Datum Systems PSM-500, Инструкция по установке и эксплуатации

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PSM-500/500L/500LT SCPC Satellite Modem Operation
PSM-500/500L/500LT - Rev. 0.91
Page 3-37
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Advantage – The second or current back-up unit can be sent its full configuration from
the on-line unit, making set-up extremely easy.
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Advantage – Since the units are fully programmable concerning alarm content that
determines the switching criteria, this method is more flexible than most redundancy
schemes.
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Advantage – The single point failure of the switch in a classic 1:1 redundancy scheme is
eliminated. Since these switches are often mechanical relays they actually have a poor
failure rate, reliability (with respect to a classic scheme) is not seriously compromised.
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Disadvantage – There is no separate physical switch which provides a positive lock-out
of a seriously failed unit that may not be able to turn its output signals off.
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Disadvantage – There is no single point control allowing forced switching away from one
unit. Forced switching is accomplished only “from” the currently on-line unit.
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Disadvantage – There is no mode forcing a priority unit. In a priority system one unit is
considered primary and the other secondary. If both units show good status the primary
is always on-line. But, the priority scheme would also create more switching and is not
normally used anyway.
Of course the major advantage to the built-in redundancy capability is its extreme low cost.
3.10.1 Setting Up 1:1 Redundancy Mode
Redundancy mode between a pair of modems is normally accomplished during installation. The
procedure outlined here provides that information again, but also additional information on
options and parameters used to determine operating modes. In overview the procedure is to:
Note: The two modems MUST be the same model number and type, and should be at the same
firmware revision for proper redundant operation.
1. Configure the first modem completely for the intended operating parameters,
including setting the redundancy parameter to “1:1”. This initial unit should not be in
alarm.
2. Physically install the second unit to be paired, but with its power off.
3. Connect the IF and data cables to both units. The special data “Y” cable is connected
between the redundant pair.
4. Turn the secondary unit on.
5. Go to the menu in the <Unit: Redundancy – Config> and press the “Edit” key. The
on-line unit will ask permission to transfer configuration to the second unit. Confirm
by pressing “Enter”. The primary unit should say “Sending Config” for approximately
1 second. If any packet transferred results in an error message a “Send Fail”
message will be displayed, but the remainder of the transfer will continue.
6. Verify that the units are functioning correctly in redundancy mode. Go to the <Unit:
Status – Redundancy> item in both units. The on-line unit will say “On-Line, Bckup
OK” while the off-line unit will say “Standby, OK”.
Tear-down or un-pairing of two units is accomplished by turning both units off before removing
the “Y” cable. Then turn the units back on and set the redundancy to “Disabled”
Two parameters are added to the unit redundancy menu when redundancy is enabled:
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<Unit: Redundncy – Sw Rqst> This parameter allows you to determine which alarm
indications result in a switch request. The possible selections are “On Any Alarm”, “On
Alarm A”, “On Alarm B”, or “On Alarm A & B”. Since the specific alarms which comprise
Alarm A and Alarm B are programmable themselves, then a switch request is highly