The midplane is located in the center of the chassis and forms the rear of the FPC card cage (see Figure 1). The FPCs install into the midplane from the front of the chassis, and the FEBs, Routing Engines, power supplies, and CBs install into the midplane from the rear of the chassis. The power supplies and cooling system components also connect to the midplane.
The midplane performs the following major functions:
Figure 1: M120 Midplane

For chassis serial number information , see Displaying M120 Router Components and Serial Numbers.