Homework SourseThe ssthresh value for a Taho TCP station is set to 6 MSS Th
The ssthresh value for a Taho TCP station is set to 6 MSS. The station now is in the slow-start state with cwnd = 4 MSS. Show the values of cwnd, sstresh, and the state of the station before and after each of following events: five consecutive nonduplicate ACKs arrived followed by a time-out, and followed by two nonduplicate ACKs.
The ssthresh value for a Taho TCP station is set to 6 MSS. The station now is in the slow-start state with cwnd = 4 MSS. Show the values of cwnd, sstresh, and the state of the station before and after each of following events: five consecutive nonduplicate ACKs arrived followed by a time-out, and followed by two nonduplicate ACKs.
The ssthresh value for a Taho TCP station is set to 6 MSS. The station now is in the slow-start state with cwnd = 4 MSS. Show the values of cwnd, sstresh, and the state of the station before and after each of following events: five consecutive nonduplicate ACKs arrived followed by a time-out, and followed by two nonduplicate ACKs.
Solution
Answer:
ACK: Acknowledgment is vaild
Initially:
cwnd=4;
ssthresh=advertised window size;
New ACK Received:
if(cwnd<ssthresh)
/*slotw star*/
cwnd=cwnd+1;
else
/*cong.Avoidance*/
cwnd=cwnd+1/cwnd;
Time out:
/*Multiplicative decrease*/
ssthrsh=cwnd/2;
==>TCP Tahoe :
a)Slow Start
b)Congestion Avoidance
c)Fast Retransmit
==>Duplicate ACKs:
Fast retransmit
Fast recovery
-->> Fast Recovery avoids slow start.
>> TCP Reno improves upon TCP Tahoe when a single packet is dropped in a round-trip time.
>> Fast recovery avoids slow start after a fast retransmit.
>> Intuition: Duplicate ACKs indicate that data sgetting through.
>> On packet loss detected by 3 dup ACKs:
ssthresh = cwnd/2
cwnd=ssthresh enter congestion avoidance.
