This section describes the options and procedures for setting up the clocking on a VISM-equipped MGX 8850 shelf.
VISM Clocking Options
VISM cards and MGX 8850 PXM cards each provide multiple clocking options. To avoid conflicts and to ensure proper operation, it is important that the settings for clocking options in both card types be considered together.
An overriding principle is that an MGX 8850 shelf consisting of PXM and VISM cards should have one and only one primary clocking source.
A second principle is that at the VISM/MGX 8850 PXM interface there are two options:
The MGX 8850 PXM card provides clock for all the VISM cards in the shelf.
One of the VISM cards on the shelf provides clock for the PXM (and hence the remainder of the shelf).
The user must choose one of these options.
Using the first option, in which the clock source originates at the PXM side of the VISM/PXM interface, the source stems from one of the following:
An external BITS clock on the PXM's T1 or E1 backcard port
An external OC3 signal on a PXM SONET backcard port
The PXM's internal crystal
The internal crystal is the default and is automatically set as the primary clock source at power-on. The user can use one of the other two clock sources by executing the cnfclksrc (configure clock source) command.
Also, in this situation, the PXM becomes the clock source for the entire shelf. As such, it uses its clock source to provide clocking for all the VISM cards in the shelf. The VISM cards, in turn, use this clock to provide clocking for their T1 or E1 lines. In order for this situation to operate correctly, all the VISM lines must be configured for local clocking using the cnfln (configure line) command.
Moving on to the second option, the clock source originates on the VISM side of the VISM/PXM interface. It stems from one of the T1 or E1 lines on one of the VISM cards (the line receiving the clock signal on the selected VISM card must be line number 1). The line number 1 that is receiving the clock source must be configured for loop clocking using the cnfln command. All the remaining T1 or E1 lines on all the VISM cards in the shelf must be configured for local clocking.
Also, in this situation, the VISM becomes the clock source for the PXM and hence the entire shelf, including the remaining VISM cards. In order for this situation to operate correctly, the PXM must be configured for a service module as the clocking source with the selected VISM and its clock line specified in the cnfclksrc command.
Follow these steps to set up clocking on a VISM-equipped MGX 8850 shelf:
Examine the entire configuration of the MGX 8850 shelf and determine the single clock source. The type of equipment connected to the VISM's T1 or E1 lines might dictate this choice. If the selected clock source is from one of the VISM's T1 or E1 lines, that line must be connected to the physical port 1 on the VISM backcard.
Configure the clocking option on the PXM card using the cnfclksrc command:
cnfclksrc <slot.port> <clktype>
The slot.port parameter specifies the clock source. The clktype parameter is either p for primary, s for secondary, or null for no external clock source. The following configurations show the criteria used to specify these parameters:
Configure the clocking option on the VISM card(s) using the cnfln command:
cnfln <line_num> <line_code> <line_len> <clk_src> <line_type> <loopback_detection>
You have successfully set up clocking on a VISM-equipped MGX 8850 shelf.