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Operation
programmable itself. For most applications though the default "On Any Alarm" is a
preferred selection.
•
<Unit: Redundncy – Sw Hold> This parameter determines how long an alarm must
exist on the on-line unit and not the off-line unit before switching will occur. Allowable
values are 0.0 to 600.0 seconds. The value could be set to zero, but this is not advised. A
nominal value of 0.5 seconds insures that intermittent cases do not cause undue
switching. A built in factor of 10 seconds is provided once a switch has occurred before a
switch back to the original unit is allowed (except in the case of a manual switch request
or loss of power in the on-line unit which requires 2 seconds).
The possible case can arise when both units go out of alarm at virtually the same time. This might
occur if both units are powered on simultaneously or the receive carrier appears after being off or
a necessary clock signal is applied to both units. In such tie cases, which unit will be placed on
line is determined by the unit serial numbers, where the highest serial number wins the tie.
3.10.2 Operating 1:1 Redundancy Mode
Operation of a redundant pair of modems consists mainly of determining the status of units and
forcing transfer of operation from one unit to the other.
A quick status to determine which modem is currently on "On-Line" and the failure state of the
paired modems is done by viewing the LED indicators on the front panels. In a fully operating set-
up there will be no alarms on either unit, but one modem will have the green Modulator Transmit
LED illuminated and the other will have the transmit LED extinguished. The other LED indicators
still show the relevant condition of the Modulator, Demodulator and Unit.
A more thorough status condition is viewed by setting both modems to the <Unit: Status –
Redundcy> parameter. The unit currently On-Line will present its status on the lower line of the
LCD display as "Online – xxxxx" where xxxxx could be one of several messages:
•
Bckup OK – This modem thinks that everything is fine.
•
BCKUP ALM – The backup modem is in an alarm state.
•
NO BCKUP – No backup modem was found via the aux communications channel.
•
The unit currently Off-Line will present its status on the lower line of the LCD display as
"Standby OK" or "OFFLINE – ALARM".
3.10.2.1 Forcing a Transfer Switch in 1:1 Redundancy Mode
The 1:1 "transfer" process of forcing the two paired modems to swap their on-line/off-line status is
a one step process. The procedure however can only be accomplished on the unit that is
currently "On-Line".
•
On the currently "On-Line" unit go to the<Unit: Status – Redundcy> parameter and
press the "Edit" key.
•
The LCD display will present the message "Enter to Xsfer?". Pressing the "enter key will
cause the unit to go off-line and the currently "Off-Line" backup unit to go "On-Line".
If there is no backup unit or the backup unit is itself in alarm then the transfer will not be
completed and an error message is displayed.
Page 3-38
PSM-500/500L/500LT SCPC Satellite Modem
PSM-500/500L/500LT - Rev. 0.91
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