Honeywell HS-700 Description And Installation Manual page 31

SYSTEM DESCRIPTION AND INSTALLATION MANUAL
(3) Power Adjustment
(a) By design, the shared HPA assumes a constant input level. Subsequently, the
HSU has to adjust its carrier level when an event causes the SDU to change its
carrier level.
(b) The SDU is responsible for informing the HSU when adjustment is required and
what the new backoff will be relative to the initial power. The HSU applies the
new backoff immediately upon reception of the SDU message.
(4) Power Preemption
(a) There are conditions when the SDU needs to ask the HSU to release the power
that has been reserved for its use. For example, a cockpit/important cabin call
needs to be made and there is not enough power available for it without
sacrificing the HSU power, the antenna gain has fallen too low to support any
channel types, etc.
(b) The preempt type indicates power is no longer available and all the HSU can do
is terminate any ongoing transmission and inform any user that the service is no
longer available. When a preemption has taken place and the SDU is still
logged--on (e.g still steering the antenna), the HSU asks for power to be
reserved every 10 seconds.
(c) An SDU ORT item governs how the SDU will manage preemption of HSD calls
when Aero--H/H+ calls (new or ongoing) require power that would otherwise be
used by HSD calls. This item has no effect on the priority preemption scheme,
whereby higher priority safety--service Aero--H/H+ calls preempt lower--priority
calls (including HSD) as required. This ORT item has separate settings for ISDN
and for MPDS. These settings govern whether or not the respective HSD service
can be preempted, as required, in favor of non--safety (public correspondence)
low--priority Aero--H/H+ calls (voice, fax, or PC modem). This item can thus be
used to favor such Aero--H/H+ calls over HSD, or vice--versa. For example, the
SDu can be set to allow Aero--H/H+ calls to preempt (as necessary) MPDS HSD,
but not ISDN HSD, assuming that active phone calls are more important than the
always--on but possibly idle MPDS, and that active ISDN HSD is more important
than voice calls.
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HS--700 High Speed Data System
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30 Aug 2002