HP Labs Technical Reports
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A CSMA/CD Compatible MAC for Real-time Transmissions Based on Varying Collision Intervals
Sharon, Oran; Spratt, Michael
Keyword(s): local area network; LAN; real-time; CSMA/CD; ethernet; delay-sensitive
Abstract: This paper suggests a CSMA/CD compatible MAC protocol for real-time transmission in a shared Home or Small Office Local Area Network. The new MAC is based on the distributed assignment of special TAG numbers to the stations transmitting real-time traffic. These TAG numbers determine a Round Robin order of transmissions among the real-time stations. They also help in resolving collisions among real time stations by setting the length of the Jam signal, transmitted in case of a collision, to be a function of the TAG number. In a collision the station with the highest TAG number, and so with the longest Jam, is persisting with its Jam transmission for the longest until all the other stations defer. Thus, the collision terminates and the longest persisting station can transmit its packet successfully. The new protocol enables stations implementing the IEEE 802.3 MAC standard to transmit on the same network with stations implementing the new protocol. After introducing the protocol, we compute an upper bound on the access delay that the protocol guarantees and prove the correctness of the distributed TAG assignment procedure. Finally, we simulate the protocol in a network consisting stations implementing the new protocol together with stations implementing the standard IEEE 802.3 MAC. We show that the access delays of the stations transmitting real-time traffic are indeed bounded as predicted. Notes: Oran Sharon, Department of Mathematics, University of Haifa, Haifa, Israel. Notes: To be published in 'Computer Networks' available from http://www.elsevier.com.
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