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/F0 10/Courier-Bold@0 SF(Internet Engineering Task Force)72 85 Q(RMT WG)
209.999 E 203.999(INTERNET-DRAFT M.Luby/Digital)72 98 R(Fountain)6 E
149.999(draft-ietf-rmt-pi-alc-08.ps J.Gemmell/Microsoft)72 111 R
(L.Vicisano/Cisco)407.999 124 Q(L.Rizzo/ACIRI and Univ. Pisa)335.999 137
Q(J. Crowcroft/UCL)407.999 150 Q(25 April 2002)425.999 163 Q
(Expires: October 2002)377.999 176 Q/F1 14/Times-Bold@0 SF(Asynchr)
129.38 201 Q(onous Lay)-.252 E(er)-.14 E(ed Coding pr)-.252 E
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(Status of this Document)72 246 Q/F3 11/Times-Roman@0 SF(This document \
is an Internet-Draft and is in full conformance with all pro)72 262.6 Q
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(Internet-Drafts are v)72 344.2 Q
(alid for a maximum of six months and may be updated, replaced, or)-.275
E(obsoleted by other documents at an)72 357.2 Q 2.75(yt)-.165 G 2.75
(ime. It)-2.75 F(is inappropriate to use Internet-Drafts as reference)
2.75 E(material or to cite them other than as a "w)72 370.2 Q
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(The list of current Internet-Drafts can be accessed at http://www)72
396.2 Q(.ietf.or)-.715 E(g/ietf/1id-abstracts.txt)-.198 E 1.76 -.88
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(This document is a product of the IETF RMT WG.)72 448.2 Q
(Comments should be addressed to the)5.5 E(authors, or the WG')72 461.2
Q 2.75(sm)-.605 G(ailing list at rmt@lbl.go)-2.75 E -.715(v.)-.165 G F2
(Abstract)267.534 493.2 Q F3(This document describes the Asynchronous L\
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(scalable reliable content deli)97 528.8 Q -.165(ve)-.275 G
(ry protocol, hereafter referred to as ALC.).165 E(ALC)5.5 E
(combines the LCT b)97 541.8 Q
(uilding block [13], a multiple rate congestion control b)-.22 E
(uilding)-.22 E
(block that is in compliance with RFC2357 [14] and the FEC b)97 554.8 Q
(uilding block [12] to)-.22 E(pro)97 567.8 Q
(vide congestion controlled reliable asynchronous deli)-.165 E -.165(ve)
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97 580.8 Q -.165(ve)-.275 G(rs from a single sender).165 E(.)-.605 E
(Luby/Gemmell/V)72 769 Q(icisano/Rizzo/Cro)-.66 E 207.017(wcroft [P)
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(October 2002)2.75 E(April 2002)118.232 E/F1 13/Times-Bold@0 SF -1.196
(Ta)239.126 85 S(ble of Contents)1.196 E/F2 10/Times-Roman@0 SF
(1. Applicability Statement)97 123 Q F0 11(..................)12.72 G F2
(3)11.5 E(1.1. Deli)107 135 Q -.15(ve)-.25 G(ry service models).15 E F0
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G F2(5)11.5 E(2. Architecture De\214nition)97 171 Q F0 11
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(3. Conformance Statement)97 243 Q F0 11(..................)11.07 G F2
(11)6.5 E(4. Functionality De\214nition)97 255 Q F0 11
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F0 11(..................)12.87 G F2(21)6.5 E(5. Security Considerations)
97 327 Q F0 11(..................)12.17 G F2(22)6.5 E(6. IAN)97 339 Q
2.5(AC)-.35 G(onsiderations)-2.5 E F0 11(...................)7.11 G F2
(23)6.5 E(7. Intellectual Property Issues)97 351 Q F0 11
(.................)12.88 G F2(23)6.5 E(8. Ackno)97 363 Q(wledgments)-.25
E F0 11(....................)5.76 G F2(24)6.5 E(9. References)97 375 Q
F0 11(......................)8.58 G F2(24)6.5 E(10. Authors' Addresses)
97 387 Q F0 11(...................)10.1 G F2(25)6.5 E(11. Full Cop)97
399 Q(yright Statement)-.1 E F0 11(..................)1.42 G F2(26)6.5 E
F0(Luby/Gemmell/V)72 769 Q(icisano/Rizzo/Cro)-.66 E 207.017(wcroft [P)
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 when the session is)72 345 Q(about to close and the Close Object \215a\
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371 Q(ets for the object is about to end.)-.11 E
(The push model is particularly attracti)72 397 Q .33 -.165(ve i)-.275 H
2.75(ns).165 G(atellite netw)-2.75 E(orks and wireless netw)-.11 E 2.75
(orks. In)-.11 F(these)2.75 E(en)72 410 Q(vironments a session may incl\
ude one channel and a sender may send pack)-.44 E(ets at a \214x)-.11 E
(ed rate to)-.165 E(this channel, b)72 423 Q(ut sending at a \214x)-.22
E(ed rate without congestion control is outside the scope of this)-.165
E(document.)72 436 Q/F1 11/Times-Bold@0 SF(On-demand content deli)72 475
Q -.11(ve)-.11 G(ry model.).11 E F0 -.165(Fo)72 491.6 S 2.75(ra).165 G
2.75(no)-2.75 G(n-demand content deli)-2.75 E -.165(ve)-.275 G
(ry service model, senders typically transmit for some gi).165 E -.165
(ve)-.275 G 2.75(nt).165 G(ime)-2.75 E
(period selected to be long enough to allo)72 504.6 Q 2.75(wa)-.275 G
(ll the intended recei)-2.75 E -.165(ve)-.275 G
(rs to join the session and).165 E(reco)72 517.6 Q -.165(ve)-.165 G 2.75
(ras).165 G(ingle object.)-2.75 E -.165(Fo)5.5 G 2.75(re).165 G
(xample a popular softw)-2.915 E
(are update might be transmitted using ALC)-.11 E(for se)72 530.6 Q
-.165(ve)-.275 G(ral days, e).165 E -.165(ve)-.275 G 2.75(nt).165 G
(hough a recei)-2.75 E -.165(ve)-.275 G 2.75(rm).165 G
(ay be able to complete the do)-2.75 E(wnload in one hour total)-.275 E
(of connection time, perhaps spread o)72 543.6 Q -.165(ve)-.165 G 2.75
(rs).165 G -2.365 -.275(ev e)-2.75 H(ral interv).275 E(als of time.)
-.275 E(In this case the recei)5.5 E -.165(ve)-.275 G(rs join).165 E
(the session at an)72 556.6 Q 2.75(yp)-.165 G
(oint in time when it is acti)-2.75 E -.165(ve)-.275 G 2.75(.R).165 G
(ecei)-2.75 E -.165(ve)-.275 G(rs lea).165 E .33 -.165(ve t)-.22 H
(he session when the).165 E 2.75(yh)-.165 G -2.475 -.22(av e)-2.75 H
(recei)72 569.6 Q -.165(ve)-.275 G 2.75(de).165 G(nough pack)-2.75 E
(ets to reco)-.11 E -.165(ve)-.165 G 2.75(rt).165 G(he object.)-2.75 E
(The recei)5.5 E -.165(ve)-.275 G(rs obtain a Session Description for)
.165 E -.165(ex)72 582.6 S(ample by contacting a web serv).165 E(er)
-.165 E(.)-.605 E F1(Other ser)72 621.6 Q(vice models.)-.11 E F0
(There may be other reliable content deli)72 638.2 Q -.165(ve)-.275 G
(ry service models that can be supported by ALC.).165 E(The)5.5 E
(description of the potential applications, the appropriate deli)72
651.2 Q -.165(ve)-.275 G(ry service model, and the).165 E(additional me\
chanisms to support such functionalities when combined with ALC is be)72
664.2 Q(yond the)-.165 E(scope of this document.)72 677.2 Q
(Luby/Gemmell/V)72 769 Q(icisano/Rizzo/Cro)-.66 E 149.267
(wcroft Section)-.275 F 2.75(1.1. [P)2.75 F(age 4])-.165 E EP
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(October 2002)2.75 E(April 2002)118.232 E/F1 11/Times-Bold@0 SF(1.2.)72
85 Q/F2 13/Times-Bold@0 SF(Scalability)5.5 E F0(Massi)72 101.6 Q .33
-.165(ve s)-.275 H(calability is a primary design goal for ALC.).165 E
(IP multicast is inherently massi)5.5 E -.165(ve)-.275 G(ly).165 E
(scalable, b)72 114.6 Q(ut the best ef)-.22 E(fort service that it pro)
-.275 E(vides does not pro)-.165 E(vide session management)-.165 E
(functionality)72 127.6 Q 2.75(,c)-.715 G
(ongestion control or reliability)-2.75 E 5.5(.A)-.715 G(LC pro)-5.5 E
(vides all of this on top of IP multicast)-.165 E
(without sacri\214cing an)72 140.6 Q 2.75(yo)-.165 G 2.75(ft)-2.75 G
(he inherent scalability of IP multicast.)-2.75 E(ALC has the follo)5.5
E(wing)-.275 E(properties:)72 153.6 Q 5.5(oT)72 183.2 S 2.75(oe)-6.38 G
(ach recei)-2.75 E -.165(ve)-.275 G .88 -.44(r, i).165 H 2.75(ta).44 G(\
ppears as if though there is a dedicated session from the sender to the)
-2.75 E(recei)83 196.2 Q -.165(ve)-.275 G .88 -.44(r, w).165 H(here the\
 reception rate adjusts to congestion along the path from sender to rec\
ei).44 E -.165(ve)-.275 G -.605(r.).165 G 5.5(oT)72 212.8 S 2.75(ot)
-6.38 G(he sender)-2.75 E 2.75(,t)-.44 G(here is no dif)-2.75 E
(ference in load or outgoing rate if one recei)-.275 E -.165(ve)-.275 G
2.75(ri).165 G 2.75(sj)-2.75 G(oined to the)-2.75 E
(session or a million \(or an)83 225.8 Q 2.75(yn)-.165 G
(umber of\) recei)-2.75 E -.165(ve)-.275 G
(rs are joined to the session, independent of when).165 E(the recei)83
238.8 Q -.165(ve)-.275 G(rs join and lea).165 E -.165(ve)-.22 G(.).165 E
5.5(oN)72 255.4 S 2.75(of)-5.5 G(eedback pack)-2.75 E
(ets are required from recei)-.11 E -.165(ve)-.275 G(rs to the sender)
.165 E(.)-.605 E 5.5(oA)72 272 S(lmost all pack)-5.5 E(ets in the sessi\
on that pass through a bottleneck link are utilized by do)-.11 E
(wnstream)-.275 E(recei)83 285 Q -.165(ve)-.275 G
(rs, and the session shares the link with competing \215o).165 E(ws f)
-.275 E(airly in proportion to their)-.11 E(utility)83 298 Q(.)-.715 E
(Thus, ALC pro)72 327.6 Q(vides a massi)-.165 E -.165(ve)-.275 G
(ly scalable content deli).165 E -.165(ve)-.275 G
(ry transport that is netw).165 E(ork friendly)-.11 E(.)-.715 E
(ALC intentionally omits an)72 353.6 Q 2.75(ya)-.165 G
(pplication speci\214c features that could potentially limit its)-2.75 E
(scalability)72 366.6 Q 5.5(.B)-.715 G 2.75(yd)-5.5 G(oing so, ALC pro)
-2.75 E(vides a minimal protocol that is massi)-.165 E -.165(ve)-.275 G
(ly scalable.).165 E(Applications may be b)72 379.6 Q
(uilt on top of ALC to pro)-.22 E
(vide additional features that may limit the)-.165 E
(scalability of the application.)72 392.6 Q
(Such applications are outside the scope of this document.)5.5 E F1
(1.3.)72 435.2 Q F2(En)5.5 E(vir)-.52 E(onmental Requir)-.234 E
(ements and Considerations)-.234 E F0(All of the en)72 451.8 Q
(vironmental requirements and considerations that apply to the LCT b)
-.44 E(uilding block)-.22 E([13], the FEC b)72 464.8 Q
(uilding block [12], the multiple rate congestion control b)-.22 E
(uilding block and to an)-.22 E(y)-.165 E(additional b)72 477.8 Q
(uilding blocks that ALC uses also apply to ALC.)-.22 E
(ALC requires connecti)72 503.8 Q(vity between a sender and recei)-.275
E -.165(ve)-.275 G(rs, b).165 E(ut does not require connecti)-.22 E
(vity from)-.275 E(recei)72 516.8 Q -.165(ve)-.275 G(rs to a sender).165
E 5.5(.A)-.605 G(LC inherently w)-5.5 E(orks with all types of netw)-.11
E(orks, including LANs, W)-.11 E(ANs,)-1.32 E
(Intranets, the Internet, asymmetric netw)72 529.8 Q
(orks, wireless netw)-.11 E(orks, and satellite netw)-.11 E 2.75
(orks. Thus,)-.11 F(the)2.75 E(inherent ra)72 542.8 Q 2.75(ws)-.165 G
(calability of ALC is unlimited.)-2.75 E(Ho)5.5 E(we)-.275 E -.165(ve)
-.275 G .88 -.44(r, A).165 H(LC requires recei).44 E -.165(ve)-.275 G
(rs to obtain the).165 E(Session Description out-of-band before joining\
 a session and some implementations of this may)72 555.8 Q
(limit scalability)72 568.8 Q(.)-.715 E(If a recei)72 594.8 Q -.165(ve)
-.275 G 2.75(ri).165 G 2.75(sj)-2.75 G
(oined to multiple ALC sessions then the recei)-2.75 E -.165(ve)-.275 G
2.75(rM).165 G(UST be able to uniquely)-2.75 E(identify and demultiple)
72 607.8 Q 2.75(xp)-.165 G(ack)-2.75 E(ets to the correct session.)-.11
E(The T)5.5 E(ransmission Session Identi\214er \(TSI\))-.385 E
(that MUST appear in each pack)72 620.8 Q
(et header is used for this purpose.)-.11 E(The TSI is scoped by the)5.5
E(IP)5.5 E(address of the sender)72 633.8 Q 2.75(,a)-.44 G(nd the IP ad\
dress of the sender together with the TSI uniquely identify the)-2.75 E
2.75(session. Thus,)72 646.8 R(the demultiple)2.75 E
(xing MUST be done on the basis of the IP address of the sender and)
-.165 E(the TSI of the session from that sender)72 659.8 Q(.)-.605 E
(ALC is presumed to be used with an underlying IP multicast netw)72
685.8 Q(ork or transport service that is a)-.11 E("best ef)72 698.8 Q
(fort" service that does not guarantee pack)-.275 E(et reception, pack)
-.11 E(et reception order)-.11 E 2.75(,a)-.44 G(nd which)-2.75 E
(does not ha)72 711.8 Q .33 -.165(ve a)-.22 H .33 -.165(ny s).165 H
(upport for \215o).165 E 2.75(wo)-.275 G 2.75(rc)-2.75 G
(ongestion control.)-2.75 E(There are currently tw)5.5 E 2.75(om)-.11 G
(odels of)-2.75 E(multicast deli)72 724.8 Q -.165(ve)-.275 G(ry).165 E
2.75(,t)-.715 G(he An)-2.75 E
(y-Source Multicast \(ASM\) model as de\214ned in RFC1112 [3] and the)
-.165 E(Luby/Gemmell/V)72 769 Q(icisano/Rizzo/Cro)-.66 E 149.267
(wcroft Section)-.275 F 2.75(1.3. [P)2.75 F(age 5])-.165 E EP
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(October 2002)2.75 E(April 2002)118.232 E
(Source-Speci\214c Multicast \(SSM\) model as de\214ned in [7]. ALC w)72
85 Q(orks with both multicast)-.11 E(models, b)72 98 Q
(ut in a slightly dif)-.22 E(ferent w)-.275 E(ay with some)-.11 E
(what dif)-.275 E(ferent en)-.275 E(vironmental concerns.)-.44 E(When)
5.5 E(using ASM, a sender S sends pack)72 111 Q
(ets to a multicast group G, and an ALC channel address)-.11 E(consists\
 of the pair \(S,G\), where S is the IP address of the sender and G is \
a multicast group)72 124 Q 2.75(address. When)72 137 R
(using SSM, a sender S sends pack)2.75 E
(ets to an SSM channel \(S,G\), and an ALC)-.11 E
(channel address coincides with the SSM channel address.)72 150 Q 2.75
(As)72 176 S
(ender can locally allocate unique SSM channel addresses, and this mak)
-2.75 E(es allocation of ALC)-.11 E(channel addresses easy with SSM.)72
189 Q 1.76 -.88(To a)5.5 H
(llocate ALC channel addresses using ASM, the sender).88 E(must uniquel\
y chose the ASM multicast group address across the scope of the group, \
and this)72 202 Q(mak)72 215 Q
(es allocation of ALC channel addresses more dif)-.11 E
(\214cult with ASM.)-.275 E
(ALC channels and SSM channels coincide, and thus the recei)72 241 Q
-.165(ve)-.275 G 2.75(rw).165 G(ill only recei)-2.75 E .33 -.165(ve p)
-.275 H(ack).165 E(ets sent to)-.11 E(the requested ALC channel.)72 254
Q -.44(Wi)5.5 G(th ASM, the recei).44 E -.165(ve)-.275 G 2.75(rj).165 G
(oins an ALC channel by joining a multicast)-2.75 E
(group G, and all pack)72 267 Q(ets sent to G, re)-.11 E -.055(ga)-.165
G(rdless of the sender).055 E 2.75(,m)-.44 G(ay be recei)-2.75 E -.165
(ve)-.275 G 2.75(db).165 G 2.75(yt)-2.75 G(he recei)-2.75 E -.165(ve)
-.275 G -.605(r.).165 G(Thus, SSM has compelling security adv)72 280 Q
(antages o)-.275 E -.165(ve)-.165 G 2.75(rA).165 G(SM for pre)-2.75 E
-.165(ve)-.275 G(ntion of denial of service).165 E 2.75(attacks. In)72
293 R(either case, recei)2.75 E -.165(ve)-.275 G
(rs SHOULD use mechanisms to \214lter out pack).165 E(ets from unw)-.11
E(anted)-.11 E(sources.)72 306 Q
(Other issues speci\214c to ALC with respect to ASM is the w)72 332 Q
(ay the multiple rate congestion control)-.11 E -.22(bu)72 345 S
(ilding block interacts with ASM.).22 E(The congestion control b)5.5 E
(uilding block may use the measured)-.22 E(dif)72 358 Q(ference in time\
 between when a join to a channel is sent and when the \214rst pack)
-.275 E(et from the)-.11 E(channel arri)72 371 Q -.165(ve)-.275 G 2.75
(si).165 G 2.75(nd)-2.75 G(eterming the recei)-2.75 E -.165(ve)-.275 G
2.75(rr).165 G(eception rate. The congestion control b)-2.75 E
(uilding block)-.22 E(may also uses pack)72 384 Q(et sequence numbers p\
er channel to measure losses, and this is also used to)-.11 E
(determine the recei)72 397 Q -.165(ve)-.275 G 2.75(rr).165 G
(eception rate.)-2.75 E(These features raise tw)5.5 E 2.75(oc)-.11 G
(oncerns with respect ASM: The)-2.75 E(time dif)72 410 Q(ference betwee\
n when the join to a channel is sent and when the \214rst pack)-.275 E
(et arri)-.11 E -.165(ve)-.275 G 2.75(sc).165 G(an be)-2.75 E
(signifcant due to the use of Rendezv)72 423 Q
(ous Points \(RPs\) and the MSDP protocol, and pack)-.22 E(ets can be)
-.11 E(lost in the switch o)72 436 Q -.165(ve)-.165 G 2.75(rf).165 G(ro\
m the \(*,G\) join to the RP and the \(S,G\) join directly to the sende\
r)-2.75 E(.)-.605 E
(Both of these issues could potentially substantially de)72 449 Q
(grade the reception rate of recei)-.165 E -.165(ve)-.275 G 2.75(rs. T)
.165 F(o)-.88 E(ameliorate these concerns, it is RECOMMENDED that the R\
P be as close to the sender as)72 462 Q 2.75(possible. SSM)72 475 R
(does not share these same concerns.)2.75 E -.165(Fo)5.5 G 2.75(raf).165
G(uller consideration of these issues,)-2.75 E
(consult the multiple rate congestion control b)72 488 Q(uilding block.)
-.22 E(Some netw)72 514 Q(orks are not amenable to some congestion cont\
rol protocols that could be used with)-.11 E 2.75(ALC. In)72 527 R
(particular)2.75 E 2.75(,f)-.44 G(or a satellite or wireless netw)-2.75
E(ork, there may be no mechanism for recei)-.11 E -.165(ve)-.275 G(rs)
.165 E(to ef)72 540 Q(fecti)-.275 E -.165(ve)-.275 G
(ly reduce their reception rate since there may be a \214x).165 E
(ed transmission rate allocated to)-.165 E(the session.)72 553 Q
(ALC is compatible with either IPv4 or IPv6 as no part of the pack)72
579 Q(et is IP v)-.11 E(ersion speci\214c.)-.165 E/F1 11/Times-Bold@0 SF
(2.)72 621.6 Q/F2 14/Times-Bold@0 SF(Ar)5.5 E(chitectur)-.252 E 3.5(eD)
-.252 G(e\214nition)-3.5 E F0(ALC uses the LCT b)72 638.2 Q
(uilding block [13] to pro)-.22 E
(vide in-band session management functionality)-.165 E(.)-.715 E
(ALC uses a multiple rate congestion control b)72 651.2 Q
(uilding block that is compliant with RFC2357 [14])-.22 E(to pro)72
664.2 Q(vide congestion control that is feedback free.)-.165 E(Recei)5.5
E -.165(ve)-.275 G(rs adjust their reception rates).165 E(indi)72 677.2
Q(vidually by joining and lea)-.275 E
(ving channels associated with the session.)-.22 E(ALC uses the FEC)5.5
E -.22(bu)72 690.2 S(ilding block [12] to pro).22 E(vide reliability)
-.165 E 5.5(.T)-.715 G
(he sender generates encoding symbols based on the)-5.5 E
(object to be deli)72 703.2 Q -.165(ve)-.275 G
(red using FEC codes and sends them in pack).165 E
(ets to channels associated with the)-.11 E 2.75(session. Recei)72 716.2
R -.165(ve)-.275 G(rs simply w).165 E(ait for enough pack)-.11 E
(ets to arri)-.11 E .33 -.165(ve i)-.275 H 2.75(no).165 G
(rder to reliably reconstruct the)-2.75 E(Luby/Gemmell/V)72 769 Q
(icisano/Rizzo/Cro)-.66 E 157.517(wcroft Section)-.275 F 2.75(2. [P)2.75
F(age 6])-.165 E EP
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(October 2002)2.75 E(April 2002)118.232 E 2.75(object. Thus,)72 85 R
(there is no request for retransmission of indi)2.75 E(vidual pack)-.275
E(ets from recei)-.11 E -.165(ve)-.275 G(rs that miss).165 E(pack)72 98
Q(ets in order to assure reliable reception of an object, and the pack)
-.11 E(ets and their rate of)-.11 E(transmission out of the sender can \
be independent of the number and the indi)72 111 Q(vidual reception)
-.275 E -.165(ex)72 124 S(periences of the recei).165 E -.165(ve)-.275 G
(rs.).165 E
(The de\214nition of a session for ALC is the same as it is for LCT)72
150 Q 5.5(.A)-.814 G 2.75(nA)-5.5 G(LC session comprises)-2.75 E(multip\
le channels originating at a single sender that are used for some perio\
d of time to carry)72 163 Q(pack)72 176 Q(ets pertaining to the transmi\
ssion of one or more objects that can be of interest to recei)-.11 E
-.165(ve)-.275 G(rs.).165 E(Congestion control is performed o)72 189 Q
-.165(ve)-.165 G 2.75(rt).165 G(he aggre)-2.75 E -.055(ga)-.165 G
(te of pack).055 E(ets sent to channels belonging to a)-.11 E 2.75
(session. The)72 202 R -.11(fa)2.75 G(ct that an ALC session is restric\
ted to a single sender does not preclude the).11 E(possibility of recei)
72 215 Q(ving pack)-.275 E
(ets for the same objects from multiple senders.)-.11 E(Ho)5.5 E(we)
-.275 E -.165(ve)-.275 G .88 -.44(r, e).165 H(ach sender).44 E -.11(wo)
72 228 S(uld be sending pack).11 E(ets to a a dif)-.11 E
(ferent session to which congestion control is indi)-.275 E(vidually)
-.275 E 2.75(applied. Although)72 241 R(recei)2.75 E
(ving concurrently from multiple sessions is allo)-.275 E(wed, ho)-.275
E 2.75(wt)-.275 G(his is done at)-2.75 E(the application le)72 254 Q
-.165(ve)-.275 G 2.75(li).165 G 2.75(so)-2.75 G
(utside the scope of this document.)-2.75 E(ALC is a protocol instantia\
tion as de\214ned in RFC3048 [18]. This document describes v)72 280 Q
(ersion 1 of)-.165 E(ALC which MUST use v)72 293 Q
(ersion 1 of LCT described in [13]. Lik)-.165 E 2.75(eL)-.11 G(CT)-2.75
E 2.75(,A)-.814 G(LC is designed to be)-2.75 E
(used with the IP multicast netw)72 306 Q(ork service.)-.11 E
(This speci\214cation de\214nes ALC as payload of the)5.5 E
(UDP transport protocol [17] that supports IP multicast deli)72 319 Q
-.165(ve)-.275 G(ry of pack).165 E 2.75(ets. Future)-.11 F -.165(ve)2.75
G(rsions of this).165 E(speci\214cation, or companion documents may e)72
332 Q(xtend ALC to use the IP netw)-.165 E(ork layer service)-.11 E
(directly)72 345 Q 5.5(.A)-.715 G
(LC could be used as the basis for designing a protocol that uses a dif)
-5.5 E(ferent underlying)-.275 E(netw)72 358 Q
(ork service such as unicast UDP)-.11 E 2.75(,b)-1.221 G
(ut the design of such a protocol is outside the scope of this)-2.97 E
(document.)72 371 Q(An ALC pack)72 397 Q(et header immediately follo)
-.11 E(ws the UDP header and consists of the def)-.275 E(ault LCT)-.11 E
(header that is described in [13] follo)72 410 Q(wed by the FEC P)-.275
E(ayload ID that is described in [12]. The)-.165 E(Congestion Control I\
nformation \214eld within the LCT header carries the required Congestio\
n)72 423 Q(Control Information that is described in the multiple rate c\
ongestion control b)72 436 Q(uilding block)-.22 E
(speci\214ed that is compliant with RFC2357 [14]. The pack)72 449 Q
(et payload that follo)-.11 E(ws the ALC pack)-.275 E(et)-.11 E
(header consists of encoding symbols that are identi\214ed by the FEC P)
72 462 Q(ayload ID as described in)-.165 E([12].)72 475 Q(Each recei)72
491.6 Q -.165(ve)-.275 G 2.75(ri).165 G 2.75(sr)-2.75 G
(equired to obtain a Session Description before joining an ALC session.)
-2.75 E(As)5.5 E(described later)72 504.6 Q 2.75(,t)-.44 G(he Session D\
escription includes out-of-band information required for the LCT)-2.75 E
(,)-.814 E(FEC and the multiple rate congestion control b)72 517.6 Q
(uilding blocks.)-.22 E(The FEC Object T)5.5 E(ransmission)-.385 E
(Information speci\214ed in the FEC b)72 530.6 Q
(uilding block [12] required for each object to be recei)-.22 E -.165
(ve)-.275 G 2.75(db).165 G 2.75(ya)-2.75 G(recei)72 543.6 Q -.165(ve)
-.275 G 2.75(rc).165 G(an be communicated to a recei)-2.75 E -.165(ve)
-.275 G 2.75(re).165 G(ither out-of-band or in-band using a Header)-2.75
E 2.75(Extension. The)72 556.6 R
(means for communicating the Session Description and the FEC Object)2.75
E -.385(Tr)72 569.6 S(ansmission Information to a recei).385 E -.165(ve)
-.275 G 2.75(ri).165 G 2.75(so)-2.75 G
(utside the scope of this document.)-2.75 E/F1 11/Times-Bold@0 SF(2.1.)
72 612.2 Q/F2 13/Times-Bold@0 SF(LCT b)5.5 E(uilding block)-.26 E F0
(LCT requires recei)72 628.8 Q -.165(ve)-.275 G
(rs to be able to uniquely identify and demultiple).165 E 2.75(xp)-.165
G(ack)-2.75 E(ets associated with an)-.11 E
(LCT session, and ALC inherits and strengthens this requirement.)72
641.8 Q 2.75(AT)5.5 G(ransport Session Identi\214er)-3.135 E(\(TSI\) MU\
ST be associated with each session and MUST be carried in the LCT heade\
r of each)72 654.8 Q(ALC pack)72 667.8 Q 2.75(et. The)-.11 F(TSI is sco\
ped by the sender IP address, and the \(sender IP address, TSI\) pair)
2.75 E(MUST uniquely identify the session.)72 680.8 Q(The LCT header co\
ntains a Congestion Control Information \(CCI\) \214eld that MUST be us\
ed to)72 706.8 Q(carry the Congestion Control Information from the spec\
i\214ed multiple rate congestion control)72 719.8 Q(Luby/Gemmell/V)72
769 Q(icisano/Rizzo/Cro)-.66 E 149.267(wcroft Section)-.275 F 2.75
(2.1. [P)2.75 F(age 7])-.165 E EP
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(October 2002)2.75 E(April 2002)118.232 E 2.75(protocol. There)72 85 R(\
is a \214eld in the LCT header that speci\214es the length of the CCI \
\214eld, and the)2.75 E(multiple rate congestion control b)72 98 Q
(uilding block MUST uniquely identify a format of the CCI \214eld)-.22 E
(that corresponds to this length.)72 111 Q
(The LCT header contains a Codepoint \214eld that MA)72 137 Q 2.75(Yb)
-1.155 G 2.75(eu)-2.75 G(sed to communicate to a recei)-2.75 E -.165(ve)
-.275 G 2.75(rt).165 G(he)-2.75 E(settings for information that may v)72
150 Q(ary during a session.)-.275 E
(If used, the mapping between settings)5.5 E(and Codepoint v)72 163 Q(a\
lues is to be communicated in the Session Description, and this mapping\
 is)-.275 E(outside the scope of this document.)72 176 Q -.165(Fo)5.5 G
2.75(re).165 G(xample, the FEC Encoding ID that is part of the FEC)
-2.915 E(Object T)72 189 Q
(ransmission Information as speci\214ed in the FEC b)-.385 E
(uilding block [12] could v)-.22 E(ary for each)-.275 E
(object carried in the session, and the Codepoint v)72 202 Q
(alue could be used to communicate the FEC)-.275 E
(Encoding ID to be used for each object.)72 215 Q
(The mapping between FEC Encoding IDs and)5.5 E
(Codepoints could be for e)72 228 Q(xample the identity mapping.)-.165 E
(If more than one object is to be carried within a session then the T)72
254 Q(ransmission Object Identi\214er)-.385 E(\(T)72 267 Q
(OI\) MUST be used in the LCT header to identify which pack)-.198 E
(ets are to be associated with which)-.11 E 2.75(objects. In)72 280 R
(this case the recei)2.75 E -.165(ve)-.275 G 2.75(rM).165 G
(UST use the T)-2.75 E(OI to associate recei)-.198 E -.165(ve)-.275 G
2.75(dp).165 G(ack)-2.75 E(ets with objects.)-.11 E(The T)72 293 Q
(OI is scoped by the IP address of the sender and the TSI, i.e., the T)
-.198 E(OI is scoped by the)-.198 E 2.75(session. The)72 306 R -.198(TO)
2.75 G 2.75(If).198 G(or each object is REQ)-2.75 E
(UIRED to be unique within a session, b)-.11 E(ut MA)-.22 E 2.75(YN)
-1.155 G .88 -.44(OT b)-2.75 H(e).44 E(unique across sessions.)72 319 Q
(Furthermore, the same object MA)5.5 E 2.75(Yh)-1.155 G -2.475 -.22
(av e)-2.75 H 2.75(ad)2.97 G(if)-2.75 E(ferent T)-.275 E(OI in dif)-.198
E(ferent)-.275 E 2.75(sessions. The)72 332 R(mapping between T)2.75 E
(OIs and objects carried in a session is outside the scope of this)-.198
E(document.)72 345 Q
(If only one object is carried within a session then the T)72 371 Q
(OI MA)-.198 E 2.75(Yb)-1.155 G 2.75(eo)-2.75 G
(mitted from the LCT header)-2.75 E(.)-.605 E(The def)72 397 Q
(ault LCT header from v)-.11 E(ersion 1 of the LCT b)-.165 E
(uilding block [13] MUST be used.)-.22 E/F1 11/Times-Bold@0 SF(2.2.)72
439.6 Q/F2 13/Times-Bold@0 SF(Multiple rate congestion contr)5.5 E(ol b)
-.234 E(uilding block)-.26 E F0(Implementors of ALC MUST implement a mu\
ltiple rate feedback-free congestion control)72 456.2 Q -.22(bu)72 469.2
S(ilding block that is in accordance to RFC2357 [14]. Congestion contro\
l MUST be applied to all).22 E(pack)72 482.2 Q(ets within a session ind\
ependently of which information about which object is carried in each)
-.11 E(pack)72 495.2 Q 2.75(et. Multiple)-.11 F(rate congestion control\
 is speci\214ed because of its suitability to scale massi)2.75 E -.165
(ve)-.275 G(ly).165 E
(and because of its suitability for reliable content deli)72 508.2 Q
-.165(ve)-.275 G(ry).165 E 5.5(.T)-.715 G
(he multiple rate congestion control)-5.5 E -.22(bu)72 521.2 S(ilding b\
lock MUST specify in-band Congestion Control Information \(CCI\) that M\
UST be).22 E(carried in the CCI \214eld of the LCT header)72 534.2 Q 5.5
(.T)-.605 G(he multiple rate congestion control b)-5.5 E(uilding block)
-.22 E(MA)72 547.2 Q 2.75(Ys)-1.155 G(pecify more than one format, b)
-2.75 E(ut it MUST specify at most one format for each of the)-.22 E
(possible lengths 32, 64, 96 or 128 bits.)72 560.2 Q(The v)5.5 E
(alue of C in the LCT header that determines the)-.275 E(length of the \
CCI \214eld MUST correspond to one of the lengths for the CCI de\214ned\
 in the multiple)72 573.2 Q(rate congestion control b)72 586.2 Q
(uilding block, this length MUST be the same for all pack)-.22 E
(ets sent to a)-.11 E(session, and the CCI format that corresponds to t\
he length as speci\214ed in the multiple rate)72 599.2 Q
(congestion control b)72 612.2 Q(uilding block MUST be the format used \
for the CCI \214eld in the LCT header)-.22 E(.)-.605 E
(When using a multiple rate congestion control b)72 638.2 Q
(uilding block a sender sends pack)-.22 E(ets in the)-.11 E
(session to se)72 651.2 Q -.165(ve)-.275 G
(ral channels at potentially dif).165 E(ferent rates. Then, indi)-.275 E
(vidual recei)-.275 E -.165(ve)-.275 G(rs adjust their).165 E
(reception rate within a session by adjusting which set of channels the)
72 664.2 Q 2.75(ya)-.165 G(re joined to at each point)-2.75 E
(in time depending on the a)72 677.2 Q -.275(va)-.22 G
(ilable bandwidth between the recei).275 E -.165(ve)-.275 G 2.75(ra).165
G(nd the sender)-2.75 E 2.75(,b)-.44 G(ut)-2.97 E
(independent of other recei)72 690.2 Q -.165(ve)-.275 G(rs.).165 E
(Luby/Gemmell/V)72 769 Q(icisano/Rizzo/Cro)-.66 E 149.267
(wcroft Section)-.275 F 2.75(2.2. [P)2.75 F(age 8])-.165 E EP
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(October 2002)2.75 E(April 2002)118.232 E/F1 11/Times-Bold@0 SF(2.3.)72
85 Q/F2 13/Times-Bold@0 SF(FEC b)5.5 E(uilding block)-.26 E F0
(The FEC b)72 101.6 Q(uilding block [12] pro)-.22 E
(vides reliable object deli)-.165 E -.165(ve)-.275 G
(ry within an ALC session.).165 E(Each)5.5 E(object sent in the session\
 is independently encoded using FEC codes as described in [11], which)72
114.6 Q(pro)72 127.6 Q(vide a more in-depth description of the use of F\
EC codes in reliable content deli)-.165 E -.165(ve)-.275 G(ry).165 E
2.75(protocols. All)72 140.6 R(pack)2.75 E
(ets in an ALC session MUST contain an FEC P)-.11 E
(ayload ID in a format that is)-.165 E(compliant with the FEC b)72 153.6
Q(uilding block [12]. The FEC P)-.22 E
(ayload ID uniquely identi\214es the)-.165 E
(encoding symbols that constitute the payload of each pack)72 166.6 Q
(et, and the recei)-.11 E -.165(ve)-.275 G 2.75(rM).165 G
(UST use the FEC)-2.75 E -.165(Pa)72 179.6 S(yload ID to determine ho)
.165 E 2.75(wt)-.275 G
(he encoding symbols carried in the payload of the pack)-2.75 E(et were)
-.11 E(generated from the object as described in the FEC b)72 192.6 Q
(uilding block.)-.22 E(As described in [12], a recei)72 218.6 Q -.165
(ve)-.275 G 2.75(ri).165 G 2.75(sR)-2.75 G(EQ)-2.75 E
(UIRED to obtain the FEC Object T)-.11 E(ransmission)-.385 E
(Information for each object for which data pack)72 231.6 Q
(ets are recei)-.11 E -.165(ve)-.275 G 2.75(df).165 G(rom the session.)
-2.75 E(The FEC)5.5 E(Object T)72 244.6 Q
(ransmission Information includes:)-.385 E 11(oT)77.5 261.2 S
(he FEC Encoding ID.)-11 E 11(oI)77.5 277.8 S 2.75(fa)-11 G 2.75(nU)
-2.75 G(nder)-2.75 E(-Speci\214ed FEC Encoding ID is used then the FEC \
Encoding Name associated)-.22 E(with the FEC Encoding ID.)94 290.8 Q 11
(oF)77.5 307.4 S
(or each object in the session, the length of the object in bytes.)
-11.165 E 11(oT)77.5 324 S(he additional required FEC Object T)-11 E
(ransmission Information for the FEC Encoding ID as)-.385 E
(prescribed in the FEC b)94 337 Q(uilding block [12]. F)-.22 E(or e)
-.165 E(xample, when the FEC Encoding ID is 128,)-.165 E
(the required FEC Object T)94 350 Q
(ransmission Information is the number of source blocks that the)-.385 E
(object is partitioned into and the length of each source block in byte\
s.)94 363 Q(Some of the FEC Object T)72 392.6 Q
(ransmission Information MA)-.385 E 2.75(Yb)-1.155 G 2.75(ei)-2.75 G
(mplicit based on the)-2.75 E 2.75(implementation. As)72 405.6 R(an e)
2.75 E(xample, source block lengths may be deri)-.165 E -.165(ve)-.275 G
2.75(db).165 G 2.75(ya\214)-2.75 G -.165(xe)-2.75 G 2.75(da).165 G
(lgorithm from)-2.75 E(the object length.)72 418.6 Q(As another e)5.5 E
(xample, it may be that all source blocks are the same length and)-.165
E(this is what is passed out-of-band to the recei)72 431.6 Q -.165(ve)
-.275 G 3.96 -.605(r. A).165 H 2.75(sa).605 G(nother e)-2.75 E
(xample, it could be that the full)-.165 E
(sized source block length is pro)72 444.6 Q
(vided and this is the length used for all b)-.165 E
(ut the last source block,)-.22 E(which is calculated based on the full\
 source block length and the object length.)72 457.6 Q(As another)8.25 E
-.165(ex)72 470.6 S(ample, it could be that the same FEC Encoding ID an\
d FEC Encoding Name are al).165 E -.11(wa)-.11 G(ys used).11 E(for a pa\
rticular application and thus the FEC Encoding ID and FEC Encoding Name\
 are)72 483.6 Q(implicitly de\214ned.)72 496.6 Q(Sometimes the objects \
that will be sent in a session are completely kno)72 522.6 Q
(wn before the recei)-.275 E -.165(ve)-.275 G(r).165 E
(joins the session, in which case the FEC Object T)72 535.6 Q
(ransmission Information for all objects in the)-.385 E
(session can be communicated to recei)72 548.6 Q -.165(ve)-.275 G
(rs before the).165 E 2.75(yj)-.165 G(oin the session.)-2.75 E
(At other times the objects)5.5 E(may not kno)72 561.6 Q
(wn when the session be)-.275 E(gins, or recei)-.165 E -.165(ve)-.275 G
(rs may join a session in progress and may not).165 E(be interested in \
some objects for which transmission has \214nished, or recei)72 574.6 Q
-.165(ve)-.275 G(rs may lea).165 E .33 -.165(ve a s)-.22 H(ession).165 E
(before some objects are e)72 587.6 Q -.165(ve)-.275 G 2.75(na).165 G
-.275(va)-2.97 G(ilable within the session.).275 E
(In these cases, the FEC Object)5.5 E -.385(Tr)72 600.6 S(ansmission In\
formation for each object may be dynamically communicated to recei).385
E -.165(ve)-.275 G(rs at or).165 E(before the time pack)72 613.6 Q
(ets for the object are recei)-.11 E -.165(ve)-.275 G 2.75(df).165 G
(rom the session.)-2.75 E(This may be accomplished)5.5 E(using either a\
n out-of-band mechanism, in-band using the Codepoint \214eld or a Heade\
r Extension,)72 626.6 Q(or an)72 639.6 Q 2.75(yc)-.165 G
(ombination of these methods.)-2.75 E(Ho)5.5 E 2.75(wt)-.275 G
(he FEC Object T)-2.75 E(ransmission Information is)-.385 E
(communicated to recei)72 652.6 Q -.165(ve)-.275 G
(rs is outside the scope of this document.).165 E(If pack)72 678.6 Q
(ets for more than one object are transmitted within a session then a T)
-.11 E(ransmission Object)-.385 E(Identi\214er \(T)72 691.6 Q(OI\) that\
 uniquely identi\214es objects within a session MUST appear in each pac\
k)-.198 E(et)-.11 E(header)72 704.6 Q 5.5(.P)-.605 G
(ortions of the FEC Object T)-5.5 E
(ransmission Information could be the same for all objects in)-.385 E(t\
he session, in which case these portions can be communicated to the rec\
ei)72 717.6 Q -.165(ve)-.275 G 2.75(rw).165 G(ith an indication)-2.75 E
(Luby/Gemmell/V)72 769 Q(icisano/Rizzo/Cro)-.66 E 149.267
(wcroft Section)-.275 F 2.75(2.3. [P)2.75 F(age 9])-.165 E EP
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(October 2002)2.75 E(April 2002)118.232 E
(that this applies to all objects in the session.)72 85 Q
(These portions may be implicitly determined based)5.5 E(on the applica\
tion, e.g., an application may use the same FEC Encoding ID for all obj\
ects in all)72 98 Q 2.75(sessions. If)72 111 R
(there is a portion of the FEC Object T)2.75 E
(ransmission Information that may v)-.385 E(ary from)-.275 E
(object to object and if this FEC Object T)72 124 Q
(ransmission Information is communicated to a recei)-.385 E -.165(ve)
-.275 G(r).165 E(out-of-band then the T)72 137 Q
(OI for the object MUST also be communicated to the recei)-.198 E -.165
(ve)-.275 G 2.75(rt).165 G(ogether)-2.75 E
(with the corresponding FEC Object T)72 150 Q
(ransmission Information, and the recei)-.385 E -.165(ve)-.275 G 2.75
(rM).165 G(UST use the)-2.75 E(corresponding FEC Object T)72 163 Q
(ransmission Information for all pack)-.385 E(ets recei)-.11 E -.165(ve)
-.275 G 2.75(dw).165 G(ith that T)-2.75 E 2.75(OI. Ho)-.198 F(w)-.275 E
(the T)72 176 Q(OI and corresponding FEC Object T)-.198 E
(ransmission Information is communicated out-of-band)-.385 E(to recei)72
189 Q -.165(ve)-.275 G(rs is outside the scope of this document.).165 E
(It is also possible that there is a portion of the FEC Object T)72 215
Q(ransmission Information that may)-.385 E -.275(va)72 228 S
(ry from object to object that is carried in-band, for e).275 E
(xample in the CodePoint \214eld or in Header)-.165 E 2.75
(Extensions. Ho)72 241 R 2.75(wt)-.275 G
(his is done is outside the scope of this document.)-2.75 E
(In this case the FEC Object)5.5 E -.385(Tr)72 254 S(ansmission Informa\
tion is associated with the object identi\214ed by the T).385 E
(OI carried in the pack)-.198 E(et.)-.11 E/F1 11/Times-Bold@0 SF(2.4.)72
296.6 Q/F2 13/Times-Bold@0 SF(Session Description)5.5 E F0
(The Session Description that a recei)72 313.2 Q -.165(ve)-.275 G 2.75
(ri).165 G 2.75(sR)-2.75 G(EQ)-2.75 E
(UIRED to obtain before joining an ALC session)-.11 E
(MUST contain the follo)72 326.2 Q(wing information:)-.275 E 11(oT)77.5
355.8 S(he multiple rate congestion control b)-11 E
(uilding block to be used for the session;)-.22 E 11(oT)77.5 372.4 S
(he sender IP address;)-11 E 11(oT)77.5 389 S
(he number of channels in the session;)-11 E 11(oT)77.5 405.6 S
(he address and port number used for each channel in the session;)-11 E
11(oT)77.5 422.2 S(he T)-11 E
(ransport Session ID \(TSI\) to be used for the session;)-.385 E 11(oA)
77.5 438.8 S 2.75(ni)-11 G
(ndication of whether or not the session carries pack)-2.75 E
(ets for more than one object;)-.11 E 11(oI)77.5 455.4 S 2.75(fH)-11 G(\
eader Extensions are to be used, the format of these Header Extensions.)
-2.75 E 11(oE)77.5 472 S(nough information to determine the pack)-11 E
(et authentication scheme being used, if it is being)-.11 E(used.)94 485
Q(Ho)72 501.6 Q 2.75(wS)-.275 G
(ession Description is communicated to recei)-2.75 E -.165(ve)-.275 G
(rs is outside the scope of this document.).165 E(The Codepoint \214eld\
 within the LCT portion of the header CAN be used to communicate in-ban\
d)72 527.6 Q
(some of the dynamically changing information within a session.)72 540.6
Q 1.76 -.88(To d)5.5 H 2.75(ot).88 G(his, a mapping between)-2.75 E
(Codepoint v)72 553.6 Q(alues and the dif)-.275 E
(ferent dynamic settings MUST be included within the Session)-.275 E(De\
scription, and then settings to be used are communicated via the Codepo\
int v)72 566.6 Q(alue placed into)-.275 E(each pack)72 579.6 Q 2.75
(et. F)-.11 F(or e)-.165 E
(xample, it is possible that multiple objects are deli)-.165 E -.165(ve)
-.275 G(red within the same).165 E(session and that a dif)72 592.6 Q
(ferent FEC encoding algorithm is used for dif)-.275 E
(ferent types of objects.)-.275 E(Then)5.5 E
(the Session Description could contain the mapping between Codepoint v)
72 605.6 Q(alues and FEC Encoding)-.275 E 2.75(IDs. As)72 618.6 R
(another e)2.75 E(xample, it is possible that a dif)-.165 E(ferent pack)
-.275 E(et authentication scheme is used for)-.11 E(dif)72 631.6 Q
(ferent pack)-.275 E(ets sent to the session.)-.11 E
(In this case, the mapping between the pack)5.5 E(et authentication)-.11
E(scheme and Codepoint v)72 644.6 Q(alues could be pro)-.275 E
(vided in the session description.)-.165 E(Combinations of)8.25 E
(settings can be mapped to Codepoint v)72 657.6 Q(alues as well.)-.275 E
-.165(Fo)5.5 G 2.75(re).165 G(xample, a particular combination of a)
-2.915 E(FEC Encoding ID and a pack)72 670.6 Q
(et authentication scheme could be associated with a Codepoint)-.11 E
-.275(va)72 683.6 S(lue.).275 E
(The Session Description could also include, b)72 709.6 Q
(ut is not limited to:)-.22 E(Luby/Gemmell/V)72 769 Q(icisano/Rizzo/Cro)
-.66 E 143.767(wcroft Section)-.275 F 2.75(2.4. [P)2.75 F(age 10])-.165
E EP
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(October 2002)2.75 E(April 2002)118.232 E 11(oT)77.5 85 S
(he mappings between combinations of settings and Codepoint v)-11 E
(alues;)-.275 E 11(oT)77.5 101.6 S(he data rates used for each channel;)
-11 E 11(oT)77.5 118.2 S(he length of the pack)-11 E(et payload;)-.11 E
11(oA)77.5 134.8 S .33 -.165(ny i)-11 H(nformation that is rele).165 E
-.275(va)-.275 G
(nt to each object being transported, such as the Object).275 E -.385
(Tr)94 147.8 S
(ansmission Information for each object, when the object will be a).385
E -.275(va)-.22 G(ilable within the).275 E(session and for ho)94 160.8 Q
2.75(wl)-.275 G(ong.)-2.75 E(The Session Description could be in a form\
 such as SDP as de\214ned in RFC2327 [5], or XML)72 190.4 Q(metadata as\
 de\214ned in RFC3023 [15], or HTTP/Mime headers as de\214ned in RFC206\
8 [4], etc.)72 203.4 Q(It)5.5 E(might be carried in a session announcem\
ent protocol such as SAP as de\214ned in RFC2974 [6],)72 216.4 Q(obtain\
ed using a proprietary session control protocol, located on a web page \
with scheduling)72 229.4 Q(information, or con)72 242.4 Q -.165(vey)-.44
G(ed via E-mail or other out-of-band methods.).165 E
(Discussion of Session)5.5 E(Description formats and methods for commun\
ication of Session Descriptions to recei)72 255.4 Q -.165(ve)-.275 G
(rs is).165 E(be)72 268.4 Q(yond the scope of this document.)-.165 E/F1
11/Times-Bold@0 SF(2.5.)72 311 Q/F2 13/Times-Bold@0 SF -.13(Pa)5.5 G(ck)
.13 E(et authentication b)-.13 E(uilding block)-.26 E F0
(It is RECOMMENDED that implementors of ALC use some pack)72 327.6 Q
(et authentication scheme to)-.11 E
(protect the protocol from attacks. An e)72 340.6 Q
(xample of a possibly suitable scheme is described in [16].)-.165 E
-.165(Pa)72 353.6 S(ck).165 E
(et authentication in ALC, if used, is to be inte)-.11 E
(grated through the Header Extension support)-.165 E(for pack)72 366.6 Q
(et authentication pro)-.11 E(vided in the LCT b)-.165 E(uilding block.)
-.22 E F1(3.)72 409.2 Q/F3 14/Times-Bold@0 SF(Conf)5.5 E
(ormance Statement)-.35 E F0
(This Protocol Instantiation document, in conjunction with the LCT b)72
425.8 Q(uilding block [13], the FEC)-.22 E -.22(bu)72 438.8 S
(ilding block [12] and with a multiple rate congestion control b).22 E
(uilding block completely)-.22 E(speci\214es a w)72 451.8 Q(orking reli\
able multicast transport protocol that conforms to the requirements)-.11
E(described in RFC2357 [14].)72 464.8 Q F1(4.)72 494.4 Q F3
(Functionality De\214nition)5.5 E F0
(This section describes the format and functionality of the data pack)72
511 Q(ets carried in an ALC session)-.11 E
(as well as the sender and recei)72 524 Q -.165(ve)-.275 G 2.75(ro).165
G(perations for a session.)-2.75 E F1(4.1.)72 566.6 Q F2 -.13(Pa)5.5 G
(ck).13 E(et f)-.13 E(ormat used by ALC)-.325 E F0(The pack)72 583.2 Q
(et format used by ALC is the UDP header follo)-.11 E(wed by the def)
-.275 E(ault LCT header follo)-.11 E(wed)-.275 E(by the FEC P)72 596.2 Q
(ayload ID follo)-.165 E(wed by the pack)-.275 E(et payload.)-.11 E
(The def)5.5 E(ault LCT header is described in)-.11 E(the LCT b)72 609.2
Q(uilding block [13] and the FEC P)-.22 E
(ayload ID is described in the FEC b)-.165 E(uilding block [12].)-.22 E
(The Congestion Control Information \214eld in the LCT header contains \
the REQ)72 622.2 Q(UIRED)-.11 E(Congestion Control Information that is \
described in the multiple rate congestion control b)72 635.2 Q(uilding)
-.22 E(block used. The pack)72 648.2 Q
(et payload contains encoding symbols generated from an object. If more)
-.11 E(than one object is carried in the session then the T)72 661.2 Q
(ransmission Object ID \(T)-.385 E(OI\) within the LCT)-.198 E(header M\
UST be used to identify which object the encoding symbols are generated\
 from.)72 674.2 Q -.44(Wi)5.5 G(thin).44 E(the scope of an object, enco\
ding symbols carried in the payload of the pack)72 687.2 Q
(et are identi\214ed by the)-.11 E(FEC P)72 700.2 Q
(ayload ID as described in the FEC b)-.165 E(uilding block.)-.22 E
(Luby/Gemmell/V)72 769 Q(icisano/Rizzo/Cro)-.66 E 143.767
(wcroft Section)-.275 F 2.75(4.1. [P)2.75 F(age 11])-.165 E EP
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(October 2002)2.75 E(April 2002)118.232 E(The v)72 85 Q
(ersion number of ALC speci\214ed in this document is 1.)-.165 E
(This coincides with v)5.5 E(ersion 1 of the)-.165 E(LCT b)72 98 Q
(uilding block [13] used in this speci\214cation.)-.22 E(The LCT v)5.5 E
(ersion number \214eld should be)-.165 E(interpreted as the ALC v)72 111
Q(ersion number \214eld.)-.165 E(The o)72 137 Q -.165(ve)-.165 G
(rall ALC pack).165 E(et format is depicted in Fig. 1.)-.11 E(The pack)
5.5 E(et is an IP pack)-.11 E(et, either IPv4 or)-.11 E
(IPv6, and the IP header precedes the UDP header)72 150 Q 5.5(.T)-.605 G
(he ALC pack)-5.5 E(et format has no dependencies)-.11 E(on the IP v)72
163 Q(ersion number)-.165 E 5.5(.T)-.605 G(he def)-5.5 E
(ault LCT header MUST be used by ALC and this def)-.11 E(ault is)-.11 E
(described in detail in the LCT b)72 176 Q(uilding block [13].)-.22 E/F1
8/Courier@0 SF 91.2(0123)81.6 205.6 S 4.8
(01234567890123456789012345678901)81.6 218.6 S
(+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+)76.8
231.6 Q 120(|U)76.8 244.6 S(DP header)-120 E(|)134.4 E 302.4(||)76.8
257.6 S
(+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+)76.8
270.6 Q 100.8(|D)76.8 283.6 S(efault LCT header)-100.8 E(|)115.2 E 302.4
(||)76.8 296.6 S
(+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+)76.8
309.6 Q 110.4(|F)76.8 322.6 S(EC Payload ID)-110.4 E(|)124.8 E 302.4(||)
76.8 335.6 S
(+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+)76.8
348.6 Q 100.8(|E)76.8 361.6 S(ncoding Symbol\(s\))-100.8 E(|)115.2 E
129.6(|.)76.8 374.6 S 153.6(.. |)-129.6 F
(+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+)76.8
387.6 Q/F2 10/Times-Roman@0 SF(Fig. 1 - Ov)72 426.6 Q(erall ALC pack)
-.15 E(et format)-.1 E F0
(In some special cases an ALC sender may need to produce ALC pack)72
443.2 Q(ets that do not contain an)-.11 E(y)-.165 E
(payload. This may be required, for e)72 456.2 Q
(xample, to signal the end of a session or to con)-.165 E .33 -.165
(vey c)-.44 H(ongestion).165 E
(control information. These data-less pack)72 469.2 Q
(ets do not contain the FEC P)-.11 E(ayload ID either)-.165 E 2.75(,b)
-.44 G(ut only)-2.97 E
(the LCT header \214elds. The total datagram length, con)72 482.2 Q
-.165(vey)-.44 G(ed by outer protocol headers \(e.g. the IP).165 E
(or UDP header\), enables recei)72 495.2 Q -.165(ve)-.275 G
(rs to detect the absence of the ALC payload and FEC P).165 E
(ayload ID.)-.165 E/F3 11/Times-Bold@0 SF(4.2.)72 537.8 Q/F4 13
/Times-Bold@0 SF(Detailed Example of P)5.5 E(ack)-.13 E(et f)-.13 E
(ormat used by ALC)-.325 E F0 2.75(Ad)72 567.4 S(etailed e)-2.75 E
(xample of an ALC pack)-.165 E(et starting with the LCT header is sho)
-.11 E(wn in Fig. 2.)-.275 E(In the)5.5 E -.165(ex)72 580.4 S
(ample, the LCT header is the \214rst 5 32-bit w).165 E(ords, the FEC P)
-.11 E(ayload ID is the ne)-.165 E(xt 2 32-bit)-.165 E -.11(wo)72 593.4
S(rds, and the remainder of the pack).11 E(et is the payload.)-.11 E
(Luby/Gemmell/V)72 769 Q(icisano/Rizzo/Cro)-.66 E 143.767
(wcroft Section)-.275 F 2.75(4.2. [P)2.75 F(age 12])-.165 E EP
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/F0 11/Times-Roman@0 SF(INTERNET)72 49 Q 70.976(-DRAFT Expires:)-1.012 F
(October 2002)2.75 E(April 2002)118.232 E/F1 8/Courier@0 SF 91.2(0123)
81.6 85 S 4.8(01234567890123456789012345678901)81.6 98 S
(+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+)76.8
111 Q 14.4(|1|)76.8 124 S 4.8(0|0|)-9.6 G(1| 1 |0|1|0|0|0|)-4.8 E 33.6
(5|)33.6 G 24(128 |)-4.8 F
(+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+)76.8
137 Q 19.2(|C)76.8 150 S
(ongestion Control Information \(CCI, length = 32 bits\))-19.2 E(|)24 E
(+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+)76.8
163 Q 9.6(|T)76.8 176 S
(ransport Session Identifier \(TSI, length = 32 bits\))-9.6 E(|)43.2 E
(+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+)76.8
189 Q 14.4(|T)76.8 202 S
(ransport Object Identifier \(TOI, length = 32 bits\))-14.4 E(|)43.2 E
(+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+)76.8
215 Q 96(|S)76.8 228 S(ender Current Time)-96 E(|)115.2 E
(+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+)76.8
241 Q 96(|S)76.8 254 S(ource Block Number)-96 E(|)115.2 E
(+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+)76.8
267 Q 96(|E)76.8 280 S(ncoding Symbol ID)-96 E(|)120 E
(+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+)76.8
293 Q 96(|E)76.8 306 S(ncoding Symbol\(s\))-96 E(|)120 E 124.8(|.)76.8
319 S 158.4(.. |)-124.8 F
(+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+)76.8
332 Q/F2 10/Times-Roman@0 SF(Fig. 2 - A detailed e)72 384 Q
(xample of the ALC pack)-.15 E(et format)-.1 E F0
(The LCT portion of the o)72 400.6 Q -.165(ve)-.165 G(rall ALC pack).165
E(et header is of v)-.11 E(ariable size, which is speci\214ed by a)-.275
E(length \214eld in the third byte of the header)72 413.6 Q 5.5(.A)-.605
G(ll inte)-5.5 E(ger \214elds are carried in "big-endian" or)-.165 E
("netw)72 426.6 Q
(ork order" format, that is, most signi\214cant byte \(octet\) \214rst.)
-.11 E(Bits designated as "padding" or)5.5 E("reserv)72 439.6 Q
(ed" \(r\) MUST by set to 0 by senders and ignored by recei)-.165 E
-.165(ve)-.275 G 2.75(rs. Unless).165 F(otherwise noted,)2.75 E
(numeric constants in this speci\214cation are in decimal \(base 10\).)
72 452.6 Q(The function and length and particular setting of the v)72
482.2 Q(alue for each \214eld in this detailed e)-.275 E(xample)-.165 E
(of the header is the follo)72 495.2 Q
(wing, described in the order of their appearance in the header)-.275 E
(.)-.605 E(ALC v)83 524.8 Q(ersion number \(V\): 4 bits)-.165 E
(Indicates the ALC v)105 541.4 Q(ersion number)-.165 E(.)-.605 E
(The ALC v)105 554.4 Q
(ersion number for this speci\214cation is 1 as sho)-.165 E 2.75
(wn. This)-.275 F(is also the LCT)2.75 E -.165(ve)105 567.4 S
(rsion number).165 E(.)-.605 E(Congestion control \215ag \(C\): 2 bits)
83 597 Q(The Congestion Control Information \(CCI\) \214eld speci\214ed\
 by the multiple rate congestion)105 613.6 Q(control b)105 626.6 Q
(uilding block is a multiple of 32-bits in length.)-.22 E
(The multiple rate congestion)5.5 E(control b)105 639.6 Q(uilding block\
 MUST specify a format for the CCI. The congestion control)-.22 E -.22
(bu)105 652.6 S(ilding block MA).22 E 2.75(Ys)-1.155 G
(pecify formats for dif)-2.75 E
(ferent CCI lengths, where the set of possible)-.275 E
(lengths is 32, 64, 96 or 128 bits.)105 665.6 Q(The v)5.5 E
(alue of C MUST match the length of e)-.275 E(xactly one of)-.165 E
(the possible formats for the congestion control b)105 678.6 Q
(uilding block, and this format MUST be)-.22 E
(used for the CCI \214eld.)105 691.6 Q(The v)5.5 E
(alue of C MUST be the same for all pack)-.275 E(ets sent to a session.)
-.11 E(C=0 indicates the 32-bit CCI \214eld format is to be used.)105
704.6 Q(C=1 indicates the 64-bit CCI \214eld format is to be used.)105
717.6 Q(Luby/Gemmell/V)72 769 Q(icisano/Rizzo/Cro)-.66 E 143.767
(wcroft Section)-.275 F 2.75(4.2. [P)2.75 F(age 13])-.165 E EP
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(October 2002)2.75 E(April 2002)118.232 E
(C=2 indicates the 96-bit CCI \214eld format is to be used.)105 85 Q
(C=3 indicates the 128-bit CCI \214eld format is to be used.)105 98 Q
(In the e)105 111 Q
(xample C=0 indicates that a 32-bit format is to be used.)-.165 E
(Reserv)83 140.6 Q(ed \(r\): 2 bits)-.165 E(Reserv)105 157.2 Q
(ed for future use. A sender MUST set these bits to zero and a recei)
-.165 E -.165(ve)-.275 G 2.75(rM).165 G(UST)-2.75 E(ignore these bits.)
105 170.2 Q(As required, these bits are set to 0 in the e)105 183.2 Q
(xample.)-.165 E -.385(Tr)83 212.8 S
(ansport Session Identi\214er \215ag \(S\): 1 bit).385 E
(This is the number of full 32-bit w)105 229.4 Q
(ords in the TSI \214eld.)-.11 E(The TSI \214eld is 32*S + 16*H bits)5.5
E(in length.)105 242.4 Q -.165(Fo)5.5 G 2.75(rA).165 G
(LC the length of the TSI \214eld is REQ)-2.75 E(UIRED to be non-zero.)
-.11 E(This)5.5 E(implies that the setting S=0 and H=0 MUST NO)105 255.4
Q 2.75(Tb)-.44 G 2.75(eu)-2.75 G(sed.)-2.75 E(In the e)105 268.4 Q
(xample S=1 and H=0, and thus the TSI is 32-bits in length.)-.165 E
-.385(Tr)83 298 S(ansport Object Identi\214er \215ag \(O\): 2 bits).385
E(This is the number of full 32-bit w)105 314.6 Q(ords in the T)-.11 E
(OI \214eld.)-.198 E(The T)5.5 E(OI \214eld is 32*O + 16*H)-.198 E
(bits in length.)105 327.6 Q(If more than one object is to be deli)5.5 E
-.165(ve)-.275 G(red in the session then the T).165 E(OI)-.198 E
(MUST be used, in which case the setting O=0 and H=0 MUST NO)105 340.6 Q
2.75(Tb)-.44 G 2.75(eu)-2.75 G(sed.)-2.75 E(In the e)105 353.6 Q
(xample O=1 and H=0, and thus the T)-.165 E(OI is 32-bits in length.)
-.198 E(Half-w)83 383.2 Q(ord \215ag \(H\): 1 bit)-.11 E
(The TSI and the T)105 399.8 Q
(OI \214elds are both multiples of 32-bits plus 16*H bits in length.)
-.198 E(This)5.5 E(allo)105 412.8 Q(ws the TSI and T)-.275 E
(OI \214eld lengths to be multiples of a half-w)-.198 E
(ord \(16 bits\), while)-.11 E(ensuring that the aggre)105 425.8 Q -.055
(ga)-.165 G(te length of the TSI and T).055 E
(OI \214elds is a multiple of 32-bits.)-.198 E(In the e)105 438.8 Q
(xample H=0 which indicates that both TSI and T)-.165 E
(OI are both multiples of 32-bits in)-.198 E(length.)105 451.8 Q
(Sender Current T)83 481.4 Q(ime present \215ag \(T\): 1 bit)-.385 E
2.75(T=0i)105 498 S(ndicates that the Sender Current T)-2.75 E
(ime \(SCT\) \214eld is not present.)-.385 E 2.75(T=1i)105 511 S
(ndicates that the SCT \214eld is present.)-2.75 E
(The SCT is inserted by senders to indicate to recei)105 524 Q -.165(ve)
-.275 G(rs ho).165 E 2.75(wl)-.275 G(ong the session has been in)-2.75 E
(progress.)105 537 Q(In the e)105 550 Q
(xample T=1, which indicates that the SCT is carried in this pack)-.165
E(et.)-.11 E(Expected Residual T)83 579.6 Q
(ime present \215ag \(R\): 1 bit)-.385 E 2.75(R=0i)105 596.2 S
(ndicates that the Expected Residual T)-2.75 E(ime \(ER)-.385 E
(T\) \214eld is not present.)-.66 E 2.75(R=1i)105 609.2 S
(ndicates that the ER)-2.75 E 2.75<548c>-.66 G(eld is present.)-2.75 E
(The ER)105 622.2 Q 2.75(Ti)-.66 G 2.75(si)-2.75 G
(nserted by senders to indicate to recei)-2.75 E -.165(ve)-.275 G(rs ho)
.165 E 2.75(wm)-.275 G(uch longer pack)-2.75 E(ets will be)-.11 E(sent \
to the session for either the single object carried in the session or f\
or the object)105 635.2 Q(identi\214ed by the T)105 648.2 Q
(OI if there are multiple objects carried in the session.)-.198 E
(Senders MUST NO)105 661.2 Q 2.75(Ts)-.44 G(et R = 1 when the ER)-2.75 E
2.75(Tf)-.66 G(or the object is more than 2^32-1 time units)-2.75 E(\(a\
pproximately 49 days\), where time is measured in units of milliseconds\
.)105 674.2 Q(In the e)105 687.2 Q
(xample R=0, which indicates that the ER)-.165 E 2.75(Ti)-.66 G 2.75(sn)
-2.75 G(ot carried in this pack)-2.75 E(et.)-.11 E(Luby/Gemmell/V)72 769
Q(icisano/Rizzo/Cro)-.66 E 143.767(wcroft Section)-.275 F 2.75(4.2. [P)
2.75 F(age 14])-.165 E EP
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/F0 11/Times-Roman@0 SF(INTERNET)72 49 Q 70.976(-DRAFT Expires:)-1.012 F
(October 2002)2.75 E(April 2002)118.232 E
(Close Session \215ag \(A\): 1 bit)83 85 Q(Normally)105 101.6 Q 2.75
(,Ai)-.715 G 2.75(ss)-2.75 G(et to 0.)-2.75 E(The sender MA)5.5 E 2.75
(Ys)-1.155 G(et A to 1 when termination of transmission of)-2.75 E(pack)
105 114.6 Q(ets for the session is imminent.)-.11 E 2.75(AM)5.5 G 2.31
-1.155(AY b)-2.75 H 2.75(es)1.155 G(et to 1 in just the last pack)-2.75
E(et transmitted)-.11 E(for the session, or A MA)105 127.6 Q 2.75(Yb)
-1.155 G 2.75(es)-2.75 G(et to 1 in the last fe)-2.75 E 2.75(ws)-.275 G
(econds of pack)-2.75 E(ets transmitted for the)-.11 E 2.75
(session. Once)105 140.6 R(the sender sets A to 1 in one pack)2.75 E
(et, the sender SHOULD set A to 1 in all)-.11 E(subsequent pack)105
153.6 Q(ets until termination of transmission of pack)-.11 E
(ets for the session.)-.11 E(A)5.5 E(recei)105 166.6 Q -.165(ve)-.275 G
2.75(dp).165 G(ack)-2.75 E(et with A set to 1 indicates to a recei)-.11
E -.165(ve)-.275 G 2.75(rt).165 G(hat the sender will immediately)-2.75
E(stop sending pack)105 179.6 Q(ets for the session.)-.11 E
(When a recei)5.5 E -.165(ve)-.275 G 2.75(rr).165 G(ecei)-2.75 E -.165
(ve)-.275 G 2.75(sap).165 G(ack)-2.75 E(et with A set to 1 the)-.11 E
(recei)105 192.6 Q -.165(ve)-.275 G 2.75(rS).165 G
(HOULD assume that no more pack)-2.75 E
(ets will be sent to the session.)-.11 E(In the e)105 205.6 Q
(xample A=0, and thus this pack)-.165 E
(et does not indicate the close of the session.)-.11 E
(Close Object \215ag \(B\): 1 bit)83 235.2 Q(Normally)105 251.8 Q 2.75
(,Bi)-.715 G 2.75(ss)-2.75 G(et to 0.)-2.75 E(The sender MA)5.5 E 2.75
(Ys)-1.155 G(et B to 1 when termination of transmission of)-2.75 E(pack)
105 264.8 Q(ets for an object is imminent.)-.11 E(If the T)5.5 E
(OI \214eld is in use and B is set to 1 then)-.198 E
(termination of transmission for the object identi\214ed by the T)105
277.8 Q(OI \214eld is imminent.)-.198 E(If the)5.5 E -.198(TO)105 290.8
S 2.75<498c>.198 G(eld is not in use and B is set to 1 then termination\
 of transmission for the one object)-2.75 E
(in the session identi\214ed by out-of-band information is imminent.)105
303.8 Q 2.75(BM)5.5 G 2.31 -1.155(AY b)-2.75 H 2.75(es)1.155 G
(et to 1 in)-2.75 E(just the last pack)105 316.8 Q
(et transmitted for the object, or B MA)-.11 E 2.75(Yb)-1.155 G 2.75(es)
-2.75 G(et to 1 in the last fe)-2.75 E 2.75(ws)-.275 G(econds)-2.75 E
(pack)105 329.8 Q(ets transmitted for the object.)-.11 E
(Once the sender sets B to 1 in one pack)5.5 E(et for a)-.11 E
(particular object, the sender SHOULD set B to 1 in all subsequent pack)
105 342.8 Q(ets for the object)-.11 E
(until termination of transmission of pack)105 355.8 Q
(ets for the object.)-.11 E 2.75(Ar)5.5 G(ecei)-2.75 E -.165(ve)-.275 G
2.75(dp).165 G(ack)-2.75 E(et with B set to)-.11 E 2.75(1i)105 368.8 S
(ndicates to a recei)-2.75 E -.165(ve)-.275 G 2.75(rt).165 G
(hat the sender will immediately stop sending pack)-2.75 E(ets for the)
-.11 E 2.75(object. When)105 381.8 R 2.75(ar)2.75 G(ecei)-2.75 E -.165
(ve)-.275 G 2.75(rr).165 G(ecei)-2.75 E -.165(ve)-.275 G 2.75(sap).165 G
(ack)-2.75 E(et with B set to 1 then it SHOULD assume that no)-.11 E
(more pack)105 394.8 Q(ets will be sent for the object to the session.)
-.11 E(In the e)105 407.8 Q(xample B=0, and thus this pack)-.165 E
(et does not indicate the end of sending data pack)-.11 E(ets)-.11 E
(for the object.)105 420.8 Q(LCT header length \(HDR_LEN\): 8 bits)83
450.4 Q -.88(To)105 467 S
(tal length of the LCT header in units of 32-bit w).88 E 2.75(ords. The)
-.11 F(length of the LCT header)2.75 E(MUST be a multiple of 32-bits.)
105 480 Q
(This \214eld can be used to directly access the portion of the)5.5 E
(pack)105 493 Q(et be)-.11 E(yond the LCT header)-.165 E 2.75(,i)-.44 G
(.e., to the \214rst other header if it e)-2.75 E(xists, or to the pack)
-.165 E(et)-.11 E(payload if it e)105 506 Q
(xists and there is no other header)-.165 E 2.75(,o)-.44 G 2.75(rt)-2.75
G 2.75(ot)-2.75 G(he end of the pack)-2.75 E(et if there are no)-.11 E
(other headers or pack)105 519 Q(et payload.)-.11 E(In the e)105 532 Q(\
xample HDR_LEN=5 to indicate that the length of the LCT header portion \
of the)-.165 E -.165(ove)105 545 S(rall ALC is 5 32-bit w).165 E(ords.)
-.11 E(Codepoint \(CP\): 8 bits)83 574.6 Q(This \214eld is used by ALC \
to carry the mapping that identi\214es settings for portions of the)105
591.2 Q(Session Description that can change within the session.)105
604.2 Q(The mapping between Codepoint)5.5 E -.275(va)105 617.2 S(lues a\
nd the settings for portions of the Session Description is to be commun\
icated out-).275 E(of-band.)105 630.2 Q(In the e)105 643.2 Q(xample the\
 portion of the Session Description that can change within the session \
is)-.165 E(the FEC Encoding ID, and the identity mapping is used betwee\
n Codepoint v)105 656.2 Q(alues and)-.275 E(FEC Encoding IDs.)105 669.2
Q(Thus, CP=128 identi\214es FEC Encoding ID 128, the `)5.5 E
(`Small Block,)-.814 E(Lar)105 682.2 Q
(ge Block and Expandable FEC Codes" as described in the FEC b)-.198 E
(uilding block [12].)-.22 E(The FEC P)105 695.2 Q
(ayload ID associated with FEC Encoding ID 128 is 64-bits in length.)
-.165 E(Luby/Gemmell/V)72 769 Q(icisano/Rizzo/Cro)-.66 E 143.767
(wcroft Section)-.275 F 2.75(4.2. [P)2.75 F(age 15])-.165 E EP
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/F0 11/Times-Roman@0 SF(INTERNET)72 49 Q 70.976(-DRAFT Expires:)-1.012 F
(October 2002)2.75 E(April 2002)118.232 E
(Congestion Control Information \(CCI\): 32, 64, 96 or 128 bits)83 85 Q
(This is \214eld contains the Congestion Control Information as de\214n\
ed by the speci\214ed)105 101.6 Q(multiple rate congestion control b)105
114.6 Q(uilding block.)-.22 E
(The format of this \214eld is determined by)5.5 E
(the multiple rate congestion control b)105 127.6 Q(uilding block.)-.22
E(This \214eld MUST be 32 bits if C=0.)105 140.6 Q
(This \214eld MUST be 64 bits if C=1.)105 153.6 Q
(This \214eld MUST be 96 bits if C=2.)105 166.6 Q
(This \214eld MUST be 128 bits if C=3.)105 179.6 Q(In the e)105 192.6 Q
(xample, the CCI is 32-bits in length.)-.165 E
(The format of the CCI \214eld for the e)5.5 E(xample)-.165 E
(MUST correspond to the format for the 32-bit v)105 205.6 Q
(ersion of the CCI speci\214ed in the multiple)-.165 E
(rate congestion control b)105 218.6 Q(uilding block.)-.22 E -.385(Tr)83
248.2 S(ansport Session Identi\214er \(TSI\): 16, 32 or 48 bits).385 E(\
The TSI uniquely identi\214es a session among all sessions from a parti\
cular sender)105 264.8 Q 5.5(.T)-.605 G(he)-5.5 E(TSI is scoped by the \
sender IP address, and thus the \(sender IP address, TSI\) pair uniquel\
y)105 277.8 Q(identify the session.)105 290.8 Q -.165(Fo)5.5 G 2.75(rA)
.165 G(LC, the TSI MUST be included in the LCT header)-2.75 E(.)-.605 E
(The TSI MUST be unique among all sessions serv)105 316.8 Q
(ed by the sender during the period when)-.165 E(the session is acti)105
329.8 Q -.165(ve)-.275 G 2.75(,a).165 G(nd for a lar)-2.75 E
(ge period of time preceding and follo)-.198 E(wing when the)-.275 E
(session is acti)105 342.8 Q -.165(ve)-.275 G 5.5(.A).165 G
(primary purpose of the TSI is to pre)-2.75 E -.165(ve)-.275 G(nt recei)
.165 E -.165(ve)-.275 G(rs from inadv).165 E(ertently)-.165 E
(accepting pack)105 355.8 Q
(ets from a sender that belong to sessions other than sessions recei)
-.11 E -.165(ve)-.275 G(rs are).165 E(subscribed to.)105 368.8 Q -.165
(Fo)5.5 G 2.75(re).165 G(xample, suppose a session is deacti)-2.915 E
-.275(va)-.275 G(ted and then another session is).275 E(acti)105 381.8 Q
-.275(va)-.275 G(ted by a sender and the tw).275 E 2.75(os)-.11 G
(essions use an o)-2.75 E -.165(ve)-.165 G(rlapping set of channels.)
.165 E 2.75(Ar)5.5 G(ecei)-2.75 E -.165(ve)-.275 G(r).165 E(that connec\
ts and remains connected to the \214rst session during this sender acti)
105 394.8 Q(vity could)-.275 E(possibly accept pack)105 407.8 Q(ets fro\
m the second session as belonging to the \214rst session if the TSI)-.11
E(for the tw)105 420.8 Q 2.75(os)-.11 G(essions were identical.)-2.75 E
(The mapping of TSI \214eld v)5.5 E(alues to sessions is outside)-.275 E
(the scope of this document and is to be done out-of-band.)105 433.8 Q
(The length of the TSI \214eld is 32*S + 16*H bits.)105 446.8 Q
(Note that the aggre)5.5 E -.055(ga)-.165 G(te lengths of the).055 E
(TSI \214eld plus the T)105 459.8 Q
(OI \214eld is a multiple of 32 bits.)-.198 E(In the e)105 472.8 Q
(xample the TSI is 32 bits in length.)-.165 E -.385(Tr)83 502.4 S
(ansport Object Identi\214er \(T).385 E
(OI\): 0, 16, 32, 48, 64, 80, 96 or 112 bits.)-.198 E
(This \214eld indicates which object within the session this pack)105
519 Q(et pertains to.)-.11 E -.165(Fo)5.5 G 2.75(re).165 G(xample, a)
-2.915 E
(sender might send a number of \214les in the same session, using T)105
532 Q(OI=0 for the \214rst \214le,)-.198 E -.198(TO)105 545 S
(I=1 for the second one, etc. As another e).198 E(xample, the T)-.165 E
(OI may be a unique global)-.198 E
(identi\214er of the object that is being transmitted from se)105 558 Q
-.165(ve)-.275 G(ral senders concurrently).165 E 2.75(,a)-.715 G(nd the)
-2.75 E -.198(TO)105 571 S 2.75(Iv).198 G(alue may be the ouptut of a h\
ash function applied to the object. The mapping of T)-3.025 E(OI)-.198 E
(\214eld v)105 584 Q(alues to objects is outside the scope of this docu\
ment and is to be done out-of-band.)-.275 E(The T)105 597 Q
(OI \214eld MUST be used in all pack)-.198 E
(ets if more than one object is to be transmitted in)-.11 E 2.75(as)105
610 S(ession, i.e. the T)-2.75 E
(OI \214eld is either present in all the pack)-.198 E
(ets of a session or is ne)-.11 E -.165(ve)-.275 G(r).165 E(present.)105
623 Q(The length of the T)105 636 Q(OI \214eld is 32*O + 16*H bits.)
-.198 E(Note that the aggre)5.5 E -.055(ga)-.165 G(te lengths of the)
.055 E(TSI \214eld plus the T)105 649 Q
(OI \214eld is a multiple of 32 bits.)-.198 E(In the e)105 662 Q
(xample the T)-.165 E(OI is 32 bits in length.)-.198 E(Sender Current T)
83 691.6 Q(ime \(SCT\): 0 or 32 bits)-.385 E(This \214eld represents th\
e current clock at the sender at the time this pack)105 708.2 Q(et w)
-.11 E(as transmitted,)-.11 E(measured in units of 1ms and computed mod\
ulo 2^32 units from the start of the session.)105 721.2 Q
(Luby/Gemmell/V)72 769 Q(icisano/Rizzo/Cro)-.66 E 143.767
(wcroft Section)-.275 F 2.75(4.2. [P)2.75 F(age 16])-.165 E EP
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/F0 11/Times-Roman@0 SF(INTERNET)72 49 Q 70.976(-DRAFT Expires:)-1.012 F
(October 2002)2.75 E(April 2002)118.232 E(This \214eld MUST NO)105 85 Q
2.75(Tb)-.44 G 2.75(ep)-2.75 G
(resent if T=0 and MUST be present if T=1.)-2.75 E(In this e)105 98 Q
(xample the SCT is present.)-.165 E(Expected Residual T)83 127.6 Q
(ime \(ER)-.385 E(T\): 0 or 32 bits)-.66 E
(This \214eld represents the sender e)105 144.2 Q
(xpected residual transmission time of pack)-.165 E(ets for either)-.11
E(the single object carried in the session or for the object identi\214\
ed by the T)105 157.2 Q(OI if there are)-.198 E
(multiple objects carried in the session.)105 170.2 Q
(This \214eld MUST NO)105 183.2 Q 2.75(Tb)-.44 G 2.75(ep)-2.75 G
(resent if R=0 and MUST be present if R=1.)-2.75 E(In this e)105 196.2 Q
(xample the ER)-.165 E 2.75(Ti)-.66 G 2.75(sn)-2.75 G(ot present.)-2.75
E(FEC P)83 225.8 Q(ayload ID: X bits)-.165 E
(The length and format of the FEC P)105 242.4 Q
(ayload ID depends on the FEC Encoding ID as)-.165 E
(described in the FEC b)105 255.4 Q(uilding block [12]. The FEC P)-.22 E
(ayload ID format is determined by)-.165 E(the FEC Encoding ID that MUS\
T be communicated in the Session Description.)105 268.4 Q(The)8.25 E
(Session Description MA)105 281.4 Q 2.75(Ys)-1.155 G
(pecify that more than one FEC Encoding ID is used in the)-2.75 E(sessi\
on, in which case the Session Description MUST contain a mapping that i\
denti\214es)105 294.4 Q(which Codepoint v)105 307.4 Q
(alues correspond to which FEC Encoding IDs.)-.275 E
(This mapping, if used,)5.5 E(is outside the scope of this document.)105
320.4 Q(The e)105 333.4 Q(xample pack)-.165 E
(et format corresponds to the format for `)-.11 E(`Small Block, Lar)
-.814 E(ge Block and)-.198 E
(Expandable FEC Codes" as described in the FEC b)105 346.4 Q
(uilding block, for which the associated)-.22 E(FEC Encoding ID 128.)105
359.4 Q -.165(Fo)5.5 G 2.75(rF).165 G(EC Encoding ID 128, the FEC P)
-2.75 E(ayload ID consists of the)-.165 E(follo)105 372.4 Q(wing tw)
-.275 E 2.75<6f8c>-.11 G(elds that in total are X = 64 bits in length:)
-2.75 E(Source Block Number \(SBN\): 32 bits)105 402 Q(The Source Block\
 Number identi\214es from which source block of the object the)127 418.6
Q(encoding symbol\(s\) in the payload are generated.)127 431.6 Q
(These blocks are numbered)5.5 E(consecuti)127 444.6 Q -.165(ve)-.275 G
(ly from 0 to N-1, where N is the number of source blocks in the object\
.).165 E(Encoding Symbol ID \(ESI\): 32 bits)105 474.2 Q(The Encoding S\
ymbol ID identi\214es which speci\214c encoding symbol\(s\) generated)
127 490.8 Q(from the source block are carried in the pack)127 503.8 Q
(et payload.)-.11 E(The e)5.5 E(xact details of the)-.165 E(corresponde\
nce between Encoding Symbol IDs and the encoding symbol\(s\) in the)127
516.8 Q(pack)127 529.8 Q(et payload are dependent on the particular enc\
oding algorithm used as identi\214ed)-.11 E
(by the Fec Encoding ID and by the FEC Encoding Name.)127 542.8 Q
(Encoding Symbol\(s\): Y bits)83 572.4 Q
(The encoding symbols are what the recei)105 589 Q -.165(ve)-.275 G 2.75
(ru).165 G(ses to reconstruct an object.)-2.75 E(The total)5.5 E
(length Y of the encoding symbol\(s\) in the pack)105 602 Q
(et can be determined by the recei)-.11 E -.165(ve)-.275 G 2.75(ro).165
G 2.75(ft)-2.75 G(he)-2.75 E(pack)105 615 Q
(et by computing the total length of the recei)-.11 E -.165(ve)-.275 G
2.75(dp).165 G(ack)-2.75 E(et and subtracting of)-.11 E 2.75(ft)-.275 G
(he length)-2.75 E(of the headers.)105 628 Q/F1 11/Times-Bold@0 SF(4.3.)
72 670.6 Q/F2 13/Times-Bold@0 SF(Header)5.5 E(-Extension Fields)-.481 E
F0(Header Extensions can be used to e)72 687.2 Q
(xtend the LCT header portion of the ALC header to)-.165 E
(accommodate optional header \214elds that are not al)72 700.2 Q -.11
(wa)-.11 G(ys used or ha).11 E .33 -.165(ve v)-.22 H(ariable size.)-.11
E(Header)5.5 E(Extensions are not used in the e)72 713.2 Q
(xample ALC pack)-.165 E(et format sho)-.11 E(wn in the pre)-.275 E
(vious subsection.)-.275 E(Luby/Gemmell/V)72 769 Q(icisano/Rizzo/Cro)
-.66 E 143.767(wcroft Section)-.275 F 2.75(4.3. [P)2.75 F(age 17])-.165
E EP
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/F0 11/Times-Roman@0 SF(INTERNET)72 49 Q 70.976(-DRAFT Expires:)-1.012 F
(October 2002)2.75 E(April 2002)118.232 E
(Examples of the use of Header Extensions include:)72 85 Q 11(oE)77.5
101.6 S(xtended-size v)-11 E(ersions of already e)-.165 E
(xisting header \214elds.)-.165 E 11(oS)77.5 118.2 S(ender and Recei)-11
E -.165(ve)-.275 G 2.75(ra).165 G(uthentication information.)-2.75 E(Th\
e presence of Header Extensions can be inferred by the LCT header lengt\
h \(HDR_LEN\): if)72 134.8 Q(HDR_LEN is lar)72 147.8 Q(ger than the len\
gth of the standard header then the remaining header space is)-.198 E
(tak)72 160.8 Q(en by Header Extension \214elds.)-.11 E
(If present, Header Extensions MUST be processed to ensure that the)72
177.4 Q 2.75(ya)-.165 G(re recognized before)-2.75 E(performing an)72
190.4 Q 2.75(yc)-.165 G
(ongestion control procedure or otherwise accepting a pack)-2.75 E
(et. The def)-.11 E(ault action)-.11 E
(for unrecognized Header Extensions is to ignore them. This allo)72
203.4 Q(ws the future introduction of)-.275 E(backw)72 216.4 Q
(ard-compatible enhancements to ALC without changing the ALC v)-.11 E
(ersion number)-.165 E 5.5(.N)-.605 G(on)-5.5 E(backw)72 229.4 Q
(ard-compatible Header Extensions CANNO)-.11 E 2.75(Tb)-.44 G 2.75(ei)
-2.75 G(ntroduced without changing the ALC)-2.75 E -.165(ve)72 242.4 S
(rsion number).165 E(.)-.605 E(There are tw)72 268.4 Q 2.75(of)-.11 G
(ormats for Header Extension \214elds, as depicted belo)-2.75 E 1.43
-.715(w. T)-.275 H(he \214rst format is used for).715 E -.275(va)72
281.4 S(riable-length e).275 E(xtensions, with Header Extension T)-.165
E(ype \(HET\) v)-.88 E(alues between 0 and 127. The)-.275 E
(second format is used for \214x)72 294.4 Q(ed length \(one 32-bit w)
-.165 E(ord\) e)-.11 E(xtensions, using HET v)-.165 E(alues from 127)
-.275 E(to 255.)72 307.4 Q/F1 8/Courier@0 SF 91.2(0123)81.6 346.4 S 4.8
(01234567890123456789012345678901)81.6 359.4 S
(+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+)76.8
372.4 Q 9.6(|H)76.8 385.4 S(ET \(<=127\))-9.6 E 33.6(|H)9.6 G 19.2(EL |)
-33.6 F(|)148.8 E 144(+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +)76.8 398.4 R
302.4(..)76.8 411.4 S 67.2(.H)76.8 424.4 S
(eader Extension Content \(HEC\))-67.2 E(.)91.2 E
(+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+)76.8
437.4 Q 91.2(0123)81.6 463.4 S 4.8(01234567890123456789012345678901)81.6
476.4 S
(+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+)76.8
489.4 Q 9.6(|H)76.8 502.4 S(ET \(>=128\))-9.6 E 33.6(|H)9.6 G
(eader Extension Content \(HEC\))-33.6 E(|)48 E
(+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+)76.8
515.4 Q/F2 10/Times-Roman@0 SF(Fig. 3 - F)72 554.4 Q
(ormat of additional headers)-.15 E F0(The e)72 584 Q
(xplanation of each sub-\214eld is the follo)-.165 E(wing.)-.275 E
(Header Extension T)83 613.6 Q(ype \(HET\): 8 bits)-.88 E(The type of t\
he Header Extension. This document de\214nes a number of possible types\
.)105 630.2 Q(Additional types may be de\214ned in future v)105 643.2 Q
(ersions of this speci\214cation. HET v)-.165 E(alues from)-.275 E 2.75
(0t)105 656.2 S 2.75(o1)-2.75 G(27 are used for v)-2.75 E
(ariable-length Header Extensions. HET v)-.275 E
(alues from 128 to 255 are)-.275 E(used for \214x)105 669.2 Q
(ed-length 32-bit Header Extensions.)-.165 E
(Header Extension Length \(HEL\): 8 bits)83 698.8 Q(Luby/Gemmell/V)72
769 Q(icisano/Rizzo/Cro)-.66 E 143.767(wcroft Section)-.275 F 2.75
(4.3. [P)2.75 F(age 18])-.165 E EP
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/F0 11/Times-Roman@0 SF(INTERNET)72 49 Q 70.976(-DRAFT Expires:)-1.012 F
(October 2002)2.75 E(April 2002)118.232 E
(The length of the whole Header Extension \214eld, e)105 85 Q
(xpressed in multiples of 32-bit w)-.165 E(ords.)-.11 E
(This \214eld MUST be present for v)105 98 Q(ariable-length e)-.275 E
(xtensions \(HET between 0 and 127\) and)-.165 E(MUST NO)105 111 Q 2.75
(Tb)-.44 G 2.75(ep)-2.75 G(resent for \214x)-2.75 E(ed-length e)-.165 E
(xtensions \(HET between 128 and 255\).)-.165 E
(Header Extension Content \(HEC\): v)83 140.6 Q(ariable length)-.275 E(\
The content of the Header Extension. The format of this sub-\214eld dep\
ends on the Header)105 157.2 Q(Extension type.)105 170.2 Q -.165(Fo)5.5
G 2.75<728c>.165 G -.165(xe)-2.75 G
(d-length Header Extensions, the HEC is 24 bits.).165 E -.165(Fo)5.5 G
2.75(rv).165 G(ariable-)-3.025 E
(length Header Extensions, the HEC \214eld has v)105 183.2 Q
(ariable size, as speci\214ed by the HEL \214eld.)-.275 E(Note that the\
 length of each Header Extension \214eld MUST be a multiple of 32 bits.)
105 196.2 Q(Also)5.5 E(note that the total size of the LCT header)105
209.2 Q 2.75(,i)-.44 G(ncluding all Header Extensions and all optional)
-2.75 E(header \214elds, cannot e)105 222.2 Q(xceed 255 32-bit w)-.165 E
(ords.)-.11 E(Header Extensions are further di)72 251.8 Q
(vided between general LCT e)-.275 E
(xtensions and Protocol Instantiation)-.165 E(speci\214c e)72 264.8 Q
(xtensions \(PI-speci\214c\).)-.165 E(General LCT e)5.5 E(xtensions ha)
-.165 E .33 -.165(ve H)-.22 H(ET in the ranges 0:63 and).165 E
(128:191 inclusi)72 277.8 Q -.165(ve)-.275 G 5.5(.P).165 G
(I-speci\214c e)-5.5 E(xtensions ha)-.165 E .33 -.165(ve H)-.22 H
(ET in the ranges 64:127 and 192:255 inclusi).165 E -.165(ve)-.275 G(.)
.165 E(General LCT e)72 303.8 Q(xtensions are intended to allo)-.165 E
2.75(wt)-.275 G(he introduction of backw)-2.75 E(ard-compatible)-.11 E
(enhancements to LCT without changing the LCT v)72 316.8 Q
(ersion number)-.165 E 5.5(.N)-.605 G(on backw)-5.5 E(ard-compatible)
-.11 E(Header Extensions CANNO)72 329.8 Q 2.75(Tb)-.44 G 2.75(ei)-2.75 G
(ntroduced without changing the LCT v)-2.75 E(ersion number)-.165 E(.)
-.605 E(PI-speci\214c e)72 355.8 Q(xtensions are reserv)-.165 E
(ed for PI-speci\214c use with semantic and def)-.165 E
(ault parsing actions)-.11 E(de\214ned by the PI.)72 368.8 Q(The follo)
72 407.8 Q(wing general LCT Header Extension types are de\214ned:)-.275
E 13.662(EXT_NOP=0 No-Operation)72 424.4 R -.165(ex)2.75 G(tension.).165
E(The information present in this e)149 437.4 Q
(xtension \214eld MUST be ignored by recei)-.165 E -.165(ve)-.275 G(rs.)
.165 E(EXT_A)72 467 Q 5.72(UTH=1 P)-.605 F(ack)-.165 E
(et authentication e)-.11 E(xtension)-.165 E
(Information used to authenticate the sender of the pack)149 480 Q 2.75
(et. The)-.11 F(format of this)2.75 E(Header Extension and its processi\
ng is outside the scope of this document and is)149 493 Q
(to be communicated out-of-band as part of the Session Description.)149
506 Q(It is RECOMMENDED that senders pro)149 519 Q
(vide some form of pack)-.165 E(et)-.11 E 2.75(authentication. If)149
532 R(EXT_A)2.75 E(UTH is present, whate)-.605 E -.165(ve)-.275 G 2.75
(rp).165 G(ack)-2.75 E(et authentication)-.11 E
(checks that can be performed immediately upon reception of the pack)149
545 Q(et)-.11 E(SHOULD be performed before accepting the pack)149 558 Q
(et and performing an)-.11 E(y)-.165 E
(congestion control-related action on it.)149 571 Q(Some pack)149 584 Q
(et authentication schemes impose a delay of se)-.11 E -.165(ve)-.275 G
(ral seconds between).165 E(when a pack)149 597 Q(et is recei)-.11 E
-.165(ve)-.275 G 2.75(da).165 G(nd when the pack)-2.75 E
(et is fully authenticated.)-.11 E(An)5.5 E(y)-.165 E
(congestion control related action that is appropriate MUST NO)149 610 Q
2.75(Tb)-.44 G 2.75(ep)-2.75 G(ostponed)-2.75 E(by an)149 623 Q 2.75(ys)
-.165 G(uch full pack)-2.75 E(et authentication.)-.11 E
(All senders and recei)72 652.6 Q -.165(ve)-.275 G
(rs implementing ALC MUST support the EXT_NOP Header Extension).165 E
(and MUST recognize EXT_A)72 665.6 Q(UTH, b)-.605 E(ut MA)-.22 E 2.75
(YN)-1.155 G .88 -.44(OT b)-2.75 H 2.75(ea).44 G
(ble to parse its content.)-2.75 E -.165(Fo)72 691.6 S 2.75(rt).165 G
(his v)-2.75 E(ersion of ALC, the follo)-.165 E(wing PI-speci\214c e)
-.275 E(xtension is de\214ned:)-.165 E 13.662(EXT_FTI=64 FEC)72 708.2 R
(Object T)2.75 E(ransmission Information e)-.385 E(xtension)-.165 E
(The purpose of this e)149 721.2 Q
(xtension is to carry in-band the FEC Object T)-.165 E(ransmission)-.385
E(Luby/Gemmell/V)72 769 Q(icisano/Rizzo/Cro)-.66 E 143.767
(wcroft Section)-.275 F 2.75(4.3. [P)2.75 F(age 19])-.165 E EP
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/F0 11/Times-Roman@0 SF(INTERNET)72 49 Q 70.976(-DRAFT Expires:)-1.012 F
(October 2002)2.75 E(April 2002)118.232 E(Information for an object.)149
85 Q(The format of this Header Extension and its)5.5 E(processing is ou\
tside the scope of this document and is to be communicated out-)149 98 Q
(of-band as part of the Session Description.)149 111 Q/F1 11
/Times-Bold@0 SF(4.4.)72 153.6 Q/F2 13/Times-Bold@0 SF(Sender Operation)
5.5 E F0(The sender operation when using ALC includes all the points ma\
de about the sender operation)72 170.2 Q(when using the LCT b)72 183.2 Q
(uilding block [13], the FEC b)-.22 E
(uilding block [12] and the multiple rate)-.22 E(congestion control b)72
196.2 Q(uilding block.)-.22 E 2.75(As)72 225.8 S
(ender using ALC MUST mak)-2.75 E 2.75(ea)-.11 G -.275(va)-2.97 G
(ilable the required Session Description as described in).275 E
(Section 2.4. A sender also MUST mak)72 238.8 Q 2.75(ea)-.11 G -.275(va)
-2.97 G(ilable the required FEC Object T).275 E(ransmission)-.385 E
(Information as described in Section 2.3.)72 251.8 Q -.44(Wi)72 268.4 S
(thin a session a sender transmits a sequence of pack).44 E
(ets to the channels associated with the)-.11 E 2.75(session. The)72
281.4 R(ALC sender MUST obe)2.75 E 2.75(yt)-.165 G
(he rules for \214lling in the CCI \214eld in the pack)-2.75 E
(et headers)-.11 E(and MUST send pack)72 294.4 Q(ets at the appropriate\
 rates to the channels associated with the session as)-.11 E
(dictated by the multiple rate congestion control b)72 307.4 Q
(uilding block.)-.22 E
(The ALC sender MUST use the same TSI for all pack)72 333.4 Q
(ets in the session.)-.11 E(Se)5.5 E -.165(ve)-.275 G(ral objects MA)
.165 E 2.75(Yb)-1.155 G(e)-2.75 E(deli)72 346.4 Q -.165(ve)-.275 G
(red within the same ALC session.).165 E
(If more than one object is to be deli)5.5 E -.165(ve)-.275 G
(red within a).165 E(session then the sender MUST use the T)72 359.4 Q
(OI \214eld and each object MUST be identi\214ed by a unique)-.198 E
-.198(TO)72 372.4 S 2.75(Iw).198 G
(ithin the session, and the sender MUST use corresponding T)-2.75 E
(OI for all pack)-.198 E(ets pertaining to)-.11 E(the same object.)72
385.4 Q(The FEC P)5.5 E
(ayload ID MUST correspond to the encoding symbol\(s\) for the)-.165 E
(object carried in the payload of the pack)72 398.4 Q(et.)-.11 E
(Objects MA)72 424.4 Q 2.75(Yb)-1.155 G 2.75(et)-2.75 G
(ransmitted sequentially within a session, and the)-2.75 E 2.75(yM)-.165
G 2.31 -1.155(AY b)-2.75 H 2.75(et)1.155 G(ransmitted)-2.75 E
(concurrently)72 437.4 Q 5.5(.H)-.715 G -.275(ow)-5.5 G -2.365 -.275
(ev e).275 H .88 -.44(r, i).275 H 2.75(ti).44 G 2.75(sg)-2.75 G
(ood practice to only send objects concurrently in the same session if)
-2.75 E(the recei)72 450.4 Q -.165(ve)-.275 G
(rs that participate in that portion of the session ha).165 E .33 -.165
(ve i)-.22 H(nterest in recei).165 E(ving all the objects.)-.275 E
(The reason for this is that it w)72 463.4 Q(astes bandwidth and netw)
-.11 E(orking resources to ha)-.11 E .33 -.165(ve r)-.22 H(ecei).165 E
-.165(ve)-.275 G(rs recei).165 E -.165(ve)-.275 G
(data for objects that the)72 476.4 Q 2.75(yh)-.165 G -2.475 -.22(av e)
-2.75 H(no interest in.)2.97 E(Ho)5.5 E(we)-.275 E -.165(ve)-.275 G .88
-.44(r, t).165 H(here are no rules with respect to mixing).44 E(pack)72
489.4 Q(ets for dif)-.11 E(ferent objects carried within the session.)
-.275 E(Although this issue af)5.5 E(fects the ef)-.275 E(\214cienc)
-.275 E(y)-.165 E(of the protocol, it does not af)72 502.4 Q
(fect the correctness nor the inter)-.275 E
(-operability of ALC between senders)-.22 E(and recei)72 515.4 Q -.165
(ve)-.275 G(rs.).165 E -.88(Ty)72 541.4 S(pically).88 E 2.75(,t)-.715 G
(he sender\(s\) continues to send pack)-2.75 E
(ets in a session until the transmission is considered)-.11 E 2.75
(complete. The)72 554.4 R
(transmission may be considered complete when some time has e)2.75 E
(xpired, a certain)-.165 E(number of pack)72 567.4 Q(ets ha)-.11 E .33
-.165(ve b)-.22 H
(een sent, or some out-of-band signal \(possibly from a higher le).165 E
-.165(ve)-.275 G(l).165 E(protocol\) has indicated completion by a suf)
72 580.4 Q(\214cient number of recei)-.275 E -.165(ve)-.275 G(rs.).165 E
(It is RECOMMENDED that pack)72 606.4 Q(et authentication be used.)-.11
E(If pack)5.5 E(et authentication is used then)-.11 E(the Header Extens\
ions described in Section 4.3 MUST be used to carry the authentication.)
72 619.4 Q(This document does not pose an)72 645.4 Q 2.75(yr)-.165 G
(estriction on pack)-2.75 E(et sizes.)-.11 E(Ho)5.5 E(we)-.275 E -.165
(ve)-.275 G .88 -.44(r, n).165 H(etw).44 E(ork ef)-.11 E(\214cienc)-.275
E(y)-.165 E(considerations recommend that the sender uses as lar)72
658.4 Q(ge as possible pack)-.198 E(et payload size, b)-.11 E(ut in)-.22
E(such a w)72 671.4 Q(ay that pack)-.11 E(ets do not e)-.11 E
(xceed the netw)-.165 E(ork')-.11 E 2.75(sm)-.605 G
(aximum transmission unit size \(MTU\), or)-2.75 E
(fragmentation coupled with pack)72 684.4 Q(et loss might introduce se)
-.11 E -.165(ve)-.275 G(re inef).165 E(\214cienc)-.275 E 2.75(yi)-.165 G
2.75(nt)-2.75 G(he transmission.)-2.75 E(It)5.5 E
(is RECOMMENDED that all pack)72 697.4 Q(ets ha)-.11 E .33 -.165(ve t)
-.22 H(he same or v).165 E(ery similar sizes, as this can ha)-.165 E .33
-.165(ve a)-.22 H(se)72 710.4 Q -.165(ve)-.275 G(re impact on the ef)
.165 E(fecti)-.275 E -.165(ve)-.275 G
(ness of the multiple rate congestion control b).165 E(uilding block.)
-.22 E(Luby/Gemmell/V)72 769 Q(icisano/Rizzo/Cro)-.66 E 143.767
(wcroft Section)-.275 F 2.75(4.4. [P)2.75 F(age 20])-.165 E EP
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(October 2002)2.75 E(April 2002)118.232 E/F1 11/Times-Bold@0 SF(4.5.)72
85 Q/F2 13/Times-Bold@0 SF(Recei)5.5 E -.13(ve)-.13 G 3.25(rO).13 G
(peration)-3.25 E F0(The recei)72 101.6 Q -.165(ve)-.275 G 2.75(ro).165
G(peration when using ALC includes all the points made about the recei)
-2.75 E -.165(ve)-.275 G 2.75(ro).165 G(peration)-2.75 E
(when using the LCT b)72 114.6 Q(uilding block [13], the FEC b)-.22 E
(uilding block [12] and the multiple rate)-.22 E(congestion control b)72
127.6 Q(uilding block.)-.22 E 1.76 -.88(To b)72 153.6 T 2.75(ea).88 G
(ble to participate in a session, a recei)-2.75 E -.165(ve)-.275 G 2.75
(rM).165 G(UST obtain the REQ)-2.75 E(UIRED Session)-.11 E
(Description as listed in Section 2.4. Ho)72 166.6 Q 2.75(wr)-.275 G
(ecei)-2.75 E -.165(ve)-.275 G
(rs obtain a Session Description is outside the).165 E
(scope of this document.)72 179.6 Q 1.76 -.88(To b)72 196.2 T 2.75(ea)
.88 G(ble to be a recei)-2.75 E -.165(ve)-.275 G 2.75(ri).165 G 2.75
(nas)-2.75 G(ession, the recei)-2.75 E -.165(ve)-.275 G 2.75(rM).165 G
(UST be able to process the ALC header)-2.75 E(.)-.605 E(The recei)72
209.2 Q -.165(ve)-.275 G 2.75(rM).165 G(UST be able to discard, forw)
-2.75 E(ard, store or process the other headers and the pack)-.11 E(et)
-.11 E 2.75(payload. If)72 222.2 R 2.75(ar)2.75 G(ecei)-2.75 E -.165(ve)
-.275 G 2.75(ri).165 G 2.75(sn)-2.75 G
(ot able to process the ALC header)-2.75 E 2.75(,i)-.44 G 2.75(tM)-2.75
G(UST drop from the session.)-2.75 E 1.76 -.88(To b)72 248.2 T 2.75(ea)
.88 G(ble to participate in a session, a recei)-2.75 E -.165(ve)-.275 G
2.75(rM).165 G(UST implement the multiple rate congestion)-2.75 E
(control b)72 261.2 Q
(uilding block using the Congestion Control Information \214eld pro)-.22
E(vided in the LCT)-.165 E(header)72 274.2 Q 2.75(.I)-.605 G 2.75(far)
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(ot able to implement the multiple rate congestion control b)-2.75 E
(uilding block it)-.22 E(MUST NO)72 287.2 Q 2.75(Tj)-.44 G
(oin the session.)-2.75 E(Se)72 313.2 Q -.165(ve)-.275 G(ral objects ca\
n be carried either sequentially or concurrently within the same sessio\
n.).165 E(In this)5.5 E(case, each object is identi\214ed by a unique T)
72 326.2 Q 2.75(OI. Note)-.198 F(that e)2.75 E -.165(ve)-.275 G 2.75(ni)
.165 G 2.75(fas)-2.75 G(ender stops sending pack)-2.75 E(ets)-.11 E
(for an old object before starting to transmit pack)72 339.2 Q
(ets for a ne)-.11 E 2.75(wo)-.275 G(bject, both the netw)-2.75 E
(ork and the)-.11 E
(underlying protocol layers can cause some reordering of pack)72 352.2 Q
(ets, especially when sent o)-.11 E -.165(ve)-.165 G(r).165 E(dif)72
365.2 Q(ferent channels, and thus recei)-.275 E -.165(ve)-.275 G
(rs SHOULD NO).165 E 2.75(Ta)-.44 G(ssume that the reception of a pack)
-2.75 E(et for a)-.11 E(ne)72 378.2 Q 2.75(wo)-.275 G
(bject means that there are no more pack)-2.75 E
(ets in transit for the pre)-.11 E(vious one, at least for some)-.275 E
(amount of time.)72 391.2 Q(As described in Section 2.3, a recei)72
417.2 Q -.165(ve)-.275 G 2.75(rM).165 G
(UST obtain the required FEC Object T)-2.75 E(ransmission)-.385 E
(Information for each object for which the recei)72 430.2 Q -.165(ve)
-.275 G 2.75(rr).165 G(ecei)-2.75 E -.165(ve)-.275 G 2.75(sa).165 G
(nd processes pack)-2.75 E(ets.)-.11 E 2.75(Ar)72 456.2 S(ecei)-2.75 E
-.165(ve)-.275 G 2.75(rM).165 G 2.31 -1.155(AY c)-2.75 H(oncurrently jo\
in multiple ALC sessions from one or more senders. The recei)1.155 E
-.165(ve)-.275 G(r).165 E
(MUST perform congestion control on each such session.)72 469.2 Q
(The recei)5.5 E -.165(ve)-.275 G 2.75(rM).165 G 2.31 -1.155(AY m)-2.75
H(ak)1.155 E 2.75(ec)-.11 G(hoices to)-2.75 E(optimize the pack)72 482.2
Q(et \215o)-.11 E 2.75(wp)-.275 G
(erformance across multiple sessions, as long as the recei)-2.75 E -.165
(ve)-.275 G 2.75(rs).165 G(till)-2.75 E
(adheres to the multiple rate congestion control b)72 495.2 Q
(uilding block for each session indi)-.22 E(vidually)-.275 E(.)-.715 E
(Upon receipt of each pack)72 521.2 Q(et the recei)-.11 E -.165(ve)-.275
G 2.75(rp).165 G(roceeds with the follo)-2.75 E
(wing steps in the order listed.)-.275 E 6.424(\(1\) The)72 537.8 R
(recei)2.75 E -.165(ve)-.275 G 2.75(rM).165 G(UST parse the pack)-2.75 E
(et header and v)-.11 E(erify that it is a v)-.165 E(alid header)-.275 E
5.5(.I)-.605 G 2.75(fi)-5.5 G 2.75(ti)-2.75 G 2.75(sn)-2.75 G(ot)-2.75 E
-.275(va)94 550.8 S(lid then the pack).275 E
(et MUST be discarded without further processing.)-.11 E
(If multiple pack)5.5 E(ets are)-.11 E(recei)94 563.8 Q -.165(ve)-.275 G
2.75(dt).165 G(hat cannot be parsed then the recei)-2.75 E -.165(ve)
-.275 G 2.75(rS).165 G(HOULD lea)-2.75 E .33 -.165(ve t)-.22 H
(he session.).165 E 6.424(\(2\) The)72 580.4 R(recei)2.75 E -.165(ve)
-.275 G 2.75(rM).165 G(UST v)-2.75 E
(erify that the sender IP address together with the TSI carried in the)
-.165 E
(header matches one of the \(sender IP address, TSI\) pairs that w)94
593.4 Q(as recei)-.11 E -.165(ve)-.275 G 2.75(di).165 G 2.75(naS)-2.75 G
(ession)-2.75 E(Description and that the recei)94 606.4 Q -.165(ve)-.275
G 2.75(ri).165 G 2.75(sc)-2.75 G(urrently joined to.)-2.75 E
(If there is not a match then the)5.5 E(pack)94 619.4 Q
(et MUST be discarded without further processing.)-.11 E
(If multiple pack)5.5 E(ets are recei)-.11 E -.165(ve)-.275 G 2.75(dw)
.165 G(ith)-2.75 E(non-matching \(sender IP address, TSI\) v)94 632.4 Q
(alues then the recei)-.275 E -.165(ve)-.275 G 2.75(rS).165 G(HOULD lea)
-2.75 E .33 -.165(ve t)-.22 H(he session.).165 E(If the recei)94 645.4 Q
-.165(ve)-.275 G 2.75(ri).165 G 2.75(sj)-2.75 G
(oined to multiple ALC sessions then the remainder of the steps are)
-2.75 E(performed within the scope of the \(sender IP address, TSI\) se\
ssion of the recei)94 658.4 Q -.165(ve)-.275 G 2.75(dp).165 G(ack)-2.75
E(et.)-.11 E 6.424(\(3\) The)72 675 R(recei)2.75 E -.165(ve)-.275 G 2.75
(rM).165 G(UST process and act on the CCI \214eld in accordance with th\
e multiple rate)-2.75 E(congestion control b)94 688 Q(uilding block.)
-.22 E 6.424(\(4\) If)72 704.6 R
(more than one object is carried in the session, the recei)2.75 E -.165
(ve)-.275 G 2.75(rM).165 G(UST v)-2.75 E(erify that the T)-.165 E(OI)
-.198 E(carried in the LCT header is v)94 717.6 Q 2.75(alid. If)-.275 F
(the T)2.75 E(OI is not v)-.198 E(alid, the pack)-.275 E
(et MUST be discarded)-.11 E(Luby/Gemmell/V)72 769 Q(icisano/Rizzo/Cro)
-.66 E 143.767(wcroft Section)-.275 F 2.75(4.5. [P)2.75 F(age 21])-.165
E EP
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85 Q 6.424(\(5\) The)72 101.6 R(recei)2.75 E -.165(ve)-.275 G 2.75(rS)
.165 G(HOULD process the remainder of the pack)-2.75 E
(et, including interpreting the other)-.11 E
(header \214elds appropriately)94 114.6 Q 2.75(,a)-.715 G
(nd using the FEC P)-2.75 E
(ayload ID and the encoding symbol\(s\) in the)-.165 E
(payload to reconstruct the corresponding object.)94 127.6 Q
(It is RECOMMENDED that pack)72 157.2 Q(et authentication be used.)-.11
E(If pack)5.5 E(et authentication is used then)-.11 E
(it is RECOMMENDED that the recei)72 170.2 Q -.165(ve)-.275 G 2.75(ri)
.165 G(mmediately check the authenticity of a pack)-2.75 E(et before)
-.11 E(proceeding with step \(3\) abo)72 183.2 Q -.165(ve)-.165 G 5.5
(.I).165 G 2.75(fi)-5.5 G(mmediate checking is possible and if the pack)
-2.75 E(et f)-.11 E(ails the)-.11 E(check then the recei)72 196.2 Q
-.165(ve)-.275 G 2.75(rM).165 G(UST discard the pack)-2.75 E
(et and reduce its reception rate to a minimum)-.11 E
(before continuing to re)72 209.2 Q
(gulate its reception rate using the multiple rate congestion control.)
-.165 E(Some pack)72 235.2 Q
(et authentication schemes such as TESLA [16] do not allo)-.11 E 2.75
(wa)-.275 G 2.75(ni)-2.75 G(mmediate authenticity)-2.75 E 2.75
(check. In)72 248.2 R(this case the recei)2.75 E -.165(ve)-.275 G 2.75
(rS).165 G(HOULD check the authenticity of a pack)-2.75 E
(et as soon as possible,)-.11 E(and if the pack)72 261.2 Q(et f)-.11 E
(ails the check then it MUST be discarded before step \(5\) abo)-.11 E
.33 -.165(ve a)-.165 H(nd reduce its).165 E
(reception rate to a minimum before continuing to re)72 274.2 Q
(gulate its reception rate using the multiple)-.165 E
(rate congestion control.)72 287.2 Q/F1 11/Times-Bold@0 SF(5.)72 329.8 Q
/F2 14/Times-Bold@0 SF(Security Considerations)5.5 E F0
(The same security consideration that apply to the LCT)72 346.4 Q 2.75
(,F)-.814 G(EC and the multiple rate congestion)-2.75 E(control b)72
359.4 Q(uilding blocks also apply to ALC.)-.22 E(Because of the use of \
FEC, ALC is especially vulnerable to denial-of-service attacks by attac\
k)72 385.4 Q(ers)-.11 E(that try to send for)72 398.4 Q(ged pack)-.198 E
(ets to the session which w)-.11 E(ould pre)-.11 E -.165(ve)-.275 G
(nt successful reconstruction or).165 E
(cause inaccurate reconstruction of lar)72 411.4 Q
(ge portions of the object by recei)-.198 E -.165(ve)-.275 G 2.75
(rs. ALC).165 F(is also)2.75 E(particularly af)72 424.4 Q
(fected by such an attack because man)-.275 E 2.75(yr)-.165 G(ecei)-2.75
E -.165(ve)-.275 G(rs may recei).165 E .33 -.165(ve t)-.275 H
(he same for).165 E(ged)-.198 E(pack)72 437.4 Q 2.75(et. There)-.11 F
(are tw)2.75 E 2.75(ow)-.11 G(ays to protect ag)-2.86 E
(ainst such attacks, one at the application le)-.055 E -.165(ve)-.275 G
2.75(la).165 G(nd one at)-2.75 E(the pack)72 450.4 Q(et le)-.11 E -.165
(ve)-.275 G 2.75(l. It).165 F(is RECOMMENDED that pre)2.75 E -.165(ve)
-.275 G(ntion be pro).165 E(vided at both le)-.165 E -.165(ve)-.275 G
(ls.).165 E(At the application le)72 476.4 Q -.165(ve)-.275 G
(l, it is RECOMMENDED that an inte).165 E
(grity check on the entire recei)-.165 E -.165(ve)-.275 G(d).165 E(obje\
ct be done once the object is reconstructed to ensure it is the same as\
 the sent object.)72 489.4 Q(Moreo)72 502.4 Q -.165(ve)-.165 G .88 -.44
(r, i).165 H 2.75(no).44 G(rder to obtain strong cryptographic inte)
-2.75 E(grity protection a digital signature v)-.165 E(eri\214able)-.165
E(by the recei)72 515.4 Q -.165(ve)-.275 G 2.75(rS).165 G
(HOULD be used to pro)-2.75 E(vide this application le)-.165 E -.165(ve)
-.275 G 2.75(li).165 G(nte)-2.75 E(grity check.)-.165 E(Ho)5.5 E(we)
-.275 E -.165(ve)-.275 G .88 -.44(r, i).165 H(f).44 E -2.365 -.275(ev e)
72 528.4 T 2.75(no).275 G(ne corrupted or for)-2.75 E(ged pack)-.198 E
(et is used to reconstruct the object, it is lik)-.11 E
(ely that the recei)-.11 E -.165(ve)-.275 G(d).165 E
(object will be reconstructed incorrectly)72 541.4 Q 5.5(.T)-.715 G
(his will appropriately cause the inte)-5.5 E(grity check to f)-.165 E
(ail)-.11 E(and in this case the inaccurately reconstructed object SHOU\
LD be discarded.)72 554.4 Q(Thus, the)5.5 E(acceptance of a single for)
72 567.4 Q(ged pack)-.198 E(et can be an ef)-.11 E(fecti)-.275 E .33
-.165(ve d)-.275 H(enial of service attack for distrib).165 E(uting)-.22
E(objects, b)72 580.4 Q(ut an object inte)-.22 E
(grity check at least pre)-.165 E -.165(ve)-.275 G(nts inadv).165 E
(ertent use of inaccurately)-.165 E(reconstructed objects.)72 593.4 Q
(The speci\214cation of an application le)5.5 E -.165(ve)-.275 G 2.75
(li).165 G(nte)-2.75 E(grity check of the recei)-.165 E -.165(ve)-.275 G
(d).165 E(object is outside the scope of this document.)72 606.4 Q
(At the pack)72 632.4 Q(et le)-.11 E -.165(ve)-.275 G
(l, it is RECOMMENDED that a pack).165 E(et le)-.11 E -.165(ve)-.275 G
2.75(la).165 G(uthentication be used to ensure)-2.75 E(that each recei)
72 645.4 Q -.165(ve)-.275 G 2.75(dp).165 G(ack)-2.75 E
(et is an authentic and uncorrupted pack)-.11 E
(et containing FEC data for the)-.11 E(object arri)72 658.4 Q
(ving from the speci\214ed sender)-.275 E 5.5(.P)-.605 G(ack)-5.665 E
(et le)-.11 E -.165(ve)-.275 G 2.75(la).165 G(uthentication has the adv)
-2.75 E(antage that)-.275 E(corrupt or for)72 671.4 Q(ged pack)-.198 E
(ets can be discarded indi)-.11 E(vidually and the recei)-.275 E -.165
(ve)-.275 G 2.75(da).165 G(uthenticated pack)-2.75 E(ets can)-.11 E
(be used to accurately reconstruct the object.)72 684.4 Q(Thus, the ef)
5.5 E(fect of a denial of service attack that)-.275 E(injects for)72
697.4 Q(ged pack)-.198 E(ets is proportional only to the number of for)
-.11 E(ged pack)-.198 E(ets, and not to the object)-.11 E 2.75
(size. Although)72 710.4 R
(there is currently no IETF standard that speci\214es ho)2.75 E 2.75(wt)
-.275 G 2.75(od)-2.75 G 2.75(om)-2.75 G(ulticast pack)-2.75 E(et le)-.11
E -.165(ve)-.275 G(l).165 E(authentication, TESLA [16] is a kno)72 723.4
Q(wn multicast pack)-.275 E(et authentication scheme that w)-.11 E
(ould w)-.11 E(ork.)-.11 E(Luby/Gemmell/V)72 769 Q(icisano/Rizzo/Cro)
-.66 E 152.017(wcroft Section)-.275 F 2.75(5. [P)2.75 F(age 22])-.165 E
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(October 2002)2.75 E(April 2002)118.232 E(In addition to pro)72 85 Q
(viding protection ag)-.165 E
(ainst reconstruction of inaccurate objects, pack)-.055 E(et le)-.11 E
-.165(ve)-.275 G(l).165 E(authentication can also pro)72 98 Q
(vide some protection ag)-.165 E
(ainst denial of service attacks on the multiple)-.055 E
(rate congestion control.)72 111 Q(Attack)5.5 E
(ers can try to inject for)-.11 E(ged pack)-.198 E
(ets with incorrect congestion)-.11 E
(control information into the multicast stream, thereby potentially adv)
72 124 Q(ersely af)-.165 E(fecting netw)-.275 E(ork)-.11 E
(elements and recei)72 137 Q -.165(ve)-.275 G(rs do).165 E
(wnstream of the attack, and much less signi\214cantly the rest of the)
-.275 E(netw)72 150 Q(ork and other recei)-.11 E -.165(ve)-.275 G 2.75
(rs. Thus,).165 F(it is also RECOMMENDED that pack)2.75 E(et le)-.11 E
-.165(ve)-.275 G 2.75(la).165 G(uthentication)-2.75 E
(be used to protect ag)72 163 Q(ainst such attacks.)-.055 E
(TESLA [16] can also be used to some e)5.5 E(xtent to limit the)-.165 E
(damage caused by such attacks.)72 176 Q(Ho)5.5 E(we)-.275 E -.165(ve)
-.275 G .88 -.44(r, w).165 H(ith TESLA a recei).44 E -.165(ve)-.275 G
2.75(rc).165 G(an only determine if a pack)-2.75 E(et)-.11 E
(is authentic se)72 189 Q -.165(ve)-.275 G
(ral seconds after it is recei).165 E -.165(ve)-.275 G
(d, and thus an attack ag).165 E(ainst the congestion control)-.055 E
(protocol can be ef)72 202 Q(fecti)-.275 E .33 -.165(ve f)-.275 H(or se)
.165 E -.165(ve)-.275 G(ral seconds before the recei).165 E -.165(ve)
-.275 G 2.75(rc).165 G(an react to slo)-2.75 E 2.75(wd)-.275 G -.275(ow)
-2.75 G 2.75(nt).275 G(he)-2.75 E(session reception rate.)72 215 Q(Re)72
241 Q -.165(ve)-.275 G(rse P).165 E(ath F)-.165 E(orw)-.165 E
(arding checks SHOULD be enabled in all netw)-.11 E
(ork routers and switches along)-.11 E
(the path from the sender to recei)72 254 Q -.165(ve)-.275 G
(rs to limit the possibility of a bad agent injecting for).165 E(ged)
-.198 E(pack)72 267 Q(ets into the multicast tree data path.)-.11 E 2.75
(Ar)72 293 S(ecei)-2.75 E -.165(ve)-.275 G 2.75(rw).165 G(ith an incorr\
ect or corrupted implementation of the multiple rate congestion control)
-2.75 E -.22(bu)72 306 S(ilding block may af).22 E
(fect health of the netw)-.275 E
(ork in the path between the sender and the recei)-.11 E -.165(ve)-.275
G -.44(r,).165 G(and may also af)72 319 Q
(fect the reception rates of other recei)-.275 E -.165(ve)-.275 G
(rs joined to the session.).165 E(It is therefore)5.5 E
(RECOMMENDED that recei)72 332 Q -.165(ve)-.275 G
(rs be required to identify themselv).165 E(es as le)-.165 E
(gitimate before the)-.165 E(y)-.165 E(recei)72 345 Q .33 -.165(ve t)
-.275 H(he Session Description needed to join the session.).165 E(Ho)5.5
E 2.75(wr)-.275 G(ecei)-2.75 E -.165(ve)-.275 G(rs identify themselv)
.165 E(es as)-.165 E(le)72 358 Q
(gitimate is outside the scope of this document.)-.165 E
(Another vulnerability of ALC is the potential of recei)72 384 Q -.165
(ve)-.275 G(rs obtaining an incorrect Session).165 E
(Description for the session.)72 397 Q
(The consequences of this could be that le)5.5 E(gitimate recei)-.165 E
-.165(ve)-.275 G(rs with the).165 E
(wrong session description are unable to correctly recei)72 410 Q .33
-.165(ve t)-.275 H(he session content, or that recei).165 E -.165(ve)
-.275 G(rs).165 E(inadv)72 423 Q(ertently try to recei)-.165 E .33 -.165
(ve a)-.275 H 2.75(tam).165 G(uch higher rate than the)-2.75 E 2.75(ya)
-.165 G(re capable of, thereby disrupting)-2.75 E(traf)72 436 Q
(\214c in portions of the netw)-.275 E 2.75(ork. T)-.11 F 2.75(oa)-.88 G
-.22(vo)-2.97 G(id these problems, it is RECOMMENDED that the).22 E
(recei)72 449 Q -.165(ve)-.275 G 2.75(ra).165 G
(uthenticate the Session Description, for e)-2.75 E
(xample by using either the ESP \(with enabled)-.165 E(authentication s\
ervice\) [10] or AH [9] protocols of IPSEC [8] to ensure the authentici\
ty of the)72 462 Q(Session Description.)72 475 Q(Ho)5.5 E 2.75(wt)-.275
G(his is done is outside the scope of this document.)-2.75 E/F1 11
/Times-Bold@0 SF(6.)72 517.6 Q/F2 14/Times-Bold@0 SF(IAN)5.5 E 3.5(AC)
-.28 G(onsiderations)-3.5 E F0
(No information in this speci\214cation is directly subject to IAN)72
534.2 Q 2.75(Ar)-.385 G -.165(eg)-2.75 G 2.75(istration. Ho).165 F(we)
-.275 E -.165(ve)-.275 G .88 -.44(r, b).165 H(uilding).22 E
(blocks components used by ALC may introduce additional IAN)72 547.2 Q
2.75(Ac)-.385 G 2.75(onsiderations. In)-2.75 F(particular)2.75 E(,)-.44
E(the FEC b)72 560.2 Q(uilding block used by ALC does require IAN)-.22 E
2.75(Ar)-.385 G -.165(eg)-2.75 G(istration of the FEC codecs used.).165
E F1(7.)72 602.8 Q F2(Intellectual Pr)5.5 E(operty Issues)-.252 E F0
(No speci\214c reliability b)72 632.4 Q
(uilding block or congestion control b)-.22 E
(uilding block is speci\214ed or)-.22 E
(referenced as mandatory in this document.)72 645.4 Q
(ALC may be used with congestion control b)72 671.4 Q
(uilding blocks and other b)-.22 E(uilding blocks which)-.22 E
(contain proprietary elements, or ha)72 684.4 Q .33 -.165(ve p)-.22 H
(ending or granted patents.).165 E(Luby/Gemmell/V)72 769 Q
(icisano/Rizzo/Cro)-.66 E 152.017(wcroft Section)-.275 F 2.75(7. [P)2.75
F(age 23])-.165 E EP
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(October 2002)2.75 E(April 2002)118.232 E/F1 11/Times-Bold@0 SF(8.)72 85
Q/F2 14/Times-Bold@0 SF(Ackno)5.5 E(wledgments)-.14 E F0(Thanks to V)72
114.6 Q(incent Roca, Justin Chapwesk)-.66 E 2.75(ea)-.11 G(nd Roger K)
-2.75 E(ermode for their detailed comments on)-.275 E(this draft.)72
127.6 Q F1(9.)72 170.2 Q F2(Refer)5.5 E(ences)-.252 E F0([1] Bradner)72
186.8 Q 2.75(,S)-.44 G(., "The Internet Standards Process -- Re)-2.75 E
(vision 3", RFC2026, October 1996.)-.275 E([2] Bradner)72 212.8 Q 2.75
(,S)-.44 G(., "K)-2.75 E .33 -.165(ey w)-.275 H
(ords for use in RFCs to Indicate Requirement Le).055 E -.165(ve)-.275 G
(ls", RFC2119, March).165 E(1997.)72 225.8 Q([3] Deering, S., "Host Ext\
ensions for IP Multicasting", RFC1112, August 1989.)72 251.8 Q
([4] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Berners-Lee, T)72
277.8 Q(., "Hyperte)-.814 E(xt T)-.165 E(ransfer Protocol)-.385 E
(-- HTTP/1.1", RFC2068, January 1997.)72 290.8 Q([5] Handle)72 316.8 Q
1.43 -.715(y, M)-.165 H(., Jacobson, V).715 E
(., "SDP: Session Description Protocol", RFC2327, April 1998)-1.419 E
([6] Handle)72 342.8 Q 1.43 -.715(y, M)-.165 H(., Perkins, C., Whelan, \
E., "Session Announcement Protocol", RFC2974, October).715 E(2000.)72
355.8 Q([7] Holbrook, H. W)72 381.8 Q
(., "A Channel Model for Multicast", Ph.D. Dissertation, Stanford Uni)
-1.012 E -.165(ve)-.275 G(rsity).165 E(,)-.715 E
(Department of Computer Science, Stanford, California, August 2001.)72
394.8 Q([8] K)72 420.8 Q(ent, S., Atkinson, R., "Security Architecture \
for the Internet Protocol", RFC2401, No)-.275 E -.165(ve)-.165 G(mber)
.165 E(1998.)72 433.8 Q([9] K)72 459.8 Q
(ent, S., Atkinson, R., "IP Authentication Header", RFC2406, No)-.275 E
-.165(ve)-.165 G(mber 1998.).165 E([10] K)72 485.8 Q
(ent, S., Atkinson, R., "IP Encapsulating Security P)-.275 E
(ayload \(ESP\)", RFC2406, No)-.165 E -.165(ve)-.165 G(mber).165 E
(1998.)72 498.8 Q([11] Luby)72 524.8 Q 2.75(,M)-.715 G(., Gemmell, V)
-2.75 E(icisano, L., J., Rizzo, L., Handle)-.66 E 1.43 -.715(y, M)-.165
H(., Cro).715 E(wcroft, J., "The use of)-.275 E -.165(Fo)72 537.8 S(rw)
.165 E(ard Error Correction in Reliable Multicast", Internet Draft draf\
t-ietf-rmt-info-fec-02.txt,)-.11 E(February 2002, a w)72 550.8 Q
(ork in progress.)-.11 E([12] Luby)72 576.8 Q 2.75(,M)-.715 G
(., Gemmell, J., V)-2.75 E(icisano, L., Rizzo, L., Handle)-.66 E 1.43
-.715(y, M)-.165 H(., Cro).715 E(wcroft, J., "F)-.275 E(orw)-.165 E
(ard Error)-.11 E(Correction b)72 589.8 Q(uilding block", Internet Draf\
t draft-ietf-rmt-bb-fec-06.txt, February 2002.)-.22 E([13] Luby)72 615.8
Q 2.75(,M)-.715 G(., Gemmell, J., V)-2.75 E
(icisano, L., Rizzo, L., Handle)-.66 E 1.43 -.715(y, M)-.165 H(., Cro)
.715 E(wcroft, J., "Layered Coding)-.275 E -.385(Tr)72 628.8 S
(ansport b).385 E(uilding block", Internet Draft draft-ietf-rmt-bb-lct-\
04.txt, February 2002.)-.22 E([14] Mankin, A., Romano)72 654.8 Q 1.43
-.715(w, A)-.275 H(., Bradner).715 E 2.75(,S)-.44 G(., P)-2.75 E
(axson V)-.165 E(., "IETF Criteria for Ev)-1.419 E(aluating Reliable)
-.275 E(Multicast T)72 667.8 Q
(ransport and Application Protocols", RFC2357, June 1998.)-.385 E
([15] Murata, M., St.Laurent, S., K)72 693.8 Q(ohn, D., "XML Media T)
-.385 E(ypes", RFC3023, January 2001.)-.88 E
([16] Perrig, A., Canetti, R., Song, D., T)72 719.8 Q(yg)-.88 E(ar)-.055
E 2.75(,J)-.44 G(.D., "Ef)-2.75 E
(\214cient and Secure Source Authentication for)-.275 E(Luby/Gemmell/V)
72 769 Q(icisano/Rizzo/Cro)-.66 E 152.017(wcroft Section)-.275 F 2.75
(9. [P)2.75 F(age 24])-.165 E EP
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(October 2002)2.75 E(April 2002)118.232 E(Multicast", Netw)72 85 Q
(ork and Distrib)-.11 E
(uted System Security Symposium, NDSS 2001, pp. 35-46,)-.22 E
(February 2001.)72 98 Q
([17] Postel, J., "User Datagram Protocol", RFC768, August 1980.)72 124
Q([18] Whetten, B., V)72 150 Q(icisano, L., K)-.66 E(ermode, R., Handle)
-.275 E 1.43 -.715(y, M)-.165 H(., Flo).715 E(yd, S., Luby)-.11 E 2.75
(,M)-.715 G(., "Reliable)-2.75 E(Multicast T)72 163 Q
(ransport Building Blocks for One-to-Man)-.385 E 2.75(yB)-.165 G
(ulk-Data T)-2.75 E(ransfer", RFC3048, January)-.385 E(2001.)72 176 Q/F1
11/Times-Bold@0 SF(10.)72 228 Q/F2 14/Times-Bold@0 SF -.7(Au)5.5 G
(thors' Addr).7 E(esses)-.252 E F0(Michael Luby)80.25 244.6 Q
(luby@digitalfountain.com)80.25 257.6 Q(Digital F)80.25 270.6 Q(ountain)
-.165 E(39141 Ci)80.25 283.6 Q(vic Center Dri)-.275 E -.165(ve)-.275 G
(Suite 300)80.25 296.6 Q(Fremont, CA, USA, 94538)80.25 309.6 Q
(Jim Gemmell)80.25 335.6 Q(jgemmell@microsoft.com)80.25 348.6 Q
(Microsoft Research)80.25 361.6 Q(301 Ho)80.25 374.6 Q -.11(wa)-.275 G
(rd St., #830).11 E(San Francisco, CA, USA, 94105)80.25 387.6 Q
(Lorenzo V)80.25 413.6 Q(icisano)-.66 E(lorenzo@cisco.com)80.25 426.6 Q
(cisco Systems, Inc.)80.25 439.6 Q(170 W)80.25 452.6 Q(est T)-.88 E
(asman Dr)-.88 E(.,)-.605 E(San Jose, CA, USA, 95134)80.25 465.6 Q
(Luigi Rizzo)80.25 491.6 Q(luigi@iet.unipi.it)80.25 504.6 Q
(Dip. Ing. dell'Informazione,)80.25 517.6 Q(Uni)80.25 530.6 Q 1.43 -.715
(v. d)-.275 H 2.75(iP).715 G(isa)-2.75 E
(via Diotisalvi 2, 56126 Pisa, Italy)80.25 543.6 Q(Jon Cro)80.25 569.6 Q
(wcroft)-.275 E(J.Cro)80.25 582.6 Q(wcroft@cs.ucl.ac.uk)-.275 E
(Department of Computer Science)80.25 595.6 Q(Uni)80.25 608.6 Q -.165
(ve)-.275 G(rsity Colle).165 E(ge London)-.165 E(Go)80.25 621.6 Q
(wer Street,)-.275 E(London WC1E 6BT)80.25 634.6 Q 2.75(,U)-.814 G(K)
-2.75 E(Luby/Gemmell/V)72 769 Q(icisano/Rizzo/Cro)-.66 E 146.517
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(October 2002)2.75 E(April 2002)118.232 E/F1 11/Times-Bold@0 SF(11.)72
85 Q/F2 14/Times-Bold@0 SF(Full Copyright Statement)5.5 E F0(Cop)72
101.6 Q(yright \(C\) The Internet Society \(2001\).)-.11 E
(All Rights Reserv)5.5 E(ed.)-.165 E(This document and translations of \
it may be copied and furnished to others, and deri)72 118.2 Q -.275(va)
-.275 G(ti).275 E .33 -.165(ve w)-.275 H(orks).055 E
(that comment on or otherwise e)72 131.2 Q
(xplain it or assist in its implementation may be prepared, copied,)
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(uted, in whole or in part, without restriction of an)-.22 E 2.75(yk)
-.165 G(ind, pro)-2.75 E(vided that the)-.165 E(abo)72 157.2 Q .33 -.165
(ve c)-.165 H(op).165 E(yright notice and this paragraph are included o\
n all such copies and deri)-.11 E -.275(va)-.275 G(ti).275 E .33 -.165
(ve w)-.275 H(orks.).055 E(Ho)72 170.2 Q(we)-.275 E -.165(ve)-.275 G .88
-.44(r, t).165 H(his document itself may not be modi\214ed in an).44 E
2.75(yw)-.165 G(ay)-2.86 E 2.75(,s)-.715 G(uch as by remo)-2.75 E
(ving the)-.165 E(cop)72 183.2 Q(yright notice or references to the Int\
ernet Society or other Internet or)-.11 E -.055(ga)-.198 G(nizations, e)
.055 E(xcept as)-.165 E(needed for the purpose of de)72 196.2 Q -.165
(ve)-.275 G(loping Internet standards in which case the procedures for)
.165 E(cop)72 209.2 Q
(yrights de\214ned in the Internet languages other than English.)-.11 E
(The limited permissions granted abo)72 225.8 Q .33 -.165(ve a)-.165 H
(re perpetual and will not be re).165 E -.22(vo)-.275 G -.11(ke).22 G
2.75(db).11 G 2.75(yt)-2.75 G(he Internet)-2.75 E
(Society or its successors or assigns.)72 238.8 Q
(This document and the information contained herein is pro)72 255.4 Q
(vided on an "AS IS" basis and THE)-.165 E
(INTERNET SOCIETY AND THE INTERNET ENGINEERING T)72 268.4 Q
(ASK FORCE DISCLAIMS)-1.023 E(ALL W)72 281.4 Q
(ARRANTIES, EXPRESS OR IMPLIED, INCLUDING B)-1.32 E(UT NO)-.11 E 2.75
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S(RRANTY THA)1.32 E 2.75(TT)-1.221 G(HE USE OF THE INFORMA)-2.75 E
(TION HEREIN WILL NO)-1.221 E 2.75(TI)-.44 G(NFRINGE)-2.75 E
(ANY RIGHTS OR ANY IMPLIED W)72 307.4 Q(ARRANTIES OF MERCHANT)-1.32 E
(ABILITY OR FITNESS)-1.023 E(FOR A P)72 320.4 Q(AR)-1.012 E
(TICULAR PURPOSE.")-.66 E(Luby/Gemmell/V)72 769 Q(icisano/Rizzo/Cro)-.66
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