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. Thm scheme is an enhancement on the previously publiibed MCA scheme

Guaranteeing synchronous message deadlines with the timed token medium access control protocol

We study the problem of guaranteeing synchronous message deadlines in token ring networks where the timed token medium access control protocol is employed. Synchronous capacity, defined as the maximum time for which a node can transmit its synchronous messages every time it receives the token, is a key parameter in the control of synchronous message transmission. To ensure the transmission of synchronous messages before their deadlines, synchronous capacities must be properly allocated to individual nodes. We address the issue of appropriate allocation of the synchronous capacities. Several synchronous capacity allocation schemes are analyzed in terms of their ability to satisfy deadline constraints of synchronous messages. We show that an inappropriate allocation of the synchronous capacities could cause message deadlines to be missed even if the synchronous traffic is extremely low. We propose a scheme called the normalized proportional allocation scheme which can guarantee the synchronous message deadlines for synchronous traffic of up to 33 percent of available utilization. To date, no other synchronous capacity allocation scheme has been reported to achieve such substantial performance. Another major contribution of this paper is an extension to the previous work on the bounded token rotation time. We prove that the time elapsed between any consecutive visits to a particular node is bounded by upsilon TTRT, where TTRT is the target token rotation time set up at system initialization time. The previous result by Johnson and Sevcik is a special case where upsilon = 2. We use this result in the analysis of various synchronous allocation schemes. It can also be applied in other similar studies

Performance analysis of FDDI

The Fiber Distributed Data Interface (FDDI) is an imerging ANSI and ISO standard for a 100 megabit per second fiber optic token ring. The performance of the FDDI media access control protocol is analyzed using a simulation developed at NASA Ames. Both analyses using standard measures of performance (including average delay for asynchronous traffic, channel utilization, and transmission queue length) and analyses of characteristics of ring behavior which can be attributed to constraints imposed by the timed token protocol on token holding time (including bounded token rotation time, support for synchronous traffic, and fairness of channel access for nodes transmitting asynchronous traffic) are included

Design and Analysis of RT-Ring: A Protocol for Supporting Real-Time Communications

Distributed applications with quality of service (QoS) requirements are more and more used in several areas (e.g., automated factory networks, embedded systems, conferencing systems). These applications produce a type of traffic with hard timing requirements, i.e., transmissions must be completed within specified deadlines. To handle these transmissions, the communication system must use real-time protocols to provide a communication service that is able to satisfy the QoS requirements of the distributed applications. In this paper, we propose a new real-time protocol, called RT-Ring, able to support transmissions of both real-time and generic traffic over a ring network. RT-Ring provides both network guarantees and high network resource utilization, while ensuring the compatibility with the emerging differentiated service architectures. Network guarantees are fully proved and high network utilization is highlighted by a comparative study with the FDDI protocol. This comparison shows that RT-Ring network capacities are greater than the corresponding FDDI capacities. In fact, by assuming the FDDI frames with a length equal to the RT-Ring slot size and by using the same traffic load we show that the capacities of FDDI are equal to the lower bound capacities of RT-Ring. Index Terms Real-time protocol, quality of service (QoS) traffic, worst case analysis

Fairness of channel access for non-time-critical traffic using the FDDI token ring protocol

The Fiber Distributed Data Interface (FDDI) is an ANSI draft proposed standard for a 100 megabit per second fiber optic token ring. FDDI supports two types of traffic, synchronous and asynchronous. Synchronous traffic is time critical traffic; stations are assigned guaranteed bandwidth to support their synchronous needs. Asynchronous traffic is lower priority and is sent only if time permits. It is proved analytically that the FDDI access protocol provides all stations on the ring with equal access to the channel to transmit asynchronous frames, regardless of the relative sizes of synchronous bandwidth allocations for individual stations. Analytic results are supported with data from simulation runs

Architectural impact of FDDI network on scheduling hard real-time traffic

The architectural impact on guaranteeing synchronous message deadlines in FDDI (Fiber Distributed Data Interface) token ring networks is examined. The FDDI network does not have facility to support (global) priority arbitration which is a useful facility for scheduling hard real time activities. As a result, it was found that the worst case utilization of synchronous traffic in an FDDI network can be far less than that in a centralized single processor system. Nevertheless, it is proposed and analyzed that a scheduling method can guarantee deadlines of synchronous messages having traffic utilization up to 33 pct., the highest to date

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

We investigate the 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 token's lth arrival at any node i and its (l + v)th arrival at any node k is found. A formal proof to this generalized bound is presented

Spacelab system analysis: A study of the Marshall Avionics System Testbed (MAST)

An analysis of the Marshall Avionics Systems Testbed (MAST) communications requirements is presented. The average offered load for typical nodes is estimated. Suitable local area networks are determined

Spacelab system analysis: A study of communications systems for advanced launch systems

An analysis of the required performance of internal avionics data bases for future launch vehicles is presented. Suitable local area networks that can service these requirements are determined