Video Transcript
Analog Telephony (Part 2)
7m 3s
00:07
Welcome back. Let’s talk specifically about POTS integration in Q-SYS.
00:12
QSC supports POTS telephony integration directly on the Q-SYS Core 110f processor (with a single line)
00:18
and the CTEL4 I/O card in configurable Q-SYS devices.
00:23
In Q-SYS Designer Software, there’s a POTS out block that represents the audio signal to the far end.
00:29
There’s a POTS in block that represents the audio signal received from the far end.
00:34
And of course, there’s the DTMF control section that allows user call control.
00:39
The first thing to do is to check the POTS line’s country of use in the Core’s properties,
00:45
particularly if you are not using it in the US, which is the default for Q-SYS.
00:50
The country setting tells Q-SYS the ring voltage,
00:53
the cadence and the other country-specific signals that are used in the call control.
00:59
You can also enable a second output of the POTS Receive block.
01:03
All receive audio will go through the original receive node,
01:06
while all received DTMF and call progress tones will be routed to the second one.
01:12
The POTS controller block is, of course, the same keypad we use on most phones and is relatively self-explanatory.
01:19
Next to the Dialer tab, there are two important tabs for configuration and troubleshooting.
01:24
The controller tab has several configuration options.
01:28
The buttons at the top determine how the system handles a far-end hang-up.
01:33
There are two options: Loop drop, which is the traditional method,
01:37
and call progress, which is used by some PBX systems.
01:41
By the way, there’s no harm in having both of these options enabled at the same time.
01:46
Next we have ‘hook flash time’.
01:48
If the hook flash is being used for any special features in an installation,
01:53
the timing may need to be adjusted here depending on the needs of the system interpreting it.
01:58
Dial tone gain simply sets the level of the dial tone on the room if the interface is taken off hook before dialing.
02:05
DTMF controls in the next section are not yet user-definable.
02:09
To avoid any hiccups caused by DTMF and call progress tones being sent back to the far end,
02:16
Q-SYS does NOT play these tones in the room.
02:19
In the next section, audio files can be specified to play back into the room when the respective call progress
02:26
or DTMF tones are present on the line.
02:29
Be warned that if a given call progress tone file is not enabled, specified or at the sufficient volume,
02:36
the user will not hear anything when that tone is heard by the interface.
02:41
This sometimes gets some users pretty angry
02:45
because they expect to hear those tone as feedback from their button pushes.
02:49
We try to explain it like this:
02:51
Let’s say I’m entering a conference code and the first number is ‘1’.
02:56
I hit the ‘1’ key, and the DTMF tone plays that overhead in the room.
03:01
The microphones hear that DTMF tone and then transmit it to the far end as well.
03:07
The conferencing bridge then hears two ‘1’s in the DTMF,
03:11
making it impossible to properly enter the conference code.
03:15
We want to avoid this frustration by playing a ‘neutral’ sound
03:19
that provides end user feedback but doesn’t confuse the conference bridge.
03:23
On the status tab we find troubleshooting and the state information of the interface.
03:28
The top three pieces of information are among the most important:
03:33
line voltage, line current and line fault.
03:37
Here’s a good one: If you see 47 volts and zero amps, what does that tell me?
03:44
The answer is: I know the interface is on-hook, because there is no loop current.
03:50
And there’s adequate voltage on the line and there’s no reported fault condition,
03:55
so I can assume that the line is good.
03:58
I also see the ‘line ready’ indicator lit below, which is also a good sign.
04:03
Below the status indicator LED,
04:05
you’ll find a readout to show whether any DTMF tones have been received by the interface.
04:11
Finally, Event Logging allows you to enable POTS logging in the Q-SYS eventlog for troubleshooting.
04:18
To outline the most common states on the telephone interface,
04:21
we’ll compare what we see in the status tab and the dialer at the same time.
04:26
When you have an on-hook with a ‘good’ line, you'll see line voltage is between 40-50v,
04:33
keeping in mind that polarity doesn’t matter and the line current should always be 0A.
04:39
You’ll see a lit line ready LED and the call progress in the dialer should read ‘Idle’ in this state.
04:46
When the interface goes off hook, line voltage drops as we start to see current measured on the line.
04:53
It is typical to see the voltage drop to between 6 and 10VDC. The current will typically be around 25mA.
05:02
When dial tone is present, the corresponding led will light up there, too.
05:06
Often times, you’ll see different transitional or progress states in the dialer call progress
05:12
depending on how fast the service provider reacts to the sensing of the line current.
05:17
Telephone lines use a feature called ‘line echo cancellation’
05:22
to make sure you only hear the far end audio when in call.
05:26
“Calibrating” means that this cancellation is being calibrated on the line.
05:30
‘Waiting for dialtone’ means just that – the calibration is finished and we’re waiting for the service provider to send the dialtone.
05:39
And finally the ‘ready’ status, which means we’re ready to dial.
05:42
The transition of these states to ‘Ready’ typically happens very quickly,
05:47
so there’s not a long wait for the user.
05:49
When the number is entered by the user and the process begins, you’ll see the ‘line in use’ stay lit.
05:56
The ‘dial in progress’ LED stays lit until the ringback tone is detected,
06:00
which means that you’ve gotten through to the far end.
06:03
The ‘ring(back) tone’ led will light for the duration of the ringback tone.
06:07
The dialer call progress field will go through the states we’ve already outlined.
06:12
It will display ‘Dialing’ the number we’re calling,
06:15
and then move to ‘Call Ringing’ and then finally to ‘Connected to’ when the far end answers.
06:22
Note that the ‘off hook’ LED on the dialer will light when the interface is taken off hook.
06:29
The ‘ringing’ LED, however, only lights up when there’s an incoming call.
06:34
The interface does not need to be taken off hook before the user enters the number.
06:38
The user can enter the number first and simply hit ‘connect’. The interface will go through the same states,
06:44
only a little faster than the manual dialing process.
06:47
Okeydokey, we’ve made it through the first few stages of connection.
06:52
When we start back up, we’ll start with what happens when we’re actually in a call, hangs up and incoming calls.
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Analog Telephony (Part 2)
7m 3s