[Asterisk-Users] 5ESS central office question

[Steve Underwood]

Rich Adamson wrote:

>>>Anyone have a practical experience/knowledge relative to why a 5ESS 
>>>central office switch would require a "w" in the Dial statement to 
>>>handle analog pstn-fxo calls? 
>>>
>>>I fully understand what "w" is doing, just trying to better understand 
>>>why a 5ESS doesn't accept dtmf a little quicker then it does. Does
>>>that switch make use of dtmf receiver cards (or something) that
>>>might involve a delay in attaching it to an analog pstn line?
>>>
>>>Rich
>>> 
>>>
>>>      
>>>
>>It depends, and I am not familar with specifics of the 5ESS, but.....
>>
>>Older digital exchanges generally used shared resources for DTMF 
>>detection. Later ones tend to use something in the line card chip set 
>>for DTMF detection. When I say older and newer I mean of old or new 
>>manufacture rather than model. Exchanges change enormously in their 
>>implementation during the overall design's lifetime.
>>
>>Usually when you pick up a phone there will be a short delay before 
>>dialtone appears. Generally it is only 100-200ms, so you don't really 
>>notice it. In general, the DTMF detector will not be functioning until 
>>that tone is playing. However, even if the tone appeared in the first 
>>millisecond, the DTMF receiver tends to be paralysed for a little while 
>>by the loop current sloshing around and settling down. 100-200ms should 
>>see that fairly well settled. So, one way or another you need at least 
>>100-200ms before the DTMF receiver can start detecting reliably. If the 
>>dial tone is a bit delayed it can be longer.
>>
>>Most modern modems explicitly listen for dialtone before dialing. Older 
>>ones don't, but delay their dialing for a second or so after appling the 
>>loop.
>>    
>>
>
>I was aware of that, but more interested in specifics involving the
>5ESS since it has been involved in two cases now that need the "w", and
>I'm not familiar with internal design of the 5ESS.
>  
>
What I described *will* be like the internals o a 5ESS. Either that or a 
5ESS is different from every other exchange of its generation. If you 
are on an old one, and DTMF is a shared resource, there may be 
occasional longish delays before DTMF is accepted. That is probably what 
people have experienced.

Regards,
Steve