Interface and Router Clock Sources Overview

Interface and Router Clock Sources Description

When configuring the router, you can configure the transmit clock on each interface; the transmit clock aligns each outgoing packet transmitted over the router’s interfaces. For both the router and interfaces, the clock source can be the router’s internal Stratum 3 clock, which resides on the control board, or an external clock that is received from the interface you are configuring. For example, interface A can transmit on interface A’s received clock (external, loop timing) or the Stratum 3 clock (internal, line timing). Interface A cannot use a clock from any other source.

By default, each interface uses the router’s internal Stratum 3 clock. To configure the clock source of each interface, include the clocking statement at the [edit interfaces interface-name] hierarchy level:

[edit interfaces interface-name]
clocking (internal | external);

System reference clocks can be generated from different system components, depending on the router type. For example, Figure 1 illustrates the different clock sources on the M120 router.

Figure 1: M120 Router Clock Sources

Configuring an External Synchronization Interface

The M40e, M120, M320, T640, and T1600 routers support an external synchronization interface that can be configured to synchronize the internal Stratum 3 clock to an external source, and then synchronize the chassis interface clock to the external source.

This feature can be configured for external primary and secondary interfaces that use Building Integrated Timing System (BITS) or SDH Equipment Timing Source (SETS) timing sources. When internal timing is set for SONET/SDH, Plesiochronous Digital Hierarchy (PDH), and digital hierarchy (DS1) interfaces on the Physical Interface Cards (PICs), the transmit clock of the interface is synchronized to BITS/SETS timing and traceable to timing within the network.

To configure external synchronization on M40e, M120, M320, T640, and T1600 routers, include the synchronization statement at the [edit chassis] hierarchy level.

For more information about the external synchronization interface, see Configuring Junos OS to Support an External Clock Synchronization Interface for M Series, MX Series, and T Series Routers.