Space-time characteristics of ALOHA protocols in high-speed bidirectional bus networks

Lee, Whay Chiou;Humblet, Pierre A
IEEE/ACM transactions on networking Volume 3 N°5 - October 1995

We study the space-time characteristics of ALOHA multiple-access protocols in bidirectional bus networks where transmissions are in the form of packets of constant length, For point-to-point communications, the maximum throughput of unslotted ALOHA is known to be 1/(2e), independent of station configuration, We show that, with a uniform probabilistic station configuration, the maximum throughput of slotted ALOHA tends to a nonzero constant that is less than 1/(2e), when a, the end-to-end propagation delay normalized with respect to the packet transmission time, tends to infinity, However, when N stations are evenly spaced on the bus, the maximum throughput of slotted ALOHA vanishes as a tends to infinity, For broadcast communications, the maximum throughput of slotted ALOHA is well known to be 1/{e(1+a)}. For unslotted ALOHA, we show that, if the offered load intensity is constant along the bus, the maximum broadcast throughput achievable by a station varies along the bus and is maximized at its center, We also derive the optimal profile of the offered load intensity for achieving a constant throughput intensity, In both cases, the maximum broadcast throughput is greater than that derived by conventional analysis.

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