Real-time MAC Research Articles

A new real-time ethernet MAC protocol for time-critical applications

The authors propose a new persistent transmission-based real-time Ethernet MAC protocol that provides a predictable upper bound for the delivery delay of real-time frames. Moreover, it is compatible with the protocol used by the existing Ethernet controllers for conventional datagram traffic and thus standard Ethernet stations can be used in the system without any modification. The paper describes the protocol in detail and analyses the maximum delivery delay for real-time traffic and the efficiency of the channel.

Packetized voice transmission using RT-MAC, a wireless real-time medium access control protocol

RT-MAC is a simple, elegant, and robust medium access control (MAC) protocol for use in transmitting real-time data in point-to-point ad hoc wireless local area networks (WLANs). Our enhancement of IEEE 802.11, real-time MAC (RT-MAC), dramatically reduces missed deadlines and packet collisions while increasing throughput by selectively discarding packets and sharing station state information. For example, RT-MAC is able to successfully transmit 40 2-way voice conversations in addition to a normalized offered load of 80%. IEEE 802.11 is only able to transmit 10 2-way conversations under the same conditions. In another instance, RT-MAC reduced packet collisions from 50% to less than 15% while increasing throughput by more than 50%. Herein we extend our previous performance analysis of RT-MAC to include integrated voice-data transmission. Stations using RT-MAC are interoperable with stations using IEEE 802.11 and show a significant performance improvement even when a minority of stations in the network employ RT-MAC.

A distributed real-time MAC protocol for WDM-based LANs

In this paper, we consider the problem of developing a MAC layer protocol to support real-time as well as non-real-time packet streams in Broadcast and Select WDM optical networks having rapidly tunable transmitters. We propose a MAC layer protocol which is the best-effort in nature and has two phases: demand notification phase and packet transmission phase. In the demand notification phase, a token circulates among the nodes in a round robin manner gathering the demand information of the traffic on each node. This information is recorded in the local status tables of each node. An algorithm is run on all the nodes in a distributed manner in order to resolve the contention for each channel. The contention resolution algorithm gives due weightage to both the real-time deadline of the streams of traffic and tuning time of the transmitter. In the proposed protocol, the traffic streams on any node are not bound to a physical channel and can use any channel onto which a receiver on the destination node is tuned. Also, the protocol attempts to overlap the transmitter tuning with the packet transmission in order to minimize the channel idle time due to transmitter tuning. We demonstrate the effectiveness of the proposed protocol through extensive simulation studies.

10.1109/ETFA.2010.5641191

Wireless communication is an attractive alternative for the industry automation and related areas, due to the increased mobility coupled with a reduction of cabling costs and deployment time. However several relevant parameters exists which might influence the timely and error behaviour of industrial wireless communication systems. IEEE 802.11 based wireless local area networks have become more and more popular due to low cost and easy deployment, providing best effort services but do not have quality of service. The 802.11e standard provides two alternatives for medium access (EDCA and HCCA) by differentiating traffic into four Access Categories (ACs). This paper proposes a mechanism for controlling the medium access, so-called Wireless Real Time Medium Access Control (WRTMAC), developed from the EDCA scheme of standard 802.11e. The handling of the Arbitration Inter-Frame Space (AIFS) has been modified and replaced by the Real-Time Inter-Frame Space (RIFS) in order to make the medium access deterministic even in terms of high traffic.

A real-time medium access control protocol for ad hoc wireless local area networks

We develop and analyze a simple, elegant medium access control (MAC) protocol for use in transmitting real-time data in point to point ad hoc wireless local area networks (WLANs). Our enhancement of IEEE 802.11, real-time MAC (RT-MAC), achieves dramatic reductions in mean delay, missed deadlines, and packet collisions by selectively discarding packets and sharing station state information. For example, in a 50 station network with a normalized offered load of 0.7, mean delay is reduced from more than 14 seconds to less than 45 ms, late packets are reduced from 76% to less than 1%, and packet collisions are reduced from 36% to less than 1%. Regression models are developed from simulation data to describe network behavior in terms of throughput, mean delay, ratio of late packets, and ratio of collisions. Stations using RT-MAC are interoperable with stations using IEEE 802.11.