Configuring a TDM clock source

Introduction to TDM clock source

When digital voice E1 interfaces perform time-division multiplexing (TDM) timeslot interchange, it is important for them to achieve clock synchronization to prevent frame slips and bit errors.

Depending on your configurations on E1 interfaces, the system adopts different clocking approaches. When there is a voice co-processing module (VCPM) on the main board, the clock distribution principle is as follows:

If the clock mode is set to line for all interfaces, the clock on the interface with the lowest number is adopted. If the interface goes down, the clock on the interface with the next lowest number is adopted.
If the clock mode is set to line primary for one interface, the clock on the interface is adopted. In one system, you can do this on only one interface.
If the line keyword is specified for one interface and the internal keyword for all others, the clock on the interface is adopted.
Generally, you cannot set the clock source for all interfaces in a system to internal. This is to prevent frame slips and bit errors. You can do this, however, if the remote E1 interfaces adopt the line clock source.

When there is no VCPM on the main board, the configuration of each MIM/FIC is independent, but the clock mode of only one interface can be set to line primary on a device.

Suppose that you remove the FIC on an interface whose clock mode is set to line primary without powering it off and that you set the clock mode to line primary for another interface. In this case, if you re-insert the FIC, the clock mode of the FIC is restored to internal, instead of remaining line primary. In this way, there is only one interface whose clock mode is set to line primary on a device. For example, after the FIC in slot 5 (interface 5/0) whose clock mode is set to line primary is removed without being powered off and the clock mode of interface 6/0 is set to line primary, the clock mode of interface 5/0 will be restored to internal, instead of being line primary, if the FIC is re-inserted.

NOTE:

The line clock source and internal clock source are referred to as slave and master clock modes in some features.

Configure a TDM clock source

To configure a TDM clock source for E1 interfaces:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter E1 interface view.	controller e1 slot-number	N/A
3. Configure a TDM clock source for the E1 interface.	tdm-clock { internal \| line [ primary ] }	Optional. By default, the TDM source clock for an E1POS interface is line TDM clock, and the TDM clock source for other E1 interfaces is the internal clock.

Step

Command

Remarks

1. Enter system view.

system-view

N/A

2. Enter E1 interface view.

controller e1 slot-number

N/A

3. Configure a TDM clock source for the E1 interface.

tdm-clock { internal | line [ primary ] }

Optional.

By default, the TDM source clock for an E1POS interface is line TDM clock, and the TDM clock source for other E1 interfaces is the internal clock.

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