Steve, the stuff below was in direct response to a user question regarding T1 timing sync and understanding why that might be important relative to spandsp and/or other modem use. So it does apply directly. (Of coarse it slid into a tangent.)
------------------------ > 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 > > > > > _______________________________________________ > Asterisk-Users mailing list > [email protected] > http://lists.digium.com/mailman/listinfo/asterisk-users > To UNSUBSCRIBE or update options visit: > http://lists.digium.com/mailman/listinfo/asterisk-users > ---------------End of Original Message----------------- _______________________________________________ Asterisk-Users mailing list [email protected] http://lists.digium.com/mailman/listinfo/asterisk-users To UNSUBSCRIBE or update options visit: http://lists.digium.com/mailman/listinfo/asterisk-users
