AVPF-RTCP-Intervals

```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
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Simulated distributions of
RTCP transmission
interval
Tn is AVPF sending rules
without suppression or
reconsideration, i.e.
Td*rand(0.5,1.5)
AVPF(TN no supp) is with
reconsideration
AVP is RFC 3550 including
reconsideration
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:
FALSE
• Trr-int:5
• Tmin:5 (AVP
only)
Td << Trr-int
•
•
•
•
Here the RTCP bandwidth
portion the calculation uses
has been increased from
500 to 10k bps, i.e. 20
times
• 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:
FALSE
• Trr-int:5
• Tmin:5 (AVP
only)
Td>Trr-Int
• Same RR as the problem
slide 500 bps, but now
with 4 members, i.e. 3
• 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:
FALSE
• Trr-int:5
• Tmin:5 (AVP
only)
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
on:
• Trr-int that sets suppression
• The Td deciding values:
–
–
–
–
Members
Senders
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
performance:
• 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
Recommendations
• 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