1.635 Site-Switch

The Site-Switch logical device implements a site diversity switch control. Mostly used to backup up-link facilities at different sites, the Site-Switch device may be configured to work in various environments.

The primary equipment normally used for the up-link is monitored by the Site-Switch device. If the primary equipment fails, the local up-link gets shut down and the spare transmission facility at the remote site gets switched on. The control of the spare equipment at the remote site is done by a Site-Switch device, too. The site to site communication between the Site-Switch devices is performed via a TCP/IP network connection. The flow of signal ON/OFF commands between the sites appear as red lines in the figure below.

Due to the symmetrical design of the Site-Switch a setup like shown in the figure above can be done. The spare equipment at site B backs up the transmission from site A an vice versa. In a simpler configuration the spare equipment at site A and the primary equipment at site B do not apply.

Beside monitoring the primary equipment faults, the Site-Switch device also monitors the state of the spare equipment (in an asymmetrical setup this applies only to the Site-Switch device at site B). If the spare equipment at the redundant site fails, this is reported to the primary site and prevents the Site-Switch device there from switching to remote. The figure above shows this information as blue lines.

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 main control page for the device. The operational parameters of the Site-Switch device are described below.
• --- The fault page:
  • Remote Connection : The TCP/IP connection to the remote site is broken.
  • Local spare equipment : The spare equipment at this location is not ready.
  • Remote spare equipment : The spare equipment at the remote site ist not ready.
  • Latched condition : A site switch already occurs.
• --- The device info page.
• --- The maintenance page. The configuration parameters described later are set at this page.

Operational parameters

The operational parameters of the Site-Switch device are set at the main control page. The table below explains each parameter in particular.

• parameter --- description

• actual location --- This parameter shows if the up-link is done at this location (LOCAL) or at the backup site (REMOTE). A manual switch over between the sites may be done at any time by changing this value. Be aware, that a switch over causes a transmission outage for a couple of seconds.

• switchover mode --- The device knows three different operating modes.

  • MANUAL --- No monitoring of primary equipment faults is done. The up-link location changes only on operator request.
  • 1-SHOT --- While the actual location is "LOCAL", the device monitors the primary equipment faults. If a fault is recognized, it switches over to "REMOTE" and reverts to MANUAL mode. Hence, after a switchover occurred the up-link location remains at the backup site until an operator changes this.
  • AUTOMATIC --- In AUTOMATIC mode, the device performs site switches in both directions. If the local equipment fails, it switches to remote. If the equipment is OK again, the up-link is switched back to the primary site. You should consider that this operating mode may cause the system to "oscillate", i.e. permanent site switches from A to B and back again may occur.

• switch delay --- Faults detected at the local (primary) equipment must continuously be present for the time defined with this parameter in order to trigger switchover. Set this time to prevent the Site-Switch from reporting to momentary faults

• recovery delay --- In AUTOMATIC mode, this parameter defines the time, the local (primary) equipment continuously must be OK until the Site-Switch initiates a switch back to the primary site. Setting this time to a larger value reduces the risk that the site switching oscillates.

Configuration parameters

At the maintenance page of the device window there are a couple of configuration parameter which must be set to interconnect the Site-Switch device with the device id shall monitor/control.

Remarks

• The Site-Switch devices require a permanent network connection between the two sites. They are sensing the presence of this connection with a cyclic "ping" and will report a fault if the network link is down. If you are using an "on demand" dial-up link between the M&C computers, the ping probably will keep the link alive all the time.
• The Site-Switch provides a special fault flag called "Latched condition". This fault is set if the switch performs a switchover, it gets reset if the location is switched back manually . This is for use with the "1-SHOT" mode, the fault will tell the operator that a manual interaction is required. You may set the priority of this fault to "OFF" of you don't like the Site-Switch device to show a fault after a switchover occurred.
• If the simple OR relationship of the fault variables is not sufficient for your application, the Fault-Array logical device provides more sophisticated capabilities to link faults and other parameter values together. You may route a Fault-Array in between the fault sources and the Site-Switch device.
• A the output the Site-Switch may extended using a Switch-Cross-Link logical device. This device is capable in translating the ON/OFF command into waveguide switch settings, duplicating the commands to multiple devices or to adjust transmission levels as a result of the switchover.
• The delay times of the fault recognition are implemented by the background polling procedure which is called on a regular basis for all logical devices. With the factory preset settings, this procedure runs once a second. The resolution of the delay time is limited to this value.If your application needs a finer resolution, you may configure the polling procedures of all logical device to be called more frequently. This is done by configuring the IDLE parameter of the PORT null in the vlc.setup file. Be aware, that the workload of the M&C computer will rise dramatically if you set this parameter to very small values.

Variables defined by this device driver