AT&T DS1/DMi/ISDN-PRI manual D4 Framing

INTRODUCTION 1-11

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.