Its definitely relating to the far end because it only happens when I'm talking to a person using an analogue line on the far end but the question asked by Robert Rozman a couple of hours ago is quite interesting: how come the echo doesn't happen with other ISDN telephone equipment and only with Asterisk? I've been using ISDN for years now and the first time I ever heard any echo was with Asterisk. Unless you are right about the echo only being noticable because of the additional delay by having Asterisk in the system (I'm running Asterisk on a Pentium III 500Mhz with SCSI disks and the server doesn't do anything else in life) this could be it.
Thanks,
Derek
Peter Svensson wrote:
On Fri, 29 Oct 2004, Derek Conniffe wrote:
I've been wondering about this too. I've now got two telephone systems side by side - my old system is an analogue PBX connected to ZyXel routers (Prestige 100s) which give me POTS lines from the ISDN NT1 boxes and its only since I've started with Asterisk that I've come across echo (I have echo problems with X100P cards and analogue lines too).
Are you using TDM all the way, or do you have a voip hop somewhere? When running a pure tdm connection (i.e. one with only isdn, t1,e1 or analog lines) the round trip time is usually so short that any echo mixes with the sidetone (immediate feedback of the microphone to the earphone) that it is not perceived as an echo. For longer links the telco will switch in an echo canceler unless the fax/data guardtone is detected.
When a voip link is introduced you get a lot longer latency due to the
packetization, making the echo noticable.
Echo that you can hear and find obejctionable is usually introduced by imperfections in the transmission path *at the far end*. Most of the time there is nothing that can be done about the far end. As long as 2-wire analog connections are in use some will reflect part of the energy from you back towards you. An echo canceler can help.
Peter
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