TCP fast retransmit and recovery overview PDF - EventHelix.com

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Module Interfaces (TCP Fast Retransmit and Recovery)Client Node Internet Server Node EventStudio System Designer 6TCP SegmentTCP segment (start sequence number = 101024) is transmittedseq_num = 101024TCP Segmentseq_num = 101536TCP Segmentseq_num = 102048TCP Segmentseq_num = 102560TCP Segmentseq_num = 103072TCP Segmentseq_num = 103584TCP segment (start sequence number = 101536) is transmittedTCP segment (start sequence number = 102048) is transmittedTCP segment (start sequence number = 102560) is transmittedTCP segment (start sequence number = 103072) is transmittedTCP segment (start sequence number = 103584) is transmittedTCP Segmentseq_num = 100000TCP segment (start sequence number = 100000) is delivered to thereceiverTCP Segmentseq_num = 100512TCP segment (start sequence number = 100512) is lost due tocongestion in the network.TCP Segmentseq_num = 101024ACKack_num = 100512TCP Segmentseq_num = 101536ACKack_num = 100512TCP Segment with start sequence number 101024 is received. TCPrealizes that a segment has been missed. TCP buffers the out ofsequence segment as TCP cannot deliver out of sequence data to theapplication.TCP sends an acknowledgement to the Sender with the next expectedsequence number set to 100512.TCP receives the next segment. This and the following out of sequencesegments will be buffered by TCP.TCP sends another acknowledgement with the next expected sequencenumber still set to 100512. This is a duplicate acknowledgementTCP Segmentseq_num = 102048ACKack_num = 100512TCP keeps acknowledging the received segments with the nextexpected sequence number as 100512TCP Segmentseq_num = 102560ACKack_num = 100512TCP Segmentseq_num = 103072ACKack_num = 100512TCP Segmentseq_num = 103584
Module Interfaces (TCP Fast Retransmit and Recovery)Client Node Internet Server Node EventStudio System Designer 6ACKack_num = 100512Fast retransmitFast Retransmit: TCP receives duplicateacks and it decides to retransmit thesegment, without waiting for the segmenttimer to expire. This speeds up recoveryof the lost segmentACKack_num = 100512ACKack_num = 100512ACKack_num = 100512ACKack_num = 100512TCP Segmentseq_num = 100512Client receives acknowledgement to the segment with starting sequencenumber 100512First duplicate ack is received. TCP does not know if this ack has beenduplicated due to out of sequence delivery of segments or the duplicateack is caused by lost segment.Second duplicate ack is receivedThird duplicate ack is received. TCP now assumes that duplicate ackspoint to a segment that has been lostTCP retransmits the missing segment i.e. the segment corresponding tothe ack sequence number in the duplicate acksFast RecoveryFast Recovery: Once the lost segment has beentransmitted, TCP tries to maintain the current dataflow by not going back to slow start. TCP alsoadjusts the window for all segments that have beenbuffered by the receiver.ACKack_num = 100512ACKack_num = 100512Another duplicate ack is received. This means that the receiver hasbuffered one more segmentYet another ack is received, this will further inflate the congestionwindowTCP Segmentseq_num = 100512ACKack_num = 104096Finally, the retransmitted segment is delivered to the serverNow TCP acknowledges all the segments that it had bufferedACKack_num = 104096The cummulative TCP ack is delivered to the clientCongestion AvoidanceClient closes TCP connectionClient to server TCP connection releaseFINClient sends a TCP segment with the FIN bit set in the TCP header
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TCP fast retransmit and recovery overview PDF - EventHelix.com

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