[MMUSIC] Can we use "a=bundle-only" in subsequent offers, instead of using a "shared address"?

[Taylor Brandstetter <[e-mail]>]

In an initial offer, if we want to communicate "this 'm=' section must be
either bundled or rejected", that's accomplished with "a=bundle-only":

a=group:BUNDLE A B
m=audio 10000 ...
a=mid:A
...
m=video 0 ...
a=mid:B
a=bundle-only

In subsequent offers, this is accomplished by duplicating the IP
address/port (see section 8.3.3):

a=group:BUNDLE A B
m=audio 10000 ...
a=mid:A
...
m=video 10000 ...
a=mid:B

Is this initial vs. subsequent offer difference necessary? Both blobs of
SDP are communicating the same information, so the "shared address" rules
seem to only add complexity.

Also, the approach of using a "shared address" to communicate something
isn't extensible to protocols that don't use an address for identification,
like ICE. We'd need to define additional rules for those cases, or allow
them specifically to use "a=bundle-only" in subsequent offers.