An improved “Piggyback Ethernet” protocol and its analysis

Abstract

Collision protocols are inefficient for last or long bus networks because of the constraint on minimum packet length. Also the efficiency reduces at heavy load due to increased probability of collision. Piggyback Ethernet Schemes, based on scheduling-delay access mechanisms, have been suggested to avoid the need to inflate packets to the minimum length and to reduce the probability of collisions. This paper suggests a modification in one such scheme, and theoretically analyses the average delay incurred in the original and the modified schemes. For a slightly increased delay at very low loads we make more stations send their packets collision-free when traffic is higher. As a bonus, we obtain a bounded delay scheme for these higher loads. Then, by a small modification to the CSMA/CD scheme, we can ensure a bounded delay for any packet. Thus the scheme becomes suitable for real-time data-acquisition and control applications.