View Full Document

Van Jacobson’s Congestion Avoidance and Control



View the full content.
View Full Document
View Full Document

3 views

Unformatted text preview:

Van Jacobson s Congestion Avoidance and Control presented by Leon Poutievski Problem Congestion Congestion Load exceeds the capacity of the network Overflow at router queues ATM channel is reserved during the connection setup IP if queue is full packets are dropped Problem Congestion Problem Wasted bandwidth retransmission required Unpredictable delay October 1986 first congestion collapse Caused by TCP retransmissions Scenario TCP sends a window s worth of data Some of it gets lost the rest sits in queue Sender times out retransmits everything Result Multiple copies of same data in queue REPEAT Problem Congestion Crux of the problem When the router is congested i e its queue is full retransmitting data all at once is exactly the wrong thing to do But this is what TCP spec said to do Go back N protocol Send window is the only constraint on sending rate sending rate send window RTT Extremely important concept Problem Congestion Thus send window controls how fast sender x mits Original TCP flow control send window rcv window Conclusion sender should also consider the network capacity Idea reduce send window to reduce rate under congestion Solution add congestion window send window min rcv window congestion window Conservation of packets principle Equilibrium stable full window of data in transit Conservative packet flow New is not put into network until an old leaves Possible problems with packet conservation 1 Didn t get to equilibrium 2 Sender ejects new packets before old has exited 3 Equilibrium can t be reached Getting to Equilibrium Slow start Self clocking system Automatically adjusts to BW delay variations Sender uses ACK as a clock Hard to start Packet size area BW x time Slow start algorithm Add congestion window to algorithm send window min rcv window cwnd When starting restarting cwnd 1 packet On ACK for new data cwnd 1 packet Slow start analysis Slow is misnomer rate grows exponentially On each ack 2 pkts are sent one for the packet acked left n w one to



Access the best Study Guides, Lecture Notes and Practice Exams

Loading Unlocking...
Login

Join to view Van Jacobson’s Congestion Avoidance and Control and access 3M+ class-specific study document.

or
We will never post anything without your permission.
Don't have an account?
Sign Up

Join to view Van Jacobson’s Congestion Avoidance and Control and access 3M+ class-specific study document.

or

By creating an account you agree to our Privacy Policy and Terms Of Use

Already a member?