The E ects of Destructive Interference and Wasted

The uniform-traac capacity of switchless, non-bus-oriented, ber-optic single-hop intercon-nections among N stations, each equipped with a small number of transmitters and receivers, can be as high as (log 2 N) concurrent transmissions on a single wavelength with round-robin scheduling in a time-slotted system. However, their capacity with the Slotted ALOHA access scheme does not increase with N. (The capacity of bus-oriented interconnections, in contrast, varies across time-slotted access schemes by at most a factor of e.) This paper quantiies the contribution of several factors to capacity. Merely avoiding destructive interference with ongoing receptions contributes at most a factor of e over Slotted ALOHA, the same as in bus-oriented interconnections. For an interconnection among two-transmitter, single-receiver stations, whose capacity is log 2 N with global scheduling and 2=e with Slotted ALOHA, also avoiding transmissions to blocked receivers increases capacity to at most log 2 log 2 N. These results suggest that the added complexity of non-bus-oriented SHIs may be warranted only if they are operated in ways that permit the selection of \good" combinations of (source,destination) pairs for concurrent transmission, and further research should focus on those.