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/F0 10/Courier-Bold@0 SF(Internet Engineering Task Force)72 85 Q
(S. Floyd)197.998 E 317.998(INTERNET-DRAFT ICIR)72 98 R 149.998
(draft-floyd-ecn-alternates-02.ps 18)72 111 R(August 2005)6 E
(Expires: February 2006)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
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E F2(Copyright Notice)72 436.6 Q F3(Cop)100.8 453.2 Q
(yright \(C\) The Internet Society \(2005\). All Rights Reserv)-.11 E
(ed.)-.165 E F2(Abstract)72 479.2 Q F3(There ha)100.8 505.2 Q .33 -.165
(ve b)-.22 H(een a number of proposals for alternate semantics for the \
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2.75(OR)-.198 G(FC EDIT)-2.75 E(OR: PLEASE DELETE THIS NO)-.198 E
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2.75(*M)100.8 111 S(inor editing, from email from Mark Allman.)-2.75 E
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(3. Signalling the Use of Alternate ECN Semantics)100.8 355 Q F0 11
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E 2.75(wt)-.275 G 2.75(ou)-2.75 G(se the alternate semantics for)-2.75 E
(interpreting and setting the ECN \214eld.)100.8 254 Q
(Old ECN-capable routers that do not understand)5.5 E(this dif)100.8 267
Q(fserv codepoint w)-.275 E(ould use the def)-.11 E
(ault ECN semantics in interpreting and setting the)-.11 E(ECN \214eld.)
100.8 280 Q(In general, the dif)100.8 306 Q
(fserv codepoints are used to signal the per)-.275 E(-hop beha)-.22 E
(vior at router queues.)-.22 E(One possibility w)100.8 319 Q
(ould be to use one dif)-.11 E(fserv codepoint to signal a per)-.275 E
(-hop beha)-.22 E(vior with)-.22 E(the def)100.8 332 Q
(ault ECN semantics, and a separate dif)-.11 E
(fserv codepoint to signal a similar per)-.275 E(-hop)-.22 E(beha)100.8
345 Q(vior with the alternate ECN semantics.)-.22 E
(Another possibility w)5.5 E(ould be to use a dif)-.11 E(fserv)-.275 E
(codepoint to signal the use of best-ef)100.8 358 Q(fort per)-.275 E
(-hop queueing and scheduling beha)-.22 E(vior)-.22 E 2.75(,b)-.44 G(ut)
-2.97 E(with alternate ECN semantics.)100.8 371 Q 2.75(Ad)5.5 G
(etailed discussion of these issues is be)-2.75 E(yond the scope of)
-.165 E(this document.)100.8 384 Q 1.76 -.88(We n)100.8 410 T
(ote that this discussion does not e).88 E
(xclude the possibility of using other methods,)-.165 E(including out-o\
f-band mechanisms, for signalling the use of alternate semantics for th\
e)100.8 423 Q(ECN \214eld.)100.8 436 Q
(The considerations in the rest of this document apply re)5.5 E -.055
(ga)-.165 G(rdless of the method).055 E
(used to signal the use of alternate semantics for the ECN \214eld.)
100.8 449 Q F1(3.1.)72 488 Q/F3 13/Times-Bold@0 SF(Using the Diffser)5.5
E 3.25(vF)-.13 G(ield f)-3.25 E(or Signalling)-.325 E F0 1.76 -.88(We n)
100.8 514 T(ote that the def).88 E
(ault ECN semantics de\214ned in RFC 3168 are the current def)-.11 E
(ault)-.11 E(semantics for the ECN \214eld, re)100.8 527 Q -.055(ga)
-.165 G(rdless of the contents of an).055 E 2.75(yo)-.165 G
(ther \214elds in the IP header)-2.75 E(.)-.605 E(In particular)100.8
540 Q 2.75(,t)-.44 G(he def)-2.75 E
(ault ECN semantics apply for more than best-ef)-.11 E(fort traf)-.275 E
(\214c with a)-.275 E(codepoint of '000000' for the dif)100.8 553 Q
(fserv \214eld - the def)-.275 E(ault ECN semantics currently apply)-.11
E(re)100.8 566 Q -.055(ga)-.165 G(rdless of the contents of the dif).055
E(fserv \214eld.)-.275 E(There are tw)100.8 592 Q 2.75(ow)-.11 G
(ays to use the dif)-2.86 E
(fserv \214eld to signal the use of alternate ECN semantics.)-.275 E
(One w)100.8 605 Q(ay is to use an e)-.11 E(xisting dif)-.165 E
(fserv codepoint, and to modify the current de\214nition of)-.275 E
(that codepoint, through appro)100.8 618 Q -.165(ve)-.165 G 2.75(dI).165
G(ETF processes, to specify the use of alternate ECN)-2.75 E
(semantics with that codepoint.)100.8 631 Q 2.75(As)5.5 G(econd w)-2.75
E(ay is to de\214ne a ne)-.11 E 2.75(wd)-.275 G(if)-2.75 E
(fserv codepoint, and to)-.275 E
(specify the use of alternate ECN semantics with that codepoint.)100.8
644 Q 1.76 -.88(We n)5.5 H(ote that the \214rst of).88 E(these tw)100.8
657 Q 2.75(om)-.11 G
(echanisms raises the possibility that some routers along the path will)
-2.75 E(understand the dif)100.8 670 Q(fserv codepoint b)-.275 E
(ut will use the def)-.22 E(ault ECN semantics with this dif)-.11 E
(fserv)-.275 E(codepoint, or w)100.8 683 Q(on')-.11 E 2.75(tu)-.198 G
(se ECN at all, and that other routers will use the alternate ECN)-2.75
E(semantics with this dif)100.8 696 Q(fserv codepoint.)-.275 E(Flo)72
769 Q 309.141(yd Section)-.11 F 2.75(3.1. [P)2.75 F(age 4])-.165 E 0 Cg
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(February 2006)2.75 E(August 2005)107.534 E/F1 11/Times-Bold@0 SF(4.)72
85 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:)
100.8 111 Q(\(2\) Ho)100.8 137 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
150 Q(\(3\) Ho)100.8 176 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)100.8 189 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)100.8 215 Q
(are no problems caused by old routers along the path that don')100.8
228 Q 2.75(tu)-.198 G(nderstand the alternate)-2.75 E(ECN semantics.)
100.8 241 Q(One possible problem is that of poor performance for the al\
ternate-ECN traf)100.8 267 Q 2.75(\214c. Is)-.275 F(it)2.75 E
(essential to the performance of the alternate-ECN traf)100.8 280 Q
(\214c that all routers along the path)-.275 E
(understand the alternate-ECN semantics?)100.8 293 Q
(If not, what are the possible consequences, for)5.5 E
(the alternate-ECN traf)100.8 306 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?)100.8 319 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.)100.8 332 Q 2.75(As)100.8 358 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)100.8 371 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)
100.8 384 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.)100.8 397 Q(Does the alternate-ECN traf)
5.5 E(\214c respond to pack)-.275 E(et drops as an)-.11 E
(indication of congestion?)100.8 410 Q/F3 11/Courier@0 SF(|--------|)
305.4 442 Q(Alternate-ECN traffic ---->)114 455 Q 52.8(||)13.2 G
(---> CE-marked packet)-46.2 E 13.2(|O)305.4 468 S 13.2(ld |)-13.2 F
(Non-ECN traffic ---------->)114 481 Q 6.6(|R)13.2 G
(outer | ---> dropped packet)-6.6 E 52.8(||)305.4 494 S
(RFC-3168 ECN traffic ----->)114 507 Q 52.8(||)13.2 G
(---> CE-marked packet)-46.2 E(|--------|)305.4 520 Q
(Figure 1: Alternate-ECN traffic, an old router using RFC-3168 ECN.)114
546 Q F0(Similarly)100.8 578 Q 2.75(,w)-.715 G(hat if there is an old r\
outer along the path that understands only the def)-2.75 E(ault)-.11 E
(ECN semantics from RFC-3168, as in Figure 1 abo)100.8 591 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)100.8 604 Q(ault-ECN router could see an alternate-ECN pack)-.11 E
(et with one of the ECN-Capable)-.11 E -.385(Tr)100.8 617 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)100.8 630 Q .33 -.165(ve t)-.275 H(o).165 E(dropping the pack)
100.8 643 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)100.8 656 Q
(ould if the pack)-.11 E(et has been dropped.)-.11 E(If the)5.5 E
(alternate-ECN traf)100.8 669 Q(\214c f)-.275 E
(ails to respond appropriately to the CE codepoint being set by an old)
-.11 E(router)100.8 682 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)100.8 695 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)100.8 708 Q
(\214c cro)-.275 E(wding out the other traf)-.275 E
(\214c competing for bandwidth on that)-.275 E(link.)100.8 721 Q(Flo)72
769 Q 317.391(yd Section)-.11 F 2.75(4. [P)2.75 F(age 5])-.165 E 0 Cg EP
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(February 2006)2.75 E(August 2005)107.534 E(Basically)100.8 85 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 98 Q
(\214c competing unf)-.275 E(airly with other)-.11 E(traf)100.8 111 Q
(\214c along the path:)-.275 E(Option 1:)100.8 137 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)100.8 150 Q(Option 2:)100.8 176
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)100.8 189 Q(\214c; or)-.275 E(Option 3:)100.8 215 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)100.8 228 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)100.8 241 Q(vironments that include old routers tha\
t do not understand the alternate-ECN semantics.)-.44 E
(Each of these alternati)100.8 267 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/F1
11/Times-Bold@0 SF(4.1.)72 306 Q/F2 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)100.8 332 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)100.8 345 Q
(vironments, and as unsafe for deplo)-.44 E(yment in the global)-.11 E
2.75(Internet. This)100.8 358 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
371 Q -.22(vo)-.22 G(id the chance of the).22 E(alternate-ECN traf)100.8
384 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')100.8 397 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)
100.8 410 Q(ould not be let loose on the global Internet.)-.11 E
(This document)5.5 E(also doesn')100.8 423 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)100.8 436 Q(.)-.715 E F1(4.2.)72
475 Q F2(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)100.8 501 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)100.8 514 Q
(ECN semantics for this traf)100.8 527 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
540 Q 2.75(ya)-.165 G(gree to use the alternate)-2.75 E
(ECN semantics with this traf)100.8 553 Q 2.75(\214c. \(A)-.275 F
(similar mechanism is proposed for Quick-Start, for)2.75 E -.165(ve)
100.8 566 S(rifying that all of the routers along the path understand t\
he Quick-Start IP Option).165 E 2.75([QuickStart].\) Using)100.8 579 R
(such a mechanism, a sender could ha)2.75 E .33 -.165(ve r)-.22 H
(easonable assurance that the).165 E(pack)100.8 592 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)100.8 605 Q(act understand and agre\
e to use these alternate semantics for these pack)-.11 E(ets.)-.11 E
(Such a mechanism should be rob)100.8 631 Q
(ust in the presence of paths with multi-path routing, and in)-.22 E(th\
e presence of routing or con\214guration changes along the path while t\
he connection is in)100.8 644 Q 2.75(use. In)100.8 657 R(particular)2.75
E 2.75(,i)-.44 G 2.75(ft)-2.75 G
(his option is used, connections could include some form of)-2.75 E
(monitoring for changes in path beha)100.8 670 Q(vior)-.22 E 2.75(,a)
-.44 G(nd/or periodic monitoring that all routers along)-2.75 E
(the path continue to understand the alternate-ECN semantics.)100.8 683
Q(Flo)72 769 Q 309.141(yd Section)-.11 F 2.75(4.2. [P)2.75 F(age 6])
-.165 E 0 Cg EP
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(February 2006)2.75 E(August 2005)107.534 E/F1 11/Times-Bold@0 SF(4.3.)
72 85 Q/F2 13/Times-Bold@0 SF(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)100.8 111 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)100.8 124 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)100.8 137 Q
(ault ECN semantics.)-.11 E(In this scenario, a connection)5.5 E
(sending alternate-ECN traf)100.8 150 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)100.8 163 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
176 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)100.8 189 Q
(et, that could be a congestion indication from a)-.11 E
(router that doesn')100.8 202 Q 2.75(tu)-.198 G(se ECN.)-2.75 E
(RFC 3168 de\214nes the def)100.8 228 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
254 Q(et, the congestion)-.11 E(control algorithms follo)100.8 267 Q
(wed at the end-systems MUST be essentially the same as the)-.275 E
(congestion control response to a *single* dropped pack)100.8 280 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)100.8 293 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)100.8 306 Q(et drop or an ECN indication.")
-.11 E(The only conformant congestion control mechanisms currently stan\
dardized in the IETF)100.8 332 Q
(are TCP [RFC2581] and protocols using TCP-lik)100.8 345 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)100.8 358 Q
(protocols with TFRC-lik)100.8 371 Q 2.75(ec)-.11 G
(ongestion control \(e.g., DCCP using CCID-3 [DCCP]\).)-2.75 E(TCP)5.5 E
(uses Additi)100.8 384 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)100.8 397 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)100.8 410 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)100.8 423 Q
(ould be comparable, in pack)-.11 E(ets per)-.11 E
(round-trip-time, to that of a TCP connection e)100.8 436 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)100.8 462
Q(\214c to compete appropriately)-.275 E(with other traf)100.8 475 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 \(and therefore might be using the def)100.8 488 Q
(ault ECN semantics\)?)-.11 E(The \214rst and second)5.5 E
(requirements belo)100.8 501 Q 2.75(wc)-.275 G
(oncern compatibility between traf)-2.75 E
(\214c using alternate ECN semantics)-.275 E(and routers using def)100.8
514 Q(ault ECN semantics.)-.11 E
(The \214rst requirement for compatibility with routers using def)100.8
540 Q(ault ECN is that if a pack)-.11 E(et is)-.11 E(mark)100.8 553 Q
(ed with the ECN codepoint "11" in the netw)-.11 E
(ork, this marking is not changed on the)-.11 E(pack)100.8 566 Q(et')
-.11 E 2.75(sw)-.605 G(ay to the recei)-2.86 E -.165(ve)-.275 G 2.75
(r\().165 G(unless the pack)-2.75 E
(et is dropped before it reaches the recei)-.11 E -.165(ve)-.275 G(r\).)
.165 E(This requirement is necessary to ensure that congestion indicati\
ons from a def)100.8 579 Q(ault-ECN)-.11 E(router mak)100.8 592 Q 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 2.75(As)100.8 618 S
(econd requirement for compatibility with routers using def)-2.75 E
(ault ECN is that the end-)-.11 E(nodes respond to pack)100.8 631 Q
(ets that are mark)-.11 E(ed with the ECN codepoint "11" in a w)-.11 E
(ay that is)-.11 E(friendly to \215o)100.8 644 Q
(ws using IETF-conformant congestion control.)-.275 E
(This requirement is needed)5.5 E(because the "11"-mark)100.8 657 Q
(ed pack)-.11 E(ets might ha)-.11 E .33 -.165(ve c)-.22 H
(ome from a congested router that).165 E(understands only the def)100.8
670 Q(ault ECN semantics, and that e)-.11 E
(xpects that end-nodes will respond)-.165 E(appropriately to CE pack)
100.8 683 Q 2.75(ets. This)-.11 F(requirement w)2.75 E
(ould ensure that the traf)-.11 E(\214c using the)-.275 E
(alternate semantics does not `b)100.8 696 Q(ully' competing traf)-.22 E
(\214c that it might encounter along the)-.275 E(path, and does not dri)
100.8 709 Q .33 -.165(ve u)-.275 H 2.75(pc).165 G
(ongestion on the shared link inappropriately)-2.75 E(.)-.715 E(Flo)72
769 Q 309.141(yd Section)-.11 F 2.75(4.3. [P)2.75 F(age 7])-.165 E 0 Cg
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(February 2006)2.75 E(August 2005)107.534 E
(Additional requirements concern compatibility between traf)100.8 85 Q
(\214c using def)-.275 E(ault ECN)-.11 E
(semantics and routers using alternate ECN semantics.)100.8 98 Q
(This situation could occur if a dif)5.5 E(f-)-.275 E
(serv codepoint using def)100.8 111 Q
(ault ECN semantics is rede\214ned to use alternate ECN semantics,)-.11
E(and traf)100.8 124 Q(\214c from an "old" source tra)-.275 E -.165(ve)
-.22 G(rses a "ne).165 E(w" router)-.275 E 5.5(.I)-.605 G 2.75(ft)-5.5 G
(he router "kno)-2.75 E(ws" that a)-.275 E(pack)100.8 137 Q
(et is from a sender using alternate semantics \(e.g., because the pack)
-.11 E(et is using a certain)-.11 E(dif)100.8 150 Q
(f-serv codepoint, and all pack)-.275 E(ets with that dif)-.11 E
(f-serv codepoint use alternate semantics for)-.275 E
(the ECN \214eld\), then the requirements belo)100.8 163 Q 2.75(wa)-.275
G(re not necessary)-2.75 E 2.75(,a)-.715 G(nd the rules for the)-2.75 E
(alternate semantics apply)100.8 176 Q(.)-.715 E 2.75(Ar)100.8 202 S
(equirement for compatibility with end-nodes using def)-2.75 E
(ault ECN is that if a pack)-.11 E(et that)-.11 E(*could* be using def)
100.8 215 Q(ault semantics is mark)-.11 E
(ed with the ECN codepoint "00", this marking)-.11 E
(must not be changed to "01", "10", or "11" in the netw)100.8 228 Q 2.75
(ork. This)-.11 F(pre)2.75 E -.165(ve)-.275 G(nts the pack).165 E
(et from)-.11 E(being represented incorrectly to a def)100.8 241 Q
(ault ECN router do)-.11 E(wnstream as ECN-Capable.)-.275 E(Similarly)
100.8 254 Q 2.75(,i)-.715 G 2.75(fap)-2.75 G(ack)-2.75 E
(et that *could* be using def)-.11 E(ault semantics is mark)-.11 E
(ed with the ECN)-.11 E(codepoint "01", then this codepoint should not \
be changed to "10" in the netw)100.8 267 Q(ork \(and a)-.11 E
("10" codepoint should not be changed to "01"\).)100.8 280 Q
(This requirement is necessary to a)5.5 E -.22(vo)-.22 G(id).22 E
(interference with the transport protocol')100.8 293 Q 2.75(su)-.605 G
(se of the ECN nonce [RFC3540].)-2.75 E(As discussed earlier)100.8 319 Q
2.75(,t)-.44 G
(he current conformant congestion control responses to a dropped or)
-2.75 E(def)100.8 332 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(\(TCP-Friendly Rate Control\).)
100.8 345 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)100.8 358 Q(connection for a period \
of time if the long-term sending rate is higher than w)100.8 371 Q
(ould be that of)-.11 E 2.75(aT)100.8 384 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)100.8 397
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)100.8 410 Q
(transmission, and w)100.8 423 Q
(ould require a consideration of issues of pack)-.11 E(et size.)-.11 E
/F1 11/Times-Bold@0 SF(5.)72 462 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:)100.8 488 Q
(\(4\) Ho)100.8 514 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)100.8 527 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?)
100.8 540 Q F1(5.1.)72 579 Q/F3 13/Times-Bold@0 SF -1.3(Ve)5.5 G
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(One issue in e)100.8 605 Q -.275(va)-.275 G
(luating the alternate-ECN semantics concerns mechanisms to discourage)
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2.75(nm)-5.5 G(an)-2.75 E 2.75(yc)-.165 G(ases the sender is a)-2.75 E
(serv)100.8 631 Q
(er that has an interest in using the alternate-ECN semantics correctly)
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(has more incenti)100.8 644 Q -.165(ve)-.275 G 2.75(sf).165 G
(or lying about the congestion e)-2.75 E(xperienced along the path.)
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(Capable\(0\) and ECN-Capable\(1\).)100.8 683 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)100.8 696 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
709 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)100.8 722 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(Flo)72 769 Q 309.141
(yd Section)-.11 F 2.75(5.1. [P)2.75 F(age 8])-.165 E 0 Cg EP
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(February 2006)2.75 E(August 2005)107.534 E
(as discussed in RFC 3540 [RFC 3540].)100.8 85 Q
(This use of ECN-Capable\(0\) and ECN-Capable\(1\))5.5 E(is independent\
 of the semantics of the other ECN codepoints, and could be used, if de\
sired,)100.8 98 Q(with alternate semantics for the other codepoints.)
100.8 111 Q(If alternate semantics for the ECN codepoint don')100.8 137
Q 2.75(ti)-.198 G(nclude the use of tw)-2.75 E 2.75(os)-.11 G(eparate)
-2.75 E(codepoints to indicate ECN-Capable, then the connections using \
those semantics ha)100.8 150 Q .33 -.165(ve l)-.22 H(ost).165 E
(the ability to v)100.8 163 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)100.8 176 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
(frame)100.8 189 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)100.8 202 Q 5.5(.A)-.605 G 2.75
(so)-5.5 G(ne possibility)-2.75 E 2.75(,p)-.715 G
(olicers could be used in routers)-2.75 E
(to ensure that end nodes are responding appropriately to mark)100.8 215
Q(ed pack)-.11 E(ets.)-.11 E/F1 11/Times-Bold@0 SF(5.2.)72 254 Q/F2 13
/Times-Bold@0 SF(Co-existence with Competing T)5.5 E(raf\214c)-.962 E F0
2.75(As)100.8 280 S(econd general issue concerns the co-e)-2.75 E
(xistence of alternate-ECN traf)-.165 E(\214c with competing)-.275 E
(traf)100.8 293 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)100.8 306 Q
(\214c that speci\214es its use.)-.275 E(If the traf)100.8 332 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)100.8 345 Q
(air competition with TCP and other traf)-.11 E(\214c along the path)
-.275 E([RFC2914].)100.8 358 Q(If the traf)100.8 384 Q
(\214c using the alternate-ECN semantics is dif)-.275 E(fserv traf)-.275
E(\214c, then the requirements are)-.275 E(go)100.8 397 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)100.8 410 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)100.8 423 Q(\214c on t\
he link; this should be addressed in the speci\214cation of the dif)
-.275 E(fserv)-.275 E(codepoint itself.)100.8 436 Q F1(5.3.)72 475 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)100.8 501 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.)100.8 514 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)100.8 527 Q -.275(va)-.275 G
(luation of alternate-ECN semantics.).275 E F1(6.)72 566 Q/F3 14
/Times-Bold@0 SF(Who W)5.5 E(ants to Use Alter)-.91 E(nate Semantics f)
-.21 E(or the ECN Codepoint?)-.35 E F0(There ha)100.8 592 Q .33 -.165
(ve b)-.22 H(een a number of proposals in the IETF and in the research \
community for).165 E(alternate semantics for the ECN codepoint [ECN].)
100.8 605 Q(One such proposal, [BCF05], proposes)5.5 E
(an alternate-ECN semantics for real-time inelastic traf)100.8 618 Q
(\214c such as v)-.275 E(oice, video conferencing,)-.22 E
(and multimedia streaming in Dif)100.8 631 Q(fServ netw)-.275 E 2.75
(orks. In)-.11 F(this proposal, the alternate-ECN)2.75 E(semantics w)
100.8 644 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
(xperienced along the)-.165 E(path [BCF05].)100.8 657 Q(Some of the oth\
er proposals for alternate ECN semantics are listed on the)5.5 E(ECN W)
100.8 670 Q(eb P)-.88 E(age [ECN].)-.165 E(Flo)72 769 Q 317.391
(yd Section)-.11 F 2.75(6. [P)2.75 F(age 9])-.165 E 0 Cg EP
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(February 2006)2.75 E(August 2005)107.534 E/F1 11/Times-Bold@0 SF(7.)72
85 Q/F2 14/Times-Bold@0 SF(Security Considerations)5.5 E F0
(This document doesn')100.8 111 Q 2.75(tp)-.198 G(ropose an)-2.75 E 2.75
(yn)-.165 G .55 -.275(ew m)-2.75 H
(echanisms for the Internet protocol, and).275 E(therefore doesn')100.8
124 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.)72 163 Q F2(Ackno)5.5
E(wledgements)-.14 E F0(This document is based in part on con)100.8 189
Q -.165(ve)-.44 G(rsations with Jozef Babiarz, Kw).165 E
(ok Ho Chan, and)-.11 E -.66(Vi)100.8 202 S(ctor Firoiu on their propos\
al for an alternate use of the ECN \214eld in Dif).66 E(fServ)-.275 E
(en)100.8 215 Q 2.75(vironments. Man)-.44 F 2.75(yt)-.165 G
(hanks to Francois Le F)-2.75 E
(aucheur for feedback recommending that the)-.165 E
(document include a section at the be)100.8 228 Q
(ginning discussing the potential issues that need to be)-.165 E 2.75
(addressed. Thanks)100.8 241 R(also to Mark Allman, Fred Bak)2.75 E(er)
-.11 E 2.75(,D)-.44 G -.22(av)-2.75 G(id Black, Gorry F).22 E
(airhurst, and to)-.165 E(members of the TSVWG w)100.8 254 Q
(orking group for feedback on these issues.)-.11 E F1(9.)72 293 Q F2
(Conclusions)5.5 E F0(This document has discussed some of the issues to\
 be considered in the speci\214cation of)100.8 319 Q
(alternate semantics for the ECN \214eld in the IP header)100.8 332 Q(.)
-.605 E F1(10.)72 371 Q F2(Normati)5.5 E .28 -.14(ve R)-.14 H(efer).14 E
(ences)-.252 E F1(11.)72 410 Q F2(Inf)5.5 E(ormati)-.35 E .28 -.14(ve R)
-.14 H(efer).14 E(ences)-.252 E F0([BCF05] J. Babiarz, K. Chan, and V)
100.8 436 Q 2.75(.F)-1.419 G
(iroiu, Congestion Noti\214cation Process for Real-)-2.75 E -.385(Ti)
100.8 449 S(me T).385 E(raf)-.385 E
(\214c, internet-draft draft-babiarz-tsvwg-rtecn-04, w)-.275 E
(ork in progress, July 2005.)-.11 E([DCCP] DCCP W)100.8 475 Q(eb P)-.88
E(age, URL "http://www)-.165 E(.icir)-.715 E(.or)-.605 E(g/k)-.198 E
(ohler/dccp/".)-.11 E([ECN] ECN W)100.8 501 Q(eb P)-.88 E(age, URL "www)
-.165 E(.icir)-.715 E(.or)-.605 E(g/\215o)-.198 E(yd/ecn.html".)-.11 E
([QuickStart] Quick-Start W)100.8 527 Q(eb P)-.88 E
(age, URL "http://www)-.165 E(.icir)-.715 E(.or)-.605 E(g/\215o)-.198 E
(yd/quickstart.html".)-.11 E([RFC2581] M. Allman, V)100.8 553 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)
-.275 G(ns, TCP Congestion Control, RFC 2581,).165 E
(Proposed Standard, April 1999.)100.8 566 Q([RFC2914] S. Flo)100.8 592 Q
(yd, Congestion Control Principles, RFC 2914, Best Current Practice,)
-.11 E(September 2000.)100.8 605 Q([RFC2960] R. Ste)100.8 631 Q -.11(wa)
-.275 G(rt et al, Stream Control T).11 E
(ransmission Protocol, RFC 2960, October)-.385 E(2000.)100.8 644 Q
([RFC3168] Ramakrishnan, K.K., Flo)100.8 670 Q
(yd, S., and Black, D., The Addition of Explicit)-.11 E
(Congestion Noti\214cation \(ECN\) to IP)100.8 683 Q 2.75(,R)-1.221 G
(FC 3168, Proposed Standard, September 2001.)-2.75 E
([RFC3540] N. Spring, D. W)100.8 709 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
722 Q(Flo)72 769 Q 306.391(yd Section)-.11 F 2.75(11. [P)2.75 F(age 10])
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(February 2006)2.75 E(August 2005)107.534 E([RFC3714] S. Flo)100.8 85 Q
(yd and J. K)-.11 E(empf, Editors, IAB Concerns Re)-.275 E -.055(ga)
-.165 G(rding Congestion Control).055 E(for V)100.8 98 Q(oice T)-1.419 E
(raf)-.385 E
(\214c in the Internet, RFC 3714, Informational, March 2004.)-.275 E/F1
14/Times-Bold@0 SF(IAN)72 150 Q 3.5(AC)-.28 G(onsiderations)-3.5 E F0
(There are no IAN)100.8 176 Q 2.75(Ac)-.385 G
(onsiderations in this document.)-2.75 E F1 -.7(AU)72 215 S
(THORS' ADDRESSES).7 E F0(Sally Flo)100.8 254 Q(yd)-.11 E
(Phone: +1 \(510\) 666-2989)100.8 267 Q
(ICIR \(ICSI Center for Internet Research\))100.8 280 Q(Email: \215o)
100.8 293 Q(yd@icir)-.11 E(.or)-.605 E(g)-.198 E(URL: http://www)100.8
306 Q(.icir)-.715 E(.or)-.605 E(g/\215o)-.198 E(yd/)-.11 E F1
(Full Copyright Statement)72 345 Q F0(Cop)100.8 361.6 Q
(yright \(C\) The Internet Society 2005.)-.11 E
(This document is subject to the rights, licenses)5.5 E
(and restrictions contained in BCP 78, and e)100.8 374.6 Q
(xcept as set forth therein, the authors retain all)-.165 E
(their rights.)100.8 387.6 Q
(This document and the information contained herein are pro)100.8 404.2
Q(vided on an "AS IS" basis and)-.165 E(THE CONTRIB)100.8 417.2 Q(UT)
-.11 E(OR, THE ORGANIZA)-.198 E(TION HE/SHE REPRESENTS OR IS)-1.221 E
(SPONSORED BY \(IF ANY\), THE INTERNET SOCIETY AND THE INTERNET)100.8
430.2 Q(ENGINEERING T)100.8 443.2 Q(ASK FORCE DISCLAIM ALL W)-1.023 E
(ARRANTIES, EXPRESS OR)-1.32 E(IMPLIED, INCLUDING B)100.8 456.2 Q(UT NO)
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(ARRANTY THA)-1.32 E 2.75(TT)-1.221 G(HE USE)-2.75 E(OF THE INFORMA)
100.8 469.2 Q(TION HEREIN WILL NO)-1.221 E 2.75(TI)-.44 G
(NFRINGE ANY RIGHTS OR ANY)-2.75 E(IMPLIED W)100.8 482.2 Q
(ARRANTIES OF MERCHANT)-1.32 E(ABILITY OR FITNESS FOR A)-1.023 E -1.012
(PA)100.8 495.2 S -.66(RT)1.012 G(ICULAR PURPOSE.).66 E F1
(Intellectual Pr)72 521.2 Q(operty)-.252 E F0(The IETF tak)100.8 537.8 Q
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-2.75 E(Rights or other rights that might be claimed to pertain to the \
implementation or use of the)100.8 550.8 Q
(technology described in this document or the e)100.8 563.8 Q
(xtent to which an)-.165 E 2.75(yl)-.165 G(icense under such rights)
-2.75 E(might or might not be a)100.8 576.8 Q -.275(va)-.22 G
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G(ndependent)-2.75 E(ef)100.8 589.8 Q(fort to identify an)-.275 E 2.75
(ys)-.165 G(uch rights.)-2.75 E
(Information on the procedures with respect to rights in)5.5 E
(RFC documents can be found in BCP 78 and BCP 79.)100.8 602.8 Q
(Copies of IPR disclosures made to the IETF Secretariat and an)100.8
619.4 Q 2.75(ya)-.165 G(ssurances of licenses to)-2.75 E(be made a)100.8
632.4 Q -.275(va)-.22 G(ilable, or the result of an attempt made to obt\
ain a general license or).275 E(permission for the use of such propriet\
ary rights by implementers or users of this)100.8 645.4 Q(speci\214cati\
on can be obtained from the IETF on-line IPR repository at)100.8 658.4 Q
(http://www)100.8 671.4 Q(.ietf.or)-.715 E(g/ipr)-.198 E(.)-.605 E
(The IETF in)100.8 688 Q(vites an)-.44 E 2.75(yi)-.165 G
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(op)-2.75 E(yrights, patents or)-.11 E
(patent applications, or other proprietary rights that may co)100.8 701
Q -.165(ve)-.165 G 2.75(rt).165 G(echnology that may be)-2.75 E
(required to implement this standard.)100.8 714 Q
(Please address the information to the IETF at ietf-)5.5 E(Flo)72 769 Q
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