[asterisk-users] Clocking Multiple T1 Cards

[Steve Underwood]

Andrew Kohlsmith wrote:

>On Monday 24 July 2006 12:11, Shaw Terwilliger wrote:
>  
>
>>Thank you; this is the kind of information I was looking for.  The wiki
>>and other documents told me exactly what the configuration options did,
>>but I didn't know what kind of timing configuration was right for
>>multiple cards.
>>    
>>
>
>Essentially the timing is ONLY for the hardware on the card.  The Digium cards 
>use a quad framer chip (maybe a dual for the TE210 but I don't think so) and 
>it's a hardware limitation of the framer that all spans must share the same 
>clock source.  Sangoma's cards use individual framers and don't have this 
>limitation.  (essentially I think it was a cost/space tradeoff.)
>
>Once the data is on the PCI bus, the clock source is irrelevant.  They're all 
>close enough that it doesn't matter anymore.
>
This statement is very very wrong. The timing matters enormously. If the 
timing doesn't match, there will be frame slips, and things like modems 
will not work. The snag is, right now neither Asterisk or the cards it 
uses have the ability to lock their clocks together.

>  Those framers want exact 
>lock-step timing though, which is why your clocking settings are so very 
>important, and why with telephony in general it is crucial to think about 
>your clocking before throwing hardware at a solution.
>  
>
Steve