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Dr.Jun Takei #07 02/27/2007

Loss Detection: TCP Reno

• Coarse-grain timeout indicates packet loss
  
  
  • Sender starts a timer when TCP segment is sent
    
    
  • Timeout occurs if ACK not received before timeout
    
    
  • Retransmission occurs
    
    
  • Slow start is invoked (big reduction in rate!)
    
    
• Three duplicate ACKs indicate packet loss
  
  
  • Receiver required to send an ACK if it receives an out of order segment ? a segment may be out of order or lost
    
    
  • Sender assumes loss when it receives three duplicate ACKs
    
    
  • Fast retransmission and recovery mechanism ? retransmit the requested segment (which is presumed lost after three duplicate ACKs) without waiting for a timeout
    
    
  • Congestion avoidance (smaller reduction in rate)