AVPF vs AVP RTCP Intevals
AVP and AVPF Interop
• Whe AVP and AVPF is interoperating one must
choose certain parameters correctly.
• In trying to determine the most suitable based
on the timing rules a AVPF timing issue was
found that is problematic for interop.
• Based on simulations of the algorithm
– There might be bugs in the simulation
AVPF vs AVP Problems
Simulated distributions of
RTCP transmission
Tn is AVPF sending rules
without suppression or
reconsideration, i.e.
AVPF(TN no supp) is with
AVP is RFC 3550 including
When Td calculation
becomes close to, but
below Trr-int AVPF
suppression pushes
transmissions interval
distribution upwards and
uneven in distribution
• avg_rtcp_size:
200 bytes
• RR: 500 bps
• RS: 1000 bps
• Senders: 1
• Members: 2
• We_sent:
• Trr-int:5
• Tmin:5 (AVP
Td << Trr-int
Here the RTCP bandwidth
portion the calculation uses
has been increased from
500 to 10k bps, i.e. 20
• Reduces Td
Therefore both Tn and
AVPF without suppression
are all ending up in the
0.25-0.5 s range
As can be seen the AVPF
distribution are mostly
uniform in the range 0.51.5*Trr-int, with a little bit
of tail
However, still longer tail
than AVP
• avg_rtcp_size:
200 bytes
• RR: 10000 bps
• RS: 1000 bps
• Senders: 1
• Members: 2
• We_sent:
• Trr-int:5
• Tmin:5 (AVP
• Same RR as the problem
slide 500 bps, but now
with 4 members, i.e. 3
receivers sharing RR
• As can be seen here only a
little bit of suppression
happens at the 4-7.5 s
range, i.e. 0.5-1.5*Trr-int.
• That suppression do show
up as bit of long tail above
12.5 seconds
• avg_rtcp_size:
200 bytes
• RR: 500 bps
• RS: 1000 bps
• Senders: 1
• Members: 4
• We_sent:
• Trr-int:5
• Tmin:5 (AVP
Question: What gives best interop?
• So how does an AVPF user set his parameters to best interoperate from a
perspective of avoiding accidental timeout:
– The Regular RTCP transmission distribution is one factor which is depending
• Trr-int that sets suppression
• The Td deciding values:
RR and RS
Average RTCP packet size
– The other is when AVPF times out AVP participants
• 5*Trr-Int given that Trr-int != 0
• Thus we must combine Trr-int large enough so that an AVPF particpant do
not time out AVP participants
• At the same time AVPF regular RTCP transmission interval should not be
so long that AVP times out
• How many consecutive packet losses are needed before timeout happens?
Td parameterization
• When using AVPF one should try to avoid setting
RR and RS so that Td in the given session are close
to Trr-int.
– The tail in the AVPF RTCP interval distribution is at its
extreme at 1.5*Trr-int + 1.5*Td/1.21828
• Worst case Td = Trr-int: 2.73*Trr-int
– Td should preferably be less than 1/4th of Trr-Int
• That gives us max tail length of:
– 1.5*Trr-int + 1.5*Trr-int/(4*1.21828) ≈ 1.81 Trr-int
– AVP’s tail ends at 1.5*Tmin/1.21828 = 1.231*Tmin
• Given that Td is less than Tmin
• Otherwise replace Tmin with Td
Equalizing the tails
• If we would like to have equally values for the
extreme randomization intervals given that Td
is less than Tmin and Trr-int:
– Trr-int = 1.231/1.81*Tmin
• 1.81 (following the Td < 1/4th Trr-int recommendation)
– Tmin = 5 s => Trr-int = 3.40 s
• This ensures that no AVPF session participant
is more likely to time out than an AVP one.
• However, the reverse is not true.
Timing out AVP participants
• An AVPF participant will timeout an
participant at 5*Trr-int,
– Equivalent of AVP participants using a Trr-int as a
factor for number of intervals before timing out.
– This assumes Tmin=5s and Td<Tmin
Finding the optimal both ways
• So what is the point of least decrease in timeout robustness
• Given that Tmin = 5 s and Td < Tmin
– AVPF intervals before AVP timeout(target):
• 5*Tmin/(Trr-int)
– AVPF intervals before AVP timeout(1/4 * Trr-int):
• 5*Tmin/(Trr-int*1.81)
– AVPF Intervals before AVP timeout (1/10 * Trr-int):
• 5*Tmin/(Trr-int*1.623)
– AVP intervals before AVPF timeout (target):
• 5*Trr-int/5
– AVP intervals before AVPF timeout (worst case):
• 5*Trr-int/(1.231*Tmin)
Number of Reporting Intervals
given Trr-int
• Based on these findings it appears that the
following recommendations for AVPF vs AVP
interop should be given:
– RR and RS sufficiently large that Td becomes less
than ¼ of Trr-int
– Trr-int should be chosen as 4.0
Future Work?
• Do the Suppression algorithms bad behavior
needs to be addressed?

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