  Coded caching is a technique that promises huge reductions in network traffic
in content-delivery networks. However, the original formulation and several
subsequent contributions in the area, assume that the file requests from the
users are synchronized, i.e., they arrive at the server at the same time. In
this work we formulate and study the coded caching problem when the file
requests from the users arrive at different times. We assume that each user
also has a prescribed deadline by which they want their request to be
completed. In the offline case, we assume that the server knows the arrival
times before starting transmission and in the online case, the user requests
are revealed to the server over time. We present a linear programming
formulation for the offline case that minimizes the overall rate subject to
constraint that each user meets his/her deadline. While the online case is much
harder, we introduce a novel heuristic for the online case and show that under
certain conditions, with high probability the request of each user can be
satisfied with her/his deadline. Our simulation results indicate that in the
presence of mild asynchronism, much of the benefit of coded caching can still
be leveraged.
