One document matched: draft-ietf-tcpm-ecnsyn-00.ps

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/F0 10/Times-Roman@0 SF(Internet Engineering T)0 84 Q(ask F)-.8 E 67.5
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120 Q(K.K. Ramakrishnan)137.5 132 Q -1.11(AT)170 144 S(&T)1.11 E
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(Adding Explicit Congestion Noti\214cation \(ECN\) Capability to TCP')
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468 Q(xpire on July 2006.)-.15 E(Abstract)0 492 Q
(This draft speci\214es a modi\214cation to RFC 3168 to allo)30 516 Q
2.5(wT)-.25 G(CP SYN/A)-2.5 E(CK pack)-.4 E(ets to be ECN-Capable.)-.1 E
-.15(Fo)5 G 2.5(rT).15 G(CP)-2.5 E 2.5(,R)-1.11 G(FC)-2.5 E
(3168 only speci\214ed setting an ECN-Capable codepoint on data pack)30
528 Q(ets, and not on SYN and SYN/A)-.1 E(CK pack)-.4 E(ets.)-.1 E(Ho)30
540 Q(we)-.25 E -.15(ve)-.25 G .8 -.4(r, b).15 H
(ecause of the high cost to the TCP transfer of ha).4 E(ving a SYN/A)-.2
E(CK pack)-.4 E(et dropped, with the resulting)-.1 E(retransmit timeout\
, this document is specifying the use of ECN for the SYN/A)30 552 Q
(CK pack)-.4 E(et itself, when sent in response to a)-.1 E(SYN pack)30
564 Q(et with the tw)-.1 E 2.5(oE)-.1 G
(CN \215ags set in the TCP header)-2.5 E 2.5(,i)-.4 G
(ndicating a willingness to use ECN.)-2.5 E(Setting TCP SYN/A)5 E(CK)-.4
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(ets as ECN-Capable can be of great bene\214t to the TCP connection, a)
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/F0 10/Times-Roman@0 SF 345.94(draft-ietf-tcpm-ecnsyn-00.txt January)72
48 R(2006)2.5 E(Changes from draft-ietf-twvsg-ecnsyn:)102 84 Q 2.5(*C)
102 108 S(hanged name of draft to draft-ietf-tcpm-ecnsyn.)-2.5 E 2.5(*A)
102 132 S(dded a discussion in Section 3 of "Response to)-2.5 E
(ECN-marking of SYN/A)107 144 Q(CK pack)-.4 E 2.5(ets". Based)-.1 F(on)
2.5 E(suggestions from Mark Allman.)107 156 Q 2.5(*A)102 180 S
(dded a discussion to the Conclusions about adding)-2.5 E
(ECN-capability to rele)107 192 Q -.25(va)-.25 G(nt set-up pack).25 E
(ets in other)-.1 E 2.5(protocols. From)107 204 R 2.5(as)2.5 G
(uggestion from W)-2.5 E(esle)-.8 E 2.5(yE)-.15 G(ddy)-2.5 E(.)-.65 E
2.5(*A)102 228 S(dded a description of SYN e)-2.5 E
(xchanges with SYN cookies.)-.15 E(From a suggestion from W)107 240 Q
(esle)-.8 E 2.5(yE)-.15 G(ddy)-2.5 E(.)-.65 E 2.5(*A)102 264 S
(dded a discussion of one-w)-2.5 E(ay data transfers, where the)-.1 E
(host sending the SYN/A)107 276 Q(CK pack)-.4 E(et sends no data pack)
-.1 E(ets.)-.1 E 2.5(*M)102 300 S
(inor editing, from feedback from Mark Allman and Janardhan)-2.5 E
(Iyeng)107 312 Q(ar)-.05 E(.)-.55 E 2.5(*F)102 336 S(uture w)-2.5 E
(ork: a look at the costs of adding)-.1 E(ECN-Capability in a w)107 348
Q(orst-case scenario.)-.1 E
(From feedback from Mark Allman and Janardhan Iyeng)107 360 Q(ar)-.05 E
(.)-.55 E 2.5(*F)102 384 S(uture w)-2.5 E(ork: a comparati)-.1 E .3 -.15
(ve e)-.25 H -.25(va)-.1 G(luation of tw).25 E(o)-.1 E
(possible responses to an ECN-mark)107 396 Q(ed SYN/A)-.1 E(CK pack)-.4
E(et.)-.1 E(Changes from draft-kuzmano)102 420 Q(vic-ecn-syn-00.txt:)
-.15 E 2.5(*C)102 444 S
(hanged name of draft to draft-ietf-twvsg-ecnsyn.)-2.5 E(END OF NO)102
468 Q(TE T)-.4 E 2.5(OR)-.18 G(FC EDIT)-2.5 E(OR.)-.18 E 2.5(1. Con)72
492 R -.15(ve)-.4 G(ntions).15 E(The k)102 516 Q .3 -.15(ey w)-.1 H
(ords "MUST", "MUST NO).05 E(T", "REQ)-.4 E(UIRED", "SHALL", "SHALL NO)
-.1 E(T", "SHOULD", "SHOULD NO)-.4 E(T",)-.4 E("RECOMMENDED", "MA)102
528 Q(Y", and "OPTION)-1.05 E
(AL" in this document are to be interpreted as described in [RFC 2119].)
-.35 E 2.5(1. Introduction)72 552 R(TCP')102 576 Q 2.5(sc)-.55 G
(ongestion control mechanism has primarily used pack)-2.5 E
(et loss as the congestion indication, with pack)-.1 E(ets dropped)-.1 E
(when b)102 588 Q(uf)-.2 E(fers o)-.25 E -.15(ve)-.15 G(r\215o).15 E 3.8
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(ets only when the queue o)-.1 E -.15(ve)-.15 G(r\215o).15 E(ws, and ha)
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/F0 10/Times-Roman@0 SF 345.94(draft-ietf-tcpm-ecnsyn-00.txt January)72
48 R(2006)2.5 E(The adoption of Acti)102 84 Q .3 -.15(ve Q)-.25 H
(ueue Management \(A).15 E(QM\) mechanisms allo)-.55 E
(ws better control of bottleneck queues [RFC2309].)-.25 E(This use of A)
102 96 Q(QM has the follo)-.55 E(wing potential bene\214ts:)-.25 E
(1\) better control of the queue, with reduced queueing delay;)102 108 Q
(2\) fe)102 120 Q(wer pack)-.25 E(et drops; and)-.1 E(3\) better f)102
132 Q(airness because of fe)-.1 E(wer synchronization ef)-.25 E(fects.)
-.25 E -.4(Wi)102 156 S
(th the adoption of ECN, performance may be further impro).4 E -.15(ve)
-.15 G 2.5(d. When).15 F(the router detects congestion before b)2.5 E
(uf)-.2 E(fer)-.25 E -.15(ove)102 168 S(r\215o).15 E 1.3 -.65(w, t)-.25
H(he router can pro).65 E
(vide a congestion indication either by dropping a pack)-.15 E
(et, or by setting the Congestion)-.1 E
(Experienced \(CE\) codepoint in the)102 180 Q(Explicit Congestion Noti\
\214cation \(ECN\) \214eld in the IP header [RFC3168].)5 E(The IETF)5 E
(has standardized the use of the Congestion Experienced \(CE\) codepoin\
t in the IP header for routers to indicate)102 192 Q 2.5(congestion. F)
102 204 R(or incremental deplo)-.15 E(yment and backw)-.1 E
(ards compatibility)-.1 E 2.5(,t)-.65 G
(he RFC on ECN [RFC 3168] speci\214es that)-2.5 E
(routers may mark ECN-capable pack)102 216 Q(ets that w)-.1 E
(ould otherwise ha)-.1 E .3 -.15(ve b)-.2 H
(een dropped, using the Congestion Experienced).15 E
(codepoint in the ECN \214eld.)102 228 Q(The use of ECN allo)5 E
(ws TCP to react to congestion while a)-.25 E -.2(vo)-.2 G
(iding unnecessary).2 E
(retransmissions and, in some cases, unnecessary retransmit timeouts.)
102 240 Q(Thus, using ECN has se)5 E -.15(ve)-.25 G(ral bene\214ts:).15
E(1\) F)102 264 Q(or short transfers, a TCP connection')-.15 E 2.5(sc)
-.55 G(ongestion windo)-2.5 E 2.5(wm)-.25 G(ay be small.)-2.5 E -.15(Fo)
5 G 2.5(re).15 G(xample, if the current windo)-2.65 E 2.5(wc)-.25 G
(ontains)-2.5 E(only one pack)102 276 Q(et, and that pack)-.1 E
(et is dropped, TCP will ha)-.1 E .3 -.15(ve t)-.2 H 2.5(ow).15 G
(ait for a retransmit timeout to reco)-2.6 E -.15(ve)-.15 G .8 -.4(r, r)
.15 H(educing its o).4 E -.15(ve)-.15 G(rall).15 E 2.5
(throughput. Similarly)102 288 R 2.5(,i)-.65 G 2.5(ft)-2.5 G
(he current windo)-2.5 E 2.5(wc)-.25 G(ontains only a fe)-2.5 E 2.5(wp)
-.25 G(ack)-2.5 E(ets and one of those pack)-.1 E
(ets is dropped, there might)-.1 E(not be enough duplicate ackno)102 300
Q(wledgements for a f)-.25 E
(ast retransmission, and the sender might ha)-.1 E .3 -.15(ve t)-.2 H
2.5(ow).15 G(ait for a delay of)-2.6 E(se)102 312 Q -.15(ve)-.25 G
(ral round-trip times using Limited T).15 E(ransmit [RFC3042].)-.35 E
-.4(Wi)5 G(th the use of ECN, short \215o).4 E(ws are less lik)-.25 E
(ely to ha)-.1 E -.15(ve)-.2 G(pack)102 324 Q(ets dropped, sometimes a)
-.1 E -.2(vo)-.2 G
(iding unnecessary delays or costly retransmit timeouts.).2 E
(2\) While longer \215o)102 348 Q(ws may not see substantially impro)
-.25 E -.15(ve)-.15 G 2.5(dt).15 G(hroughput with the use of ECN, the)
-2.5 E 2.5(ye)-.15 G(xperience lo)-2.65 E(wer loss.)-.25 E
(This may bene\214t TCP applications that are latenc)102 360 Q
(y- and loss-sensiti)-.15 E -.15(ve)-.25 G 2.5(,b).15 G(ecause of the a)
-2.5 E -.2(vo)-.2 G(idance of retransmissions.).2 E(RFC 3168 only speci\
\214ed marking the Congestion Experienced codepoint on TCP')102 384 Q
2.5(sd)-.55 G(ata pack)-2.5 E(ets, and not on SYN and)-.1 E(SYN/A)102
396 Q(CK pack)-.4 E 2.5(ets. RFC)-.1 F(3168 speci\214ed the ne)2.5 E
(gotiation of the use of ECN between the tw)-.15 E 2.5(oT)-.1 G
(CP end-points in the TCP)-2.5 E(SYN and SYN-A)102 408 Q(CK e)-.4 E
(xchange, using \215ags in the TCP header)-.15 E 5(.E)-.55 G
(rring on the side of being conserv)-5 E(ati)-.25 E -.15(ve)-.25 G 2.5
(,R).15 G(FC 3168 did)-2.5 E(not specify the use of ECN for the SYN/A)
102 420 Q(CK pack)-.4 E(et itself.)-.1 E(Ho)5 E(we)-.25 E -.15(ve)-.25 G
.8 -.4(r, b).15 H(ecause of the high cost to the TCP transfer of).4 E
(ha)102 432 Q(ving a SYN/A)-.2 E(CK pack)-.4 E(et dropped, with the res\
ulting retransmit timeout, this document is specifying the use of ECN f\
or)-.1 E(the SYN/A)102 444 Q(CK pack)-.4 E(et itself.)-.1 E
(This can be of great bene\214t to the TCP connection, a)5 E -.2(vo)-.2
G(iding the se).2 E -.15(ve)-.25 G(re penalty of a).15 E(retransmit tim\
eout for a connection that has not yet started placing a load on the ne\
tw)102 456 Q 2.5(ork. The)-.1 F(sender of the SYN/A)2.5 E(CK)-.4 E(pack)
102 468 Q(et must respond to an ECN mark by reducing its initial conges\
tion windo)-.1 E 2.5(wf)-.25 G(rom tw)-2.5 E(o, three, or four se)-.1 E
(gments to one)-.15 E(se)102 480 Q
(gment, reducing the subsequent load from that connection on the netw)
-.15 E(ork.)-.1 E(The use of ECN for SYN/A)102 504 Q(CK pack)-.4 E
(ets has the follo)-.1 E(wing potential bene\214ts:)-.25 E(1\) A)102 516
Q -.2(vo)-.74 G(idance of a retransmit timeout;).2 E(2\) Impro)102 528 Q
-.15(ve)-.15 G(ment in the throughput of short connections.).15 E
(This draft speci\214es a modi\214cation to RFC 3168 to allo)102 552 Q
2.5(wT)-.25 G(CP SYN/A)-2.5 E(CK pack)-.4 E(ets to be ECN-Capable.)-.1 E
(Section 2 contains)5 E(the speci\214cation of the change, while Sectio\
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564 Q(ork.)-.1 E(Section 5 contains an e)102 576 Q -.25(va)-.25 G
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48 R(2006)2.5 E(The ECN \214eld in the IP header:)102 84 Q 5(oC)102 96 S
(E: the Congestion Experienced codepoint; and)-5 E 5(oE)102 108 S(CT)-5
E 2.5(:e)-.5 G(ither one of the tw)-2.5 E 2.5(oE)-.1 G(CN-Capable T)-2.5
E(ransport codepoints.)-.35 E(The ECN \215ags in the TCP header:)102 132
Q 5(oC)102 144 S(WR: the Congestion W)-5 E(indo)-.4 E 2.5(wR)-.25 G
(educed \215ag; and)-2.5 E 5(oE)102 156 S(CE: the ECN-Echo \215ag.)-5 E
(ECN-setup pack)102 180 Q(ets:)-.1 E 5(oE)102 192 S(CN-setup SYN pack)-5
E(et: a SYN pack)-.1 E(et with the ECE and CWR \215ags;)-.1 E 5(oE)102
204 S(CN-setup SYN-A)-5 E(CK pack)-.4 E(et: a SYN-A)-.1 E(CK pack)-.4 E
(et with ECE b)-.1 E(ut not CWR.)-.2 E
(RFC 3168 in Section 6.1.1. states that "A host MUST NO)102 228 Q 2.5
(Ts)-.4 G(et ECT on SYN or SYN-A)-2.5 E(CK pack)-.4 E
(ets." In this section, we)-.1 E(specify that a TCP node MA)102 240 Q
2.5(Yr)-1.05 G(espond to an ECN-setup SYN pack)-2.5 E
(et by setting ECT in the responding ECN-setup)-.1 E(SYN/A)102 252 Q
(CK pack)-.4 E(et, indicating to routers that the SYN/A)-.1 E(CK pack)
-.4 E(et is ECN-Capable.)-.1 E(This allo)5 E
(ws a congested router along)-.25 E(the path to mark the pack)102 264 Q
(et instead of dropping the pack)-.1 E
(et as an indication of congestion.)-.1 E
(Assume that TCP node A transmits to TCP node B an ECN-setup SYN pack)
102 288 Q(et, indicating willingness to use ECN for this)-.1 E 2.5
(connection. As)102 300 R(speci\214ed by RFC 3168, if TCP node B is wil\
ling to use ECN, node B responds with an ECN-setup SYN-)2.5 E -.4(AC)102
312 S 2.5(Kp).4 G(ack)-2.5 E(et.)-.1 E -.8(Ta)102 336 S(ble 1 sho).8 E
(ws an interchange with the SYN/A)-.25 E(CK pack)-.4 E
(et dropped by a congested router)-.1 E 5(.N)-.55 G(ode B w)-5 E
(aits for a retransmit)-.1 E(timeout, and then retransmits the SYN/A)102
348 Q(CK pack)-.4 E(et.)-.1 E
(---------------------------------------------------------------)108 378
Q(TCP Node A)115.5 390 Q 42.5(Router TCP)32.5 F(Node B)2.5 E 30
(---------- ------)115.5 402 R(----------)45 E(ECN-setup SYN pack)115.5
426 Q(et --->)-.1 E(ECN-setup SYN pack)198 438 Q(et --->)-.1 E
(<--- ECN-setup SYN/A)170.5 462 Q(CK, possibly ECT)-.4 E
(3-second timer set)215.5 474 Q(SYN/A)165.5 486 Q(CK dropped)-.4 E(.)
37.5 E(.)240.5 498 Q(.)240.5 510 Q(3-second timer e)205.5 522 Q(xpires)
-.15 E(<--- ECN-setup SYN/A)183 534 Q(CK, not ECT)-.4 E
(<--- ECN-setup SYN/A)115.5 546 Q(CK)-.4 E(Data/A)115.5 558 Q(CK --->)
-.4 E(Data/A)228 570 Q(CK --->)-.4 E(<--- Data \(one to four se)180.5
582 Q(gments\))-.15 E
(---------------------------------------------------------------)108 594
Q -.8(Ta)115.5 618 S(ble 1: SYN e).8 E(xchange with the SYN/A)-.15 E
(CK pack)-.4 E(et dropped.)-.1 E(If the SYN/A)102 648 Q(CK pack)-.4 E
(et is dropped in the netw)-.1 E
(ork, the TCP host \(node B\) responds by w)-.1 E
(aiting three seconds for the)-.1 E -.15(Ku)72 696 S(zmano).15 E 173.445
(vic Standards)-.15 F -.35(Tr)2.5 G 190.795(ack [P).35 F(age 4])-.15 E 0
Cg EP
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48 R(2006)2.5 E(retransmit timer to e)102 84 Q(xpire [RFC2988].)-.15 E
(If a SYN/A)5 E(CK pack)-.4 E
(et with the ECT codepoint is dropped, the TCP node)-.1 E
(SHOULD resend the SYN/A)102 96 Q(CK pack)-.4 E
(et without the ECN-Capable codepoint.)-.1 E(\(Although we are not a)5 E
-.1(wa)-.15 G(re of an).1 E(y)-.15 E(middlebox)102 108 Q
(es that drop SYN/A)-.15 E(CK pack)-.4 E
(ets that contain an ECN-Capable codepoint in the IP header)-.1 E 2.5
(,w)-.4 G 2.5(eh)-2.5 G -2.25 -.2(av e)-2.5 H(learned to)2.7 E
(design our protocols defensi)102 120 Q -.15(ve)-.25 G(ly in this re).15
E -.05(ga)-.15 G(rd [RFC3360].\)).05 E 1.6 -.8(We n)102 144 T
(ote that if syn-cookies were used by Node B in the e).8 E(xchange in T)
-.15 E(able 1, TCP Node B w)-.8 E(ouldn')-.1 E 2.5(ts)-.18 G
(et a timer upon)-2.5 E(transmission of the SYN/A)102 156 Q(CK pack)-.4
E(et [SYN-COOK].)-.1 E(In this case, if the SYN/A)5 E(CK pack)-.4 E
(et w)-.1 E(as lost, the initiator \(Node)-.1 E(A\) w)102 168 Q(ould ha)
-.1 E .3 -.15(ve t)-.2 H 2.5(ot).15 G
(imeout and retransmit the SYN pack)-2.5 E
(et in order to trigger another SYN-A)-.1 E(CK.)-.4 E -.8(Ta)102 192 S
(ble 2 sho).8 E(ws an interchange with the SYN/A)-.25 E(CK pack)-.4 E
(et sent as ECN-Capable, and ECN-mark)-.1 E(ed instead of dropped at)-.1
E(the congested router)102 204 Q(.)-.55 E
(---------------------------------------------------------------)108 234
Q(TCP Node A)115.5 246 Q 42.5(Router TCP)32.5 F(Node B)2.5 E 30
(---------- ------)115.5 258 R(----------)45 E(ECN-setup SYN pack)115.5
282 Q(et --->)-.1 E(ECN-setup SYN pack)195.5 294 Q(et --->)-.1 E
(<--- ECN-setup SYN/A)190.5 318 Q(CK, ECT)-.4 E(<--- Sets CE on SYN/A)
163 330 Q(CK)-.4 E(<--- ECN-setup SYN/A)115.5 342 Q(CK, CE)-.4 E(Data/A)
115.5 366 Q(CK, ECN-Echo --->)-.4 E(Data/A)200.5 378 Q
(CK, ECN-Echo --->)-.4 E -.4(Wi)183 390 S(ndo).4 E 2.5(wr)-.25 G
(educed to one se)-2.5 E(gment.)-.15 E(<--- Data, CWR \(one se)175.5 402
Q(gment only\))-.15 E
(---------------------------------------------------------------)108 414
Q -.8(Ta)115.5 438 S(ble 2: SYN e).8 E(xchange with the SYN/A)-.15 E
(CK pack)-.4 E(et mark)-.1 E(ed.)-.1 E(If the recei)102 468 Q
(ving node \(node A\) recei)-.25 E -.15(ve)-.25 G 2.5(saS).15 G(YN/A)
-2.5 E(CK pack)-.4 E(et that has been mark)-.1 E
(ed by the congested router)-.1 E 2.5(,w)-.4 G(ith the CE)-2.5 E
(codepoint set, the recei)102 480 Q(ving node MUST respond by setting t\
he ECN-Echo \215ag in the TCP header of the responding A)-.25 E(CK)-.4 E
(pack)102 492 Q 2.5(et. As)-.1 F(speci\214ed in RFC 3168, the recei)2.5
E(ving node continues to set the ECN-Echo \215ag in pack)-.25 E
(ets until it recei)-.1 E -.15(ve)-.25 G 2.5(sa).15 G(pack)102 504 Q
(et with the CWR \215ag set.)-.1 E
(When the sending node \(node B\) recei)102 528 Q -.15(ve)-.25 G 2.5(st)
.15 G(he ECN-Echo pack)-2.5 E
(et reporting the Congestion Experienced indication in the)-.1 E(SYN/A)
102 540 Q(CK pack)-.4 E
(et, the node MUST set the initial congestion windo)-.1 E 2.5(wt)-.25 G
2.5(oo)-2.5 G(ne se)-2.5 E(gment, instead of tw)-.15 E 2.5(os)-.1 G -.15
(eg)-2.5 G(ments as allo).15 E(wed)-.25 E
(by [RFC2581], or three or four se)102 552 Q(gments allo)-.15 E
(wed by [RFC3390].)-.25 E(If the sending node \(node B\) w)5 E
(as going to use an initial)-.1 E(windo)102 564 Q 2.5(wo)-.25 G 2.5(fo)
-2.5 G(ne se)-2.5 E(gment, and recei)-.15 E -.15(ve)-.25 G 2.5(sa).15 G
2.5(nE)-2.5 G(CN-Echo pack)-2.5 E
(et informing it of a Congestion Experienced indication on its)-.1 E
(SYN/A)102 576 Q(CK pack)-.4 E(et, the sending node MA)-.1 E 2.5(Yc)
-1.05 G(ontinue to send with an initial windo)-2.5 E 2.5(wo)-.25 G 2.5
(fo)-2.5 G(ne se)-2.5 E(gment, without w)-.15 E(aiting for a)-.1 E
(retransmit timeout.)102 588 Q 1.6 -.8(We n)5 H(ote that this updates R\
FC 3168, which speci\214es that "the sending TCP MUST reset the).8 E
(retransmit timer on recei)102 600 Q(ving the ECN-Echo pack)-.25 E
(et when the congestion windo)-.1 E 2.5(wi)-.25 G 2.5(so)-2.5 G 2.5
(ne." As)-2.5 F(speci\214ed by RFC 3168, the)2.5 E(sending node \(node \
B\) also sets the CWR \215ag in the TCP header of the ne)102 612 Q
(xt data pack)-.15 E(et sent, to ackno)-.1 E(wledge its receipt)-.25 E
(of and reaction to the ECN-Echo \215ag.)102 624 Q
(If the data transfer in T)102 648 Q
(able 2 is entirely from Node A to Node B, then data pack)-.8 E
(ets from Node A continue to set the)-.1 E -.15(Ku)72 696 S(zmano).15 E
173.445(vic Standards)-.15 F -.35(Tr)2.5 G 190.795(ack [P).35 F(age 5])
-.15 E 0 Cg EP
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48 R(2006)2.5 E(ECN-Echo \215ag in data pack)102 84 Q(ets, w)-.1 E
(aiting for the CWR \215ag from Node B ackno)-.1 E
(wledging a response to the ECN-Echo \215ag.)-.25 E 2.5(3. Discussion)72
108 R(Moti)102 132 Q -.25(va)-.25 G(tion:).25 E
(The rationale for the proposed change is the follo)102 144 Q 2.5
(wing. When)-.25 F(node B recei)2.5 E -.15(ve)-.25 G 2.5(saT).15 G
(CP SYN pack)-2.5 E(et with ECN-Echo bit set)-.1 E(in the TCP header)102
156 Q 2.5(,t)-.4 G(his indicates that node A is ECN-capable. If node B \
is also ECN-capable, there are no obstacles to)-2.5 E(immediately setti\
ng one of the ECN-Capable codepoints in the IP header in the responding\
 TCP SYN/A)102 168 Q(CK pack)-.4 E(et.)-.1 E(There can be a great bene\
\214t in setting an ECN-capable codepoint in SYN/A)102 192 Q(CK pack)-.4
E(ets, as is discussed further in Section)-.1 E 2.5(4. Congestion)102
204 R(is most lik)2.5 E(ely to occur in the serv)-.1 E(er)-.15 E
(-to-client direction.)-.2 E
(As a result, setting an ECN-capable codepoint in)5 E(SYN/A)102 216 Q
(CK pack)-.4 E(ets can reduce the occurence of three-second retransmit \
timeouts resulting from the drop of SYN/A)-.1 E(CK)-.4 E(pack)102 228 Q
(ets.)-.1 E(Flooding attacks:)102 252 Q
(Setting an ECN-Capable codepoint in the responding TCP SYN/A)102 264 Q
(CK pack)-.4 E(ets does not raise an)-.1 E 2.5(yn)-.15 G -.15(ove)-2.5 G
2.5(ls).15 G(ecurity)-2.5 E 2.5(vulnerabilities. F)102 276 R(or e)-.15 E
(xample, pro)-.15 E -.2(vo)-.15 G(king serv).2 E
(ers or hosts to send SYN/A)-.15 E(CK pack)-.4 E
(ets to a third party in order to perform a)-.1 E("SYN/A)102 288 Q
(CK \215ood" attack w)-.4 E(ould be greatly inef)-.1 E 2.5
(\214cient. Third)-.25 F(parties w)2.5 E
(ould immediately drop such pack)-.1 E(ets, since the)-.1 E(y)-.15 E -.1
(wo)102 300 S(uld kno).1 E 2.5(wt)-.25 G(hat the)-2.5 E 2.5(yd)-.15 G
(idn')-2.5 E 2.5(tg)-.18 G(enerate the TCP SYN pack)-2.5 E
(ets in the \214rst place.)-.1 E(Moreo)5 E -.15(ve)-.15 G .8 -.4(r, s)
.15 H(uch SYN/A).4 E(CK attacks w)-.4 E(ould)-.1 E(ha)102 312 Q .3 -.15
(ve t)-.2 H(he same signatures as the e).15 E
(xisting TCP SYN attacks. Pro)-.15 E -.2(vo)-.15 G(king serv).2 E
(ers or hosts to reply with SYN/A)-.15 E(CK pack)-.4 E(ets in)-.1 E
(order to congest a certain link w)102 324 Q(ould also be highly inef)
-.1 E(\214cient because SYN A)-.25 E(CK pack)-.4 E
(ets are small in size.)-.1 E(Ho)102 348 Q(we)-.25 E -.15(ve)-.25 G .8
-.4(r, t).15 H(he addition of ECN-Capability to SYN/A).4 E(CK pack)-.4 E
(ets could allo)-.1 E 2.5(wS)-.25 G(YN/A)-2.5 E(CK pack)-.4 E
(ets to persist for more hops)-.1 E(along a netw)102 360 Q
(ork path before being dropped, thus adding some)-.1 E
(what to the ability of a SYN/A)-.25 E(CK attack to \215ood a netw)-.4 E
(ork)-.1 E(link.)102 372 Q(The TCP SYN pack)102 396 Q(et:)-.1 E
(There are se)102 408 Q -.15(ve)-.25 G(ral reasons wh).15 E 2.5(ya)-.05
G 2.5(nE)-2.5 G(CN-Capable codepoint MUST NO)-2.5 E 2.5(Tb)-.4 G 2.5(es)
-2.5 G(et in the IP header of the initiating TCP SYN)-2.5 E(pack)102 420
Q 2.5(et. First,)-.1 F(when the TCP SYN pack)2.5 E(et is sent, there ar\
e no guarantees that the other TCP endpoint \(node B in T)-.1 E
(able 2\))-.8 E(is ECN-capable, or that it w)102 432 Q
(ould be able to understand and react if the ECN CE codepoint w)-.1 E
(as set by a congested router)-.1 E(.)-.55 E
(Second, the ECN-Capable codepoint in TCP SYN pack)102 456 Q
(ets could be misused by malicious clients to `impro)-.1 E -.15(ve)-.15
G 2.5('t).15 G(he well-)-2.5 E(kno)102 468 Q
(wn TCP SYN attack. By setting an ECN-Capable codepoint in TCP SYN pack)
-.25 E(ets, a malicious host might be able to)-.1 E(inject a lar)102 480
Q(ge number of TCP SYN pack)-.18 E
(ets through a potentially congested ECN-enabled router)-.1 E 2.5(,c)-.4
G(ongesting it e)-2.5 E -.15(ve)-.25 G(n).15 E(further)102 492 Q(.)-.55
E -.15(Fo)102 516 S 2.5(rb).15 G
(oth these reasons, we continue the restriction that the TCP SYN pack)
-2.5 E(et MUST NO)-.1 E 2.5(Th)-.4 G -2.25 -.2(av e)-2.5 H
(the ECN-Capable)2.7 E(codepoint in the IP header set.)102 528 Q(Backw)
102 552 Q(ards compatibility:)-.1 E
(If there are some older TCP implementations that don')102 564 Q 2.5(tr)
-.18 G(espond to the Congestion Experienced codepoint in a SYN/A)-2.5 E
(CK)-.4 E(pack)102 576 Q(et, that w)-.1 E
(ould not be an insurmountable problem.)-.1 E(It w)5 E
(ould mean that the sender of the SYN/A)-.1 E(CK pack)-.4 E(et w)-.1 E
(ould not)-.1 E(reduce the initial congestion windo)102 588 Q 2.5(wf)
-.25 G(rom tw)-2.5 E(o, three, or four se)-.1 E(gments do)-.15 E
(wn to one se)-.25 E(gment, as it should.)-.15 E(Ho)5 E(we)-.25 E -.15
(ve)-.25 G .8 -.4(r, t).15 H(he).4 E(TCP sender w)102 600 Q
(ould still respond correctly to an)-.1 E 2.5(ys)-.15 G
(ubsequent CE indications on data pack)-2.5 E
(ets later on in the connection.)-.1 E(SYN/A)102 624 Q(CK pack)-.4 E
(ets and pack)-.1 E(et size:)-.1 E(There are a number of router b)102
636 Q(uf)-.2 E(fer architectures that ha)-.25 E .3 -.15(ve s)-.2 H
(maller dropping rates for small \(SYN\) pack).15 E(ets than for lar)-.1
E(ge)-.18 E(\(data\) pack)102 648 Q 2.5(ets. F)-.1 F(or e)-.15 E
(xample, for a Drop T)-.15 E(ail queue in units of pack)-.8 E
(ets, where each pack)-.1 E(et tak)-.1 E(es a single slot in the b)-.1 E
(uf)-.2 E(fer)-.25 E -.15(Ku)72 696 S(zmano).15 E 173.445(vic Standards)
-.15 F -.35(Tr)2.5 G 190.795(ack [P).35 F(age 6])-.15 E 0 Cg EP
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48 R(2006)2.5 E(re)102 84 Q -.05(ga)-.15 G(rdless of pack).05 E
(et size, small and lar)-.1 E(ge pack)-.18 E(ets are equally lik)-.1 E
(ely to be dropped.)-.1 E(Ho)5 E(we)-.25 E -.15(ve)-.25 G .8 -.4(r, f)
.15 H(or a Drop T).4 E(ail queue in)-.8 E(units of bytes, small pack)102
96 Q(ets are less lik)-.1 E(ely to be dropped than are lar)-.1 E
(ge ones.)-.18 E(Similarly)5 E 2.5(,f)-.65 G(or RED in pack)-2.5 E
(et mode, small)-.1 E(and lar)102 108 Q(ge pack)-.18 E
(ets are equally lik)-.1 E(ely to be dropped or mark)-.1 E
(ed, while for RED in byte mode, a pack)-.1 E(et')-.1 E 2.5(sc)-.55 G
(hance of being)-2.5 E(dropped or mark)102 120 Q
(ed is proportional to the pack)-.1 E(et size in bytes.)-.1 E -.15(Fo)
102 144 S 2.5(rac).15 G(ongested router with an A)-2.5 E
(QM mechanism in byte mode, where a pack)-.55 E(et')-.1 E 2.5(sc)-.55 G
(hance of being dropped or mark)-2.5 E(ed is)-.1 E
(proportional to the pack)102 156 Q
(et size in bytes, the drop or marking rate for TCP SYN/A)-.1 E(CK pack)
-.4 E(ets should generally be lo)-.1 E 3.8 -.65(w. I)-.25 H(n).65 E
(this case, the bene\214t of making SYN/A)102 168 Q(CK pack)-.4 E
(ets ECN-Capable should be similarly moderate.)-.1 E(Ho)5 E(we)-.25 E
-.15(ve)-.25 G .8 -.4(r, f).15 H(or a).4 E
(congested router with a Drop T)102 180 Q(ail queue in units of pack)-.8
E(ets or with an A)-.1 E(QM mechanism in pack)-.55 E
(et mode, and with no)-.1 E(priority queueing for smaller pack)102 192 Q
(ets, small and lar)-.1 E(ge pack)-.18 E(ets should ha)-.1 E .3 -.15
(ve t)-.2 H(he same probability of being dropped or).15 E(mark)102 204 Q
2.5(ed. In)-.1 F(such a case, making SYN/A)2.5 E(CK pack)-.4 E
(ets ECN-Capable should be of signi\214cant bene\214t.)-.1 E 1.6 -.8
(We b)102 228 T(elie).8 E .3 -.15(ve t)-.25 H
(hat there are a wide range of beha).15 E(viors in the real w)-.2 E
(orld in terms of the drop or mark beha)-.1 E(vior at routers as a)-.2 E
(function of pack)102 240 Q(et size [T)-.1 E(ools, Section 10].)-.8 E
1.6 -.8(We n)5 H(ote that all of these alternati).8 E -.15(ve)-.25 G 2.5
(sl).15 G(isted abo)-2.5 E .3 -.15(ve a)-.15 H(re a).15 E -.25(va)-.2 G
(ilable in the NS).25 E(simulator \(Drop T)102 252 Q
(ail queues are by def)-.8 E(ault in units of pack)-.1 E
(ets, while the def)-.1 E(ault for RED queue management has been)-.1 E
(changed from pack)102 264 Q(et mode to byte mode\).)-.1 E
(Response to ECN-marking of SYN/A)102 288 Q(CK pack)-.4 E(ets:)-.1 E
(One question is wh)102 300 Q 2.5(yT)-.05 G(CP SYN/A)-2.5 E(CK pack)-.4
E(ets should be treated dif)-.1 E(ferently from other pack)-.25 E
(ets in terms of the pack)-.1 E(et)-.1 E(sender')102 312 Q 2.5(sr)-.55 G
(esponse to an ECN-mark)-2.5 E(ed pack)-.1 E 2.5(et. Section)-.1 F 2.5
(5o)2.5 G 2.5(fR)-2.5 G(FC 3168 speci\214es the follo)-2.5 E(wing:)-.25
E("Upon the receipt by an ECN-Capable transport of a single CE pack)102
336 Q(et, the congestion control algorithms follo)-.1 E(wed at the)-.25
E(end-systems MUST be essentially the same as the congestion control re\
sponse to a *single* dropped pack)102 348 Q 2.5(et. F)-.1 F(or)-.15 E
-.15(ex)102 360 S
(ample, for ECN-Capable TCP the source TCP is required to halv).15 E 2.5
(ei)-.15 G(ts congestion windo)-2.5 E 2.5(wf)-.25 G(or an)-2.5 E 2.5(yw)
-.15 G(indo)-2.5 E 2.5(wo)-.25 G 2.5(fd)-2.5 G(ata)-2.5 E
(containing either a pack)102 372 Q(et drop or an ECN indication.")-.1 E
(In particular)102 396 Q 2.5(,S)-.4 G(ection 6.1.2 of RFC 3168 speci\
\214es that when the TCP congestion windo)-2.5 E 2.5(wc)-.25 G
(onsists of a single pack)-2.5 E(et and)-.1 E(that pack)102 408 Q
(et is ECN-mark)-.1 E(ed in the netw)-.1 E
(ork, then the sender must reduce the sending rate belo)-.1 E 2.5(wo)
-.25 G(ne pack)-2.5 E(et per round-trip)-.1 E(time, by w)102 420 Q
(aiting for one R)-.1 E .36 -.18(TO b)-.6 H(efore sending another pack)
.18 E 2.5(et. If)-.1 F(the R)2.5 E .36 -.18(TO w)-.6 H(as set to the a)
.08 E -.15(ve)-.2 G(rage round-trip time, this).15 E -.1(wo)102 432 S
(uld result in halving the sending rate; because the R).1 E .36 -.18
(TO i)-.6 H 2.5(si).18 G 2.5(nf)-2.5 G(act lar)-2.6 E(ger than the a)
-.18 E -.15(ve)-.2 G(rage round-trip time, the sending).15 E
(rate is reduced to less than half of its pre)102 444 Q(vious v)-.25 E
(alue.)-.25 E(TCP')102 468 Q 2.5(sc)-.55 G
(ongestion control response to the *dropping* of a SYN/A)-2.5 E(CK pack)
-.4 E(et is to w)-.1 E(ait a def)-.1 E(ault time before sending)-.1 E
(another pack)102 480 Q 2.5(et. This)-.1 F(document ar)2.5 E
(gues that ECN gi)-.18 E -.15(ve)-.25 G 2.5(se).15 G
(nd-systems a wider range of possible responses to the *marking*)-2.5 E
(of a SYN/A)102 492 Q(CK pack)-.4 E(et, and that w)-.1 E(aiting a def)
-.1 E(ault time before sending a data pack)-.1 E
(et is not the desired response.)-.1 E(On the conserv)102 516 Q(ati)-.25
E .3 -.15(ve e)-.25 H(nd, one could assume an ef).15 E(fecti)-.25 E .3
-.15(ve c)-.25 H(ongestion windo).15 E 2.5(wo)-.25 G 2.5(fo)-2.5 G
(ne pack)-2.5 E(et for the SYN/A)-.1 E(CK pack)-.4 E(et, and)-.1 E
(respond to an ECN-mark)102 528 Q(ed SYN/A)-.1 E(CK pack)-.4 E
(et by reducing the sending rate to one pack)-.1 E(et e)-.1 E -.15(ve)
-.25 G(ry tw).15 E 2.5(or)-.1 G(ound-trip times.)-2.5 E(As)5 E(an appro\
ximation, the TCP end-node could measure the round-trip time T between \
the sending of the SYN/A)102 540 Q(CK pack)-.4 E(et)-.1 E
(and the receipt of the ackno)102 552 Q
(wledgement, and reply to the ackno)-.25 E(wledgement of the ECN-mark)
-.25 E(ed SYN/A)-.1 E(CK pack)-.4 E(et by)-.1 E -.1(wa)102 564 S
(iting T seconds before sending a data pack).1 E 2.5(et. Ho)-.1 F(we)
-.25 E -.15(ve)-.25 G .8 -.4(r, w).15 H 2.5(en).4 G
(ote that for an ECN-mark)-2.5 E(ed SYN/A)-.1 E(CK pack)-.4 E
(et, halving)-.1 E(the *congestion windo)102 576 Q(w* is not the same a\
s halving the *sending rate*; there is no `sending rate' associated wit\
h an)-.25 E(ECN-Capable SYN/A)102 588 Q(CK pack)-.4 E(et, as such pack)
-.1 E(ets are only sent as the \214rst pack)-.1 E
(et in a connection from that host.)-.1 E(Further)5 E(,)-.4 E 2.5(ar)102
600 S(outer')-2.5 E 2.5(sm)-.55 G(arking of a SYN/A)-2.5 E(CK pack)-.4 E
(et is not af)-.1 E(fected by an)-.25 E 2.5(yp)-.15 G
(ast history of that connection.)-2.5 E(Adding ECN-Capability to SYN/A)
102 624 Q(CK pack)-.4 E(ets allo)-.1 E
(ws the simple response of setting the initial congestion windo)-.25 E
2.5(wt)-.25 G 2.5(oo)-2.5 G(ne)-2.5 E(pack)102 636 Q
(et, instead of its allo)-.1 E(wed def)-.25 E(ault v)-.1 E(alue of tw)
-.25 E(o, three, or four pack)-.1 E
(ets, with the host proceeding with a cautious)-.1 E
(sending rate of one pack)102 648 Q(et per round-trip time.)-.1 E
(If that pack)5 E(et is ECN-mark)-.1 E
(ed or dropped, then the sender will w)-.1 E(ait an)-.1 E -.15(Ku)72 696
S(zmano).15 E 173.445(vic Standards)-.15 F -.35(Tr)2.5 G 190.795(ack [P)
.35 F(age 7])-.15 E 0 Cg EP
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48 R(2006)2.5 E -1.48 -.6(RT O)102 84 T(before sending another pack)3.1
E 2.5(et. This)-.1 F(document ar)2.5 E
(gues that such an approach is useful to users, with no dangers of)-.18
E(congestion collapse or of starv)102 96 Q(ation of competing traf)-.25
E(\214c.)-.25 E 1.6 -.8(We n)102 120 T(ote that if the data transfer is\
 entirely from Node A to Node B, then there is no ef).8 E(fecti)-.25 E
.3 -.15(ve d)-.25 H(if).15 E(ference between the tw)-.25 E(o)-.1 E
(possible responses to an ECN-mark)102 132 Q(ed SYN/A)-.1 E(CK pack)-.4
E(et outlined abo)-.1 E -.15(ve)-.15 G 5(.I).15 G 2.5(ne)-5 G
(ither case, Node B sends no data pack)-2.5 E(ets,)-.1 E
(only sending ackno)102 144 Q(wledgement pack)-.25 E
(ets in response to recei)-.1 E -.15(ve)-.25 G 2.5(dd).15 G(ata pack)
-2.5 E(ets.)-.1 E 2.5(4. Related)72 168 R -.8(Wo)2.5 G(rk).8 E
(The addition of ECN-capability to TCP')102 192 Q 2.5(sS)-.55 G(YN/A)
-2.5 E(CK pack)-.4 E(ets w)-.1 E(as proposed in [ECN+].)-.1 E
(The paper includes an e)5 E(xtensi)-.15 E -.15(ve)-.25 G
(set of simulation and testbed e)102 204 Q(xperiments to e)-.15 E -.25
(va)-.25 G(luate the ef).25 E(fects of the proposal, using se)-.25 E
-.15(ve)-.25 G(ral Acti).15 E .3 -.15(ve Q)-.25 H(ueue Management).15 E
(\(A)102 216 Q(QM\) mechanisms, including Random Early Detection \(RED\
\) [RED], Random Exponential Marking \(REM\) [REM],)-.55 E
(and Proportional Inte)102 228 Q(grator \(PI\) [PI].)-.15 E
(The performance measures were the end-to-end response times for each)5
E(request/response pair)102 240 Q 2.5(,a)-.4 G(nd the aggre)-2.5 E -.05
(ga)-.15 G(te throughput on the bottleneck link.).05 E
(The end-to-end response time w)5 E(as computed)-.1 E(as the time from \
the moment when the request for the \214le is sent to the serv)102 252 Q
(er)-.15 E 2.5(,u)-.4 G(ntil that \214le is successfully do)-2.5 E
(wnloaded)-.25 E(by the client.)102 264 Q
(The measurements from [ECN+] sho)102 288 Q
(wed that setting an ECN-Capable codepoint in the IP pack)-.25 E
(et header in TCP)-.1 E(SYN/A)102 300 Q(CK pack)-.4 E
(ets systematically impro)-.1 E -.15(ve)-.15 G 2.5(sp).15 G
(erformance with all e)-2.5 E -.25(va)-.25 G(luated A).25 E(QM schemes.)
-.55 E(When SYN/A)5 E(CK pack)-.4 E(ets at)-.1 E 2.5(ac)102 312 S
(ongested router are ECN-mark)-2.5 E(ed instead of dropped, this can a)
-.1 E -.2(vo)-.2 G(id a long initial retransmit timeout, impro).2 E
(ving the)-.15 E(response time for the af)102 324 Q(fected \215o)-.25 E
2.5(wd)-.25 G(ramatically)-2.5 E(.)-.65 E([ECN+] sho)102 348 Q
(wed that the impact on aggre)-.25 E -.05(ga)-.15 G
(te throughput can also be quite signi\214cant, because marking SYN A)
.05 E(CK)-.4 E(pack)102 360 Q(ets can pre)-.1 E -.15(ve)-.25 G(nt lar)
.15 E(ger \215o)-.18 E(ws from suf)-.25 E
(fering long timeouts before being "admitted" into the netw)-.25 E 2.5
(ork. In)-.1 F(addition, the)2.5 E(testbed measurements from [ECN+] sho)
102 372 Q(wed that W)-.25 E(eb serv)-.8 E
(ers setting the ECN-Capable codepoint in TCP SYN/A)-.15 E(CK)-.4 E
(pack)102 384 Q(ets could serv)-.1 E 2.5(em)-.15 G(ore requests.)-2.5 E
(As a \214nal step, [ECN+] e)102 408 Q(xplored the co-e)-.15 E
(xistence of \215o)-.15 E(ws that do and don')-.25 E 2.5(ts)-.18 G
(et the ECN-capable codepoint in TCP)-2.5 E(SYN/A)102 420 Q(CK pack)-.4
E 2.5(ets. The)-.1 F(results in [ECN+] sho)2.5 E 2.5(wt)-.25 G
(hat both types of \215o)-2.5 E(ws can coe)-.25 E
(xist, with some performance de)-.15 E(gradation)-.15 E(for \215o)102
432 Q(ws that don')-.25 E 2.5(ta)-.18 G(pply the change.)-2.5 E(Flo)5 E
(ws that apply the change impro)-.25 E .3 -.15(ve t)-.15 H
(heir end-to-end performance.).15 E(At the same)5 E
(time, the performance de)102 444 Q(gradation for \215o)-.15 E
(ws that don')-.25 E 2.5(ta)-.18 G
(pply the change, as a result of the \215o)-2.5 E
(ws that do apply the change,)-.25 E
(increases as a greater fraction of \215o)102 456 Q
(ws apply the change.)-.25 E 2.5(5. Performance)72 480 R(Ev)2.5 E
(aluation)-.25 E 2.5(5.1. The)72 504 R
(Costs and Bene\214t of Adding ECN-Capability)2.5 E([ECN+] e)102 528 Q
(xplored the costs and bene\214ts of adding ECN-Capability to SYN/A)-.15
E(CK pack)-.4 E(ets with both simulations and)-.1 E -.15(ex)102 540 S
2.5(periments. The).15 F(addition of ECN-capability to SYN/A)2.5 E
(CK pack)-.4 E(ets could be of signi\214cant bene\214t for those ECN)-.1
E(connections that w)102 552 Q(ould ha)-.1 E .3 -.15(ve h)-.2 H
(ad the SYN/A).15 E(CK pack)-.4 E(et dropped in the netw)-.1 E
(ork, and for which the ECN-Capability w)-.1 E(ould)-.1 E(allo)102 564 Q
2.5(wt)-.25 G(he SYN/A)-2.5 E(CK to be mark)-.4 E
(ed rather than dropped.)-.1 E(The percent of SYN/A)102 588 Q(CK pack)
-.4 E(ets on a link can be quite high. In particular)-.1 E 2.5(,m)-.4 G
(easurements on links dominated by W)-2.5 E(eb)-.8 E(traf)102 600 Q
(\214c indicate that 15-20% of the pack)-.25 E(ets can be SYN/A)-.1 E
(CK pack)-.4 E(ets [SCJO01].)-.1 E
(The bene\214t of adding ECN-capability to SYN/A)102 624 Q(CK pack)-.4 E
(ets depends in part on the size of the data transfer)-.1 E 5(.T)-.55 G
(he drop of a)-5 E(SYN/A)102 636 Q(CK pack)-.4 E(et can increase the do)
-.1 E(wnload time of a short \214le by an order of magnitude, by requir\
ing a three-second)-.25 E(retransmit timeout.)102 648 Q -.15(Fo)5 G 2.5
(rl).15 G(onger)-2.5 E(-li)-.2 E -.15(ve)-.25 G 2.5<648d>.15 G -.25(ow)
-2.5 G(s, the ef).25 E(fect of a dropped SYN/A)-.25 E(CK pack)-.4 E
(et on \214le do)-.1 E(wnload time is less)-.25 E -.15(Ku)72 696 S
(zmano).15 E 173.445(vic Standards)-.15 F -.35(Tr)2.5 G 190.795(ack [P)
.35 F(age 8])-.15 E 0 Cg EP
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/F0 10/Times-Roman@0 SF 345.94(draft-ietf-tcpm-ecnsyn-00.txt January)72
48 R(2006)2.5 E 2.5(dramatic. Ho)102 84 R(we)-.25 E -.15(ve)-.25 G .8
-.4(r, e).15 H -.15(ve).15 G 2.5(nf).15 G(or longer)-2.5 E(-li)-.2 E
-.15(ve)-.25 G 2.5<648d>.15 G -.25(ow)-2.5 G
(s, the addition of ECN-capability to SYN/A).25 E(CK pack)-.4 E
(ets can impro)-.1 E .3 -.15(ve t)-.15 H(he).15 E -.1(fa)102 96 S
(irness among long-li).1 E -.15(ve)-.25 G 2.5<648d>.15 G -.25(ow)-2.5 G
(s, as ne).25 E(wly-arri)-.25 E(ving \215o)-.25 E(ws w)-.25 E
(ould be less lik)-.1 E(ely to ha)-.1 E .3 -.15(ve t)-.2 H 2.5(ow).15 G
(ait for retransmit timeouts.)-2.6 E
(The question that arises of course is what fraction of connections w)
102 120 Q(ould see the bene\214t from making SYN/A)-.1 E(CK pack)-.4 E
(ets)-.1 E(ECN-capable, in a particular scenario?)102 132 Q
(Speci\214cally:)5 E(\(1\) What fraction of arri)102 156 Q(ving SYN/A)
-.25 E(CK pack)-.4 E
(ets are dropped at the congested router when the SYN/A)-.1 E(CK pack)
-.4 E(ets are not)-.1 E(ECN-capable?)102 168 Q(\(2\) Of those SYN/A)102
192 Q(CK pack)-.4 E
(ets that are dropped, what fraction of those drops w)-.1 E(ould ha)-.1
E .3 -.15(ve b)-.2 H(een ECN-marks instead of).15 E(drops if the SYN/A)
102 204 Q(CK pack)-.4 E(ets had been ECN-capable?)-.1 E 1.6 -.8(To a)102
228 T(nswer \(1\), it is necessary to consider not only the le).8 E -.15
(ve)-.25 G 2.5(lo).15 G 2.5(fc)-2.5 G(ongestion b)-2.5 E
(ut also the queue architecture at the congested)-.2 E 2.5(link. As)102
240 R(described in Section 3 abo)2.5 E -.15(ve)-.15 G 2.5(,f).15 G
(or some queue architectures small pack)-2.5 E(ets are less lik)-.1 E
(ely to be dropped than lar)-.1 E(ge)-.18 E 2.5(ones. In)102 252 R
(such an en)2.5 E(vironment, SYN/A)-.4 E(CK pack)-.4 E(ets w)-.1 E
(ould ha)-.1 E .3 -.15(ve l)-.2 H -.25(ow).15 G(er pack).25 E
(et drop rates; question \(1\) could not necessarily)-.1 E
(be inferred from the o)102 264 Q -.15(ve)-.15 G(rall pack).15 E
(et drop rate, b)-.1 E
(ut could be answered by measuring the drop rate for SYN/A)-.2 E
(CK pack)-.4 E(ets)-.1 E(directly)102 276 Q 5(.I)-.65 G 2.5(ns)-5 G
(uch an en)-2.5 E(vironment, adding ECN-capability to SYN/A)-.4 E
(CK pack)-.4 E(ets w)-.1 E(ould be of less dramatic bene\214t than in)
-.1 E(en)102 288 Q(vironments where all pack)-.4 E(ets are equally lik)
-.1 E(ely to be dropped re)-.1 E -.05(ga)-.15 G(rdless of pack).05 E
(et size.)-.1 E(As question \(2\) implies, e)102 312 Q -.15(ve)-.25 G
2.5(ni).15 G 2.5(fa)-2.5 G(ll of the SYN/A)-2.5 E(CK pack)-.4 E
(ets were ECN-capable, there could still be some SYN/A)-.1 E(CK)-.4 E
(pack)102 324 Q(ets dropped instead of mark)-.1 E(ed at the congested l\
ink; the full answer to question \(2\) depends on the details of the)-.1
E(queue management mechanism at the router)102 336 Q 5(.I)-.55 G 2.5(fc)
-5 G(ongestion is suf)-2.5 E
(\214ciently bad, and the queue management mechanism)-.25 E(cannot pre)
102 348 Q -.15(ve)-.25 G(nt the b).15 E(uf)-.2 E(fer from o)-.25 E -.15
(ve)-.15 G(r\215o).15 E(wing, then SYN/A)-.25 E(CK pack)-.4 E
(ets will be dropped rather than mark)-.1 E(ed upon b)-.1 E(uf)-.2 E
(fer)-.25 E -.15(ove)102 360 S(r\215o).15 E 2.5(ww)-.25 G
(hether or not the)-2.5 E 2.5(ya)-.15 G(re ECN-capable.)-2.5 E -.15(Fo)
102 384 S 2.5(rs).15 G(ome A)-2.5 E(QM mechanisms, ECN-capable pack)-.55
E(ets are mark)-.1 E(ed instead of dropped an)-.1 E 2.5(yt)-.15 G
(ime this is possible, that is, an)-2.5 E(y)-.15 E(time the b)102 396 Q
(uf)-.2 E(fer is not yet full.)-.25 E -.15(Fo)5 G 2.5(ro).15 G(ther A)
-2.5 E(QM mechanisms ho)-.55 E(we)-.25 E -.15(ve)-.25 G .8 -.4(r, s).15
H(uch as the RED mechanism as recommended in).4 E([RED], pack)102 408 Q
(ets are dropped rather than mark)-.1 E(ed when the pack)-.1 E
(et drop/mark rate e)-.1 E(xceeds a certain threshold, e.g., 10%,)-.15 E
-2.15 -.25(ev e)102 420 T 2.5(ni).25 G 2.5(ft)-2.5 G(he pack)-2.5 E
(ets are ECN-capable.)-.1 E -.15(Fo)5 G 2.5(rar).15 G
(outer with such an A)-2.5 E(QM mechanism, when congestion is suf)-.55 E
(\214ciently se)-.25 E -.15(ve)-.25 G(re).15 E
(to cause a high drop/mark rate, some SYN/A)102 432 Q(CK pack)-.4 E
(ets w)-.1 E(ould be dropped instead of mark)-.1 E
(ed whether or not the)-.1 E 2.5(yw)-.15 G(ere)-2.5 E(ECN-capable.)102
444 Q(Thus, the de)102 468 Q
(gree of bene\214t of adding ECN-Capability to SYN/A)-.15 E(CK pack)-.4
E(ets depends not only on the o)-.1 E -.15(ve)-.15 G(rall pack).15 E
(et drop)-.1 E(rate in the netw)102 480 Q(ork, b)-.1 E
(ut also on the queue management architecture at the congested link.)-.2
E 2.5(5.2. An)72 504 R(Ev)2.5 E(aluation of Dif)-.25 E
(ferent Responses to ECN-Mark)-.25 E(ed SYN/A)-.1 E(CK P)-.4 E(ack)-.15
E(ets.)-.1 E(This document speci\214es that the end-node responds to th\
e report of an ECN-mark)102 528 Q(ed SYN/A)-.1 E(CK pack)-.4 E
(et by setting the)-.1 E(initial congestion windo)102 540 Q 2.5(wt)-.25
G 2.5(oo)-2.5 G(ne pack)-2.5 E(et, instead of its possible def)-.1 E
(ault v)-.1 E(alue of tw)-.25 E 2.5(ot)-.1 G 2.5(of)-2.5 G(our pack)-2.5
E 2.5(ets. Ho)-.1 F(we)-.25 E -.15(ve)-.25 G .8 -.4(r, i).15 H 2.5(nS).4
G(ection)-2.5 E 2.5(3w)102 552 S 2.5(ed)-2.5 G
(iscussed another possible response to an ECN-mark)-2.5 E(ed SYN/A)-.1 E
(CK pack)-.4 E(et, of the end-node w)-.1 E(aiting an R)-.1 E(TT before)
-.6 E(sending a data pack)102 564 Q 2.5(et. Future)-.1 F -.1(wo)2.5 G
(rk will include a comparati).1 E .3 -.15(ve e)-.25 H -.25(va)-.1 G
(luation of these tw).25 E 2.5(om)-.1 G(ethods.)-2.5 E 2.5(6. Security)
72 588 R(Considerations)2.5 E(TCP pack)102 612 Q
(ets carrying the ECT codepoint in IP headers can be mark)-.1 E
(ed rather than dropped by ECN-capable routers. This)-.1 E(raises se)102
624 Q -.15(ve)-.25 G(ral security concerns that we discuss belo).15 E
-.65(w.)-.25 G("Bad" middlebox)102 648 Q(es:)-.15 E -.15(Ku)72 696 S
(zmano).15 E 173.445(vic Standards)-.15 F -.35(Tr)2.5 G 190.795(ack [P)
.35 F(age 9])-.15 E 0 Cg EP
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/F0 10/Times-Roman@0 SF 345.94(draft-ietf-tcpm-ecnsyn-00.txt January)72
48 R(2006)2.5 E(There is a small b)102 84 Q
(ut decreasing number of middlebox)-.2 E
(es that drop or reset SYN and SYN/A)-.15 E(CK pack)-.4 E
(ets based on the ECN-)-.1 E
(related \215ags in the TCP header [MAF05,RFC3360].)102 96 Q
(While there is no e)5 E(vidence that an)-.25 E 2.5(ym)-.15 G(iddlebox)
-2.5 E(es drop SYN/A)-.15 E(CK)-.4 E(pack)102 108 Q(ets that contain an\
 ECN-Capable codepoint in the *IP header*, such beha)-.1 E
(vior cannot be e)-.2 E 2.5(xcluded. Thus,)-.15 F(as speci\214ed)2.5 E
(in Section 2, if a SYN/A)102 120 Q(CK pack)-.4 E(et with the ECT codep\
oint is dropped, the TCP node SHOULD resend the SYN/A)-.1 E(CK)-.4 E
(pack)102 132 Q(et without the ECN-Capable codepoint.)-.1 E
(Congestion collapse:)102 156 Q(Because TCP SYN/A)102 168 Q(CK pack)-.4
E(ets carrying an ECT codepoint could be ECN-mark)-.1 E
(ed instead of dropped at an ECN-)-.1 E(capable router)102 180 Q 2.5(,t)
-.4 G(he concern is whether this can either in)-2.5 E -.2(vo)-.4 G .2
-.1(ke c).2 H(ongestion, or w).1 E
(orsen performance in highly congested)-.1 E 2.5(scenarios. This)102 192
R(is not a problem because after learning that the SYN/A)2.5 E(CK pack)
-.4 E(et w)-.1 E(as ECN-mark)-.1 E(ed, the sender of that)-.1 E(pack)102
204 Q(et will only send one data pack)-.1 E
(et; in the case that this data pack)-.1 E(et is ECN-mark)-.1 E
(ed, the sender will w)-.1 E(ait for a)-.1 E(retransmission timeout.)102
216 Q(In addition, routers are free to drop rather than mark arri)5 E
(ving pack)-.25 E(ets in times of high congestion,)-.1 E(re)102 228 Q
-.05(ga)-.15 G(rdless of whether the pack).05 E(ets are ECN-capable.)-.1
E 2.5(7. Conclusions)72 252 R
(This draft speci\214es a modi\214cation to RFC 3168 to allo)102 276 Q
2.5(wT)-.25 G(CP nodes to send SYN/A)-2.5 E(CK pack)-.4 E
(ets as being ECN-Capable.)-.1 E(Making the SYN/A)102 288 Q(CK pack)-.4
E(et ECN-Capable a)-.1 E -.2(vo)-.2 G
(ids the high cost to a TCP transfer when a SYN/A).2 E(CK pack)-.4 E
(et is dropped)-.1 E(by a congested router)102 300 Q 2.5(,b)-.4 G 2.5
(ya)-2.5 G -.2(vo)-2.7 G(iding the resulting retransmit timeout.).2 E
(This impro)5 E -.15(ve)-.15 G 2.5(st).15 G
(he throughput of short connections.)-2.5 E(The sender of the SYN/A)102
312 Q(CK pack)-.4 E
(et responds to an ECN mark by reducing its initial congestion windo)-.1
E 2.5(wf)-.25 G(rom tw)-2.5 E(o, three,)-.1 E(or four se)102 324 Q
(gments to one se)-.15 E
(gment, reducing the subsequent load from that connection on the netw)
-.15 E 2.5(ork. The)-.1 F(addition of)2.5 E(ECN-capability to SYN/A)102
336 Q(CK pack)-.4 E(ets is particularly bene\214cial in the serv)-.1 E
(er)-.15 E(-to-client direction, where congestion is more)-.2 E(lik)102
348 Q(ely to occur)-.1 E 5(.I)-.55 G 2.5(nt)-5 G
(his case, the initial information pro)-2.5 E
(vided by the ECN marking in the SYN/A)-.15 E(CK pack)-.4 E
(et enables the)-.1 E(serv)102 360 Q
(er to more appropriately adjust the initial load it places on the netw)
-.15 E(ork.)-.1 E(Future w)102 384 Q(ork will address the more general \
question of adding ECN-Capability to rele)-.1 E -.25(va)-.25 G
(nt handshak).25 E 2.5(ep)-.1 G(ack)-2.5 E(ets in other)-.1 E(protocols\
 that use retransmission-based reliability in their setup phase \(e.g.,\
 SCTP)102 396 Q 2.5(,D)-1.11 G(CCP)-2.5 E 2.5(,H)-1.11 G(IP)-2.5 E 2.5
(,a)-1.11 G(nd the lik)-2.5 E(e\).)-.1 E 2.5(8. Ackno)72 420 R
(wledgements)-.25 E 1.6 -.8(We t)102 444 T(hank Mark Allman, W).8 E
(esle)-.8 E 2.5(yE)-.15 G(ddy)-2.5 E 2.5(,J)-.65 G(anardhan Iyeng)-2.5 E
(ar)-.05 E 2.5(,a)-.4 G(nd P)-2.5 E
(asi Sarolahti for feedback on earlier v)-.15 E(ersions of this draft.)
-.15 E 2.5(9. Normati)72 468 R .3 -.15(ve R)-.25 H(eferences).15 E
([RFC3168] K.K. Ramakrishnan, S. Flo)102 492 Q(yd, and D. Black, The Ad\
dition of Explicit Congestion Noti\214cation \(ECN\) to IP)-.1 E(,)-1.11
E(RFC 3168, Proposed Standard, September 2001.)102 504 Q
([RFC3390] M. Allman, S. Flo)102 528 Q(yd, and C. P)-.1 E
(artridge, Increasing TCP')-.15 E 2.5(sI)-.55 G(nitial W)-2.5 E(indo)-.4
E 1.3 -.65(w, R)-.25 H(FC 3390, October 2002.).65 E 2.5(10. Informati)72
552 R .3 -.15(ve R)-.25 H(eferences).15 E([ECN+] A. K)102 576 Q(uzmano)
-.15 E(vic, The Po)-.15 E
(wer of Explicit Congestion Noti\214cation, SIGCOMM 2005.)-.25 E
([MAF05] A. Medina, M. Allman, and S. Flo)102 600 Q 2.5(yd. Measuring)
-.1 F(the Ev)2.5 E(olution of T)-.2 E
(ransport Protocols in the Internet, A)-.35 E(CM)-.4 E(CCR, April 2005.)
102 612 Q([PI] C. Hollot, V)102 636 Q 2.5(.M)-1.29 G(isra, W)-2.5 E 2.5
(.G)-.92 G(ong, and D. T)-2.5 E -.25(ow)-.8 G(sle).25 E 1.3 -.65(y, O)
-.15 H 2.5(nD).65 G(esigning Impro)-2.5 E -.15(ve)-.15 G 2.5(dC).15 G
(ontrollers for A)-2.5 E(QM Routers Supporting)-.55 E(TCP Flo)102 648 Q
(ws, INFOCOM, June 2001.)-.25 E -.15(Ku)72 696 S(zmano).15 E 173.445
(vic Standards)-.15 F -.35(Tr)2.5 G 185.795(ack [P).35 F(age 10])-.15 E
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/F0 10/Times-Roman@0 SF 345.94(draft-ietf-tcpm-ecnsyn-00.txt January)72
48 R(2006)2.5 E([RED] S. Flo)102 84 Q(yd and V)-.1 E 2.5(.J)-1.29 G
(acobson, Random Early Detection Gate)-2.5 E -.1(wa)-.25 G
(ys for Congestion A).1 E -.2(vo)-.74 G(idance, IEEE/A).2 E(CM T)-.4 E
(ransactions)-.35 E(on Netw)102 96 Q(orking, V)-.1 E(.1, N.4, 1993.)
-1.29 E([REM] S. Athuraliya, V)102 120 Q 2.5(.L)-1.29 G(i, S. Lo)-2.5 E
1.3 -.65(w, a)-.25 H(nd Q Y).65 E(in, REM: Acti)-.55 E .3 -.15(ve Q)-.25
H(ueue Management, IEEE Netw).15 E(ork, V)-.1 E(.15, N. 3, May 2001.)
-1.29 E([RFC2309] B. Braden et al., Recommendations on Queue Management\
 and Congestion A)102 144 Q -.2(vo)-.74 G(idance in the Internet, RFC).2
E(2309, April 1998.)102 156 Q([RFC2581] M. Allman, V)102 180 Q 2.5(.P)
-1.29 G(axson, and W)-2.65 E 2.5(.S)-.92 G(te)-2.5 E -.15(ve)-.25 G
(ns, TCP Congestion Control, RFC 2581, April 1999.).15 E([RFC2988] V)102
204 Q 2.5(.P)-1.29 G(axson and M. Allman, Computing TCP')-2.65 E 2.5(sR)
-.55 G(etransmission T)-2.5 E(imer)-.35 E 2.5(,R)-.4 G(FC 2988, No)-2.5
E -.15(ve)-.15 G(mber 2000.).15 E
([RFC3042] M. Allman, H. Balakrishnan, and S. Flo)102 228 Q
(yd, Enhancing TCP')-.1 E 2.5(sL)-.55 G(oss Reco)-2.5 E -.15(ve)-.15 G
(ry Using Limited T).15 E(ransmit, RFC)-.35 E
(3042, Proposed Standard, January 2001.)102 240 Q([RFC3360] S. Flo)102
264 Q(yd, Inappropriate TCP Resets Considered Harmful, RFC 3360, August\
 2002.)-.1 E([SCJO01] F)102 288 Q 2.5(.S)-.8 G(mith, F)-2.5 E 2.5(.C)-.8
G(ampos, K. Jef)-2.5 E -.1(fa)-.25 G 1.3 -.65(y, D).1 H 2.5(.O).65 G
(tt, What {TCP/IP} Protocol Headers Can T)-2.5 E(ell us about the W)-.7
E(eb,)-.8 E(SIGMETRICS, June 2001.)102 300 Q 5([SYN-COOK] Dan)102 324 R
(J. Bernstein, SYN cookies, 1997, see also <http://cr)2.5 E
(.yp.to/syncookies.html>)-.55 E([T)102 348 Q(ools] S. Flo)-.8 E
(yd and E. K)-.1 E(ohler)-.35 E 2.5(,T)-.4 G(ools for the Ev)-3.3 E
(aluation of Simulation and T)-.25 E
(estbed Scenarios, Internet-draft draft-irtf-)-.7 E(tmr)102 360 Q
(g-tools-00, w)-.18 E(ork in progress, September 2005.)-.1 E 2.5
(11. IAN)72 384 R 2.5(AC)-.35 G(onsiderations)-2.5 E(There are no IAN)
102 408 Q 2.5(Ac)-.35 G(onsiderations re)-2.5 E -.05(ga)-.15 G
(rding this document.).05 E -.55(AU)102 432 S(THORS' ADDRESSES).55 E
(Aleksandar K)132 468 Q(uzmano)-.15 E(vic)-.15 E
(Phone: +1 \(847\) 467-5519)132 480 Q(Northwestern Uni)132 492 Q -.15
(ve)-.25 G(rsity).15 E(Email: akuzma@northwestern.edu)132 504 Q
(URL: http://cs.northwestern.edu/~a)132 516 Q(Sally Flo)132 540 Q(yd)-.1
E(Phone: +1 \(510\) 666-2989)132 552 Q
(ICIR \(ICSI Center for Internet Research\))132 564 Q(Email: \215o)132
576 Q(yd@icir)-.1 E(.or)-.55 E(g)-.18 E(URL: http://www)132 588 Q(.icir)
-.65 E(.or)-.55 E(g/\215o)-.18 E(yd/)-.1 E(K. K. Ramakrishnan)132 612 Q
(Phone: +1 \(973\) 360-8764)132 624 Q -1.11(AT)132 636 S
(&T Labs Research)1.11 E(Email: kkrama@research.att.com)132 648 Q -.15
(Ku)72 696 S(zmano).15 E 173.445(vic Standards)-.15 F -.35(Tr)2.5 G
185.795(ack [P).35 F(age 11])-.15 E 0 Cg EP
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/F0 10/Times-Roman@0 SF 345.94(draft-ietf-tcpm-ecnsyn-00.txt January)72
48 R(2006)2.5 E(URL: http://www)132 84 Q(.research.att.com/info/kkrama)
-.65 E(Full Cop)72 108 Q(yright Statement)-.1 E(Cop)102 132 Q
(yright \(C\) The Internet Society \(2006\).)-.1 E
(This document is subject)5 E
(to the rights, licenses and restrictions contained in BCP 78, and)102
144 Q -.15(ex)102 156 S
(cept as set forth therein, the authors retain all their rights.).15 E
(This document and the information contained herein are pro)102 180 Q
(vided on)-.15 E(an "AS IS" basis and THE CONTRIB)102 192 Q(UT)-.1 E
(OR, THE ORGANIZA)-.18 E(TION HE/SHE)-1.11 E
(REPRESENTS OR IS SPONSORED BY \(IF ANY\), THE INTERNET SOCIETY AND THE)
102 204 Q(INTERNET ENGINEERING T)102 216 Q(ASK FORCE DISCLAIM ALL W)-.93
E(ARRANTIES, EXPRESS OR)-1.2 E(IMPLIED, INCLUDING B)102 228 Q(UT NO)-.1
E 2.5(TL)-.4 G(IMITED T)-2.5 E 2.5(OA)-.18 G(NY W)-2.5 E(ARRANTY THA)
-1.2 E 2.5(TT)-1.11 G(HE USE OF)-2.5 E(THE INFORMA)102 240 Q
(TION HEREIN WILL NO)-1.11 E 2.5(TI)-.4 G
(NFRINGE ANY RIGHTS OR ANY IMPLIED)-2.5 E -1.2(WA)102 252 S
(RRANTIES OF MERCHANT)1.2 E(ABILITY OR FITNESS FOR A P)-.93 E(AR)-.92 E
(TICULAR PURPOSE.)-.6 E(Intellectual Property)72 276 Q(The IETF tak)102
300 Q(es no position re)-.1 E -.05(ga)-.15 G(rding the v).05 E
(alidity or scope of an)-.25 E(y)-.15 E
(Intellectual Property Rights or other rights that might be claimed)102
312 Q
(to pertain to the implementation or use of the technology described)102
324 Q(in this document or the e)102 336 Q(xtent to which an)-.15 E 2.5
(yl)-.15 G(icense under such)-2.5 E(rights might or might not be a)102
348 Q -.25(va)-.2 G(ilable; nor does it represent that).25 E
(it has made an)102 360 Q 2.5(yi)-.15 G(ndependent ef)-2.5 E
(fort to identify an)-.25 E 2.5(ys)-.15 G(uch rights.)-2.5 E
(Information on the procedures with respect to rights in RFC)102 372 Q
(documents can be found in BCP 78 and BCP 79.)102 384 Q
(Copies of IPR disclosures made to the IETF Secretariat and an)102 408 Q
(y)-.15 E(assurances of licenses to be made a)102 420 Q -.25(va)-.2 G
(ilable, or the result of an).25 E
(attempt made to obtain a general license or permission for the use)102
432 Q(of such proprietary rights by implementers or users of this)102
444 Q
(speci\214cation can be obtained from the IETF on-line IPR repository)
102 456 Q(at http://www)102 468 Q(.ietf.or)-.65 E(g/ipr)-.18 E(.)-.55 E
(The IETF in)102 480 Q(vites an)-.4 E 2.5(yi)-.15 G
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492 Q(yrights, patents or patent applications, or other proprietary)-.1
E(rights that may co)102 504 Q -.15(ve)-.15 G 2.5(rt).15 G
(echnology that may be required to implement)-2.5 E(this standard.)102
516 Q(Please address the information to the IETF at ietf-)5 E
(ipr@ietf.or)102 528 Q(g.)-.18 E -.15(Ku)72 696 S(zmano).15 E 173.445
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