[Tmrg] Scenario "Impact of transient states on CC"

[Romaric Guillier]

Hi!

Here is my proposal for a scenario to test the impact of transient states on CC
methods and some points that need to be discussed.

Cheers
Romaric Guillier
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*Scenario transient events


Through this scenario, we are trying to evaluate the impact of a sudden change of congestion level on a given congestion control method. We are considering both the case where there is a sudden decrease or increase of the congestion level. 

This scenario is composed of three parts: the control, the uphill test and the downhill test. The control corresponds to a file transfer of a given volume of data, so as to check the necessary time to complete its transfer without perturbations. The downhill test consists in abruptly applying a given congestion level while a file transfer is occuring, the uphill test is done by starting a file transfer when there is congestion in the system, later the congestion abruptly desappears. 


*Parameters

V, the size of the transfer 
Cg, the congestion level that is applied to the system

 
*Metrics

Aggressiveness = (Tuphill - Tcontrol)/ Tcontrol
Responsiveness = (Tdownhill - Tcontrol)/ Tcontrol


*Timeline


--Control
At time = 0, a transfer of size V is started
At time = Tcontrol, the transfer completes

--Downhill test
At time = 0, a transfer of size V is started 
At time = Tcong, Cg is applied to the system
At time = Tdownhill, the transfer completes

--Uphill test
At time = -1, Cg is applied to the system
At time = 0, a transfer of size V is started
At time = Tcong, Cg is removed from the system
At time = Tuphill, the transfer completes


*To be discussed:

- Why not putting the uphill/downhill phase during the same transfer ?  So that we don't need to ask ourselves questions about convergence and when to switch, we would still need to perform two tests to covert every possibilities  
- Should we remove the slow start phase ?  
- How to generate the congestion: *UDP, similar TCP flows (interaction with the interfairness problem), reference TCP flows (interaction with the intra-fairness problem)
- Tcong is a function of V(,RTT) : time to transfer X% of V when there is no congestion , time to be well out of the slow start phase, etc..