[Asterisk-Users] Outbound dialing issue with FXO

[John Novack]

Rich Adamson wrote:

>>>>However, outbound calls are hit or miss. Sometimes they work fine and other times we get a "you must first dial a 1 or 0" message back from telco when dialing out standard POTS lines.
>>>>        
>>>>
>>>Did you get this working yet?
>>>
>>>
>>>      
>>>
>>Yes, it does seem to be working fine now by adding the "w"s to the  dialstring.
>>    
>>
>
>The following is intended to provide a little bit of info as to why
>the "w" is needed when dialing via some central offices (pstn fxo's).
>
>Several telephone companies still have older electro-mechanical central office switches. 
>
Perhaps, bu AFAIK, there are NONE left in North America, certainly none 
left in the US or Canada.

>The majority of these older switches have a bank of "dtmf receivers" that are shared across all pstn lines, and are only
>attached to each pstn line during the initial few seconds of a pstn
>call. 
>
Crossbar systems. Step by step systems converted to DTMF had DTMF to 
pulse dedicated to each linefinder.

>(There might be 20 or 30 receivers for a central office switch
>that supports 5,000 pstn lines.)
>
>When asterisk seizes the pstn line (goes off-hook), dial tone is 
>usually provided within a second or two. However, the dtmf receiver
>may or may not be attached and ready to receive dtmf digits in that
>short period of time. 
>
Not so sure about that. IF dial tone is provided, the receiver is ready 
and waiting,

>(If the central office switch is slightly under-engneered,
>
OR overloaded,

> there could also be a shortage of dtmf receivers
>that _could_ result in a receiver not being attached to the pstn
>line within the first second or so.)
>
>  
>
None of this excuses the inability or unwillingness of Asterisk to 
listen for Dial Tone. The modem card used for single FXO (  the X100P 
and clones ) certainly had that ability in its former life as a modem.
Has this ever been reported as a bug?

Or would this be considered a "feature request" , along with detection 
of stutter dial tone on analog lines.

>One or more "w" in the dial string causes asterisk to delay sending
>the dtmf digits, compensating for the delayed attachment of the dtmf receiver in those central offices.
>
>  
>
It seems to be necessary in electronic offices as well, when dial tone 
is delayed.

John Novack