Reference10:Interfaces/FXS/Advanced

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There are also other versions of this article available: Reference10 (this version) | Reference11r2 | Reference12r1

The advanced settings of the analogue interfaces can be made here:

Optimization grade: As per default the TEL ports are optimized for low power consumption (Optimization 'high' and 'mid'). This decreases the usual on-hook supply voltage of 48V down to 24V. Most conventional phones and faxes can deal with this. In case a special phone is connected that cannot deal with this low voltage or if a long cable is used this dropdown can be modified.
'high' and 'mid' both set 24V on-hook voltage. The off-hook loop current is set to 20mA.
'low' sets 48V on-hook-voltage.
Ringing Voltage This topic modifies the ringing voltage used for ringing. Ringing frequency is 25Hz.
'low' sets 65Vpk/45Vrms, 'mid' sets 68Vpk/48Vrms and 'high' sets 70Vpk/49,5Vrms AC.
Loop length present on ip28 gateways only

Loop length can be set to 'low' for 500ft/155m or 'high' for 5000ft/1550m. Checking this topic to 'high' decreases ring-trip threshold by 20% so that off-hook detection becomes more sensitive.

RingTrip Threshold present on ip22/24/302/305 gateways only

Ring-Trip threshold can be adjusted using an absolute value in milliamperes.

Loop Current Loop current can be adjusted using an absolute value in milliamperes.

Note: there is no difference between PoE and PSU powering of the IP2x.

For possible line lengths, see Maximum wire length.

Recommendation for Use with long Wire Length

For best performance with long wires, use the following settings:

  • Optimization grade low
  • Ringing Voltage 49.5 Vrms (high)
  • Loop length 1550 m

The setting for Loop Current depends on the terminal requirements, not wire length.