Reference13r2:Interfaces/FXS/Physical

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

Pulse:	A checked check box enables the recognition of pulse dialling on the relevant interface.
Pulse dial type:	Determines which digit is related to the number of received dial pulses. Normally this relation follows ETUT E:161 but there are country-specific exceptions : Normal ITUT E:161, 1 pulse is '1', ... 9 pulses is '9', 10 pulses is '0' This is the most common setting for all countries all over the world with only few exceptions. Swedish, 1 pulse is '0', ... 10 pulses is '9' This very uncommon relation is seen in sweden, but even there it is very uncommon. Newzealand, 1 pulse is '0', 2 pulses is '9', ... 10 pulses is '1' This relation is used in Newzealand.
Reverse:	A checked check box inverts the wiring of the relevant interface. This is only necessary in the event of incompatibility of the terminals, since some terminals (for example, in the US) are wired the opposite way.
Ring cadence and CLIP transmission sequence:	Set the interworking of CLIP and Ring cadence to different combinations. Possible options are : Normal cadence, CLIP transmission 200ms after first AC ring ended Typically internal and external calls use different cadence to give the user an audible hint of the orgin of a call. Normally the internal ringing cadence starts with two short ring pulses. But there is not enough time to place CLIP information between these two ring pulses, so CLIP transmission will be postponed after the second ring pulse. If this doesn't matter you can use this option. Short AC ring pulse of 160ms, 200ms pause, CLIP transmission, pause min. 800ms, normal cadence Some telephones can explicitly suppress the first ring just to receive and present CLIP before audible ringing (often called 1.st Ring OFF in menues). In this case the 'short AC ring' option is recommended, but not essential for correct working. But : There are also telephones that do not accept CLIP information after the second AC ring pulse, like happening within the 'Normal cadence' option. Here the 'short AC ring' option is mandatory to get CLIP working. Here it is guaranteed that CLIP is sent after exacly ONE AC ring. One known model of that kind is the T-COM Concept P412. Line polarity reversed, 200ms pause, CLIP transmission (duration depending on data amount), line polarity normal, 1000ms pause, normal cadence In some countries it is common that CLIP is preceded by a line polarity reversal instead of a AC ring pulse prior to CLIP transmission. In this case the 'Line polarity reversed' option must be chosen. This procedure is very common with CLIP using DTMF transmission and can be found in Sweden and other countries.
Ring cadence generation timing:	Normally internal and external calls are distinguished by terms of different rythms of the ringing voltage. Normally external calls use 1sec ringing voltage - 4sec pause. Internal calls normally use 375ms ringing voltage - 250ms pause - 375ms ringing voltage - 4sec pause. Select swiss to assign this rythms the opposite way. You can also select one rythm to be used permanently, no matter if the calls are external or internal.
Number of CLIPs:	You can change the number of CLIPs to be sent in AC ring pauses from 0 up to 5. 0 will completely suppress CLIP.
Receive gain:	Set the loudness a user receives at this interface. Default is -10dB for short lines and -7 dB for long lines.
Transmit gain:	Set the loudness a user transmits at this interface. Default is -3dB for short lines and 0 dB for long lines. Some fax devices may need a lower transmit level to avoid clipping.
Country:	Set the line impedance for different countries. In Europe CTR21 is used.
Metering pulse frequency:	possible values : 16kHz or 12kHz. 16kHz is common for most countries. Austria and Swiss use 12kHz.

Receive and transmit sides

FXS Gateway representing central office/PABX	::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::direction:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::	phone
PCM DAC	>>>>>>>>>>>>>>>>>>>>>>>>>>>>>----receive direction---->>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>	phone speakerphone
PCM ADC	<<<<<<<<<<<<<<<<<<<<<<<<<<<<<----transmit direction----<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<	phone microphone

Some considerations about Flash, R and Dial-pulses

The a/b ports support further signaling through Flash-key (other sources call it R-key, what means exactly the same) followed by DTMF-Key combinations. For example, pressing Flash while already having a peer connection will set the current connection into call-hold state (the peer side hears Music-On-Hold) and establish a new call.

From a technical point of view Flash is a short interruption in offhook loop-current. You can imagine Flash as a very short hook-on/hook-off event. The on-hook duration of a Flash event is normally between 100ms and 300ms. Shorter durations are regarded as dial-pulses (if enabled), longer durations are regarded as seperate hook-on and hook-off events. If you encounter difficulties regarding Flash, be sure you have configured a flash-time between 100ms and 300ms in your phone.

Dial-pulses are also short interruptions of the offhook loop-current and can also be imagined as short hook-on/hook-off events. The only difference to Flash is, Dial-pulses have a much shorter duration of 40ms to 80ms.
Several successive Dial-pulses form a digit of a number. The pulses of one digit are seperated by a pause of about 60-80ms. Different digits are seperated with pauses that are much longer (at least 80ms, but can be much more). The digit '1' consists of one single pulse, '2' is two successive pulses and so on, '0' is ten successive pulses.

Pinout of the a/b connector IP29-2, IP29-4, IP29-8

Pin	Function
3	TIP
4	RING

Pinout of the a/b connector IP29-20

Pin	Function
1	RING-2
2	TIP-2
3	RING-3
4	TIP-1
5	RING-1
6	TIP-3
7	RING-4
8	TIP-4

This pinout is especially designed for use with twisted-pair Ethernet patch cables