Subject: RE: [Megaco] signal directionality

From: "Kevin Boyle" <[email-masked]>
Date: Wed, 8 Dec 2004 11:03:47 -0500

Generally speaking, the vendors that are highly active in the VoIP market
today are deploying solutions that are functionally equivalne tot he PSTN.
Subscribers understand how the PSTN works, so it is seen as desireable for
the PSTN replacement to work more-or-less equivalently.
 
If the MGCs can communicate the intention of where to play the ringbakc,
then great.  But in the absence of that capability, the MGC should take the
actions it thinks are necessary.  I belive it is a fine assumption to try to
function the same way as the PSTN.
 
Kevin

  _____  

From: Matia Marcu [mailto:[email-masked]]
Sent: Wed 12/8/2004 10:45 AM
To: Boyle, Kevin [NCRTP:3Z40:EXCH]; [email-masked]
Subject: RE: [Megaco] signal directionality

Kevin,
 
Thanks for the answer. 
Right, in my text it should have been User A and User B.
 
Concerning the ringback applied from the terminating side:
 
"I can think of several cases where it would be better to place the ringback
on ephemB; what if party B is on a different MG, controlled by a different
MGC?"
 
Classic telephony advocates tones being applied from the side close to the
user receiving the tone, because this way the users receive the tones they
are used to (example: in case of a call between US and Italy, if the call is
broken, the US user would receive a US tone /English announcement and the
user in Italy would receive an Italian tone /Italian announcement). Classic
telephony also refers to ringback tone as a case when this rule must be
broken (when the far-party answers, if the ringback tone comes from the
originating side, there will be some switching in the exchanges on the way,
which can lead to voice clipping).
 
In case of both user A and user B being served by VoIP networks connected by
a PSTN network, I guess that the ringback should come from ephemB. But what
about a purely VoIP network - wouldn't it be preferable to have the ringback
come from the outgoing gateway? Same for an unsuccessful call that fails in
the terminating side backyard - I think that it's better to have the
terminating exchange signal the call result out-of-band and have the
outgoing side apply the tone /announcement. Of course, this requires some
exchange of information between the involved MGC (and interworking signaling
gateways, when relevant). Is this how things are happening today?
 
Thank you,
 
Matia Marcu
Teledata Networks

-----Original Message-----
From: Kevin Boyle [mailto:[email-masked]]
Sent: Wednesday, December 08, 2004 9:47 AM
To: Matia Marcu; [email-masked]
Subject: RE: [Megaco] signal directionality

Directionality is being added in H.248 version 3 as a default signal
parameter.  In the definition there, "internal" plays the signal toward the
center of the context.  To have it play in both directions, one would use
"both". This means that the wording in Q.1950 section 4.4.48 appears to be
incorrect.  Note that the wording in the packages themselves (Annex A) is
correct.
 
In your example, note that there are 4 terminations, not two.  I assume
terminations A and B are the physical terminations in this case.  Keep in
mind that physical and ephemeral terminations are not linked in H.248,
except by being placed in a context together.
 
Your examples on the ringback are all ok.  In theory, you could also put
ringback on physB and use internal.  I can think of several cases where it
would be better to place the ringback on ephemB; what if party B is on a
different MG, controlled by a different MGC?
 
A revision of H.248.8 is upcoming and will be released in conjunction with
H.248.1v3.  We are defining a new error code that will cover this case: 449
"Unsupported or Unknown Parameter or Property Value".
 
As for where this is useful, that would depend upon the requirements of the
applications you are providing in your system.  I can think of several,
including the "remote ringback" case discussed here.
 
Kevin

  _____  

From: [email-masked] on behalf of Matia Marcu
Sent: Wed 12/8/2004 9:09 AM
To: [email-masked]
Subject: [Megaco] signal directionality

Please, I have a few questions concerning signal directionality.

1. I think that there is a slight difference between the definitions of
directionality in Q.1950 and H.248.23 /H.248.27. 

All the sources are clear concerning "external" and "both"; I quote here the
explanations concerning "internal":

H.248.2x: "Internal" denotes that the signal shall proceed toward the centre
of the context from the termination.

Q.1950 - 4.4.48 signal direction: The stimulus can be placed on a
termination so that none of the other terminations in the context "hear" it
(external) or so that other terminations in the context "hear" it also
(internal).                                             

I understand the first definition as saying that only the other terminations
in the context "hear" the signal while the second definition says that these
terminations also "hear" the signal. In the Q.1950 case, who is also hearing
the signal? The termination itself (i.e. like in the "external" case)? If
so, what's the difference between "internal" and "both"?

2. Assuming that the H.248.2x definition is correct, I'd like to verify a
simple example of tone application:

Termination A (physA, ephemA in context C1) is calling termination B (physB,
ephemB in context C2); termination A must receive ringback tone. The
softswitch may request either bcg/brt (or cg/rt) on physA ("external"
direction explicit or implied) or bcg/brt -"internal" on ephemA. Is it also
ok to request bcg/brt-"external" on ephemB? This would be similar to
ringback tone application in classical telephony (from the terminating side,
to avoid clipping on answer), but in VoIP is there any reason to do so? 

3. What should a gateway answer if it receives a ring command with an
incorrect direction (like - using the example above - alert/ri-"internal" on
physB)? The message is legal, so no error of this kind applies; on the other
hand, it's not exactly a case for answering "513"; error "421" Unknown
action or illegal combination of actions (also not an exact match) appears
in H.248.8 as "not used"...

4. The usefullness of "internal" and "both" directions is clear for
multi-party sessions (conference, announcements...). Are there other types
of applications where directionality is very useful?

Many thanks,

Matia Marcu

Teledata Networks

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Megaco mailing list
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---

From: Christian Groves <[email-masked]>
Date: Thu, 09 Dec 2004 16:10:19 +1100

With respect to Q.1950 I believe the intention is not to re-define how direction 
is used. The full quote for:
4.4.48	signal direction: Indicates the directionality of a stimulus applied to a 
termination. The stimulus can be placed on a termination so that none of the 
other terminations in the context "hear" it (external) or so that other 
terminations in the context "hear" it also (internal). The direction may be set 
to (both way) indicating that all the terminations in the context "hear" it as 
well as it being sent external to the BIWF.

Its clear that "both" and "internal" are distinguished. The use of "also" is 
meant to refer to the additional capability of "internal" rather than "also" 
with regards to the termination played.

Christian

Kevin Boyle wrote:

> Generally speaking, the vendors that are highly active in the VoIP 
> market today are deploying solutions that are functionally equivalne tot 
> he PSTN.  Subscribers understand how the PSTN works, so it is seen as 
> desireable for the PSTN replacement to work more-or-less equivalently.
>  
> then great.  But in the absence of that capability, the MGC should take 
> the actions it thinks are necessary.  I belive it is a fine assumption 
> to try to function the same way as the PSTN.
>  
> Kevin
> 
> ------------------------------------------------------------------------
> "I can think of several cases where it would be better to place the 
> ringback on ephemB; what if party B is on a different MG, controlled by 
> a different MGC?"
>  
> Classic telephony advocates tones being applied from the side close to 
> the user receiving the tone, because this way the users receive the 
> tones they are used to (example: in case of a call between US and Italy, 
> if the call is broken, the US user would receive a US tone /English 
> announcement and the user in Italy would receive an 
> Italian tone /Italian announcement). Classic telephony also refers to 
> ringback tone as a case when this rule must be broken (when the 
> far-party answers, if the ringback tone comes from the originating side, 
> there will be some switching in the exchanges on the way, which can lead 
> to voice clipping).
>  
> In case of both user A and user B being served by VoIP 
> networks connected by a PSTN network, I guess that the ringback should 
> come from ephemB. But what about a purely VoIP network - wouldn't it 
> be preferable to have the ringback come from the outgoing gateway? Same 
> for an unsuccessful call that fails in the terminating side backyard - I 
> think that it's better to have the terminating exchange signal the call 
> result out-of-band and have the outgoing side apply the tone 
> /announcement. Of course, this requires some exchange of information 
> between the involved MGC (and interworking signaling gateways, when 
> relevant). Is this how things are happening today?
>  
> Thank you,
>  
> Matia Marcu
> Teledata Networks
> 
>     parameter.  In the definition there, "internal" plays the signal
>     toward the center of the context.  To have it play in both
>     directions, one would use "both". This means that the wording in
>     Q.1950 section 4.4.48 appears to be incorrect.  Note that the
>     wording in the packages themselves (Annex A) is correct.
>      
>     In your example, note that there are 4 terminations, not two.  I
>     assume terminations A and B are the physical terminations in this
>     case.  Keep in mind that physical and ephemeral terminations are not
>     linked in H.248, except by being placed in a context together.
>      
>     Your examples on the ringback are all ok.  In theory, you could also
>     put ringback on physB and use internal.  I can think of several
>     cases where it would be better to place the ringback on ephemB; what
>     if party B is on a different MG, controlled by a different MGC?
>      
>     A revision of H.248.8 is upcoming and will be released in
>     conjunction with H.248.1v3.  We are defining a new error code that
>     will cover this case: 449 "Unsupported or Unknown Parameter or
>     Property Value".
>      
>     As for where this is useful, that would depend upon the requirements
>     of the applications you are providing in your system.  I can think
>     of several, including the "remote ringback" case discussed here.
>      
>     Kevin
> 
>     ------------------------------------------------------------------------
>     1. I think that there is a slight difference between the definitions
>     of directionality in Q.1950 and H.248.23 /H.248.27.
> 
>     All the sources are clear concerning "external" and "both"; I quote
>     here the explanations concerning "internal":
> 
>     H.248.2x: "Internal" denotes that the signal shall proceed toward
>     the centre of the context from the termination.
> 
>      
> 
>     termination so that none of the other terminations in the context
>     "hear" it (external) or so that other terminations in the context
>     "hear" it also (internal).                                            
> 
>     I understand the first definition as saying that only the other
>     terminations in the context "hear" the signal while the second
>     definition says that these terminations also "hear" the signal. In
>     the Q.1950 case, who is also hearing the signal? The termination
>     itself (i.e. like in the "external" case)? If so, what's the
>     difference between "internal" and "both"?
> 
>     2. Assuming that the H.248.2x definition is correct, I'd like to
>     verify a simple example of tone application:
> 
>     Termination A (physA, ephemA in context C1) is calling termination B
>     (physB, ephemB in context C2); termination A must receive ringback
>     tone. The softswitch may request either bcg/brt (or cg/rt) on physA
>     ("external" direction explicit or implied) or bcg/brt -"internal" on
>     ephemA. Is it also ok to request bcg/brt-"external" on ephemB? This
>     would be similar to ringback tone application in classical telephony
>     (from the terminating side, to avoid clipping on answer), but in
>     VoIP is there any reason to do so?
> 
>     3. What should a gateway answer if it receives a ring command with
>     an incorrect direction (like - using the example above -
>     alert/ri-"internal" on physB)? The message is legal, so no error of
>     this kind applies; on the other hand, it's not exactly a case for
>     answering "513"; error "421" Unknown action or illegal combination
>     of actions (also not an exact match) appears in H.248.8 as "not used"...
> 
>     multi-party sessions (conference, announcements...). Are there other
>     types of applications where directionality is very useful?
> 
>     Many thanks,
> 
>     Matia Marcu
> 
>     Teledata Networks
> 
> 
> 
> ------------------------------------------------------------------------
>