Clock Cable

Overview

The external clock ports of a switch are used for clock and time synchronization.

A clock cable connects a switch to an external clock source or a time source device.

When a switch connects to external devices through clock cables, it provides the following functions:

• Receives 2-channel 2.048 MHz or 2.048 Mbit/s clock signals from the upstream device and delivers 2-channel 2.048 MHz or 2.048 Mbit/s clock signals to the downstream device.
• Receives 2-channel ToD or DCLS time signals from the upstream device and delivers 2-channel ToD or DCLS time signals to the downstream device.

Appearance and Structure

RJ48 Cable

RJ48 cables applicable to the CE6875 switch are 120-ohm trunk cables (shielded cables), as shown in Figure 6-18.

Figure 6-18 Structure of a 120-ohm trunk cable

An RJ48 cable can connect a CE6875 switch to a clock source device with an RJ45 interface.

RJ45 Cable

RJ45 cables applicable to the CE6875 switch are straight-through cables (shielded cables), as shown in Figure 6-19.

Figure 6-19 Structure of a straight-through cable

An RJ45 cable can connect a CE6875 switch to a time source device with an RJ45 interface.

To connect a switch to a clock source that has a sub-miniature B (SMB) or bayonet-neill-concelman (BNC) interface, use an RJ45 cable and a transmultiplexer.

SMB/SMB Trunk Cable

An SMB/SMB trunk cable is a 75-ohm trunk cable with SMB connectors at both ends, as shown in Figure 6-20.

Figure 6-20 SMB/SMB trunk cable

SMB/BNC Trunk Cable

An SMB/BNC trunk cable is a 75-ohm trunk cable with an SMB connector and a BNC connector, as shown in Figure 6-21.

Figure 6-21 SMB/BNC trunk cable

Connection

One end of the clock cable is the RJ45 connector, which is connected to the BITS port on a CE6875 switch. The other end of the clock cable is connected to an external clock device. The connector type depends on the type of the external clock device. The external clock device can be a clock source that has an SMB, BNC, or RJ45 interface or a time source providing an RJ45 interface.

Figure 6-22 Clock cable connections

Based on the functions and interface types of the external clock device connected to the 6875 switch, the following cables can be selected:

• When the connected device is a clock source with an RJ45 interface:

  Cable 1 can be an RJ48 cable. No transmultiplexer or cable 2 is required.

• When the connected device is a time source with an RJ45 interface:

  Cable 1 can be an RJ45 cable. No transmultiplexer or cable 2 is required.

• When the connected device is a clock source with an SMB interface:

  Cable 1 can be an RJ45 cable, and cable 2 can be an SMB/SMB trunk cable. A transmultiplexer is required.

• When the connected device is a clock source with a BNC interface:

  Cable 1 can be an RJ45 cable, and cable 2 can be an SMB/BNC trunk cable. A transmultiplexer is required.