[M4IF Technotes] Switching between different bit-rates

[Lucia]

Hallo everybody,
I would like to know if there are specifications in the standard about the
switching between files with different bit-rates assuming that a server uses
the switching to adapt to the channel variations.
For example having a 32Kbps file and a 64Kbps file stored in the server, and
assuming the channel capacity varies between this rates, is it possible to
transmit on file or the other? That is, is the reference decoder able to
decode a mixed flow?
Is there some standardization on how to switch among files with different
encoding rates?
Is there a reference software that allows the switching between the two
 files?
I guess, if something exist it would be in the System part, Am i right?
Thanks in advantage for your answer.
Lucia Valentini