  The essential interactive capacity of a discrete memoryless channel is
defined in this paper as the maximal rate at which the transcript of any
interactive protocol can be reliably simulated over the channel, using a
deterministic coding scheme. In contrast to other interactive capacity
definitions in the literature, this definition makes no assumptions on the
order of speakers (which can be adaptive) and does not allow any use of private
/ public randomness; hence, the essential interactive capacity is a function of
the channel model only. It is shown that the essential interactive capacity of
any binary memoryless symmetric (BMS) channel is at least $0.0302$ its Shannon
capacity. To that end, we present a simple coding scheme, based on
extended-Hamming codes combined with error detection, that achieves the lower
bound in the special case of the binary symmetric channel (BSC). We then adapt
the scheme to the entire family of BMS channels, and show that it achieves the
same lower bound using extremes of the Bhattacharyya parameter.
