Guilherme Arroz

Fault-tolerant broadcasts in CAN

Fault-tolerant distributed systems based on field-buses may take advantage from reliable and atomic broadcast. There is a current belief that CAN native mechanisms provide atomic broadcast. In this paper, we dismiss this misconception, explaining how network errors may lead to: inconsistent message delivery; generation of message duplicates. These errors may occur when faults hit the last two bits of the end of frame delimiter. Although rare, its influence cannot be ignored, for highly fault-tolerant systems. Finally, we give a protocol suite that handles the problem effectively.

A Columbus' egg idea for CAN media redundancy

Network media redundancy is a clean and effective way of achieving high levels of reliability against temporary medium faults and availability in the presence of permanent faults. This is specially true of critical control applications such as those supported by the Controller Area Network (CAN). In our endeavor to provide CAN with media redundancy we ended-up devising a scheme which is extraordinarily simpler than previous approaches known for CAN or other LANs and field-buses.

Enforcing Dependability and Timeliness in Controller Area Networks

Standard fieldbuses, such as the controller area network (CAN), are today a cost-effective solution for distributed computer control systems. However, the standard CAN protocol exhibits a set of severe shortcomings in respect to the provision of strict dependability and timeliness guarantees. This paper identifies those shortcomings and discusses the main design challenges we have been tackling in a comprehensive way to provide a CAN-based infrastructure support for extremely reliable hard real-time communications, dubbed CAN enhanced layer (CANELy)

Embedded platforms for distributed real-time computing: challenges and results

Object oriented techniques have been along the last decade one of the most useful programming paradigms. However, for distributed embedded systems, the semantic gap between the object orientation layer and the underlying infrastructure is extremely large. This gap can be narrowed, should the embedded system platform provide semantically rich communication and management services. The paper outlines our research effort in the provision of such services by CAN based (Controller Area Network) systems.

Review: Providing service differentiation in pure IP-based networks

The lack of an effective cooperation between the data, control and management plane of QoS routing solutions presented so far, prevents the implementation of service differentiation in the context of pure IP-based networks. Most of paths calculation proposals performed by the control plane are unaware of service characteristics of each flow. Scalable data plane QoS proposals ignore the issue about selecting the best paths to route the traffic. Proposed management plane schemes do not perform the network state maintenance and service level monitoring. Multi-service routing is a flow-based forwarding protocol that implements the service differentiation in pure IP-based networks, using a straight cooperation between data, control and management plane. This cooperation is accomplished by a data plane supporting the DiffServ model and performs route selection based on flows service class, which is exploited by the management plane to carry out the network state maintenance, and performance monitoring by using the RTCP protocol, to provide service metrics to control plane for route calculation. Simulation experiments show better performance results achieved by Multi-service routing compared to those obtained by traditional link state protocol with the DiffServ model and QoS routing in heavy loaded network scenarios of mixed traffic having different service requirements.

Hardware support for CAN fault-tolerant communication

Fault-tolerant distributed applications based on field-buses may take advantage from the availability of highly-dependable communication systems. In this paper, we address this problem in the context of CAN, the Controller Area Network, to conclude that CAN native mechanisms alone are unable to fulfil all the attributes of fault-tolerant communication protocols. The paper discusses how existing CAN controllers can be complemented with some simple machinery and low-level protocol modules, handling the problem effectively. The result is an enhanced CAN infra-structure able to provide extremely reliable communication.

Design of bus media redundancy in CAN

Network media redundancy is a clean and effective way of achieving high levels of reliability against temporary medium faults and availability in the presence of permanent faults. This is specially true of critical control applications such as those supported by the Controller Area Network (CAN). This paper deals with the complexity of implementing bus media redundancy in CAN, discussing how this can be done through a simple scheme that uses inexpensive off-the-shelf components.

Multi-service routing: a routing proposal for the next generation internet

Quality of Service support plays a major role in the Next Generation Internet. QoS routing protocols must cope with service differentiation to enhance this support. This paper proposes a service aware QoS routing protocol, the Multi-Service routing, which is an extension to traditional intra-domain routing protocols. It proposes a new path selection policy that guides higher priority traffic through the shortest path and diverts lower priority traffic through longer paths when service performance degradation is foreseen. Simulations results shows that the proposed routing performs better than existing QoS routing and link-state protocols.

Integrating Inaccessibility Control and Timer Management in CANELy

The CAN Enhanced Layer (CANELy) is a CAN-based infrastructure capable of extremely reliable communication. This paper describes the mechanisms and the techniques used in CANELy to enforce system correctness in the time-domain despite the occurrence of network errors (inaccessibility). The paper discusses how to integrate in the existing CANELy machinery, the control of inaccessibility and the management of timers, at several levels of the system. In particular, application and low-level protocol layers are addressed. In addition, a relevant set of parameters are available for system monitoring, allowing the validation/enforcement of the system model.

Multi-service routing - a new QoS routing approach supporting service differentiation

Several quality of service models have been proposed for the next generation of Internet, with differentiated service being foreseen to support it in core networks. A new routing architecture must be adopted to cope efficiently with these service differentiation mechanisms. The paper proposes an extension to traditional intra-domain routing protocols which takes into account service differentiation. In the new approach, routing paths must be selected according to network traffic conditions and service level agreements. A new path selection mechanism is proposed, which guides higher priority traffic through the shortest path and diverts lower priority traffic through longer paths when service performance degradation is foreseen.