INTRODUCTION
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Figure 1-4. D4 Framing
The D4 framing is the format compatible with D4-channel banks. The D4 framing is the only
framing format supported by all equipment used with System 75 and System 85 DS1 (such as CEMs
and CDMs).
The DS1, while providing an error-detection capability, monitors the receive sequence of framing bits
to detect transmission errors. If a transmission error (such as a noise hit) causes a bit in the framing
pattern to be in error, a misframe is said to have occurred. The DS1 counts misframes and uses the
count for processing the facility performance indicators, such as bit error rates, major alarms, and
minor alarms.