T1600 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.
A nonredundant SCG is hot-pluggable. For redundant SCGs, the master SCG is hot-pluggable. The backup SCG is hot-removable and hot-insertable if the master SCG is functioning. Removing the backup SCG does not affect the functioning of the router. Taking the master SCG offline might result in a brief loss of SONET clock lock while the backup SCG becomes the master.
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.
- 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 supported for Junos OS Release 10.2 and later.
- Three LEDs—OK, FAIL, and MASTER, located on the SCG faceplate, that display the status of the SCG.
