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Congestion Control Theory and IEEE Standardization
Final Project Network Simulation ModelingPresented by:Denis Surkes ID 321416505Ran Levy ID 36679215
QCN (Quantitazed Congestion Notification)The QCN Algorithm has been developed to
provide congestion control at the Ethernet layer, or at L2.
The algorithm issues a pause message to upstream buffers, when the buffer at a congested link fills up.
This action ensures packets do not get dropped due to congestion.
The QCN Algorithm
QCN
CP Algorith
m
RP Algorith
m
The CP Algorithm (Brief review)
The CP AlgorithmCalculate Fb (feedback value that indicate
the level of congestion) for each income frame
Fb = (Qeq-Qlen) – w*(Qlen-Qlen_old)If Fb<0 send a congestion message back with
quantized Fb value
The RP AlgorithmTwo counters: byte-counter and timerBoth reset by Fb < 0 signal
Byte-Counter• 5 cycles of FR (150KB/cycle)• AI cycles afterwards (75KB/cycle)
Timer• 5 cycles of FR (TIMER_PERIOD msec/cycle)• AI cycles afterwards (TIMER_PERIOD/2msec/cycle)
RL 3 states – Fast recoveryActive increasehyperActive increase
Simulation GoalAnalyze a network with high dataRates, and a
congested links.Activate the QCN algoritm in such a network
and analayze the RTT times and stabilty of the network
Compare the behavior of congested link with and without the QCN algorithm.
Compare several parameters in the QCN algorithm itself.
Implementation descriptionNetwork Topology
Switch
Message Controlle
r
CP
CP
CP
CP
CP
In[0]
Out[0]
In[1]
Out[1]
In[2]
Out[3]
Out[2]
In[3]
In[4]
Out[4]
To Host
To Host
To Host
To Host
To Switch
Switch DescriptionManage Controller – control flow of income
packets from input to CP and feedback Messages from CP to output
Manage switch routing table that configured through switch configuration file
CP (Congestion Point) - simulate output buffer and apply CP algorithm to all income packets
Host DescriptionRP algrotihm is implemented hereCreating the packets according to current
Rate by changing the datarate channel.Distributing the packets:
UniformlyAlways sends through bottle neck
Calculates RTT
AssumptionsSwitch is ideal, i.e routing the packets don’t
take time and routing tables are already configured.
No delay and errors on channelsHost doesn’t create packets faster than the
current rate.Packets are normal distributed (1000,200)Feedback messages have priority over
regular messages.
QCN Off Preventing the switch from sending feedback
messages
QCN offQueue length Host datarate
Queue length:Mean: 299.59290915772 Stddev: 3.0531562271108 Max: 300.0Packets loss: 3696354
QCN On Feedback messages generated to prevent queue
overload and packets lost.
Queue length on switch
Mean: 60.27619Stddev: 1.5215605
dataRates hosts 0-3
Mean: 2.3249501*10^9Stddev: 1.1768111*10^8
Mean: 2.3903864*10^9Stddev: 1.5451428*10^8
Mean: 2.72004*10^9Stddev: 9.306672*10^7
Mean: 2.5859536*10^9
Stddev: 7.528326*10^7
Host datarate zoomed
Feedback count
Mean: 34.05208Stddev: 4.104861
Uniform distribution Hosts - sends packets uniformly
Queue Length, HistogramMean 33.4116
Stddev 24.4033
Feedback counter interval 1ms
Mean 30.8372Stddev 11.8787
RTT
Mean 3.92304e-05
Stddev 3.63771e-05
Max 0.000488596
DataRate hosts 0-3
Mean:4.361909*10^9 Mean: 4.43117*10^9Stddev: 4.917516*10^8 Stddev: 4.841612*10^8
Mean: 4.6436*10^9 Mean: 4.14858*10^9Stddev: 3.271976*10^8 Stddev: 2.638262*10^8
Host datarate zoomed
Short timer Hosts- sends to bottlneck
Timer- set to 1ms
Queue length
Mean 60.9034
Stddev 11.8053
Datarate host0-3
Mean: 2.72934*10^9 Mean: 2.399835*10^9Stddev: 2.79716*10^8 Stddev: 2.22185*10^8
Mean: 2.541936*10^9 Mean: 2.392924*10^9Stddev: 1.45063*10^8 Stddev: 1.01734*10^8
Host Datarate hyperactive increase
Feedback counter
Mean 40.1959
Stddev 16.0076
RTT
Mean 0.000108274
Stddev 1.45964e-05
Conclutions The QCN algorithm is essential in data centers
because it allows the ability to transfer huge amounts of data without any loss of packets
When QCN is active there is almost no reduction In RTT.
Congested link is fully optimized while maintaining fairness to all hosts.
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