TCP T ransmission Control Protocol TCP TCP TCP TCP TCP TCP TCP TCP c /(18)

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1 TCP T ransmission Control Protocol TCP TCP TCP TCP TCP TCP TCP TCP c /(18)

2 TCP TCP Transmission Control Protocol TCP TCP TCP 1981 RFC 793 Request for Comments 1) RFC 2) RFC 793 TCP 3) 5) TCP TCP 6) Segment TCP 13) TCP TCP TCP TCP TCP TCP TCP c /(18)

3 TCP TCP 1 1 1)2)11) TCP TCP TCP!"#$%&! $*)+,!-&! 89::;<=>?@=A!!B?:=!,$(! "'$(%)! $*)E$*)G.!7! $*)E$*)G.!7! $=AFE$*)!!B?:=!.CD<=>?@=A> E$*)! $*)+$%)&!!B?:=E1')!.!7! %$(./"'$0%&! $*)G.!7E.!7!!B?:=E1')! 1')+2.'(+3! 1')E.!7!.!7!.!7G1')E.!7! 1')E.!7! 1')+2.'(+4! 1')E.!7!!"#$%+2.'(!!B?:=E1')!!"#$')5! ".$(+.!7!.!7! (;H=?IJ>9K=L>JM?>H9N;O> HIH>:=PH=AJ>B;Q=DH=:! ('6%+2.'(!.!7!!"#$%&! 1 1 TCP 2 OPEN SEND CLOSE SYN ACK RST FIN SYN SEND ESTABLISHED SYN+ACK/ACKSYN SEND SYN ACK, SYN ACK ESTABLISHED TCP LISTEN c /(18)

4 SYN SEND SYN RCVD ACK ESTABLISHED FIN WAIT 1 ACK FIN WAIT 2 CLOSE WAIT CLOSING ACK LAST ACK TIME WAIT ACK ACK 2 CLOSED CLOSED TCP 1 1 TCP 1 1 c /(18)

5 TCP TCP TCP CLOSED SYN SEND ESTABLISHED 1 2 CLOSED LISTEN SYN RCVD ESTABLISHED TCP 3 Three-way Handshake !!25625! -BC629@A23!!"#$!%#&! %!)-.'(!/%&!!"#$1!!"#$789-+:$1;<! -+:$7;<!!!!! =>??1629@A23! '(!)%#!!"#$*+,&! %!)-.'(!/%&! 1 2 TCP 1. i SYN 2. SYN i + 1 ACK k SYN 3. k SYN k + 1 ACK 3 14) c /(18)

6 1 3 2 TCP !,47847! &?A84>?2@=4!!!!!!"#$%&"'$(!!"#$%&"'$1! '")*$%&"'!!"#$5! &-.$59(!!"#$:! &-.$:9(! ;<==384>?2@=4! -+/,*$%&"'! +&,'$&-.! -+/,*0! 1 3 TCP TCP FIN FIN TCP ESTABLISHED FIN WAIT 1 FIN WAIT 2 TIME WAIT CLOSED 1 1 FIN WAIT 2 ACK TIME WAIT 2 CLOSED ESTABLISHED CLOSE WAIT LAST ACK CLOSED 1 3 FIN n ACK n+1 FIN m ACK m+1 11) c /(18)

7 TCP TCP TCP Fast Retransmit SACK Selective Acknowledgment TCP MSS Maximum Segment Size MSS TCP IP ACK Acknowledgment ACK ACK 2460 ACK ACK ACK TCP ACK Cumulative ACK ACK TCP ACK 1 8 bit 1 8 byte bit 1 byte c /(18)

8 ACK RTT Round Trip Time RTT RTT + 4 RTT RTT n (1 α) RTT (n 1) + α RTT n RTT n (1 β) RTT (n 1) + β RTT n RTT n n α β RTT RTT RTT Fast Retransmit TCP ACK Fast Retransmit 15) 3 ACK Fast Recovery ACK TCP ACK ACK ACK SACK Selective Acknowledgment SACK Selective Acknowledgment 16)17) ACK TCP ACK ACK SACK TCP SACK 4 c /(18)

9 TCP TCP Congestion Control 18) Congestion Flow Control TCP TCP TCP Reno TCP TCP *+,-*./0! "1!!!!!""!!"#$$"%$$"&$$"'$$"(!!!!")! :;<=,>!?789@234!?7CDE! AB:;<=,>! ;<=,>! FGH! IJKL/-! "1$$""$$"#!!"%$$"&$$"'$$"($$")! :;<=,>! 234AB!?7CDE! :;<=,>!;<=,>! FMH! ACK (a) 11 c /(18)

10 ACK ACK (b) 12 ACK 17 ACK TCP TCP TCP TCP min (1 1) TCP (1 1) (1 1) TCP 0 ACK 0 ACK ACK TCP AIMD Additive Increase Multiplicative Decrease 18)19) AIMD TCP (1 2) c /(18)

11 /2 (1 2) ACK (1 3) MSS 1460 ACK / MSS 2 2 ACK RTT MSS 2 RTT MSS 3 1 RTT 1 MSS 1 5 (1 3) + MSS MSS/ (1 3) -./! 0./!!"#"$)! "&'$)!!"#"$(!!"#"$%! "&'$(! "&'$%!!"#"$*!!"#"$+!!"#"$,! 1 5 AIMD TCP AIMD (1) Slow Start (2) Congestion Avoidance (3) ssthresh Slow Start Threshold 1 Slow Start TCP 1 MSS ssthresh c /(18)

12 64 K 18)20) ACK (1 4) ssthresh 1 RTT MSS (1 4)./0! 1/0!!"#"$)! "&'$)!!"#"$(!!"#"$%! "&'$(! "&'$%!!"#"$*!!"#"$+!!"#"$,!!"#"$-! Congestion Avoidance ssthresh 18)20) (1 3) ssthresh ssthresh ssthresh (1 5) ssthresh 18) AIMD c /(18)

13 ssthresh /2 MSS (1 5)!"#$%&'"#()*#+",(-*.%(/0123%45! '#" '!" &#" &!" %#" %!" $#" $!" #"!"#$%!&'(&%)*'+,! -#./,+&0#.%12#03'.4,%)*'+,!!"!" #" $!" $#" %!" %#" &!" 6*7%(/&5! s ssthresh 20 packet TCP Reno TCP TCP Tahoe TCP Reno (1), (2), (3) ACK < ssthresh ssthresh ACK ssthresh c /(18)

14 TCP TCP Fast Retransmit Fast Recovery 15) TCP Reno Fast Retransmit TCP TCP ssthresh MSS 1 ACK ACK ACK ACK ACK Fast Recovery (1) ACK ACK ssthresh 3 MSS ACK ssthresh /2 ssthresh + 3MSS (2) ACK ACK + MSS (3) ACK ACK ssthresh ssthresh (1) ssthresh c /(18)

15 1 8 TCP Reno 1 7!"#$%&'"#()*#+",(-*.%(/0123%45! '#" '!" &#" &!" %#" %!" $#" $!" #"!"#$%!&'(&%)*'+,! -#./,+&0#.%12#03'.4,%)*'+,!!"!" #" $!" $#" %!" %#" &!" 6*7%(/&5! 1 8 TCP Reno c /(18)

16 TCP TCP 1 9 TCP 1)21) 32 bit 43) 53) 643) 673) 893)!"#$%&'() *+$%&'(),%-./'() 01234!"#5'() 6789) :;<= " ( & " $>?@%) ' () ) ' * GH7IDJ)! " # +, - ',.), / AB.CADEF) KL$E.M) NO,P.) QRB.S) TEU%C4R%M TCP 16 bit 16 bit 32 bit ACK 32 bit ACK 4 bit 32 bit TCP TCP 32 bit 4 bit CWR, ECE,, FIN 8 bit CWR 1 bit IP ECN Explicit Congestion Notification ECE ECN-Echo 1 ECN-Echo bit c /(18)

17 ECN URG 1 bit 1 0 ACK 1 bit 1 ACK 0 ACK PSH 1 bit 1 RST 1 bit 1 SYN 1 bit 1 SYN FIN 1 bit 1 FIN 16 bit 16 bit TCP IP 1) IP 16 bit bit bit bit 1 16 bit 8 bit SACK TCP TCP IP IP IP well-known IP IP TCP 16 bit 0 c /(18)

18 22) Internet Assigned Numbers Authority IANA web HTTP 80 web 80 web well-known 1) J. Postel (ed.), Transmission Control Protocol, RFC 793, ) R. Braden (ed.), Requirements for Internet hosts - communication layers, RFC 1122, ) V. Cerf and R. Kahn, A protocol for packet network intercommunication, IEEE Trans on Commun., vol.com-22, no.5, pp , ) B. Leiner, R. Cole, J. Postel, and D. Mills, The DARPA internet protocol suite IEEE Communications Magazine, vol.23, no.3, pp.29-34, ) D. D. Clark, The design philosophy of the DARPA Internet protocols, Proc. SIGCOMM 88, Computer Communication Review, vol.18, no.4, pp , ),,,, ),,, ),,,, 3,, ) D. E. Comer (, ), /IP TCP Vol. I 4,, ),,,, ) A. S. Tanenbaum (,,,, ), 4, BP, ),,,, TCP/IP 4,, ),,,, ) R. S. Tomlinson, Selecting sequence numbers, Proc. the 1975 ACM SIGCOMM/GIGOPS Workshop on Interprocess Communications, pp.11-23, ) V. Jacobson, Modified TCP congestion avoidance algorithm, end2end-interest mailing list, April 30, ) M. Mathis, J. Mahdavi, S. Floyd, and A. Romanow, TCP selective acknowledgment options, RFC 2018, ) S. Floyd, J. Mahdavi, M. Mathis, and M. Podolsky, An extension to the selective acknowledgement (SACK) option for TCP, RFC 2883, ) V. Jacobson, Congestion avoidance and control, Proc. ACM SIGCOMM 88, pp , ) R. Jain, K. Ramakrishnan, and D.-M., Chiu, Congestion avoidance in computer networks with a connectionless network layer, Tech. Rep. DEC-TR-506, Digital Equipment Corporation, ) M. Allman, V. Paxson, and W. Richard Stevens, TCP Congestion Control, RFC 2581, ) K. Ramakrishnan, S. Floyd, and D. Black, The addition of explicit congestion notification (ECN) to IP, RFC 3168, ) J. Reynolds and J. Postel, Assigned numbers, RFC 1700, c /(18)

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