[Users] add/rewrite a tag/parameter in SDP

[Daniel-Constantin Mierla]

Hello,

On 02/18/06 05:07, Lenir wrote:
>
> Hey guys,
>
> What is the best way to modify the SDP message to always include (if 
> not replace) the a= tags in a SDP message?
>
> My problem is specifically with g729, according to the RFC, if the 
> parameter: “a=fmtp:18 annexb=yes” is present or missing then it is 
> assumed that g729b (g729 with VAD) and if “a=fmtp:18 annexb=no” is 
> present then the devices will use g729a (g729 with VAD Disabled). My 
> problem is that some cisco gateways and ATAs behave differently (of 
> course Cisco always doing it their way), if “a=fmtp:18 annexb=no” is 
> missing then it assumes that g729a will be used, instead of following 
> the RFC where it should negotiate g729b. Also, asterisk doesn’t 
> support g729b so I want to avoid using g729b everywhere in my network.
>
> So what is the best way or is there a way, to either:
> a) insert “a=fmtp:18 annexb=no” if is not present
>
> b) replace “a=fmtp:18 annexb=yes” for “a=fmtp:18 annexb=no” if it is 
> present
>
you can use textops module. You have functions to search a string and 
replace it with another value (replace()). If the line does not exist 
then you have to use search_append(). It is in roadmap to add specific 
functions to search/replace only withing the body of the message...

http://openser.org/docs/modules/1.0.x/textops.html

Cheers,
Daniel

> Thanks in advance!!
>
> Lenir
>
> p.s. Please see the below excerpt from RFC 3555 regarding how to 
> specify G729.
>
> RFC 3555 MIME Type Registration of RTP Payload Formats July 2003
>
> 4.1.9. Registration of MIME media type audio/G729
>
> MIME media type name: audio
>
> MIME subtype name: G729
>
> Required parameters: None
>
> Optional parameters:
>
> ptime, maxptime
>
> annexb: indicates that Annex B, voice activity detection, is used or 
> preferred. Permissible values are "yes" and "no" (without the quotes); 
> "yes" is implied if this parameter is omitted
>
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