2. Content
Rate control definition
Non Linear Theory
Recent Development of research
Solution proposal
3. Facts about Rate Control
End to end protocol
It is used to deliver UDP packet, via RTP as the
carriage
in certain speed based on the information
The information used is RTCP packet, which is
feedbacked through the source
8. How to control it ?
We have information from the feedback,
− What kind of information available ?
We have to use equation to control the speed,
− What kind of equation we will use ?
9. Feedback Information
1. Number of packet delivered at receiver
2. Loss occurred at receiver
3. Time needed to travel from source to receiver
(RTT)
10. Non Linear Theory
Total rate defines the rate from the source
Constitute of the
− constant source rate, Ini(k) ;
− feedback rate, U(k).
We use feedback to control rate
If packet dropping occurs, the feedback rate is negative
and source will reduce its rate.
If no packet dropping, the feedback rate is positive and
the source will increase the rate
We called it non linear because the theory predict
the packet accumulation non linearly
13. State of Research
We still use priority for RTCP packet on the router
− Without priority, RTCP packet will be dropped just
like RTP packet, therefore the rate control won't work
efficiently
− New time out mechanism is necessary to smooth out
some lost RTCP packets
Start up mechanism had not been decided
− Before RTCP packet is received, we can not control the
speed
− Any idea ?
14. Delayed feedback problem
− If the propagation delay is too big, then the
information will be too late to be received and
processed. The feedback will be obsolete, because by
that time the network condition already change
− Can not be avoided because this is the nature of
network
23. Shortcomings :
If we sent RTCP after drop happens, it will be too
late to prevent dropping
We can schedule some RTCP packet to be sent
ahead in the prescribed interval by looking at
RTT, but the questions are
− How many RTCP is necessary ?
− When we need to launch RTCP or what is the ideal
RTCP interval ?
We do not want to flood the network with RTCP
packet
24. Solution (1/2)
Start Up problem :
− We use back to back packet to detect the bottleneck
link
− We have bottleneck bw, we can start with it ->
SOLVED
Back to back (B2B) packet : 1500 bytes
We measure interval between 2 consecutive B2B
Bottleneck bandwidth = (1500*8)/interval
As initial state, we use B2B bandwidth as RTP
rate
25. Solution (2/2)
Delayed Feedback problem :
− The RTCP maybe too late whilst network condition
change.
− Why don't we predict the network condition to prevent
dropping
− Prediction by the following method
Combining ARMAX algorithm and neural network or
Analyzing group behaviour of group flow
26. Combining ARMAX with
Neural Network
The author of non linear already presume the
problem with variable delay, therefore he propose
a more complicated NN to deal with delay
NN can have unpredictable result (which is why
we do not prefer)
NN is used to find the parameter for accumulated
traffic
What kind of NN suitable for our model ?
27. Analysing Group Behaviour
Dropping occurs because all flows put high
number of packet in the network
Dropping in one flow reflects all other flow
condition
Using this information, we can predict group
behavior
Group behavior will be used to detect when we
should launch RTCP packet