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Wait for call from above

packet = make_pkt(data) udt_send(packet) rdt_send(data) extract (packet,data) deliver_data(data)

Wait for call from below

rdt_rcv(packet)

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Wait for call from above

snkpkt = make_pkt(data, checksum) udt_send(sndpkt) extract(rcvpkt,data) deliver_data(data) udt_send(ACK) rdt_rcv(rcvpkt) && notcorrupt(rcvpkt) rdt_rcv(rcvpkt) && isACK(rcvpkt) udt_send (sndpkt) rdt_rcv(rcvpkt) && isNAK(rcvpkt) udt_send(NAK) rdt_rcv(rcvpkt) && corrupt(rcvpkt)

Wait for ACK or NAK Wait for call from below

54<749$ 94I46N49$

rdt_send(data) !"

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Wait for call from above

snkpkt = make_pkt(data, checksum) udt_send(sndpkt) extract(rcvpkt,data) deliver_data(data) udt_send(ACK) rdt_rcv(rcvpkt) && notcorrupt(rcvpkt) rdt_rcv(rcvpkt) && isACK(rcvpkt) udt_send (sndpkt) rdt_rcv(rcvpkt) && isNAK(rcvpkt) udt_send(NAK) rdt_rcv(rcvpkt) && corrupt(rcvpkt)

Wait for ACK or NAK Wait for call from below

rdt_send(data) !"

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Wait for call from above

snkpkt = make_pkt(data, checksum) udt_send(sndpkt) extract(rcvpkt,data) deliver_data(data) udt_send(ACK) rdt_rcv(rcvpkt) && notcorrupt(rcvpkt) rdt_rcv(rcvpkt) && isACK(rcvpkt) udt_send (sndpkt) rdt_rcv(rcvpkt) && isNAK(rcvpkt) udt_send(NAK) rdt_rcv(rcvpkt) && corrupt(rcvpkt)

Wait for ACK or NAK Wait for call from below

rdt_send(data) !"

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Wait for call 0 from above

sndpkt = make_pkt(0, data, checksum) udt_send(sndpkt) rdt_send(data)

Wait for ACK or NAK 0

udt_send(sndpkt) rdt_rcv(rcvpkt) && ( corrupt(rcvpkt) || isNAK(rcvpkt) ) sndpkt = make_pkt(1, data, checksum) udt_send(sndpkt) rdt_send(data) rdt_rcv(rcvpkt) && notcorrupt(rcvpkt) && isACK(rcvpkt) udt_send (sndpkt) rdt_rcv(rcvpkt) && ( corrupt(rcvpkt) || isNAK(rcvpkt) ) rdt_rcv(rcvpkt) && notcorrupt(rcvpkt) && isACK(rcvpkt)

Wait for call 1 from above Wait for ACK or NAK 1

!" !" K#V"#2>#(W@(

V*$

K#V"#2>#(W@(

Wait for 0 from below sndpkt = make_pkt(NAK, chksum) udt_send(sndpkt) rdt_rcv(rcvpkt) && not corrupt(rcvpkt) && has_seq0(rcvpkt) rdt_rcv(rcvpkt) && notcorrupt(rcvpkt) && has_seq1(rcvpkt) extract(rcvpkt,data) deliver_data(data) sndpkt = make_pkt(ACK, chksum) udt_send(sndpkt) Wait for 1 from below rdt_rcv(rcvpkt) && notcorrupt(rcvpkt) && has_seq0(rcvpkt) extract(rcvpkt,data) deliver_data(data) sndpkt = make_pkt(ACK, chksum) udt_send(sndpkt) rdt_rcv(rcvpkt) && (corrupt(rcvpkt) sndpkt = make_pkt(ACK, chksum) udt_send(sndpkt) rdt_rcv(rcvpkt) && not corrupt(rcvpkt) && has_seq1(rcvpkt) rdt_rcv(rcvpkt) && (corrupt(rcvpkt) sndpkt = make_pkt(ACK, chksum) udt_send(sndpkt) sndpkt = make_pkt(NAK, chksum) udt_send(sndpkt)

V_$

K#2%#-O(

! 14h$f$-7747$@2$CJ@$ ! BY2$54hk$fi5$E0>)H$Y6..$

5;nI4k$$X3'Y(

! ';5@$IA4IJ$68$94I46N47$

M#:%XM:$I299;C@47$$

! BY6I4$-5$3-<D$5@-@45$

! 1@-@4$3;5@$O94343U49P$

YA4@A49$OI;994<@P$C-IJ4@$A-5$ 54h;4<I4$<;3U49$28$0$29$)$

L#>#0M#-O(

! ';5@$IA4IJ$68$94I46N47$

C-IJ4@$65$7;C.6I-@4$

! 1@-@4$6<76I-@45$YA4@A49$0$29$)$

65$4aC4I@47$C-IJ4@$54h;4<I4$ <;3U49$

! =4I46N49$I-<$."&$J<2Y$68$6@5$

.-5@$M#:%XM:$94I46N47$&:$

• @$54<749$

V`$

! 1-34$:%.1&-".20-&;$-5$97@/k)$ ! X2$XM:5^$ ! =4I46N49$6<5@4-7$54<75$M#:$829$.-5@$C-IJ4@$

94I46N47$&:$

! =4I46N49$3;5@$4aC.6I6@.D$6<I.;74$54h$f$28$C-IJ4@$

U46<K$M#:47$$

! G;C.6I-@4$M#:$-@$54<749$945;.@5$6<$5-34$

• I@62<$-5$XM:$

! =4@9-<536@$I;994<@$C-IJ4@$

W0$

Wait for call 0 from above

sndpkt = make_pkt(0, data, checksum) udt_send(sndpkt) rdt_send(data) udt_send(sndpkt) rdt_rcv(rcvpkt) && ( corrupt(rcvpkt) || isACK(rcvpkt,1) ) rdt_rcv(rcvpkt) && notcorrupt(rcvpkt) && isACK(rcvpkt,0)

Wait for ACK

54<749$,1'$ 89-K34<@$

Wait for 0 from below

rdt_rcv(rcvpkt) && notcorrupt(rcvpkt) && has_seq1(rcvpkt) extract(rcvpkt,data) deliver_data(data) sndpkt = make_pkt(ACK1, chksum) udt_send(sndpkt) rdt_rcv(rcvpkt) && (corrupt(rcvpkt) || has_seq1(rcvpkt)) udt_send(sndpkt)

94I46N49$,1'$ 89-K34<@$

!"

W)$

! X4Y$-55;3C@62<$

! F<749.D6<K$IA-<<4.$I-<$

• .52$:*$#(=&>.#6$((

E7-@-$*-(M#:5H$

! #A4IJ5;3>$54hk$f>$M#:5>$

• <7$94@9-<5365562<5$Y6..$

A4.C$U;@$-94$<2@$ 5;nI64<@$

! X4Y$-CC92-IA$

! 14<749$Y-6@5$O94-52<-U.4P$

• 32;<@$28$@634$829$M#:$$

! =4@9-<536@5$68$<2$M#:$

94I46N47$6<$@A65$@634$

! L8$CJ@$E29$M#:H$65$m;5@$

74.-D47$U;@$<2@$.25@[$

! =4@9-<5365562<$Y6..$U4$$ 7;C.6I-@4>$U;@$54hk$fi5$52.N45$ @A65$C92U.43$ ! =4I46N49$3;5@$5C4I68D$54h$f$ 28$CJ@$U46<K$M#:47$

! =4h;6945$I2;<@72Y<$@6349$

W/$

sndpkt = make_pkt(0, data, checksum) udt_send(sndpkt) start_timer rdt_send(data) Wait for ACK0 rdt_rcv(rcvpkt) && ( corrupt(rcvpkt) || isACK(rcvpkt,1) ) Wait for call 1 from above sndpkt = make_pkt(1, data, checksum) udt_send(sndpkt) start_timer rdt_send(data) rdt_rcv(rcvpkt) && notcorrupt(rcvpkt) && isACK(rcvpkt,0) rdt_rcv(rcvpkt) && ( corrupt(rcvpkt) || isACK(rcvpkt,0) ) rdt_rcv(rcvpkt) && notcorrupt(rcvpkt) && isACK(rcvpkt,1) stop_timer stop_timer udt_send(sndpkt) start_timer timeout udt_send(sndpkt) start_timer timeout rdt_rcv(rcvpkt) Wait for call 0 from above Wait for ACK1

!"

rdt_rcv(rcvpkt)

!" !" !"

WV$

WW$

W?$

! 97@Vk0$Y29J5>$U;@$=#-I*-+&2>#($602.$( ! ,29$)$eUC5$.6<J>$)?$35$C92Ck$74.-D>$_000$U6@$C-IJ4@[$ ! F$54<749[$;@6.6o-@62<$[$89-I@62<$28$@634$54<749$U;5D$54<76<K$ ! ):Z$C-IJ4@$4N49D$V0$354I$ ! ;;.7F$#>(63-*"13="6(*M#-(Z(N9=$(:02.( ! X4@Y29J$C92@2I2.$.636@5$;54$28$CAD56I-.$9452;9I45^$

U

sender

= .008

30.008

= 0.00027

microsec

L / R RTT + L / R =

$

ds microsecon 8 bps 10 bits 8000

9

= = = R L dtrans

<"+)0"./)-&)&2,'6)&")$%6=) $21,'&)"%&)".&")+-(')

W\$

first packet bit transmitted, t = 0 sender receiver RTT last packet bit transmitted, t=L / R first packet bit arrives last packet bit arrives, send ACK ACK arrives, send next packet, t = RTT + L / R

U

sender

= .008

30.008

= 0.00027

microsec

L / R RTT + L / R =

W*$

80=#:02021O(54<749$-..2Y5$3;.@6C.4>$O6<Tl6KA@P>$D4@T@2TU4T

• IJ<2Y.47K47$C-IJ4@5$

! =-<K4$28$54h;4<I4$<;3U495$3;5@$U4$6<I94-547$ ! Z;c496<K$-@$54<749$-<7%29$94I46N49$

! BY2$K4<496I$82935$28$C6C4.6<47$C92@2I2.5[$$

/">?21,>*)2.5)6'0'1&-@')('$'2&)

W_$

first packet bit transmitted, t=0

sender receiver RTT

last bit transmitted, t=L / R first packet bit arrives last packet bit arrives, send ACK

ACK arrives, send next packet, t = RTT + L / R

last bit of 2nd packet arrives, send ACK last bit of 3rd packet arrives, send ACK

U

sender

= .024

30.008

= 0.0008

microsecon

3 * L / R RTT + L / R =

L<I94-54$;@6.6o-@62<$ UD$-$8-I@29$28$V^$

W`$

NAD7TEUD4(

! 14<749$

! FC$@2$X$;<M#:47$CJ@5$6<$

C6C4.6<4$

! =4I46N49$

! &<.D$54<75$I;3;.-@6N4$M#:5$ ! G245<i@$M#:$CJ@$68$@A494i5$-$

K-C$

! 14<749$

! S-5$@6349$829$2.745@$;<M#:47$

CJ@$

! L8$@6349$4aC6945[$94@9-<536@$-..$

;<M#:47$C-IJ4@5$

KB[BE!C\B(LB8BT!(

! 14<749$

! FC$@2$X$;<M#:47$C-IJ4@5$6<$

C6C4.6<4$

! =4I46N49$

! M#:5$6<76N67;-.$CJ@5$

! 14<749$

! '-6<@-6<5$@6349$829$4-IA$

;<M#:47$CJ@$

! L8$@6349$4aC6945[$94@9-<536@$

2<.D$;<M#:47$C-IJ4@$

?0$

! JTU6@$54h;4<I4$f$6<$C-IJ4@$A4-749$ ! Og6<72YP$28$;C$@2$X>$I2<54I;@6N4$;<M#:47$CJ@5$-..2Y47$ ! M#:E<H[$M#:5$-..$CJ@5$;C$@2>$6<I.;76<K$54h$f$<$ ! =4849947$@2$-5$-$OI;3;.-@6N4$M#:P$ ! '-D$94I46N4$7;C.6I-@4$M#:5$A6'')('1'-@'(B) ! B6349$829$2.745@$6<Tl6KA@$C-IJ4@$ ! @6342;@E<H[$94@9-<536@$C-IJ4@$<$&2%(&::(3013#-(54h$f$

C-IJ4@5$6<$Y6<72Y$

?)$

Wait

start_timer udt_send(sndpkt[base]) udt_send(sndpkt[base+1]) " udt_send(sndpkt[nextseqnum-1]) timeout rdt_send(data) if (nextseqnum < base+N) { sndpkt[nextseqnum] = make_pkt(nextseqnum,data,chksum) udt_send(sndpkt[nextseqnum]) if (base == nextseqnum) start_timer nextseqnum++ } else refuse_data(data) base = getacknum(rcvpkt)+1 If (base == nextseqnum) stop_timer else start_timer rdt_rcv(rcvpkt) && notcorrupt(rcvpkt) base=1 nextseqnum=1 rdt_rcv(rcvpkt) && corrupt(rcvpkt)

!" !"

?/$

! M#:T2<.D[$-.Y-D5$54<7$M#:$829$I2994I@.DT94I46N47$CJ@$Y6@A$A6KA45@$

1$2'"3,"(54h$f$

! '-D$K4<49-@4$7;C.6I-@4$M#:5$ ! X447$2<.D$94343U49$expectedseqnum ! &;@T28T29749$CJ@[$$ ! G65I-97$E72<i@$U;c49H$Tp$<2$94I46N49$U;c496<K^$E947;I45$I23C.4a6@DH$ ! =4TM#:$CJ@$Y6@A$A6KA45@$6<T29749$54h$f$

Wait

udt_send(sndpkt) default rdt_rcv(rcvpkt) && notcurrupt(rcvpkt) && hasseqnum(rcvpkt,expectedseqnum) extract(rcvpkt,data) deliver_data(data) sndpkt = make_pkt(expectedseqnum,ACK,chksum) udt_send(sndpkt) expectedseqnum++ expectedseqnum=1 sndpkt = make_pkt(expectedseqnum,ACK,chksum)

!"

?V$

?W$

! =4I46N49$-.5-@-5%200;)-IJ<2Y.47K45$-..$

I2994I@.D$94I46N47$C-IJ4@5$

! Z;c495$C-IJ4@5>$-5$<44747>$829$4N4<@;-.$6<T29749$

74.6N49D$@2$;CC49$.-D49$

! 14<749$2<.D$9454<75$C-IJ4@5$829$YA6IA$M#:$

<2@$94I46N47$

! 14<749$@6349$829$4-IA$;<M#:47$C-IJ4@5$ ! 14<749$Y6<72Y$ ! X$I2<54I;@6N4$54h$fi5$ ! MK-6<$.636@5$54h$f5$28$54<@>$;<M#:47$C-IJ4@5$

??$

?\$

KB4HBL(

! G-@-$8923$-U2N4$[$

! L8$<4a@$-N-6.-U.4$54h$f$6<$

Y6<72Y>$54<7$CJ@$

! @6342;@E<H[$

! =454<7$CJ@$<>$945@-9@$@6349$

! M#:E<H$6<$

q54<7U-54>54<7U-54bXr[$

! '-9J$CJ@$<$-5$94I46N47$ ! L8$<$65$53-..45@$;<M#:47$CJ@>$

• 7N-<I4$Y6<72Y$U-54$@2$<4a@$

;<M#:47$54h$f$$

LBEBC\BL(

! CJ@$<$6<$$

q9INU-54>$9INU-54bXT)r$

! 14<7$M#:E<H$ ! &;@T28T29749[$U;c49$ ! L<T29749[$74.6N49$E-.52$74.6N49$

U;c4947>$6<T29749$CJ@5H>$

• 7N-<I4$Y6<72Y$@2$<4a@$<2@T

D4@T94I46N47$CJ@$

! CJ@$<$6<$$

q9INU-54TX>9INU-54T)r$

! M#:E<H$A&=-6)-6)2)$21,'&)&=2&)+26)

$('@-"%60;)('1'-@'58B$

! &@A49Y654[$$ ! LK<294$$

?*$

?_$

! !a-3C.4$

!

54h$fi5[$0>$)>$/>$V$

!

Y6<72Y$56o4dV$ ! =4I46N49$5445$<2$

76c494<I4$6<$@Y2$ 5I4<-9625^$

!

L5$6@$-$94@9-<536@@47$C-IJ4@>$ 29$-$<4Y$C-IJ4@R$

!

L<I2994I@.D$C-5545$7;C.6I-@4$ 7-@-$-5$<4Y$6<$E-H$

s[$gA-@$94.-@62<5A6C$65$ <44747$U4@Y44<$54h$f$ 56o4$-<7$Y6<72Y$56o4R$ M[$BY6I4$-5$3-<D$54h$fi5$

?`$

\0$

! ,;..$7;C.4a$7-@-[$

! Z6T7694I@62<-.$7-@-$l2Y$6<$

5-34$I2<<4I@62<$

! '11[$3-a63;3$54K34<@$

56o4$

! #2<<4I@62<T2964<@47[$$

! S-<75A-J6<K$E4aIA-<K4$28$

I2<@92.$35K5H$6<6@6-.6o45$ 54<749>$94I46N49$5@-@4$U48294$ 7-@-$4aIA-<K4$

! ,.2Y$I2<@92..47[$

! 14<749$Y6..$<2@$2N49YA4.3$

94I46N49$

! (26<@T@2TC26<@[$

! &<4$54<749>$2<4$94I46N49$$

! =4.6-U.4>$6<T29749$C;&')

6&'2#D)

! X2$O3455-K4$U2;<7-9645P$

! (6C4.6<47[$

! B#($I2<K45@62<$-<7$l2Y$

I2<@92.$54@$Y6<72Y$56o4$

! E'.5)F)('1'-@')C%G'(6)

socket door TCP send buffer TCP receive buffer socket door

segment

application writes data application reads data

\)$

\/$

52;9I4$C29@$f 745@$C29@$f

V/$U6@5

• CC.6I-@62<$

7-@-$$ EN-96-U.4$.4<K@AH 54h;4<I4$<;3U49

• IJ<2Y.47K434<@$<;3U49

=4I46N4$Y6<72Y F9K$7-@-$C26<@49 IA4IJ5;3 , 1 = ( M F

A4-7$ .4< <2@$ ;547

&C@62<5$EN-96-U.4$.4<K@AH

F=e[$;9K4<@$7-@-$$ EK4<49-..D$<2@$;547H M#:[$M#:$f$ N-.67 (1S[$C;5A$7-@-$<2Y$ EK4<49-..D$<2@$;547H$ =1B>$1jX>$,LX[$ I2<<4I@62<$45@-U$ E54@;C>$@4-972Y<$ I233-<75H$ f$UD@45$$ 94I46N49$Y6..6<K$ @2$-II4C@$ I2;<@6<K$ UD$UD@45$$ 28$7-@-$ E<2@$54K34<@5^H$ L<@49<4@$ IA4IJ5;3$ E-5$6<$FG(H$

14hk$fi5[$

! UD@4$5@94-3$O<;3U49P$

28$Q95@$UD@4$6<$ 54K34<@i5$7-@-$ M#:5[$

! 54h$f$28$<4a@$UD@4$

4aC4I@47$8923$2@A49$ 5674$

! I;3;.-@6N4$M#:$

s[$A2Y$94I46N49$A-<7.45$ 2;@T28T29749$54K34<@5$

! M[$B#($5C4I$7245<i@$

5-D>$T$;C$@2$ 63C.434<@49$

S25@$M S25@$Z

Seq=42, ACK=79, data = ‘C’ S e q = 7 9 , A C K = 4 3 , d a t a = ‘ C ’ Seq=43, ACK=80

F549$ @DC45$ t#i A25@$M#:5$ 94I46C@$$ 28$4IA247$ t#i A25@$M#:5$ 94I46C@$28$ t#i>$4IA245$ U-IJ$t#i @634 563C.4$@4.<4@$5I4<-962

\V$

! )*,(6*($#6(!E8(60+#*"6(

M&:"#Y(

! 1A2;.7$U4$.2<K49$@A-<$

=BB$E92;<7T@96CT@634H$

! Z;@$=BB$N-9645u$

! L8$6@$65$@22$5A29@$

! (943-@;94$@6342;@$ ! F<<4I455-9D$

94@9-<5365562<5u$

! L8$6@$65$@22$.2<K$

! 1.2Y$94-I@62<$@2$54K34<@$

.255$

! )*,(>&2(,#(#$60+&6#(

L!!Y(

! '4-5;94$@634$8923$

54K34<@$@9-<5365562<$ ;<@6.$M#:$94I46C@$

! LK<294$94@9-<5365562<5$ ! #-..$@A65$O1-3C.4=BBP$

! 1-3C.4=BB$Y6..$N-9D$

! g4$Y-<@$-$O5322@A49P$

45@63-@47$=BB$

! MN49-K4$54N49-.$94I4<@$

34-5;9434<@5>$<2@$m;5@$ I;994<@$1-3C.4=BB$

\W$

! !aC2<4<@6-.$Y46KA@47$32N6<K$-N49-K4$ ! L<l;4<I4$28$C-5@$5-3C.4$74I94-545$

4aC2<4<@6-..D$8-5@$

! BDC6I-.$N-.;4[$#$d$0k)/?$

\?$

EstimatedRTT = (1- #)*EstimatedRTT + #*SampleRTT

\\$

RTT: gaia.cs.umass.edu to fantasia.eurecom.fr

100 150 200 250 300 350 1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106 time (seconnds) RTT (milliseconds) SampleRTT Estimated RTT

! 14@@6<K$@A4$B#($@6342;@$ ! !5@63@47=BB$C.;5$O5-84@D$3-9K6<P$ ! BA4$.-9K49$@A4$N-96-@62<$6<$!5@63-@47=BB>$@A4$

.-9K49$@A4$5-84@D$3-9K6<$

\*$

! B#($I94-@45$97@$549N6I4$

2<$@2C$28$;<94.6-U.4$L($

! ,4-@;945$28$B#($$

! (6C4.6<47$54K34<@5$ ! #;3;.-@6N4$M#:5$

! B#($;545$56<K.4$

94@9-<5365562<$@6349$

! =4@9-<5365562<5$-94$

@96KK4947$UD$

! @6342;@$4N4<@5$ ! 7;C.6I-@4$M#:5$

! L<6@6-..D$I2<56749$

563C.6Q47$B#($54<749[$

! LK<294$7;C.6I-@4$M#:5$ ! LK<294$l2Y$I2<@92.$ ! LK<294$I2<K45@62<$

I2<@92.$

\_$

! G-@-$94I46N47$8923$-CC[$

! #94-@4$54K34<@$Y6@A$54h$f$ ! 54h$f$65$UD@4T5@94-3$

<;3U49$28$Q95@$7-@-$UD@4$6<$$ 54K34<@$

! 1@-9@$@6349$68$<2@$-.94-7D$

9;<<6<K$E@A6<J$28$@6349$-5$ 829$2.745@$;<M#:47$ 54K34<@H$

! !aC69-@62<$6<@49N-.[$

B634&;@L<@49N-.$$ ! B6342;@[$ ! =4@9-<536@$54K34<@$@A-@$

I-;547$@6342;@$

! =45@-9@$@6349$

! $M#:$94I46N47[$

! L8$-IJ<2Y.47K45$

C94N62;5.D$;<M#:47$ 54K34<@5$

! FC7-@4$YA-@$65$J<2Y<$@2$ U4$M#:47$ ! 1@-9@$@6349$68$@A494$-94$$ 2;@5@-<76<K$54K34<@5$

\`$

*)$

S25@$M

Seq=100, 20 bytes data

@634 C943-@;94$@6342;@$5I4<-962 S25@$Z

Seq=92, 8 bytes data Seq=92, 8 bytes data 14hd`/$@6342;@

S25@$M

Seq=92, 8 bytes data ACK=100

.255 @6342;@ .25@$M#:$5I4<-962 S25@$Z

X

Seq=92, 8 bytes data A C K = 1

@634$

14hd`/$@6342;@

14<7Z-54$ d$)00$ 14<7Z-54$ d$)/0$ 14<7Z-54$ d$)/0$ 14<7U-54$ d$)00$

*/$

S25@$M

Seq=92, 8 bytes data ACK=100

.255 @6342;@ #;3;.-@6N4$M#:$5I4<-962 S25@$Z

X

Seq=100, 20 bytes data A C K = 1 2

@634$ 14<7Z-54$ d$)/0$

*V$

Event at Receiver

Arrival of in-order segment with expected seq #. All data up to expected seq # already ACKed Arrival of in-order segment with expected seq #. One other segment has ACK pending Arrival of out-of-order segment higher-than-expect seq. # . Gap detected Arrival of segment that partially or completely fills gap

TCP Receiver action

Delayed ACK. Wait up to 500ms for next segment. If no next segment, send ACK Immediately send single cumulative ACK, ACKing both in-order segments Immediately send duplicate ACK, indicating seq. # of next expected byte Immediate send ACK, provided that segment starts at lower end of gap

! B634T2;@$C49627$$28@4<$

94.-@6N4.D$.2<K$

! "2<K$74.-D$U48294$

9454<76<K$.25@$C-IJ4@$

! G4@4I@$.25@$54K34<@5$N6-$

7;C.6I-@4$M#:5k$

! 14<749$28@4<$54<75$3-<D$

54K34<@5$U-IJT@2TU-IJ$

! L8$54K34<@$65$.25@>$@A494$

Y6..$.6J4.D$U4$3-<D$ 7;C.6I-@4$M#:5$829$@A-@$ 54K34<@$ ! L8$54<749$94I46N45$V$

M#:5$829$5-34$7-@->$6@$

• 55;345$@A-@$54K34<@$
• 8@49$M#:47$7-@-$Y-5$

.25@[$

! Q&$6(-#6-&2$+06[$9454<7$

54K34<@$U48294$@6349$ 4aC6945$

*W$

S25@$M @6342;@ S25@$Z @634$

X

resend seq X2

54h$f$a)$ 54h$f$a/$ 54h$f$aV$ 54h$f$aW$ 54h$f$a?$ M#:$a)$ M#:$a)$ M#:$a)$ M#:$a)$ @96C.4$ 7;C.6I-@4$ M#:5$

*?$

! =4I46N4$5674$28$B#($

I2<<4I@62<$A-5$-$94I46N4$ U;c49[$

L($ 7-@-K9-35$

B#($7-@-$ E6<$U;c49H$ EI;994<@.DH$ ;<;547$U;c49$ 5C-I4$

• CC.6I-@62<$

C92I455$

**$

! MCC.6I-@62<$C92I455$3-D$U4$

5.2Y$-@$94-76<K$8923$U;c49$

! gA-@$68$U;c49$Q..5$;CR$

( Q:*,(E*26-*:O(

$ (94N4<@5$$#2%#-$8923$ *M#-S*,021(-#>#0M#-]$( 9"^#-$UD$@9-<536@@6<K$@22$ 3;IA>$@22$8-5@$ $ K=##%(+&6>3021($#-M0>#O( 3-@IA6<K$54<7$9-@4$@2$ 94I46N6<K$-CC.6I-@62<x5$79-6<$ 9-@4$

! 1;CC254$B#($94I46N49$

765I-975$2;@T28T29749$ 54K34<@5u$

! F<;547$U;c49$5C-I4$

d$9Y<7$ d$=INZ;c49Tq"-5@ZD@4=IN7$T$"-5@ZD@4=4-7r$

! =4I46N49$<2@6Q45$

54<749$28$;<;547$ U;c49$5C-I4$

! 14K34<@$A4-749$

6<I.;745$@A4$rwnd$N-.;4$$

! 14<749$.636@5$f$28$

;<M#:47$UD@45$@2$ rwnd

! e;-9-<@445$94I46N49i5$

U;c49$7245<i@$2N49l2Y$

*_$

L($ 7-@-K9-35$

B#($7-@-$ E6<$U;c49H$ EI;994<@.DH$ ;<;547$U;c49$ 5C-I4$

• CC.6I-@62<$

C92I455$

9Y<7$ =INZ;c49$

! B#($54<749$-<7$94I46N49$

45@-U.65A$OI2<<4I@62<P$ U48294$4aIA-<K6<K$7-@-$ 54K34<@5$

! #.64<@$6<6@6-@45$I2<<4I@62<$

! #-..5$I2<<4I@EH$@2$-<$L(%C29@$

! 149N49$65$I2<@-I@47$UD$I.64<@$

! #-..5$-II4C@EH$

! B#($N-96-U.45$6<6@6-.6o47$

YA6.4$45@-U.65A6<K$ I2<<4I@62<$

! 14h;4<I4$f5$ ! Z;c495$-<7$l2Y$I2<@92.$6<82$

E4kKk$=INg6<72YH$

! BA944$Y-D$A-<75A-J4[$ ! K6#=(ZO(I.64<@$A25@$54<75$

B#($1jX$54K34<@$@2$ 549N49$

! 1C4I6Q45$6<6@6-.$54h$f$ ! X2$7-@-$

! K6#=(/O(549N49$A25@$94I46N45$

1jX>$94C.645$Y6@A$1jXM#:$ 54K34<@$

! 149N49$-..2I-@45$U;c495$ ! 1C4I6Q45$549N49$6<6@6-.$54hk$f$

! K6#=(;O$I.64<@$94I46N45$

1jXM#:>$94C.645$Y6@A$M#:$ 54K34<@>$YA6IA$3-D$ I2<@-6<$7-@-$

*`$

_0$

#.256<K$-$I2<<4I@62<[$

I.64<@$I.2545$52IJ4@$N6-$I.254EH[$

1@4C$)[$I.64<@$5D5@43$54<75$B#($

,LX$I2<@92.$54K34<@$@2$549N49$$

1@4C$/[$549N49$94I46N45$,LX>$

94C.645$Y6@A$M#:k$#.2545$ I2<<4I@62<>$54<75$,LXk$$

I.64<@

FIN

549N49

A C K ACK F I N

I.254$ I.254$ I.2547$ @6347$Y-6@$

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1@4C$V[$I.64<@$94I46N45$,LX>$94C.645$

Y6@A$M#:k$$

! !<@495$O@6347$Y-6@P$T$Y6..$

945C2<7$Y6@A$M#:$@2$94I46N47$ ,LX5$$

! gAD$<2@$I.254$633476-@4.DR$

MN2675$C2@4<@6-.$C92U.435$68$-$ .'+$52IJ4@$EY6@A$5-34$C29@5$

• <7$L(5H$65$I94-@47>$-<7$@A4<$

2.7$74.-D47$7-@-$65$ 74.6N4947u$

1@4C$W[$549N49>$94I46N45$M#:k$$

#2<<4I@62<$I.2547$

I.64<@

FIN

549N49

A C K ACK F I N

I.254$ I.254$ I.2547$ @6347$Y-6@$

_/$

B#($I.64<@$.684IDI.4 B#($549N49$.684IDI.4

(96<I6C.45$-<7$B#($1C4I6QI5$

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! gA-@$65$I2<K45@62<R$ ! L<8293-..D[$O@22$3-<D$52;9I45$54<76<K$@22$3;IA$

7-@-$@22$8-5@$829$2#6,*-.(@2$A-<7.4P$

! G6c494<@$8923$l2Y$I2<@92.^$ ! '-<6845@-@62<5$ ! "25@$C-IJ4@5$EU;c49$2N49l2Y$-@$92;@495H$ ! "2<K$74.-D5$Eh;4;46<K$6<$92;@49$U;c495H$

_W$

! BY2$54<7495>$@Y2$

94I46N495$

! &<4$92;@49>$

02P206#$U;c495$$

! X2$94@9-<5365562<$ ! "6<J$Zg$28$=$ ! [&-1#(%#:&'$(

YA4<$ I2<K45@47$

! '-a63;3$

• IA64N-U.4$

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unlimited shared

• utput link buffers$

Host A$

$in : original data$

Host B$

$out$

=%/$ =%/$ =%/$

! &<4$92;@49>$P206#(U;c495$$ ! 14<749$94@9-<5365562<$28$.25@$C-IJ4@$

_\$

finite shared output link buffers$ Host A$

$in : original data$

Host B$ $out$

$'in : original data, plus retransmitted data$

_*$

R/2 R/2

$in $out

b.

R/2 R/2

$in $out

a.

R/2 R/2

$in $out

c.

R/4 R/3

! #-54$-[$14<749$2<.D$@9-<536@5$YA4<$6@$J<2Y5$U;c49$5C-I4$65$

• N-6.-U.4$6<$92;@49$E;<94-.65@6IH$

! #-54$U[$14<749$94@9-<536@5$2<.D$YA4<$C-IJ4@$65$J<2Y<$@2$U4$.25@$ ! X4Y$I25@$28$I2<K45@62<[$'294$54<749$Y29J$E94@9-<5H$829$K6N4<$

OK227C;@P$

! #-54$I[$M55;34$54<749$-.52$94@9-<536@5$YA4<$-$C-IJ4@$65$74.-D47$

E<2@$.25@H>$6k4k$-$C943-@;94$@6342;@$EU6KK49$$6<iH$$

! X4Y$I25@$28$I2<K45@62<[$92;@49$2;@C;@$.6<J$I-99645$3;.@6C.4$I2C645$28$

C-IJ4@$

$"in $"out

=

$"in $"out

>

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>

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! ,2;9$54<7495$ ! ';.@6A2C$C-@A5$ ! B6342;@%94@9-<536@$

$"in

s[$YA-@$A-CC4<5$-5$$$$$$

• <7$$$$$$$$$$6<I94-54R$

$"in

finite shared

• utput link

buffers$

Host A$

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Host B$

$out$ $'in : original data, plus retransmitted data$

! M$<4Y$I25@$28$I2<K45@62<$$ ! gA4<$C-IJ4@$792CC47>$-<D$;C5@94-3$@9-<5365562<$

I-C-I6@D$;547$829$@A-@$C-IJ4@$Y-5$Y-5@47^$

_`$

H

• st

A$ H

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t

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! B2%D#2%(>*21#$60*2(

>*26-*:O(

! X2$4aC.6I6@$8447U-IJ$

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! #2<K45@62<$6<849947$

8923$4<7T5D5@43$ 2U549N47$.255>$74.-D$

! T==-*&>3(6&.#2(9'(!E8(

! 4#6,*-.D&$$0$6#%(

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! 16<K.4$U6@$6<76I-@6<K$

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! !aC.6I6@$9-@4$54<749$

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!,*(9-*&%(&==-*&>3#$(6*(>*21#$60*2(>*26-*:O(

! e2-.[$$B#($54<749$5A2;.7$@9-<536@$&$(I&$6(&$(

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! S2Y$72$Y4$Q<7$@A4$9-@4$m;5@$U4.2Y$

I2<K45@62<$.4N4.R$

! G4I4<@9-.6o47$-CC92-IA$+$4-IA$B#($54<749$54@5$6@5$

2Y<$9-@4>$U-547$2<$-#$0-1-&$8447U-IJ[$$

! M#:$6<76I-@45$54K34<@$94I46N47$E-$K227$@A6<K^H$

! X4@Y29J$<2@$I2<K45@47>$52$6<I94-54$54<76<K$9-@4$

! "25@$54K34<@$+$-55;34$.255$65$7;4$@2$I2<K45@47$

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! (92U6<K$829$U-<7Y67@A$ ! L<I94-54$@9-<5365562<$9-@4$2<$94I46C@$28$M#:>$;<@6.$

4N4<@;-..D$.255$2II;95>$@A4<$74I94-54$@9-<5365562<$9-@4$$

`/$

M#:5$U46<K$94I46N47>$$ 52$6<I94-54$9-@4$ _( _( _( _( _( .255>$52$74I94-54$9-@4$ 54<76<K$9-@4$ @634$

B#(i5$ O5-Y@22@AP$ U4A-N629$

! S2Y$8-5@$@2$6<I94-54$29$74I94-54R$

! 14<749$.636@5$9-@4$UD$.636@6<K$<;3U49$28$

;<M#:47$UD@45$O6<$C6C4.6<4P[$

! cwnd: 76c495$8923$rwnd EA2Y>$YADRH$ ! 54<749$.636@47$UD min(cwnd,rwnd)

! =2;KA.D>$ ! cwnd$EI2<K45@62<$Y6<72YH$65$-$8;<I@62<$28$

C49I46N47$<4@Y29J$I2<K45@62<$

! rwnd$E94I46N49$Y6<72YH$65$4aC.6I6@.D$

IA-<K47$UD$94I46N49$

9-@4$d IY<7 =BB UD@45%54I LastByteSent-LastByteAcked % cwnd

$ cwnd UD@45$ =BB$ M#:E5H$

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7THO(HT!T([AKK(

! ;(%"=:0>&6#(TEU$Y(

! M@$.4-5@$5234$54K34<@5$

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! #;@$cwnd$6<$A-.8$

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! K:*,$6&-6(=3&$#(

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! L<I94-54$cwnd$4aC2<4<@6-..D$

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! gA4<$I2<<4I@62<$U4K6<5>$

cwnd$d$)$'11$

! !a-3C.4[$'11$d$?00$UD@45$]$

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! MN-6.-U.4$U-<7Y67@A$3-D$$

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S25@$M

• ne segment

=BB

S25@$Z @634

two segments four segments

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! 1.2Y$5@-9@$CA-54$3;5@$4<7$

! L8$Y4$J44C$4aC2<4<@6-..D$6<I94-56<K$2;9$U-<7Y67@A$

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! Z-547$2<$-$<4Y$N-.;4[$ssthresh

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! 1@-9@5$2c$A6KA$-@$Q95@$ ! 14@$@2$ssthresh=cwnd/2$YA4<$7-@-$.255$

2II;95$

! =4343U49$EA-.8$28H$B#($9-@4$YA4<$I2<K45@62<$.-5@$2II;9947

`\$

! X4Y$CA-54[$YA4<$$

cwnd > ssthresh>$$ K92Y$cwnd$.6<4-9.D$

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! MCC92-IA$C2556U.4$

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$ $

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)$'11$C49$=BB[$-776@6N4$ 6<I94-54$

! .255[$I;@$cwnd$6<$A-.8$

E<2<T@6342;@T74@4I@47$ .255$H[$3;.@6C.6I-@6N4$ 74I94-54$ $

ML'G$

ML'G[$M776@6N4$L<I94-54$ ';.@6C.6I-@6N4$G4I94-54$

`_$

``$

slow start congestion avoidance fast recovery cwnd > ssthresh loss: timeout loss: timeout new ACK loss: 3dupACK loss: 3dupACK loss: timeout

! gA4<$cwnd$<$ssthresh>$54<749$6<$$

$:*,D$6&-6(=3&$#(

! g6<72Y$K92Y5$4aC2<4<@6-..Dk$ ! gA4<$cwnd$>=$ssthresh>$54<749$65$6<$$

>*21#$60*2D&M*0%&2>#(=3&$#(

! g6<72Y$K92Y5$.6<4-9.Dk$ ! gA4<$V$7;C.6I-@4$M#:5$94I46N47$ ! ssthresh$54@$@2$cwnd/2 ! cwnd$54@$@2$z$ssthresh ! gA4<$@6342;@$2II;95$ ! ssthresh$54@$@2$cwnd/2 ! cwnd$54@$@2$)$'11k$$

)0)$

)0/$

8-69<455$K2-.[$68$:$B#($545562<5$5A-94$5-34$U2@@.4<4IJ$.6<J$ 28$U-<7Y67@A$=>$4-IA$5A2;.7$A-N4$-N49-K4$9-@4$28$=%:$

B#($I2<<4I@62<$) U2@@.4<4IJ$ 92;@49$ I-C-I6@D$= B#($$ I2<<4I@62<$/

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= =

4h;-.$U-<7Y67@A$5A-94 #2<<4I@62<$)$@A92;KAC;@ # 2 < < 4 I @ 6 2 < $ / $ @ A 9 2 ; K A C ; @ I2<K45@62<$-N267-<I4[$-776@6N4$6<I94-54 .255[$74I94-54$Y6<72Y$UD$8-I@29$28$/ I2<K45@62<$-N267-<I4[$-776@6N4$6<I94-54 .255[$74I94-54$Y6<72Y$UD$8-I@29$28$/

)0V$

B2@-.$U-<7Y67@A$28$U2@A$ I2<<4I@62<5$

! Q&0-2#$$(&2%(GH8(

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! (;3C$-;762%N6742$-@$ I2<5@-<@$9-@4$ ! B2.49-@4$C-IJ4@$.255$

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)0W$

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! FG($65$-$I2<<4I@62<.455$7-@-K9-3$549N6I4k$ ! BA494$65$<2$I2<<4I@62<$45@-U.65A34<@[$C-IJ4@5$3-D$5A2Y$

;C$-@$-<D$@634k$$

! FG($C-IJ4@5$-94$54.8TI2<@-6<47k$$ ! FG($65$;<94.6-U.4[$ ! X2$-IJ<2Y.47K434<@5$@2$6<76I-@4$74.6N49D$28$7-@-k$ ! #A4IJ5;35$I2N49$@A4$A4-749>$-<7$2<.D$2C@62<-..D$I2N49$

@A4$7-@-k$

! #2<@-6<5$<2$34IA-<653$@2$74@4I@$36556<K$29$365T

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! B#($65$I2<<4I@62<T2964<@47k$ ! VTY-D$A-<75A-J4$;547$829$I2<<4I@62<$54@;C$ ! B#($C92N6745$-$5@94-3T28TUD@45$549N6I4$ ! B#($65$94.6-U.4[$ ! MIJ<2Y.47K434<@5$6<76I-@4$74.6N49D$28$7-@-$ ! #A4IJ5;35$-94$;547$@2$74@4I@$I299;C@47$7-@-$ ! 14h;4<I4$<;3U495$74@4I@$36556<K>$29$365T54h;4<I47$7-@-$ ! #299;C@47$7-@-$65$94@9-<536@@47$-8@49$-$@6342;@$ ! '65T54h;4<I47$7-@-$65$94T54h;4<I47$ ! Eg6<72YTU-547H$,.2Y$I2<@92.$C94N4<@5$2N49T9;<$28$94I46N49$ ! B#($;545$I2<K45@62<$I2<@92.$@2$5A-94$<4@Y29J$I-C-I6@D$

• 32<K$;5495$

)0*$