Subject: RE: Basic Model & Near End Definition; RE: [Megaco] Question on e cho control direction

From: Jon Rowland <[email-masked]>
Date: Tue, 30 Mar 2004 11:15:29 +0100

Adrian,

Your new package proposal seems like a sensible idea (although I agree with
Albrecht that we should be very clear everyone's in agreement on the
definitions of how echo cancellation should work).

I've got one more point to throw into the mix, which is something I've
considered before when thinking about how an MGC controls echo cancellation.

Typically (and this obviously dependent on MG implementation), I think that
inserting a resource like an echo canceller into a call is not necessarily a
trivial thing. For example, an MG may not be able to do this at any
arbitrary point in a call without introducing glitches into the media path,
which would be bad. Better that the MG know in advance that echo
cancellation might be required as early in the call as possible.

In general, an MGC probably knows that a call _might_ require echo
cancellation as soon as it starts being set up, but doesn't necessarily know
it _will_ require echo cancellation until the call has been fully routed.

To allow a wider range of MG implementations (without dictating what those
implementations should be), I there think it would make sense to extend the
echo cancellation, and equivalent resource properties to be tri-stated as
follows:

- none
- reserved-disabled
- enabled

To maintain compatibility, MGs would have to support the transition
'none'->'enabled' directly, but may not guarantee to add the resource
glitchlessly in this case. MGC implementations requiring it could use the
'reserve-disabled' state. MGs with no corresponding function would be free
to treat 'reserve-disabled' the same as 'none'.

Thoughts?

Regards,
Jon Rowland.

-----Original Message-----
From: Soncodi, Adrian [mailto:[email-masked]]
Sent: 29 March 2004 20:55
To: [email-masked]
Cc: [email-masked]
Subject: Re: Basic Model & Near End Definition; RE: [Megaco] Question on
echo control direction

Albrecht,

Still on the EC issue... I may be jumping ahead here while you are trying to
propose a resolution, but this is what I think:

First, it doesn't look like we can "fix" the EC omission in the TDM package
without affecting either some existing MG implementations or some MGC-MG
procedures on deployed systems.

Then there are also other capabilities similar to EC, and for which there is
currently no H.248 package. For example:
- ANR automatic noise reduction
- ALC automatic level control
- ALE adaptive listener enhancement
These are used mostly (but not only) for wireless calls.

So I was thinking we might as well define a new package, to fix the EC and
also provide the above capabilities.

Attached is an outline of what this "Enhanced Acoustic Control Package"
might contain. I did not include the "audio gain", which is defined in the
TDM package. (Maybe I should have, because this is also directional, so
apparently it has the same problem as EC.)

Please let me know what you think. If anyone is interested in pursuing this
work in the ITU-T group, please let me know.

Regards,

Adrian

-----Original Message-----
From: [email-masked] [mailto:[email-masked]]
Sent: Wednesday, March 24, 2004 11:09 AM
To: Soncodi, Adrian
Cc: [email-masked]
Subject: Basic Model & Near End Definition; RE: [Megaco] Question on
echo control direction

Adrian,

you are addressing a bunch of valid questions.
Before responding on your details, I'd like to synchronize our
understanding.

Please find enclosed some powerpoint slides
(NGN_EchoCanceller_Principle_r02.PPT), these pictures reflecting my "world
view" on H.248 MG-embedded ECs:-)
Do you agree with "near end", "half way" definitions?
Is my view inline with yours?

Perhaps one issue is the use of term "near end" in NGN environments,
whereas G.168 precisely talks about "cancelled end" since the 2002 version.

Any G.168 experts view? Please correct me if I'm wrong.

Best regards,
Albrecht

(See attached file: NGN_EchoCanceller_Principle_r02.PPT)(See attached file:
NGN_EchoCanceller_Principle_r02.pdf)

                      "Soncodi, Adrian"

                      <Adrian.Soncodi@t         To:      Albrecht
SCHWARZ/DE/ALCATEL@ALCATEL

                      ekelec.com>               cc:      <[email-masked]>

                                                Subject: RE: [Megaco]
Question on echo control direction

                      19.03.2004 18:46

Albrecht,

Let's say both switches perform near-end, half way EC as you suggest. Then
the question is: what do you mean by "near-end half way EC"? Is it:
a) Cancelling echo towards the near-end user, so that he does not hear
echo? or
b) Cancelling echo generated by the near end, so that the far end user does
not hear echo?

In other words, which one happens when the MGC instructs the MG to turn EC
on? I'm not saying it should be one or another, I'm saying that the H.248
standard should specify it, because it matters.

Kevin says it should be a). I just point out that most of the MGs today do
b). And I found one MG that does a). So if MGCs follow the ISUP procedures
to turn EC on at both ends using b), they may have the surprise that some
EC devices are "flipped over", and thus they become ineffective as they
work over the long path. Or, instead of being complementary, both EC
devices cancel in the same direction ... you see the problem.

I don't quite understand the rest of you e-mail. What do you mean by "Any
EC requirement in addition ... must be signalled correspondingly." Signaled
where? in H.248 you only have one ec property.

Are you suggesting that the MGC just signals "ec=on", and then the exact
behavior of the MG (i.e. the direction of the half-way EC device etc.)
depends on the local MG provisioning? This could be a solution, but even
so, the H.248 standard should make it clear. And the MGC would still have
to know what is the case in order to properly implement two-way echo
control procedures.

To conclude, I'm still trying to find out what the MG's expected behavior
is. See my long e-mail for pros and cons of a) and b). But I believe if we
don't clarify it, there will be interop problems.

Adrian

[Message Truncated]

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---

From: Jon Rowland <[email-masked]>
Date: Tue, 30 Mar 2004 11:15:29 +0100

Adrian,

- none
- reserved-disabled
- enabled

Thoughts?

Regards,
Jon Rowland.

-----Original Message-----
From: Soncodi, Adrian [mailto:[email-masked]]
Sent: 29 March 2004 20:55
To: [email-masked]
Cc: [email-masked]
Subject: Re: Basic Model & Near End Definition; RE: [Megaco] Question on
echo control direction

Albrecht,

Regards,

Adrian

-----Original Message-----
From: [email-masked] [mailto:[email-masked]]
Sent: Wednesday, March 24, 2004 11:09 AM
To: Soncodi, Adrian
Cc: [email-masked]
Subject: Basic Model & Near End Definition; RE: [Megaco] Question on
echo control direction

Adrian,

Best regards,
Albrecht

 

                      "Soncodi, Adrian"

                                                Subject: RE: [Megaco]

                      19.03.2004 18:46

Albrecht,

Adrian

[Message Truncated]