Very informative post Vinícius ! 2010/3/5 Vinícius Fontes <[email protected]>
> ----- "Chandrakant Solanki" <[email protected]> escreveu: > > > Hello > > > > I have successfully compiled OSLEC for echo cancellation for DAHDI > > channel. > > > > Is there any way to do echo cancellation for SIP Channel. > > > > Is any, please suggest me.?? > > > > Thanks in advance.. > > > > -- > > Regards, > > > > Chandrakant Solanki > > Short answer: Maybe. Depends on the SIP device you're using. > > Long answer: > *takes a deep breath* > > First you gotta understand why echo occurs. Every single call you've ever > made on your life has echo. You can hear yourself when you're speaking. If > that was not the case, it would feel like talking on a push-to-talk system. > So echo is a natural and even desirable phenomenom. What makes echo > unconfortable is when the echo is *delayed* too much. > > There's a number of causes for this to happen. First and foremost, > sometimes a part of the signal you're transmitting is reflected back to you. > That usually happens on the analog part of the system (analog phones as a > whole, the handset of an IP phone, the headset connected to your computer's > sound card, etc). When we're talking about VoIP, the latencies involved are > much higher than a completely TDM system. There's the encoding latency, > easily understood as the time the device takes to convert the analog signal > (your voice) in RTP packets, then there's the transmission latency, inherent > to any network, and so on. All those latencies add up to each other, making > the total latency go skyhigh and making you hear your own voice delayed by > some milisseconds - the infamous echo. > > Asterisk cannot cancel echo when the call is entirely IP, from an IP phone > to another, for example. There's simply no need for that. That's because > it's the device's job to cancel the echo caused by its own TX reflections or > analog/digital conversions. On the other hand, Asterisk can and will cancel > echo if you have a hardware echo canceller or a software based one, like > OSLEC -- which is by far the best software echo canceller I've ever seen. > > Finally, in order to solve your problem, you'll need to check a few things. > If the call is entirely VoIP, from one end to other, then the IP phones, > ATAs, gateways, softphones, whatever, are the sole responsibles on > cancelling the echo. You'll need to turn on echo cancelling on this devices > or tweak its parameters. Also, don't forget that latency makes echo much > worse. If you control the entire network between the two phones, you MUST > set up a QoS policy in order to minimize the latency as much as possible. > I've solved many echo problems by just implementing end-to-end QoS on the > network. > > Lastly (I swear I'm finishing this essay right here :), if that's not your > case and you're having echo issues calling from a SIP phone to an external > number, double check if OSLEC is indeed set as the echo canceller on > /etc/dahdi/system.conf and enabled with echocancel=yes on your > chan_dahdi.conf. You can always check if the echo canceller is active on a > certain DAHDI channel by issuing the command "dahdi show channel XX" on > Asterisk CLI, where XX of course is the said DAHDI channel. > > -- > _____________________________________________________________________ > -- Bandwidth and Colocation Provided by http://www.api-digital.com -- > New to Asterisk? Join us for a live introductory webinar every Thurs: > http://www.asterisk.org/hello > > asterisk-users mailing list > To UNSUBSCRIBE or update options visit: > http://lists.digium.com/mailman/listinfo/asterisk-users >
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