You may not understand it, however echo has been an issue in the PSTN for whatever length of time that there have been phones. You most likely haven't frequently experienced it, because the telecom business has gone through huge entireties of cash structuring costly echo cancellation gadgets. Additionally, when the endpoints are genuinely closee.g., when you telephone your neighbor down the streetthe delay is negligible to such an extent that anything you transmit will be returned back so rapidly that it will be indistinct from the sidetone ordinarily happening in your phone.
As talked about in Understanding Telephony, sidetone is a capacity in your phone that profits some portion of what you state back to your own ear, to give a progressively normal sounding discussion.
Why Echo Occurs
Before we examine measures to manage echo, allows first investigate why echo happens in the simple world.
In the event that you hear echo, it's not your telephone that is causing the issue; it's the most distant finish of the circuit. On the other hand, echo heard on the far end is being created at your end. Echo is caused by the way that a simple neighborhood circle circuit needs to transmit and get on a similar pair of wires. On the off chance that this circuit isn't electrically adjusted, or if a low-quality phone is associated with the finish of the circuit, signals it gets can be reflected back, turning out to be a piece of the arrival transmission. At the point when this reflected circuit hits you up, you will hear the words you expressed only minutes prior. The human ear will see an echo after a deferral of about 40 milliseconds.
In a modest phone, it is feasible for echo to be created in the body of the handset. This is the reason some modest IP telephones can cause echo in any event, when the whole start to finish association doesn't contain a simple circuit. All things considered, the handset in any telephone, be it conventional or VoIP, is a simple association.
In the zconfig.h setup record, you can look over one of a few echo canceller calculations, with the default being MARK2. Test with the different echo cancellers on your network to decide the best one for your condition. Asterisk likewise has a choice in the zconfig.h record to make the echo cancellation increasingly forceful. You can empower it by uncommenting the accompanying line:
Note that forceful echo cancellation can make a walkie-talkie, half-duplex impact. This ought to be empowered just if every single other technique for decreasing echo have fizzled.
Empower echo cancellation for Zaptel interfaces in the zapata.conf record. The default setup empowers echo cancellation with echocancel=yes. echocancelwhenbridged=yes will empower echo cancellation for TDM crossed over calls. While crossed over calls ought not require echo cancellation, this may improve call quality.
At the point when echo cancellation is empowered, the echo canceller learns of echo on the line by tuning in for it for the length of the call. Therefore, echo might be heard toward the start of a call and in the long run reduce after timeframe. To maintain a strategic distance from this circumstance, you can utilize a technique called "echo preparing ," which will quiet the line quickly toward the start of a call, and afterward send a tone from which the measure of echo on the line can be resolved. This permits Asterisk to manage the echo all the more rapidly. Echo preparing can be empowered with echotraining=yes.