[Asterisk-Users] echo cancel from telco

[Krystian Filiks]

That is not the whole trough.

First you have to make sure that the echo is'nt generated locally by 
your server hardware, headset, handset, software etc....

First then you can go to your provider and tell them that you hear echo.

The post that you read is talking about the principle of echo cancelling 
from a telco point of view.

here is a little explanation:

End user (You) ---------> Your Telco ----------> Carrier 1 -----------> 
Carrier 2 ------------ Carrier 3 -----------> Carrier 4(PTT) 
--------------- > Far End User

So basically, the Echo cancelling work backwards usually cancellation 
for you would be done by Carrier 4, 3, 2, 1, or your Telco in that order 
and echo for the Far End User would be done by Your Telco, Carrier 1, 2, 
3, or 4 in that order.

Why in that order?

When the call progresses through the network using SS7 signalling (99% 
of the time) there is a parameter included in The IAM(Initial Address 
Message) the first message ever sent by the originating Telco and in the 
ACM (Address Complete Message) the first responce to the IAM sent back 
from the receiving Telco, this parameter tells the part that receives 
the message if echo cancelling is or is not included and this telco 
based on this message can decide if they should turn Cancelling on or not.

In our example we have 5 players (you will never know how many, your 
telco will not tell you who they use and the chain could be 10, 20... 
players long) and one of then should do echo cancelling (In theory) this 
almost newer works out in practise due to price tags on the Echo 
cancellers, for example lets say that Carrier 1 has 20E1's to Carrier 2 
that means that Carrier 1 teoretickly would have to have 20 Echo 
Cancellers and so on and so on

So to sumerize you have to find out if it is not your equipment 
generating the echo (then no external canceller will help) if it is not 
then you have to speak to your telco and tell them your findings then 
thay have to speak to their provider or decide if they will do 
cancelling them self.

Or, you buy a canceller and use it for cancelling the Echo for your 
users, only then you might have the problem with echo on the other side 
and you will end up having to put 2 Cancellers turned with the back to 
eachother.

It would be wise to aproach the telco first and first then plan to 
deploy your own cancelling, if you decide to deploy cancelling on your 
own be sure to messure the echo delay first, then buy a canceller that 
will give you an overhead so that you still can cancell echo bigger then 
the originally mesures without need of buying a new canceller.

I hope that I did'nt confuse you to much!

Krystian


Michael Sampson wrote:

> I get an echo when going from a SIP phone to a PRI trunk. I hear the 
> echo on the SIP phone. From reading some other post I think that I 
> need to tell me phone company to turn on echo canceling. If the echo 
> was on the other end than it would be my problem?
>
> Is this right? What exactly should I say to my phone company so they 
> know exactly what I'm talking about?
>