One document matched: draft-ietf-dccp-ccid2-07.ps

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/F0 10/Courier-Bold@0 SF(Internet Engineering Task Force)72 85 Q
(Sally Floyd)179.999 E 317.999(INTERNET-DRAFT ICIR)72 98 R 191.999
(draft-ietf-dccp-ccid2-07.ps Eddie)72 111 R(Kohler)6 E
(Expires: 25 April 2005)72 124 Q(UCLA)275.999 E(25 October 2004)413.999
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(yright \(C\) The Internet Society \(2004\). All Rights Reserv)-.11 E
(ed.)-.165 E F2(Abstract)72 492.2 Q F3(This document contains the pro\
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228 S(dded references to RFC 2988 and RFC 2018.)-2.75 E 2.75(*S)100.8
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-2.75 G(nly increased for pack)-2.75 E(ets that aren')-.11 E 2.75(tE)
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E 2.75(,i)-.715 G(ncluding some reordering of sections.)-2.75 E 2.75(*A)
100.8 410 S
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based on feedback from Nils-Erik Mattsson.)-2.75 E
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(dded Intellectual Property Notice.)-2.75 E
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(dded a paragraph about pack)-2.75 E(et sizes.)-.11 E
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(1. Introduction)100.8 110 Q F0 11(.......................)11.01 G F2(5)
11.5 E(2. Con)100.8 122 Q -.15(ve)-.4 G(ntions and Notation).15 E F0 11
(...................)11 G F2(5)11.5 E(3. Usage)100.8 134 Q F0 11
(.........................)7.96 G F2(5)11.5 E
(3.1. Relationship with TCP)115.8 146 Q F0 11(...................)1.27 G
F2(6)11.5 E(3.2. Example Half-Connection)115.8 158 Q F0 11
(..................)1.44 G F2(6)11.5 E(4. Connection Establishment)100.8
170 Q F0 11(...................)10.17 G F2(7)11.5 E
(5. Congestion Control on Data P)100.8 182 Q(ack)-.15 E(ets)-.1 E F0 11
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(5.1. Response to Idle and Application-limited Periods)115.8 194 Q F0 11
(...........)5.46 G F2(8)11.5 E(5.2. Response to Data Dropped and Slo)
115.8 206 Q 2.5(wR)-.25 G(ecei)-2.5 E -.15(ve)-.25 G(r).15 E F0 11
(............)4.33 G F2(9)11.5 E(5.3. P)115.8 218 Q(ack)-.15 E(et Size)
-.1 E F0 11(......................)5.57 G F2(9)11.5 E(6. Ackno)100.8 230
Q(wledgements)-.25 E F0 11(.....................)8.77 G F2(9)11.5 E
(6.1. Congestion Control on Ackno)115.8 242 Q(wledgements)-.25 E F0 11
(.............)2.65 G F2(10)6.5 E(6.1.1. Detecting Lost and Mark)130.8
254 Q(ed Ackno)-.1 E(wledgements)-.25 E F0 11(..........)2.92 G F2(10)
6.5 E(6.1.2. Changing Ack Ratio)130.8 266 Q F0 11(..................)
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(wledgements)-.25 E F0 11(.............)3.76 G F2(11)6.5 E
(6.2.1. Determining Quiescence)130.8 290 Q F0 11(................)12.56
G F2(11)6.5 E(7. Explicit Congestion Noti\214cation)100.8 302 Q F0 11
(.................)12.94 G F2(12)6.5 E(8. Options and Features)100.8 314
Q F0 11(.....................)2.96 G F2(12)6.5 E
(9. Security Considerations)100.8 326 Q F0 11(....................)5.87
G F2(12)6.5 E(10. IAN)100.8 338 Q 2.5(AC)-.35 G(onsiderations)-2.5 E F0
11(....................)9.56 G F2(12)6.5 E(11. Thanks)100.8 350 Q F0 11
(........................)12.26 G F2(13)6.5 E(A. Appendix: Deri)100.8
362 Q -.25(va)-.25 G(tion of Ack Ratio Decrease).25 E F0 11
(..............)1.69 G F2(13)6.5 E
(B. Appendix: Cost of Loss Inference Mistak)100.8 374 Q(es to Ack Ratio)
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(ve R)-.25 H(eferences).15 E F0 11(.....................)8.66 G F2(14)
6.5 E(Informati)100.8 398 Q .3 -.15(ve R)-.25 H(eferences).15 E F0 11
(.....................)4.22 G F2(15)6.5 E(Authors' Addresses)100.8 410 Q
F0 11(......................)5.05 G F2(15)6.5 E(Full Cop)100.8 422 Q
(yright Statement)-.1 E F0 11(....................)10.12 G F2(15)6.5 E
(Intellectual Property)100.8 434 Q F0 11(......................)2.27 G
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100.8 101.6 Q(e)-.11 E(Congestion Control, in the Datagram Congestion C\
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127.6 Q(mechanism in use on a half-connection.)100.8 140.6 Q
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(The terms "HC-Sender" and)5.5 E("HC-Recei)100.8 346.4 Q -.165(ve)-.275
G(r" denote the endpoints sending application data and ackno).165 E
(wledgements,)-.275 E(respecti)100.8 359.4 Q -.165(ve)-.275 G(ly).165 E
5.5(.S)-.715 G(ince CCIDs apply at the le)-5.5 E -.165(ve)-.275 G 2.75
(lo).165 G 2.75(fh)-2.75 G(alf-connections, we abbre)-2.75 E
(viate HC-Sender)-.275 E(to "sender" and HC-Recei)100.8 372.4 Q -.165
(ve)-.275 G 2.75(rt).165 G 2.75(o")-2.75 G(recei)-2.75 E -.165(ve)-.275
G(r" in this document.).165 E(See [DCCP] for more)5.5 E(discussion.)
100.8 385.4 Q -.165(Fo)100.8 402 S 2.75(rs).165 G(implicity)-2.75 E 2.75
(,w)-.715 G 2.75(es)-2.75 G(ay that senders send DCCP-Data pack)-2.75 E
(ets and recei)-.11 E -.165(ve)-.275 G(rs send DCCP-).165 E(Ack pack)
100.8 415 Q 2.75(ets. Both)-.11 F(of these cate)2.75 E
(gories are meant to include DCCP-DataAck pack)-.165 E(ets.)-.11 E F1
(3.)72 441 Q F2(Usage)5.5 E F0(CCID 2, TCP-lik)100.8 457.6 Q 2.75(eC)
-.11 G(ongestion Control, is appropriate for DCCP \215o)-2.75 E
(ws that w)-.275 E(ould lik)-.11 E 2.75(et)-.11 G(o)-2.75 E(recei)100.8
470.6 Q .33 -.165(ve a)-.275 H 2.75(sm).165 G
(uch bandwidth as possible o)-2.75 E -.165(ve)-.165 G 2.75(rt).165 G
(he long term, consistent with the use of end-)-2.75 E
(to-end congestion control, and that can tolerate the lar)100.8 483.6 Q
(ge sending rate v)-.198 E(ariations)-.275 E(characteristic of AIMD con\
gestion control, including halving of the congestion windo)100.8 496.6 Q
2.75(wi)-.275 G(n)-2.75 E(response to a congestion e)100.8 509.6 Q -.165
(ve)-.275 G(nt.).165 E(CCID 2 is recommended for applications that simp\
ly need to transfer as much data as)100.8 526.2 Q
(possible in as short a time as possible.)100.8 539.2 Q
(This contrasts with CCID 3, TCP-Friendly Rate)5.5 E
(Control \(TFRC\) Congestion Control [CCID 3 PR)100.8 552.2 Q
(OFILE], which is appropriate for \215o)-.44 E(ws)-.275 E(that w)100.8
565.2 Q(ould prefer to minimize abrupt changes in the sending rate.)-.11
E -.165(Fo)5.5 G 2.75(re).165 G(xample, CCID 2 is)-2.915 E
(recommended o)100.8 578.2 Q -.165(ve)-.165 G 2.75(rC).165 G
(CID 3 for streaming media applications that b)-2.75 E(uf)-.22 E
(fer a considerable)-.275 E(amount of data at the application recei)
100.8 591.2 Q -.165(ve)-.275 G 2.75(rb).165 G
(efore playback time, insulating the application)-2.75 E(some)100.8
604.2 Q(what from abrupt changes in the sending rate.)-.275 E
(Such applications could easily choose)5.5 E(DCCP')100.8 617.2 Q 2.75
(sC)-.605 G(CID 2 o)-2.75 E -.165(ve)-.165 G 2.75(rT).165 G
(CP itself, possibly adding some form of selecti)-2.75 E .33 -.165(ve r)
-.275 H(eliability at the).165 E(application layer)100.8 630.2 Q 5.5(.C)
-.605 G(CID 2 is also recommended o)-5.5 E -.165(ve)-.165 G 2.75(rC).165
G(CID 3 for applications where the)-2.75 E
(halving of the sending rate in response to congestion is not lik)100.8
643.2 Q(ely to interfere with)-.11 E(application-le)100.8 656.2 Q -.165
(ve)-.275 G 2.75(lp).165 G(erformance.)-2.75 E(An additional adv)100.8
672.8 Q(antage of CCID 2 is that its TCP-lik)-.275 E 2.75(ec)-.11 G
(ongestion control mechanisms are)-2.75 E
(reasonably well-understood, with traf)100.8 685.8 Q
(\214c dynamics quite similar to those of TCP)-.275 E 5.5(.W)-1.221 G
(hile the)-5.5 E(netw)100.8 698.8 Q(ork research community is still lea\
rning about the dynamics of TCP after 15 years of)-.11 E(TCP congestion\
 control as the dominant transport protocol in the Internet, some)100.8
711.8 Q(applications might prefer the more well-kno)100.8 724.8 Q
(wn dynamics of TCP-lik)-.275 E 2.75(ec)-.11 G(ongestion control)-2.75 E
(Flo)72 769 Q(yd/K)-.11 E 284.171(ohler Section)-.385 F 2.75(3. [P)2.75
F(age 5])-.165 E 0 Cg EP
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(25 April 2005)2.75 E(October 2004)105.252 E -.165(ove)100.8 85 S 2.75
(rt).165 G(hat of ne)-2.75 E
(wer congestion control mechanisms, which ha)-.275 E -.165(ve)-.22 G(n')
.165 E 2.75(ty)-.198 G(et met the test of)-2.75 E
(widespread Internet deplo)100.8 98 Q(yment.)-.11 E/F1 11/Times-Bold@0
SF(3.1.)72 124 Q/F2 13/Times-Bold@0 SF(Relationship with TCP)5.5 E F0
(The congestion control mechanisms described here closely follo)100.8
140.6 Q 2.75(wm)-.275 G(echanisms)-2.75 E
(standardized by the IETF for use in SA)100.8 153.6 Q(CK-based TCP)-.44
E 2.75(,a)-1.221 G(nd we rely partially on e)-2.75 E(xisting)-.165 E(TC\
P documentation, such as [RFC 793], [RFC 2581], [RFC 3465], and [RFC 35\
17].)100.8 166.6 Q(TCP)5.5 E(congestion control continues to e)100.8
179.6 Q -.22(vo)-.275 G(lv).22 E(e, b)-.165 E
(ut CCID 2 implementations SHOULD w)-.22 E(ait for)-.11 E -.165(ex)100.8
192.6 S(plicit updates to CCID 2 rather than track TCP').165 E 2.75(se)
-.605 G -.22(vo)-3.025 G(lution directly).22 E 5.5(.T)-.715 G(he dif)
-5.5 E(ferences)-.275 E(between CCID 2 and straight TCP include: CCID 2\
 applies congestion control to)100.8 205.6 Q(ackno)100.8 218.6 Q
(wledgements, a mechanism not currently standardized for use in TCP)
-.275 E 5.5(.D)-1.221 G(CCP is a)-5.5 E(datagram protocol, so se)100.8
231.6 Q -.165(ve)-.275 G
(ral parameters whose units are speci\214ed in bytes in TCP).165 E 2.75
(,s)-1.221 G(uch as)-2.75 E(the congestion windo)100.8 244.6 Q 2.75(wc)
-.275 G(wnd, ha)-2.75 E .33 -.165(ve u)-.22 H(nits of pack).165 E
(ets in DCCP)-.11 E 5.5(.U)-1.221 G(nreliability also leads to)-5.5 E
(dif)100.8 257.6 Q(ferences from TCP: DCCP ne)-.275 E -.165(ve)-.275 G
2.75(rr).165 G(etransmits a pack)-2.75 E(et, so congestion control)-.11
E(mechanisms that distinguish retransmissions from ne)100.8 270.6 Q 2.75
(wp)-.275 G(ack)-2.75 E(ets ha)-.11 E .33 -.165(ve b)-.22 H
(een redesigned for).165 E(the DCCP conte)100.8 283.6 Q(xt.)-.165 E F1
(3.2.)72 309.6 Q F2(Example Half-Connection)5.5 E F0(This e)100.8 326.2
Q(xample sho)-.165 E
(ws the typical progress of a half-connection using TCP-lik)-.275 E 2.75
(eC)-.11 G(ongestion)-2.75 E(Control speci\214ed by CCID 2, not includi\
ng connection initiation and termination.)100.8 339.2 Q(The)5.5 E -.165
(ex)100.8 352.2 S(ample is informati).165 E -.165(ve)-.275 G 2.75(,n)
.165 G(ot normati)-2.75 E -.165(ve)-.275 G(.).165 E 11(1. The)100.8
368.8 R(sender sends DCCP-Data pack)2.75 E
(ets, where the number of pack)-.11 E(ets sent is go)-.11 E -.165(ve)
-.165 G(rned).165 E(by a congestion windo)122.8 381.8 Q 1.43 -.715(w, c)
-.275 H(wnd, as in TCP).715 E 5.5(.E)-1.221 G(ach DCCP-Data pack)-5.5 E
(et uses a sequence)-.11 E(number)122.8 394.8 Q 5.5(.T)-.605 G(he sende\
r also sends an Ack Ratio feature option specifying the number of)-5.5 E
(data pack)122.8 407.8 Q(ets to be co)-.11 E -.165(ve)-.165 G
(red by an Ack pack).165 E(et from the recei)-.11 E -.165(ve)-.275 G
(r; Ack Ratio def).165 E(aults to)-.11 E(tw)122.8 420.8 Q 2.75(o. The)
-.11 F(DCCP header')2.75 E 2.75(sC)-.605 G(CV)-2.75 E
(al \214eld is set to zero.)-1.221 E(Assuming that the half-connection \
is Explicit Congestion Noti\214cation \(ECN\) capable)122.8 437.4 Q
(\(the ECN Incapable feature is zero -- the def)122.8 450.4 Q
(ault\), each DCCP-Data pack)-.11 E(et is sent as)-.11 E(ECN-Capable wi\
th either the ECT\(0\) or the ECT\(1\) codepoint set, as described in)
122.8 463.4 Q([RFC 3540].)122.8 476.4 Q 11(2. The)100.8 493 R(recei)2.75
E -.165(ve)-.275 G 2.75(rs).165 G(ends a DCCP-Ack pack)-2.75 E(et ackno)
-.11 E(wledging the data pack)-.275 E(ets for e)-.11 E -.165(ve)-.275 G
(ry Ack).165 E(Ratio data pack)122.8 506 Q
(ets transmitted by the sender)-.11 E 5.5(.E)-.605 G(ach DCCP-Ack pack)
-5.5 E(et uses a sequence)-.11 E(number and contains an Ack V)122.8 519
Q(ector)-1.221 E 5.5(.T)-.605 G(he sequence number ackno)-5.5 E
(wledged in a)-.275 E(DCCP-Ack pack)122.8 532 Q(et is that of the recei)
-.11 E -.165(ve)-.275 G 2.75(dp).165 G(ack)-2.75 E
(et with the highest sequence number)-.11 E(,)-.44 E
(rather than a TCP-lik)122.8 545 Q 2.75(ec)-.11 G(umulati)-2.75 E .33
-.165(ve a)-.275 H(ckno).165 E(wledgement.)-.275 E
(If the half-connection is ECN capable, the recei)122.8 561.6 Q -.165
(ve)-.275 G 2.75(rr).165 G(eturns the sum of recei)-2.75 E -.165(ve)
-.275 G 2.75(dE).165 G(CN)-2.75 E(Nonces via Ack V)122.8 574.6 Q
(ector options, allo)-1.221 E(wing the sender to probabilistically v)
-.275 E(erify that the)-.165 E(recei)122.8 587.6 Q -.165(ve)-.275 G 2.75
(ri).165 G 2.75(sn)-2.75 G(ot misbeha)-2.75 E 2.75(ving. DCCP-Ack)-.22 F
(pack)2.75 E(ets from the recei)-.11 E -.165(ve)-.275 G 2.75(ra).165 G
(re also sent as)-2.75 E
(ECN-Capable, since the sender will control the ackno)122.8 600.6 Q
(wledgement rate in a roughly)-.275 E(TCP-friendly w)122.8 613.6 Q
(ay using the Ack Ratio feature.)-.11 E
(There is little need for the recei)5.5 E -.165(ve)-.275 G 2.75(rt).165
G(o)-2.75 E -.165(ve)122.8 626.6 S(rify the nonces of its DCCP-Ack pack)
.165 E(ets, since the sender cannot get signi\214cant)-.11 E
(bene\214t from misreporting the ack mark rate.)122.8 639.6 Q 11(3. The)
100.8 656.2 R(sender continues sending DCCP-Data pack)2.75 E
(ets as controlled by the congestion)-.11 E(windo)122.8 669.2 Q 4.18
-.715(w. U)-.275 H(pon recei).715 E(ving DCCP-Ack pack)-.275 E
(ets, the sender e)-.11 E(xamines their Ack V)-.165 E(ectors)-1.221 E
(to learn about mark)122.8 682.2 Q(ed or dropped data pack)-.11 E
(ets, and adjusts its congestion windo)-.11 E(w)-.275 E(accordingly)
122.8 695.2 Q 5.5(.B)-.715 G(ecause this is unreliable transfer)-5.5 E
2.75(,t)-.44 G(he sender does not retransmit)-2.75 E(dropped pack)122.8
708.2 Q(ets.)-.11 E(Flo)72 769 Q(yd/K)-.11 E 275.921(ohler Section)-.385
F 2.75(3.2. [P)2.75 F(age 6])-.165 E 0 Cg EP
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(25 April 2005)2.75 E(October 2004)105.252 E 11(4. Because)100.8 85 R
(DCCP-Ack pack)2.75 E
(ets use sequence numbers, the sender has some information)-.11 E
(about lost or mark)122.8 98 Q(ed DCCP-Ack pack)-.11 E 2.75(ets. The)
-.11 F(sender responds to lost or mark)2.75 E(ed)-.11 E(DCCP-Ack pack)
122.8 111 Q(ets by modifying the Ack Ratio sent to the recei)-.11 E
-.165(ve)-.275 G -.605(r.).165 G 11(5. The)100.8 127.6 R(sender ackno)
2.75 E(wledges the recei)-.275 E -.165(ve)-.275 G(r').165 E 2.75(sa)
-.605 G(ckno)-2.75 E(wledgements at least once per)-.275 E
(congestion windo)122.8 140.6 Q 4.18 -.715(w. I)-.275 H 2.75(fb).715 G
(oth half-connections are acti)-2.75 E -.165(ve)-.275 G 2.75(,t).165 G
(he sender')-2.75 E(s)-.605 E(ackno)122.8 153.6 Q
(wledgement of the recei)-.275 E -.165(ve)-.275 G(r').165 E 2.75(sa)
-.605 G(ckno)-2.75 E(wledgements is included in the sender')-.275 E(s)
-.605 E(ackno)122.8 166.6 Q(wledgement of the recei)-.275 E -.165(ve)
-.275 G(r').165 E 2.75(sd)-.605 G(ata pack)-2.75 E 2.75(ets. If)-.11 F
(the re)2.75 E -.165(ve)-.275 G(rse-path half-connection is).165 E
(quiescent, the sender sends a DCCP-DataAck pack)122.8 179.6 Q
(et that includes an)-.11 E(Ackno)122.8 192.6 Q
(wledgement Number in the header)-.275 E(.)-.605 E 11(6. The)100.8 209.2
R(sender estimates round-trip times, either through k)2.75 E
(eeping track of)-.11 E(ackno)122.8 222.2 Q
(wledgement round-trip times as TCP does or through e)-.275 E(xplicit T)
-.165 E(imestamp)-.385 E(options, and calculates a T)122.8 235.2 Q
(imeOut \(T)-.385 E(O\) v)-.198 E(alue much as the R)-.275 E .396 -.198
(TO \()-.66 H(Retransmit T).198 E(imeout\))-.385 E(is calculated in TCP)
122.8 248.2 Q 5.5(.T)-1.221 G(he T)-5.5 E 2.75(Oi)-.198 G 2.75(su)-2.75
G(sed to determine when a ne)-2.75 E 2.75(wD)-.275 G(CCP-Data pack)-2.75
E(et)-.11 E(can be transmitted when the sender has been limited by the \
congestion windo)122.8 261.2 Q 2.75(wa)-.275 G(nd no)-2.75 E
(feedback has been recei)122.8 274.2 Q -.165(ve)-.275 G 2.75(df).165 G
(rom the recei)-2.75 E -.165(ve)-.275 G -.605(r.).165 G/F1 11
/Times-Bold@0 SF(4.)72 300.2 Q/F2 14/Times-Bold@0 SF
(Connection Establishment)5.5 E F0(Use of the Ack V)100.8 316.8 Q
(ector is MAND)-1.221 E -.506 -1.221(AT O)-.44 H 1.43 -.715(RY o)1.221 H
2.75(nC).715 G(CID 2 half-connections, so the sender MUST)-2.75 E
(send a "Change R\(Send Ack V)100.8 329.8 Q(ector)-1.221 E 2.75(,1)-.44
G(\)" option to the recei)-2.75 E -.165(ve)-.275 G 2.75(ra).165 G 2.75
(sp)-2.75 G(art of connection)-2.75 E 2.75(establishment. The)100.8
342.8 R(sender SHOULD NO)2.75 E 2.75(Ts)-.44 G
(end data until it has recei)-2.75 E -.165(ve)-.275 G 2.75(dt).165 G(he)
-2.75 E(corresponding "Con\214rm L\(Send Ack V)100.8 355.8 Q(ector)
-1.221 E 2.75(,1)-.44 G(\)" from the recei)-2.75 E -.165(ve)-.275 G .88
-.44(r, e).165 H(xcept for possible data).275 E
(included on the initial DCCP-Request pack)100.8 368.8 Q(et.)-.11 E F1
(5.)72 394.8 Q F2(Congestion Contr)5.5 E(ol on Data P)-.252 E(ack)-.14 E
(ets)-.14 E F0(CCID 2')100.8 411.4 Q 2.75(sc)-.605 G
(ongestion control mechanisms are based on those for SA)-2.75 E
(CK-based TCP [RFC)-.44 E(3517], since the Ack V)100.8 424.4 Q
(ector pro)-1.221 E
(vides all the information that might be transmitted in)-.165 E(SA)100.8
437.4 Q(CK options.)-.44 E 2.75(AC)100.8 454 S
(CID 2 data sender maintains three inte)-2.75 E
(ger parameters measured in pack)-.165 E(ets.)-.11 E 11(1. The)100.8
470.6 R(congestion windo)2.75 E 2.75(w")-.275 G
(cwnd", which equals the maximum number of data pack)-2.75 E(ets)-.11 E
(allo)122.8 483.6 Q(wed in the netw)-.275 E(ork at an)-.11 E 2.75(yt)
-.165 G 2.75(ime. \("Data)-2.75 F(pack)2.75 E(et" means an)-.11 E 2.75
(yD)-.165 G(CCP pack)-2.75 E(et that)-.11 E(contains user data: DCCP-Da\
ta, DCCP-DataAck, and occasionally DCCP-Request,)122.8 496.6 Q
(DCCP-Response, and DCCP-Mo)122.8 509.6 Q -.165(ve)-.165 G(.\)).165 E 11
(2. The)100.8 526.2 R(slo)2.75 E
(w-start threshold "ssthresh", which controls adjustments to cwnd.)-.275
E 11(3. The)100.8 542.8 R(pipe v)2.75 E
(alue "pipe", which is the sender')-.275 E 2.75(se)-.605 G
(stimate of the number of data pack)-2.75 E(ets)-.11 E
(outstanding in the netw)122.8 555.8 Q(ork.)-.11 E
(These parameters are manipulated, and their initial v)100.8 572.4 Q
(alues determined, according to SA)-.275 E(CK-)-.44 E(based TCP')100.8
585.4 Q 2.75(sb)-.605 G(eha)-2.75 E(vior)-.22 E 2.75(,e)-.44 G
(xcept that the)-2.915 E 2.75(ya)-.165 G(re measured in pack)-2.75 E
(ets, not bytes.)-.11 E(The rest of this)5.5 E(section pro)100.8 598.4 Q
(vides more speci\214c guidance.)-.165 E(The sender MA)100.8 615 Q 2.75
(Ys)-1.155 G(end a data pack)-2.75 E(et when pipe < cwnd, b)-.11 E
(ut MUST NO)-.22 E 2.75(Ts)-.44 G(end a data pack)-2.75 E(et)-.11 E
(when pipe >= cwnd.)100.8 628 Q(Ev)5.5 E(ery data pack)-.165 E
(et sent increases pipe by 1.)-.11 E
(The sender reduces pipe as it infers that data pack)100.8 644.6 Q
(ets ha)-.11 E .33 -.165(ve l)-.22 H(eft the netw).165 E
(ork, either by being)-.11 E(recei)100.8 657.6 Q -.165(ve)-.275 G 2.75
(do).165 G 2.75(rb)-2.75 G 2.75(yb)-2.75 G(eing dropped.)-2.75 E
(In particular:)5.5 E(1.)100.8 674.2 Q F1(Ack)13.75 E(ed data pack)-.11
E(ets.)-.11 E F0(The sender reduces pipe by 1 for each data pack)5.5 E
(et ne)-.11 E(wly-)-.275 E(ackno)122.8 687.2 Q(wledged as recei)-.275 E
-.165(ve)-.275 G 2.75(d\().165 G(Ack V)-2.75 E
(ector State 0 or State 1\) by some DCCP-Ack.)-1.221 E(2.)100.8 703.8 Q
F1(Dr)13.75 E(opped data pack)-.198 E(ets.)-.11 E F0
(The sender reduces pipe by 1 for each data pack)5.5 E(et it can infer)
-.11 E(as lost due to the DCCP equi)122.8 716.8 Q -.275(va)-.275 G
(lent of TCP').275 E 2.75(s")-.605 G(duplicate ackno)-2.75 E 2.75
(wledgements". This)-.275 F(Flo)72 769 Q(yd/K)-.11 E 284.171
(ohler Section)-.385 F 2.75(5. [P)2.75 F(age 7])-.165 E 0 Cg EP
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(25 April 2005)2.75 E(October 2004)105.252 E(depends on the NUMDUP)122.8
85 Q -.44(AC)-1.012 G 2.75(Kp).44 G(arameter)-2.75 E 2.75(,t)-.44 G
(he number of duplicate)-2.75 E(ackno)122.8 98 Q
(wledgements needed to infer a loss.)-.275 E(The NUMDUP)5.5 E -.44(AC)
-1.012 G 2.75(Kp).44 G(arameter is set to)-2.75 E
(three, as is currently the case in TCP)122.8 111 Q 5.5(.A)-1.221 G
(pack)-2.75 E(et P is inferred to be lost, rather than)-.11 E
(delayed, when at least NUMDUP)122.8 124 Q -.44(AC)-1.012 G 2.75(Kp).44
G(ack)-2.75 E(ets transmitted after P ha)-.11 E .33 -.165(ve b)-.22 H
(een).165 E(ackno)122.8 137 Q(wledged as recei)-.275 E -.165(ve)-.275 G
2.75(d\().165 G(Ack V)-2.75 E(ector State 0 or 1\) by the recei)-1.221 E
-.165(ve)-.275 G 3.96 -.605(r. N).165 H(ote that the).605 E(ackno)122.8
150 Q(wledged pack)-.275 E(ets follo)-.11 E
(wing the hole may be DCCP-Acks or other non-data)-.275 E(pack)122.8 163
Q(ets.)-.11 E(3.)100.8 179.6 Q/F1 11/Times-Bold@0 SF -.814(Tr)13.75 G
(ansmit timeouts.).814 E F0(Finally)5.5 E 2.75(,t)-.715 G
(he sender needs transmit timeouts, handled lik)-2.75 E 2.75(eT)-.11 G
(CP')-2.75 E(s)-.605 E(retransmission timeouts, in case an entire windo)
122.8 192.6 Q 2.75(wo)-.275 G 2.75(fp)-2.75 G(ack)-2.75 E(ets is lost.)
-.11 E(The sender)5.5 E
(estimates the round-trip time at most once per windo)122.8 205.6 Q 2.75
(wo)-.275 G 2.75(fd)-2.75 G(ata, and uses the TCP)-2.75 E
(algorithms for maintaining the a)122.8 218.6 Q -.165(ve)-.22 G
(rage round-trip time, mean de).165 E(viation, and timeout)-.275 E -.275
(va)122.8 231.6 S(lue [RFC 2988]. \(If more than one round-trip time me\
asurement per round-trip time).275 E -.11(wa)122.8 244.6 S 2.75(su).11 G
(sed for these calculations, then the weights of the a)-2.75 E -.165(ve)
-.22 G(ragers w).165 E(ould ha)-.11 E .33 -.165(ve t)-.22 H 2.75(ob).165
G(e)-2.75 E(adjusted, so that the a)122.8 257.6 Q -.165(ve)-.22 G
(rage round-trip time is ef).165 E(fecti)-.275 E -.165(ve)-.275 G
(ly deri).165 E -.165(ve)-.275 G 2.75(df).165 G(rom measurements)-2.75 E
-.165(ove)122.8 270.6 S 2.75(rm).165 G(ultiple round-trip times.\))-2.75
E(Because DCCP does not retransmit data, DCCP does)5.5 E
(not require TCP')122.8 283.6 Q 2.75(sr)-.605 G
(ecommended minimum timeout of one second.)-2.75 E(The e)5.5 E
(xponential)-.165 E(back)122.8 296.6 Q(of)-.11 E 2.75(fo)-.275 G 2.75
(ft)-2.75 G(he timer is e)-2.75 E(xactly as in TCP)-.165 E 5.5(.W)-1.221
G(hen a transmit timeout occurs, the sender)-5.5 E(sets pipe to zero.)
122.8 309.6 Q(The adjustments to cwnd and ssthresh are described belo)
5.5 E -.715(w.)-.275 G(The sender MUST NO)100.8 326.2 Q 2.75(Td)-.44 G
(ecrement pipe more than once per data pack)-2.75 E 2.75(et. T)-.11 F
(rue duplicate)-.385 E(ackno)100.8 339.2 Q(wledgements, for e)-.275 E
(xample, MUST NO)-.165 E 2.75(Ta)-.44 G -.275(ff)-2.75 G(ect pipe.).275
E(Furthermore, the sender MUST)5.5 E(NO)100.8 352.2 Q 2.75(Td)-.44 G
(ecrement pipe for non-data pack)-2.75 E(ets, such as DCCP-Acks, e)-.11
E -.165(ve)-.275 G 2.75(nt).165 G(hough the Ack)-2.75 E -1.221(Ve)100.8
365.2 S(ctor will contain information about them.)1.221 E(Congestion e)
100.8 381.8 Q -.165(ve)-.275 G(nts, namely one or more pack).165 E
(ets lost or mark)-.11 E(ed from a windo)-.11 E 2.75(wo)-.275 G 2.75(fd)
-2.75 G(ata,)-2.75 E(cause CCID 2 to reduce its congestion windo)100.8
394.8 Q 4.18 -.715(w. F)-.275 H(or each congestion e).55 E -.165(ve)
-.275 G(nt, either indicated).165 E -.165(ex)100.8 407.8 S
(plicitly as an Ack V).165 E(ector State 1 \(ECN-mark)-1.221 E
(ed\) ackno)-.11 E(wledgement or inferred via)-.275 E("duplicate ackno)
100.8 420.8 Q(wledgements", cwnd is halv)-.275 E
(ed, then ssthresh is set to the ne)-.165 E 2.75(wc)-.275 G(wnd.)-2.75 E
(Cwnd is ne)100.8 433.8 Q -.165(ve)-.275 G 2.75(rr).165 G(educed belo)
-2.75 E 2.75(wo)-.275 G(ne pack)-2.75 E 2.75(et. After)-.11 F 2.75(at)
2.75 G(imeout, the slo)-2.75 E(w-start threshold is set to)-.275 E
(cwnd/2, then cwnd is set to one pack)100.8 446.8 Q 2.75(et. When)-.11 F
(halv)2.75 E(ed, cwnd and ssthresh ha)-.165 E .33 -.165(ve t)-.22 H
(heir v).165 E(alues)-.275 E(rounded do)100.8 459.8 Q(wn, e)-.275 E
(xcept that cwnd is ne)-.165 E -.165(ve)-.275 G 2.75(rl).165 G
(ess than one, and ssthresh is ne)-2.75 E -.165(ve)-.275 G 2.75(rl).165
G(ess than tw)-2.75 E(o.)-.11 E
(When cwnd < ssthresh, meaning that the sender is in slo)100.8 476.4 Q
(w-start, the congestion windo)-.275 E 2.75(wi)-.275 G(s)-2.75 E
(increased by one pack)100.8 489.4 Q(et for e)-.11 E -.165(ve)-.275 G
(ry ne).165 E(wly ackno)-.275 E(wledged data pack)-.275 E(et with Ack V)
-.11 E(ector State)-1.221 E 2.75(0\()100.8 502.4 S(not ECN-mark)-2.75 E
(ed\), up to a maximum of Ack Ratio pack)-.11 E(ets per ackno)-.11 E
2.75(wledgement. This)-.275 F(dif)100.8 515.4 Q(fers from TCP')-.275 E
2.75(sh)-.605 G(istorical beha)-2.75 E(vior)-.22 E 2.75(,w)-.44 G
(hich \(in DCCP terms\) w)-2.75 E(ould increase cwnd by)-.11 E
(one per DCCP-Ack recei)100.8 528.4 Q -.165(ve)-.275 G
(d, not by one per pack).165 E(et ne)-.11 E(wly ackno)-.275 E
(wledged by some DCCP-)-.275 E(Ack; b)100.8 541.4 Q
(ut it is in line with TCP')-.22 E 2.75(sb)-.605 G(eha)-2.75 E
(vior with Appropriate Byte Counting [RFC 3465].)-.22 E
(When cwnd >= ssthresh, the congestion windo)100.8 554.4 Q 2.75(wi)-.275
G 2.75(si)-2.75 G(ncreased by one pack)-2.75 E(et for e)-.11 E -.165(ve)
-.275 G(ry).165 E(windo)100.8 567.4 Q 2.75(wo)-.275 G 2.75(fd)-2.75 G
(ata ackno)-2.75 E(wledged without lost or mark)-.275 E(ed pack)-.11 E
2.75(ets. The)-.11 F(cwnd parameter is)2.75 E
(initialized to at most four pack)100.8 580.4 Q(ets for ne)-.11 E 2.75
(wc)-.275 G(onnections, follo)-2.75 E(wing the rules from RFC 3390)-.275
E([RFC 3390]; the ssthresh parameter is initialized to an arbitrarily h\
igh v)100.8 593.4 Q(alue.)-.275 E(Senders MA)100.8 610 Q 2.75(Yu)-1.155
G(se a form of rate-based pacing when sending multiple data pack)-2.75 E
(ets)-.11 E(liberated by a single ack pack)100.8 623 Q
(et, rather than sending all liberated data pack)-.11 E(ets in a single)
-.11 E -.22(bu)100.8 636 S(rst.).22 E F1(5.1.)72 662 Q/F2 13
/Times-Bold@0 SF(Response to Idle and A)5.5 E(pplication-limited P)-.325
E(eriods)-.26 E F0(CCID 2 is designed to follo)100.8 678.6 Q 2.75(wT)
-.275 G(CP')-2.75 E 2.75(sc)-.605 G
(ongestion control mechanisms to the e)-2.75 E(xtent possible,)-.165 E
-.22(bu)100.8 691.6 S 2.75(tT).22 G(CP does not ha)-2.75 E .33 -.165
(ve c)-.22 H
(omplete standardization for its congestion control response to idle)
.165 E(periods \(when no data pack)100.8 704.6 Q
(ets are sent\) or to application-limited periods \(when the sending)
-.11 E(rate is less than that allo)100.8 717.6 Q(wed by cwnd\).)-.275 E
(This section is a brief guide to the standards for)5.5 E(Flo)72 769 Q
(yd/K)-.11 E 275.921(ohler Section)-.385 F 2.75(5.1. [P)2.75 F(age 8])
-.165 E 0 Cg EP
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(25 April 2005)2.75 E(October 2004)105.252 E(TCP in this area.)100.8 85
Q -.165(Fo)100.8 101.6 S 2.75(ri).165 G
(dle periods, RFC 2581 recommends that the TCP sender SHOULD slo)-2.75 E
(w-start after an)-.275 E
(idle period, where an idle period is de\214ned as a period e)100.8
114.6 Q(xceeding the timeout interv)-.165 E(al.)-.275 E([RFC 2861], cur\
rently Experimental, suggests a slightly more moderate mechanism, where)
100.8 127.6 Q(the congestion windo)100.8 140.6 Q 2.75(wi)-.275 G 2.75
(sh)-2.75 G(alv)-2.75 E(ed for e)-.165 E -.165(ve)-.275 G
(ry round-trip time that the sender has remained).165 E(idle.)100.8
153.6 Q(There are currently no standards go)100.8 170.2 Q -.165(ve)-.165
G(rning TCP').165 E 2.75(su)-.605 G(se of the congestion windo)-2.75 E
2.75(wd)-.275 G(uring an)-2.75 E(application-limited period.)100.8 183.2
Q(In particular)5.5 E 2.75(,i)-.44 G 2.75(ti)-2.75 G 2.75(sp)-2.75 G
(ossible for TCP')-2.75 E 2.75(sc)-.605 G(ongestion windo)-2.75 E 2.75
(wt)-.275 G(o)-2.75 E(gro)100.8 196.2 Q 2.75(wq)-.275 G(uite lar)-2.75 E
(ge during a long uncongested period when the sender is application-lim\
ited,)-.198 E(sending at a lo)100.8 209.2 Q 2.75(wr)-.275 G 2.75
(ate. RFC)-2.75 F(2861 essentially suggests that TCP')2.75 E 2.75(sc)
-.605 G(ongestion windo)-2.75 E 2.75(wn)-.275 G(ot be)-2.75 E(increased\
 during application-limited periods, when the congestion windo)100.8
222.2 Q 2.75(wi)-.275 G 2.75(sn)-2.75 G(ot being)-2.75 E
(fully utilized.)100.8 235.2 Q/F1 11/Times-Bold@0 SF(5.2.)72 261.2 Q/F2
13/Times-Bold@0 SF(Response to Data Dr)5.5 E(opped and Slo)-.234 E 3.25
(wR)-.13 G(ecei)-3.25 E -.13(ve)-.13 G(r).13 E F0(As described in [DCCP\
], the Data Dropped option lets an endpoint declare that a pack)100.8
277.8 Q(et)-.11 E -.11(wa)100.8 290.8 S 2.75(sd).11 G
(ropped at the end host before deli)-2.75 E -.165(ve)-.275 G
(ry to the application -- for instance, because of).165 E
(corruption or recei)100.8 303.8 Q .33 -.165(ve b)-.275 H(uf)-.055 E
(fer o)-.275 E -.165(ve)-.165 G(r\215o).165 E 4.18 -.715(w. C)-.275 H
(CID 2 senders respond to pack).715 E(ets ackno)-.11 E(wledged as)-.275
E(Data Dropped as described in [DCCP], with the follo)100.8 316.8 Q
(wing further clari\214cations.)-.275 E<83>100.8 333.4 Q F1(Dr)12.65 E
(op Code 2 \("r)-.198 E(ecei)-.198 E .22 -.11(ve b)-.11 H(uffer dr)-.11
E(op"\).)-.198 E F0(The congestion windo)5.5 E 2.75(w")-.275 G
(cwnd" is reduced by)-2.75 E(one for each pack)117.3 346.4 Q(et ne)-.11
E(wly ackno)-.275 E(wledged as Drop Code 2, e)-.275 E
(xcept that it is ne)-.165 E -.165(ve)-.275 G(r).165 E(reduced belo)
117.3 359.4 Q 2.75(wo)-.275 G(ne.)-2.75 E<83>100.8 376 Q F1(Exiting slo)
12.65 E(w-start.)-.11 E F0(The sender MUST e)5.5 E(xit slo)-.165 E 2.75
(ws)-.275 G(tart whene)-2.75 E -.165(ve)-.275 G 2.75(ri).165 G 2.75(tr)
-2.75 G(ecei)-2.75 E -.165(ve)-.275 G 2.75(sar).165 G(ele)-2.75 E -.275
(va)-.275 G(nt).275 E(Data Dropped or Slo)117.3 389 Q 2.75(wR)-.275 G
(ecei)-2.75 E -.165(ve)-.275 G 2.75(ro).165 G(ption.)-2.75 E F1(5.3.)72
415 Q F2 -.13(Pa)5.5 G(ck).13 E(et Size)-.13 E F0
(CCID 2 is optimized for applications that generally use a \214x)100.8
431.6 Q(ed pack)-.165 E(et size, and that v)-.11 E(ary)-.275 E
(their sending rate in pack)100.8 444.6 Q
(ets per second in response to congestion.)-.11 E(CCID 2 is not)5.5 E
(appropriate for applications that require a \214x)100.8 457.6 Q
(ed interv)-.165 E(al of time between pack)-.275 E(ets, and v)-.11 E
(ary)-.275 E(their pack)100.8 470.6 Q(et size instead of their pack)-.11
E(et rate in response to congestion.)-.11 E(CCID 2 maintains a)5.5 E
(congestion windo)100.8 483.6 Q 2.75(wi)-.275 G 2.75(np)-2.75 G(ack)
-2.75 E(ets, and does not increase the congestion windo)-.11 E 2.75(wi)
-.275 G 2.75(nr)-2.75 G(esponse to)-2.75 E 2.75(ad)100.8 496.6 S
(ecrease in the pack)-2.75 E(et size.)-.11 E(Ho)5.5 E(we)-.275 E -.165
(ve)-.275 G .88 -.44(r, s).165 H
(ome attention might be required for applications).44 E
(using CCID 2 that v)100.8 509.6 Q(ary their pack)-.275 E
(et size not in response to congestion, b)-.11 E(ut in response to)-.22
E(other application-le)100.8 522.6 Q -.165(ve)-.275 G 2.75(lr).165 G
(equirements.)-2.75 E(CCID 2 implementations MA)100.8 539.2 Q 2.75(Yc)
-1.155 G(heck for applications that appear to be manipulating the)-2.75
E(pack)100.8 552.2 Q(et size inappropriately)-.11 E 5.5(.F)-.715 G(or e)
-5.665 E(xample, an application might send small pack)-.165 E(ets for a)
-.11 E(while, b)100.8 565.2 Q(uilding up a f)-.22 E
(ast rate, then switch to lar)-.11 E(ge pack)-.198 E(ets to tak)-.11 E
2.75(ea)-.11 G(dv)-2.75 E(antage of the f)-.275 E(ast rate.)-.11 E(\(Pr\
eliminary simulations indicate that applications may not be able to inc\
rease their o)100.8 578.2 Q -.165(ve)-.165 G(rall).165 E
(transfer rates this w)100.8 591.2 Q(ay)-.11 E 2.75(,s)-.715 G 2.75(oi)
-2.75 G 2.75(ti)-2.75 G 2.75(sn)-2.75 G
(ot clear this manipulation will occur in practice [V03].\))-2.75 E F1
(6.)72 617.2 Q/F3 14/Times-Bold@0 SF(Ackno)5.5 E(wledgements)-.14 E F0
(CCID 2 ackno)100.8 633.8 Q
(wledgements are generally paced by the sender')-.275 E 2.75(sd)-.605 G
(ata pack)-2.75 E 2.75(ets. Each)-.11 F(required ackno)100.8 646.8 Q
(wledgement MUST contain Ack V)-.275 E(ector options that declare e)
-1.221 E(xactly which)-.165 E(pack)100.8 659.8 Q(ets arri)-.11 E -.165
(ve)-.275 G(d, and whether those pack).165 E(ets were ECN-mark)-.11 E
2.75(ed. Ackno)-.11 F(wledgement data in)-.275 E(the Ack V)100.8 672.8 Q
(ector options SHOULD generally co)-1.221 E -.165(ve)-.165 G 2.75(rt)
.165 G(he recei)-2.75 E -.165(ve)-.275 G(r').165 E 2.75(se)-.605 G
(ntire Ackno)-2.75 E(wledgement)-.275 E -.44(Wi)100.8 685.8 S(ndo).44 E
2.75(w\()-.275 G(Section 11.4.2 of [DCCP]\).)-2.75 E
(CCID 2 senders use DCCP')100.8 702.4 Q 2.75(sA)-.605 G
(ck Ratio feature to in\215uence the rate at which DCCP-Ack)-2.75 E
(pack)100.8 715.4 Q(ets are generated, thus controlling re)-.11 E -.165
(ve)-.275 G(rse-path congestion.).165 E(This dif)5.5 E(fers from TCP)
-.275 E(,)-1.221 E(Flo)72 769 Q(yd/K)-.11 E 284.171(ohler Section)-.385
F 2.75(6. [P)2.75 F(age 9])-.165 E 0 Cg EP
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(25 April 2005)2.75 E(October 2004)105.252 E
(which presently has no congestion control for pure ackno)100.8 85 Q
(wledgement traf)-.275 E 2.75(\214c. CCID)-.275 F(2')2.75 E(s)-.605 E
(re)100.8 98 Q -.165(ve)-.275 G(rse-path congestion control does not tr\
y to be TCP-friendly; it just tries to a).165 E -.22(vo)-.22 G(id).22 E
(congestion collapse, and to be some)100.8 111 Q
(what better than TCP in the presence of a high pack)-.275 E(et)-.11 E
(loss or mark rate on the re)100.8 124 Q -.165(ve)-.275 G(rse path.).165
E(The def)5.5 E(ault Ack Ratio is tw)-.11 E(o, and CCID 2 with this)-.11
E(Ack Ratio beha)100.8 137 Q -.165(ve)-.22 G 2.75(sl).165 G(ik)-2.75 E
2.75(eT)-.11 G(CP with delayed acks.)-2.75 E
(Section 11.3 of [DCCP] describes the Ack)5.5 E
(Ratio in more detail, including its relationship to ackno)100.8 150 Q
(wledgement pacing and DCCP-)-.275 E(DataAck pack)100.8 163 Q 2.75
(ets. Section)-.11 F(6.1.1 belo)2.75 E 2.75(wd)-.275 G
(escribes the sender')-2.75 E 2.75(sd)-.605 G(etection of lost or mark)
-2.75 E(ed)-.11 E(ackno)100.8 176 Q(wledgements, and Section 6.1.2 gi)
-.275 E -.165(ve)-.275 G 2.75(st).165 G(he sender')-2.75 E 2.75(sr)-.605
G(ules for changing the Ack Ratio.)-2.75 E/F1 11/Times-Bold@0 SF(6.1.)72
202 Q/F2 13/Times-Bold@0 SF(Congestion Contr)5.5 E(ol on Ackno)-.234 E
(wledgements)-.13 E F0(When Ack Ratio is R, the recei)100.8 218.6 Q
-.165(ve)-.275 G 2.75(rs).165 G(ends one DCCP-Ack pack)-2.75 E
(et per R data pack)-.11 E(ets, more)-.11 E(or less.)100.8 231.6 Q
(Since the sender sends cwnd data pack)5.5 E
(ets per round-trip time, the)-.11 E(ackno)100.8 244.6 Q
(wledgement rate equals cwnd/R DCCP-Ack pack)-.275 E
(ets per round-trip time.)-.11 E(The sender)5.5 E
(modi\214es R so as to k)100.8 257.6 Q(eep the ackno)-.11 E
(wledgement rate roughly TCP-friendly)-.275 E 2.75(,b)-.715 G 2.75(ym)
-2.75 G(onitoring)-2.75 E(the ackno)100.8 270.6 Q
(wledgement stream for lost and mark)-.275 E(ed DCCP-Ack pack)-.11 E
2.75(ets. F)-.11 F(or e)-.165 E -.165(ve)-.275 G(ry R).165 E(TT)-.66 E
(containing a DCCP-Ack congestion e)100.8 283.6 Q -.165(ve)-.275 G
(nt \(that is, a lost or mark).165 E(ed DCCP-Ack\), the sender)-.11 E
(halv)100.8 296.6 Q(es the ackno)-.165 E
(wledgement rate by doubling Ack Ratio; for e)-.275 E -.165(ve)-.275 G
(ry R).165 E(TT containing no)-.66 E(DCCP-Ack congestion e)100.8 309.6 Q
-.165(ve)-.275 G(nt, it additi).165 E -.165(ve)-.275 G
(ly increases the ackno).165 E(wledgement rate through)-.275 E
(gradual decreases in Ack Ratio.)100.8 322.6 Q F1 2.75(6.1.1. Detecting)
72 348.6 R(Lost and Mark)2.75 E(ed Ackno)-.11 E(wledgements)-.11 E F0
(All pack)100.8 365.2 Q(ets from the recei)-.11 E -.165(ve)-.275 G 2.75
(rc).165 G(ontain sequence numbers, so the sender can detect both)-2.75
E(losses and marks on the recei)100.8 378.2 Q -.165(ve)-.275 G(r').165 E
2.75(sp)-.605 G(ack)-2.75 E 2.75(ets. The)-.11 F(sender infers recei)
2.75 E -.165(ve)-.275 G 2.75(rp).165 G(ack)-2.75 E(et loss in the)-.11 E
(same w)100.8 391.2 Q(ay as it infers losses of its data pack)-.11 E
(ets: a pack)-.11 E(et from the recei)-.11 E -.165(ve)-.275 G 2.75(ri)
.165 G 2.75(sc)-2.75 G(onsidered lost)-2.75 E(after at least NUMDUP)
100.8 404.2 Q -.44(AC)-1.012 G 2.75(Kp).44 G(ack)-2.75 E
(ets with greater sequence numbers ha)-.11 E .33 -.165(ve b)-.22 H
(een recei).165 E -.165(ve)-.275 G(d.).165 E(DCCP-Ack pack)100.8 420.8 Q
(ets are generally small, so the)-.11 E 2.75(ym)-.165 G
(ight impose less load on congested)-2.75 E(netw)100.8 433.8 Q
(ork links than DCCP-Data and DCCP-DataAck pack)-.11 E 2.75(ets. F)-.11
F(or this reason, Ack Ratio)-.165 E
(depends on losses and marks on the recei)100.8 446.8 Q -.165(ve)-.275 G
(r').165 E 2.75(sn)-.605 G(on-data pack)-2.75 E(ets, not on aggre)-.11 E
-.055(ga)-.165 G(te losses).055 E(and marks on all of the recei)100.8
459.8 Q -.165(ve)-.275 G(r').165 E 2.75(sp)-.605 G(ack)-2.75 E 2.75
(ets. The)-.11 F(non-data pack)2.75 E(et cate)-.11 E
(gory consists of those)-.165 E(pack)100.8 472.8 Q(et types that cannot\
 carry application data: DCCP-Ack, DCCP-Close, DCCP-)-.11 E
(CloseReq, DCCP-Reset, DCCP-Sync, and DCCP-SyncAck.)100.8 485.8 Q
(The sender can easily)5.5 E
(distinguish non-data marks from other marks.)100.8 498.8 Q
(This is harder for losses, though, since the)5.5 E(sender can')100.8
511.8 Q 2.75(ta)-.198 G -.11(lwa)-2.75 G(ys kno).11 E 2.75(ww)-.275 G
(hether a lost pack)-2.75 E(et carried data.)-.11 E
(Unless it has better)5.5 E(information, the sender SHOULD assume, for \
the purpose of Ack Ratio calculation, that)100.8 524.8 Q -2.365 -.275
(ev e)100.8 537.8 T(ry lost pack).275 E(et w)-.11 E(as a non-data pack)
-.11 E 2.75(et. Better)-.11 F(information is a)2.75 E -.275(va)-.22 G
(ilable via DCCP').275 E 2.75(sN)-.605 G(DP)-2.75 E
(Count option, if necessary)100.8 550.8 Q 5.5(.\()-.715 G
(Appendix B discusses the costs of mistaking data pack)-5.5 E(et loss)
-.11 E(for non-data pack)100.8 563.8 Q(et loss.\))-.11 E 2.75(Ar)100.8
580.4 S(ecei)-2.75 E -.165(ve)-.275 G 2.75(rt).165 G
(hat implements its o)-2.75 E(wn ackno)-.275 E
(wledgement congestion control SHOULD NO)-.275 E(T)-.44 E
(reduce its DCCP-Ack ackno)100.8 593.4 Q
(wledgement rate due to losses or marks on its data pack)-.275 E(ets.)
-.11 E F1 2.75(6.1.2. Changing)72 619.4 R(Ack Ratio)2.75 E F0
(Ack Ratio al)100.8 636 Q -.11(wa)-.11 G
(ys meets three constraints: \(1\) Ack Ratio is an inte).11 E(ger)-.165
E 5.5(.\()-.605 G(2\) Ack Ratio does)-5.5 E(not e)100.8 649 Q
(xceed cwnd/2, rounded up, e)-.165 E(xcept that Ack Ratio 2 is al)-.165
E -.11(wa)-.11 G(ys acceptable.).11 E(\(3\) Ack)5.5 E(Ratio is tw)100.8
662 Q 2.75(oo)-.11 G 2.75(rm)-2.75 G(ore for a congestion windo)-2.75 E
2.75(wo)-.275 G 2.75(ff)-2.75 G(our or more pack)-2.75 E(ets.)-.11 E
(The sender changes Ack Ratio within those constraints as follo)100.8
678.6 Q 2.75(ws. F)-.275 F(or each congestion)-.165 E(windo)100.8 691.6
Q 2.75(wo)-.275 G 2.75(fd)-2.75 G(ata with lost or mark)-2.75 E
(ed DCCP-Ack pack)-.11 E(ets, Ack Ratio is doubled; and for)-.11 E
(each cwnd/\(R^2 - R\) consecuti)100.8 704.6 Q .33 -.165(ve c)-.275 H
(ongestion windo).165 E(ws of data with no lost or mark)-.275 E(ed)-.11
E(DCCP-Ack pack)100.8 717.6 Q(ets, Ack Ratio is decreased by 1.)-.11 E
(\(See Appendix A for the deri)5.5 E -.275(va)-.275 G(tion.\)).275 E
(Flo)72 769 Q(yd/K)-.11 E 262.171(ohler Section)-.385 F 2.75(6.1.2. [P)
2.75 F(age 10])-.165 E 0 Cg EP
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(25 April 2005)2.75 E(October 2004)105.252 E
(Changes in Ack Ratio are signalled through feature ne)100.8 85 Q
(gotiation; see Section 11.3 of)-.165 E([DCCP].)100.8 98 Q -.165(Fo)
100.8 114.6 S 2.75(rac).165 G(onstant congestion windo)-2.75 E 1.43
-.715(w, t)-.275 H(his gi).715 E -.165(ve)-.275 G 2.75(sa).165 G 2.75
(nA)-2.75 G(ck sending rate that is roughly TCP-)-2.75 E(friendly)100.8
127.6 Q 5.5(.O)-.715 G 2.75(fc)-5.5 G(ourse, cwnd usually v)-2.75 E
(aries o)-.275 E -.165(ve)-.165 G 2.75(rt).165 G
(ime; the dynamics will be rather comple)-2.75 E(x,)-.165 E -.22(bu)
100.8 140.6 S 2.75(tr).22 G(oughly TCP-friendly)-2.75 E 5.5(.W)-.715 G
2.75(er)-6.38 G(ecommend that the sender use the most recent v)-2.75 E
(alue of)-.275 E
(cwnd when determining whether to decrease Ack Ratio by 1.)100.8 153.6 Q
(The sender need not k)100.8 170.2 Q
(eep Ack Ratio completely up to date.)-.11 E -.165(Fo)5.5 G 2.75(ri).165
G(nstance, it MA)-2.75 E 2.75(Yr)-1.155 G(ate-limit)-2.75 E
(Ack Ratio rene)100.8 183.2 Q(gotiations to once e)-.165 E -.165(ve)
-.275 G(ry four or \214v).165 E 2.75(er)-.165 G
(ound-trip times, or to once e)-2.75 E -.165(ve)-.275 G(ry).165 E
(second or tw)100.8 196.2 Q 2.75(o. The)-.11 F
(sender SHOULD not attempt Ack Ratio rene)2.75 E
(gotiations more than once)-.165 E(per round-trip time.)100.8 209.2 Q
(Additionally)5.5 E 2.75(,i)-.715 G 2.75(tM)-2.75 G 2.31 -1.155(AY b)
-2.75 H(ound Ack Ratio belo)1.155 E 2.75(wb)-.275 G 2.75(yt)-2.75 G -.11
(wo)-2.75 G 2.75(,o).11 G 2.75(ri)-2.75 G 2.75(tM)-2.75 G 2.31 -1.155
(AY s)-2.75 H(et)1.155 E
(Ack Ratio to one for half-connections with persistent congestion windo)
100.8 222.2 Q(ws of 1 or 2)-.275 E(pack)100.8 235.2 Q(ets.)-.11 E
(Putting it all together)100.8 251.8 Q 2.75(,t)-.44 G(he recei)-2.75 E
-.165(ve)-.275 G 2.75(ra).165 G -.11(lwa)-2.75 G
(ys sends at least one ackno).11 E(wledgement per windo)-.275 E(w)-.275
E(of data when cwnd = 1, and at least tw)100.8 264.8 Q 2.75(oa)-.11 G
(ckno)-2.75 E(wledgements per windo)-.275 E 2.75(wo)-.275 G 2.75(fd)
-2.75 G(ata otherwise.)-2.75 E(Thus, the recei)100.8 277.8 Q -.165(ve)
-.275 G 2.75(rc).165 G(ould be sending tw)-2.75 E 2.75(oa)-.11 G
(ck pack)-2.75 E(ets per windo)-.11 E 2.75(wo)-.275 G 2.75(fd)-2.75 G
(ata e)-2.75 E -.165(ve)-.275 G 2.75(ni).165 G 2.75(nt)-2.75 G(he f)
-2.75 E(ace of)-.11 E -.165(ve)100.8 290.8 S(ry hea).165 E
(vy congestion on the re)-.22 E -.165(ve)-.275 G(rse path.).165 E 1.76
-.88(We w)5.5 H(ould note, ho).77 E(we)-.275 E -.165(ve)-.275 G .88 -.44
(r, t).165 H(hat if congestion is).44 E(suf)100.8 303.8 Q
(\214ciently hea)-.275 E(vy that all of the ack pack)-.22 E
(ets are dropped, then the sender f)-.11 E(alls back on an)-.11 E -.165
(ex)100.8 316.8 S(ponentially-back).165 E(ed-of)-.11 E 2.75(ft)-.275 G
(imeout, as in TCP)-2.75 E 5.5(.T)-1.221 G(hus, if congestion is suf)
-5.5 E(\214ciently hea)-.275 E(vy on)-.22 E(the re)100.8 329.8 Q -.165
(ve)-.275 G
(rse path, then the sender reduces its sending rate on the forw).165 E
(ard path, which)-.11 E(reduces the rate on the re)100.8 342.8 Q -.165
(ve)-.275 G(rse path as well.).165 E/F1 11/Times-Bold@0 SF(6.2.)72 368.8
Q/F2 13/Times-Bold@0 SF(Ackno)5.5 E(wledgements of Ackno)-.13 E
(wledgements)-.13 E F0(An acti)100.8 385.4 Q .33 -.165(ve s)-.275 H
(ender DCCP A MUST occasionally ackno).165 E(wledge its peer DCCP B')
-.275 E(s)-.605 E(ackno)100.8 398.4 Q
(wledgements, so that DCCP B can free up Ack V)-.275 E(ector state.)
-1.221 E(When both half-)5.5 E(connections are acti)100.8 411.4 Q -.165
(ve)-.275 G 2.75(,A).165 G 1.21 -.605('s a)-3.971 H(ckno).605 E
(wledgements of B')-.275 E 2.75(sa)-.605 G(ckno)-2.75 E
(wledgements are automatically)-.275 E(contained in A)100.8 424.4 Q 1.21
-.605('s a)-1.221 H(ckno).605 E(wledgements of B')-.275 E 2.75(sd)-.605
G(ata. If the B-to-A half-connection is quiescent,)-2.75 E(ho)100.8
437.4 Q(we)-.275 E -.165(ve)-.275 G .88 -.44(r, D).165 H
(CCP A must occasionally send ackno).44 E(wledgements proacti)-.275 E
-.165(ve)-.275 G(ly).165 E 2.75(,s)-.715 G(uch as by)-2.75 E
(sending a DCCP-DataAck pack)100.8 450.4 Q(et that includes an Ackno)
-.11 E(wledgement Number in the)-.275 E(header)100.8 463.4 Q(.)-.605 E
(An acti)100.8 480 Q .33 -.165(ve s)-.275 H(ender SHOULD ackno).165 E
(wledge the recei)-.275 E -.165(ve)-.275 G(r').165 E 2.75(sa)-.605 G
(ckno)-2.75 E(wledgements at least once)-.275 E(per congestion windo)
100.8 493 Q 1.43 -.715(w. O)-.275 H 2.75(fc).715 G(ourse, the sender')
-2.75 E 2.75(sa)-.605 G(pplication might f)-2.75 E(all silent.)-.11 E
(This is no)5.5 E
(problem; when neither side is sending data, a sender can w)100.8 506 Q
(ait arbitrarily long before)-.11 E(sending an ack.)100.8 519 Q F1 2.75
(6.2.1. Determining)72 545 R(Quiescence)2.75 E F0(This section refers t\
o quiescence in the DCCP sense \(see section 8.1 of [DCCP]\): Ho)100.8
561.6 Q(w)-.275 E(does a CCID 2 recei)100.8 574.6 Q -.165(ve)-.275 G
2.75(rd).165 G(etermine that the corresponding sender is not sending an)
-2.75 E 2.75(yd)-.165 G(ata?)-2.75 E
(Let T equal the greater of 0.2 seconds and tw)100.8 591.2 Q 2.75(or)
-.11 G(ound-trip times.)-2.75 E(\(The recei)5.5 E -.165(ve)-.275 G 2.75
(rm).165 G(ay kno)-2.75 E(w)-.275 E(the round-trip time in its role as \
the sender for the other half-connection; or if it does not, it)100.8
604.2 Q(should use an estimated R)100.8 617.2 Q(TT of 0.1 seconds.\))
-.66 E(Once the sender ackno)5.5 E(wledges the recei)-.275 E -.165(ve)
-.275 G(r').165 E(s)-.605 E(Ack V)100.8 630.2 Q(ectors, and the sender \
has not sent additional data for at least T seconds, the recei)-1.221 E
-.165(ve)-.275 G(r).165 E(can infer that the sender is quiescent.)100.8
643.2 Q(More precisely)5.5 E 2.75(,t)-.715 G(he recei)-2.75 E -.165(ve)
-.275 G 2.75(ri).165 G(nfers that the sender has)-2.75 E
(gone quiescent when at least T seconds ha)100.8 656.2 Q .33 -.165(ve p)
-.22 H(assed without recei).165 E(ving an)-.275 E 2.75(yd)-.165 G
(ata from the)-2.75 E(sender)100.8 669.2 Q 2.75(,a)-.44 G
(nd the sender has ackno)-2.75 E(wledged recei)-.275 E -.165(ve)-.275 G
2.75(rA).165 G(ck V)-2.75 E(ectors co)-1.221 E -.165(ve)-.165 G
(ring all data pack).165 E(ets)-.11 E(recei)100.8 682.2 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 -.605
(r.).165 G(Flo)72 769 Q(yd/K)-.11 E 262.171(ohler Section)-.385 F 2.75
(6.2.1. [P)2.75 F(age 11])-.165 E 0 Cg EP
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(25 April 2005)2.75 E(October 2004)105.252 E/F1 11/Times-Bold@0 SF(7.)72
85 Q/F2 14/Times-Bold@0 SF(Explicit Congestion Noti\214cation)5.5 E F0(\
Explicit Congestion Noti\214cation \(ECN\) [RFC 3168] may be used with \
CCID 2.)100.8 101.6 Q(If ECN is)5.5 E
(used, then the ECN Nonce will automatically be used for the data pack)
100.8 114.6 Q(ets, follo)-.11 E(wing the)-.275 E
(speci\214cation for the ECN Nonce in TCP [RFC 3540].)100.8 127.6 Q
(The sender sets either the ECT\(0\) or)5.5 E
(ECT\(1\) codepoint in the IP header on Data pack)100.8 140.6 Q 2.75
(ets. Information)-.11 F(about mark)2.75 E(ed pack)-.11 E(ets is)-.11 E
(returned in the Ack V)100.8 153.6 Q(ector)-1.221 E 5.5(.B)-.605 G
(ecause the information in the Ack V)-5.5 E(ector is reliably)-1.221 E(\
transferred, DCCP does not need the TCP \215ags of ECN-Echo and Congest\
ion W)100.8 166.6 Q(indo)-.44 E(w)-.275 E(Reduced.)100.8 179.6 Q -.165
(Fo)100.8 196.2 S 2.75(ru).165 G(nmark)-2.75 E(ed data pack)-.11 E
(ets, the recei)-.11 E -.165(ve)-.275 G 2.75(rc).165 G
(omputes the ECN Nonce Echo as in [RFC 3540],)-2.75 E
(and returns it as part of its Ack V)100.8 209.2 Q(ector options.)-1.221
E(The sender SHOULD check these ECN)5.5 E(Nonce Echoes ag)100.8 222.2 Q
(ainst the e)-.055 E(xpected v)-.165 E(alues, thus protecting ag)-.275 E
(ainst the accidental or)-.055 E(malicious concealment of mark)100.8
235.2 Q(ed pack)-.11 E(ets.)-.11 E(Because CCID 2 ackno)100.8 251.8 Q
(wledgements are congestion-controlled, ECN may also be used for)-.275 E
(its ackno)100.8 264.8 Q 2.75(wledgements. In)-.275 F
(this case we do not mak)2.75 E 2.75(eu)-.11 G
(se of the ECN Nonce, because it)-2.75 E -.11(wo)100.8 277.8 S
(uld not be easy to pro).11 E(vide protection ag)-.165 E
(ainst the concealment of mark)-.055 E(ed ack pack)-.11 E(ets by)-.11 E
(the sender)100.8 290.8 Q 2.75(,a)-.44 G
(nd because the sender does not ha)-2.75 E .33 -.165(ve m)-.22 H
(uch moti).165 E -.275(va)-.275 G(tion for lying about the mark).275 E
(rate on ackno)100.8 303.8 Q(wledgements.)-.275 E F1(8.)72 329.8 Q F2
(Options and F)5.5 E(eatur)-.35 E(es)-.252 E F0(DCCP')100.8 346.4 Q 2.75
(sA)-.605 G(ck V)-2.75 E
(ector option, and its ECN Capable, Ack Ratio, and Send Ack V)-1.221 E
(ector)-1.221 E(features, are rele)100.8 359.4 Q -.275(va)-.275 G
(nt for CCID 2.).275 E F1(9.)72 385.4 Q F2(Security Considerations)5.5 E
F0(Security considerations for DCCP ha)100.8 402 Q .33 -.165(ve b)-.22 H
(een discussed in [DCCP], and security).165 E(considerations for TCP ha)
100.8 415 Q .33 -.165(ve b)-.22 H(een discussed in [RFC 2581].).165 E
([RFC 2581] discusses w)100.8 431.6 Q(ays that an attack)-.11 E
(er could impair the performance of a TCP)-.11 E
(connection by dropping pack)100.8 444.6 Q(ets, or by for)-.11 E(ging e)
-.198 E(xtra duplicate ackno)-.165 E(wledgements or)-.275 E(ackno)100.8
457.6 Q(wledgements for ne)-.275 E 2.75(wd)-.275 G 2.75(ata. W)-2.75 F
2.75(ea)-.88 G(re not a)-2.75 E -.11(wa)-.165 G(re of an).11 E 2.75(yn)
-.165 G .55 -.275(ew s)-2.75 H(ecurity considerations).275 E
(created by this document in its use of TCP-lik)100.8 470.6 Q 2.75(ec)
-.11 G(ongestion control.)-2.75 E F1(10.)72 496.6 Q F2(IAN)5.5 E 3.5(AC)
-.28 G(onsiderations)-3.5 E F0(This speci\214cation de\214nes the v)
100.8 513.2 Q(alue 2 in the DCCP CCID namespace managed by IAN)-.275 E
(A.)-.385 E(This assignment is also mentioned in [DCCP].)100.8 526.2 Q
(CCID 2 also introduces the follo)100.8 542.8 Q
(wing three sets of numbers whose v)-.275 E(alues should be)-.275 E
(allocated by IAN)100.8 555.8 Q 2.75(A. F)-.385 F(ollo)-.165 E
(wing the policies outlined in [RFC 2434], these sets of numbers)-.275 E
(are allocated through an IETF Consensus action, with the speci\214ed e)
100.8 568.8 Q(xceptions for)-.165 E -.165(ex)100.8 581.8 S
(perimental and testing use [RFC 3692].).165 E 12.65<8343>100.8 598.4 S
(CID 2-speci\214c option numbers 128-183, 191-247, and 255 are allocate\
d through an)-12.65 E(IETF Consensus action.)117.3 611.4 Q
(Option numbers 184-190 and 248-254 are reserv)5.5 E(ed for)-.165 E
-.165(ex)117.3 624.4 S(perimental and testing use.).165 E 12.65<8343>
100.8 641 S(CID 2-speci\214c feature numbers 128-183, 191-247, and 255 \
are allocated through an)-12.65 E(IETF Consensus action.)117.3 654 Q
(Feature numbers 184-190 and 248-254 are reserv)5.5 E(ed for)-.165 E
-.165(ex)117.3 667 S(perimental and testing use.).165 E 12.65<8343>100.8
683.6 S(CID 2-speci\214c Reset Codes 128-183, 191-247, and 255 are allo\
cated through an IETF)-12.65 E(Consensus action.)117.3 696.6 Q
(Reset Codes 184-190 and 248-254 are reserv)5.5 E(ed for e)-.165 E
(xperimental)-.165 E(and testing use.)117.3 709.6 Q(Flo)72 769 Q(yd/K)
-.11 E 273.171(ohler Section)-.385 F 2.75(10. [P)2.75 F(age 12])-.165 E
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(25 April 2005)2.75 E(October 2004)105.252 E/F1 11/Times-Bold@0 SF(11.)
72 85 Q/F2 14/Times-Bold@0 SF(Thanks)5.5 E F0 1.76 -.88(We t)100.8 101.6
T(hank Mark Handle).88 E 2.75(ya)-.165 G(nd Jitendra P)-2.75 E(adh)-.165
E(ye for their help in de\214ning CCID 2.)-.055 E 1.76 -.88(We a)5.5 H
(lso).88 E(thank Mark Allman, Aaron F)100.8 114.6 Q
(alk, Nils-Erik Mattsson, Gre)-.165 E 2.75(gM)-.165 G(inshall, Arun V)
-2.75 E(enkataramani,)-1.221 E(Magnus W)100.8 127.6 Q
(esterlund, and members of the DCCP W)-.88 E
(orking Group for feedback on this)-.88 E(document.)100.8 140.6 Q F1(A.)
72 166.6 Q F2 -.35(Ap)5.5 G(pendix: Deri).35 E -.14(va)-.14 G
(tion of Ack Ratio Decr).14 E(ease)-.252 E F0(This section justi\214es \
the algorithm for increasing and decreasing the Ack Ratio gi)100.8 183.2
Q -.165(ve)-.275 G 2.75(ni).165 G(n)-2.75 E(Section 6.1.2.)100.8 196.2 Q
(The congestion a)100.8 212.8 Q -.22(vo)-.22 G(idance phase of TCP halv)
.22 E(es the cwnd for e)-.165 E -.165(ve)-.275 G(ry windo).165 E 2.75
(ww)-.275 G(ith)-2.75 E 2.75(congestion. Similarly)100.8 225.8 R 2.75
(,C)-.715 G(CID 2 doubles Ack Ratio for e)-2.75 E -.165(ve)-.275 G
(ry windo).165 E 2.75(ww)-.275 G(ith congestion on)-2.75 E
(the return path, roughly halving the DCCP-Ack sending rate.)100.8 238.8
Q(The congestion a)100.8 255.4 Q -.22(vo)-.22 G
(idance phase of TCP increases cwnd by one MSS for e).22 E -.165(ve)
-.275 G(ry congestion-).165 E(free windo)100.8 268.4 Q 4.18 -.715(w. A)
-.275 H(pplying this congestion a).715 E -.22(vo)-.22 G(idance beha).22
E(vior to ackno)-.22 E(wledgement traf)-.275 E(\214c,)-.275 E(this w)
100.8 281.4 Q(ould correspond to increasing the number of DCCP-Ack pack)
-.11 E(ets per windo)-.11 E 2.75(wb)-.275 G 2.75(yo)-2.75 G(ne)-2.75 E
(after e)100.8 294.4 Q -.165(ve)-.275 G(ry congestion-free windo).165 E
2.75(wo)-.275 G 2.75(fD)-2.75 G(CCP-Ack pack)-2.75 E 2.75(ets. W)-.11 F
2.75(ec)-.88 G(annot achie)-2.75 E .33 -.165(ve t)-.275 H(his e).165 E
(xactly)-.165 E(using Ack Ratio, since it is an inte)100.8 307.4 Q(ger)
-.165 E 5.5(.I)-.605 G
(nstead, we must decrease Ack Ratio by one after K)-5.5 E(windo)100.8
320.4 Q(ws ha)-.275 E .33 -.165(ve b)-.22 H
(een sent without a congestion e).165 E -.165(ve)-.275 G(nt on the re)
.165 E -.165(ve)-.275 G(rse path, where K is chosen).165 E
(so that the long-term number of DCCP-Ack pack)100.8 333.4 Q
(ets per congestion windo)-.11 E 2.75(wi)-.275 G 2.75(sr)-2.75 G(oughly)
-2.75 E(TCP-friendly)100.8 346.4 Q 2.75(,f)-.715 G(ollo)-2.75 E
(wing AIMD congestion control.)-.275 E
(In CCID 2, rough TCP-friendliness for the ack traf)100.8 363 Q
(\214c can be accomplished by setting K to)-.275 E
(cwnd/\(R^2 - R\), where R is the current Ack Ratio.)100.8 376 Q
(This result w)100.8 392.6 Q(as calculated as follo)-.11 E(ws:)-.275 E
/F3 11/Courier@0 SF 6.6(R=A)147 411.6 S
(ck Ratio = # data packets / ack packets, and)-6.6 E 6.6(W=C)147 424.6 S
(ongestion Window = # data packets / window, so)-6.6 E
(W/R = # ack packets / window.)147 437.6 Q
(Requirement: Increase W/R by 1 per congestion-free window.)127.2 463.6
Q(Since we can only reduce R by increments of one, we find K)127.2 476.6
Q(so that, after K congestion-free windows,)127.2 489.6 Q
(W/R + K would equal W/\(R-1\).)127.2 502.6 Q
(\(W/R\) + K = W/\(R-1\), so)127.2 528.6 Q 6.6(K=W)180 541.6 S
(/\(R-1\) - W/R = W/\(R^2 - R\).)-6.6 E F1(B.)72 573.6 Q F2 -.35(Ap)5.5
G(pendix: Cost of Loss Infer).35 E(ence Mistak)-.252 E(es to Ack Ratio)
-.14 E F0(As discussed in Section 6.1.1, the sender often cannot determ\
ine whether lost pack)100.8 590.2 Q(ets)-.11 E(carried data.)100.8 603.2
Q(This hinders its ability to separate non-data loss e)5.5 E -.165(ve)
-.275 G(nts from other loss e).165 E -.165(ve)-.275 G(nts.).165 E(In th\
e absence of better information, the sender assumes, for the purpose of\
 Ack Ratio)100.8 616.2 Q(calculation, that all lost pack)100.8 629.2 Q
(ets were non-data pack)-.11 E 2.75(ets. This)-.11 F(may o)2.75 E -.165
(ve)-.165 G(restimate the non-).165 E(data loss e)100.8 642.2 Q -.165
(ve)-.275 G
(nt rate, which can lead to a too-high Ack Ratio, and thus a too-slo)
.165 E(w)-.275 E(ackno)100.8 655.2 Q(wledgement rate.)-.275 E(All ackno)
5.5 E(wledgement information will still get through -- DCCP)-.275 E
(ackno)100.8 668.2 Q(wledgements are reliable -- b)-.275 E(ut ackno)-.22
E(wledgement information will arri)-.275 E .33 -.165(ve i)-.275 H 2.75
(nab).165 G(urstier)-2.97 E -.11(fa)100.8 681.2 S 2.75(shion. Absent).11
F(some form of rate-based pacing, this could lead to increased b)2.75 E
(urstiness for)-.22 E(the sender')100.8 694.2 Q 2.75(sd)-.605 G
(ata traf)-2.75 E(\214c.)-.275 E(There are se)100.8 710.8 Q -.165(ve)
-.275 G(ral cases when the problem of an o).165 E -.165(ve)-.165 G
(rly-high Ack Ratio, and the resulting).165 E(increased b)100.8 723.8 Q
(urstiness of the data traf)-.22 E(\214c, will not arise.)-.275 E
(In particular)5.5 E 2.75(,c)-.44 G(all the recei)-2.75 E -.165(ve)-.275
G 2.75(rD).165 G(CCP)-2.75 E(Flo)72 769 Q(yd/K)-.11 E 276.834
(ohler Section)-.385 F 2.75(B. [P)2.75 F(age 13])-.165 E 0 Cg EP
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(25 April 2005)2.75 E(October 2004)105.252 E 2.75(Ba)100.8 85 S
(nd the sender DCCP A.)-2.75 E(Then:)5.5 E 12.65<8354>100.8 101.6 S
(he problem w)-12.65 E(on')-.11 E 2.75(ta)-.198 G
(rise unless DCCP B is sending a signi\214cant amount of data itself.)
-2.75 E(When the B-to-A half-connection is quiescent or lo)117.3 114.6 Q
(w-rate, most pack)-.275 E(ets sent by DCCP)-.11 E 2.75(Bw)117.3 127.6 S
(ill, in f)-2.75 E(act, be pure ackno)-.11 E(wledgements, and DCCP A)
-.275 E 1.21 -.605('s e)-1.221 H(stimate of the DCCP-Ack).605 E
(loss rate will be reasonably accurate.)117.3 140.6 Q 12.65<8354>100.8
157.2 S(he problem w)-12.65 E(on')-.11 E 2.75(ta)-.198 G
(rise if DCCP B habitually piggybacks ackno)-2.75 E(wledgement)-.275 E
(information on its data pack)117.3 170.2 Q 2.75(ets. The)-.11 F
(piggyback)2.75 E(ed ackno)-.11 E(wledgements are not limited)-.275 E
(by Ack Ratio, so the)117.3 183.2 Q 2.75(yc)-.165 G(an arri)-2.75 E .33
-.165(ve f)-.275 H(requently enough to pre).165 E -.165(ve)-.275 G(nt b)
.165 E(urstiness.)-.22 E 12.65<8354>100.8 199.8 S(he problem w)-12.65 E
(on')-.11 E 2.75(ta)-.198 G(rise if DCCP A)-2.75 E 1.21 -.605('s s)
-1.221 H(ending rate is lo).605 E 1.43 -.715(w, s)-.275 H(ince b).715 E
(urstiness isn')-.22 E 2.75(ta)-.198 G(problem at lo)117.3 212.8 Q 2.75
(wr)-.275 G(ates.)-2.75 E 12.65<8354>100.8 229.4 S(he problem w)-12.65 E
(on')-.11 E 2.75(ta)-.198 G(rise if DCCP B')-2.75 E 2.75(ss)-.605 G
(ending rate is high relati)-2.75 E .33 -.165(ve t)-.275 H 2.75(oD).165
G(CCP A)-2.75 E -.605('s)-1.221 G
(sending rate, since the B-to-A loss rate must be lo)117.3 242.4 Q 2.75
(wt)-.275 G 2.75(os)-2.75 G(upport DCCP B')-2.75 E 2.75(ss)-.605 G
(ending rate.)-2.75 E(This bounds the Ack Ratio to reasonable v)117.3
255.4 Q(alues e)-.275 E -.165(ve)-.275 G 2.75(nw).165 G
(hen DCCP A labels e)-2.75 E -.165(ve)-.275 G(ry loss).165 E
(as a DCCP-Ack loss.)117.3 268.4 Q 12.65<8354>100.8 285 S(he problem w)
-12.65 E(on')-.11 E 2.75(ta)-.198 G
(rise if DCCP B sends NDP Count options when appropriate \(the)-2.75 E
(Send NDP Count/B feature is true\).)117.3 298 Q
(Then the sender can use the recei)5.5 E -.165(ve)-.275 G(r').165 E 2.75
(sN)-.605 G(DP Count)-2.75 E
(options to detect, in most cases, whether lost pack)117.3 311 Q
(ets were data pack)-.11 E(ets or DCCP-Acks.)-.11 E 12.65<8346>100.8
327.6 S(inally)-12.65 E 2.75(,t)-.715 G(he problem w)-2.75 E(on')-.11 E
2.75(ta)-.198 G(rise if DCCP A rate-paces its data pack)-2.75 E(ets.)
-.11 E(This lea)100.8 344.2 Q -.165(ve)-.22 G 2.75(st).165 G
(he case when DCCP B is sending roughly the same amount of data pack)
-2.75 E(ets)-.11 E(and non-data pack)100.8 357.2 Q
(ets, without NDP Count options, and with all ackno)-.11 E(wledgement)
-.275 E(information in DCCP-Ack pack)100.8 370.2 Q 2.75(ets. W)-.11 F
2.75(en)-.88 G .55 -.275(ow q)-2.75 H
(uantify the potential cost, in terms of a too-).275 E(lar)100.8 383.2 Q
(ge Ack Ratio, due to the sender')-.198 E 2.75(sm)-.605 G
(isclassifying data pack)-2.75 E(et losses as DCCP-Ack losses.)-.11 E
-.165(Fo)100.8 396.2 S 2.75(rs).165 G(implicity)-2.75 E 2.75(,w)-.715 G
2.75(ea)-2.75 G(ssume an en)-2.75 E(vironment of lar)-.44 E
(ge-scale statistical multiple)-.198 E(xing, where the)-.165 E(pack)
100.8 409.2 Q(et drop rate is independent of the sending rate of an)-.11
E 2.75(yi)-.165 G(ndi)-2.75 E(vidual connection.)-.275 E(Assume that wh\
en DCCP A correctly counts non-data losses, Ack Ratio is set so that B-\
to-)100.8 425.8 Q 2.75(Ad)100.8 438.8 S(ata and ackno)-2.75 E
(wledgement traf)-.275 E(\214c both ha)-.275 E .33 -.165(ve a s)-.22 H
(ending rate of D pack).165 E(ets per second.)-.11 E(Then when DCCP A i\
ncorrectly counts data losses as non-data losses, the sending rate for)
100.8 451.8 Q(the B-to-A data traf)100.8 464.8 Q
(\214c is still D pps, b)-.275 E
(ut the reduced sending rate for the B-to-A)-.22 E(ackno)100.8 477.8 Q
(wledgement traf)-.275 E(\214c is f*D pps, with f < 1.)-.275 E
(Let the pack)5.5 E(et loss rate be p.)-.11 E(The sender)5.5 E
(incorrectly estimates the non-data loss rate as \(pD+pfD\)/fD, or)100.8
490.8 Q 2.75(,e)-.44 G(qui)-2.75 E -.275(va)-.275 G(lently).275 E 2.75
(,a)-.715 G 2.75(sp)-2.75 G(\(1 + 1/f\).)-2.75 E
(Because the congestion control mechanism for ackno)100.8 503.8 Q
(wledgement traf)-.275 E(\214c is roughly TCP-)-.275 E(friendly)100.8
516.8 Q 2.75(,a)-.715 G(nd therefore the non-data sending rate and the \
data sending rate both gro)-2.75 E 2.75(wa)-.275 G(s)-2.75 E
(1/sqrt\(x\) for x the pack)100.8 529.8 Q(et drop rate, we ha)-.11 E
-.165(ve)-.22 G(fD/D = sqrt\(p\)/sqrt\(p\(1 + 1/f\)\),)120.05 542.8 Q
(so)100.8 555.8 Q(f^2 = 1/\(1 + 1/f\).)120.05 568.8 Q
(Solving, we get f = 0.62.)100.8 581.8 Q
(If the sender incorrectly counts lost data pack)5.5 E
(ets as non-data in)-.11 E(this scenario, the ackno)100.8 594.8 Q
(wledgement rate is decreased by a f)-.275 E(actor of 0.62.)-.11 E
(This w)5.5 E(ould result)-.11 E(in a moderate increase in b)100.8 607.8
Q(urstiness for the A-to-B data traf)-.22 E(\214c, which could be mitig)
-.275 E(ated by)-.055 E(sending NDP Count options or piggyback)100.8
620.8 Q(ed ackno)-.11 E(wledgements, or by rate-pacing out the)-.275 E
(data.)100.8 633.8 Q/F1 14/Times-Bold@0 SF(Normati)72 659.8 Q .28 -.14
(ve R)-.14 H(efer).14 E(ences)-.252 E F0([DCCP] E. K)100.8 676.4 Q
(ohler)-.385 E 2.75(,M)-.44 G 2.75(.H)-2.75 G(andle)-2.75 E 1.43 -.715
(y, a)-.165 H(nd S. Flo).715 E 2.75(yd. Datagram)-.11 F
(Congestion Control Protocol,)2.75 E(draft-ietf-dccp-spec-07.txt, w)
129.6 689.4 Q(ork in progress, July 2004.)-.11 E
([RFC 793] J. Postel, editor)100.8 706 Q 5.5(.T)-.605 G
(ransmission Control Protocol.)-5.885 E(RFC 793.)5.5 E(Flo)72 769 Q
(yd/K)-.11 E 328.171(ohler [P)-.385 F(age 14])-.165 E 0 Cg EP
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/F0 11/Times-Roman@0 SF(INTERNET)72 49 Q 70.206(-DRAFT Expires:)-1.012 F
(25 April 2005)2.75 E(October 2004)105.252 E
([RFC 2018] M. Mathis, J. Mahda)100.8 85 Q(vi, A. Flo)-.22 E
(yd, and A. Romano)-.11 E 1.43 -.715(w. T)-.275 H(CP Selecti).715 E
-.165(ve)-.275 G(Ackno)129.6 98 Q
(wledgement Options, RFC 2018, October 1996.)-.275 E
([RFC 2119] S. Bradner)100.8 114.6 Q 5.5(.K)-.605 G .33 -.165(ey W)
-5.775 H(ords F)-.715 E(or Use in RFCs to Indicate Requirement Le)-.165
E -.165(ve)-.275 G(ls.).165 E(RFC 2119.)129.6 127.6 Q([RFC 2434] T)100.8
144.2 Q 2.75(.N)-.814 G(arten and H. Alv)-2.75 E 2.75
(estrand. Guidelines)-.165 F(for Writing an IAN)2.75 E 2.75(AC)-.385 G
(onsiderations)-2.75 E(Section in RFCs.)129.6 157.2 Q(RFC 2434.)5.5 E
([RFC 2581] M. Allman, V)100.8 173.8 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 2.75(ns. TCP).165
F(Congestion Control.)2.75 E(RFC 2581.)5.5 E([RFC 2988] V)100.8 190.4 Q
2.75(.P)-1.419 G(axson and M. Allman, Computing TCP')-2.915 E 2.75(sR)
-.605 G(etransmission T)-2.75 E(imer)-.385 E 2.75(,R)-.44 G(FC)-2.75 E
(2988, No)129.6 203.4 Q -.165(ve)-.165 G(mber 2000.).165 E
([RFC 3168] K.K. Ramakrishnan, S. Flo)100.8 220 Q(yd, and D. Black.)-.11
E(The Addition of Explicit)5.5 E
(Congestion Noti\214cation \(ECN\) to IP)129.6 233 Q 5.5(.R)-1.221 G
(FC 3168.)-5.5 E([RFC 3390] M. Allman, S. Flo)100.8 249.6 Q
(yd, and C. P)-.11 E 2.75(artridge. Increasing)-.165 F(TCP')2.75 E 2.75
(sI)-.605 G(nitial W)-2.75 E(indo)-.44 E -.715(w.)-.275 G(RFC 3390.)
129.6 262.6 Q([RFC 3517] E. Blanton, M. Allman, K. F)100.8 279.2 Q
(all, and L. W)-.165 E 2.75(ang. A)-.88 F(Conserv)2.75 E(ati)-.275 E .33
-.165(ve S)-.275 H(electi).165 E -.165(ve)-.275 G(Ackno)129.6 292.2 Q
(wledgment \(SA)-.275 E(CK\)-based Loss Reco)-.44 E -.165(ve)-.165 G
(ry Algorithm for TCP).165 E 5.5(.R)-1.221 G(FC 3517.)-5.5 E
([RFC 3692] T)100.8 308.8 Q 2.75(.N)-.814 G 2.75(arten. Assigning)-2.75
F(Experimental and T)2.75 E(esting Numbers Considered Useful.)-.77 E
(RFC 3692.)129.6 321.8 Q/F1 14/Times-Bold@0 SF(Inf)72 347.8 Q(ormati)
-.35 E .28 -.14(ve R)-.14 H(efer).14 E(ences)-.252 E F0([CCID 3 PR)100.8
364.4 Q(OFILE] S. Flo)-.44 E(yd, E. K)-.11 E(ohler)-.385 E 2.75(,a)-.44
G(nd J. P)-2.75 E(adh)-.165 E 2.75(ye. Pro\214le)-.055 F
(for DCCP Congestion)2.75 E(Control ID 3: TFRC Congestion Control.)129.6
377.4 Q(draft-ietf-dccp-ccid3-06.txt, w)5.5 E(ork in)-.11 E
(progress, July 2004.)129.6 390.4 Q([RFC 2861] M. Handle)100.8 407 Q
1.43 -.715(y, J)-.165 H 2.75(.P).715 G(adh)-2.915 E(ye, and S. Flo)-.055
E 2.75(yd. TCP)-.11 F(Congestion W)2.75 E(indo)-.44 E 2.75(wV)-.275 G
(alidation.)-3.971 E(RFC 2861.)129.6 420 Q([RFC 3465] M. Allman. TCP Co\
ngestion Control with Appropriate Byte Counting \(ABC\).)100.8 436.6 Q
(RFC 3465.)129.6 449.6 Q([RFC 3540] N. Spring, D. W)100.8 466.2 Q
(etherall, and D. Ely)-.88 E 5.5(.R)-.715 G(ob)-5.5 E
(ust Explicit Congestion Noti\214cation)-.22 E
(\(ECN\) Signaling with Nonces.)129.6 479.2 Q(RFC 3540.)5.5 E
([V03] Arun V)100.8 495.8 Q(enkataramani, August 2003.)-1.221 E
(Citation for ackno)5.5 E(wledgement purposes only)-.275 E(.)-.715 E F1
-.7(Au)72 521.8 S(thors' Addr).7 E(esses)-.252 E F0(Sally Flo)100.8
538.4 Q(yd <\215o)-.11 E(yd@icir)-.11 E(.or)-.605 E(g>)-.198 E
(ICSI Center for Internet Research)100.8 551.4 Q
(1947 Center Street, Suite 600)100.8 564.4 Q(Berk)100.8 577.4 Q(ele)-.11
E 1.43 -.715(y, C)-.165 H 2.75(A9).715 G(4704)-2.75 E(USA)100.8 590.4 Q
(Eddie K)100.8 607 Q(ohler <k)-.385 E(ohler@cs.ucla.edu>)-.11 E
(4531C Boelter Hall)100.8 620 Q(UCLA Computer Science Department)100.8
633 Q(Los Angeles, CA 90095)100.8 646 Q(USA)100.8 659 Q F1
(Full Copyright Statement)72 685 Q F0(Cop)100.8 701.6 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)100.8 714.6 Q
(xcept as set forth therein, the authors retain all)-.165 E(Flo)72 769 Q
(yd/K)-.11 E 328.171(ohler [P)-.385 F(age 15])-.165 E 0 Cg EP
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/F0 11/Times-Roman@0 SF(INTERNET)72 49 Q 70.206(-DRAFT Expires:)-1.012 F
(25 April 2005)2.75 E(October 2004)105.252 E(their rights.)100.8 85 Q
(This document and the information contained herein are pro)100.8 101.6
Q(vided on an "AS IS" basis and)-.165 E(THE CONTRIB)100.8 114.6 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
127.6 Q(ENGINEERING T)100.8 140.6 Q(ASK FORCE DISCLAIM ALL W)-1.023 E
(ARRANTIES, EXPRESS OR)-1.32 E(IMPLIED, INCLUDING B)100.8 153.6 Q(UT NO)
-.11 E 2.75(TL)-.44 G(IMITED T)-2.75 E 2.75(OA)-.198 G(NY W)-2.75 E
(ARRANTY THA)-1.32 E 2.75(TT)-1.221 G(HE USE)-2.75 E(OF THE INFORMA)
100.8 166.6 Q(TION HEREIN WILL NO)-1.221 E 2.75(TI)-.44 G
(NFRINGE ANY RIGHTS OR ANY)-2.75 E(IMPLIED W)100.8 179.6 Q
(ARRANTIES OF MERCHANT)-1.32 E(ABILITY OR FITNESS FOR A)-1.023 E -1.012
(PA)100.8 192.6 S -.66(RT)1.012 G(ICULAR PURPOSE.).66 E/F1 14
/Times-Bold@0 SF(Intellectual Pr)72 218.6 Q(operty)-.252 E F0
(The IETF tak)100.8 235.2 Q(es no position re)-.11 E -.055(ga)-.165 G
(rding the v).055 E(alidity or scope of an)-.275 E 2.75(yI)-.165 G
(ntellectual Property)-2.75 E(Rights or other rights that might be clai\
med to pertain to the implementation or use of the)100.8 248.2 Q
(technology described in this document or the e)100.8 261.2 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)100.8 274.2 Q -.275(va)-.22 G
(ilable; nor does it represent that it has made an).275 E 2.75(yi)-.165
G(ndependent)-2.75 E(ef)100.8 287.2 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.)100.8 300.2 Q
(Copies of IPR disclosures made to the IETF Secretariat and an)100.8
316.8 Q 2.75(ya)-.165 G(ssurances of licenses to)-2.75 E(be made a)100.8
329.8 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)100.8 342.8 Q(speci\214cati\
on can be obtained from the IETF on-line IPR repository at)100.8 355.8 Q
(http://www)100.8 368.8 Q(.ietf.or)-.715 E(g/ipr)-.198 E(.)-.605 E
(The IETF in)100.8 385.4 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
398.4 Q -.165(ve)-.165 G 2.75(rt).165 G(echnology that may be)-2.75 E
(required to implement this standard.)100.8 411.4 Q
(Please address the information to the IETF at ietf-)5.5 E(ipr@ietf.or)
100.8 424.4 Q(g.)-.198 E(Flo)72 769 Q(yd/K)-.11 E 328.171(ohler [P)-.385
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