Каково использование компенсатора эха в платах ISDN, если все мои конечные точки имеют отмену эха?
Сегодня большинство дистрибутивов Linux имеет клиент OpenSSH. Встроенный Linux содержит сервер Dropbear SSH и клиент.
Дуга Linux прибывает без ssh клиента по умолчанию.
It is because not all legs / providers properly cancel echo in their network. So, in theory you should not need to have a line side echocan on a digital line, but in practice you sometimes do.
For example, a provider might not cancel echo out to each analog endpoint in their network. If you have a digital connection to this network, you get the signal with the echo in it because they know on their network that the delay is small enough that you will perceive the echo as side tone. But since you are hooking up your IP PBX, and connecting to VOIP handsets, your PBX users will hear the echo since the delay is larger than what the provider expects for it's normal customers.
There is latency in the speech path. Not just due to the propagation distance but also to buffering along the way, both CODEC and otherwise.
For example, if one end happens to be a USB-based speakerphone hung off of a PC, the delay added by just that can be substantial enough to overwhelm a large echo-canceller.
in all-digital communications, why echo canceling is required?
There is NO all digital audio communication path and there will never be.
The recording has to come from an analog medium (sound waves) and the output is analog (sound waves).
And this is exactly the echo line that is hard to control. Not the headset - but the conference room setup where the audio output (loudspeaker) goes back into the audio input (microphone).