[MMUSIC] RTP/AVP vs RTP/AVPF vs RTP/SAVPF vs .... how to pick a default?

[Emil Ivov <[e-mail]>]

Hey all,

We've recently implemented support for DTLS/SRTP and a question that
we had somehow avoided in the past with SDES and ZRTP is now back on
the table:

By default, which profile would a SIP UA use in an outgoing offer?

Until recently recently we were offering RTP/AVP by default, which is
ok for ZRTP and tolerated by most of the endpoints that support SDES.

We also had a couple of config options that allowed Jitsi to (A)
create offers with RTP/SAVP(F) in case someone turned out to be picky
about the transport or (B) duplicate all m= lines and offer them with
every supported transport so that the remote endpoint would pick what
it likes.

Obviously option (A) is not a suitable default for a generic SIP UA
because that would make it incompatible with the majority of the
endpoints that exist today. (B) could have worked but now that we are
going for "Unified", having the same "m=" line appear with RTP/AVP and
then again with RTP/SAVPF would have to be interpreted as two
independent streams rather than the same stream being available over
two different transports.

So, do we have a story here or do we need to create one?

Emil

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