This chapter explains how the standard frames and packets are constructed. It describes the standard Inter-Range Instrumentation Group (IRIG) frame structure and define such terms as major and minor frame, commutated, subcommutated, and supercommutated data. The chapter presents a data set in the IRIG frame format with reasonable efficiency and discusses the strengths and weaknesses of packet versus frame telemetry systems and describes basic packet structure requirements for packet telemetry systems. It examines the means, purposes, and results of data formatters used prior to transmission of digital data. Telemetry frames are data link protocols designed to support time-division multiplexing of sensor data over point-to-point link configurations. Telemetry frames typically have two major synchronization markers: the minor frame synchronization code and the subframe identifier. Packet telemetry is a relatively new area in the telemetering field, as compared to traditional frame formatting. Frame telemetry is best for use over relatively bad, point-to-point wireless transmission links where the data format is relatively fixed.