Especially the info that the X100P is 600 ohm only would have made it a lot clearer to me that I needn't buy an X100P (clone) for use in Europe
On Sun, 30 Jan 2005, Rich Adamson wrote:
Why does the X100P have echo and the Wildcard TDM400P have no echo?
I thought the only advantage of using the TDM400P was that it used less interrupts than the X100P?
Are there any other advantages?
One of the major differences between the two cards is that tdm fxo modules have support for multiple country pstn interfaces where the x100p was designed for the 600 ohm US pstn standard only. Mismatches associated with a 600 ohm card and pstn interface is known to be a source of echo.
The internal rtp data path in * for both the x100p and tdm card is basically the same path (and the same echo canceller).
The interrupts for both cards is exactly the same; 1,000 interrupts per second. The interrupt rate is associated with the sampling of digitized voice (data), and is not a hardware-card dependent item in this case.
The tdm card uses a Silcon Labs chipset that includes a two wire to four wire hybrid, which _should_ contribute to reducing fxo echo. However, the default driver does not currently preload (or dynamically) adjust the hybrid coefficients to optimize the pstn line interface. There has been some work going on recently to do that, but I don't believe the code is production ready as yet. Setting the coefficients is primarily a near-end echo optimization.
The tdm card currently has another issue that causes at least some implementations to fail after several days/weeks of operation. There is some work going on at digium to identify the source of that problem, however with intermitant problems that only show up over long periods of time, it is very difficult to catch and identify the root cause. The failure requires asterisk to be stopped and the card drivers to be reloaded to correct the issue.
Once the tdm issues have been resolved, its my opinion the card will be a very cost effective way to interface to pstn lines in the small office (and home) environment.
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