Howto:Having ECHO problems

Applies To

This information applies to

• all innovaphone products

any build

FIXME: has to be updated and corrected

More Information

Having Echo on the Ip Phones

General

The presence of echo occurs whenever the replicated signal delay exceeds 10msec , and becomes apparent to the speaker as reflected voice when the delay exceeds as little as 16 msec.

It is manifested to the far end as an altered replica of the speaker original.

Causes of Delay

Delay in telephony context is the time during which voice signals travel across the network.

End-to-end delay is the sum of delays required for a voice signal generated by the speaker's mouth to cross the different network devices and network links in order to reach the listener's ear.

Roundtrip delay is the sum of end-to-end delay in both directions as it is reflected back to the speaker's ear.

The two directions can take separate paths over the Pstn, one through a satellite and one via land-lines, for example.

Echo Cancellation

The term echo cancellation is used in telephony to describe the process of removing echo from a voice communication in order to improve voice quality on a telephone call.

In addition to improving subjective quality, this process increases the capacity achieved through silence suppression by preventing echo from traveling across a network.

Echo cancellation involves first recognizing the originally transmitted signal that re-appears, with some delay, in the transmitted or received signal.

Once the echo is recognized, it can be removed by 'subtracting' it from the transmitted or received signal.

This technique is implemented using a digital signal processor (DSP).

By sampling the voice signal, the echo canceller can create a model of the echo path which is in turn used to estimate the echo.

This estimation is then subtracted from the incoming voice signal allowing normal speech to pass through.

This is a very simplistic view, as echo cancellers need to have the capability to sample multiple echoes occurring at different times and at different levels.

Echo cancellation is done with innovaphone products using echo cancellers.

So an Echo Problem is mostly an Delay Problem and is not a jitter or packet loss problem on the Network.

Mostly at echo problems the PSTN provider has an big delay on his Network.

So If you hear on your Ip Phone an Echo the innovaphone gateway is responsible to delete this echo.

We support the The G.168 Echo Canceller on all our product.

You can Disable the Echo canceller but no adjustments to set- it is default enabled.

Our echo compression is dynamic - contend sensitive -. no values to set.

Maximum Echo cancellation - maximum echo lenght (echo Tail)

IP400                     16msec
IP3000                    24msec
IP302,IP305,IP800,IP6000  64msec
IP1200                    32msec

Phone

accoustic Echo cancelling on Handsfree Mode
Normal Mode 16msec 

It is no solution to make volume adjustments on the Endpoints for solving the Echo problem

If you encounter an echo problem – pleas check this :

Do you meet the Echo problem always ?

• between IP phones ?

• between Isdn and IP phones ?

• between analog phones and/or Dect phones to IP phones or Isdn (connected an analog adapter IP21,IP22,IP24)?

IF this problem is with analog or Dect Phone - occurs with very old Dect phones in very few cases - the best solution here is - eliminate this phone.

If you have a general echo problem - you have a delay Problem in your Network

To find this out

Pleas watch PBX – Call screen (administration - pbx - calls)

Extension A  NameA H323EFC:TRANSIT G729AB (42,6,3)  >> Extension B NameB H323EFC:TRANSIT G729AB (47,2,5)  Connected 

The explanation for that screen is here Reference:Administration/PBX/Calls

The values in the brackets are

Round trip (RT) = Transit time of a data packet from A to B and back again.

Jitter = Latency time (time interval from the end of an event up to the start of the response).

Loss (PL) = Number of lost packets (packet loss).