Sijing Zhang

An optimal synchronous bandwidth allocation scheme for guaranteeing synchronous message deadlines with the timed-token MAC protocol

This paper investigates the inherent timing properties of the timed-token medium access control (MAC) protocol necessary to guarantee synchronous message deadlines in a timed token ring network such as, fiber distributed data interface (FDDI), where the timed-token MAC protocol is employed. As a result, an exact upper bound, tighter than previously published, on the elapse time between any number of successive token arrivals at a particular node has been derived. Based on the exact protocol timing property, an optimal synchronous bandwidth allocation (SBA) scheme named enhanced MCA (EMCA) for guaranteeing synchronous messages with deadlines equal to periods in length is proposed. This scheme is an enhancement on the previously published MCA scheme.

Vehicular ad hoc networks (VANETs): Current state, challenges, potentials and way forward

Recent advances in wireless communication technologies and auto-mobile industry have triggered a significant research interest in the field of VANETs over the past few years. VANET consists of vehicle-to-vehicle (V2V) and vehicle-to-infrastructure (V2I) communications supported by wireless access technologies such as IEEE 802.11p. This innovation in wireless communication has been envisaged to improve road safety and motor traffic efficiency in near future through the development of Intelligent Transport Systems (ITS). Hence, government, auto-mobile industries and academia are heavily partnering through several ongoing research projects to establish standards for VANETs. The typical set of VANET application areas, such as vehicle collision warning and traffic information dissemination have made VANET an interested field of wireless communication. This paper provides an overview on current research state, challenges, potentials of VANETs as well the way forward to achieving the long awaited ITS.

An efficient and practical local synchronous bandwidth allocation scheme for the timed-token MAC protocol

This paper is concerned with deadline guarantees of synchronous messages with deadlines equal to periods, in a timed token ring network such as FDDI where the timed token medium access control (MAC) protocol is used. The timed token protocol guarantees a bounded access time and an average bandwidth for synchronous traffic. However, this guarantee alone, though necessary, is insufficient for guaranteeing the transmission of synchronous messages before their deadlines. To ensure timely delivery, the synchronous bandwidth must be carefully allocated to individual nodes. We propose and analyse an efficient and practical local synchronous bandwidth allocation (SBA) scheme. The new scheme performs better than any previously published as it calculates the synchronous bandwidth such that during the message period, the total synchronous transmission time definitely available (when judged only by local information) is exactly equal to the transmission time required. Our scheme also differs significantly from previously reported ones by explicitly taking into account the synchronous bandwidth allocation for message sets whose minimum message deadlines (D/sub min/) are less than twice the target token rotation time (TTRT), and consequently can apply to any synchronous message set (with D/sub min/>TTRT). The feasibility of the allocations produced by the proposed scheme and the worst case achievable utilisation of the scheme are also discussed.

Hard Real-Time Communication with the Timed Token Protocol: Current State and Challenging Problems

With the increasing use of distributed real-time systems, the ability of communication networks to handle real-time traffic is becoming more and more important. The timed token medium access control protocol, which has been now incorporated into several network standards such as FDDI and SAFENET due to its special timing property of bounded medium access time, is one of the most suitable and attractive candidate communication protocols for supporting distributed hard real-time applications. Extensive research has been conducted on using the timed token protocol to guarantee timely transmission of messages in a communication environment with hard real-time requirements. This paper intends to present a comprehensive review on recent advances in hard real-time communication with the timed token protocol. In addition, several challenging problems are identified.

Cycle-time properties of the timed token medium access control protocol

We investigate timing properties of the timed token protocol that are necessary to guarantee synchronous message deadlines. A tighter upper bound on the elapse time between the tokens lth arrival at any node i and its (l + /spl nu/)th arrival at any node k is found. A formal proof of this generalized bound is presented.

Guaranteeing Synchronous Message Sets in FDDI Networks

Abstract This paper addresses the issue related to the deadline guarantees of synchronous messages in FDDI networks. The exact value of Xi (the minimum amount of time for each node i on the network to transmit its synchronous messages during the message’s (relative) deadline Di), which is better than the previously published, is derived. Based on this result, the schedulability of synchronous message sets is generally analysed. This analysis differs from previous ones by taking into account synchronous message sets with the minimum message deadline (Dmin) less than twice the Target Token Rotation Time (TTRT).

Testing the Schedulability of Synchronous Traffic for the Timed Token Medium Access Control Protocol

One of the key issues related to guaranteeing synchronous message deadlines in a timed token network (such as fiber distributed data interface) where the timed token medium access control protocol is used is the schedulability test of synchronous traffic (i.e., testing whether or not all synchronous messages can be transmitted before their deadlines, under a given setting of network parameters). Much work has been done on how to assign network parameters appropriately in order to guarantee timely transmission of synchronous traffic. As a result quite a few synchronous bandwidth allocation schemes and some good guidelines on selection of the target token rotation time have been proposed. In contrast, limited research has been conducted on how to effectively test whether or not given network parameters can guarantee timely transmission of all synchronous messages (of a considered synchronous message set) before their deadlines. The previous testing methods for synchronous message schedulability only provide a sufficient (but not necessary) test and therefore fail to always keep effective for any synchronous message set considered. In this paper, we propose two testing methods for determining the schedulability of a synchronous message set with message deadlines no longer than periods. The proposed tests perform better than any previous test in the sense that they are both sufficient and necessary. Some numerical examples are given to compare different testing methods, all of which have demonstrated the superiority of the proposed tests to other existing testing methods.

The worst-case scenario for transmission of synchronous traffic in an FDDI network

We study the problem of guaranteeing deadlines of synchronous messages with their deadlines no more than periods in an FDDI network. In order to guarantee the transmission of a synchronous message before its deadline, a precise knowledge of the worst-case situation for such transmission is required. This paper studies the worst-case scenario for transmission of a synchronous message in an FDDI network, in which the time elapsed between arrival of the message and completion of its transmission will reach its maximum (i.e., the longest possible interval). A few conditions under which the worst-case situation can happen are formally derived.

On the schedulability of synchronous message sets with the minimum message deadline less than 2/spl middot/TTRT in an FDDI network

We study the problem of guaranteeing synchronous message sets with the minimum message deadline (D/sub min/) less than twice the target token rotation time (TTRT), i.e., D/sub min/<2/spl middot/TTRT, in an FDDI network. While the restriction of D/sub min//spl ges/2/spl middot/TTRT on a synchronous message set is generally accepted as a necessary condition for all message deadlines to be guaranteed, our study shows that this is not always the case. Some synchronous message sets with D/sub min/<2/spl middot/TTRT may still be guaranteed. We show that there is no need to retain the above restriction on a synchronous message set before determining its schedulability. Furthermore an improved version of a previously-published local synchronous bandwidth allocation scheme, with removal of this restriction, is proposed.

Testing the feasibility of synchronous bandwidth allocation for time-critical communication in FDDI networks

One of the key issues related to deadline guarantees of synchronous messages in FDDI networks is the feasibility test of synchronous bandwidth allocation (SBA). Much work has been done on how to allocate synchronous bandwidth properly in order to guarantee synchronous messages transmission before their deadlines, and as a result quite a few SBA schemes have been proposed. In contrast, limited research has been done on how to effectively test the feasibility of a given allocation of synchronous bandwidths (i.e., whether or not a given allocation can guarantee the synchronous message set considered), and the existing approach cannot always give an effective test and may even produce wrong testing results. This paper presents an algorithm of polynomial time worst-case complexity which ensures the correctness and effectiveness of the testing for any given synchronous message set with message deadlines equal to periods.