Subject: H.248.xx Enhanced Acoustic Control Package; RE: Basic Model & Near End Definition; RE: [Megaco] Question on echo control direction

From: [email-masked]
Date: Tue, 30 Mar 2004 12:57:32 +0200

Adrian,

when reading the Half Echo-Control Device (HECD) section, I was reminded to
Q.115.1 and G.799.1:

ITU-T Recommendation Q.115.1
Logic for the control of echo control devices and functions

ITU-T Recommendation G.799.1

Functionality and Interface Specifications for GSTN Transport Network
Equipment for Interconnecting GSTN and IP Networks

For instance, Q.115.1 is, inter alia, providing definitions for incoming
echo control device (IECD) and outgoing echo control device (OECD), G.799.1
is extensively dealing with EC in TDM-to-Packet media gateways.

Did you already consider these ITU-T recs. in your package proposal? I
guess that we need alignment.

May anyone of the Q7/15 experts comment on the HECD block in the proposed
H.248 package.

Regards,

Albrecht

                      "Soncodi, Adrian"                                                                                                              
                      <Adrian.Soncodi@t         To:      Albrecht SCHWARZ/DE/ALCATEL@ALCATEL                                                         
                      ekelec.com>               cc:      <[email-masked]>                                                                           
                                                Subject: H.248.xx Enhanced Acoustic Control Package; RE: Basic Model & Near End Definition; RE:      
                      29.03.2004 21:17          [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

-----Original Message-----
From: [email-masked] [mailto:[email-masked]]
Sent: Friday, March 19, 2004 3:06 AM
To: Soncodi, Adrian
Cc: Kevin Boyle; [email-masked]; [email-masked]
Subject: RE: [Megaco] Question on echo control direction

Adrian,
I couldn't find any contradiction between Kevin's and your statements.

My understanding is that the "basic" EC settings for circuit-to-packet MGs,
where the POTS/ISDN terminal is accessed via a circuit-switched network,
are:
- near-end EC, and
- half way only ("I don't know the exact G.168 terminology").

I think that this common understanding may be derived from legacy PSTN/ISDN
networks.
Any EC requirement in addition, e.g., like
- far-end EC,
- 2 near-end "H.248 TDM Terminations" (in a TDM-to-TDM call), and/or
- full way
must be signalled correspondingly.

My impression is that the "basic settings" are sufficient for almost all
cases. The additional EC capabilities are valid network scenarios (e.g.,
inter-operater interworking, replacement of an international exchange,
tandem echo cancellation, two satellite links in the TDM-to-TDM call
scenario, missing near-end EC capability in peer MG, etc), but rather
exeptional cases (like in pre-NGN TDM networks).

Regards,
Albrecht

                      "Soncodi, Adrian"

                      <Adrian.Soncodi@t         To:      "Kevin Boyle"
<[email-masked]>, <[email-masked]>

                      ekelec.com>               cc:

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

                      megaco-admin@ietf

                      .org

                      18.03.2004 18:13

Kevin,

In your message you say:

 "I cannot find anything that specifies this, but I don't know why someone
would use an echo canceller to cancel echo inside the context... Why not
just fix the DSP to not introduce the echo in the first place?  You don't
generally find echo on the transition from TDM<->packet."

Actually, it's not the DSP that introduces echo. It's the 4-wire to 2-wire
conversion beyond the TDM termination. So for a TDM-packet-TDM call, we
have the following:

- Typically, echo is cancelled at both ends of the call. Originating and
terminating switch each cancel in different directions.

- For an echo device to cancel in one direction, it has to take the other
path as reference, wait for the signal to turn around from the user, and
then compare the two and clean the echo. This involves a delay buffer (echo
tail), typically up to 64 ms, sometimes up to 128 ms (I don't know of MGs
that can do more).

- As a consequence, each switch typically cancels echo over the short path.
For a TDM-packet-TDM call, the short path is usually the TDM, while the
long path is the packet network plus the other TDM. If you wait for the
signal to turn around on the packet side, many times the delay is bigger
than the buffer size and the EC device becomes ineffective.

- Consider two MG-s interconnected by a packet network. If these were
traditional TDM switches, each one would clean the stream going towards the
other (for example, the echo indications in ISUP IAM/ACM are designed to
achieve this result). This corresponds to the direction into the packet
network.

- Another reason to clean the stream into the packet network is that if the
stream has echo, then the encoding/decoding performed by some compression
algorithms results in lower quality voice (i.e. some algorithms are
optimized for "clean" voice).

- A solution for this would be to turn echo control on the packet-side
terminations. Then if these terminations work like you say they should, the
desired result would be achieved. Unfortunately, all the MGs I know cannot
do this. They can only apply a half EC device on the TDM termination
(probably because the package name is TDM)

- Another aspect: For a conference call with N TDM terminations in a
context, in order cancel the echo generated by one TDM circuit it is
simpler to clean its stream going into the context than the other N-1 going
out of the context.

- Until now, I thought I knew the answer to this one. Although this does
not seem to be clearly specified either in MGCP or in MEGACO, for all the
MGs I've seen, if you turn on echo on a TDM termination they clear the
stream going into the packet network. They reference the backwards stream
to TDM, which is turned around over the short path. So it looks like most
of the existing MGs do not work like you recommended -- people, correct me
if I'm wrong here.

- However, recently I stumbled upon an MG that behaves exactly the
opposite. So now I really have a problem, because there is no way for an
MGC to know whether the ec property results in the insertion of a full EC
device or a half device, and which direction.

- By analogy with signals (although ec is a propery not a signal), this
should work as you said, i.e. towards the outside of the context. But if
you would like to standardize this behavior, already a lot of MGs would be
non-compliant (again, people?).

- There is also no way for an MGC to audit for this behavior. But if MGs
were allowed to behave both ways, then you could have different MGs at the
two ends and then of a TDM-packet-TDM call, and it becomes impossible to
provide two-way echo cancellation.

So how do you propose we clarify all this?

Thanks,

Adrian

      -----Original Message-----
      From: Kevin Boyle [mailto:[email-masked]]
      Sent: Wednesday, March 17, 2004 6:12 PM
      To: Soncodi, Adrian; [email-masked]
      Subject: RE: [Megaco] Question on echo control direction

      Ecan generally applies to the network transition point to avoid
      reflections off the transition.  Therefore, it would make sense that
      the echo canceller on the TDM termination would cancel echo outwards
      toward the TDM facility.

      I cannot find anything that specifies this, but I don't know why
      someone would use an echo canceller to cancel echo inside the
      context... Why not just fix the DSP to not introduce the echo in the
      first place?  You don't generally find echo on the transition from
      TDM<->packet.

      Kevin

      -----Original Message-----
      From: Soncodi, Adrian [mailto:[email-masked]]
      Sent: Wednesday, March 17, 2004 6:51 PM
      To: [email-masked]
      Subject: [Megaco] Question on echo control direction

      Hi,

      When an MCG turns on echo control for a TDM termination on the MG,
      which one of the following audio streams becomes "clean" of echo:

      a) The stream from the termination outwards to the TDM facility, or
      b) The stream from the termination inwards into the context
      (presumably going out on another facility associated with another
      termination in the context) (I am assuming that only a half-echo
      canceller is inserted, because most of the MGs can only do that. The
      other half would be on the other termination.)

      Where is this specified? the TDM package in H.248 annex E does not
      say.

      Thanks,

      Adrian

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---

From: "Soncodi, Adrian" <[email-masked]>
Date: Tue, 30 Mar 2004 12:50:06 -0600

Albrecht,

As mentioned, this is just an "outline" for a package, meaning it's only an initial thought about what should be covered and how it should explain the behavior. Its main objectives are:
1) Provide an unambiguous specification of how directional EC should be controlled, i.e. what TDM "ec" is missing; include bidirectional EC blocks if necessary, although from my experience one half-block on each termination is most common.
2) Include the other acoustic processing blocks (ALC, ANR, ALE, see description in document). This is because they have similar directionality issues. Also, because they are or will be needed, and I would like to avoid seeing them appear all in different packages, with conflicting and/or incomplete specifications.

I definitely agree that the package should be in-line with the other specs.

Regards,

Adrian

-----Original Message-----
From: [email-masked] [mailto:[email-masked]]
Sent: Tuesday, March 30, 2004 4:58 AM
To: Soncodi, Adrian
Cc: [email-masked]; [email-masked]
Subject: H.248.xx Enhanced Acoustic Control Package; RE: Basic Model &
Near End Definition; RE: [Megaco] Question on echo control direction

Adrian,

Regards,

Albrecht

                      "Soncodi, Adrian"                                                                                                              

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

-----Original Message-----
From: [email-masked] [mailto:[email-masked]]
Sent: Friday, March 19, 2004 3:06 AM
To: Soncodi, Adrian
Cc: Kevin Boyle; [email-masked]; [email-masked]
Subject: RE: [Megaco] Question on echo control direction

Adrian,

Regards,
Albrecht

                      "Soncodi, Adrian"

                      ekelec.com>               cc:

                      megaco-admin@ietf

                      .org

                      18.03.2004 18:13

Kevin,

In your message you say:

Thanks,

Adrian

      -----Original Message-----
      From: Kevin Boyle [mailto:[email-masked]]
      Sent: Wednesday, March 17, 2004 6:12 PM
      To: Soncodi, Adrian; [email-masked]
      Subject: RE: [Megaco] Question on echo control direction

      Kevin

      -----Original Message-----
      From: Soncodi, Adrian [mailto:[email-masked]]
      Sent: Wednesday, March 17, 2004 6:51 PM
      To: [email-masked]
      Subject: [Megaco] Question on echo control direction

      Hi,

      Thanks,

      Adrian

---

From: "Soncodi, Adrian" <[email-masked]>
Date: Tue, 30 Mar 2004 12:50:06 -0600

Albrecht,

Regards,

Adrian

-----Original Message-----
From: [email-masked] [mailto:[email-masked]]
Sent: Tuesday, March 30, 2004 4:58 AM
To: Soncodi, Adrian
Cc: [email-masked]; [email-masked]
Subject: H.248.xx Enhanced Acoustic Control Package; RE: Basic Model &

Adrian,

Regards,

Albrecht

                      "Soncodi, Adrian"                                                                                                              

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

-----Original Message-----
From: [email-masked] [mailto:[email-masked]]
Sent: Friday, March 19, 2004 3:06 AM
To: Soncodi, Adrian
Cc: Kevin Boyle; [email-masked]; [email-masked]
Subject: RE: [Megaco] Question on echo control direction

Adrian,

Regards,
Albrecht

                      "Soncodi, Adrian"

                      ekelec.com>               cc:

                      megaco-admin@ietf

                      .org

                      18.03.2004 18:13

Kevin,

In your message you say:

Thanks,

Adrian

      -----Original Message-----
      From: Kevin Boyle [mailto:[email-masked]]
      Sent: Wednesday, March 17, 2004 6:12 PM
      To: Soncodi, Adrian; [email-masked]
      Subject: RE: [Megaco] Question on echo control direction

      Kevin

      -----Original Message-----
      From: Soncodi, Adrian [mailto:[email-masked]]
      Sent: Wednesday, March 17, 2004 6:51 PM
      To: [email-masked]
      Subject: [Megaco] Question on echo control direction

      Hi,

      Thanks,

      Adrian

---

From: [email-masked]
Date: Wed, 31 Mar 2004 10:12:21 +0200

----- Forwarded message from [email-masked] -----
    From: [email-masked]
Reply-To: [email-masked]
 Subject: Re: H.248.xx Enhanced Acoustic Control Package; RE: Basic Model & 
Near End Definition; RE: [Megaco] Question on echo control direction
      To: [email-masked]

Dear All,

ITU-T Rec.Q.115.1 describes where and when Echo Control Devices are needed and 
provided in a voice call. This nezwork logic is independent of the signalling 
systems used and the network technology (TDM, Mobile, Packet).
ITU-T Rec.Q.115.0 describes protocols to control Echo Control Devices (on a per 
call basis). In a TDM network this may be something like c-bit of time slot 16 
(PCM 30); in a VoIP GW a H.248 SPNE (Signal Processing Network Equipment) 
Package has been defined, this allows a MGC to control a ECD associated with a 
MG. This package complements the TDM Package which does not provide the 
required flexibility (an ECD may have to be controlled at any point in time of 
a call).
ITU-T Rec. Q.115.1 refers to Network Echo Control Devices (e.g. Echo 
Cancellers, Echosuppressors).
There exist a final draft new REC.Q.115.2 Logic for the Control of VEDs (Voice 
Enhancement Devices/Functions). Acoustic Echo Control is part of such a 
device/function.
>From the control point of view Echo Control Devices are considered to 
be "half", i.e. an ECD is controlling the echo from only one echo source. If a 
specific implementation provides "full" echo control then this is considered as 
two "halfs" and the two "halfs" are controlled independently.

regards;
Peter Goldstein
Siemens Switzerland
(Rapporteur Q.10/11)

Quoting [email-masked]:

>                                                 Subject: H.248.xx Enhanced
> Acoustic Control Package; RE: Basic Model & Near End Definition; RE:

---

From: [email-masked]
Date: Wed, 31 Mar 2004 10:12:21 +0200

----- Forwarded message from [email-masked] -----
    From: [email-masked]
Reply-To: [email-masked]
 Subject: Re: H.248.xx Enhanced Acoustic Control Package; RE: Basic Model & 

Dear All,

regards;
Peter Goldstein
Siemens Switzerland
(Rapporteur Q.10/11)