Understanding the SCG

Purpose

You monitor the SCGs to ensure that they provide a clock signal for the SONET/SDH interfaces on the router and that they select a clock signal from any FPC, or from the external clock inputs.

What Is an SCG

The SCGs provide a 19.44-MHz Stratum 3 clock signal for the SONET/SDH interfaces on the router. The SCGs can also select a clock signal from any FPC, or from the external clock inputs (see Figure 131).

Figure 131: SCG Component

Two SCGs are installed in the T320 router and the T640 routing node. The SCGs install into the upper rear of the chassis in the slots labeled SCG0 and SCG1.

If both SCGs are installed and functioning normally, SCG0 is master and SCG1 is backup. Removing the backup SCG does not affect the functioning of the router or routing node. Taking the master SCG offline might result in a brief loss of SONET clock lock while the backup SCG becomes master.

The SCGs are hot-pluggable.

Figure 132 shows the location of the SCGs on the T320 router and T640 routing node.

Figure 132: T320 Router and T640 Routing Node SCG Location