Paradise P300 specifications For 1 Operation, Theory, Switching Philosophy

9 1 FOR 1 OPERATION

9.1THEORY

Any two Modem's will operate as a 1 FOR 1 redundant pair, with no other equipment except for a single interconnecting lead, two power splitter/combiners and cable forms to parallel up the interfaces of both units.

Both Modem's of the pair operate continuously, performing their function on the incoming data and IF signals, but only one Modem enables its output, and drives the signals towards the terrestrial device and towards the satellite. For P310 L-Band modems, by default the standby modem also disables and DC & 10MHz reference it might be feeding to a BUC/LNB `up the coax` (this can be changed, See “Relay Mode 4” in Appendix E: Customer Specific Features on page 201 for a description)

The diagram on the right illustrates the equivalence of a standard Modem and a 1 FOR 1 redundant pair. The pair of units, with suitable cables, may be used as a direct replacement for a single unit, with all connectors and pin assignments remaining the same. A particular advantage of this arrangement is that one unit of the pair may be replaced without interrupting traffic.

To enable the parallelling of all the interfaces the off line unit provides no terminating load so the correct impedance is maintained even when two are connected in parallel. All interfaces also have the facility to disable the outputs (either by making the outputs high impedance, or by relay switching), enabling one of a parallelled pair to drive the outputs without line contention.

DATA

DATA

'Y' CABLE DATA

DATA

MOD

DEMOD

MOD

DEMOD

P1391

DEMOD

MOD

EQUIVALENT 1:1 PAIR

TX IF

RX IF

TX IF

RX IF

RX IF

TX IF

PASSIVE

SPLITTER/ COMBINER

PASSIVE

SPLITTER/ COMBINER

RX IF

TX IF

In the event of a catastrophic failure, such as a power supply etc, the switching circuitry (which is distributed between the two units) will switch over to the operational unit. All interface cards guarantee not to increase the load on signal lines in the powered down condition, i.e. the pair will work (and switch over) successfully even if one unit fails totally.

9.2SWITCHING PHILOSOPHY

Both Modem's operate continuously, with each providing a regularly updated status to their half of the 1 FOR 1 control logic. There is no pre-assigned master and slave unit.

Changeovers are minimised, i.e. a unit taken off line due to a reported failure, will remain off line even if it returns to the OK state. If it does return to the OK state then it will act as the standby unit. The software provides the necessary delays of status to the control logic, to prevent unnecessary switching. There is no delay in the case of catastrophic failures, when the hardware performs the switching regardless of the software, and its associated built in delays. The 1 FOR 1 system has no `memory', i.e. a unit taken off line because of an indicated failure, will be put on line again if it now indicates OK, (but only if the on-line unit has now failed, otherwise it would be an unnecessary changeover).

P300H P300 Series Modem Installation and Operating Handbook Page 163