  Consider the channel coding problem where two users are interacting in order
to communicate an i.i.d. source X1 from User 1 to User 2 with distortion D1 and
an i.i.d. source X2 from User 2 to User 1 with distortion D2. X1 and X2 may be
dependent. Communication occurs from User 1 to User 2 via a DMC C1 and from
User 2 to User 1 over a DMC C2, where C1 and C2 act independently of each
other. Communication occurs during each time slot between both users and each
user can make a coding and decoding based on all past available knowledge. This
interactive communication problem is formulated and it is proved that
source-channel separation based architectures are optimal.
