Computer networks
Download
1 / 12

Recall - PowerPoint PPT Presentation


  • 298 Views
  • Updated On :

Computer Networks Congestion Avoidance Recall TCP Sliding Window Operation Important Terms Maximum Segment Size (MSS) Window Retransmission Timer Delayed ACK Duplicate ACK Congestion Window Sender based flow control Sender uses min( cwnd ,advertised window) Tranmission window

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'Recall' - johana


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
Computer networks l.jpg
Computer Networks

Congestion Avoidance


Recall l.jpg
Recall

TCP Sliding Window Operation


Important terms l.jpg
Important Terms

  • Maximum Segment Size (MSS)

  • Window

  • Retransmission

  • Timer

  • Delayed ACK

  • Duplicate ACK


Congestion window l.jpg
Congestion Window

  • Sender based flow control

  • Sender uses min(cwnd,advertised window)

    • Tranmission window

  • Detect network condition and adjust

  • Use timers, ACKs and network feedback


Retransmitting segments l.jpg
Retransmitting Segments

  • TCP starts timer after sending a segment

  • If ACK returns, reset timer

  • If no ACK, retransmit and increase timer (2x) after resetting


Round trip time rtt l.jpg
Round Trip Time (RTT)

  • TCP measures RTT and uses RTT to calculate timer values

  • If ACKs returning quickly, timer values are kept low

  • Retransmit quickly when throughput is high

  • Allow time for ACK to return when throughput is low


Slow start l.jpg
Slow Start

  • Initialize cwnd to 1 MSS

  • Increase cwnd by 1 MSS for every ACK

  • Not very slow!


Congestion avoidance l.jpg
Congestion Avoidance

  • When packet loss occurs, TCP must slow its flow of traffic

  • When retranmission timer expires, save value of transmission window * ½ (ssthresh)

  • If congestion occurred due to a timeout, set cwnd to 1 segment

  • When data is ACK'd, increase cwnd via slow start up to ssthresh

  • Thereafter increase cwnd by 1/cwnd for each ACK



Fast retransmit l.jpg
Fast Retransmit

  • If > 2 duplicate ACKs are received, a segment was probably lost

  • Sender assumes enough time has elapsed for out of order segments to have arrived and assembled

  • Retransmit segment without waiting for a retransmission timer to expire

  • Enter Fast Recovery


Fast recovery l.jpg
Fast Recovery

  • Sender has to assume data is still flowing due to the reception of duplicate ACKs

  • Loss was probably a rare or temporary event

  • Do not go into slow start, just go into congestion avoidance mode


Other mechanisms l.jpg
Other mechanisms

  • Selective Acknowledgements (SACK)

  • TCP Pacing

    • Packeteer

  • RED

  • ECN

  • Network pricing


ad