[asterisk-dev] Supported: ms-early-media

Klaus Darilion klaus.mailinglists at pernau.at
Fri Nov 19 06:19:44 CST 2010



On 18.11.2010 23:16, CDR wrote:
> Please somebody confirm if the supported header may appear more than once.

Next time please go to RFC 3261, check the ABNF and verify it yourself. 
This time the answer is:yes

   [H4.2] also specifies that multiple header fields of the same field
    name whose value is a comma-separated list can be combined into one
    header field.  That applies to SIP as well, but the specific rule is
    different because of the different grammars.  Specifically, any SIP
    header whose grammar is of the form

       header  =  "header-name" HCOLON header-value *(COMMA header-value)

Let's check the Supported header:

Supported  =  ( "Supported" / "k" ) HCOLON
               [option-tag *(COMMA option-tag)]

So I would say the Supported header qualifies for multiple headers in a 
single message.


Asterisk only sends:

   Supported: replaces, timer

Actually, there shouldn't be a need to explicitly signal support for 
early-media as every device should support it. But to do it the MS way 
you can try:

exten => _X.,1,SIPAddHeader(Supported: ms-early-media)
exten => _X.,1,Dial(SIP/wahtever......)

This should give you a request with 2 Supported headers and it should work.

Anyway, next time you should just try it yourself - that would have been 
much faster.

regards
klaus
> Yours
> Feerico
>
> On Thu, Nov 18, 2010 at 6:33 AM, Klaus Darilion
> <klaus.mailinglists at pernau.at <mailto:klaus.mailinglists at pernau.at>> wrote:
>
>     I think the Supported header may appear several times, so you can
>     try using the SIP ADD HEADER function and add the header yourself
>
>     regards
>     klaus
>
>
>     On 18.11.2010 01:33, CDR wrote:
>
>         Is there an option in sip.conf for 1.6.2 that would add this to
>         the INVITE?
>         Supported: ms-early-media
>         In my invites I see:
>         Supported: replaces, timer
>         But I have not seen any option that would add the ms-early-media
>         option.
>
>         Here’s a link to the RFC3960 Describing the benefits of early
>         media vs
>         late media.    In summary you eliminate “clipping” as it’s called.
>
>             Media clipping occurs when the user (or the machine
>         generating media)
>             believes that the media session is already established but the
>             establishment process has not finished yet. The user starts
>         speaking
>             (i.e., generating media) and the first few syllables or even the
>             first few words are lost.
>
>
>



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