Addressing Christian's last questions, the answerer CAN send
telephone-events (with PT 101) and the offerer should be prepared to
receive them. The 3rd paragraph in Section 5.1 of 3264 describes this.
IMHO, if it is desired to free an advertised codec that was not
advertised by the peer, the session needs to be re-negotiated.
Best regards,
Bert
Paul Kyzivat wrote:
Christian,
As I understand offer/answer, the offer and answer you show mean that
only PCMU may be used, in both directions. AFAIK there is no way to
express that PCMU may be used in both directions and telephone-event may
only be used in one direction on the same media stream. The best I could
see to approximate that wojuld be to have one sendrecv stream for PCMU
and a separate sendonly stream for telephone-events.
Paul
Christian Jansson wrote:
Imagine an INVITE with an SDP that looks roughly like this that is
received by a UA:
v=0
m=audio 10000 AVP/RTP 0 101
a=rtpmap:0 PCMU/8000
a=rtpmap:101 telephone-event/8000
a=fmtp:101 0-11
If that UA can send, but not receive telephone-event, what is the answer
SDP then supposed to look like? More exactly what would the SDP answer
below indicate?
v=0
m=audio 20000 AVP/RTP 0
a=rtpmap:0 PCMU/8000
Of course it means that both sides will use PCMU for both send and
receive with PT=0. The question is if the UA that sent the answer if
allowed to send telephone-event's with PT=101? Should the UA that sent
the offer always be prepared to receive with all the codecs it announced
or should it "cease to listen" to codecs that wasn't mentioned in the
SDP answer?
/ Christian Jansson
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