[AVTCORE] Security/Performance issue in circuit breakers

[Magnus Westerlund <[e-mail]>]

Hi,

In a discussion in the RTCWEB around consent and circuit breakers I made
a realization that there exist a significant issue in circuit breakers
that isn't document nor dealt with.

This has to do with the configuration of the RTCP bandwidth. If a
malicious user of circuit breakers wants to make it really inefficient
one can achieve that by configuring the RTCP bandwidth really low. So
assuming b=RR and b=RS exists in an implementation that has circuit
breakers. The method for making it inefficient and not affect the
traffic pattern is to set the RTCP bandwidth really low. Using an RR=1
bps would mean that the Td deterministic reporting interval would be ~45
min. Thus, putting all of these limits on traffic to be no reactive
until roughly 2-3 reporting interval, i.e. 1.5-2.25 hours have passed.
Which is longer duration than many real-time interactive media sessions
are to start with.

I think we need to ensure that RTCP reporting is not happening less
often than what the fixed minimal interval (5s) will mean. Thus, I see
that including circuit breaker would require a hard requirement that one
configure the RTCP bandwidth to allow for at least each SSRC reporting
each 5 seconds.

This also needs to go into the security consideration section to make
clear that this is an issue.

Cheers

Magnus Westerlund

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