AT&T DS1/DMi/ISDN-PRI manual 16SYNCHRONIZATION of Digital Facilities

5-16SYNCHRONIZATION OF DIGITAL FACILITIES

Figure 5-8.External Clock

Private network applications that do not have digital connections to the public network will not provide the Reference 1 and Reference 2 inputs or the clock-input #1 and clock-input #2 circuit packs. These types of network applications are not allowed.

For public-network applications, the clock-input circuit pack derives a 1.544M-bps clock signal from the reference. The clock #1 and #2 circuit packs generate a 64K-bps stratum-3 clock signal. The composite clock output circuit pack monitors the 64K-bps signals from the references and clocks and, on detecting a failure or other error, automatically changes from the online reference clock to an alternate. Furthermore, an alarm signal alerting you of the problem is generated. Additionally, the composite clock output circuit pack generates a 64K-bps composite clock signal. This signal is a special bipolar (return-to-zero) signal that contains a bipolar violation every eighth bit and is cabled to the switch (for System 85 and Generic 2, the TN2131 circuit pack).