The article presents a quantitative evaluation by simulation of the relative performance of three HF radio network connectivity categories. These are differentiated by their method of choosing the channels: (1) sound before linking; (2) intermittent sounding (in advance of linking); and (3) continuous sounding (by base stations). Category 1 and 2 networks use a symmetric linking protocol. That is, the base stations (BSs) and mobile stations (MSs) use the same linking protocol. Category 1 network nodes perform sounding to choose a channel, just before opening a link. Category 2 network nodes assess the two-way channel quality by sounding intermittently. Channel choice is determined from past sounding measurements only. Category 3 networks use an asymmetric connectivity protocol. Base stations sound continuously on free channels so that mobile stations can assess the (one-way) channel quality. Channel choice is determined from these measurements. HF links are opened only between the mobile and base stations. Base stations are assumed connected to each other by non-HF means. Categories 1 and 2 represent two different ways of using standard ALE (FED-STD-1045). Category 3 represents networks based on the author's proposed SMASH protocol (Synchronous Multi-channel Access Signalling for HF). Only the basic sounding aspects of SMASH have been implemented to date.
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