[Asterisk-Users] Digium cards, so disappointing !

[Steve Underwood]

Begumisa Gerald M wrote:

>Hi Steve,
>
>Thank you for your very enlightening message!
>
>      On Sat, 15 Apr 2006, Steve Underwood wrote:
>      [...]
>    > modem it must be applied end to end by the modems themselves. The
>    > real killer, though, is imperfect timing.
>      [...]
>    > and its not always always available within a PC. PCs are designed
>    > around best efforts handling of data. They don't handle continuous
>    > streaming of media well, even if the data rate is fairly low. They
>    > handle it especially badly if latency must be kept low, as is the
>    > case with
>
>I have come to understand and appreciate this fact more and more through
>painful experience.
>
>      [...]
>    > That said, a well design PC environment can achieve the timing
>    > needed for FAX calls, as long as you don't load it up too much.
>
>In your opinion, short of re-engineering the PC, is there anything that
>can be done to step up the timing accuracy (and hence up the real-time
>performance) of the PC?  What [hardware-based] technical action would you
>think can up the real-time performance of the PC?
>  
>
There are certainly some things that should be been done with the 
telephony cards. Right now they don't sync together. That's true for all 
the non-H.100/non-SC-BUS/non-MVIP cards I know of. If you have all your 
E1s/T1s on one board you can route from one to another with clean 
timing. If they are on different cards the only way they will have 
matching timing is if they are both slaving to the outside world, and 
the outside world is keeping them in sync (e.g. directly or indirectly 
they are both synced to the PSTN). Right now there is no possibility to 
sync, say, an E1 port to an FXS port. That means the cards are incapable 
of things like reliable FAXing from an TE405 port to an analogue FAX 
machine on a TDM400 port.

The clocks could be carried between cards, using a simple mezzanine two 
wire cable, to keep them all in sync. It was short sighted of people not 
to do this.

Regards,
Steve