On 2/22/12 6:51 AM, [email protected] wrote:
> Hi,
>
> I am struggling to find out this from long time, however have seen
> some implementation as follows;
>
> 1. First of all, you can't know whether remote end has a capability to
> detect DTMF in Inband.
> 2. For SIP INFO, your device can consider that remote end supports SIP
> INFO if received in Allow header. If received, it's upto your device
> whether to generate DTMF in Inband or SIP INFO.
> 3. You can't always fallback to SIP INFO if RFC 2833 negotiation
> fails. Remote end must be capable of detecting DTMF in SIP INFO and
> this would be known only if INFO is received in Allow header. If RFC
> 2833 negotiation fails and remote end hasn't capability of detecting
> DTMF in SIP INFO, you haven't any other choice than sending DTMF in
> Inband :)
>
> Different people may have different views but that is what implemented
> in most of the live products.
The problem is more difficult than you have described.
There is no official standardized info package for DTMF, though there is
a defacto one that is used a number of places. Then there is the KPML
event package. And Cisco also has a different event package that they
use with unsolicited NOTIFYs without any subscription, which of course
is entirely nonconforming.
Cisco uses some proprietary indications with some heuristics to decide
which to use. But I don't have the details. And other companies must
also have their own techniques.
Good Luck,
Paul
> Best Regards,
> Vivek Batra
>
> Quoting "Manoj Priyankara"<[email protected]>:
>
>> Folks,
>>
>> I wonder how the offerer recognizes whether a particular SIP end point
>> supports in-band DTMF or SIP INFO by negotiating SDP? SIP INFO is assumed
>> when RFC2833 negotiation fails but how exactly we know whether the endpoint
>> supports SIP INFO not In Band?
>>
>> Cheers!
>> Manoj
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