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/F0 10/Courier-Bold@0 SF(Internet Engineering Task Force)72 85 Q
(S. Floyd)197.999 E 317.999(INTERNET-DRAFT ICIR)72 98 R 155.999
(draft-floyd-ecn-alternates-00.ps 21)72 111 R(April 2005)6 E
(Expires: October 2005)72 124 Q/F1 14/Times-Bold@0 SF(Specifying Alter)
112.902 149 Q(nate Semantics f)-.21 E(or the Explicit Congestion)-.35 E
(Noti\214cation \(ECN\) Field)214.892 162 Q/F2 11/Times-Bold@0 SF
(Status of this Memo)72 194 Q/F3 11/Times-Roman@0 SF
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(of which we are a)100.8 233 Q -.11(wa)-.165 G(re ha).11 E .33 -.165
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-.165 G 2.75(fw)-2.75 G(hich we)-2.75 E(become a)100.8 246 Q -.11(wa)
-.165 G(re will be disclosed, in accordance with RFC 3668 \(BCP 79\).)
.11 E(By submitting this Internet-Draft, we accept the pro)100.8 272 Q
(visions of Section 3 of RFC 3667)-.165 E(\(BCP 78\).)100.8 285 Q
(Internet-Drafts are w)100.8 311 Q
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(Internet-Drafts are draft documents v)100.8 363 Q
(alid for a maximum of six months and may be)-.275 E
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2.75(yt)-.165 G(ime. It is inappropriate to use)-2.75 E(Internet- Draft\
s as reference material or to cite them other than as "w)100.8 389 Q
(ork in progress.")-.11 E
(The list of current Internet-Drafts can be accessed at http://www)100.8
415 Q(.ietf.or)-.715 E(g/ietf/1id-)-.198 E(abstracts.txt)100.8 428 Q
(The list of Internet-Draft Shado)100.8 454 Q 2.75(wD)-.275 G
(irectories can be accessed at)-2.75 E(http://www)100.8 467 Q(.ietf.or)
-.715 E(g/shado)-.198 E -.715(w.)-.275 G(html.).715 E F2(Abstract)72 493
Q F3(There ha)100.8 519 Q .33 -.165(ve b)-.22 H(een a number of proposa\
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(header [ECN].)100.8 532 Q(This document discusses some of the issues i\
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(for the ECN \214eld, and speci\214es requirements for a safe co-e)100.8
545 Q(xistence in an Internet that)-.165 E(could include routers that d\
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E(document e)100.8 571 Q -.22(vo)-.275 G(lv).22 E(ed as a result of dis\
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253.526 623 S(ble of Contents)1.196 E/F5 10/Times-Roman@0 SF
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(9. Conclusions)100.8 180 Q F0 11(.......................)11 G F1(9)11.5
E(10. Normati)100.8 192 Q .3 -.15(ve R)-.25 H(eferences).15 E F0 11
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(Full Cop)100.8 240 Q(yright Statement)-.1 E F0 11(....................)
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/Times-Bold@0 SF(4.)72 254 Q/F2 14/Times-Bold@0 SF(Issues of Incr)5.5 E
(emental Deployment)-.252 E F0
(This section discusses questions \(2\) and \(3\) posed in Section 2:)
100.8 280 Q(\(2\) Ho)100.8 306 Q 2.75(wd)-.275 G
(oes the possible presence of old routers af)-2.75 E
(fect the performance of the alternate-)-.275 E(ECN connections?)100.8
319 Q(\(3\) Ho)100.8 345 Q 2.75(wd)-.275 G
(oes the possible presence of old routers af)-2.75 E(fect the co-e)-.275
E(xistence of the alternate-)-.165 E(ECN traf)100.8 358 Q
(\214c with competing traf)-.275 E(\214c on the path?)-.275 E(When alte\
rnate semantics are de\214ned for the ECN \214eld, it is necessary to e\
nsure that there)100.8 384 Q
(are no problems caused by old routers along the path that don')100.8
397 Q 2.75(tu)-.198 G(nderstand the alternate)-2.75 E(ECN semantics.)
100.8 410 Q(One possible problem is that of poor performance for the al\
ternate-ECN traf)100.8 436 Q 2.75(\214c. Is)-.275 F(it)2.75 E
(essential to the performance of the alternate-ECN traf)100.8 449 Q
(\214c that all routers along the path)-.275 E
(understand the alternate-ECN semantics?)100.8 462 Q
(If not, what are the possible consequences, for)5.5 E
(the alternate-ECN traf)100.8 475 Q
(\214c itself, when some old routers along the path don')-.275 E 2.75
(tu)-.198 G(nderstand the)-2.75 E(alternate-ECN semantics?)100.8 488 Q
(These issues ha)5.5 E .33 -.165(ve t)-.22 H 2.75(ob).165 G 2.75(ea)
-2.75 G(nswered in the conte)-2.75 E(xt of each speci\214c)-.165 E
(proposal for alternate ECN semantics.)100.8 501 Q 2.75(As)100.8 527 S
(econd speci\214c problem is that of possible unf)-2.75 E
(air competition with other traf)-.11 E(\214c along the)-.275 E 2.75
(path. If)100.8 540 R(there is an old router along the path that doesn')
2.75 E 2.75(tu)-.198 G(se ECN, that old router could)-2.75 E(drop pack)
100.8 553 Q(ets from the alternate-ECN traf)-.11 E(\214c, and e)-.275 E
(xpect the alternate-ECN traf)-.165 E(\214c to reduce)-.275 E
(its sending rate as a result.)100.8 566 Q(Does the alternate-ECN traf)
5.5 E(\214c respond to pack)-.275 E(et drops as an)-.11 E
(indication of congestion?)100.8 579 Q(Flo)72 769 Q 317.391(yd Section)
-.11 F 2.75(4. [P)2.75 F(age 4])-.165 E 0 Cg EP
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(October 2005)2.75 E(April 2005)118.232 E/F1 11/Courier@0 SF(|--------|)
305.4 85 Q(Alternate-ECN traffic ---->)114 98 Q 52.8(||)13.2 G
(---> CE-marked packet)-46.2 E 13.2(|O)305.4 111 S 13.2(ld |)-13.2 F
(Non-ECN traffic ---------->)114 124 Q 6.6(|R)13.2 G
(outer | ---> dropped packet)-6.6 E 52.8(||)305.4 137 S
(RFC-3168 ECN traffic ----->)114 150 Q 52.8(||)13.2 G
(---> CE-marked packet)-46.2 E(|--------|)305.4 163 Q
(Figure 1: Alternate-ECN traffic with an old router using RFC-3168 ECN.)
114 189 Q F0(Similarly)100.8 221 Q 2.75(,w)-.715 G(hat if there is an o\
ld router along the path that understands only the def)-2.75 E(ault)-.11
E(ECN semantics from RFC-3168, as in Figure 1 abo)100.8 234 Q -.165(ve)
-.165 G 5.5(?I).165 G 2.75(nt)-5.5 G(imes of congestion, the old)-2.75 E
(def)100.8 247 Q(ault-ECN router could see an alternate-ECN pack)-.11 E
(et with one of the ECN-Capable)-.11 E -.385(Tr)100.8 260 S
(ansport \(ECT\) codepoints set in the ECN \214eld in the IP header).385
E 2.75(,a)-.44 G 2.75(sd)-2.75 G(e\214ned in RFC 3168,)-2.75 E(and set \
the Congestion Experienced \(CE\) codepoint in the ECN \214eld as an al\
ternati)100.8 273 Q .33 -.165(ve t)-.275 H(o).165 E(dropping the pack)
100.8 286 Q 2.75(et. The)-.11 F(router in this case w)2.75 E(ould e)-.11
E(xpect the alternate-ECN connection to)-.165 E
(respond, in terms of congestion control, as it w)100.8 299 Q
(ould if the pack)-.11 E(et has been dropped.)-.11 E(If the)5.5 E
(alternate-ECN traf)100.8 312 Q(\214c f)-.275 E
(ails to respond appropriately to the CE codepoint being set by an old)
-.11 E(router)100.8 325 Q 2.75(,t)-.44 G(his could increase the aggre)
-2.75 E -.055(ga)-.165 G(te traf).055 E(\214c arri)-.275 E
(ving at the old router)-.275 E 2.75(,r)-.44 G(esulting in an)-2.75 E
(increase in the pack)100.8 338 Q(et-marking and pack)-.11 E
(et-dropping rates at that router)-.11 E 2.75(,f)-.44 G
(urther resulting in)-2.75 E(the alternate-ECN traf)100.8 351 Q
(\214c cro)-.275 E(wding out the other traf)-.275 E
(\214c competing for bandwidth on that)-.275 E(link.)100.8 364 Q
(Basically)100.8 390 Q 2.75(,t)-.715 G
(here are three possibilities for a)-2.75 E -.22(vo)-.22 G
(iding scenarios where the presence of old).22 E
(routers along the path results in the alternate-ECN traf)100.8 403 Q
(\214c competing unf)-.275 E 2.75(airly with)-.11 F(other)2.75 E(traf)
100.8 416 Q(\214c along the path:)-.275 E(Option 1:)100.8 442 Q
(Alternate-ECN traf)5.5 E
(\214c is clearly understood as unsafe for deplo)-.275 E(yment in the)
-.11 E(global Internet; or)100.8 455 Q(Option 2:)100.8 481 Q
(All alternate-ECN traf)5.5 E(\214c deplo)-.275 E
(ys some mechanism for v)-.11 E(erifying that all routers)-.165 E(on th\
e path understand and agree to use the alternate ECN semantics for this\
 traf)100.8 494 Q(\214c; or)-.275 E(Option 3:)100.8 520 Q
(The alternate-ECN semantics are de\214ned in such a w)5.5 E
(ay as to ensure the f)-.11 E(air and)-.11 E(peaceful co-e)100.8 533 Q
(xistence of the alternate-ECN traf)-.165 E(\214c with best-ef)-.275 E
(fort and other traf)-.275 E(\214c, e)-.275 E -.165(ve)-.275 G 2.75(ni)
.165 G(n)-2.75 E(en)100.8 546 Q(vironments that include old routers tha\
t do not understand the alternate-ECN semantics.)-.44 E
(Each of these alternati)100.8 572 Q -.165(ve)-.275 G 2.75(si).165 G
2.75(se)-2.75 G(xplored in more detail belo)-2.915 E -.715(w.)-.275 G/F2
11/Times-Bold@0 SF(4.1.)72 611 Q/F3 13/Times-Bold@0 SF(Option 1:)5.5 E
(Unsafe f)6.5 E(or Deployment in the Inter)-.325 E(net)-.195 E F0
(The \214rst option speci\214ed abo)100.8 637 Q .33 -.165(ve i)-.165 H
2.75(sf).165 G(or the alternate-ECN traf)-2.75 E
(\214c to be clearly understood as)-.275 E
(only suitable for enclosed en)100.8 650 Q
(vironments, and as unsafe for deplo)-.44 E(yment in the global)-.11 E
2.75(Internet. This)100.8 663 R -.11(wo)2.75 G(uld mean that it w).11 E
(ould be unsafe for pack)-.11 E(ets using the alternate ECN)-.11 E
(semantics to be unleashed in the global Internet, in order to a)100.8
676 Q -.22(vo)-.22 G(id the chance of the).22 E(alternate-ECN traf)100.8
689 Q(\214c tra)-.275 E -.165(ve)-.22 G(rsing an old router that don')
.165 E 2.75(tu)-.198 G(nderstand the alternate semantics.)-2.75 E
(This document doesn')100.8 702 Q 2.75(tc)-.198 G
(omment on whether a mechanism w)-2.75 E
(ould be required to ensure that)-.11 E(the alternate-ECN semantics w)
100.8 715 Q(ould not be let loose on the global Internet.)-.11 E
(This document)5.5 E(Flo)72 769 Q 309.141(yd Section)-.11 F 2.75
(4.1. [P)2.75 F(age 5])-.165 E 0 Cg EP
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(October 2005)2.75 E(April 2005)118.232 E(also doesn')100.8 85 Q 2.75
(tc)-.198 G(omment on the chances that this scenario w)-2.75 E
(ould be considered acceptable for)-.11 E
(standardization by the IETF community)100.8 98 Q(.)-.715 E/F1 11
/Times-Bold@0 SF(4.2.)72 137 Q/F2 13/Times-Bold@0 SF(Option 2:)5.5 E
-1.3(Ve)6.5 G(ri\214cation that Routers Understand the Alter)1.3 E
(nate Semantics)-.195 E F0(The second option speci\214ed abo)100.8 163 Q
.33 -.165(ve i)-.165 H 2.75(sf).165 G(or the alternate-ECN traf)-2.75 E
(\214c to include a mechanism)-.275 E(for ensuring that all routers alo\
ng the path understand and agree to the use of the alternate)100.8 176 Q
(ECN semantics for this traf)100.8 189 Q 2.75(\214c. As)-.275 F(an e)
2.75 E(xample, such a mechanism could consist of a \214eld)-.165 E
(in an IP option that all routers along the path decrement if the)100.8
202 Q 2.75(ya)-.165 G(gree to use the alternate)-2.75 E
(ECN semantics with this traf)100.8 215 Q 2.75(\214c. \(A)-.275 F
(similar mechanism is proposed for Quick-Start, for)2.75 E -.165(ve)
100.8 228 S(rifying that all of the routers along the path understand t\
he Quick-Start IP Option).165 E 2.75([QuickStart].\) Using)100.8 241 R
(such a mechanism, a sender could ha)2.75 E .33 -.165(ve r)-.22 H
(easonable assurance that the).165 E(pack)100.8 254 Q(ets that are sent\
 specifying the use of alternate ECN semantics only tra)-.11 E -.165(ve)
-.22 G(rse routers).165 E(that in f)100.8 267 Q(act understand and agre\
e to use these alternate semantics for these pack)-.11 E(ets.)-.11 E F1
(4.3.)72 306 Q F2(Option 3:)5.5 E
(Friendly Co-existence with Competing T)6.5 E(raf\214c)-.962 E F0
(The third option speci\214ed abo)100.8 332 Q .33 -.165(ve i)-.165 H
2.75(sf).165 G(or the alternate ECN semantics to be de\214ned so that)
-2.75 E(traf)100.8 345 Q(\214c using the alternate semantics w)-.275 E
(ould co-e)-.11 E(xist safely in the Internet on a path with one)-.165 E
(or more old routers that use only the def)100.8 358 Q
(ault ECN semantics.)-.11 E(In this scenario, a connection)5.5 E
(sending alternate-ECN traf)100.8 371 Q(\214c w)-.275 E(ould ha)-.11 E
.33 -.165(ve t)-.22 H 2.75(or).165 G(espond appropriately to a CE pack)
-2.75 E(et \(a pack)-.11 E(et)-.11 E
(with the ECN codepoint "11"\) recei)100.8 384 Q -.165(ve)-.275 G 2.75
(da).165 G 2.75(tt)-2.75 G(he recei)-2.75 E -.165(ve)-.275 G .88 -.44
(r, u).165 H(sing a conformant congestion).44 E(control response.)100.8
397 Q(Hopefully)5.5 E 2.75(,t)-.715 G
(he connection sending alternate-ECN traf)-2.75 E(\214c w)-.275 E
(ould also)-.11 E(respond appropriately to a dropped pack)100.8 410 Q
(et, that could be a congestion indication from a)-.11 E
(router that doesn')100.8 423 Q 2.75(tu)-.198 G(se ECN at all.)-2.75 E
(RFC 3168 de\214nes the def)100.8 449 Q(ault ECN semantics as follo)-.11
E(ws:)-.275 E
("Upon the receipt by an ECN-Capable transport of a single CE pack)100.8
475 Q(et, the congestion)-.11 E(control algorithms follo)100.8 488 Q
(wed at the end-systems MUST be essentially the same as the)-.275 E
(congestion control response to a *single* dropped pack)100.8 501 Q 2.75
(et. F)-.11 F(or e)-.165 E(xample, for ECN-Capable)-.165 E
(TCP the source TCP is required to halv)100.8 514 Q 2.75(ei)-.165 G
(ts congestion windo)-2.75 E 2.75(wf)-.275 G(or an)-2.75 E 2.75(yw)-.165
G(indo)-2.75 E 2.75(wo)-.275 G 2.75(fd)-2.75 G(ata)-2.75 E
(containing either a pack)100.8 527 Q(et drop or an ECN indication.")
-.11 E(The only conformant congestion control mechanisms currently stan\
dardized in the IETF)100.8 553 Q
(are TCP [RFC2581] and protocols using TCP-lik)100.8 566 Q 2.75(ec)-.11
G(ongestion control \(e.g., SCTP)-2.75 E([RFC2960], DCCP with CCID-2 [D\
CCP]\), and TCP-Friendly Rate Control \(TFRC\) and)100.8 579 Q
(protocols with TFRC-lik)100.8 592 Q 2.75(ec)-.11 G
(ongestion control \(e.g., DCCP using CCID-3 [DCCP]\).)-2.75 E(TCP)5.5 E
(uses Additi)100.8 605 Q -.165(ve)-.275 G(-Increase Multiplicati).165 E
-.165(ve)-.275 G(-Decrease congestion control, and responds to the).165
E(loss or ECN-marking of a single pack)100.8 618 Q
(et by halving its congestion windo)-.11 E 4.18 -.715(w. I)-.275 H 2.75
(nc).715 G(ontrast, the)-2.75 E(equation-based congestion control mecha\
nism in TFRC estimates the loss e)100.8 631 Q -.165(ve)-.275 G
(nt rate o).165 E -.165(ve)-.165 G(r).165 E
(some period of time, and uses a sending rate that w)100.8 644 Q
(ould be comparable, in pack)-.11 E(ets per)-.11 E
(round-trip-time, to that of a TCP connection e)100.8 657 Q
(xperiencing the same loss e)-.165 E -.165(ve)-.275 G(nt rate.).165 E
(So what are the requirements in order for alternate-ECN traf)100.8 683
Q(\214c to compete appropriately)-.275 E(with other traf)100.8 696 Q
(\214c on a path through an old router that doesn')-.275 E 2.75(tu)-.198
G(nderstand the alternate ECN)-2.75 E
(semantics \(and therefore might be using the def)100.8 709 Q
(ault ECN semantics\)?)-.11 E(Flo)72 769 Q 309.141(yd Section)-.11 F
2.75(4.3. [P)2.75 F(age 6])-.165 E 0 Cg EP
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(October 2005)2.75 E(April 2005)118.232 E
(The \214rst requirement is that if a pack)100.8 85 Q(et is mark)-.11 E
(ed with the ECN codepoint "11" in the)-.11 E(netw)100.8 98 Q
(ork, this marking is not changed on the pack)-.11 E(et')-.11 E 2.75(sw)
-.605 G(ay to the recei)-2.86 E -.165(ve)-.275 G 2.75(r\().165 G
(unless the pack)-2.75 E(et)-.11 E
(is dropped before it reaches the recei)100.8 111 Q -.165(ve)-.275 G
2.75(r\). This).165 F(requirement is necessary to ensure that)2.75 E
(congestion indications from a def)100.8 124 Q(ault-ECN router mak)-.11
E 2.75(ei)-.11 G 2.75(tt)-2.75 G 2.75(ot)-2.75 G(he transport recei)
-2.75 E -.165(ve)-.275 G -.605(r.).165 G(The second requirement is that\
 the end-nodes respond in a TCP-friendly manner to pack)100.8 150 Q(ets)
-.11 E(recei)100.8 163 Q -.165(ve)-.275 G 2.75(dt).165 G(hat are mark)
-2.75 E(ed with the ECN codepoint "11" \(because these pack)-.11 E
(ets might ha)-.11 E -.165(ve)-.22 G
(come from a congested router that understands only the def)100.8 176 Q
(ault ECN semantics\).)-.11 E(This)5.5 E -.11(wo)100.8 189 S
(uld ensure that the traf).11 E
(\214c using the alternate semantics does not `b)-.275 E
(ully' competing traf)-.22 E<8c63>-.275 E
(that it might encounter along the path, and does not dri)100.8 202 Q
.33 -.165(ve u)-.275 H 2.75(pc).165 G(ongestion on the shared link)-2.75
E(inappropriately)100.8 215 Q(.)-.715 E(As discussed earlier)100.8 241 Q
2.75(,t)-.44 G
(he current conformant congestion control responses to a dropped or)
-2.75 E(def)100.8 254 Q(ault-ECN-mark)-.11 E(ed pack)-.11 E
(et consist of TCP and TCP-lik)-.11 E 2.75(ec)-.11 G
(ongestion control, and of TFRC)-2.75 E(\(TCP-Friendly Rate Control\).)
100.8 267 Q(Another possible response considered in RFC 3714, b)5.5 E
(ut not)-.22 E(standardized in a standards-track document, is that of s\
imply terminating an alternate-ECN)100.8 280 Q(connection for a period \
of time if the long-term sending rate is higher that w)100.8 293 Q
(ould be that of)-.11 E 2.75(aT)100.8 306 S(CP connection e)-2.75 E
(xperiencing the same pack)-.165 E
(et dropping or marking rates [RFC3714].)-.11 E 1.76 -.88(We n)100.8 319
T(ote that the use of such a congestion control response to CE-mark).88
E(ed pack)-.11 E(ets w)-.11 E(ould)-.11 E(require speci\214cation of ti\
me constants for measuring the loss rates and for stopping)100.8 332 Q
(transmission, and w)100.8 345 Q
(ould require a consideration of issues of pack)-.11 E(et size.)-.11 E
/F1 11/Times-Bold@0 SF(5.)72 384 Q/F2 14/Times-Bold@0 SF(Ev)5.5 E
(aluation of the Alter)-.14 E(nate-ECN Semantics)-.21 E F0
(This section discusses question \(4\) posed in Section 2:)100.8 410 Q
(\(4\) Ho)100.8 436 Q 2.75(ww)-.275 G(ell does the alternate-ECN traf)
-2.75 E(\214c perform, and ho)-.275 E 2.75(ww)-.275 G(ell does it co-e)
-2.75 E(xist with)-.165 E(competing traf)100.8 449 Q
(\214c on the path, in a "clean" en)-.275 E(vironment with ne)-.44 E
2.75(wr)-.275 G(outers and with the)-2.75 E
(unambiguous speci\214cation of the use of alternate-ECN semantics?)
100.8 462 Q F1(5.1.)72 501 Q/F3 13/Times-Bold@0 SF -1.3(Ve)5.5 G
(ri\214cation of F)1.3 E(eedback fr)-.325 E(om the Router)-.234 E F0
(One issue in e)100.8 527 Q -.275(va)-.275 G
(luating the alternate-ECN semantics concerns mechanisms to discourage)
.275 E(lying from the transport recei)100.8 540 Q -.165(ve)-.275 G 2.75
(rt).165 G 2.75(ot)-2.75 G(he transport sender)-2.75 E 5.5(.I)-.605 G
2.75(nm)-5.5 G(an)-2.75 E 2.75(yc)-.165 G(ases the sender is a)-2.75 E
(serv)100.8 553 Q
(er that has an interest in using the alternate-ECN semantics correctly)
-.165 E 2.75(,w)-.715 G(hile the recei)-2.75 E -.165(ve)-.275 G(r).165 E
(has more incenti)100.8 566 Q -.165(ve)-.275 G 2.75(sf).165 G
(or lying about the congestion e)-2.75 E(xperienced along the path.)
-.165 E(In the def)100.8 592 Q(ault ECN semantics, tw)-.11 E 2.75(oo)
-.11 G 2.75(ft)-2.75 G(he four ECN codepoints are used for ECN-)-2.75 E
(Capable\(0\) and ECN-Capable\(1\).)100.8 605 Q(The use of tw)5.5 E 2.75
(oc)-.11 G(odepoints for ECN-Capable, instead of)-2.75 E
(one, permits the data sender to v)100.8 618 Q(erify recei)-.165 E -.165
(ve)-.275 G(r').165 E 2.75(sr)-.605 G(eports that pack)-2.75 E
(ets were actually recei)-.11 E -.165(ve)-.275 G(d).165 E(unmark)100.8
631 Q(ed at the recei)-.11 E -.165(ve)-.275 G 3.96 -.605(r. I).165 H
2.75(np).605 G(articular)-2.75 E 2.75(,t)-.44 G
(he sender can specify that the recei)-2.75 E -.165(ve)-.275 G 2.75(rr)
.165 G(eport to the)-2.75 E(sender whether each unmark)100.8 644 Q
(ed pack)-.11 E(et w)-.11 E(as recei)-.11 E -.165(ve)-.275 G 2.75(dE)
.165 G(CN-Capable\(0\) or ECN-Capable\(1\),)-2.75 E
(as discussed in RFC 3540 [RFC 3540].)100.8 657 Q
(If alternate semantics for the ECN codepoint don')100.8 683 Q 2.75(ti)
-.198 G(nclude the use of tw)-2.75 E 2.75(os)-.11 G(eparate)-2.75 E(cod\
epoints to indicate ECN-Capable, then the connections using those seman\
tics ha)100.8 696 Q .33 -.165(ve l)-.22 H(ost).165 E(the ability to v)
100.8 709 Q(erify that the data recei)-.165 E -.165(ve)-.275 G 2.75(ri)
.165 G 2.75(sa)-2.75 G(ccurately reporting the recei)-2.75 E -.165(ve)
-.275 G 2.75(dE).165 G(CN)-2.75 E(codepoint to the data sender)100.8 722
Q 5.5(.I)-.605 G 2.75(nt)-5.5 G
(his case, it might be necessary for the alternate-ECN)-2.75 E(Flo)72
769 Q 309.141(yd Section)-.11 F 2.75(5.1. [P)2.75 F(age 7])-.165 E 0 Cg
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(October 2005)2.75 E(April 2005)118.232 E(frame)100.8 85 Q -.11(wo)-.275
G(rk to include alternate mechanisms for ensuring that the data recei)
.11 E -.165(ve)-.275 G 2.75(ri).165 G 2.75(sr)-2.75 G(eporting)-2.75 E
(feedback appropriately to the sender)100.8 98 Q(.)-.605 E/F1 11
/Times-Bold@0 SF(5.2.)72 137 Q/F2 13/Times-Bold@0 SF
(Co-existence with Competing T)5.5 E(raf\214c)-.962 E F0 2.75(As)100.8
163 S(econd general issue concerns the co-e)-2.75 E
(xistence of alternate-ECN traf)-.165 E(\214c with competing)-.275 E
(traf)100.8 176 Q(\214c along the path, in a clean en)-.275 E
(vironment where all routers understand and are willing)-.44 E
(to use the alternate-ECN semantics for the traf)100.8 189 Q
(\214c that speci\214es its use.)-.275 E(If the traf)100.8 215 Q
(\214c using the alternate-ECN semantics is best-ef)-.275 E(fort traf)
-.275 E(\214c, then it is subject to the)-.275 E
(general requirement of f)100.8 228 Q
(air competition with TCP and other traf)-.11 E(\214c along the path)
-.275 E([RFC2914].)100.8 241 Q(If the traf)100.8 267 Q
(\214c using the alternate-ECN semantics is dif)-.275 E(fserv traf)-.275
E(\214c, then the requirements are)-.275 E(go)100.8 280 Q -.165(ve)-.165
G(rned by the o).165 E -.165(ve)-.165 G
(rall guidelines for that class of dif).165 E(fserv traf)-.275 E 2.75
(\214c. It)-.275 F(is be)2.75 E(yond the scope)-.165 E
(of this document to specify the requirements, if an)100.8 293 Q 1.43
-.715(y, f)-.165 H(or the co-e).715 E(xistence of dif)-.165 E
(fserv traf)-.275 E<8c63>-.275 E(with other traf)100.8 306 Q(\214c on t\
he link; this should be addressed in the speci\214cation of the dif)
-.275 E(fserv)-.275 E(codepoint itself.)100.8 319 Q F1(5.3.)72 358 Q F2
3.25(AG)5.5 G(eneral Ev)-3.25 E(aluation of the Alter)-.13 E
(nate-ECN Semantics)-.195 E F0 2.75(At)100.8 384 S
(hird general issue concerns the e)-2.75 E -.275(va)-.275 G
(luation of the general merits of the proposed).275 E
(alternate-ECN semantics.)100.8 397 Q(Ag)5.5 E(ain, it w)-.055 E
(ould be be)-.11 E(yond the scope of this document to specify)-.165 E
(requirements for the general e)100.8 410 Q -.275(va)-.275 G
(luation of alternate-ECN semantics.).275 E F1(6.)72 449 Q/F3 14
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community for).165 E(alternate semantics for the ECN codepoint [ECN].)
100.8 488 Q(One such proposal, [BCF05], proposes)5.5 E
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(and multimedia streaming in Dif)100.8 514 Q(fServ netw)-.275 E 2.75
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100.8 527 Q(ould pro)-.11 E(vide information about tw)-.165 E 2.75(ol)
-.11 G -2.365 -.275(ev e)-2.75 H(ls of congestion e).275 E
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100.8 540 Q 2.75(we)-.275 G(nd-systems should)-2.75 E
(react to ECN bit marking" [BCF05].)100.8 553 Q
(Some of the other proposals for alternate ECN)5.5 E
(semantics are listed on the ECN W)100.8 566 Q(eb P)-.88 E(age [ECN].)
-.165 E F1(7.)72 605 Q F3(Security Considerations)5.5 E F0
(This document doesn')100.8 631 Q 2.75(tp)-.198 G(ropose an)-2.75 E 2.75
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(echanisms for the Internet protocol, and).275 E(therefore doesn')100.8
644 Q 2.75(ti)-.198 G(ntroduce an)-2.75 E 2.75(yn)-.165 G .55 -.275
(ew s)-2.75 H(ecurity considerations.).275 E F1(8.)72 683 Q F3(Ackno)5.5
E(wledgements)-.14 E F0(This document is based in part on con)100.8 709
Q -.165(ve)-.44 G(rsations with Jozef Babiarz, Kw).165 E
(ok Ho Chan, and)-.11 E -.66(Vi)100.8 722 S(ctor Firoiu on their propos\
al for an alternate use of the ECN \214eld in Dif).66 E(fServ)-.275 E
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(,D)-.44 G -.22(av)-2.75 G(id Black, and to members of the TSVWG).22 E
-.11(wo)100.8 124 S(rking group for feedback on these issues.).11 E/F1
11/Times-Bold@0 SF(9.)72 163 Q/F2 14/Times-Bold@0 SF(Conclusions)5.5 E
F0(This document has discussed some of the issues to be considered in t\
he speci\214cation of)100.8 189 Q
(alternate semantics for the ECN \214eld in the IP header)100.8 202 Q(.)
-.605 E F1(10.)72 241 Q F2(Normati)5.5 E .28 -.14(ve R)-.14 H(efer).14 E
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100.8 306 Q 2.75(.F)-1.419 G
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100.8 319 S(me T).385 E(raf)-.385 E
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-.88 E(age, URL "http://www)-.165 E(.icir)-.715 E(.or)-.605 E(g/k)-.198
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(yd/ecn.html".)-.11 E([QuickStart] Quick-Start W)100.8 397 Q(eb P)-.88 E
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(yd/quickstart.html".)-.11 E([RFC2581] M. Allman, V)100.8 423 Q 2.75(.P)
-1.419 G(axson, and W)-2.915 E 2.75(.S)-1.012 G(te)-2.75 E -.165(ve)
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(Proposed Standard, April 1999.)100.8 436 Q([RFC2914] S. Flo)100.8 462 Q
(yd, Congestion Control Principles, RFC 2914, Best Current Practice,)
-.11 E(September 2000.)100.8 475 Q([RFC2960] R. Ste)100.8 501 Q -.11(wa)
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(ransmission Protocol, RFC 2960, October)-.385 E(2000.)100.8 514 Q
([RFC3168] Ramakrishnan, K.K., Flo)100.8 540 Q
(yd, S., and Black, D., The Addition of Explicit)-.11 E
(Congestion Noti\214cation \(ECN\) to IP)100.8 553 Q 2.75(,R)-1.221 G
(FC 3168, Proposed Standard, September 2001.)-2.75 E
([RFC3540] N. Spring, D. W)100.8 579 Q(etherall, and D. Ely)-.88 E 2.75
(,R)-.715 G(ob)-2.75 E(ust Explicit Congestion Noti\214cation)-.22 E
(\(ECN\) Signaling with Nonces, RFC 3540, Experimental, June 2003.)100.8
592 Q([RFC3714] S. Flo)100.8 618 Q(yd and J. K)-.11 E
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72 85 S(THORS' ADDRESSES).7 E F0(Sally Flo)100.8 124 Q(yd)-.11 E
(Phone: +1 \(510\) 666-2989)100.8 137 Q
(ICIR \(ICSI Center for Internet Research\))100.8 150 Q(Email: \215o)
100.8 163 Q(yd@icir)-.11 E(.or)-.605 E(g)-.198 E(URL: http://www)100.8
176 Q(.icir)-.715 E(.or)-.605 E(g/\215o)-.198 E(yd/)-.11 E F1
(Full Copyright Statement)72 228 Q F0(Cop)100.8 254 Q
(yright \(C\) The Internet Society 2004.)-.11 E
(This document is subject to the rights, licenses)5.5 E
(and restrictions contained in BCP 78, and e)100.8 267 Q
(xcept as set forth therein, the authors retain all)-.165 E
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(This document and the information contained herein are pro)100.8 306 Q
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(OR, THE ORGANIZA)-.198 E(TION HE/SHE REPRESENTS OR IS)-1.221 E
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332 Q(ENGINEERING T)100.8 345 Q(ASK FORCE DISCLAIM ALL W)-1.023 E
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100.8 371 Q(TION HEREIN WILL NO)-1.221 E 2.75(TI)-.44 G
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-2.75 E(Rights or other rights that might be claimed to pertain to the \
implementation or use of the)100.8 475 Q
(technology described in this document or the e)100.8 488 Q
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obtained from the IETF on-line IPR repository at)100.8 592 Q(http://www)
100.8 605 Q(.ietf.or)-.715 E(g/ipr)-.198 E(.)-.605 E(The IETF in)100.8
631 Q(vites an)-.44 E 2.75(yi)-.165 G
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