[Asterisk-Users] which TDM to use? DID line from telco with no dial tone and no voltage

[Steve Underwood]

Hi Patrick,

 From memory (I haven't lived in the UK for 11 years) the electrical 
characteristics are pretty much the same: -48V, 35mA loop current, 
600ohm complex impedance. One key difference is an extension needs to 
ring, but a DDI line does not. The different cards you see used may be 
because the DDI port has no ringer, or it may be a marketecture issue - 
they can probably squeeze more money out of the customers for the DDI 
ports. If they get full approvals only on the DDI card, then only a 
pricy DDI card can be used to attach to the DDI lines.

Regards,
Steve

hkirrc.patrick wrote:

> Hello Steve,
>
> You are exactly right about the DDI line and thank you for clearing up 
> the 600 ohm loop.
>
> Can you tell me other electrical details?  It's just that all the 
> PBXes (that I know)  uses
> different cards for DDI lines and analog extension lines and since the 
> CO normally or at
> least, expected to be much further away than an extension phone, I was 
> wondering if  there's
> a difference in the electrical requirment.
>
> thanks again,
> patrick
>
>
> Steve Underwood wrote:
>
>> Hi Patrick,
>>
>> You are in the UK, right (at least DDI strongly suggests that)? This 
>> is the commonest signalling for a DDI line on an analogue pair. The 
>> line is behaving just like the main exchange is a telephone. It picks 
>> up the line, by applying a 600ohm loop, and dials (with pulses per 
>> second or DTMF)  into your PBX. Your PBX port is behaving like it is 
>> a public exchange, with a phone attached.
>>
>> Electrically, Digium's FXS card should do the job you need, but 
>> others will have to tell you whether * has the software features 
>> needed to make this work (it should certainly be pretty close).
>>
>> Regards,
>> Steve
>>
>>
>> hkirrc.patrick wrote:
>>
>>> as my first project with *, i would like to replace our old 
>>> neax2400(sds) with an * server.
>>> i've got an X100p and a TDM400 on hand already.
>>>
>>> for the CO lines, the X100p works ok with fxsks signaling though 
>>> there are still strange
>>> things happening every now and again but more testing is on the way.
>>>
>>> my real big problem is the DID lines which our telcos call DDI lines;
>>> (incoming calls only)
>>> i disconnected a running DID line from our PBX and did a bunch of
>>> tests on it and found the following:
>>>
>>> * line from telco has NO voltage
>>>
>>> * the port from pbx is supplying the power(voltage) but no dial tone
>>>
>>> *the moment i disconnected the DID line from the PBX port,
>>> an alarm is triggered at the telco CO
>>>
>>> * i can attach an ordinary analog phone to the PBX PORT, pick up the 
>>> handset and
>>>  send (dial) 4 dtmf digits (being the last 4 digits of our DID number),
>>>  the PBX  will bridge me to the appropriate extension phone.
>>>
>>> * if or when the extension phone picks up, the PBX reverses the 
>>> polarity on the line
>>>
>>> what type of signaling should i be using for such a line?
>>>
>>> many thanks in advance,
>>> patrick
>>