[Asterisk-Users] Asterisk - fax - spandsp

[Steve Underwood]

It doesn't help at all, since you are talking rubbish. Try to keep track 
of the subject matter. We are discussing modems, where not slipping is 
vital.

Regards,
Steve

Rich Adamson wrote:

>It doesn't make any difference. The pcm data that arrives from the telco
>is buffered in the zaptel and/or asterisk code, and sent out the second
>T1 card as soon as it can. That buffering reduces (or eliminates) the
>need to sync one T1 card to another.  However, if the clock on the second 
>card were "way off" frequency, there could be a missed pcm frame from
>time to time. The missed frame would not even be noticed by users in
>most cases. (There was some discussion about how great of an impact
>that really has several months ago. Personal opinion plus experience 
>says its a non-issue other then on some very extreme cases where a clock
>is way off frequency. That tends not to happen with today's electronics.)
>If you think about the variable delays that occur because of contention
>for the pci bus, interrupt latency, etc, there are likely larger swings
>in dropped packets resulting from that then there would be from multiple
>T1 cards not having the exact same clock frequency.
>
>The bigger issue with multiple T1's occurs with the Quad T1 cards, where
>a single on-card clock is used with all four T1's. Syncing that clock
>"to the pstn" is the only correct way (timing=1), making all other 
>downstream T1's (eg, channel banks, pbx's, other * boxes) subservant 
>to it (timing=0).
>
>If you had multiple asterisk boxes located in several cities, and each
>of those asterisk boxes had a pstn T1, then you better read and understand
>T1 clock syncing very well as it will make a signifcant difference how
>each box obtains clock sync since there is a potential for a circular
>timing loop if one doesn't think that process through very carefully.
>
>Hope that helps...
>
>Rich
>  
>