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Echo is either acoustic (the microphone picking up the speaker directly), or occurs where the signal is in analog form. The VoIP signal is not prone to echo as the tx and rx signals are separate. VoIP does, however, introduce time delays. When the digital signal connects to an analog POTS network there will be a mixing of the rx and tx streams, so you get crosstalk, which you hear as echo. This, combined with any transmission delays can cause multiple echoes of different time delays. Generally the longer the echo, the further (distance) up the signal chain it is occurring. The VoIP, and any subsequent digital conversion, can introduce a variable time delay, depending in the codecs used, bandwidth congestion etc. It would be difficult to pinpoint the echo by analysing the packets on the network using wireshark or equivalent. Echo cancellation can itself introduce echos if it is not working correctly. I had to design some tools to analyse exactly this a couple of years ago. It is a non-trivial problem. Dave Berkeley On Thursday 28 February 2008 07:30:14 stinga wrote: > On 27/02/08 21:25:24, sam@xxxxxxxxxxxxxxxxx wrote: > > Hi > > > > we are currently using Diguim 410p PCI with hardware echo cancelling > > which > > plugs into 2 * ISDN 2e boxes. > > > > the phones are Cisco 941/921 models > > > > all plugged into a separate switch Netgear GS924T 1GB ports > > > > we have 20 DDI's > > > > The echo problem could be the Cisco phones as I haven't noticed the > > echo > > when using a software phone X-lite, we are using the SIP protocol, > > but > > I > > don't know what codex is being used. > > > > How would you track down the echo problem, is there anything like > > wireshark > > can pick out. > > I have split this into two questions. > > There are many places where echo can be caused and the first jobs is to > determine where it is happening, by the process of elimination. > > Where does the echo happen. > internal to internal > internal to external > external to internal > > and who hears the echo, the caller or the callee. > > You say that it does not happen when using a soft phone, if this is > true then I would suspect the hardware to be the issue. > > Echo can be caused by electronic or physical problems. > > By physical I mean that the microphone on the phone is picking up the > speaker and feeding it back. This would usually manifest its self in > the other end hearing an echo. > > Also is it all phones or just on or two? > > Once we have some more info we might be able to determine where the > problem is and help. No guarantees though! > > -- > 'ooroo > > stinga...(:)-) > --------------------------------------------------- > Email: stinga@xxxxxxxxxxxxx o > You need only two tools. o ///// > A hammer and duct tape. If it /@ `\ /) ~ > doesn't move and it should, > (O) X< ~ Fish!! > use the hammer. If it moves and `\___/' \) ~ > shouldn't, use the tape. \\\ > --------------------------------------------------- -- The Mailing List for the Devon & Cornwall LUG http://mailman.dclug.org.uk/listinfo/list FAQ: http://www.dcglug.org.uk/linux_adm/list-faq.html