  Cellular wireless systems rely on frame-based transmissions. The frame design
is conventionally based on heuristics, consisting of a frame header and a data
part. The frame header contains control information that provides pointers to
the messages within the data part. In this paper, we revisit the principles of
frame design and show the impact of the new design in scenarios that feature
short data packets which are central to various 5G and Internet of Things
applications. We treat framing for downlink transmission in an AWGN broadcast
channel with K users, where the sizes of the messages to the users are random
variables. Using approximations from finite blocklength information theory, we
establish a framework in which a message to a given user is not necessarily
encoded as a single packet, but may be grouped with the messages to other users
and benefit from the improved efficiency of longer codes. This requires changes
in the way control information is sent, and it requires that the users need to
spend power decoding other messages, thereby increasing the average power
consumption. We show that the common heuristic design is only one point on a
curve that represents the trade-off between latency and power consumption.
