On 1/15/2014 5:50 AM, Gareth Blades wrote:
On 15/01/14 09:39, Francesco Namuri wrote:
Hello James,
thanks for your answer, I supposed this too, but my provider answered me
that as
m=audio 43718 RTP/AVP 8 18 3 101
^ ^ ^---- GSM proposal
^ ^------- G729 proposal
^---------- aLaw proposal
And that
a=rtpmap:18 G729/8000 proposed as media conversion
a=rtpmap:3 GSM/8000/1 because the call is made by a mobile
I would agree with what your service provider has said. If you look at
the RFC http://tools.ietf.org/html/rfc4566#section-5.14 the '8 18 3 101'
parameters are a list of media formats. The first is the one which
should be used but (preferred choice) but the other may be used. Numbers
in the range 96-127 are dynamic payload types and these must have a
corresponding 'a=' line specifying the payload type and the codec options.
Lower numbers have static payload assignments and according to that RFC
dont have to have corresponding 'a=' lines. A list of types can be found
at http://www.iana.org/assignments/rtp-parameters/rtp-parameters.xhtml
However in all SIP traces I have seen there has always been a 'a=' line
for every payload type offered. The static payload type numbers are used
but there is still the 'a=' line.
I missed the RTP/AVP line. I'll go back to lurking for a bit :)
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