The efficiency of multi-channel MAC protocols depends on the channel assignment mechanism which must coordinate the channel usage in a better way. Several multi-channel MAC approaches have been proposed in the literature. In this paper we propose a formal modelling and analysis of the multi-channel MAC protocols based on the Split Phase (SP) approach using Stochastic Timed Petri Nets (STPN). We analyze the fundamental properties of this approach.

The use of multiple channels in MAC protocols offers a great potentiality for improving the network throughput. But consequently to the multi-channel aspect and with respect to a mono-channel network, a MAC protocol has now a supplementary function which is the channel assignment. There are many variations for the channel assignment which have been defined and studied in the literature. However, there are few studies with formal models and verification techniques for analysis of these protocols. The goal of this paper is precisely to propose a formal modelling and verification of the multi-channel MAC protocols based on the common hopping approach using Stochastic Timed Petri Net (STPN). We verify the properties of the common hopping pattern (rendezvous) of all nodes and the resynchronization of the sender and receiver nodes on the common hopping sequence after the end of a successful transmission.

IEEE 802.11-based backbone mesh networks comprise of static wireless mesh routers (WMRs) which create a wireless multihop backbone to provide high-speed last-mile wireless Internet access to communities. Specialized WMRs called gateways provide the interconnection between the mesh network and fixed IP networks. Mesh routers perform backhaul routing and may additionally serve as access points (APs) for clients. Their main task is to maintain backhaul mesh connectivity and find routes to gateways for clients. An important research problem which has received little attention is the optimal selection of gateway and the route to that gateway by mesh routers within the mesh backbone. We propose an efficient gateway and route selection scheme for backbone mesh networks which can be adopted for upcoming 802.11s mesh standard with minimal changes. Gateway load, route interference and path quality metrics are used to select the best available gateway and the route to that gateway. Simulation results show improved performance compared to schemes using nearest gateway, gateway load metric or the ETX metric for gateway selection.

This paper presents the expected link performance (ELP) metric for finding high throughput, low delay paths in 802.11 mesh networks. ELP combines three different mechanisms to accurately determine the expected link performance. Link quality information is combined with cross-layered link interference estimation to select optimal paths. Simulation results show that ELP significantly outperforms both hop count as well as the popular ETX metric. ELP has up to 12% higher throughput and about 40% smaller delay than ETX.

The message scheduling is an essential mechanism in the context of networked control systems (NCS) which are systems based on communication networks and which allow, in particular, the implementation of closed loop distributed control applications. The scheduling of the messages of the flows of these closed loop distributed applications strongly influences the stability of these applications. The message scheduling is, in several networks, mainly based on fixed (static) priorities associated to the messages (for example the network CAN). In previous works, we have shown that the static priority scheme has intrinsic limitations and so, we propose in this paper, in order to overcome these limitations, the concept of hybrid (hierarchical) priority. Different hybrid priority schemes are presented and evaluated with respect to the stability performances of the closed loop distributed process control applications. We show, in particular, the advantage of a scheduling based on a scheme "hybrid priority + time strategy".

The goal of this paper is to show the interest of the stochastic timed Petri net (STPN) model for the analysis of the data transfer phase of Bluetooth baseband layer. The contribution is double: at first in terms of the modeling power of the model which is well adapted to represent the complex format of the packets (several parts with their own redundancy and sometimes two levels of redundancy); then in terms of the performances which are evaluated for the different types of data packets (DM(y) and DH(y), with y=(1, 3, 5)) and taking into account for different probabilities of error per bit.

Addresses the problem of transmitting real-time periodic traffic in a DQDB network. In a DQDB network, connection-oriented isochronous services use the pre-arbitrated (PA) access. The standard specifies that isochronous connections must have guaranteed periodic bandwidth but mechanisms to provide it, such as the slot allocation scheme, are not described. We propose a real-time service provider (RTSP) based on the use of the PA access. The RTSP consists of an off-line centralized scheduling algorithm and an on-line mode change algorithm which allows to take into account load changes. Means are also provided to guarantee a minimum fairness level for the asynchronous traffic.>

Proposes the observer concept for designing self-checking distributed systems, i.e. systems that detect erroneous behaviors as soon as errors act at some observable output level. The approach provides a solution to build systems whose on-line behavior is checked against a formal model derived from a formal description. In other words, the actual implementation is continuously checked against a reference, this reference being a formal and verified model of some adequately selected aspects of the system behavior. The corresponding methodology, the software concepts and some applications of the observer are presented. General definitions are given first that theoretically define self-checking systems as systems that include and implement complete on-line validation. The basic concepts and the difficulties to implement self-checking validation are then given. In order to provide simple implementations, the previous definitions are weakened to design quasi-self-checking observers for LANs using a broadcast service. Three specific applications are given to illustrate the proposed approach: testing a virtual ring MAC protocol, checking the link and transport layers in an industrial LAN, and managing a complete OSI layering, from layer 2 to layer 6, in an open system architecture.>

The advantages of an initial specification based on the knowledge properties of the service users and service providers for specifying the communication mechanisms of a layer is discussed. This particular way of proceeding with specification causes the designer to express pertinent high level properties that enable the designer to rationally infer a complete specification of the mechanistic attributes of an operational specification.>

Two important design steps are presented of a gateway for connecting a local area network (LAN) and a remote computer through an ISDN (integrated services digital network). The first step concerns the specification of the gateway architecture: the inconsistencies have to be considered between the LAN architecture and the communication architecture of the remote computer (which has an ISDN interface). The second step concerns the formal specification of the behavior of the gateway, using Petri nets: this step is essential in order to verify if the specification is complete and correct.>

An architecture model and a subset of a behavior model of the ISO virtual terminal (VT) are specified in the formal description technique Estelle. The architecture model includes modules and their appropriate interconnections (channels) for a VT-user, a VT protocol machine (VTPM), an association control service entity (ACSE), autonomous-abort internal events, a presentation layer element, and a mapping machine to map protocol data units of the VTPM onto service primitives of the ACSE and the presentation layer. The behavior model specifies the association establishment phase of the VTPM for the synchronous mode of operation, assuming that no optimal function units are selected. The combination of VT and Estelle represents ISO's effort toward implementing the Open Systems Interconnection (OSI) model.>

The authors are concerned with the design of multilayer architectures in distributed systems and computer networks. First, they give the basic knowledge that any designer must have for designing, in a consistent way, a set of layers. This knowledge concerns the objects of a layer, their attributes and their relationships. Second, they consider an example of network interconnection, at the network layer, on the basis of the internal organization of the network layer defined by ISO and apply this basic knowledge for specifying the architecture for internetworking.>