6.11 System

The System device with the name SYSTEM is present on every M&C/VLC server. It does not appear in the "vlc.setup" file, the server creates it automatically as a gateway to some of it's internal services. You mainly use the system device to tell the M&C/VLC server on which way and on which conditions the server shall send event messages to the event log.

To understand the parameters provided by the System device, it is necessary to know that the M&C/VLC server routes all faults and other messages through the so called "log-queue".

With a NMS/VLC network control system, all event messages are stored at a central place at the NMS. As the VLC usually has no permanent data link to the NMS, the log-queue holds the messages until a network link to the NMS is available and the queue gets flushed to the central event database.

The VLC is capable to dial to the NMS by itself. To limit the costs of the dial up connections, time delays may be specified to prevent the VLC from dialing with each message that occurs. If the log-queue gets flushed (which implies a dial-up from the VLC to the NMS) depends on the following. The queue gets flushed if:

• it contains at least one message of priority "ALARM", regardless of the age of the message.
• it contains at least one message of priority "FAULT" which is older than the parameter "fault delay".
• it contains at least one message of priority "INFO" which is older than the parameter "informational delay".
• the queue is full.
• a dial-up connection setup from NMS becomes on-line.

With a M&C system, the M&C computer itself provides the event database in most cases. The M&C server still routes the event messages through the log-queue, the timing parameter described above still apply, but they are set in a way that all messages go straight through into the event database.

Clock synchronisation

Another task of the SYSTEM device is to control the synchronization of the VLC's clock to the NMS time. This synchronization is essential for the link management as scheduled links are planned on the base of the NMS' clock but executed following the VLC's clock. The synchronization works as follows:

Each time, the NMS connects to a VLC, it sends the actual time to the VLC. The SYSTEM device compares the local time to the time received from the NMS and -- depending on the difference -- tunes the VLC's clock a little bit faster or slower. With VLCs being accessed at least once a month, this keeps the VLC's clock well in tune with the NMS without producing any leaps in the local time. This clock synchronization is made once when a VLC becomes 'on-line'.

If the clocks of NMS and VLC differ by more than 30 seconds, the SYSTEM device treas this as an error. It states a FAULT (it's icon at the user interface becomes red) and writes a message to the event log with a message text like:

Clock differs by 1523 secs from NMS time. Please reboot.

There may be several reasons for this fault:

• You have set the NMS clock manually, now each VLC states this fault until all VLCs are in tune again.
• The VLC was not accessed for a long time. A time drift of 15 secs / month is quite usual.
• The same applies if the VLC has been on-line for a very long time without interruption. As the clock synchronization only happens when the VLC becomes on-line, the clock will drift out of tune in this case.

When the SYSTEM device has recognized this fault, the VLC already is about to adjust the clock to the right time. It however cannot set the correct time immediately because the time leap could mess up the software's timeout recognition. The VLC smoothly tunes the clock with a maximum rate of 10 minutes per day. Hence, with relative small time differences you might ignore the fault, for larger differences a re-boot of the VLC will speed up this procedure, the correct time is set when the VLC starts (see section 'SYSTEM Device fault' below for details).

Device window pages

The following table shows which device window pages are available with this individual device type. Tool-bar functions not mentioned here are described at the general description of device windows .

• --- The parameters at this page define on which way event messages shall be sent to the event database.

  • NMSnetworkaddress --- Defines the host name / IP address of the NMS / event database server.

    • If you are configuring a VLC and this unit is connected to the NMS via Ethernet or a permanent SCC link, enter the IP address of the NMS.
    • For a VLC exclusively using dial up connections to the NMS enter the word "offline".
    • For M&C computers enter "localhost" or "127.0.0.1".

  • dial command 1 dial command 2 dial command 3 --- For a VLC you can specify up to three dial commands (AT.. command sequences) the VLC shall use to connect to the NMS. The VLC always tries dial command 1 first, if this fails it tries the second one an so on. You must enter the complete modem AT command, not only the phone number. This lets you prepend some additional commands like "X3" or some switches in front of the "D" command.With a M&C system or a VLC which communicates to NMS via Ethernet, let all three dial commands empty. This prevents the machine from doing any dial attempts.

• --- Contains the size and timing parameter of the log queue.

  • size --- The number of event messages the queue can hold. If the queue is full, the last (youngest) message in the queue gets replaced by a overflow message and all further messages are discarded.
  • fault delay --- The time delay for FAULT messages. With a M&C system, you should set this value to 0.
  • informational --- The time delay for INFO messages. With a M&C system, you should set this value to 0.
  • redial delay --- Defines the pause between two dialing attempts a VLC makes. This should be set to about 5 minutes, some modems decline more frequent dialing commands to the same phone number.

• --- Contains the macro backup function which permits to store all parameter settings known to the M&C/VLC into a macro definition for later retrieval.

• --- The device info page. You see the software revision number/date of the M&C/VLC server at this place

SYSTEM Device Fault

If the SYSTEM device states a fault, this indicates that the clocks of NMS and VLC are not in tune. The VLC will correct the clock difference automatically after some time, but actually any scheduled links from this VLC will start or stop at the wrong time.

If the time difference is relative small you may ignore the fault. The time difference is stated in the event log, search for the VLC ID and the text 'Clock differs'. Clicking the 'RESET' button on 'Maintenance' page of the device window will reset the fault until the VLC goes on-line the next time.

If the time difference is larger or if you need the clock to be set precisely at once, you may re-boot the VLC. This means to restart the VLC's operating system, not only to restart the VLC application. The procedure for this is as follows:

1. Establish an on-line connection to the VLC.
2. Open a telnet window to the VLC (Depending on your network settings, this might require that you are working directly at the NMS server).
3. Log in as user 'satnms' (password 'satnms').
4. Enter 'su', enter the password 'root' when prompted.
5. Enter 'reboot'.

The connection to the VLC will break after this, about 3 minutes later the VLC will be accessible again with the clock set properly.

Remarks

• When setting up a M&C system, ensure that "localhost" is set as the NMS network address and both delays for FAULT and INFO messages are set to 0. You will see the event messages delayed or event not at all in the event log if you leave these parameters unconfigured.
• VLC may be configured to talk to the NMS using a permanent network link and a dial up connection as a fall back. You might use this constellation with an SCC connection. If the satellite link fails, the VLC tries to use the terrestrial phone line to send it's fault messages.
• Setting the "fault delay" and "informational delay" parameters for a VLC which uses a dial-up connection to the NMS always is a compromise. If you are small values, you get informed earlier about malfunctions in the VLC, but there will be higher connection costs.

Variables defined by this device driver