Subject: [Megaco] Question regarding the Call Type Discrimination Package

From: [email-masked]
Date: Fri, 13 Dec 2002 16:11:27 -0600

Hi.

I am trying to understand better how the Call Type Discrimination Package
would be used by a pair of IP trunking gateways. I have focused so far on
T.38 and G.711 fallback but assume most of the logic would also apply to
data detection.

Can someone clarify for me the use of the calltyp property?  The property
description says it is used to "select the types of calls for which the
termination is monitored".  If the MGC sets it to FAX and DATA for example
what would be the expected behavior of the MG? Does this conflict or
somehow augment the MGC's ability to program the MG to report specific data
and fax call type discrimination events?

The package description talks about an exchange of signals "until the call
type is determined". Once the call type is determined, would the MGC set
the calltyp property to a single value, e.g. FAX or DATA?

Finally, is it valid for both the originating and terminating MGs to detect
and report all call type discrimination events that the MGC programs them
for? E.g. is it valid for the terminating MG to report CNG or for the
originating MG to detect and report CED and V.21 flags?

For the nonce, I have looked at the T.38 H.248 call flows but these use the
case of two MGs talking to the same MGC. The MGC detects fax signals and
plays them out on the opposite end MG. This would be analogous to
propagating fax signals through the signaling path between two MGCs (e.g.
using SIP). When I look at the Mule draft for SIP, it does no such thing.

Thanks,

John

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From: Gunnar Hellstrom <[email-masked]>
Date: Mon, 16 Dec 2002 23:16:19 +0100

Hi,

Explanations below

-------------------------------------------
Gunnar Hellstrom
Omnitor AB
Renathvagen 2
SE 121 37 Johanneshov
SWEDEN
+46 8 556 002 03
Mob: +46 708 204 288
www.omnitor.se
[email-masked]
--------------------------------------------

> -----Ursprungligt meddelande-----
> Fran: [email-masked] [mailto:[email-masked]]For
> [email-masked]
> Skickat: den 13 december 2002 23:11
> Till: [email-masked]
> Amne: [Megaco] Question regarding the Call Type Discrimination Package
>
>
> Hi.
>

I hope you are also considering text. Text telephony is an important part of
the telecom system, but sometimes forgotten, causing problems to get it
implemented as an expensive fix afterwards rather than integrated at design
time.

> and fax call type discrimination events?

The "calltyp" property selects what signals the termination shall be
sensitive to detection of.
The effect is easiest to see in the "dtone" event.
If "calltyp" is set to a limited subset of TEXT, FAX and DATA, the
termination needs not to listen for some signals. That will ease the
resource usage in the termination.
The T.30 FAX signal CNG is unique, so if you are not interested to support
FAX, you can reduce the load on the termination slightly by not setting FAX
in "calltyp".

> the calltyp property to a single value, e.g. FAX or DATA?

No, there are too many cases when deeper analysis of the detected events is
needed to make the discrimination. It may for example be depending on data
values in the V.8 signals. The MGC is expected to make the judgement and
continue handling the call according to the discriminated call type and
modulation mode.

The termination should not detect the same signals as the ones transmitted.
Otherwise, the procedure does not tell about any limitation.

> originating MG to detect and report CED and V.21 flags?

Yes.

> using SIP). When I look at the Mule draft for SIP, it does no such thing.

Your assumption sounds right.

For text telephony, I assume that the normal case would not be to repeat
exactly the received signal at the other termination. Rather the other
termination should be open for a connection with another type of textphone,
and the gateways and inter-connection operate as a mode converter between
different kinds of textphones.

> John

Best regards

Gunnar

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From: Gunnar Hellstrom <[email-masked]>
Date: Mon, 16 Dec 2002 23:16:19 +0100

Hi,

Explanations below

Yes.

Best regards

Gunnar