T640 SONET Clock Generators (SCGs) Description
The SONET Clock Generators (SCGs) provide 19.44-MHz Stratum 3 clock signal for the SONET/SDH interfaces on the router (see Figure 1).
One SCG is shipped as part of the standard router configuration, but up to two SCGs can be installed to provide redundancy. SCGs are installed into the upper rear of the chassis in the slots labeled SCG0 and SCG1.
Backup SCGs are hot-removable and hot-insertable. Master and nonredundant SCGs are hot-pluggable.
Figure 1: SCG
Each SCG consists of the following components:
- 19.44-MHz Stratum 3 clock.
- Field-programmable gate array (FPGA) that performs multiplexing of clock sources.
- Three LEDs, located on the SCG faceplate, that display the status of the SCG.
- SCG online/offline button, located on the SCG faceplate.
- Two external clock inputs.
 | Note: The external clock inputs on the SONET Clock Generators (SCGs) are not supported. |
