  Consider a pair of terminals connected by two independent additive white
Gaussian noise channels, and limited by individual power constraints. The first
terminal would like to reliably send information to the second terminal, within
a given error probability. We construct an explicit interactive scheme
consisting of only (non-linear) scalar operations, by endowing the
Schalkwijk-Kailath noiseless feedback scheme with modulo arithmetic. Our scheme
achieves a communication rate close to the Shannon limit, in a small number of
rounds. For example, for an error probability of $10^{-6}$, if the Signal to
Noise Ratio ($\mathrm{SNR}$) of the feedback channel exceeds the $\mathrm{SNR}$
of the forward channel by $20\mathrm{dB}$, our scheme operates $0.8\mathrm{dB}$
from the Shannon limit with only $19$ rounds of interaction. In comparison,
attaining the same performance using state of the art Forward Error Correction
(FEC) codes requires two orders of magnitude increase in delay and complexity.
On the other extreme, a minimal delay uncoded system with the same error
probability is bounded away by $9\mathrm{dB}$ from the Shannon limit.
