Hi,
Each set of DSPs will have it's own clocking source. If all the DSPs are on the motherboards, such as PVDM2-X on an ISR like this, then they will all be on voice-card 0.
In this case the clocking source can either come from an external source (clock source line), or the gateway will create it's own internal clock and trust that.
For clock source internal there is no need to 'select' this clock because it is assumed.
For clock source line there are multiple possible clocking sources, because the router has no way of knowing whether or not all of the lines are on the same clocking domain. For this reason there is the 'network-clock-select' command. It will tell the router which of the external clocks to send over the backplane.
When your selected clock is active, this clock is sent over the backplane and the other DSPs will use this. If you're in a situation where you have multiple clocking domains, all the clocks that match the internal clock, which would be an external clock, will be fine. But the external clocks that do not match the selected clocks with probably have slips and errors.
If you're in a situation where there are mutliple clocks, the solution is to get something like an NM-HDV card where those DSPs would be able to provider a new clock on the 'backplane' of the card.
hth,
nick
