[SIPForum-discussion] Decoding G711 audio

Thu May 22 09:54:33 UTC 2008

>> It all depends on your final application,
so if you have a setup where you know exactly what the other end will  >> be setup
to do, and you can rely on it handling SIP INFO, then great. 

Hi Malcom, 

I am fortunate enough to say that in our case, I can ensure that the SIP Phones that we are using (at both ends) will be configured to send DTMF as SIP INFO. Good for me. Again, thanks for your comments. :-)

-----Original Message-----
From: Malcolm Howlett <malcolm at c3.co.uk>
To: discussion at sipforum.org
Sent: Thu, 22 May 2008 2:40 pm
Subject: Re: [SIPForum-discussion] Decoding G711 audio

Well Rajesh, I’m afraid it m
 ay not
be as simple as that.

It all rather depends on what the other
end you want to communicate also wants to talk. Some one more up with all the intricacies
of the different SIP RFCs will be better qualified to comment than me, but
there is no way, as I understand it, to negotiate that you are going to
transfer DTMF via SIP INFO.

You might get it, you might not.

The only one of the 3 methods that you
actually negotiate is RFC2833 in the SDP.

It all depends on your final application,
so if you have a setup where you know exactly what the other end will be setup
to do, and you can rely on it handling SIP INFO, then great. If you want=2
 0your
application to talk to more generic SIP phones, then you might not be so lucky,
as it will depend on how they are configured.

For example, one of our test phones is a
Grandstream (http://www.voiptalk.org/products/Video+Phones/Grandstream+GXV-3000+IP+Videophone),
and the setting on whether it will send its DTMF in SIP INFO is in its config,
and I have yet to see any indication of the setting in any of the SIP call
setup messaging coming out of it.

Welcome to the wonderful, dubiously
defined, world of SIP J

Regards

Malcolm Howlett

From: mfc at aol.in
[mailto:mfc at aol.in] 

Sent: 22 May 2008 09:
 48

To: malcolm at c3.co.uk

Cc: discussion at sipforum.org

Subject: Re: [SIPForum-discussion]
Decoding G711 audio

I thank you for your valuable information and time, Mr. Malcom. I've selected
the SIP INFO message way of doing this. Thanks again and I really appreciate
your help. There's just the third question left unanswered and I'm hoping that
someone would answer that too. :-)

Rajesh R.

-----Original Message-----

From: Malcolm Howlett <malcolm at c3.co.uk>

To: discussion at sipforum.org

Sent: Thu, 22 May 2008 1:33 pm

Subject: Re: [SIPForum-discussion] Decoding G711 audio

From: mfc at aol.in [mailto:mfc at aol.in]

Sent: 22 May 2008 06:26

To: discussion at sipforum.org

Subject: [SIPForum-discussion]
Decoding G711 audio

Hello all,

I have a few queries and I am totally new to VoIP.

|1. Is there a way to
convert G711 (both alaw and mulaw) back to PCM? I searched through the internet
and am still |searching,
but I thought I will put up this query to you people as someone might have
experienced this problem |already.

Well at a minimum there are lots of people
who do hardware cards with DSPs that do it. Aculab, Pika technologies are 2
companies that spring to mind, not a cheap alternative

2
 . How are DTMF tones transmitted over a SIP call? If I dial say 34 when a call
is mature, how is this tone sent to the other end? What are the commands used?
Is it sent as a MESSAGE?

Any one of (and indeed combination of) 3
ways

In band audio – dependant on the
audio codec as some of them can’t carry it

RFC2833 – negotiated in SDP

SIP INFO messages

3. Is there a way to retrieve all the registered client information (the client
extension and ID/name) from the SIP Server/Registrar? Is this possible? Can you
provide me some leads to a program or some API/Functions?

 0A 

I thank you all for your time. I appreciate it.

Warm Regards,

Rajesh R.

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