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4.6 Clock Configuration

The boards in an MVIP system are synchronized via clocks. Each device may use its own oscillator or may synchronize to clocks that are provided by the telephone network or by other devices in the system. Some boards have secondary clocks that are used if the primary clock fails. These secondary clocks are synchronized via the network or by other devices in the system.

The CT Access Switching service provides functions to allow you to control the clocks on the underlying MVIP switching device. It provides functions for configuring the

The following table lists when to use the clock configuration functions available in the CT Access Switching service:
If you want to...

 Then use this function...

Establish the clocking mode of an MVIP board

 swiConfigBoardClock

Configure the source of the secondary 8 KHz clock on the board

 swiConfigSec8KClock

Define the source of the 8KHz reference signal on a board that conforms to the MC1 standard

 swiConfig8KRefClock

Presented here are two examples of clock configuration. The first example uses swiConfigBoardClock and swiConfigSec8KClock on AG-T1 boards. The second example uses swiConfigBoardClock and swiConfig8KRefClock on MC1 boards.

4.6.1 MVIP Clock Configuration Example

Scenario

There are two AG-T1s in the system. The first AG-T1 is the MVIP master which drives the MVIP clock from the PSTN network connection. The second AG-T1 drives the SEC8K signal from the PSTN network connection in case the first
AG-T1 loses its network connection.

If the first AG-T1, which is the MVIP master, loses its network connection, software must intervene to choose SEC8K as its clock source for the first AG-T1. The second AG-T1 synchronizes off the MVIP clock being driven by the first AG-T1.

This example

  1. Configures the board clock of the first AG-T1 to synchronize to the PSTN clocks and become the MVIP master.

    

  2. Configures the board clock of the second AG-T1 to synchronize off the MVIP clock.
    

    

  3. Configures the second AG-T1 to drive the SEC8K signal on the MVIP bus from its PSTN connection.
    

    

  4. Explains what to do if the first AG-T1 loses its PSTN connection. Configure the board clock of the first AG-T1 to synchronize to the SEC8K signal on the MVIP bus (being driven by the second AG-T1 from its PSTN connection).
    




Hardware



For purposes of this example, the hardware is 2 AG-T1 boards with independent connections to the PSTN.



Program



1. Configure the board clock of the first AG-T1 to synchronize to the PSTN clocks and become the MVIP clock master.


 SWI_CLOCK_ARGS boardclock;

    /* Make first AG-T1 sync off the PSTN digital trunk 1 */
    boardclock.size = sizeof(SWI_CLOCK_ARGS);
    boardclock.clocktype = MVIP95_STD_CLOCKING;
    boardclock.clocksource = MVIP95_SOURCE_NETWORK;
    boardclock.network = 1;

    swiConfigBoardClock(firstt1, &boardclock);



2. Configure the board clock of the second AG-T1 to synchronize off the MVIP clock.


 /* Make second AG-T1 sync off MVIP bus clock being driven by first AG-T1 */
    boardclock.size = sizeof(SWI_CLOCK_ARGS);
    boardclock.clocktype = MVIP95_STD_CLOCKING;
    boardclock.clocksource = MVIP95_SOURCE_MVIP;
    boardclock.network = 0;

    swiConfigBoardClock(secondt1, &boardclock);



3. Configure the second AG-T1 to drive the SEC8K signal on the MVIP bus from its PSTN connection.


 /* Make second AG-T1's network 1 provide the source of the Sec8K signal */
    swiConfigSec8KClock(secondt1, MVIP95_SOURCE_NETWORK, 1);



This is the state of the clocks after you have configured the two AG-T1 boards and the SEC8K signal on the MVIP bus.






Figure 36.	 State of the Clocks After the First Trunk Failure




4. If the first AG-T1 loses its PSTN connection, configure its board clock to synchronize to the SEC8K signal on the MVIP bus (being driven by the second AG-T1 from its PSTN connection).


 
    /* Make AG-T1 sync off SEC8K */
    boardclock.size = sizeof(SWI_CLOCK_ARGS);
    boardclock.clocktype = MVIP95_STD_CLOCKING;
    boardclock.clocksource = MVIP95_SOURCE_SEC8K;

    swiConfigBoardClock(firstt1, &boardclock);



This is the state of the clocks after the first AG-T1 has been configured to synchronize to the SEC8K signal on the MVIP bus.






Figure 37.	 State of the Clocks






4.6.2	 MC1 Clock Configuration Example





There are three chassis in the system. Each chassis has an MC1 board. Two of the MC1 boards have an AG-T1 associated with them. The third MC1 board is the MC1 bus master and drives the MC1 Left clock. The AG-T1s drive the SEC8K signal on the MVIP bus from their independent PSTN network connections. One of the MC1 boards synchronizes to the SEC8K signal on the MVIP bus and drives the 8KREF signal on the MC1 bus. The third MC1 board which is the MC1 bus master synchronizes to the 8KREF signal.



This example


    


  1. Configures the MC1 board to drive the 8KREF signal on the MC1 bus from the SEC8K signal on the MVIP bus. (The SEC8K signal is being driven by the associated AG-T1 board from its PSTN connection).
    

    

  2. Explains what to do if the AG-T1 board (associated with the MC1 board that is driving the 8KREF signal on the MC1 bus) loses its PSTN connection. You would configure the MC1 board to no longer drive the 8KREF signal. You would also configure the other MC1 board that is associated with the other AG-T1 board to drive the 8KREF signal.
    




Example



1. Configure the MC1 board to drive the 8KREF signal on the MC1 bus from the SEC8K signal on the MVIP bus. (The SEC8K signal is being driven by the associated AG-T1 from its PSTN connection).


 void myMc1Initialize(SWIHD mc1hd)
{
    SWI_CLOCK_ARGS boardclock;

    /*
    * Make MC1 board be a slave, with clock source coming from the left,
    * and make it fall back to right clock if it loses the left clock.
    * Also, make this MC1 board drive the 8KREF signal on the MC1 bus that
    * the MC1 primary master will sync to.
    */

    boardclock.size = sizeof(SWI_CLOCK_ARGS);
    boardclock.clocktype = MVIP95_MC1_CLOCKING;
    boardclock.clocksource = MVIP95_SOURCE_MC1_LEFT;
    boardclock.network = 0;
    boardclock.ext.mc1.mc1clockmode = MVIP95_MC1_SLAVE;
    boardclock.ext.mc1.autofallback = MVIP95_MC1_ENABLE_AUTO_FB;
    swiConfigBoardClock(mc1hd, &boardclock);

    /* Make MC1 8KREF come off SEC8K on MVIP bus */
    swiConfig8KRefClock(mc1hd, MVIP95_SOURCE_SEC8K, 0);
}



This is the state of the system after you have configured one MC1 board to drive the 8KREF signal on the MC1 bus.






Figure 38.	 State of the System




2. If the AG-T1 (associated with the MC1 that is driving the 8KREF signal on the MC1 bus) loses its PSTN connection, configure the MC1 board to no longer drive the 8KREF signal. Instead, configure the other MC1 board that is associated with the other AG-T1 to drive the 8KREF signal.


 /* Disable first MC1 from driving the 8KREF signal on the MC1 bus */
swiConfig8KRefClock(mc1hd1, MVIP95_SOURCE_DISABLE, 0);


 /* Make second MC1 drive the 8KREF signal from SEC8K signal on the MVIP bus */
swiConfig8KRefClock(mc1hd2, MVIP95_SOURCE_SEC8K, 0);



This is the state of the system after the first AG-T1 has lost its PSTN connection and you have configured the other MC1 board to drive the 8KREF signal on the MC1 bus.






Figure 39.	 State of the System








 
    (Page 7 of 11 in this chapter)









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