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Revision as of 10:28, 22 September 2019

65 bytes removed ,  4 years ago
→‎TCP
Line 208:
 
[[File:Mtu mss.png|center]]
 
* '''RTO:''' Four ACKs acknowledging the same packet, which are not piggybacked on data and do not change the receiver's advertised window.▼
 
*Fast Retransmission▼
- If RTO has a larger value▼
- If sender receives four acknowledgments with same value (three duplicates)▼
- Segment expected by all of these Ack is resent immediately▼
 
*Fast Recovery:
| -▼
-
 
*Congestion Control
 
;Slow Start - Exponential Increase
- Sender starts with cwnd = 1 MSS, Size increases 1 MSS each time one Ack arrives, Increases the rate exponentially(1,2,4,8....) until a threshold is reached
Line 236 ⟶ 248:
* Behavior of Tahoe and Reno differ primarily in how they react to duplicate ACKs.
 
<center>
Reno:
If three duplicate ACKs are received, Reno will
Skip the slow start phase by instead halving the congestion window (instead of setting it to 1 MSS like Tahoe),
Setting the slow start threshold equal to the new congestion window
Enter a phase called fast recovery.
 
* In both Tahoe and Reno, if an ACK times out (RTO timeout), slow start is used, and both algorithms reduce congestion window to 1 MSS.
▲* Four ACKs acknowledging the same packet, which are not piggybacked on data and do not change the receiver's advertised window.
 
 
{| class="wikitable"
|-
! Event !! Tahoe !! Reno
|-
| 3 Dup Acks || performsPerforms a fast retransmit<br> Sets the slow start threshold to half of the current congestion window<br>Reduces the congestion window to 1 MSS<br>Resets to slow start state || performPerform a fast retransmit<br>Skip the slow start phase by instead halving the congestion window<br>(instead of setting it to 1 MSS like Tahoe)<br>Setting the slow start threshold equal to the new congestion window<br>Enter a phase called fast recovery.
|-
| RTO (Ack time out) || Slow start is used<br>Reduce congestion window to 1 MSS || Slow start is used<br>Reduce congestion window to 1 MSS
| RTOs || Example || Example
▲|-
| Example || Example || Example
|}
</center>
 
----
 
*Silly Window Syndrome: Sender creates data slowly or Receiver consumes slowly or both.
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- '''Delayed Acknowledgment''': Segment not acknowledged immediately, Sender TCP does not slide its window, reduces traffic, sender may unnecessarily retransmit, Not delay more than 500 ms.
 
▲*Fast Retransmission
▲ - If RTO has a larger value
▲ - If sender receives four acknowledgments with same value (three duplicates)
▲ - Segment expected by all of these Ack is resent immediately
 
*Persistence Timer
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