Presented by: Denis Surkes ID 321416505 Ran 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 CP Algorithm Calculate 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 Algorithm Two counters: byte-counter and timer Both 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/2 msec/cycle) RL 3 states – Fast recovery Active increase hyperActive increase
Simulation Goal Analyze 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.
Switch Message Controller CP In Out In Out In Out Out In In Out To Host To Switch
Switch Description Manage 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 Description RP algrotihm is implemented here Creating the packets according to current Rate by changing the datarate channel. Distributing the packets: Uniformly Always sends through bottle neck Calculates RTT
Assumptions Switch is ideal, i.e routing the packets dont take time and routing tables are already configured. No delay and errors on channels Host doesnt create packets faster than the current rate. Packets are normal distributed (1000,200) Feedback messages have priority over regular messages.
Preventing the switch from sending feedback messages
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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