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/F0 10/Courier-Bold@0 SF(Internet Engineering Task Force)72 85 Q
(Sally Floyd)179.998 E 317.998(INTERNET-DRAFT ICIR)72 98 R 167.998
(draft-ietf-dccp-tfrc-voip-00.ps Eddie)72 111 R(Kohler)6 E
(Expires: July 2005)72 124 Q(UCLA)299.998 E 6(6J)419.998 137 S
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(yright \(C\) The Internet Society \(2004\). All Rights Reserv)-.11 E
(ed.)-.165 E F2(Abstract)72 505.2 Q F3(TCP-Friendly Rate Control \(TFRC\
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E(ackno)129.6 691.6 Q(wledgement pack)-.275 E(ets on the re)-.11 E -.165
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(he ar)-2.75 E(guments abo)-.198 E -.165(ve)-.165 G 2.75(,i).165 G 2.75
(ts)-2.75 G(eems)-2.75 E(acceptable to us to assume a netw)129.6 704.6 Q
(ork limitation in Bps rather than in pps in)-.11 E
(considering the minimum sending rate of telephon)129.6 717.6 Q 2.75(yt)
-.165 G(raf)-2.75 E(\214c.")-.275 E(Flo)72 769 Q(yd/K)-.11 E 284.171
(ohler Section)-.385 F 2.75(2. [P)2.75 F(age 3])-.165 E 0 Cg EP
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(July 2005)2.75 E(January 2005)115.79 E -.385(Tr)100.8 85 S(anslating t\
he discussion in [RFC 3714] to the congestion control mechanisms of TFR\
C,).385 E(it seems acceptable to standardize a v)100.8 98 Q
(ariant of TFRC that allo)-.275 E(ws V)-.275 E(oIP \215o)-1.419 E
(ws sending small)-.275 E(pack)100.8 111 Q(ets to achie)-.11 E .33 -.165
(ve a r)-.275 H(ough f).165 E(airness with TCP \215o)-.11 E
(ws in terms of the sending rate in Bps,)-.275 E
(rather than in terms of the sending rate in pps.)100.8 124 Q
(This is accomplished by a simple tw)5.5 E(o-line)-.11 E
(modi\214cation at the TFRC sender)100.8 137 Q 2.75(,a)-.44 G 2.75(sd)
-2.75 G(escribed belo)-2.75 E 4.18 -.715(w. N)-.275 H 2.75(oc).715 G
(hanges are required at the)-2.75 E(TFRC recei)100.8 150 Q -.165(ve)
-.275 G -.605(r.).165 G(Ho)100.8 166.6 Q(we)-.275 E -.165(ve)-.275 G .88
-.44(r, b).165 H(ecause the bottlenecks in the netw).44 E(ork in f)-.11
E(act can include limitations in pps as)-.11 E(well as in Bps, we pay s\
pecial attention to the potential dangers of encouraging a lar)100.8
179.6 Q(ge)-.198 E(deplo)100.8 192.6 Q(yment of best-ef)-.11 E
(fort traf)-.275 E
(\214c in the Internet consisting entirely of small pack)-.275 E 2.75
(ets. This)-.11 F(is)2.75 E
(discussed in more detail in Section 4.3. In addition, as ag)100.8 205.6
Q(ain discussed in Section 4.3, the)-.055 E -1.419(Vo)100.8 218.6 S
(IP v)1.419 E(ariant of TFRC includes the limitation of the Min Interv)
-.275 E(al between pack)-.275 E(ets of 10 ms.)-.11 E/F1 11/Times-Bold@0
SF(3.)72 244.6 Q/F2 14/Times-Bold@0 SF -1.4(Vo)5.5 G(IP V)1.4 E
(ariant Congestion Contr)-1.288 E(ol)-.252 E F0
(TFRC uses the TCP throughput equation gi)100.8 261.2 Q -.165(ve)-.275 G
2.75(ni).165 G 2.75(nS)-2.75 G(ection 3.1 of [RFC 3448], which gi)-2.75
E -.165(ve)-.275 G(s).165 E(the allo)100.8 274.2 Q
(wed sending rate X in bytes per second as a function of the loss e)
-.275 E -.165(ve)-.275 G(nt rate, pack).165 E(et)-.11 E
(size, and round-trip time.)100.8 287.2 Q
([RFC 3448] speci\214es that the pack)5.5 E(et size s used in the)-.11 E
(throughput equation should be the pack)100.8 300.2 Q
(et size used by the application, or the estimated)-.11 E(mean pack)
100.8 313.2 Q(et size if there are v)-.11 E(ariations in the pack)-.275
E(et size depending on the data.)-.11 E(This gi)5.5 E -.165(ve)-.275 G
(s).165 E(rough f)100.8 326.2 Q(airness with TCP \215o)-.11 E
(ws using the same pack)-.275 E(et size.)-.11 E(The V)100.8 342.8 Q
(oIP v)-1.419 E(ariant changes this beha)-.275 E(vior in the follo)-.22
E(wing w)-.275 E(ays.)-.11 E 12.65<8354>100.8 359.4 S(he nominal pack)
-12.65 E(et size s is set to 1460 bytes.)-.11 E -.165(Fo)5.5 G(llo).165
E(wing [RFC 3714], this pro)-.275 E(vides a)-.165 E(goal of f)117.3
372.4 Q(airness, in terms of the sending rate in bytes per second, with\
 a TCP \215o)-.11 E 2.75(ww)-.275 G(ith)-2.75 E
(1460 bytes of application data per pack)117.3 385.4 Q(et.)-.11 E 12.65
<8354>100.8 402 S(he allo)-12.65 E
(wed transmit rate X in bytes per second is reduced by a f)-.275 E
(actor that accounts for)-.11 E(pack)117.3 415 Q(et header size.)-.11 E
(This gi)5.5 E -.165(ve)-.275 G 2.75(st).165 G
(he application some incenti)-2.75 E -.165(ve)-.275 G 2.75(,b).165 G
-.165(ey)-2.75 G(ond the Min Interv).165 E(al,)-.275 E
(not to use unnecessarily small pack)117.3 428 Q 2.75(ets. In)-.11 F
(particular)2.75 E 2.75(,w)-.44 G 2.75(ei)-2.75 G(ntroduce a ne)-2.75 E
2.75(wp)-.275 G(arameter H,)-2.75 E(which represents the e)117.3 441 Q
(xpected size in bytes of netw)-.165 E
(ork and transport headers to be used)-.11 E(on the TFRC connection')
117.3 454 Q 2.75(sp)-.605 G(ack)-2.75 E 2.75(ets. This)-.11 F
(is used to reduce the allo)2.75 E(wed transmit rate X)-.275 E(as follo)
117.3 467 Q(ws:)-.275 E 2.75(X<)117.3 483.6 S 2.75(-X*s)-2.75 G
(_true / \(s_true + H\),)-2.75 E(where s_true is the true a)117.3 500.2
Q -.165(ve)-.22 G(rage pack).165 E(et size for the connection in bytes.)
-.11 E(The H parameter is set to the constant 40 bytes.)117.3 516.8 Q
(Thus, if the V)5.5 E(oIP TFRC application)-1.419 E
(used 40-byte data se)117.3 529.8 Q(gments, the allo)-.165 E
(wed transmit rate X w)-.275 E(ould be halv)-.11 E(ed to account for)
-.165 E(the f)117.3 542.8 Q(act that half of the sending rate w)-.11 E
(ould be used by the headers.)-.11 E(Section 4.2 justi\214es)5.5 E
(this de\214nition.)117.3 555.8 Q(Ho)5.5 E(we)-.275 E -.165(ve)-.275 G
.88 -.44(r, a c).165 H(onnection using the V).44 E(oIP v)-1.419 E
(ariant MA)-.275 E 2.75(Yi)-1.155 G(nstead use a more)-2.75 E
(precise estimate of H, based on the actual netw)117.3 568.8 Q
(ork and transport headers to be used on)-.11 E(the connection')117.3
581.8 Q 2.75(sp)-.605 G(ack)-2.75 E 2.75(ets. F)-.11 F(or e)-.165 E
(xample, a DCCP connection [DCCP] o)-.165 E -.165(ve)-.165 G 2.75(rI)
.165 G(Pv4, where)-2.75 E(data pack)117.3 594.8 Q
(ets use the DCCP-Data pack)-.11 E
(et type, and there are no IP or DCCP options,)-.11 E
(could set H to 20 + 12 = 32 bytes.)117.3 607.8 Q 12.65<8346>100.8 624.4
S(inally)-12.65 E 2.75(,t)-.715 G(he V)-2.75 E(oIP v)-1.419 E
(ariant of TFRC enforces a Min Interv)-.275 E(al between pack)-.275 E
(ets of 10 ms.)-.11 E 2.75<418d>117.3 637.4 S .55 -.275(ow t)-2.75 H
(hat wished to e).275 E(xceed this Min Interv)-.165 E
(al MUST use the con)-.275 E -.165(ve)-.44 G(ntional TFRC).165 E
(equations, rather than the V)117.3 650.4 Q(oIP v)-1.419 E 2.75
(ariant. The)-.275 F(moti)2.75 E -.275(va)-.275 G
(tion for this is discussed belo).275 E -.715(w.)-.275 G F1(4.)72 676.4
Q F2 -1.4(Vo)5.5 G(IP V)1.4 E(ariant Discussion)-1.288 E F0(Flo)72 769 Q
(yd/K)-.11 E 284.171(ohler Section)-.385 F 2.75(4. [P)2.75 F(age 4])
-.165 E 0 Cg EP
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(July 2005)2.75 E(January 2005)115.79 E/F1 11/Times-Bold@0 SF(4.1.)72 85
Q/F2 13/Times-Bold@0 SF(The TCP Thr)5.5 E(oughput Equation)-.234 E F0
(The V)100.8 101.6 Q(oIP v)-1.419 E
(ariant of TFRC uses the TCP throughput equation gi)-.275 E -.165(ve)
-.275 G 2.75(ni).165 G 2.75(n[)-2.75 G(RFC 3448].)-2.75 E(As)5.5 E(sho)
100.8 114.6 Q(wn in T)-.275 E(able 1 of [RFC 3714], for high pack)-.88 E
(et drop rates, this throughput equation gi)-.11 E -.165(ve)-.275 G(s)
.165 E(rough f)100.8 127.6 Q(airness with most aggressi)-.11 E .33 -.165
(ve p)-.275 H(ossible current TCP: a SA).165 E(CK TCP \215o)-.44 E 2.75
(wu)-.275 G(sing)-2.75 E(timestamps and ECN.)100.8 140.6 Q F1(4.2.)72
166.6 Q F2(Accounting f)5.5 E(or Header Size)-.325 E F0([RFC 3714] mak)
100.8 183.2 Q
(es the optimistic assumption that the limitation of the netw)-.11 E
(ork is in)-.11 E
(bandwidth in bytes per second \(Bps\), and not in CPU c)100.8 196.2 Q
(ycles or in pack)-.165 E(ets per second \(pps\).)-.11 E(Ho)100.8 209.2
Q(we)-.275 E -.165(ve)-.275 G .88 -.44(r, s).165 H(ome attention must b\
e paid to the load in pps as well as to the load in Bps.).44 E(Ev)100.8
222.2 Q(en aside from the Min Interv)-.165 E(al, the V)-.275 E(oIP v)
-1.419 E(ariant of TFRC gi)-.275 E -.165(ve)-.275 G 2.75(st).165 G
(he application some)-2.75 E(incenti)100.8 235.2 Q .33 -.165(ve t)-.275
H 2.75(ou).165 G(se fe)-2.75 E(wer b)-.275 E(ut lar)-.22 E(ger pack)
-.198 E(ets, when lar)-.11 E(ger pack)-.198 E(ets w)-.11 E(ould suf)-.11
E(\214ce, by including)-.275 E(the bandwidth used by the pack)100.8
248.2 Q(et header in the allo)-.11 E(wed sending rate.)-.275 E(As an e)
100.8 264.8 Q(xample, a sender using 120-byte pack)-.165 E
(ets needs a TCP-friendly rate of 128 Kbps to)-.11 E
(send 96 Kbps of application data.)100.8 277.8 Q
(This is because the TCP-friendly rate is reduced by a)5.5 E -.11(fa)
100.8 290.8 S
(ctor of s_true/\(s_true + H\) = 120/160, to account for the ef).11 E
(fect of pack)-.275 E(et headers.)-.11 E(If the)5.5 E
(sender suddenly switched to 40-byte data se)100.8 303.8 Q
(gments, the allo)-.165 E(wed sending rate w)-.275 E(ould reduce)-.11 E
(to 64 Kbps of application data; and one-byte data se)100.8 316.8 Q
(gments w)-.165 E(ould reduce the allo)-.11 E(wed)-.275 E
(sending rate to 3.12 Kbps of application data.)100.8 329.8 Q(\(In f)5.5
E(act, the Min Interv)-.11 E(al w)-.275 E(ould pre)-.11 E -.165(ve)-.275
G(nt).165 E(senders from achie)100.8 342.8 Q
(ving these rates, since applications using the V)-.275 E(oIP v)-1.419 E
(ariant cannot send)-.275 E(more than 100 pack)100.8 355.8 Q
(ets per second.\))-.11 E(The V)100.8 372.4 Q(oIP v)-1.419 E(ariant ass\
umes 40 bytes for the header size, although the header could be lar)
-.275 E(ger)-.198 E(\(due to IP options, IPv6, IP tunnels, and the lik)
100.8 385.4 Q(e\) or smaller \(due to header compression\))-.11 E
(on the wire, because using the e)100.8 398.4 Q
(xact header size in bytes w)-.165 E(ould ha)-.11 E .33 -.165(ve l)-.22
H(ittle additional).165 E 2.75(bene\214t. The)100.8 411.4 R -1.419(Vo)
2.75 G(IP v)1.419 E(ariant')-.275 E 2.75(su)-.605 G
(se of an assumed 40-byte header is suf)-2.75 E
(\214cient to get a rough)-.275 E(estimate of the throughput, and to gi)
100.8 424.4 Q .33 -.165(ve t)-.275 H(he application some incenti).165 E
.33 -.165(ve n)-.275 H(ot to use).165 E(unnecessarily-man)100.8 437.4 Q
2.75(ys)-.165 G(mall pack)-2.75 E 2.75(ets. Because)-.11 F
(we are only aiming at rough f)2.75 E(airness, and at a)-.11 E
(rough incenti)100.8 450.4 Q .33 -.165(ve f)-.275 H(or applications, th\
e use of a 40-byte header in the calculations of the).165 E
(header bandwidth seems suf)100.8 463.4 Q(\214cient.)-.275 E F1(4.3.)72
489.4 Q F2(The V)5.5 E(oIP Min Inter)-1.3 E -.13(va)-.13 G(l).13 E F0
(The header size calculation pro)100.8 506 Q(vides an incenti)-.165 E
.33 -.165(ve f)-.275 H(or applications to use fe).165 E(wer)-.275 E 2.75
(,b)-.44 G(ut lar)-2.97 E(ger)-.198 E(,)-.44 E(pack)100.8 519 Q 2.75
(ets. Another)-.11 F(incenti)2.75 E .33 -.165(ve i)-.275 H 2.75(st).165
G(hat when the path limitation is in pps, the application using)-2.75 E
(more small pack)100.8 532 Q(ets is lik)-.11 E(ely to recei)-.11 E .33
-.165(ve m)-.275 H(ore pack).165 E(et drops, and to ha)-.11 E .33 -.165
(ve t)-.22 H 2.75(or).165 G(educe its sending)-2.75 E(rate accordingly)
100.8 545 Q 5.5(.T)-.715 G
(hat is, if the congestion is in terms of pps, then the \215o)-5.5 E
2.75(ws)-.275 G(ending more)-2.75 E(pps will recei)100.8 558 Q .33 -.165
(ve m)-.275 H(ore congestion indications, and ha).165 E .33 -.165(ve t)
-.22 H 2.75(oa).165 G(djust its sending rate)-2.75 E(accordingly)100.8
571 Q 5.5(.H)-.715 G -.275(ow)-5.5 G -2.365 -.275(ev e).275 H .88 -.44
(r, t).275 H(he increased congestion caused by the use of small pack).44
E(ets in an)-.11 E(en)100.8 584 Q(vironment limited by pps is e)-.44 E
(xperienced not only by the \215o)-.165 E 2.75(wu)-.275 G
(sing the small pack)-2.75 E(ets, b)-.11 E(ut)-.22 E
(by all of the competing traf)100.8 597 Q(\214c on that congested link.)
-.275 E(These incenti)5.5 E -.165(ve)-.275 G 2.75(sa).165 G
(re therefore)-2.75 E(insuf)100.8 610 Q(\214cient to pro)-.275 E
(vide suf)-.165 E(\214cient protection for pps netw)-.275 E
(ork limitations.)-.11 E(The V)100.8 626.6 Q(oIP v)-1.419 E
(ariant for TFRC, then, includes a Min Interv)-.275 E(al of 10 ms.)-.275
E(This pro)5.5 E(vides)-.165 E
(additional restrictions on the use of unnecessarily man)100.8 639.6 Q
2.75(ys)-.165 G(mall pack)-2.75 E(ets.)-.11 E
(One justi\214cation for the Min Interv)100.8 656.2 Q
(al is the practical one that the applications that currently)-.275 E
-.11(wa)100.8 669.2 S(nt to send small pack).11 E(ets are the V)-.11 E
(oIP applications that send at most one pack)-1.419 E(et e)-.11 E -.165
(ve)-.275 G(ry 10).165 E(ms, so this restriction does not af)100.8 682.2
Q(fect current traf)-.275 E 2.75(\214c. A)-.275 F
(second justi\214cation is that there is)2.75 E
(no pressing need for best-ef)100.8 695.2 Q(fort traf)-.275 E
(\214c in the current Internet to send small pack)-.275 E(ets more)-.11
E(frequently than once e)100.8 708.2 Q -.165(ve)-.275 G
(ry 10 ms \(rather than taking the 10 ms delay at the sender).165 E 2.75
(,a)-.44 G(nd)-2.75 E(mer)100.8 721.2 Q(ging the tw)-.198 E 2.75(os)-.11
G(mall pack)-2.75 E(ets into one lar)-.11 E(ger one\).)-.198 E
(This 10 ms delay for mer)5.5 E(ging small)-.198 E(Flo)72 769 Q(yd/K)
-.11 E 275.921(ohler Section)-.385 F 2.75(4.3. [P)2.75 F(age 5])-.165 E
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/F0 11/Times-Roman@0 SF(INTERNET)72 49 Q 79.523(-DRAFT Expires:)-1.012 F
(July 2005)2.75 E(January 2005)115.79 E(pack)100.8 85 Q(ets is lik)-.11
E(ely to be dominated by the netw)-.11 E(ork propag)-.11 E
(ation, transmission, and queueing)-.055 E(delays of best-ef)100.8 98 Q
(fort traf)-.275 E(\214c in the current Internet.)-.275 E
(As a result, our judgement w)5.5 E(ould be that)-.11 E
(the bene\214t to the user of ha)100.8 111 Q
(ving less than 10 ms between pack)-.22 E(ets is outweighed by the)-.11
E(bene\214t to the netw)100.8 124 Q(ork of a)-.11 E -.22(vo)-.22 G
(iding unnecessarily man).22 E 2.75(ys)-.165 G(mall pack)-2.75 E(ets.)
-.11 E(The Min Interv)100.8 140.6 Q(al causes the V)-.275 E(oIP v)-1.419
E(ariant of TFRC not to support applications sending)-.275 E(small pack)
100.8 153.6 Q(ets v)-.11 E(ery frequently)-.165 E 5.5(.C)-.715 G
(onsider a TFRC \215o)-5.5 E 2.75(ww)-.275 G(ith a \214x)-2.75 E
(ed pack)-.165 E(et size of 100 bytes,)-.11 E -.22(bu)100.8 166.6 S 2.75
(tw).22 G(ith a v)-2.75 E(ariable sending rate and a f)-.275 E
(airly uncongested path.)-.11 E(When this \215o)5.5 E 2.75(ww)-.275 G
(as sending)-2.86 E(at most 100 pps, it w)100.8 179.6 Q
(ould be able to use the V)-.11 E(oIP v)-1.419 E(ariant of TFRC.)-.275 E
(If the \215o)5.5 E 2.75(ww)-.275 G(ished to)-2.75 E
(increase its sending rate to more than 100 pps, b)100.8 192.6 Q
(ut to k)-.22 E(eep the same pack)-.11 E(et size, it w)-.11 E(ould)-.11
E(no longer be able to achie)100.8 205.6 Q .33 -.165(ve t)-.275 H
(his with the V).165 E(oIP v)-1.419 E(ariant to TFRC, and w)-.275 E
(ould ha)-.11 E .33 -.165(ve t)-.22 H 2.75(os).165 G(wich)-2.75 E
(to the def)100.8 218.6 Q(ault TFRC, recei)-.11 E
(ving a dramatic, discontinuous decrease in its allo)-.275 E
(wed sending)-.275 E 2.75(rate. This)100.8 231.6 R
(seems not only acceptable, b)2.75 E
(ut desirable for the global Internet.)-.22 E(What is to pre)100.8 248.2
Q -.165(ve)-.275 G(nt \215o).165 E
(ws from opening multiple connections, each with a 10 ms Min)-.275 E
(Interv)100.8 261.2 Q
(al, and thereby getting around the limitation of the Min Interv)-.275 E
2.75(al? Ob)-.275 F(viously)-.165 E 2.75(,t)-.715 G(here is)-2.75 E
(nothing to pre)100.8 274.2 Q -.165(ve)-.275 G(nt \215o).165 E
(ws from doing this, just as there is currently nothing to pre)-.275 E
-.165(ve)-.275 G(nt \215o).165 E(ws)-.275 E(from using UDP)100.8 287.2 Q
2.75(,o)-1.221 G 2.75(rf)-2.75 G
(rom opening multiple parallel TCP connections, or from using their)
-2.75 E -.275(ow)100.8 300.2 S 2.75(nc).275 G
(ongestion control mechanism.)-2.75 E
(Of course, implementations are also free to limit the)5.5 E(number of \
parallel TFRC connections opened to the same destination in times of)
100.8 313.2 Q(congestion, if that seems desirable.)100.8 326.2 Q
(And \215o)5.5 E(ws that open multiple parallel connections are)-.275 E
(subject to the incon)100.8 339.2 Q -.165(ve)-.44 G
(niences of reordering and the lik).165 E 2.75(e. But)-.11 F -2.365
-.275(ev e)2.75 H 2.75(nw).275 G(ithout a mechanism to)-2.75 E(pre)100.8
352.2 Q -.165(ve)-.275 G(nt \215o).165 E(ws from sub)-.275 E -.165(ve)
-.165 G(rting the Min Interv).165 E
(al by opening multiple parallel connections, it)-.275 E
(seems useful to include the Min Interv)100.8 365.2 Q(al in the V)-.275
E(oIP v)-1.419 E(ariant of TFRC.)-.275 E/F1 11/Times-Bold@0 SF(5.)72
391.2 Q/F2 14/Times-Bold@0 SF -.35(Fa)5.5 G(ster Restart Intr).35 E
(oduction)-.252 E F0(In an)100.8 407.8 Q 2.75(yR)-.165 G(TT)-3.41 E 2.75
(,aT)-.814 G(FRC \215o)-2.75 E 2.75(wm)-.275 G
(ay not send more than twice X_recv)-2.75 E 2.75(,t)-.715 G
(he amount that w)-2.75 E(as)-.11 E(recei)100.8 420.8 Q -.165(ve)-.275 G
2.75(di).165 G 2.75(nt)-2.75 G(he pre)-2.75 E(vious R)-.275 E(TT)-.66 E
5.5(.T)-.814 G(he TFRC nofeedback timer reduces this number by half)-5.5
E(during each nofeedback timer interv)100.8 433.8 Q
(al \(at least four R)-.275 E(TT\) in which no feedback is recei)-.66 E
-.165(ve)-.275 G(d.).165 E(The ef)100.8 446.8 Q
(fect of this is that applications must slo)-.275 E 2.75(ws)-.275 G
(tart after going idle for an)-2.75 E 2.75(ys)-.165 G(igni\214cant)-2.75
E(length of time.)100.8 459.8 Q(This beha)100.8 476.4 Q
(vior is safe for the netw)-.22 E 2.75(ork. A)-.11 F
(silent application stops recei)2.75 E(ving feedback about)-.275 E
(current netw)100.8 489.4 Q(ork conditions, and thus should not be able\
 to send at an arbitrary rate.)-.11 E(But)5.5 E(this beha)100.8 502.4 Q
(vior can damage the percei)-.22 E -.165(ve)-.275 G 2.75(dp).165 G
(erformance of interacti)-2.75 E .33 -.165(ve a)-.275 H
(pplications, such as).165 E -.22(vo)100.8 515.4 S 2.75
(ice. Connections).22 F(for interacti)2.75 E .33 -.165(ve t)-.275 H
(elephon).165 E 2.75(ya)-.165 G(nd conference applications, for e)-2.75
E(xample,)-.165 E(will usually ha)100.8 528.4 Q .33 -.165(ve o)-.22 H
(ne party acti).165 E .33 -.165(ve a)-.275 H 2.75(tat).165 G
(ime, with seamless switching between acti)-2.75 E -.165(ve)-.275 G 2.75
(parties. Incurring)100.8 541.4 R(slo)2.75 E 2.75(ws)-.275 G(tart on e)
-2.75 E -.165(ve)-.275 G(ry switch between parties may cause percei).165
E -.165(ve)-.275 G(d).165 E(performance to seriously de)100.8 554.4 Q
2.75(grade. Some)-.165 F(of the strate)2.75 E
(gies suggested for coping with this)-.165 E(problem, such as sending p\
adding data during application idle periods, might ha)100.8 567.4 Q .33
-.165(ve w)-.22 H(orse).055 E(ef)100.8 580.4 Q(fects on the netw)-.275 E
(ork than simply switching onto the desired rate with no slo)-.11 E 2.75
(ws)-.275 G(tart.)-2.75 E(There is some justi\214cation for some)100.8
597 Q(what accelerating the slo)-.275 E 2.75(ws)-.275 G
(tart process after idle)-2.75 E(periods \(as opposed to at the be)100.8
610 Q(ginning of a connection\).)-.165 E 2.75(Ac)5.5 G(onnection that f)
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(d, at least, that some path between the endpoints can support).165 E
(that rate.)100.8 636 Q(The path might change, due to endpoint reset or\
 routing adjustments; or man)5.5 E(y)-.165 E(ne)100.8 649 Q 2.75(wc)
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(onnections might start up, signi\214cantly reducing the application')
-2.75 E 2.75(sf)-.605 G(air rate.)-2.86 E(Ho)5.5 E(we)-.275 E -.165(ve)
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(This document suggests a relati)100.8 691.6 Q -.165(ve)-.275 G
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(using TFRC [CCID 3 PR)100.8 704.6 Q
(OFILE] already specify that the allo)-.44 E(wed sending rate is ne)
-.275 E -.165(ve)-.275 G(r).165 E(reduced belo)100.8 717.6 Q 2.75(wt)
-.275 G(he RFC-3390 sending rate of four pack)-2.75 E(ets per R)-.11 E
(TT during an idle period.)-.66 E(Flo)72 769 Q(yd/K)-.11 E 284.171
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111 Q(aster Restart allo)-.165 E(ws \215o)-.275 E
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(DRAFT DRAFT DRAFT)100.8 179.6 Q 2.75(Ac)100.8 196.2 S(onnection goes "\
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k)-2.75 E(interv)100.8 209.2 Q(al \(as least four round-trip times\).)
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(transport layer MUST send a "ping" pack)100.8 222.2 Q(et e)-.11 E -.165
(ve)-.275 G(ry se).165 E -.165(ve)-.275 G
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(ws.)-.275 E(T_idle)100.8 268.4 Q(The time the connection went idle.)
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(The rate at which to turn of)129.6 311 Q 2.75(ff)-.275 G
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(The rate at which pack)129.6 340.6 Q(ets were recei)-.11 E -.165(ve)
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(is initialized to 0 until there has been an acti)129.6 366.6 Q .33
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-.275 G(_recv).165 E(The most recent time in an acti)129.6 396.2 Q .33
-.165(ve s)-.275 H(ending period.).165 E(Se)100.8 412.8 Q -.165(ve)-.275
G(ral pre).165 E(viously e)-.275 E(xisting state v)-.165 E
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(XT)100.8 446 S(he current allo)-20.858 E
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479.2 Q(The rate at which the recei)129.6 492.2 Q -.165(ve)-.275 G 2.75
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2.75(ds).165 G(ince the last)-2.75 E(feedback report w)129.6 505.2 Q
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-.11 E(Other v)100.8 534.8 Q(ariables ha)-.275 E .33 -.165(ve v)-.22 H
(alues as described in [RFC 3448].)-.11 E F1(6.1.)72 560.8 Q/F3 13
/Times-Bold@0 SF(Entering and Lea)5.5 E(ving Idle P)-.325 E(eriods)-.26
E F0(When the application has nothing to send \(an idle period is enter\
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100.8 633 Q(aster Restart up to the full last f)-.165 E
(air rate after an idle period of 10 minutes or)-.11 E
(less; will not use F)100.8 646 Q(ast T)-.165 E
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-.77 E(between these e)100.8 659 Q
(xtremes after idle periods between 10 and 30 minutes.)-.165 E(Flo)72
769 Q(yd/K)-.11 E 275.921(ohler Section)-.385 F 2.75(6.1. [P)2.75 F
(age 7])-.165 E 0 Cg EP
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(If \(now - T_idle\) > max\(R, 1 / max\(X_calc, s/t_mbi\)\),)100.8 85 Q
(/* If idle for <= 10 minutes, end fast start at the)120.6 98 Q
(full last fair rate; if idle for >= 30 minutes,)140.4 111 Q
(don't do fast start; in between, interpolate. */)140.4 124 Q
(delta_T := now - T_active_recv)120.6 137 Q 6.6(F:)120.6 150 S 6.6(=\()
-6.6 G(30 min - min\(max\(delta_T, 10 min\), 30 min\)\) / 20 min)-6.6 E
(/* Initialize X_fast_max to a fraction of the last active)120.6 163 Q
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(Fe)5.5 G(edback P).325 E(ack)-.13 E(ets)-.13 E F0(The core of the F)
100.8 276.6 Q(aster Restart algorithm is a replacement for the 4th step\
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(d, of [RFC 3448], as follo).165 E(ws.)-.275 E F1
(To update X when you receive a feedback packet)100.8 308.6 Q
(----------------------------------------------)100.8 321.6 Q
(If \(2*X_recv < X_fast_max\) and the feedback packet)100.8 334.6 Q
(indicates a loss or mark,)140.4 347.6 Q
(/* Stop faster restart at the first sign of congestion */)120.6 360.6 Q
(X_fast_max := 0,)120.6 373.6 Q(X_recv := X_recv/2.)120.6 386.6 Q
(If p > 0,)100.8 399.6 Q
(Calculate X_calc using the TCP throughput equation.)120.6 412.6 Q
(If \(2*X_recv < X_fast_max\),)120.6 425.6 Q(/* Faster restart case */)
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(Fa)5.5 G(ster Restart Discussion).35 E F0
(TCP has historically dealt with idleness either by k)100.8 591.2 Q
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(start"\) or by entering slo)100.8 604.2 Q 2.75(ws)-.275 G
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E(liberal, the second too conserv)100.8 617.2 Q(ati)-.275 E -.165(ve)
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(wc)-.275 G(onnection:)-2.75 E(recent e)100.8 630.2 Q(vidence sho)-.275
E(ws that the connection could f)-.275 E(airly sustain some rate.)-.11 E
(Ho)5.5 E(we)-.275 E -.165(ve)-.275 G .88 -.44(r, l).165 H(onger).44 E
(idle periods are more problematic, and idle periods of hours w)100.8
643.2 Q(ould seem to require slo)-.11 E(w)-.275 E 2.75(start. RFC)100.8
656.2 R(2861 [RFC 2861], which is f)2.75 E
(airly widely implemented [MAF04], gi)-.11 E -.165(ve)-.275 G 2.75(sa)
.165 G(moderate mechanism for TCP)100.8 669.2 Q 2.75(,w)-1.221 G
(here the congestion windo)-2.75 E 2.75(wi)-.275 G 2.75(sh)-2.75 G(alv)
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2.75(wi)-.275 G 2.75(nr)-2.75 G(e-opened in slo)-2.75 E
(w-start when the)-.275 E(idle period is o)100.8 695.2 Q -.165(ve)-.165
G -.605(r.).165 G -.165(Fa)100.8 711.8 S
(ster Restart should be acceptable for TFRC if its w).165 E
(orst-case scenario is acceptable.)-.11 E(Realistic w)100.8 724.8 Q
(orst-case scenarios might include the follo)-.11 E(wing scenarios:)
-.275 E(Flo)72 769 Q(yd/K)-.11 E 284.171(ohler Section)-.385 F 2.75
(7. [P)2.75 F(age 8])-.165 E 0 Cg EP
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(ath too, so F)-2.75 E
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-.66 E(not just one.)117.3 111 Q 12.65<8354>100.8 127.6 S .22 -.11
(wo \()-13.53 H(or more\) connections enter F).11 E
(aster Restart simultaneously)-.165 E 5.5(.T)-.715 G(he pack)-5.5 E
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2.75(na)-12.65 G(ddition to connections F)-2.75 E
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(starting and stopping all the time, with initial windo)117.3 170.2 Q
(ws of three or four pack)-.275 E 2.75(ets. There)-.11 F
(are also TCP connections with short quiescent periods \(web bro)117.3
183.2 Q(wsing sessions using)-.275 E(HTTP 1.1\).)117.3 196.2 Q
(The audio and video connections ha)5.5 E .33 -.165(ve i)-.22 H
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(bandwidth might v)117.3 209.2 Q(ary o)-.275 E -.165(ve)-.165 G 2.75(rt)
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-.22 E<8c63>-.275 E(\(routing traf)117.3 222.2 Q(\214c, and dif)-.275 E
2.75(fserv\). All)-.275 F(of this is happening at once, so the aggre)
2.75 E -.055(ga)-.165 G(te arri).055 E -.275(va)-.275 G(l).275 E
(rate naturally v)117.3 235.2 Q(aries from one R)-.275 E(TT to the ne)
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-2.75 G(ly white noise.).165 E
(Further analysis is required to analyze the ef)100.8 277.8 Q
(fects of these scenarios.)-.275 E 1.76 -.88(We n)100.8 294.4 T
(ote that F).88 E(aster Restart in V)-.165 E
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(oIP TFRC, the sender is restricted to sending at most one)-1.419 E
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2.75(al. Similarly)-.275 F 2.75(,F)-.715 G(aster Restart in the def)
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(aster Restart w)-.165 E(ould be if added to TCP;)-.11 E
(TFRC is controlled of a sending rate, while)5.5 E
(TCP is controlled by a windo)100.8 346.4 Q 1.43 -.715(w, a)-.275 H
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Q/F1 11/Times-Bold@0 SF(8.)72 402 Q/F2 14/Times-Bold@0 SF
(Simulations of the V)5.5 E(oIP V)-1.4 E(ariant of TFRC)-1.288 E F0
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(IP mode for TFRC has been added to the NS simulator)1.419 E 2.75(,a)
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474.2 Q(ault TFRC, without the V)-.11 E(oIP v)-1.419 E(ariant, w)-.275 E
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100.8 526.2 Q(oIP pack)-1.419 E(ets just as lik)-.11 E
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555.8 Q(ws competing with a V)-.275 E(oIP TFRC \215o)-1.419 E 2.75(ww)
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(in a scenario with a congested router with a DropT)100.8 568.8 Q
(ail queue, the V)-.88 E(oIP TCP \215o)-1.419 E 2.75(wr)-.275 G(ecei)
-2.75 E -.165(ve)-.275 G(s).165 E(more than its f)100.8 581.8 Q
(air share in bytes per second.)-.11 E(This is the case e)5.5 E -.165
(ve)-.275 G 2.75(nf).165 G(or a scenario where the)-2.75 E(TCP \215o)
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E -.165(ve)-.275 G 2.75(no).165 G(ne measured in pack)-2.75 E
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E -.165(ve)-.275 G 2.75(sa).165 G(smaller pack)100.8 633.8 Q
(et drop rate than the TCP \215o)-.11 E 2.75(ww)-.275 G(ith a b)-2.75 E
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100.8 650.4 Q(xpected, the pack)-.165 E(et dropping beha)-.11 E
(vior can be v)-.22 E(aried by v)-.275 E(arying the Acti)-.275 E .33
-.165(ve Q)-.275 H(ueue).165 E(Management mechanism in the router)100.8
663.4 Q 5.5(.W)-.605 G(hen the routers use RED in pack)-5.5 E
(et mode, where)-.11 E(each *pack)100.8 676.4 Q
(et* has the same probability of being dropped, the TFRC and TCP \215o)
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689.4 Q(et drop rate.)-.11 E
(In contrast, when the routers use RED in byte mode,)5.5 E(where each *\
byte* has the same probability of being dropped, the TFRC \215o)100.8
702.4 Q 2.75(ws)-.275 G(ees a much)-2.75 E(smaller pack)100.8 715.4 Q
(et drop rate than the TCP \215o)-.11 E(ws.)-.275 E(Flo)72 769 Q(yd/K)
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(oIP v)-1.419 E(ariant of TFRC has been for the TCP \215o)-.275 E
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.33 -.165(ve r)-.22 H(ough f).165 E
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100.8 124 Q(ely to be dropped than small pack)-.11 E
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E(are more lik)100.8 137 Q(ely to ha)-.11 E .33 -.165(ve p)-.22 H(ack)
.165 E(ets dropped than are \215o)-.11 E
(ws with a smooth sending rate, \215o)-.275 E(ws)-.275 E(using the V)
100.8 150 Q(oIP v)-1.419 E(ariant of TFRC could recei)-.275 E .33 -.165
(ve m)-.275 H(ore bandwidth than competing TCP \215o).165 E(ws.)-.275 E
(Although the V)100.8 166.6 Q(oIP v)-1.419 E(ariant of TFRC doesn')-.275
E 2.75(tr)-.198 G(equire that applications are limited by a)-2.75 E
(maximum sending rate, in f)100.8 179.6 Q(act V)-.11 E(oIP \215o)-1.419
E(ws do ha)-.275 E .33 -.165(ve s)-.22 H(uch a limitation.).165 E
(As illustrated in the)5.5 E(simulations by T)100.8 192.6 Q
(om Phelan, this complicates the issue of e)-.88 E(xploring the f)-.165
E(airness between)-.11 E(TCP and V)100.8 205.6 Q(oIP TFRC \215o)-1.419 E
(ws.)-.275 E(In addition, for V)100.8 222.2 Q(oIP TFRC \215o)-1.419 E
(ws with a maximum sending rate of 96 Kbps, or with a)-.275 E
(smaller maximum sending rate, V)100.8 235.2 Q
(oIP TFRC only reduces the sending rate of these \215o)-1.419 E(ws)-.275
E(when the pack)100.8 248.2 Q(et drop rate is f)-.11 E(airly high.)-.11
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412.8 Q(Los Angeles, CA 90095)100.8 425.8 Q(USA)100.8 438.8 Q F1
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(yright \(C\) The Internet Society 2004.)-.11 E
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