their lack of generality. In this paper we present a context aware management architecture that adapts the behavior of the node to the current environment. The protocols and applications are responsible only for the tasks for which they have originally been designed, and need not be aware of the environment at all. The CAM architecture is especially suitable to mobile military ad hoc networks, which are seen as a possible future communication network solution on the battlefield.

Repair algorithms for mirrored disk systems

This paper analyzes different repair methods of a mirrored disk subsystem. The main interest is focused on disk faults and how the repair process is copying data from a fault-free disk to a spare disk with the least performance degradation for user disk requests. The objective of this study is to compare how different repair algorithms affect system performance. Two different repair algorithms are compared. Two different access patterns (uniform and non-uniform) are studied to establish their effects on the repair process and performance. Simulation results of this research indicate that the performance degradation of user disk requests can be significantly reduced by introducing a short delay in the repair algorithm. A new algorithm for detecting sector faults is also presented. This algorithm scans the disk space, while there are no user disk requests issued and detects deteriorated media using the advanced statistics of modern SCSI disks. The advantage of the proposed algorithm is that it can repair the disk subsystem before data is actually lost due to a media defect (bad sector).

Scheduling policies for fault tolerance in a VLSI processor

This paper presents analytical and simulation models for evaluating the operation of a VLSI processor (in a uniprocessor configuration) which utilizes a time-redundant approach (such as recomputation by shifted operands) for fault-tolerant computing. In the proposed approach, all incoming jobs to the uniprocessor are duplicated, thus two versions of each job must be processed. A discrepancy in the results produced by comparing the outcomes of the two versions of the same job indicates that a fault may have occurred. Several methods for appropriately scheduling the primary and secondary versions of the jobs are proposed and analyzed.

Detecting latent sector faults in modern SCSI disks

The authors present new improved methods for detecting latent sector faults in a disk subsystem as caused by media deterioration of the disk magnetic storage material. In case of media deterioration on the rarely accessed sectors, a latent disk fault may remain undetected for a long time. An adaptive algorithm is proposed to utilize the idle time of the disk for scanning commonly used SCSI disks.<<ETX>>