One of the biggest open problems in Shannon theory 
is the effect of feedback on the capacity of multiuser 
channels and multihop networks, especially when that 
feedback is of finite rate or noisy. On the other hand, 
ARQ is ubiquitious as low-rate noisy feedback in practical 
designs of these systems, in part due to its reduction of 
end-to-end delay. This talk will present some recent capacity 
and diversity-multiplexing-delay tradeoff results for multiuser 
and multihop networks under different forms of feedback, and 
explore connections between source-channel coding of feedback 
channels and feedback control.