Ken Williams wrote:
I've never understood why people would think it's a PSTN issue.
Echo *IS* a PSTN issue. Telcos have been dealing with this for years. Telcos do have high latency paths (granted less so these days).
Cell companies use hardware echo cancelers to remove the echo. Cell phones are high latency devices so users will hear the echo that is inherent in the PSTN unless it is removed.
Long distance companies use echo cancelers too. These days latency on toll calls tends to be so low I doubt EC is still required in most situations. When calls go over satellite or very, very long runs of copper (thousands of miles) there will be echo.
I get my hardware echo cancelers from eBay. Many of them still have the telco sticker on them (usually AT&T).
Echo is not new and is not unique to Asterisk or VoIP. It's just that Asterisk and VoIP are most people's exposure to high latency voice. Echo is usually canceled at the interface between the high latency leg of the call and the low latency leg of the call (Asterisk). If all legs of a call are digital (PRI into Asterisk and ISDN or cell or something else digital on the other end) there will be no echo.
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