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• External Clock Interface Ports on the M120 Craft Interface    

• Related Topics
• RJ-45 Connector Pinouts for the M120 Routing Engine ETHERNET Port
• RJ-45 Connector Pinouts for the Routing Engine AUX and CONSOLE Ports
• RJ-45 Connector Pinouts for the External Clock Ports

External Clock Interface Ports on the M120 Craft Interface

Two external clock ports EXT CLOCK to the right of the craft interface alarm LEDs enable you to connect the router’s internal Stratum 3 clock to an external reference clock source with an RJ-45 cable. Using the router’s software, you can configure the internal Stratum 3 clock to synchronize with an external Building Integrated Timing System (BITS) or SDH Equipment Timing Source (SETS) timing source by including a clock synchronization statement at the [edit chassis] hierarchy level. Refer to the System Basics and to the System Basics Command Reference for configuration information.

The EXT CLOCK ports are labeled A and B. They accept two RJ-45 connectors for external clock inputs with T1 or E1 reference clocks.

Two bi-color LEDs in the lower left and right corners of each port indicate port status. The LED on the lower left as you face the craft interface indicates whether an external clock source is present. The LED on the lower right as you face the craft interface indicates if there is a fault. Table 1 describes the external clock port LEDs,

Table 1: External Clock LEDs on the M120 Craft Interface

Label	Color	State	Description
A	Green	On steadily	External clock source is plugged into the port, physical signal is present.
	Not illuminated	Off	No external clock source is plugged into the port, no physical signal is present.
B (Fault LED)	Amber	On steadily	Fault condition; external reference clock frequency is out of the tolerance threshold deviation of 10 parts-per-million (PPM).
	Not illuminated	Off	External clock signal is validated or no external clock source is plugged into the port.