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/F0 10/Palatino-Roman@0 SF(Reliable Multicast T)72 84 Q
(ransport \(RMT\))-.9 E(B. Adamson)221.268 E -.92(Wo)72 96 S(rking Gr)
.92 E 338.658(oup NRL)-.18 F 314.748(Internet-Draft C.)72 108 R(Bormann)
2.5 E(Expir)72 120 Q(es: 17 Mar)-.18 E(ch 2006)-.18 E(Universitaet Br)
220.878 E(emen TZI)-.18 E(M. Handley)451.028 132 Q(UCL)483.018 144 Q
(J. Macker)462.468 156 Q(NRL)482.898 168 Q(October 2005)446.208 180 Q/F1
12/Palatino-Bold@0 SF(Negative-Acknowledgment \(NACK\)-Oriented Reliabl\
e Multicast \(NORM\) Building Blocks)72 210 Q
(draft-ietf-rmt-bb-norm-revised-00)195.684 222 Q/F2 10/Palatino-Bold@0
SF(Status of this Memo)72 246 Q F0
(By submitting this Internet-Draft, each author r)93.6 261.6 Q(epr)-.18
E(esents that any applicable patent or other)-.18 E
(IPR claims of which he or she is awar)93.6 273.6 Q 2.5(eh)-.18 G
(ave been or will be disclosed, and any of which he)-2.5 E
(or she becomes awar)93.6 285.6 Q 2.5(ew)-.18 G
(ill be disclosed, in accor)-2.5 E(dance with Section 6 of BCP 79.)-.18
E(Internet-Drafts ar)93.6 309.6 Q 2.5(ew)-.18 G
(orking documents of the Internet Engineering T)-2.5 E(ask For)-.92 E
(ce \(IETF\), its)-.18 E(ar)93.6 321.6 Q(eas, and its working gr)-.18 E
2.5(oups. Note)-.18 F(that other gr)2.5 E
(oups may also distribute working)-.18 E(documents as Internet-Drafts.)
93.6 333.6 Q(Internet-Drafts ar)93.6 357.6 Q 2.5(ed)-.18 G
(raft documents valid for a maximum of six months and may be)-2.5 E
(updated, r)93.6 369.6 Q
(eplaced, or obsoleted by other documents at any time.)-.18 E
(It is inappr)5 E(opriate to use)-.18 E(Internet-Drafts as r)93.6 381.6
Q(efer)-.18 E(ence material or to cite them other than as "work in pr)
-.18 E(ogr)-.18 E(ess.")-.18 E(The list of curr)93.6 405.6 Q
(ent Internet-Drafts can be accessed at http://www)-.18 E(.ietf.or)-.92
E(g/ietf/1id-)-.18 E(abstracts.txt.)93.6 417.6 Q
(The list of Internet-Draft Shadow Dir)93.6 441.6 Q
(ectories can be accessed at)-.18 E(http://www)93.6 453.6 Q(.ietf.or)
-.92 E(g/shadow)-.18 E(.html.)-.92 E(This Internet-Draft will expir)93.6
477.6 Q 2.5(eo)-.18 G 2.5(nM)-2.5 G(ar)-2.5 E(ch 17, 2006.)-.18 E F2
(Copyright Notice)72 501.6 Q F0
(Copyright \(C\) The Internet Society \(2005\).)93.6 517.2 Q F2
(Abstract)72 541.2 Q/F3 10/Palatino-Italic@0 SF
(This document discusses the cr)93.6 556.8 Q
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-.18 E(multicast \(NORM\) pr)93.6 568.8 Q 2.5(otocols. The)-.18 F
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(re)-2.5 G(sented.).18 E -1.11(Te)93.6 580.8 S
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-.18 E F0(Adamson, et al.)72 768 Q(Expir)96.06 E(es: 17 Mar)-.18 E
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(1. Introduction)72 156 Q F0 10(............................)7.56 G F2
(3)10 E(2. Rationale)72 168 Q F0 10(.............................)6.17 G
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11.45 G F2(5)10 E(2.5. Data Deli)82 228 Q -.15(ve)-.25 G(ry Performance)
.15 E F0 10(......................)4.94 G F2(5)10 E(2.6. Netw)82 240 Q
(ork En)-.1 E(vironments)-.4 E F0 10(.......................)8.9 G F2(5)
10 E(2.7. Router/Intermediate System Assistance)82 252 Q F0 10
(..................)6.74 G F2(6)10 E(3. Functionality)72 264 Q F0 10
(............................)3.66 G F2(6)10 E(3.1. NORM Sender T)82 276
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G 2.5(KP).4 G(rocess Initiation)-2.5 E F0 10(..................)9.56 G
F2(10)5 E(3.2.2. N)92 312 Q -.4(AC)-.35 G 2.5(KS).4 G(uppression)-2.5 E
F0 10(.......................)5.53 G F2(10)5 E(3.2.3. N)92 324 Q -.4(AC)
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F2(14)5 E(3.2.3.1. N)102 336 Q -.4(AC)-.35 G 2.5(Ka).4 G
(nd FEC Repair Strate)-2.5 E(gies)-.15 E F0 10(.................)5.69 G
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(ormat)-.15 E F0 10(....................)11.51 G F2(16)5 E
(3.2.4. Sender Repair Response)92 360 Q F0 10(.....................)
11.74 G F2(17)5 E(3.3. NORM Recei)82 372 Q -.15(ve)-.25 G 2.5(rJ).15 G
(oin Policies and Procedures)-2.5 E F0 10(................)4.65 G F2(19)
5 E(3.4. Reliable Multicast Member Identi\214cation)82 384 Q F0 10
(.................)11.18 G F2(19)5 E(3.5. Data Content Identi\214cation)
82 396 Q F0 10(......................)5.62 G F2(20)5 E(3.6. F)82 408 Q
(orw)-.15 E(ard Error Correction \(FEC\))-.1 E F0 10
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(TT Adv)-.6 E(ertisement)-.15 E F0 10(....................)4.99 G F2(24)
5 E(3.8. Group Size Determination/Estimation)82 480 Q F0 10
(...................).34 G F2(25)5 E(3.9. Congestion Control Operation)
82 492 Q F0 10(.....................)5.89 G F2(25)5 E
(3.10. Router/Intermediate System Assistance)82 504 Q F0 10
(..................)1.74 G F2(25)5 E(3.11. NORM Applicability)82 516 Q
F0 10(.......................)11.72 G F2(25)5 E
(4. Security Considerations)72 528 Q F0 10(........................)
11.17 G F2(26)5 E(5. Ackno)72 540 Q(wledgements)-.25 E F0 10
(..........................)2.82 G F2(26)5 E(6. References)72 552 Q F0
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Q F0 10(..........................)2.85 G F2(27)5 E(8. Full Cop)72 600 Q
(yright Statement)-.1 E F0 10(........................)5.42 G F2(28)5 E
F0(Adamson, et al.)72 768 Q(Expir)96.06 E(es: 17 Mar)-.18 E(ch 2006)-.18
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(1.)72 120 Q/F2 13/Palatino-Bold@0 SF(Introduction)5 E F0
(Reliable multicast transport is a desirable technology for the ef)93.6
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(distribution of data to a gr)93.6 147.6 Q(oup on the Internet.)-.18 E
(The complexities of gr)5 E(oup communication)-.18 E
(paradigms necessitate dif)93.6 159.6 Q(fer)-.18 E(ent pr)-.18 E
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E(fer)-.18 E(ent)-.18 E(pr)93.6 207.6 Q(otocol instantiations may be r)
-.18 E(equir)-.18 E(ed to meet specific application and network)-.18 E
(ar)93.6 219.6 Q(chitectur)-.18 E 2.5(ed)-.18 G(emands [4], ther)-2.5 E
2.5(ea)-.18 G .36 -.18(re a n)-2.5 H
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93.6 231.6 Q(fer)-.18 E(ent instantiations.)-.18 E
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(esses in detail the following building blocks which ar)-.18 E 2.5(en)
-.18 G(ot addr)-2.5 E(essed in other IETF)-.18 E(documents:)93.6 291.6 Q
14.17(1\) NORM)97 307.2 R(sender transmission strategies,)2.5 E 14.17
(2\) NACK-oriented)97 322.8 R -.18(re)2.5 G(pair pr).18 E
(ocess with timer)-.18 E(-based feedback suppr)-.18 E(ession, and)-.18 E
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(oduct of the IETF RMT WG and follows the guidelines)-.18 E(pr)93.6 390
Q(ovided in RFC 3269 [5].)-.18 E(The key wor)5 E
(ds "MUST", "MUST NOT", "REQUIRED", "SHALL",)-.18 E
("SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MA)93.6 402 Q
(Y", and)-1.11 E("OPTIONAL" in this document ar)93.6 414 Q 2.5(et)-.18 G
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(Statement of Intent)72 438 Q F0(This memo contains part of the definit\
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(Tr)93.6 465.6 S(ansport pr).9 E(otocol in accor)-.18 E
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(oup Size Scalability)-.18 E(,)-1.11 E 14.17(5\) Data)97 144 R
(Delivery Performance,)2.5 E 14.17(6\) Network)97 156 R(Envir)2.5 E
(onments, and)-.18 E 14.17(7\) Router/Intermediate)97 168 R
(System Interactions.)2.5 E(All of these ar)93.6 183.6 Q(eas ar)-.18 E
2.5(ea)-.18 G 2.5(tl)-2.5 G(east briefly discussed.)-2.5 E(Additionally)
5 E 2.5(,o)-1.11 G(ther r)-2.5 E(eliable multicast)-.18 E
(transport building block documents such as [9] have been cr)93.6 195.6
Q(eated to addr)-.18 E(ess ar)-.18 E(eas outside of)-.18 E
(the scope of this document.)93.6 207.6 Q(NORM pr)5 E
(otocol instantiations may depend upon these other)-.18 E
(building blocks as well as the ones pr)93.6 219.6 Q(esented her)-.18 E
2.5(e. This)-.18 F(document focuses on ar)2.5 E(eas that ar)-.18 E(e)
-.18 E(unique to NORM but may be used in concert with the other buildin\
g block ar)93.6 231.6 Q 2.5(eas. In)-.18 F(some)2.5 E
(cases, a building block may be able addr)93.6 243.6 Q
(ess a wide range of assumptions, while in other)-.18 E(cases ther)93.6
255.6 Q 2.5(ew)-.18 G(ill be trade-of)-2.5 E(fs r)-.18 E(equir)-.18 E
(ed to meet dif)-.18 E(fer)-.18 E(ent application needs or operating)
-.18 E(envir)93.6 267.6 Q 2.5(onments. Wher)-.18 F 2.5(en)-.18 G
(ecessary)-2.5 E 2.5(,b)-1.11 G(uilding block featur)-2.5 E(es ar)-.18 E
2.5(ed)-.18 G(esigned to be parametric to)-2.5 E(meet dif)93.6 279.6 Q
(fer)-.18 E(ent r)-.18 E(equir)-.18 E 2.5(ements. Of)-.18 F
(course, an underlying goal will be to minimize design)2.5 E
(complexity and to at least r)93.6 291.6 Q
(ecommend default values for any such parameters that meet a)-.18 E
(general purpose "bulk data transfer" r)93.6 303.6 Q(equir)-.18 E
(ement in a typical Internet envir)-.18 E(onment.)-.18 E/F1 10
/Palatino-Bold@0 SF(2.1.)72 339.6 Q/F2 12/Palatino-Bold@0 SF
(Delivery Service Model)5 E F0(The implicit goal of a r)93.6 355.2 Q
(eliable multicast transport pr)-.18 E(otocol is the r)-.18 E
(eliable delivery of data)-.18 E(among a gr)93.6 367.2 Q
(oup of members communicating using IP multicast datagram service.)-.18
E(However)5 E(,)-.74 E
(the specific service the application is attempting to pr)93.6 379.2 Q
(ovide can impact design decisions.)-.18 E(A)5 E
(most basic service model for r)93.6 391.2 Q
(eliable multicast transport is that of "bulk transfer" which is a)-.18
E(primary focus of this and other r)93.6 403.2 Q(elated RMT working gr)
-.18 E(oup documents.)-.18 E(However)5 E 2.5(,t)-.74 G(he same)-2.5 E
(principles in pr)93.6 415.2 Q
(otocol design may also be applied to other services models, e.g., mor)
-.18 E(e)-.18 E
(interactive exchanges of small messages such as with white-boar)93.6
427.2 Q(ding or text chat.)-.18 E -.55(Wi)5 G(thin).55 E(these dif)93.6
439.2 Q(fer)-.18 E(ent models ther)-.18 E 2.5(ea)-.18 G .36 -.18(re i)
-2.5 H(ssues such as the sender).18 E('s ability).74 E
(to cache transmitted data)5 E(\(or state r)93.6 451.2 Q(efer)-.18 E
(encing it\) for r)-.18 E(etransmission or r)-.18 E(epair)-.18 E 5(.T)
-.74 G(he needs for or)-5 E(dering and/or causality)-.18 E
(in the sequence of transmissions and r)93.6 463.2 Q
(eceptions among members in the gr)-.18 E(oup may be)-.18 E(dif)93.6
475.2 Q(fer)-.18 E(ent depending upon data content.)-.18 E(The gr)5 E
(oup communication paradigm dif)-.18 E(fers)-.18 E(significantly fr)93.6
487.2 Q(om the point-to-point model in that, depending upon the data co\
ntent type,)-.18 E(some r)93.6 499.2 Q(eceivers may complete r)-.18 E
(eception of a portion of data content and be able to act upon it)-.18 E
(befor)93.6 511.2 Q 2.5(eo)-.18 G(ther members have r)-2.5 E
(eceived the content.)-.18 E
(This may be acceptable \(or even desirable\))5 E
(for some applications but not for others.)93.6 523.2 Q(These varying r)
5 E(equir)-.18 E(ements drive the need for a)-.18 E(number of dif)93.6
535.2 Q(fer)-.18 E(ent pr)-.18 E(otocol instantiation designs.)-.18 E
2.5(As)5 G(ignificant challenge in developing)-2.5 E(generally useful b\
uilding block mechanisms is accommodating even a limited range of these)
93.6 547.2 Q
(capabilities without defining specific application-level details.)93.6
559.2 Q F1(2.2.)72 595.2 Q F2(Group Membership Dynamics)5 E F0(One ar)
93.6 610.8 Q(ea wher)-.18 E 2.5(eg)-.18 G -.18(ro)-2.5 G
(up communication can dif).18 E(fer fr)-.18 E
(om point-to-point communications is that)-.18 E
(even if the composition of the gr)93.6 622.8 Q(oup changes, the "thr)
-.18 E(ead" of communication can still exist.)-.18 E
(This contrasts with the point-to-point communication model wher)93.6
634.8 Q(e, if either of the two)-.18 E
(parties leave, the communication pr)93.6 646.8 Q
(ocess \(exchange of data\) is terminated \(or at least)-.18 E 2.5
(paused\). Depending)93.6 658.8 R 2.5(upon application)2.5 F
(goals, senders and r)2.5 E(eceivers participating in a)-.18 E -.18(re)
93.6 670.8 S(liable multicast transport "session" may be able to join l\
ate, leave, and/or potentially r).18 E(ejoin)-.18 E
(while the ongoing gr)93.6 682.8 Q(oup communication "thr)-.18 E 2.5
(ead" still)-.18 F -.18(re)2.5 G(mains functional and useful.).18 E
(Also)5 E(note that this can impact pr)93.6 694.8 Q
(otocol message content.)-.18 E(If "late joiners" ar)5 E 2.5(es)-.18 G
(upported, some)-2.5 E
(amount of additional information may be placed in)93.6 706.8 Q
(message headers to accommodate this)5 E(functionality)93.6 718.8 Q 5
(.A)-1.11 G(lternatively)-5 E 2.5(,t)-1.11 G
(he information may be sent in its own message \(on demand or)-2.5 E
(Adamson, et al.)72 768 Q(Expir)96.06 E(es: 17 Mar)-.18 E(ch 2006)-.18 E
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(Building Blocks)2.5 E(October 2005)106.015 E
(intermittently\) if the impact to the over)93.6 120 Q
(head of typical message transmissions is deemed too)-.18 E(gr)93.6 132
Q 2.5(eat. Gr)-.18 F(oup dynamics can also impact other pr)-.18 E
(otocol mechanisms such as NACK timing,)-.18 E(congestion contr)93.6 144
Q(ol operation, etc.)-.18 E/F1 10/Palatino-Bold@0 SF(2.3.)72 180 Q/F2 12
/Palatino-Bold@0 SF(Sender/Receiver Relationships)5 E F0(The r)93.6
195.6 Q(elationship of senders and r)-.18 E(eceivers among gr)-.18 E
(oup members r)-.18 E(equir)-.18 E(es consideration.)-.18 E(In)5 E
(some applications, ther)93.6 207.6 Q 2.5(em)-.18 G
(ay be a single sender multicasting to a gr)-2.5 E(oup of r)-.18 E 2.5
(eceivers. In)-.18 F(other cases, ther)93.6 219.6 Q 2.5(em)-.18 G
(ay be mor)-2.5 E 2.5(et)-.18 G
(han one sender or the potential for everyone in the gr)-2.5 E(oup to)
-.18 E(be a sender _and_ r)93.6 231.6 Q(eceiver of data may exist.)-.18
E F1(2.4.)72 267.6 Q F2(Group Size Scalability)5 E F0
(Native IP multicast [2] may scale to extr)93.6 283.2 Q(emely lar)-.18 E
(ge gr)-.18 E(oup sizes.)-.18 E(It may be desirable for)5 E
(some applications to scale along with the multicast infrastr)93.6 295.2
Q(uctur)-.08 E(e's ability to scale.)-.18 E(In its)5 E
(simplest form, ther)93.6 307.2 Q 2.5(ea)-.18 G .36 -.18(re l)-2.5 H
(imits to the gr).18 E(oup size to which a NACK-oriented pr)-.18 E
(otocol can)-.18 E(apply without NACK implosion pr)93.6 319.2 Q 2.5
(oblems. Resear)-.18 F(ch suggests that NORM gr)-.18 E(oup sizes on)-.18
E(the or)93.6 331.2 Q(der of tens of thousands of r)-.18 E
(eceivers may operate with modest feedback to the sender)-.18 E
(using pr)93.6 343.2 Q(obabilistic, timer)-.18 E(-based suppr)-.18 E
(ession techniques [7].)-.18 E(However)5 E 2.5(,t)-.74 G
(he potential for)-2.5 E -.18(ro)93.6 355.2 S
(uter assistance and/or other NACK suppr).18 E
(ession heuristics may enable these pr)-.18 E(otocols to)-.18 E
(scale to very lar)93.6 367.2 Q(ge gr)-.18 E(oup sizes.)-.18 E(In lar)5
E(ge scale cases, it may be pr)-.18 E(ohibitive for members to)-.18 E
(maintain state on all other members \(in particular)93.6 379.2 Q 2.5
(,o)-.74 G(ther r)-2.5 E(eceivers\) in the gr)-.18 E 2.5(oup. The)-.18 F
(impact)2.5 E(of gr)93.6 391.2 Q(oup size needs to be consider)-.18 E
(ed in the development of applicable building blocks.)-.18 E F1(2.5.)72
427.2 Q F2(Data Delivery Performance)5 E F0(Ther)93.6 442.8 Q 2.5(ei)
-.18 G 2.5(sat)-2.5 G(rade-of)-2.5 E 2.5(fb)-.18 G
(etween scalability and data delivery latency when designing NACK-)-2.5
E(oriented pr)93.6 454.8 Q 2.5(otocols. If)-.18 F(pr)2.5 E
(obabilistic, timer)-.18 E(-based NACK suppr)-.18 E
(ession is to be used, ther)-.18 E 2.5(ew)-.18 G(ill)-2.5 E
(be some delays built into the NACK pr)93.6 466.8 Q
(ocess to allow suppr)-.18 E(ession to occur and for the)-.18 E
(sender of data to identify appr)93.6 478.8 Q(opriate content for ef)
-.18 E(ficient r)-.18 E(epair transmission.)-.18 E(For example,)5 E
(backof)93.6 490.8 Q 2.5(ft)-.18 G(imeouts can be used to ensur)-2.5 E
2.5(ee)-.18 G -.18(ff)-2.5 G(icient NACK suppr).18 E(ession and r)-.18 E
(epair transmission,)-.18 E(but this comes at a cost of incr)93.6 502.8
Q(eased delivery latency and incr)-.18 E(eased buf)-.18 E(fering r)-.18
E(equir)-.18 E(ements)-.18 E(for both senders and r)93.6 514.8 Q 2.5
(eceivers. The)-.18 F
(building blocks SHOULD allow applications to establish)2.5 E
(bounds for data delivery performance.)93.6 526.8 Q
(Note that application designers must be awar)5 E 2.5(eo)-.18 G 2.5(ft)
-2.5 G(he)-2.5 E(scalability trade-of)93.6 538.8 Q 2.5(ft)-.18 G
(hat is made when such bounds ar)-2.5 E 2.5(ea)-.18 G(pplied.)-2.5 E F1
(2.6.)72 574.8 Q F2(Network Environments)5 E F0(The Internet Pr)93.6
590.4 Q(otocol has historically assumed a r)-.18 E(ole of pr)-.18 E
(oviding service acr)-.18 E(oss)-.18 E(heter)93.6 602.4 Q
(ogeneous network topologies.)-.18 E(It is desirable that a r)5 E
(eliable multicast pr)-.18 E(otocol be)-.18 E(capable of ef)93.6 614.4 Q
(fectively operating acr)-.18 E
(oss a wide range of the networks to which general)-.18 E
(purpose IP service applies.)93.6 626.4 Q
(The bandwidth available on the links between the members of a)5 E
(single gr)93.6 638.4 Q
(oup today may vary between low numbers of kbit/s for wir)-.18 E
(eless links and multiple)-.18 E
(Gbit/s for high speed LAN connections, with varying degr)93.6 650.4 Q
(ees of contention fr)-.18 E(om other)-.18 E 2.5(flows. Recently)93.6
662.4 R 2.5(,an)-1.11 G
(umber of asymmetric network services including 56K/ADSL modems,)-2.5 E
(CA)93.6 674.4 Q(TV Internet service, satellite and other wir)-.74 E
(eless communication services have begun to)-.18 E(pr)93.6 686.4 Q 2.5
(oliferate. Many)-.18 F(of these ar)2.5 E 2.5(ei)-.18 G(nher)-2.5 E
(ently br)-.18 E(oadcast media with potentially lar)-.18 E
(ge "fan-out" to)-.18 E
(which IP multicast service is highly applicable.)93.6 698.4 Q
(Additionally)5 E 2.5(,p)-1.11 G(olicy and/or technical issues)-2.5 E
(may r)93.6 710.4 Q(esult in topologies wher)-.18 E 2.5(em)-.18 G
(ulticast connectivity is limited to a single sour)-2.5 E(ce multicast)
-.18 E(\(SSM\) model fr)93.6 722.4 Q(om a specific sour)-.18 E(ce [8].)
-.18 E(Receivers in the gr)5 E(oup may be r)-.18 E(estricted to unicast)
-.18 E(Adamson, et al.)72 768 Q(Expir)96.06 E(es: 17 Mar)-.18 E(ch 2006)
-.18 E([Page 5])129.71 E 0 Cg EP
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/F0 10/Palatino-Roman@0 SF 99.635(Internet-Draft NORM)72 66 R
(Building Blocks)2.5 E(October 2005)106.015 E
(feedback for NACKs and other messages.)93.6 120 Q
(Consideration must be given, in building block)5 E(development and pr)
93.6 132 Q(otocol design, to the natur)-.18 E 2.5(eo)-.18 G 2.5(ft)-2.5
G(he underlying networks.)-2.5 E/F1 10/Palatino-Bold@0 SF(2.7.)72 168 Q
/F2 12/Palatino-Bold@0 SF(Router/Intermediate System Assistance)5 E F0
(While intermediate assistance fr)93.6 183.6 Q
(om devices/systems with dir)-.18 E(ect knowledge of the)-.18 E(underly\
ing network topology may be used to leverage the performance and scalab\
ility of)93.6 195.6 Q -.18(re)93.6 207.6 S(liable multicast pr).18 E
(otocols, ther)-.18 E 2.5(ew)-.18 G
(ill continue to be a number of instances wher)-2.5 E 2.5(et)-.18 G
(his is not)-2.5 E(available or practical.)93.6 219.6 Q
(Any building block components for NACK-oriented r)5 E
(eliable multicast)-.18 E
(SHALL be capable of operating without such assistance.)93.6 231.6 Q
(However)5 E 2.5(,i)-.74 G 2.5(ti)-2.5 G 2.5(sR)-2.5 G(ECOMMENDED)-2.5 E
(that such pr)93.6 243.6 Q(otocols also consider utilizing these featur)
-.18 E(es when available.)-.18 E F1(3.)72 279.6 Q/F3 13/Palatino-Bold@0
SF(Functionality)5 E F0(The pr)93.6 295.2 Q(evious section has pr)-.18 E
(esented the r)-.18 E(ole of pr)-.18 E
(otocol building blocks and some of the)-.18 E(criteria that may af)93.6
307.2 Q(fect NORM building block identification/design.)-.18 E
(This section describes)5 E(dif)93.6 319.2 Q(fer)-.18 E
(ent building block ar)-.18 E(eas applicable to NORM pr)-.18 E 2.5
(otocols. Some)-.18 F(of these ar)2.5 E(eas ar)-.18 E(e)-.18 E
(specific to NACK-oriented pr)93.6 331.2 Q 2.5(otocols. Detailed)-.18 F
(descriptions of such)2.5 E(ar)5 E(eas ar)-.18 E 2.5(ep)-.18 G -.18(ro)
-2.5 G 2.5(vided. In).18 F(other cases, the ar)93.6 343.2 Q
(eas \(e.g., node identifiers, forwar)-.18 E 2.5(de)-.18 G(rr)-2.5 E
(or corr)-.18 E(ection \(FEC\), etc.\) may be)-.18 E
(applicable to other forms of r)93.6 355.2 Q(eliable multicast.)-.18 E
(In those cases, the discussion below describes)5 E -.18(re)93.6 367.2 S
(quir).18 E(ements placed on those other general building block ar)-.18
E(eas fr)-.18 E(om the standpoint of)-.18 E(NACK-oriented r)93.6 379.2 Q
(eliable multicast.)-.18 E(Wher)5 E 2.5(ea)-.18 G
(pplicable, other building block documents ar)-2.5 E(e)-.18 E -.18(re)
93.6 391.2 S(fer).18 E(enced for possible contribution to NORM pr)-.18 E
(otocols.)-.18 E
(For each building block, a notional "interface description" is pr)93.6
415.2 Q(ovided to illustrate any)-.18 E(dependencies of one building bl\
ock component upon another or upon other pr)93.6 427.2 Q(otocol)-.18 E
2.5(parameters. A)93.6 439.2 R(building block component may r)2.5 E
(equir)-.18 E 2.5(es)-.18 G(ome form of "input" fr)-2.5 E(om another)
-.18 E(building block component or other sour)93.6 451.2 Q
(ce to perform its function.)-.18 E(Any "inputs" r)5 E(equir)-.18 E
(ed by)-.18 E 2.5(ab)93.6 463.2 S(uilding block component and/or any r)
-2.5 E(esultant "output" pr)-.18 E(ovided will be defined and)-.18 E
(described in each building block component's interface description.)
93.6 475.2 Q(Note that the set of)5 E(building blocks pr)93.6 487.2 Q
(esented her)-.18 E 2.5(ed)-.18 G 2.5(on)-2.5 G
(ot fully satisfy each other)-2.5 E('s "input" and "output" needs.).74 E
(In some cases, "inputs" for the building blocks her)93.6 499.2 Q 2.5
(em)-.18 G(ust come fr)-2.5 E(om other building blocks)-.18 E
(external to this document \(e.g., congestion contr)93.6 511.2 Q
(ol or FEC\).)-.18 E(In other cases NORM building)5 E
(block "inputs" must be satisfied by the specific pr)93.6 523.2 Q
(otocol instantiation or implementation)-.18 E
(\(e.g., application data and contr)93.6 535.2 Q(ol\).)-.18 E
(The following building block components r)93.6 559.2 Q
(elevant to NORM ar)-.18 E 2.5(ei)-.18 G(dentified:)-2.5 E/F4 10
/Palatino-BoldItalic@0 SF(\(NORM-Specific\))93.6 583.2 Q F0 14.17
(1\) NORM)97 595.2 R(Sender T)2.5 E(ransmission)-.9 E 14.17(2\) NORM)97
607.2 R(Repair Pr)2.5 E(ocess)-.18 E 14.17(3\) NORM)97 619.2 R
(Receiver Join Policies)2.5 E(Adamson, et al.)72 768 Q(Expir)96.06 E
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(Building Blocks)2.5 E(October 2005)106.015 E/F1 10
/Palatino-BoldItalic@0 SF(\(General Purpose\))93.6 120 Q F0 14.17
(4\) Node)97 135.6 R(\(member\) Identification)2.5 E 14.17(5\) Data)97
151.2 R(Content Identification)2.5 E 14.17(6\) Forwar)97 166.8 R 2.5(dE)
-.18 G(rr)-2.5 E(or Corr)-.18 E(ection \(FEC\))-.18 E 14.17
(7\) Round-trip)97 182.4 R -.55(Ti)2.5 G(ming Collection).55 E 14.17
(8\) Gr)97 198 R(oup Size Determination/Estimation)-.18 E 14.17
(9\) Congestion)97 213.6 R(Contr)2.5 E(ol Operation)-.18 E 9.17
(10\) Router/Intermediate)97 229.2 R(System Assistance)2.5 E -.55(11)97
244.8 S 12.22(\)A).55 G(ncillary Pr)-12.22 E(otocol Mechanisms)-.18 E
(Figur)93.6 260.4 Q 2.5(e1p)-.18 G -.18(ro)-2.5 G
(vides a pictorial overview of these building block ar).18 E
(eas and some of their)-.18 E -.18(re)93.6 272.4 S 2.5(lationships. For)
.18 F(example, the content of the data messages that a sender initially\
 transmits)2.5 E(depends upon the "Node Identification", "Data Content \
Identification", and "FEC")93.6 284.4 Q(components while the rate of me\
ssage transmission will generally depend upon the)93.6 296.4 Q
("Congestion Contr)93.6 308.4 Q(ol" component.)-.18 E(Subsequently)5 E
2.5(,t)-1.11 G(he r)-2.5 E(eceivers' r)-.18 E(esponse to these)-.18 E
(transmissions \(e.g., NACKing for r)93.6 320.4 Q
(epair\) will depend upon the data message content and)-.18 E(inputs fr)
93.6 332.4 Q(om other building block components.)-.18 E(Finally)5 E 2.5
(,t)-1.11 G(he sender)-2.5 E('s pr).74 E(ocessing of r)-.18 E(eceiver)
-.18 E -.18(re)93.6 344.4 S
(sponses will feed back into its transmission strategy).18 E(.)-1.11 E
(The components on the left side of this figur)93.6 368.4 Q 2.5(ea)-.18
G .36 -.18(re a)-2.5 H -.18(re).18 G(as that may be applicable beyond)
.18 E 2.5(NORM. The)93.6 380.4 R
(most significant of these components ar)2.5 E 2.5(ed)-.18 G
(iscussed in other building block)-2.5 E(documents such as [9].)93.6
392.4 Q 2.5(Ab)5 G(rief description of these ar)-2.5 E(eas and their r)
-.18 E(ole in the NORM)-.18 E(pr)93.6 404.4 Q(otocol is given below)-.18
E 5(.T)-.92 G(he components on the right ar)-5 E 2.5(es)-.18 G
(een as specific to NORM)-2.5 E(pr)93.6 416.4 Q
(otocols, most notably the NACK r)-.18 E(epair pr)-.18 E 2.5
(ocess. These)-.18 F(ar)2.5 E(eas ar)-.18 E 2.5(ed)-.18 G
(iscussed in detail below)-2.5 E(.)-.92 E(Some other components \(e.g.,\
 "Security"\) impact many aspects of the pr)93.6 428.4 Q
(otocol, and others)-.18 E(such as "Router Assistance" may be mor)93.6
440.4 Q 2.5(et)-.18 G(ranspar)-2.5 E(ent to the cor)-.18 E 2.5(ep)-.18 G
-.18(ro)-2.5 G(tocol pr).18 E 2.5(ocessing. The)-.18 F
(sections below describe the "NORM Sender T)93.6 452.4 Q
(ransmission", "NORM Repair Pr)-.9 E(ocess", and)-.18 E("R)93.6 464.4 Q
(TT Collection" building blocks in detail.)-.37 E(The r)5 E
(elationships to and among the other)-.18 E(building block ar)93.6 476.4
Q(eas ar)-.18 E 2.5(ea)-.18 G
(lso discussed, focusing on issues applicable to NORM pr)-2.5 E(otocol)
-.18 E 2.5(design. Wher)93.6 488.4 R 2.5(ea)-.18 G
(pplicable, specific technical r)-2.5 E(ecommendations ar)-.18 E 2.5(em)
-.18 G(ade for mechanisms)-2.5 E(that will pr)93.6 500.4 Q
(operly satisfy the goals of NORM transport for the Internet.)-.18 E
(Adamson, et al.)72 768 Q(Expir)96.06 E(es: 17 Mar)-.18 E(ch 2006)-.18 E
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(Building Blocks)2.5 E(October 2005)106.015 E/F1 10/Courier@0 SF
(Application Data and Control)315.6 120 Q(|)387.6 132 Q(V)387.6 144 Q 66
(.---------------------. .-----------------------.)117.6 156 R 6(|N)
117.6 168 S(ode Identification |----------->|)-6 E(Sender Transmission)
12 E(|<----.)12 E 36(`---------------------' _.-')117.6 180 R 24
(`-----------------------' |)6 F 12(.---------------------. _.-')117.6
192 R 60(.' |)6 F 12(.--------------. |)6 F 6(|D)117.6 204 S
(ata Identification |--')-6 E 66(.'' |)18 F 12(|J)6 G(oin Policy |)-12 E
(|)18 E 18(`---------------------' .')117.6 216 R 78('V)6 G 12
(`--------------' |)-72 F 6(.---------------------. .' ')117.6 228 R 30
(.----------------------. |)30 F(.->| Congestion Control)99.6 240 Q 12
(|-' ')12 F 6(|R)36 G(eceiver NACK)-6 E 36(||)48 G 12(|`)99.6 252 S 12
(---------------------' .')-12 F 6(|R)42 G(epair Process)-6 E 36(||)42 G
12(|.)99.6 264 S(---------------------. .')-12 E 6(|.)54 G
(------------------. |)-6 E(|)36 E 18 12(|| F)99.6 276 T 54(EC |'. |)-12
F 6(|N)6 G(ACK Initiation)-6 E 18 6(|| |)12 H 12(|`)99.6 288 S
(---------------------'` `._)-12 E 6(|`)42 G(------------------' |)-6 E
(|)36 E 12(|.)99.6 300 S(---------------------. ``. `-._)-12 E 6(|.)18 G
(------------------. |)-6 E(|)36 E 18(`--| RTT)99.6 312 R 12
(Collection |._`)6 F 24(``)6 G(->| | NACK Content)-24 E 18 6(|| |)30 H
(`---------------------'` `` `)117.6 324 Q 6(|`)36 G
(------------------' |)-6 E(|)36 E 6(.---------------------. `)117.6 336
R 6(``-`._ |)6 F(.------------------. |)6 E(|)36 E 24(|G)117.6 348 S
(roup Size Est.)-24 E(|---`-`---`->| | NACK Suppression | |)12 E(|)36 E
6(`---------------------'`. `)117.6 360 R 30(`|)6 G
(`------------------' |)-24 E(|)36 E 6(.---------------------. ` `)117.6
372 R 24(``)6 G 30(----------------------' |)-24 F 42(|O)117.6 384 S 48
(ther |)-42 F 12(``)18 G 66(`|)-6 G(+-----------------+ |)-60 E 18
(`---------------------' `)117.6 396 R 42 6(`` ||)12 H
(Router Assistance| |)-6 E(`. ` `)285.6 408 Q 6(V+)54 G
(-----------------+ |)-6 E(`-` >.-------------------------.)297.6 420 Q
(|)18 E 6(|S)327.6 432 S(ender NACK Processing)-6 E(|___/)12 E 6(|a)
327.6 444 S(nd Repair Response)-6 E(|)30 E(`-------------------------')
327.6 456 Q 150(^^)213.6 468 S 150(||)213.6 480 S
(.-----------------------------.)201.6 492 Q 54(|\()201.6 504 S 54
(Security\) |)-54 F(`-----------------------------')201.6 516 Q/F2 10
/Palatino-Italic@0 SF(Fig. 1 - NORM Building Block Framework)211.9 528 Q
/F3 10/Palatino-Bold@0 SF(3.1.)72 567.6 Q/F4 12/Palatino-Bold@0 SF
(NORM Sender T)5 E(ransmission)-1.332 E F0
(NORM senders will transmit data content to the multicast session.)93.6
583.2 Q(The data content will be)5 E(application dependent.)93.6 595.2 Q
(The sender will transmit data content at a rate, and with message)5 E
(sizes, determined by application and/or network ar)93.6 607.2 Q
(chitectur)-.18 E 2.5(er)-.18 G(equir)-2.68 E 2.5(ements. Any)-.18 F
(FEC)2.5 E(encoding of sender transmissions SHOULD conform with the gui\
delines of [9].)93.6 619.2 Q(When)5 E(congestion contr)93.6 631.2 Q
(ol mechanisms ar)-.18 E 2.5(en)-.18 G
(eeded \(REQUIRED for general Internet operation\), the)-2.5 E
(NORM transmission rate SHALL be contr)93.6 643.2 Q
(olled by the congestion contr)-.18 E(ol mechanism.)-.18 E(In any)5 E
(case, it is RECOMMENDED that all data transmissions fr)93.6 655.2 Q 2.5
(om NORM)-.18 F(senders be subject to)2.5 E
(rate limitations determined by the application or congestion contr)93.6
667.2 Q(ol algorithm.)-.18 E(The sender)5 E('s).74 E(transmissions SHOU\
LD make good utilization of the available capacity \(which may be)93.6
679.2 Q(limited by the application and/or by congestion contr)93.6 691.2
Q 2.5(ol\). As)-.18 F 2.5(ar)2.5 G(esult, it is expected ther)-2.68 E(e)
-.18 E(will be overlap and multiplexing of new data content transmissio\
n with r)93.6 703.2 Q(epair content.)-.18 E(Other factors r)93.6 715.2 Q
(elated to application operation may determine sender transmission form\
ats)-.18 E(Adamson, et al.)72 768 Q(Expir)96.06 E(es: 17 Mar)-.18 E
(ch 2006)-.18 E([Page 8])129.71 E 0 Cg EP
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/F0 10/Palatino-Roman@0 SF 99.635(Internet-Draft NORM)72 66 R
(Building Blocks)2.5 E(October 2005)106.015 E(and methods.)93.6 120 Q
(For example, some consideration needs to be given to the sender)5 E
('s behavior).74 E
(during intermittent idle periods when it has no data to transmit.)93.6
132 Q(In addition to data content, other sender messages or commands ma\
y be employed as part)93.6 156 Q(of pr)93.6 168 Q(otocol operation.)-.18
E(These messages may occur outside of the scope of application data)5 E
(transfer)93.6 180 Q 5(.I)-.74 G 2.5(nN)-5 G(ORM pr)-2.5 E(otocols, r)
-.18 E(eliability of such pr)-.18 E(otocol messages may be attempted by)
-.18 E -.18(re)93.6 192 S
(dundant transmission when positive acknowledgement is pr).18 E
(ohibitive due to gr)-.18 E(oup size)-.18 E(scalability concerns.)93.6
204 Q(Note that pr)5 E(otocol design SHOULD pr)-.18 E
(ovide mechanisms for dealing)-.18 E(with cases wher)93.6 216 Q 2.5(es)
-.18 G(uch messages ar)-2.5 E 2.5(en)-.18 G(ot r)-2.5 E
(eceived by the gr)-.18 E 2.5(oup. As)-.18 F(an example, a command)2.5 E
(message might be r)93.6 228 Q(edundantly transmitted by a sender to in\
dicate that it is temporarily \(or)-.18 E
(permanently\) halting transmission.)93.6 240 Q
(At this time, it may be appr)5 E(opriate for r)-.18 E(eceivers to)-.18
E -.18(re)93.6 252 S(spond with NACKs for any outstanding r).18 E
(epairs they r)-.18 E(equir)-.18 E 2.5(ef)-.18 G(ollowing the r)-2.5 E
(ules of the)-.08 E(NORM NACK pr)93.6 264 Q(ocedur)-.18 E 2.5(e. For)
-.18 F(ef)2.5 E(ficiency)-.18 E 2.5(,t)-1.11 G
(he sender should allow suf)-2.5 E(ficient time between)-.18 E(the r)
93.6 276 Q(edundant transmissions to r)-.18 E
(eceive any NACK-oriented r)-.18 E(esponses fr)-.18 E(om the r)-.18 E
(eceivers to)-.18 E(this command.)93.6 288 Q(In general, when ther)93.6
312 Q 2.5(ei)-.18 G 2.5(sa)-2.5 G(ny r)-2.5 E
(esultant NACK or other feedback operation, the timing of)-.18 E -.18
(re)93.6 324 S(dundant transmission of contr).18 E
(ol messages issued by a sender and other NORM pr)-.18 E(otocol)-.18 E
(timeouts should be dependent upon the gr)93.6 336 Q(oup gr)-.18 E
(eatest r)-.18 E(ound trip timing \()-.18 E/F1 10/Courier@0 SF(GRTT)A F0
2.5(\)e)C(stimate)-2.5 E(and any expected r)93.6 348 Q
(esultant NACK or other feedback operation.)-.18 E(The NORM)5 E F1(GRTT)
2.5 E F0(is an)2.5 E(estimate of the worst-case r)93.6 360 Q
(ound-trip timing fr)-.18 E(om a sender to any r)-.18 E
(eceivers in the gr)-.18 E 2.5(oup. It)-.18 F(is assumed that the)93.6
372 Q F1(GRTT)2.5 E F0
(interval is a conservative estimate of the maximum span \(with)2.5 E
-.18(re)93.6 384 S(spect to delay\) of the multicast gr).18 E(oup acr)
-.18 E(oss a network topology with r)-.18 E(espect to given)-.18 E
(sender)93.6 396 Q 5(.N)-.74 G(ORM instantiations SHOULD be able to dyn\
amically adapt to a wide range of)-5 E(multicast network topologies.)
93.6 408 Q/F2 10/Palatino-BoldItalic@0 SF(Sender T)72 432 Q
(ransmission Interface Description)-.92 E/F3 10/Palatino-Italic@0 SF
(Inputs:)93.6 447.6 Q F0 14.17(1\) Application)97 463.2 R
(data and contr)2.5 E(ol)-.18 E 14.17(2\) Sender)97 475.2 R
(node identifier)2.5 E 14.17(3\) Data)97 487.2 R(identifiers)2.5 E 14.17
(4\) Segmentation)97 499.2 R(and FEC parameters)2.5 E 14.17(5\) T)97
511.2 R(ransmission rate)-.9 E 14.17(6\) Application)97 523.2 R(contr)
2.5 E(ols)-.18 E 14.17(7\) Receiver)97 535.2 R
(feedback messages \(e.g., NACKs\))2.5 E F3(Outputs:)93.6 550.8 Q F0
14.17(1\) Contr)97 566.4 R(olled transmission of messages with headers \
uniquely identifying data or r)-.18 E(epair)-.18 E
(content within the context of the NORM session.)122 578.4 Q 14.17
(2\) Commands)97 590.4 R(indicating sender)2.5 E
('s status or other transport contr).74 E(ol actions to be taken.)-.18 E
/F4 10/Palatino-Bold@0 SF(3.2.)72 614.4 Q/F5 12/Palatino-Bold@0 SF
(NORM Repair Process)5 E F0 2.5(Ac)93.6 630 S
(ritical component of NORM pr)-2.5 E(otocols is the NACK r)-.18 E
(epair pr)-.18 E 2.5(ocess. This)-.18 F(includes the)2.5 E -.18(re)93.6
642 S -1.76(ceiver 's).18 F -.18(ro)2.5 G(le in detecting and r).18 E
(equesting r)-.18 E(epair needs, and the sender)-.18 E('s r).74 E
(esponse to such)-.18 E -.18(re)93.6 654 S 2.5(quests. Ther).18 F 2.5
(ea)-.18 G .36 -.18(re f)-2.5 H(our primary elements of the NORM r).18 E
(epair pr)-.18 E(ocess:)-.18 E 14.17(1\) Receiver)97 669.6 R(NACK pr)2.5
E(ocess initiation,)-.18 E 14.17(3\) NACK)97 685.2 R(suppr)2.5 E
(ession,)-.18 E 14.17(2\) NACK)97 700.8 R(message content,)2.5 E
(Adamson, et al.)72 768 Q(Expir)96.06 E(es: 17 Mar)-.18 E(ch 2006)-.18 E
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/F0 10/Palatino-Roman@0 SF 99.635(Internet-Draft NORM)72 66 R
(Building Blocks)2.5 E(October 2005)106.015 E 14.17(4\) Sender)97 120 R
(NACK pr)2.5 E(ocessing and r)-.18 E(esponse.)-.18 E/F1 10
/Palatino-Bold@0 SF 2.5(3.2.1. Receiver)72 144 R
(NACK Process Initiation)2.5 E F0(The NORM NACK pr)93.6 159.6 Q
(ocess \(cycle\) will be initiated by r)-.18 E
(eceivers that detect a need for r)-.18 E(epair)-.18 E(transmissions fr)
93.6 171.6 Q(om a specific sender to achieve r)-.18 E(eliable r)-.18 E
2.5(eception. When)-.18 F(FEC is applied, a)2.5 E -.18(re)93.6 183.6 S
(ceiver should initiate the NACK pr).18 E
(ocess only when it is known its r)-.18 E(epair r)-.18 E(equir)-.18 E
(ements)-.18 E(exceed the amount of pending FEC transmission for a give\
n coding block of data content.)93.6 195.6 Q
(This can be determined at the end of the curr)93.6 207.6 Q
(ent transmission block \(if it is indicated\) or)-.18 E
(upon the start of r)93.6 219.6 Q
(eception of a subsequent coding block or transmission object.)-.18 E
(This implies)5 E(the NORM data content is marked to identify its FEC b\
lock number and that or)93.6 231.6 Q(dinal)-.18 E -.18(re)93.6 243.6 S
(lationship is pr).18 E(eserved in or)-.18 E(der of transmission.)-.18 E
(Alternatively)93.6 267.6 Q 2.5(,i)-1.11 G 2.5(ft)-2.5 G(he sender)-2.5
E('s transmission advertises the quantity of r).74 E
(epair packets it is)-.18 E(alr)93.6 279.6 Q
(eady planning to send for a block, the r)-.18 E
(eceiver may be able to initiate the NACK pr)-.18 E(ocessor)-.18 E
(earlier)93.6 291.6 Q 5(.A)-.74 G(llowing r)-5 E
(eceivers to initiate NACK cycles at any time they detect their r)-.18 E
(epair needs)-.18 E(have exceeded pending r)93.6 303.6 Q
(epair transmissions may r)-.18 E(esult in slightly quicker r)-.18 E
(epair cycles.)-.18 E(However)93.6 315.6 Q 2.5(,i)-.74 G 2.5(tm)-2.5 G
(ay be useful to limit NACK pr)-2.5 E
(ocess initiation to specific events such as at the)-.18 E(end-of-trans\
mission of an FEC coding block or upon detection of subsequent coding b\
locks.)93.6 327.6 Q(This can allow r)93.6 339.6 Q(eceivers to aggr)-.18
E(egate NACK content into a smaller number of NACK)-.18 E
(messages and pr)93.6 351.6 Q(ovide some implicit loose synchr)-.18 E
(onization among the r)-.18 E(eceiver set to help)-.18 E(facilitate ef)
93.6 363.6 Q(fective pr)-.18 E(obabilistic suppr)-.18 E
(ession of NACK feedback.)-.18 E(The r)5 E(eceiver MUST)-.18 E
(maintain a history of data content r)93.6 375.6 Q(eceived fr)-.18 E
(om the sender to determine its curr)-.18 E(ent r)-.18 E(epair)-.18 E
2.5(needs. When)93.6 387.6 R
(FEC is employed, it is expected that the history will corr)2.5 E
(espond to a r)-.18 E(ecor)-.18 E 2.5(do)-.18 G(f)-2.5 E
(pending or partially-r)93.6 399.6 Q(eceived coding blocks.)-.18 E
(For pr)93.6 423.6 Q(obabilistic, timer)-.18 E(-base suppr)-.18 E
(ession of feedback, the NACK cycle should begin with)-.18 E -.18(re)
93.6 435.6 S(ceivers observing backof).18 E 2.5(ft)-.18 G 2.5
(imeouts. In)-2.5 F(conjunction with initiating this backof)2.5 E 2.5
(ft)-.18 G(imeout, it is)-2.5 E(important that the r)93.6 447.6 Q
(eceivers r)-.18 E(ecor)-.18 E 2.5(dt)-.18 G(he curr)-2.5 E
(ent position in the sender)-.18 E('s transmission).74 E
(sequence at which they initiate the NACK cycle.)93.6 459.6 Q
(When the suppr)5 E(ession backof)-.18 E 2.5(ft)-.18 G(imeout)-2.5 E
(expir)93.6 471.6 Q(es, the r)-.18 E
(eceivers should only consider their r)-.18 E(epair needs up to this r)
-.18 E(ecor)-.18 E(ded)-.18 E
(transmission position in making the decision to transmit or suppr)93.6
483.6 Q(ess a NACK.)-.18 E -.55(Wi)5 G(thout this).55 E -.18(re)93.6
495.6 S(striction, suppr).18 E(ession is gr)-.18 E(eatly r)-.18 E
(educed as additional content is r)-.18 E(eceived fr)-.18 E
(om the sender)-.18 E(during the time a NACK message pr)93.6 507.6 Q
(opagates acr)-.18 E(oss the network to the sender and other)-.18 E -.18
(re)93.6 519.6 S(ceivers.).18 E/F2 10/Palatino-BoldItalic@0 SF
(Receiver NACK Pr)72 543.6 Q(ocess Initiation Interface Description)-.18
E/F3 10/Palatino-Italic@0 SF(Inputs:)93.6 559.2 Q F0 14.17(1\) Sender)97
574.8 R(data content with sequencing identifiers fr)2.5 E
(om sender transmissions.)-.18 E 14.17(2\) History)97 590.4 R
(of content r)2.5 E(eceived fr)-.18 E(om sender)-.18 E(.)-.74 E F3
(Outputs:)93.6 606 Q F0 14.17(1\) NACK)97 621.6 R(pr)2.5 E
(ocess initiation decision)-.18 E 14.17(2\) Recor)97 637.2 R
(ded sender transmission sequence position.)-.18 E F1 2.5(3.2.2. NACK)72
661.2 R(Suppression)2.5 E F0(An ef)93.6 676.8 Q
(fective NORM feedback suppr)-.18 E
(ession mechanism is the use of random backof)-.18 E 2.5(ft)-.18 G
(imeouts)-2.5 E(prior to NACK transmission by r)93.6 688.8 Q(eceivers r)
-.18 E(equiring r)-.18 E(epairs [10].)-.18 E(Upon expiration of the)5 E
(backof)93.6 700.8 Q 2.5(ft)-.18 G(imeout, a r)-2.5 E(eceiver will r)
-.18 E(equest r)-.18 E(epairs unless its pending r)-.18 E
(epair needs have been)-.18 E
(completely superseded by NACK messages hear)93.6 712.8 Q 2.5(df)-.18 G
-.18(ro)-2.5 G 2.5(mo).18 G(ther r)-2.5 E(eceivers \(when r)-.18 E
(eceivers ar)-.18 E(e)-.18 E(Adamson, et al.)72 768 Q(Expir)96.06 E
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/F0 10/Palatino-Roman@0 SF 99.635(Internet-Draft NORM)72 66 R
(Building Blocks)2.5 E(October 2005)106.015 E
(multicasting NACKs\) or fr)93.6 120 Q(om some indicator fr)-.18 E
(om the sender)-.18 E 5(.W)-.74 G(hen r)-5 E(eceivers ar)-.18 E(e)-.18 E
(unicasting NACK messages, the sender may facilitate NACK suppr)93.6 132
Q(ession by forwar)-.18 E(ding a)-.18 E -.18(re)93.6 144 S(pr).18 E
(esentation of NACK content it has r)-.18 E(eceived to the gr)-.18 E
(oup at lar)-.18 E(ge or pr)-.18 E(ovide some other)-.18 E
(indicator of the r)93.6 156 Q
(epair information it will be subsequently transmitting.)-.18 E(For ef)
93.6 180 Q(fective and scalable suppr)-.18 E
(ession performance, the backof)-.18 E 2.5(ft)-.18 G
(imeout periods used by)-2.5 E -.18(re)93.6 192 S
(ceivers should be independently).18 E 2.5(,r)-1.11 G
(andomly picked by r)-2.5 E(eceivers with a tr)-.18 E(uncated)-.08 E
(exponential distribution [6].)93.6 204 Q(This r)5 E
(esults in the majority of the r)-.18 E(eceiver set holding of)-.18 E(f)
-.18 E(transmission of NACK messages under the assumption that the smal\
ler number of "early)93.6 216 Q(NACKers" will supersede the r)93.6 228 Q
(epair needs of the r)-.18 E(emainder of the gr)-.18 E 2.5(oup. The)-.18
F(mean of the)2.5 E
(distribution should be determined as a function of the curr)93.6 240 Q
(ent estimate of sender<->gr)-.18 E(oup)-.18 E/F1 10/Courier@0 SF(GRTT)
93.6 252 Q F0(and a gr)2.5 E
(oup size estimate that is determined by other mechanisms within the pr)
-.18 E(otocol)-.18 E(or pr)93.6 264 Q
(eset by the multicast application.)-.18 E 2.5(As)93.6 288 S
(imple algorithm can be constr)-2.5 E(ucted to generate random backof)
-.08 E 2.5(ft)-.18 G(imeouts with the)-2.5 E(appr)93.6 300 Q
(opriate distribution.)-.18 E(Additionally)5 E 2.5(,t)-1.11 G
(he algorithm may be designed to optimize the)-2.5 E(backof)93.6 312 Q
2.5(fd)-.18 G(istribution given the number of r)-2.5 E
(eceivers \(R\) potentially generating feedback.)-.18 E(This)5 E("optim\
ization" minimizes the number of feedback messages \(e.g., NACK\) in th\
e worst-case)93.6 324 Q(situation wher)93.6 336 Q 2.5(ea)-.18 G(ll r)
-2.5 E(eceivers generate a NACK. The maximum backof)-.18 E 2.5(ft)-.18 G
(imeout)-2.5 E(\()93.6 348 Q F1(T_maxBackoff)A F0 2.5(\)c)C
(an be set to contr)-2.5 E(ol r)-.18 E
(eliable delivery latency versus volume of feedback)-.18 E(traf)93.6 360
Q 2.5(fic. A)-.18 F(lar)2.5 E(ger value of)-.18 E F1(T_maxBackoff)2.5 E
F0(will r)2.5 E(esult in a lower density of feedback traf)-.18 E
(fic for)-.18 E 2.5(ag)93.6 372 S(iven r)-2.5 E(epair cycle.)-.18 E 2.5
(As)5 G(maller value of)-2.5 E F1(T_maxBackoff)2.5 E F0 -.18(re)2.5 G
(sults in shorter latency which also).18 E -.18(re)93.6 384 S
(duces the buf).18 E(fering r)-.18 E(equir)-.18 E
(ements of senders and r)-.18 E(eceivers for r)-.18 E
(eliable transport.)-.18 E(Given the r)93.6 408 Q(eceiver gr)-.18 E
(oup size \()-.18 E F1(R)A F0(\), and maximum allowed backof)A 2.5(ft)
-.18 G(imeout \()-2.5 E F1(T_maxBackoff)A F0(\),)A(random backof)93.6
420 Q 2.5(ft)-.18 G(imeouts \()-2.5 E F1(t')A F0 2.5(\)w)C(ith a tr)-2.5
E(uncated exponential distribution can be picked with)-.08 E
(the following algorithm:)93.6 432 Q 14.17(1\) Establish)97 459.6 R
(an optimal mean \()2.5 E F1(L)A F0 2.5(\)f)C(or the exponential backof)
-2.5 E 2.5(fb)-.18 G(ased on the gr)-2.5 E(oup size:)-.18 E F1 6(L=l)274
483.6 S(n\(R\) + 1)-6 E F0 14.17(2\) Pick)97 511.2 R 2.5(ar)2.5 G
(andom number \()-2.5 E F1(x)A F0 2.5(\)f)C -.18(ro)-2.5 G 2.5(mau).18 G
(niform distribution over a range of:)-2.5 E F1 162(LL)176 535.2 S(L)-48
E 6(-------------------- to)128 547.2 R 6
(-------------------- + ----------)18 F 18
(T_maxBackoff*\(exp\(L\)-1\) T_maxBackoff*\(exp\(L\)-1\))122 559.2 R
(T_maxBackoff)12 E F0 14.17(3\) T)97 586.8 R
(ransform this random variate to generate the desir)-.9 E
(ed random backof)-.18 E 2.5(ft)-.18 G(ime \()-2.5 E F1(t')A F0 2.5(\)w)
C(ith)-2.5 E(the following equation:)122 598.8 Q F1
(t' = T_maxBackoff/L * ln\(x * \(exp\(L\) - 1\) * \(T_maxBackoff/L\)\))
130 622.8 Q F0(Adamson, et al.)72 768 Q(Expir)96.06 E(es: 17 Mar)-.18 E
(ch 2006)-.18 E([Page 1)125.26 E(1])-.55 E 0 Cg EP
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/F0 10/Palatino-Roman@0 SF 99.635(Internet-Draft NORM)72 66 R
(Building Blocks)2.5 E(October 2005)106.015 E(This)93.6 120 Q/F1 10
/Courier@0 SF(C)2.5 E F0
(language function can be used to generate an appr)2.5 E
(opriate random backof)-.18 E 2.5(ft)-.18 G(ime)-2.5 E(interval:)93.6
132 Q F1(double RandomBackoff\(double maxTime, double groupSize\))97 156
Q({)97 168 Q(double lambda = log\(groupSize\) + 1;)121 180 Q
(double x = UniformRand\(lambda/maxTime\) +)121 192 Q
(lambda / \(maxTime*\(exp\(lambda\)-1\)\);)187 204 Q
(return \(\(maxTime/lambda\) *)121 216 Q
(log\(x*\(exp\(lambda\)-1\)*\(maxTime/lambda\)\)\);)169 228 Q 12(}/)97
240 S 6(/e)-12 G(nd RandomBackoff\(\))-6 E F0(wher)93.6 255.6 Q(e)-.18 E
F1(UniformRand\(double max\))2.5 E F0 -.18(re)2.5 G
(turns random numbers with a uniform distribution).18 E(fr)93.6 267.6 Q
(om the range of)-.18 E F1(0..max)2.5 E F0 5(.F)C
(or example, based on the POSIX ")-5 E F1(rand\(\))A F0 2.5("f)C
(unction, the)-2.5 E(following C code can be used:)93.6 279.6 Q F1
(double UniformRand\(double max\))97 303.6 Q({)97 315.6 Q
(return \(max * \(\(double\)rand\(\)/\(double\)RAND_MAX\)\);)121 327.6 Q
(})97 339.6 Q F0(The number of expected NACK messages generated \()93.6
355.2 Q F1(N)A F0 2.5(\)w)C(ithin the first r)-2.5 E
(ound trip time for a)-.18 E(single feedback event is appr)93.6 367.2 Q
(oximately:)-.18 E F1 6(N=e)178.8 391.2 S
(xp\(1.2 * L / \(2*T_maxBackoff/GRTT\)\))-6 E F0
(Thus the maximum backof)93.6 415.2 Q 2.5(ft)-.18 G
(ime can be adjusted to tradeof)-2.5 E 2.5(fw)-.18 G
(orst-case NACK feedback)-2.5 E(volume versus latency)93.6 427.2 Q 5(.T)
-1.11 G(his is derived fr)-5 E(om [6] and assumes)-.18 E F1
(T_maxBackoff >= GRTT)5 E F0(,)A(and)93.6 439.2 Q F1(L)2.5 E F0
(is the mean of the distribution optimized for the given gr)2.5 E
(oup size as shown in the)-.18 E(algorithm above.)93.6 451.2 Q
(Note that other mechanisms within the pr)5 E(otocol may work to r)-.18
E(educe)-.18 E -.18(re)93.6 463.2 S(dundant NACK generation further).18
E 5(.I)-.74 G 2.5(ti)-5 G 2.5(ss)-2.5 G(uggested that)-2.5 E F1
(T_maxBackoff)2.5 E F0(be selected as an)2.5 E
(integer multiple of the sender)93.6 475.2 Q('s curr).74 E
(ent advertised)-.18 E F1(GRTT)2.5 E F0(estimate such that:)2.5 E F1
(T_maxBackoff = K * GRTT)192.545 499.2 Q F0(;wher)6 E(e)-.18 E F1 6(K>)
2.5 G 6(=1)-6 G F0(For general Internet operation, a default value of)
93.6 523.2 Q F1(K=4)2.5 E F0(is RECOMMENDED for operation)2.5 E
(with multicast \(to the gr)93.6 535.2 Q(oup at lar)-.18 E
(ge\) NACK delivery and a value of)-.18 E F1(K=6)2.5 E F0
(for unicast NACK)2.5 E(delivery)93.6 547.2 Q 5(.A)-1.11 G
(lternate values may be used to for buf)-5 E(fer utilization, r)-.18 E
(eliable delivery latency and)-.18 E(gr)93.6 559.2 Q
(oup size scalability tradeof)-.18 E(fs.)-.18 E(Given that \()93.6 583.2
Q F1(K*GRTT)A F0 2.5(\)i)C 2.5(st)-2.5 G(he maximum backof)-2.5 E 2.5
(ft)-.18 G(ime used by the r)-2.5 E(eceivers to initiate NACK)-.18 E
(transmission, other timeout periods r)93.6 595.2 Q
(elated to the NACK r)-.18 E(epair pr)-.18 E(ocess can be scaled)-.18 E
(accor)93.6 607.2 Q(dingly)-.18 E 5(.O)-1.11 G
(ne of those timeouts is the amount of time a r)-5 E
(eceiver should wait after)-.18 E(generating a NACK message befor)93.6
619.2 Q 2.5(ea)-.18 G(llowing itself to initiate another NACK)-2.5 E
(backof)93.6 631.2 Q(f/transmission cycle \()-.18 E F1(T_rcvrHoldoff)A
F0 2.5(\). This)B(delay should be suf)2.5 E(ficient for the)-.18 E
(sender to r)93.6 643.2 Q(espond to the r)-.18 E(eceived NACK with r)
-.18 E(epair messages.)-.18 E(An appr)5 E(opriate value)-.18 E
(depends upon the amount of time for the NACK to r)93.6 655.2 Q
(each the sender and the sender to)-.18 E(pr)93.6 667.2 Q(ovide a r)-.18
E(epair r)-.18 E 2.5(esponse. This)-.18 F
(MUST include any amount of sender NACK aggr)2.5 E(egation)-.18 E
(period during which possible multiple NACKs ar)93.6 679.2 Q 2.5(ea)-.18
G(ccumulated to determine an ef)-2.5 E(ficient)-.18 E -.18(re)93.6 691.2
S(pair r).18 E 2.5(esponse. These)-.18 F(timeouts ar)2.5 E 2.5(ef)-.18 G
(urther discussed in the section below on "Sender)-2.5 E(NACK Pr)93.6
703.2 Q(ocessing and Repair Response".)-.18 E(Adamson, et al.)72 768 Q
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/F0 10/Palatino-Roman@0 SF 99.635(Internet-Draft NORM)72 66 R
(Building Blocks)2.5 E(October 2005)106.015 E(Ther)93.6 120 Q 2.5(ea)
-.18 G .36 -.18(re a)-2.5 H(lso secondary measur).18 E
(es that can be applied to impr)-.18 E(ove the performance of)-.18 E
(feedback suppr)93.6 132 Q 2.5(ession. For)-.18 F(example, the sender)
2.5 E('s data content transmissions can follow an).74 E(or)93.6 144 Q
(dinal sequence of transmission.)-.18 E(When r)5 E
(epairs for data content occur)-.18 E 2.5(,t)-.74 G(he r)-2.5 E
(eceiver can note)-.18 E(that the sender has "r)93.6 156 Q
(ewound" its data content transmission position by observing the data)
-.18 E(object, FEC block number)93.6 168 Q 2.5(,a)-.74 G
(nd FEC symbol identifiers. Receivers SHOULD limit)-2.5 E
(transmission of NACKs to only when the sender)93.6 180 Q('s curr).74 E
(ent transmission position exceeds the)-.18 E(point to which the r)93.6
192 Q(eceiver has incomplete r)-.18 E(eception. This r)-.18 E(educes pr)
-.18 E(ematur)-.18 E 2.5(er)-.18 G(equests for)-2.68 E -.18(re)93.6 204
S(pair of data the sender may be planning to pr).18 E(ovide in r)-.18 E
(esponse to other r)-.18 E(eceiver r)-.18 E(equests.)-.18 E
(This mechanism can be very ef)93.6 216 Q(fective for pr)-.18 E
(otocol conver)-.18 E(gence in high loss conditions when)-.18 E
(transmissions of NACKs fr)93.6 228 Q(om other r)-.18 E
(eceivers \(or indicators fr)-.18 E(om the sender\) ar)-.18 E 2.5(el)
-.18 G(ost.)-2.5 E(Another mechanism \(particularly applicable when FEC\
 is used\) is for the sender to embed)93.6 240 Q
(an indication of impending r)93.6 252 Q(epair transmissions in curr)
-.18 E(ent packets sent.)-.18 E(For example, the)5 E(indication may be \
as simple as an advertisement of the number of FEC packets to be sent f\
or)93.6 264 Q(the curr)93.6 276 Q(ent applicable coding block.)-.18 E
(Finally)93.6 300 Q 2.5(,s)-1.11 G
(ome consideration might be given to using the NACKing history of r)-2.5
E(eceivers to)-.18 E(weight their selection of NACK backof)93.6 312 Q
2.5(ft)-.18 G(imeout intervals.)-2.5 E(For example, if a r)5 E
(eceiver has)-.18 E(historically been)93.6 324 Q(experiencing the gr)5 E
(eatest degr)-.18 E(ee of loss, it may pr)-.18 E(omote itself to)-.18 E
(statistically NACK sooner than other r)93.6 336 Q 2.5(eceivers. Note)
-.18 F(this r)2.5 E(equir)-.18 E(es ther)-.18 E 2.5(ei)-.18 G 2.5(sc)
-2.5 G(orr)-2.5 E(elation over)-.18 E
(successive intervals of time in the loss experienced by a r)93.6 348 Q
(eceiver)-.18 E 5(.S)-.74 G(uch corr)-5 E(elation MA)-.18 E 2.5(Yn)-1.11
G(ot)-2.5 E(always be pr)93.6 360 Q(esent in multicast networks.)-.18 E
(This adjustment of backof)5 E 2.5(ft)-.18 G(imeout selection may)-2.5 E
-.18(re)93.6 372 S(quir).18 E 2.5(et)-.18 G(he cr)-2.5 E
(eation of an "early NACK" slot for these historical NACKers.)-.18 E
(This additional)5 E(slot in the NACK backof)93.6 384 Q 2.5(fw)-.18 G
(indow will r)-2.5 E(esult in a longer r)-.18 E(epair cycle pr)-.18 E
(ocess that may not be)-.18 E(desirable for some applications.)93.6 396
Q(The r)5 E(esolution of these trade-of)-.18 E(fs may be dependent upon)
-.18 E(the pr)93.6 408 Q(otocol's tar)-.18 E
(get application set or network.)-.18 E(After the random backof)93.6 432
Q 2.5(ft)-.18 G(imeout has expir)-2.5 E(ed, the r)-.18 E
(eceiver will make a decision on whether)-.18 E(to generate a NACK r)
93.6 444 Q(epair r)-.18 E(equest or not \(i.e., it has been suppr)-.18 E
2.5(essed\). The)-.18 F(NACK will be)2.5 E(suppr)93.6 456 Q
(essed when any of the following conditions has occurr)-.18 E(ed:)-.18 E
14.17(1\) The)97 483.6 R(accumulated state of NACKs hear)2.5 E 2.5(df)
-.18 G -.18(ro)-2.5 G 2.5(mo).18 G(ther r)-2.5 E(eceivers \(or forwar)
-.18 E(ding of this)-.18 E
(state by the sender\) is equal to or supersedes the r)122 495.6 Q
(epair needs of the local r)-.18 E(eceiver)-.18 E(.)-.74 E
(Note that the local r)122 507.6 Q(eceiver should consider its r)-.18 E
(epair needs only up to the sender)-.18 E(transmission position r)122
519.6 Q(ecor)-.18 E(ded at the NACK cycle initiation \(when the backof)
-.18 E 2.5(ft)-.18 G(imer)-2.5 E(was activated\).)122 531.6 Q 14.17
(2\) The)97 559.2 R -1.76(sender 's)2.5 F
(data content transmission position "r)2.5 E(ewinds" to a point or)-.18
E(dinally less)-.18 E
(than that of the lowest sequence position of the local r)122 571.2 Q
-1.76(eceiver 's)-.18 F -.18(re)2.5 G(pair needs. \(This).18 E
(detection of sender "r)122 583.2 Q(ewind" indicates the sender has alr)
-.18 E(eady r)-.18 E(esponded to other)-.18 E -.18(re)122 595.2 S
(ceiver r).18 E(epair needs of which the local r)-.18 E
(eceiver may not have been awar)-.18 E 2.5(e\). This)-.18 F("r)122 607.2
Q(ewind" event can occur any time between 1\) when the NACK cycle was i\
nitiated)-.18 E(with the backof)122 619.2 Q 2.5(ft)-.18 G
(imeout activation and 2\) the curr)-2.5 E(ent moment when the backof)
-.18 E(f)-.18 E(timeout has expir)122 631.2 Q(ed to suppr)-.18 E
(ess the NACK.)-.18 E(Another NACK cycle must be initiated)5 E(by the r)
122 643.2 Q(eceiver when the sender)-.18 E
('s transmission sequence position exceeds the).74 E -.18(re)122 655.2 S
-1.76(ceiver 's).18 F(lowest or)2.5 E(dinal r)-.18 E(epair point.)-.18 E
(Note it is possible that the local r)5 E(eceiver may)-.18 E
(have had its r)122 667.2 Q(epair needs satisfied as a r)-.18 E
(esult of the sender)-.18 E('s r).74 E(esponse to the r)-.18 E(epair)
-.18 E(needs of other r)122 679.2 Q
(eceivers and no further NACKing is r)-.18 E(equir)-.18 E(ed.)-.18 E
(If these conditions have not occurr)93.6 706.8 Q(ed and the r)-.18 E
(eceiver still has pending r)-.18 E(epair needs, a)-.18 E
(NACK message is generated and transmitted.)93.6 718.8 Q
(The NACK should consist of an accumulation)5 E(Adamson, et al.)72 768 Q
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/F0 10/Palatino-Roman@0 SF 99.635(Internet-Draft NORM)72 66 R
(Building Blocks)2.5 E(October 2005)106.015 E(of r)93.6 120 Q
(epair needs fr)-.18 E(om the r)-.18 E -1.76(eceiver 's)-.18 F
(lowest or)2.5 E(dinal r)-.18 E(epair point up to the curr)-.18 E
(ent sender)-.18 E(transmission sequence position.)93.6 132 Q 2.5(As)5 G
(ingle NACK message should be generated and the)-2.5 E
(NACK message content should be tr)93.6 144 Q
(uncated if it exceeds the payload size of single pr)-.08 E(otocol)-.18
E 2.5(message. When)93.6 156 R(such NACK payload limits occur)2.5 E 2.5
(,t)-.74 G(he NACK content SHOULD contain)-2.5 E -.18(re)93.6 168 S
(quests for the or).18 E(dinally lowest r)-.18 E
(epair content needed fr)-.18 E(om the sender)-.18 E(.)-.74 E/F1 10
/Palatino-BoldItalic@0 SF(NACK Suppr)72 204 Q
(ession Interface Description)-.18 E/F2 10/Palatino-Italic@0 SF(Inputs:)
93.6 219.6 Q F0 14.17(1\) NACK)97 235.2 R(pr)2.5 E
(ocess initiation decision.)-.18 E 14.17(2\) Recor)97 247.2 R
(ded sender transmission sequence position.)-.18 E 14.17(3\) Sender)97
259.2 R(GR)2.5 E(TT)-.37 E(.)-.74 E 14.17(4\) Sender)97 271.2 R(gr)2.5 E
(oup size estimate.)-.18 E 14.17(5\) Application-defined)97 283.2 R
(bound on backof)2.5 E 2.5(ft)-.18 G(imeout period.)-2.5 E 14.17
(6\) NACKs)97 295.2 R(fr)2.5 E(om other r)-.18 E(eceivers.)-.18 E 14.17
(7\) Pending)97 307.2 R -.18(re)2.5 G(pair indication fr).18 E
(om sender \(may be forwar)-.18 E(ded NACKs\).)-.18 E 14.17(8\) Curr)97
319.2 R(ent sender transmission sequence position.)-.18 E F2(Outputs:)
93.6 334.8 Q F0 14.17(1\) Y)97 350.4 R
(es/no decision to generate NACK message upon backof)-.92 E 2.5(ft)-.18
G(imer expiration.)-2.5 E/F3 10/Palatino-Bold@0 SF 2.5(3.2.3. NACK)72
374.4 R(Content)2.5 E F0(The content of NACK messages generated by r)
93.6 390 Q(eliable multicast r)-.18 E(eceivers will include)-.18 E
(information detailing their curr)93.6 402 Q(ent r)-.18 E(epair needs.)
-.18 E(The specific information depends on the)5 E
(use and type of FEC in the NORM r)93.6 414 Q(epair pr)-.18 E 2.5
(ocess. The)-.18 F(identification of r)2.5 E(epair needs is)-.18 E(depe\
ndent upon the data content identification \(See Section 3.5 below\).)
93.6 426 Q(At the highest level)5 E
(the NACK content will identify the sender to which the NACK is addr)
93.6 438 Q(essed and the data)-.18 E(transport object \(or str)93.6 450
Q(eam\) within the sender)-.18 E('s transmission that needs r).74 E
(epair)-.18 E 5(.F)-.74 G(or the)-5 E(indicated transport entity)93.6
462 Q 2.5(,t)-1.11 G
(he NACK content will then identify the specific FEC coding)-2.5 E
(blocks and/or symbols it r)93.6 474 Q(equir)-.18 E(es to r)-.18 E
(econstr)-.18 E(uct the complete transmitted data.)-.08 E(This content)5
E(may consist of FEC block erasur)93.6 486 Q 2.5(ec)-.18 G
(ounts and/or explicit indication of missing blocks or)-2.5 E
(symbols \(segments\) of data and FEC content.)93.6 498 Q
(It should also be noted that NORM can be)5 E(ef)93.6 510 Q
(fectively instantiated without a r)-.18 E(equir)-.18 E(ement for r)-.18
E(eliable NACK delivery using the)-.18 E(techniques discussed her)93.6
522 Q(e.)-.18 E F3 2.5(3.2.3.1. NACK)72 546 R(and FEC Repair Strategies)
2.5 E F0(Wher)93.6 561.6 Q 2.5(eF)-.18 G(EC-based r)-2.5 E(epair is use\
d, the NACK message content will minimally need to identify)-.18 E
(the coding block\(s\) for which r)93.6 573.6 Q
(epair is needed and a count of erasur)-.18 E
(es \(missing packets\) for)-.18 E(the coding block.)93.6 585.6 Q
(An exact count of erasur)5 E
(es implies the FEC algorithm is capable of)-.18 E -.18(re)93.6 597.6 S
(pairing _any_ loss combination within the coding block.).18 E
(This count may need to be)5 E(adjusted for some FEC algorithms.)93.6
609.6 Q(Considering that multiple r)5 E(epair r)-.18 E(ounds may be)-.18
E -.18(re)93.6 621.6 S(quir).18 E(ed to successfully complete r)-.18 E
(epair)-.18 E 2.5(,a)-.74 G 2.5(ne)-2.5 G(rasur)-2.5 E 2.5(ec)-.18 G
(ount also implies that the quantity of)-2.5 E(unique FEC parity packet\
s the server has available to transmit is essentially unlimited \(i.e.,)
93.6 633.6 Q(the server will always be able to pr)93.6 645.6 Q
(ovide new)-.18 E 2.5(,u)-.92 G(nique, pr)-2.5 E
(eviously unsent parity packets in)-.18 E -.18(re)93.6 657.6 S
(sponse to any subsequent r).18 E(epair r)-.18 E
(equests for the same coding block\).)-.18 E(Alternatively)5 E 2.5(,t)
-1.11 G(he)-2.5 E(sender may "r)93.6 669.6 Q(ound-r)-.18 E
(obin" transmit thr)-.18 E
(ough its available set of FEC symbols for a given)-.18 E
(coding block, and eventually af)93.6 681.6 Q(fect r)-.18 E(epair)-.18 E
5(.F)-.74 G(or a most ef)-5 E(ficient r)-.18 E(epair strategy)-.18 E 2.5
(,t)-1.11 G(he NACK)-2.5 E(content will need to also _explicitly_ ident\
ify which symbols \(information and/or parity\) the)93.6 693.6 Q -.18
(re)93.6 705.6 S(ceiver r).18 E(equir)-.18 E(es to successfully r)-.18 E
(econstr)-.18 E(uct the content of the coding block.)-.08 E
(This will be)5 E(particularly tr)93.6 717.6 Q(ue of small to medium si\
ze block FEC codes \(e.g., Reed Solomon\) that ar)-.08 E(e)-.18 E
(Adamson, et al.)72 768 Q(Expir)96.06 E(es: 17 Mar)-.18 E(ch 2006)-.18 E
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/F0 10/Palatino-Roman@0 SF 99.635(Internet-Draft NORM)72 66 R
(Building Blocks)2.5 E(October 2005)106.015 E(capable of pr)93.6 120 Q
(ovided a limited number of parity symbols per FEC coding block.)-.18 E
(When FEC is not used as part of the r)93.6 144 Q(epair pr)-.18 E
(ocess, or the pr)-.18 E(otocol instantiation is r)-.18 E(equir)-.18 E
(ed)-.18 E(to pr)93.6 156 Q(ovide r)-.18 E(eliability even when the sen\
der has transmitted all available parity for a given)-.18 E
(coding block \(or the sender)93.6 168 Q('s ability to buf).74 E
(fer transmission history is exceeded by the)-.18 E/F1 10/Courier@0 SF
(delay*bandwidth*loss)93.6 180 Q F0
(characteristics of the network topology\), the NACK content will)2.5 E
(need to contain _explicit_)93.6 192 Q
(coding block and/or segment loss information so that the sender)5 E
(can pr)93.6 204 Q(ovide appr)-.18 E(opriate r)-.18 E
(epair packets and/or data r)-.18 E 2.5(etransmissions. Explicit)-.18 F
(loss)2.5 E
(information in NACK content may also potentially serve other purposes.)
93.6 216 Q(For example, it)5 E(may be useful for decorr)93.6 228 Q
(elating loss characteristics among a gr)-.18 E(oup of r)-.18 E
(eceivers to help)-.18 E(dif)93.6 240 Q(fer)-.18 E
(entiate candidate congestion contr)-.18 E(ol bottlenecks among the r)
-.18 E(eceiver set.)-.18 E
(When FEC is used and NACK content is designed to contain explicit r)
93.6 264 Q(epair r)-.18 E(equests, ther)-.18 E 2.5(ei)-.18 G(s)-2.5 E
2.5(as)93.6 276 S(trategy wher)-2.5 E 2.5(et)-.18 G(he r)-2.5 E
(eceivers can NACK for specific content that will help facilitate NACK)
-.18 E(suppr)93.6 288 Q(ession and r)-.18 E(epair ef)-.18 E(ficiency)
-.18 E 5(.T)-1.11 G(he assumptions for this strategy ar)-5 E 2.5(et)-.18
G(hat sender may)-2.5 E(potentially exhaust its supply of new)93.6 300 Q
2.5(,u)-.92 G(nique parity packets available for a given coding)-2.5 E
(block and be r)93.6 312 Q(equir)-.18 E(ed to explicitly r)-.18 E
(etransmit some data or parity symbols to complete)-.18 E -.18(re)93.6
324 S(liable transfer).18 E 5(.A)-.74 G
(nother assumption is that an FEC algorithm wher)-5 E 2.5(ea)-.18 G
(ny parity packet can)-2.5 E(fill any erasur)93.6 336 Q 2.5(ew)-.18 G
(ithin the coding block \(e.g., Reed Solomon\) is used.)-2.5 E
(The goal of this)5 E
(strategy is to make maximum use of the available parity and pr)93.6 348
Q(ovide the minimal amount of)-.18 E(data and r)93.6 360 Q
(epair transmissions during r)-.18 E
(eliable transfer of data content to the gr)-.18 E(oup.)-.18 E
(When systematic FEC codes ar)93.6 384 Q 2.5(eu)-.18 G
(sed, the sender transmits the data content of the coding)-2.5 E(block \
\(and optionally some quantity of parity packets\) in its initial trans\
mission.)93.6 396 Q(Note that a)5 E
(systematic FEC coding block is consider)93.6 408 Q
(ed to be logically made up of the contiguous set of)-.18 E(sour)93.6
420 Q
(ce data vectors plus parity vectors for the given FEC algorithm used.)
-.18 E(For example, a)5 E(systematic coding scheme that pr)93.6 432 Q
(ovides for 64 data symbols and 32 parity symbols per)-.18 E(coding blo\
ck would contain FEC symbol identifiers in the range of 0 to 95.)93.6
444 Q(Receivers then can constr)93.6 468 Q(uct NACK messages r)-.08 E
(equesting suf)-.18 E(ficient content to satisfy their)-.18 E -.18(re)
93.6 480 S(pair needs.).18 E(For example, if the r)5 E(eceiver has thr)
-.18 E(ee erasur)-.18 E(es in a given r)-.18 E(eceived coding)-.18 E
(block, it will r)93.6 492 Q(equest transmission of the thr)-.18 E
(ee lowest or)-.18 E(dinal parity vectors in the coding)-.18 E
(block. In our example coding scheme fr)93.6 504 Q(om the pr)-.18 E
(evious paragraph, the r)-.18 E(eceiver would)-.18 E(explicitly r)93.6
516 Q(equest parity symbols 64 to 66 to fill its thr)-.18 E(ee erasur)
-.18 E(es for the coding block.)-.18 E(Note)5 E(that if the r)93.6 528 Q
-1.76(eceiver 's)-.18 F(loss for the coding block exceeds the available\
 parity quantity \(i.e.,)2.5 E(gr)93.6 540 Q
(eater than 32 missing symbols in our example\), the r)-.18 E
(eceiver will be r)-.18 E(equir)-.18 E(ed to constr)-.18 E(uct a)-.08 E
(NACK r)93.6 552 Q(equesting all \(32\) of the available parity symbols\
 plus some additional portions of its)-.18 E(missing data symbols in or)
93.6 564 Q(der to r)-.18 E(econstr)-.18 E(uct the block.)-.08 E
(If this is done consistently acr)5 E(oss the)-.18 E -.18(re)93.6 576 S
(ceiver gr).18 E(oup, the r)-.18 E
(esulting NACKs will comprise a minimal set of sender transmissions to)
-.18 E(satisfy their r)93.6 588 Q(epair needs.)-.18 E(In summary)93.6
612 Q 2.5(,t)-1.11 G(he r)-2.5 E(ule is to r)-.08 E(equest the lower or)
-.18 E(dinal portion of the parity content for the FEC)-.18 E
(coding block to satisfy the erasur)93.6 624 Q 2.5(er)-.18 G
(epair needs on the first NACK cycle.)-2.68 E(If the available)5 E
(number of parity symbols is insuf)93.6 636 Q(ficient, the r)-.18 E
(eceiver will also r)-.18 E(equest the subset of or)-.18 E(dinally)-.18
E(highest missing data symbols to cover what the parity symbols will no\
t fill.)93.6 648 Q(Note this)5 E(strategy assumes FEC codes such as Ree\
d-Solomon for which a single parity symbol can)93.6 660 Q -.18(re)93.6
672 S(pair any erased symbol.).18 E
(This strategy would need minor modification to take into account)5 E
(the possibly limited r)93.6 684 Q(epair capability of other FEC types.)
-.18 E(On subsequent NACK r)5 E(epair)-.18 E(cycles wher)93.6 696 Q 2.5
(et)-.18 G(he r)-2.5 E(eceiver may have r)-.18 E
(eceived some portion of its pr)-.18 E(eviously r)-.18 E(equested r)-.18
E(epair)-.18 E(content, the r)93.6 708 Q
(eceiver will use the same strategy)-.18 E 2.5(,b)-1.11 G
(ut only NACK for the set of parity and/or)-2.5 E
(data symbols it has not yet r)93.6 720 Q 2.5(eceived. Optionally)-.18 F
2.5(,t)-1.11 G(he r)-2.5 E(eceivers could also pr)-.18 E
(ovide a count of)-.18 E(Adamson, et al.)72 768 Q(Expir)96.06 E
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/F0 10/Palatino-Roman@0 SF 99.635(Internet-Draft NORM)72 66 R
(Building Blocks)2.5 E(October 2005)106.015 E(erasur)93.6 120 Q(es as a\
 convenience to the sender or intermediate systems assisting NACK opera\
tion.)-.18 E(Other types of FEC schemes may r)93.6 144 Q(equir)-.18 E
2.5(ea)-.18 G(lteration to the NACK and r)-2.5 E(epair strategy)-.18 E
(described her)93.6 156 Q 2.5(e. For)-.18 F(example, some of the lar)2.5
E(ge block or expandable FEC codes described in)-.18 E 2.5([14] may)93.6
168 R(be less deterministic with r)2.5 E(espect to defining optimal r)
-.18 E(epair r)-.18 E(equests by r)-.18 E(eceivers)-.18 E(or r)93.6 180
Q(epair transmission strategies by senders.)-.18 E
(For these types of codes, it may be suf)5 E(ficient for)-.18 E -.18(re)
93.6 192 S(ceivers to NACK with an estimate of the quantity of addition\
al FEC symbols r).18 E(equir)-.18 E(ed to)-.18 E(complete r)93.6 204 Q
(eliable r)-.18 E(eception and for the sender to r)-.18 E(espond accor)
-.18 E(dingly)-.18 E 5(.T)-1.11 G(his appar)-5 E(ent)-.18 E
(disadvantage as compar)93.6 216 Q
(ed to codes such as Reed Solomon may be of)-.18 E(fset by r)-.18 E
(educed)-.18 E(computational r)93.6 228 Q(equir)-.18 E
(ements and/or ability to support lar)-.18 E(ge coding blocks for incr)
-.18 E(eased)-.18 E -.18(re)93.6 240 S(pair ef).18 E
(ficiency that these codes can of)-.18 E(fer)-.18 E(.)-.74 E(After r)
93.6 264 Q(eceipt and accumulation of NACK messages during the aggr)-.18
E(egation period, the)-.18 E(sender can begin transmission of fr)93.6
276 Q(esh \(pr)-.18 E(eviously untransmitted\) parity symbols for the)
-.18 E(coding block based on the highest r)93.6 288 Q(eceiver erasur)
-.18 E 2.5(ec)-.18 G(ount _if_ it has a suf)-2.5 E(ficient quantity of)
-.18 E(parity symbols that wer)93.6 300 Q 2.5(e_)-.18 G(not_ pr)-2.5 E
(eviously transmitted.)-.18 E(Otherwise, the sender MUST r)5 E(esort)
-.18 E(to transmitting the explicit set of r)93.6 312 Q(epair vectors r)
-.18 E 2.5(equested. W)-.18 F(ith this appr)-.55 E(oach, the sender)-.18
E(needs to maintain very little state on r)93.6 324 Q(equests it has r)
-.18 E(eceived fr)-.18 E(om the gr)-.18 E(oup without need)-.18 E
(for synchr)93.6 336 Q(onization of r)-.18 E(epair r)-.18 E(equests fr)
-.18 E(om the gr)-.18 E 2.5(oup. Since)-.18 F(all r)2.5 E
(eceivers use the same)-.18 E(consistent algorithm to expr)93.6 348 Q
(ess their explicit r)-.18 E(epair needs, NACK suppr)-.18 E
(ession among)-.18 E -.18(re)93.6 360 S
(ceivers is simplified over the course of multiple r).18 E
(epair cycles.)-.18 E(The r)5 E(eceivers can simply)-.18 E(compar)93.6
372 Q 2.5(eN)-.18 G(ACKs hear)-2.5 E 2.5(df)-.18 G -.18(ro)-2.5 G 2.5
(mo).18 G(ther r)-2.5 E(eceivers against their own calculated r)-.18 E
(epair needs to)-.18 E(determine whether they should transmit or suppr)
93.6 384 Q(ess their pending NACK messages.)-.18 E/F1 10/Palatino-Bold@0
SF 2.5(3.2.3.2. NACK)72 408 R(Content Format)2.5 E F0
(The format of NACK content will depend on the pr)93.6 423.6 Q
(otocol's data service model and the)-.18 E
(format of data content identification the pr)93.6 435.6 Q(otocol uses.)
-.18 E(This NACK format also depends)5 E
(upon the type of FEC encoding \(if any\) used.)93.6 447.6 Q(Figur)5 E
2.5(e2i)-.18 G(llustrates a logical, hierar)-2.5 E(chical)-.18 E(transm\
ission content identification scheme, denoting that the notion of objec\
ts \(or str)93.6 459.6 Q(eams\))-.18 E
(and/or FEC blocking is optional at the pr)93.6 471.6 Q
(otocol instantiation's discr)-.18 E 2.5(etion. Note)-.18 F(that the)2.5
E(identification of objects is with r)93.6 483.6 Q
(espect to a given sender)-.18 E 5(.I)-.74 G 2.5(ti)-5 G 2.5(sr)-2.5 G
(ecommended that transport)-2.68 E(data content identification is done \
within the context of a sender in a given session. Since the)93.6 495.6
Q(notion of session "str)93.6 507.6 Q
(eams" and "blocks" is optional, the framework degenerates to that of)
-.18 E(typical transport data segmentation and r)93.6 519.6 Q
(eassembly in its simplest form.)-.18 E/F2 10/Courier@0 SF(Session_)93.6
543.6 Q(\\_)141.6 555.6 Q(Sender_)159.6 567.6 Q(\\_)201.6 579.6 Q
([Object/Stream\(s\)]_)219.6 591.6 Q(\\_)333.6 603.6 Q([FEC Blocks]_)
351.6 615.6 Q(\\_)429.6 627.6 Q(Symbols)447.6 639.6 Q/F3 10
/Palatino-Italic@0 SF(Fig. 2: NORM Data Content Identification Hierar)
190.095 663.6 Q(chy)-.18 E F0
(The format of NACK messages should meet the following goals:)93.6 687.6
Q(Adamson, et al.)72 768 Q(Expir)96.06 E(es: 17 Mar)-.18 E(ch 2006)-.18
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/F0 10/Palatino-Roman@0 SF 99.635(Internet-Draft NORM)72 66 R
(Building Blocks)2.5 E(October 2005)106.015 E 14.17(1\) Able)72 120 R
(to identify transport data unit transmissions r)2.5 E(equir)-.18 E
(ed to r)-.18 E(epair a portion of the)-.18 E -.18(re)97 132 S
(ceived content, whether it is an entir).18 E 2.5(em)-.18 G
(issing object/str)-2.5 E(eam \(or range\), entir)-.18 E 2.5(eF)-.18 G
(EC coding)-2.5 E(block\(s\), or sets of symbols,)97 144 Q 14.17(2\) Be)
72 159.6 R(simple to pr)2.5 E(ocess for NACK aggr)-.18 E
(egation and suppr)-.18 E(ession,)-.18 E 14.17(3\) Be)72 175.2 R(capabl\
e of including NACKs for multiple objects, FEC coding blocks and/or sym\
bols in)2.5 E 2.5(as)97 187.2 S(ingle message, and)-2.5 E 14.17
(4\) Have)72 202.8 R 2.5(ar)2.5 G(easonably compact format.)-2.68 E
(If the NORM transport object/str)93.6 218.4 Q
(eam is identified with an)-.18 E/F1 10/Palatino-Italic@0 SF(<objectId>)
2.5 E F0(and the FEC symbol)2.5 E
(being transmitted is identified with an)93.6 230.4 Q F1(<fecPayloadId>)
2.5 E F0 2.5(,t)C(he concatenation of)-2.5 E F1
(<objectId::fecPayloadId>)93.6 242.4 Q F0
(comprises a basic transport pr)2.5 E
(otocol data unit \(TPDU\) identifier for)-.18 E(symbols fr)93.6 254.4 Q
(om a given sour)-.18 E 2.5(ce. NACK)-.18 F
(content can be composed of lists and/or ranges of)2.5 E
(these TPDU identifiers to build up NACK messages to describe the r)93.6
266.4 Q(eceivers r)-.18 E(epair needs.)-.18 E(If)5 E(no hierar)93.6
278.4 Q(chical object delineation or FEC blocking is used, the TPDU is \
a simple linear)-.18 E -.18(re)93.6 290.4 S(pr).18 E
(esentation of the data symbols transmitted by the sender)-.18 E 5(.W)
-.74 G(hen the TPDU r)-5 E(epr)-.18 E(esents a)-.18 E(hierar)93.6 302.4
Q(chy for purposes of object/str)-.18 E
(eam delineation and/or FEC blocking, the NACK)-.18 E
(content unit may r)93.6 314.4 Q(equir)-.18 E 2.5(ef)-.18 G
(lags to indicate which portion of the TPDU is applicable.)-2.5 E(For)5
E(example, if an entir)93.6 326.4 Q 2.5(e")-.18 G
(object" \(or range of objects\) is missing in the r)-2.5 E
(eceived data, the r)-.18 E(eceiver)-.18 E
(will not necessarily know the appr)93.6 338.4 Q(opriate range of)-.18 E
F1(<sour)2.5 E(ceBlockNumbers>)-.18 E F0(or)2.5 E F1
(<encodingSymbolIds>)93.6 350.4 Q F0(for which to r)2.5 E(equest r)-.18
E(epair and thus r)-.18 E(equir)-.18 E(es some mechanism to)-.18 E -.18
(re)93.6 362.4 S(quest r).18 E(epair \(or r)-.18 E
(etransmission\) of the entir)-.18 E 2.5(eu)-.18 G(nit r)-2.5 E(epr)-.18
E(esented by an)-.18 E F1(<objectId>)2.5 E F0 5(.T)C(he same)-5 E(is tr)
93.6 374.4 Q(ue if entir)-.08 E 2.5(eF)-.18 G(EC coding blocks r)-2.5 E
(epr)-.18 E(esented by one or a range of)-.18 E F1(<sour)2.5 E
(ceBlockNumbers>)-.18 E F0(have been lost.)93.6 386.4 Q/F2 10
/Palatino-BoldItalic@0 SF(NACK Content Interface Description)72 422.4 Q
F1(Inputs:)93.6 438 Q F0 14.17(1\) Sender)97 453.6 R(identification.)2.5
E 14.17(2\) Sender)97 465.6 R(data identification.)2.5 E 14.17
(3\) Sender)97 477.6 R(FEC Object T)2.5 E(ransmission Information.)-.9 E
14.17(4\) Recor)97 489.6 R(ded sender transmission sequence position.)
-.18 E 14.17(5\) Curr)97 501.6 R
(ent sender transmission sequence position.)-.18 E(History of r)5 E
(epair needs for this)-.18 E(sender)122 513.6 Q(.)-.74 E F1(Outputs:)
93.6 529.2 Q F0 14.17(1\) NACK)97 544.8 R(message with r)2.5 E(epair r)
-.18 E(equests.)-.18 E/F3 10/Palatino-Bold@0 SF 2.5(3.2.4. Sender)72
568.8 R(Repair Response)2.5 E F0(Upon r)93.6 584.4 Q(eception of a r)
-.18 E(epair r)-.18 E(equest fr)-.18 E(om a r)-.18 E(eceiver in the gr)
-.18 E(oup, the sender will initiate a)-.18 E -.18(re)93.6 596.4 S
(pair r).18 E(esponse pr)-.18 E(ocedur)-.18 E 2.5(e. The)-.18 F
(sender may wish to delay transmission of r)2.5 E(epair content)-.18 E
(until it has had)93.6 608.4 Q(suf)5 E
(ficient time to accumulate potentially multiple NACKs fr)-.18 E(om the)
-.18 E -.18(re)5 G(ceiver).18 E 2.5(set. This)93.6 620.4 R
(allows the sender to determine the most ef)2.5 E(ficient r)-.18 E
(epair strategy for a given)-.18 E(transport str)93.6 632.4 Q
(eam/object or FEC coding block.)-.18 E(Depending upon the appr)5 E
(oach used, some)-.18 E(pr)93.6 644.4 Q
(otocols may find it beneficial for the sender to pr)-.18 E
(ovide an indicator of pending r)-.18 E(epair)-.18 E
(transmissions as part of its curr)93.6 656.4 Q
(ent transmitted message content.)-.18 E(This can aid some NACK)5 E
(suppr)93.6 668.4 Q(ession mechanisms.)-.18 E
(The amount of time to perform this NACK aggr)5 E(egation should be)-.18
E(suf)93.6 680.4 Q(ficient to allow for the maximum r)-.18 E
(eceiver NACK backof)-.18 E 2.5(fw)-.18 G(indow \(")-2.5 E/F4 10
/Courier@0 SF(T_maxBackoff)A F0(")A(fr)93.6 692.4 Q
(om Section 3.2.2\) and pr)-.18 E(opagation of NACK messages fr)-.18 E
(om the r)-.18 E(eceivers to the sender)-.18 E(.)-.74 E
(Note the maximum transmission delay of a message fr)93.6 704.4 Q
(om a r)-.18 E(eceiver to the sender may be)-.18 E(appr)93.6 716.4 Q
(oximately)-.18 E F4(\(1*GRTT\))2.5 E F0
(in the case of very asymmetric network topology with r)2.5 E(espect to)
-.18 E(Adamson, et al.)72 768 Q(Expir)96.06 E(es: 17 Mar)-.18 E(ch 2006)
-.18 E([Page 17])124.71 E 0 Cg EP
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/F0 10/Palatino-Roman@0 SF 99.635(Internet-Draft NORM)72 66 R
(Building Blocks)2.5 E(October 2005)106.015 E(transmission delay)93.6
120 Q 5(.T)-1.11 G(hus, if the maximum r)-5 E(eceiver NACK backof)-.18 E
2.5(ft)-.18 G(ime is)-2.5 E/F1 10/Courier@0 SF(T_maxBackoff)2.5 E 6(=K)
93.6 132 S(*GRTT)-6 E F0 2.5(,t)C(he sender NACK aggr)-2.5 E
(egation period should be equal to at least:)-.18 E F1
(T_sndrAggregate = T_maxBackoff + 1*GRTT = \(K+1\)*GRTT)142.8 156 Q F0
(Immediately after the sender NACK aggr)93.6 180 Q
(egation period, the sender will begin transmitting)-.18 E -.18(re)93.6
192 S(pair content determined fr).18 E(om the aggr)-.18 E
(egate NACK state and continue with any new)-.18 E 2.5
(transmission. Also,)93.6 204 R
(at this time, the sender should observe a "holdof)2.5 E(f" period wher)
-.18 E 2.5(ei)-.18 G(t)-2.5 E(constrains itself fr)93.6 216 Q
(om initiating a new NACK aggr)-.18 E(egation period to allow pr)-.18 E
(opagation of the)-.18 E
(new transmission sequence position due to the r)93.6 228 Q(epair r)-.18
E(esponse to the r)-.18 E(eceiver gr)-.18 E 2.5(oup. T)-.18 F(o)-.92 E
(allow for worst case asymmetry)93.6 240 Q 2.5(,t)-1.11 G(his "holdof)
-2.5 E(f" time should be:)-.18 E F1(T_sndrHoldoff = 1*GRTT)232.8 264 Q
F0(Recall that the r)93.6 288 Q(eceivers will also employ a "holdof)-.18
E(f" timeout after generating a NACK)-.18 E
(message to allow time for the sender)93.6 300 Q('s r).74 E 2.5
(esponse. Given)-.18 F 2.5(as)2.5 G(ender)-2.5 E F1(<T_sndrAggregate>)
2.5 E F0(plus)93.6 312 Q F1(<T_sndrHoldoff>)2.5 E F0(time of)2.5 E F1
(\(K+1\)*GRTT)2.5 E F0 2.5(,t)C(he r)-2.5 E(eceivers should use holdof)
-.18 E 2.5(ft)-.18 G(imeouts of:)-2.5 E F1
(T_rcvrHoldoff = T_sndrAggregate + T_sndrHoldoff = \(K+2\)*GRTT)118.8
336 Q F0(This allows for a worst-case pr)93.6 360 Q
(opagation time of the r)-.18 E -1.76(eceiver 's)-.18 F
(NACK to the sender)2.5 E 2.5(,t)-.74 G(he)-2.5 E -1.76(sender 's)93.6
372 R(aggr)2.5 E(egation time and pr)-.18 E(opagation of the sender)-.18
E('s r).74 E(esponse back to the r)-.18 E(eceiver)-.18 E(.)-.74 E
(Additionally)93.6 384 Q 2.5(,i)-1.11 G 2.5(nt)-2.5 G
(he case of unicast feedback fr)-2.5 E(om the r)-.18 E
(eceiver set, it may be useful for the)-.18 E(sender to forwar)93.6 396
Q 2.5(d\()-.18 G(via multicast\) a r)-2.5 E(epr)-.18 E
(esentation of its aggr)-.18 E(egated NACK content to the)-.18 E(gr)93.6
408 Q(oup to allow for NACK suppr)-.18 E(ession when ther)-.18 E 2.5(ei)
-.18 G 2.5(sn)-2.5 G(ot multicast connectivity among the)-2.5 E -.18(re)
93.6 420 S(ceiver set.).18 E(At the expiration of the)93.6 444 Q F1
(<T_sndrAggregate>)2.5 E F0(timeout, the sender will begin transmitting)
2.5 E -.18(re)93.6 456 S(pair messages accor).18 E
(ding to the accumulated content of NACKs r)-.18 E 2.5(eceived. Ther)
-.18 F 2.5(ea)-.18 G .36 -.18(re s)-2.5 H(ome).18 E(guidelines with r)
93.6 468 Q(egar)-.18 E(ds to FEC-based r)-.18 E(epair and the or)-.18 E
(dering of the r)-.18 E(epair r)-.18 E(esponse fr)-.18 E(om the)-.18 E
(sender that can impr)93.6 480 Q(ove r)-.18 E(eliable multicast ef)-.18
E(ficiency:)-.18 E 14.17(1\) When)72 507.6 R
(FEC is used, it is beneficial that the sender transmit pr)2.5 E
(eviously untransmitted parity)-.18 E(content as r)97 519.6 Q
(epair messages whenever possible.)-.18 E 2.5(This maximizes)5 F(the r)
2.5 E(eceiving nodes' ability)-.18 E(to r)97 531.6 Q(econstr)-.18 E
(uct the entir)-.08 E 2.5(et)-.18 G(ransmitted content fr)-2.5 E
(om their individual subsets of r)-.18 E(eceived)-.18 E(messages.)97
543.6 Q 14.17(2\) The)72 571.2 R(transmitted object and/or str)2.5 E
(eam data and r)-.18 E(epair content should be indexed with)-.18 E
(monotonically incr)97 583.2 Q(easing sequence numbers \(within a r)-.18
E(easonably lar)-.18 E(ge or)-.18 E(dinal space\).)-.18 E(If)5 E
(the sender observes the discipline of)97 595.2 Q(transmitting r)5 E
(epair for the earliest content \(e.g.,)-.18 E(or)97 607.2 Q
(dinally lowest FEC blocks\) first, the r)-.18 E
(eceivers can use a strategy of withholding r)-.18 E(epair)-.18 E -.18
(re)97 619.2 S(quests for later content until the sender once again r)
.18 E(eturns to that point in the)-.18 E(object/str)97 631.2 Q
(eam transmission sequence.)-.18 E(This can incr)5 E
(ease overall message ef)-.18 E(ficiency among)-.18 E(the gr)97 643.2 Q
(oup and help work to keep r)-.18 E(epair cycles r)-.18 E
(elatively synchr)-.18 E(onized without dependence)-.18 E
(upon strict time synchr)97 655.2 Q(onization among the sender and r)
-.18 E 2.5(eceivers. This)-.18 F(also helps minimize)2.5 E(the buf)97
667.2 Q(fering r)-.18 E(equir)-.18 E(ements of r)-.18 E
(eceivers and senders and r)-.18 E(educes r)-.18 E
(edundant transmission of)-.18 E(data to the gr)97 679.2 Q(oup at lar)
-.18 E(ge.)-.18 E(Adamson, et al.)72 768 Q(Expir)96.06 E(es: 17 Mar)-.18
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/F0 10/Palatino-Roman@0 SF 99.635(Internet-Draft NORM)72 66 R
(Building Blocks)2.5 E(October 2005)106.015 E/F1 10
/Palatino-BoldItalic@0 SF(Sender Repair Response Interface Description)
72 120 Q/F2 10/Palatino-Italic@0 SF(Inputs:)93.6 135.6 Q F0 14.17
(1\) Receiver)97 151.2 R(NACK messages)2.5 E 14.17(2\) Gr)97 166.8 R
(oup timing information)-.18 E F2(Outputs)93.6 182.4 Q F0 14.17
(1\) Repair)97 198 R(messages \(FEC and/or Data content r)2.5 E
(etransmission\))-.18 E 14.17(2\) Advertisement)97 210 R(of curr)2.5 E
(ent pending r)-.18 E(epair transmissions when unicast r)-.18 E(eceiver)
-.18 E(feedback is detected.)122 222 Q/F3 10/Palatino-Bold@0 SF(3.3.)72
246 Q/F4 12/Palatino-Bold@0 SF
(NORM Receiver Join Policies and Procedures)5 E F0
(Consideration should be given to the policies and pr)93.6 261.6 Q
(ocedur)-.18 E(es by which new r)-.18 E(eceivers join a)-.18 E(gr)93.6
273.6 Q(oup \(per)-.18 E(haps wher)-.18 E 2.5(er)-.18 G
(eliable transmission is alr)-2.68 E(eady in pr)-.18 E(ogr)-.18 E
(ess\) and begin r)-.18 E(equesting)-.18 E -.18(re)93.6 285.6 S(pair).18
E 2.5(.I)-.74 G 2.5(fr)-2.5 G(eceiver joins ar)-2.68 E 2.5(eu)-.18 G
(nconstrained, the dynamics of gr)-2.5 E(oup membership may impede)-.18
E(the application's ability to meet its goals for forwar)93.6 297.6 Q
2.5(dp)-.18 G -.18(ro)-2.5 G(gr).18 E(ession of data transmission.)-.18
E(Policies limiting the opportunities when r)93.6 309.6 Q
(eceivers begin participating in the NACK pr)-.18 E(ocess)-.18 E
(may be used to achieve the desir)93.6 321.6 Q(ed behavior)-.18 E 5(.F)
-.74 G(or example, it may be beneficial for r)-5 E(eceivers)-.18 E
(to attempt r)93.6 333.6 Q(eliable r)-.18 E(eception fr)-.18 E
(om a newly-hear)-.18 E 2.5(ds)-.18 G(ender only upon non-r)-2.5 E
(epair transmissions)-.18 E(of data in the first FEC block of an object\
 or logical portion of a str)93.6 345.6 Q 2.5(eam. The)-.18 F
(sender may also)2.5 E(implement policies limiting the r)93.6 357.6 Q
(eceivers fr)-.18 E(om which it will accept NACK r)-.18 E
(equests, but this)-.18 E(may be pr)93.6 369.6 Q
(ohibitive for scalability r)-.18 E(easons in some situations.)-.18 E
(Alternatively)5 E 2.5(,i)-1.11 G 2.5(tm)-2.5 G(ay be)-2.5 E
(desirable to have a looser transport synchr)93.6 381.6 Q
(onization policy and r)-.18 E(ely upon session)-.18 E
(management mechanisms to limit gr)93.6 393.6 Q
(oup dynamics that can cause poor performance, in)-.18 E(some types of \
bulk transfer applications \(or for potential interactive r)93.6 405.6 Q
(eliable multicast)-.18 E(applications\).)93.6 417.6 Q F1(Gr)72 453.6 Q
(oup Join Policy Interface Description)-.18 E F2(Inputs:)93.6 469.2 Q F0
14.17(1\) Curr)97 484.8 R(ent object/str)-.18 E(eam data/r)-.18 E
(epair content and sequencing identifiers fr)-.18 E(om sender)-.18 E
(transmissions.)122 496.8 Q F2(Outputs:)93.6 512.4 Q F0 14.17
(1\) Receiver)97 528 R(yes/no decision to begin r)2.5 E
(eceiving and NACKing for r)-.18 E(eliable r)-.18 E(eception of)-.18 E
(data)122 540 Q F3(3.4.)72 564 Q F4
(Reliable Multicast Member Identification)5 E F0(In a NORM pr)93.6 579.6
Q(otocol \(or other multicast pr)-.18 E(otocols\) wher)-.18 E 2.5(et)
-.18 G(her)-2.5 E 2.5(ei)-.18 G 2.5(st)-2.5 G(he potential for multiple)
-2.5 E(sour)93.6 591.6 Q(ces of data, it is necessary to pr)-.18 E
(ovide some mechanism to uniquely identify the sour)-.18 E(ces)-.18 E
(\(and possibly some or all r)93.6 603.6 Q
(eceivers in some cases\) within the gr)-.18 E 2.5(oup. Identity)-.18 F
(based on)2.5 E(arriving packet sour)93.6 615.6 Q(ce addr)-.18 E
(esses is insuf)-.18 E(ficient for several r)-.18 E 2.5(easons. These)
-.18 F -.18(re)2.5 G(asons include).18 E -.18(ro)93.6 627.6 S
(uting changes for hosts with multiple interfaces that r).18 E
(esult in dif)-.18 E(fer)-.18 E(ent packet sour)-.18 E(ce)-.18 E(addr)
93.6 639.6 Q(esses for a given host over time, network addr)-.18 E
(ess translation \(NA)-.18 E(T\) or fir)-.74 E(ewall devices,)-.18 E
(or other transport/network bridging appr)93.6 651.6 Q 2.5(oaches. As)
-.18 F 2.5(ar)2.5 G(esult, some type of unique sour)-2.68 E(ce)-.18 E
(identifier)93.6 663.6 Q F2(<sour)2.5 E(ceId>)-.18 E F0
(field should be pr)2.5 E(esent in packets transmitted by r)-.18 E
(eliable multicast)-.18 E(session members.)93.6 675.6 Q(Adamson, et al.)
72 768 Q(Expir)96.06 E(es: 17 Mar)-.18 E(ch 2006)-.18 E([Page 19])124.71
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(Building Blocks)2.5 E(October 2005)106.015 E/F1 10/Palatino-Bold@0 SF
(3.5.)72 120 Q/F2 12/Palatino-Bold@0 SF(Data Content Identification)5 E
F0(The data and r)93.6 135.6 Q
(epair content transmitted by a NORM sender r)-.18 E(equir)-.18 E
(es some form of)-.18 E(identification in the pr)93.6 147.6 Q
(otocol header fields.)-.18 E(This identification is r)5 E(equir)-.18 E
(ed to facilitate the)-.18 E -.18(re)93.6 159.6 S
(liable NACK-oriented r).18 E(epair pr)-.18 E 2.5(ocess. These)-.18 F
(identifiers will also be used in NACK)2.5 E(messages generated.)93.6
171.6 Q
(This building block document assumes two very general types of data)5 E
(that may comprise bulk transfer session content.)93.6 183.6 Q
(One type is static, discr)5 E(ete objects of finite)-.18 E
(size and the other is continuous non-finite str)93.6 195.6 Q 2.5
(eams. A)-.18 F(given application)2.5 E(may wish to)5 E -.18(re)93.6
207.6 S(liably multicast data content using either one or both of these\
 paradigms.).18 E(While it may be)5 E
(possible for some applications to further generalize this model and pr)
93.6 219.6 Q(ovide mechanisms to)-.18 E
(encapsulate static objects as content embedded within a str)93.6 231.6
Q(eam, ther)-.18 E 2.5(ea)-.18 G .36 -.18(re a)-2.5 H(dvantages in).18 E
(many applications to pr)93.6 243.6 Q
(ovide distinct support for static bulk objects and messages with the)
-.18 E(context of a r)93.6 255.6 Q(eliable multicast session.)-.18 E
(These applications may include content caching)5 E
(servers, file transfer)93.6 267.6 Q 2.5(,o)-.74 G 2.5(rc)-2.5 G
(ollaborative tools with bulk content.)-2.5 E(Applications with)5 E -.18
(re)93.6 279.6 S(quir).18 E(ements for these static object types can th\
en take advantage of transport layer)-.18 E
(mechanisms \(i.e., segmentation/r)93.6 291.6 Q(eassembly)-.18 E 2.5(,c)
-1.11 G(aching, integrated forwar)-2.5 E 2.5(de)-.18 G(rr)-2.5 E
(or corr)-.18 E(ection)-.18 E(coding, etc.\) rather than being r)93.6
303.6 Q(equir)-.18 E(ed to pr)-.18 E
(ovide their own mechanisms for these functions)-.18 E
(at the application layer)93.6 315.6 Q(.)-.74 E
(As noted, some applications may alternatively desir)93.6 339.6 Q 2.5
(et)-.18 G 2.5(ot)-2.5 G(ransmit bulk content in the form of)-2.5 E
(one or mor)93.6 351.6 Q 2.5(es)-.18 G(tr)-2.5 E
(eams of non-finite size.)-.18 E(Example str)5 E
(eams include continuous quasi-r)-.18 E(eal-time)-.18 E(message br)93.6
363.6 Q(oadcasts \(e.g., stock ticker\) or some content types that ar)
-.18 E 2.5(ep)-.18 G(art of collaborative)-2.5 E
(tools or other applications.)93.6 375.6 Q
(And, as indicated above, some applications may wish to)5 E
(encapsulate other bulk content \(e.g., files\) into one or mor)93.6
387.6 Q 2.5(es)-.18 G(tr)-2.5 E(eams within a multicast)-.18 E(session.)
93.6 399.6 Q
(The components described within this building block document ar)93.6
423.6 Q 2.5(ee)-.18 G(nvisioned to be)-2.5 E
(applicable to both of these models with the)93.6 435.6 Q
(potential for a mix of both types within a single)5 E
(multicast session.)93.6 447.6 Q 1.84 -.92(To s)5 H(upport this r).92 E
(equir)-.18 E(ement, the normal data content identification)-.18 E
(should include a field to uniquely identify the object or str)93.6
459.6 Q(eam)-.18 E/F3 10/Palatino-Italic@0 SF(<objectId>)2.5 E F0
(within some)2.5 E -.18(re)93.6 471.6 S(asonable temporal or or).18 E
(dinal interval.)-.18 E
(Note that it is _not_ expected that this data content)5 E
(identification will be globally unique.)93.6 483.6 Q
(It is expected that the object/str)5 E(eam identifier will be)-.18 E
(unique with r)93.6 495.6 Q(espect to a given sender within the r)-.18 E
(eliable multicast session and during the)-.18 E(time that sender is su\
pporting a specific transport instance of that object or str)93.6 507.6
Q(eam.)-.18 E(Since the "bulk" object/str)93.6 531.6 Q
(eam content usually r)-.18 E(equir)-.18 E
(es segmentation, some form of segment)-.18 E
(identification must also be)93.6 543.6 Q(pr)5 E 2.5(ovided. This)-.18 F
(segment identifier will be r)2.5 E(elative to any object)-.18 E(or str)
93.6 555.6 Q(eam identifier that has been pr)-.18 E 2.5(ovided. Thus,)
-.18 F(in some cases, NORM pr)2.5 E(otocol)-.18 E
(instantiations may be able to r)93.6 567.6 Q
(eceive transmissions and r)-.18 E(equest r)-.18 E
(epair for multiple str)-.18 E(eams)-.18 E(and one or mor)93.6 579.6 Q
2.5(es)-.18 G(ets of static objects in parallel.)-2.5 E(For pr)5 E
(otocol instantiations employing FEC)-.18 E(the segment identification \
portion of the data content identifier may consist of a logical)93.6
591.6 Q(concatenation of a coding block identifier)93.6 603.6 Q F3
(<sour)2.5 E(ceBlockNumber>)-.18 E F0(and an identifier for the)2.5 E
(specific data or parity symbol)93.6 615.6 Q F3(<encodingSymbolId>)2.5 E
F0(of the code block.)2.5 E(The FEC Basic Schemes)5 E(document [1)93.6
627.6 Q(1] and descriptions of additional FEC schemes that may be docum\
ented later)-.55 E(pr)93.6 639.6 Q(ovide a standar)-.18 E 2.5(dm)-.18 G
(essage format for identifying FEC transmission content. NORM)-2.5 E(pr)
93.6 651.6 Q
(otocol instantiations using FEC SHOULD follow such guidelines.)-.18 E
(Additionally)93.6 675.6 Q 2.5(,f)-1.11 G(lags to determine the usage o\
f the content identifier fields \(e.g., str)-2.5 E(eam vs.)-.18 E
(object\) may be applicable.)93.6 687.6 Q
(Flags may also serve other purposes in data content)7.5 E 2.5
(identification. It)93.6 699.6 R
(is expected that any flags defined will be dependent upon individual)
2.5 E(pr)93.6 711.6 Q(otocol instantiations.)-.18 E(Adamson, et al.)72
768 Q(Expir)96.06 E(es: 17 Mar)-.18 E(ch 2006)-.18 E([Page 20])124.71 E
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(Building Blocks)2.5 E(October 2005)106.015 E(In summary)93.6 120 Q 2.5
(,t)-1.11 G(he following data content identification fields may be r)
-2.5 E(equir)-.18 E(ed for NORM)-.18 E(pr)93.6 132 Q
(otocol data content messages:)-.18 E 14.17(1\) Sour)97 147.6 R
(ce node identifier \()-.18 E/F1 10/Palatino-Italic@0 SF(<sour)A(ceId>)
-.18 E F0(\))A 14.17(2\) Object/Str)97 163.2 R(eam identifier \()-.18 E
F1(<objectId>)A F0(\), if applicable.)A 14.17(3\) FEC)97 178.8 R
(Block identifier \()2.5 E F1(<sour)A(ceBlockNumber>)-.18 E F0
(\), if applicable.)A 14.17(4\) FEC)97 194.4 R(Symbol identifier \()2.5
E F1(<encodingSymbolId>)A F0(\))A 14.17(5\) Flags)97 210 R(to dif)2.5 E
(fer)-.18 E(entiate interpr)-.18 E
(etation of identifier fields or identifier str)-.18 E(uctur)-.08 E 2.5
(et)-.18 G(hat)-2.5 E(implicitly indicates usage.)122 222 Q 14.17
(6\) Additional)97 237.6 R
(FEC transmission content fields per FEC Building Block)2.5 E(These fie\
lds have been identified because any generated NACK messages will use t\
hese)93.6 253.2 Q(identifiers in r)93.6 265.2 Q(equesting r)-.18 E
(epair or r)-.18 E(etransmission of data.)-.18 E(NORM pr)5 E
(otocols that use these)-.18 E(data content fields should also be compa\
tible with support for intermediate system)93.6 277.2 Q(assistance to r)
93.6 289.2 Q(eliable multicast transport operation when available.)-.18
E/F2 10/Palatino-Bold@0 SF(3.6.)72 313.2 Q/F3 12/Palatino-Bold@0 SF
(Forward Error Correction \(FEC\))5 E F0(Multiple forwar)93.6 328.8 Q
2.5(de)-.18 G(rr)-2.5 E(or corr)-.18 E(ection \(FEC\) appr)-.18 E
(oaches have been identified that can pr)-.18 E(ovide)-.18 E(gr)93.6
340.8 Q(eat performance enhancements to the r)-.18 E(epair pr)-.18 E
(ocess of NACK-oriented and other r)-.18 E(eliable)-.18 E(multicast pr)
93.6 352.8 Q(otocols [12], [13], [14].)-.18 E(NORM pr)5 E(otocols can r)
-.18 E(eap additional benefits since FEC-)-.18 E(based r)93.6 364.8 Q
(epair does not _generally_ r)-.18 E(equir)-.18 E 2.5(ee)-.18 G
(xplicit knowledge of r)-2.5 E(epair content within the)-.18 E
(bounds of its coding block size \(in symbols\).)93.6 376.8 Q
(In NORM, parity r)5 E(epair packets generated will)-.18 E
(generally be transmitted only in r)93.6 388.8 Q(esponse to NACK r)-.18
E(epair r)-.18 E(equests fr)-.18 E(om r)-.18 E(eceiving nodes.)-.18 E
(However)93.6 400.8 Q 2.5(,t)-.74 G(her)-2.5 E 2.5(ea)-.18 G .36 -.18
(re b)-2.5 H(enefits in some network envir).18 E
(onments for transmitting some)-.18 E(pr)93.6 412.8 Q
(edetermined quantity of FEC r)-.18 E
(epair packets multiplexed with the r)-.18 E(egular data symbol)-.18 E
(transmissions [15].)93.6 424.8 Q(This can r)5 E
(educe the amount of NACK traf)-.18 E(fic generated with r)-.18 E
(elatively)-.18 E(little over)93.6 436.8 Q(head cost when gr)-.18 E
(oup sizes ar)-.18 E 2.5(ev)-.18 G(ery lar)-2.5 E(ge or the network)-.18
E(connectivity has a lar)5 E(ge)-.18 E/F4 10/Courier@0 SF
(delay*bandwidth)93.6 448.8 Q F0(pr)2.5 E
(oduct with some nominal level of expected packet loss.)-.18 E
(While the)5 E
(application of FEC is not unique to NORM, these sorts of r)93.6 460.8 Q
(equir)-.18 E(ements may dictate the types)-.18 E(of algorithms and pr)
93.6 472.8 Q(otocol appr)-.18 E(oaches that ar)-.18 E 2.5(ea)-.18 G
(pplicable.)-2.5 E 2.5(As)93.6 496.8 S(pecific issue r)-2.5 E(elated to\
 the use of FEC with NORM is the mechanism used to identify the)-.18 E(\
portion\(s\) of transmitted data content to which specific FEC packets \
ar)93.6 508.8 Q 2.5(ea)-.18 G 2.5(pplicable. It)-2.5 F(is)2.5 E(expecte\
d that FEC algorithms will be based on generating a set of parity r)93.6
520.8 Q(epair packets for a)-.18 E(corr)93.6 532.8 Q
(esponding block of transmitted data packets.)-.18 E
(Since data content packets ar)5 E 2.5(eu)-.18 G(niquely)-2.5 E
(identified by the concatenation of)93.6 544.8 Q F1(<sour)2.5 E
(ceId::objectId::sour)-.18 E(ceBlockNumber::encodingSymbolId>)-.18 E F0
(during transport, it is expected that FEC packets will be identified i\
n a similar manner)93.6 556.8 Q 5(.T)-.74 G(he)-5 E
(FEC Building Block document [9] pr)93.6 568.8 Q(ovides detailed r)-.18
E(ecommendations concerning)-.18 E(application of FEC and standar)93.6
580.8 Q 2.5(df)-.18 G(ormats for r)-2.5 E(elated r)-.18 E
(eliable multicast pr)-.18 E(otocol messages.)-.18 E F2(3.7.)72 604.8 Q
F3(Round-trip T)5 E(iming Collection)-.66 E F0(The measur)93.6 620.4 Q
(ement of packet pr)-.18 E(opagation r)-.18 E(ound-trip time \(R)-.18 E
(TT\) among members of the)-.37 E(gr)93.6 632.4 Q(oup is r)-.18 E(equir)
-.18 E(ed to support timer)-.18 E(-based NACK suppr)-.18 E
(ession algorithms, timing of sender)-.18 E(commands or certain r)93.6
644.4 Q(epair functions, and congestion contr)-.18 E(ol operation.)-.18
E(The natur)5 E 2.5(eo)-.18 G 2.5(ft)-2.5 G(he)-2.5 E -.18(ro)93.6 656.4
S(und-trip information collected is dependent upon the type of interact\
ion among the).18 E(members of the gr)93.6 668.4 Q 2.5(oup. In)-.18 F
(the case wher)2.5 E 2.5(eo)-.18 G(nly "one-to-many" transmission is r)
-2.5 E(equir)-.18 E(ed, it)-.18 E(may be that only the sender r)93.6
680.4 Q(equir)-.18 E 2.5(eR)-.18 G(TT knowledge of the gr)-2.87 E
(eatest R)-.18 E(TT \(GR)-.37 E(TT\) among the)-.37 E -.18(re)93.6 692.4
S(ceiver set and/or R).18 E(TT knowledge of only a portion of the gr)
-.37 E 2.5(oup. Her)-.18 F(e, the GR)-.18 E(TT)-.37 E
(information might be collected in a r)93.6 704.4 Q
(easonably scalable manner)-.18 E 5(.F)-.74 G(or congestion contr)-5 E
(ol)-.18 E(operation, it is possible that R)93.6 716.4 Q
(TT information may be r)-.37 E(equir)-.18 E(ed by each r)-.18 E
(eceiver in the gr)-.18 E(oup.)-.18 E(Adamson, et al.)72 768 Q(Expir)
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(Building Blocks)2.5 E(October 2005)106.015 E
(In this case, an alternative R)93.6 120 Q
(TT collection scheme may be utilized wher)-.37 E 2.5(er)-.18 G
(eceivers collect)-2.68 E(individual R)93.6 132 Q(TT measur)-.37 E
(ements with r)-.18 E(espect to the sender and advertise them to the gr)
-.18 E(oup or)-.18 E(sender)93.6 144 Q 5(.W)-.74 G(her)-5 E 2.5(ei)-.18
G 2.5(ti)-2.5 G 2.5(sl)-2.5 G(ikely that exchange of r)-2.5 E
(eliable multicast data will occur among the)-.18 E(gr)93.6 156 Q
(oup on a "many-to-many" basis, ther)-.18 E 2.5(ea)-.18 G .36 -.18(re a)
-2.5 H(lternative measur).18 E(ement techniques that might)-.18 E
(be employed for incr)93.6 168 Q(eased ef)-.18 E(ficiency [16].)-.18 E
(And in some cases, ther)5 E 2.5(em)-.18 G(ight be absolute time)-2.5 E
(synchr)93.6 180 Q(onization among hosts that may simplify R)-.18 E
(TT measur)-.37 E 2.5(ement. Ther)-.18 F 2.5(ea)-.18 G .36 -.18(re t)
-2.5 H(rade-of).18 E(fs in)-.18 E(multicast congestion contr)93.6 192 Q
(ol design that r)-.18 E(equir)-.18 E 2.5(ef)-.18 G
(urther consideration befor)-2.5 E 2.5(eau)-.18 G(niversal)-2.5 E -.18
(re)93.6 204 S(commendation on R).18 E(TT \(or GR)-.37 E(TT\) measur)
-.37 E(ement can be specified.)-.18 E(Regar)5 E(dless of how the)-.18 E
-.37(RT)93.6 216 S 2.5(Ti).37 G(nformation is collected \(and mor)-2.5 E
2.5(es)-.18 G(pecifically GR)-2.5 E(TT\) with r)-.37 E
(espect to congestion contr)-.18 E(ol)-.18 E(or other r)93.6 228 Q
(equir)-.18 E(ements, the sender will need to advertise its curr)-.18 E
(ent GR)-.18 E(TT estimate to the)-.37 E(gr)93.6 240 Q
(oup for various timeouts used by r)-.18 E(eceivers.)-.18 E/F1 10
/Palatino-Bold@0 SF 2.5(3.7.1. One-to-Many)72 264 R(Sender GR)2.5 E
(TT Measurement)-.55 E F0(The goal of this form of R)93.6 279.6 Q
(TT measur)-.37 E(ement is for the sender to learn the GR)-.18 E
(TT among the)-.37 E -.18(re)93.6 291.6 S(ceivers who ar).18 E 2.5(ea)
-.18 G(ctively participating in NORM operation.)-2.5 E(The set of r)5 E
(eceivers)-.18 E(participating in this pr)93.6 303.6 Q
(ocess may be the entir)-.18 E 2.5(eg)-.18 G -.18(ro)-2.5 G
(up or some subset of the gr).18 E(oup determined)-.18 E(fr)93.6 315.6 Q
(om another mechanism within the pr)-.18 E(otocol instantiation.)-.18 E
(An appr)5 E(oach to collect this)-.18 E(GR)93.6 327.6 Q
(TT information follows.)-.37 E(The sender periodically polls the gr)
93.6 351.6 Q(oup with a message \(independent or "piggy-backed")-.18 E
(with other transmissions\) containing a)93.6 363.6 Q/F2 10/Courier@0 SF
(<sendTime>)2.5 E F0(timestamp r)2.5 E(elative to an internal clock)-.18
E(at the sender)93.6 375.6 Q 5(.U)-.74 G(pon r)-5 E
(eception of this message, the r)-.18 E(eceivers will r)-.18 E(ecor)-.18
E 2.5(dt)-.18 G(his)-2.5 E F2(<sendTime>)2.5 E F0
(timestamp and the time \(r)93.6 387.6 Q(efer)-.18 E
(enced to their own clocks\) at which it was r)-.18 E(eceived)-.18 E F2
(<recvTime>)93.6 399.6 Q F0 5(.W)C(hen the r)-5 E(eceiver pr)-.18 E
(ovides feedback to the sender \(either explicitly or as part)-.18 E
(of other feedback messages depending upon pr)93.6 411.6 Q
(otocol instantiation specification\), it will)-.18 E(constr)93.6 423.6
Q(uct a "r)-.08 E(esponse" using the formula:)-.18 E F2
(grttResponse = sendTime + \(currentTime - recvTime\))148.8 447.6 Q F0
(wher)93.6 471.6 Q 2.5(et)-.18 G(he)-2.5 E F2(<sendTime>)2.5 E F0
(is the timestamp fr)2.5 E(om the last pr)-.18 E(obe message r)-.18 E
(eceived fr)-.18 E(om the)-.18 E(sour)93.6 483.6 Q(ce and the \()-.18 E
F2(<currentTime> - <recvTime>)A F0 2.5(\)i)C 2.5(st)-2.5 G
(he amount of time dif)-2.5 E(fer)-.18 E(ential since)-.18 E(that r)93.6
495.6 Q(equest was r)-.18 E(eceived until the r)-.18 E
(eceiver generated the r)-.18 E(esponse.)-.18 E(The sender pr)93.6 519.6
Q(ocesses each r)-.18 E(eceiver r)-.18 E(esponse by calculating a curr)
-.18 E(ent R)-.18 E(TT measur)-.37 E(ement for)-.18 E(the r)93.6 531.6 Q
(eceiver fr)-.18 E(om whom the r)-.18 E(esponse was r)-.18 E
(eceived using the following formula:)-.18 E F2
(RTT_rcvr = currentTime - grttResponse)187.8 555.6 Q F0
(During the each periodic GR)93.6 579.6 Q(TT pr)-.37 E
(obing interval, the sour)-.18 E(ce keeps the peak r)-.18 E(ound trip)
-.18 E(timing measur)93.6 591.6 Q(ement \()-.18 E F2(RTT_peak)A F0 2.5
(\)f)C -.18(ro)-2.5 G 2.5(mt).18 G(he set of r)-2.5 E(esponses it has r)
-.18 E 2.5(eceived. A)-.18 F(conservative)2.5 E(estimate of)93.6 603.6 Q
F2(GRTT)2.5 E F0(is kept to maximize the ef)2.5 E(ficiency of r)-.18 E
(edundant NACK suppr)-.18 E(ession and)-.18 E -.18(re)93.6 615.6 S
(pair aggr).18 E 2.5(egation. The)-.18 F(update to the sour)2.5 E
(ce's ongoing estimate of)-.18 E F2(GRTT)2.5 E F0(is done observing)2.5
E(the following r)93.6 627.6 Q(ules:)-.08 E 14.17(1\) If)97 655.2 R 2.5
(ar)2.5 G -1.76(eceiver 's)-2.68 F -.18(re)2.5 G(sponse r).18 E
(ound trip time \()-.18 E F2(RTT_rcvr)A F0 2.5(\)i)C 2.5(sg)-2.5 G -.18
(re)-2.5 G(ater than the curr).18 E(ent)-.18 E F2(GRTT)2.5 E F0
(estimate, the)122 667.2 Q F2(GRTT)2.5 E F0
(is immediately updated to this new peak value:)2.5 E F2
(GRTT = RTT_rcvr)268 691.2 Q F0(Adamson, et al.)72 768 Q(Expir)96.06 E
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(Building Blocks)2.5 E(October 2005)106.015 E 14.17(2\) At)97 120 R
(the end of the r)2.5 E(esponse collection period \(i.e., the GR)-.18 E
(TT pr)-.37 E(obe interval\), if the)-.18 E -.18(re)122 132 S(cor).18 E
(ded "peak" r)-.18 E(esponse)-.18 E/F1 10/Courier@0 SF(RTT_peak)2.5 E F0
2.5(\)i)C 2.5(sl)-2.5 G(ess than the curr)-2.5 E(ent GR)-.18 E
(TT estimate, the)-.37 E(GR)122 144 Q(TT is updated to:)-.37 E F1
(GRTT = MAX\(0.9*GRTT, RTT_peak\))223 168 Q F0 14.17(3\) If)97 195.6 R
(no feedback is r)2.5 E(eceived, the sender)-.18 E F1(GRTT)2.5 E F0
(estimate r)2.5 E(emains unchanged.)-.18 E 14.17(4\) At)97 223.2 R
(the end of the r)2.5 E
(esponse collection period, the peak tracking value \()-.18 E F1
(RTT_peak)A F0 2.5(\)i)C(s)-2.5 E -.18(re)122 235.2 S
(set to ZERO for subsequent peak detection.).18 E(The)93.6 250.8 Q F1
(GRTT)2.5 E F0(collection period \(i.e., period of pr)2.5 E
(obe transmission\) could be fixed at a value on)-.18 E(the or)93.6
262.8 Q(der of that expected for gr)-.18 E
(oup membership and/or network topology dynamics.)-.18 E(For)5 E -.18
(ro)93.6 274.8 S(bustness, mor).18 E 2.5(er)-.18 G(apid pr)-2.5 E
(obing could be used at pr)-.18 E(otocol startup befor)-.18 E 2.5(es)
-.18 G(ettling to a less)-2.5 E(fr)93.6 286.8 Q
(equent, steady-state interval.)-.18 E(Optionally)5 E 2.5(,a)-1.11 G 2.5
(na)-2.5 G(lgorithm may be developed to adjust the)-2.5 E F1(GRTT)93.6
298.8 Q F0(collection period dynamically in r)2.5 E(esponse to the curr)
-.18 E(ent)-.18 E F1(GRTT)2.5 E F0(estimate \(or variations)2.5 E
(in it\) and to an estimation of packet loss.)93.6 310.8 Q(The over)5 E
(head of pr)-.18 E(obing messages could then be)-.18 E -.18(re)93.6
322.8 S(duced when the).18 E F1(GRTT)2.5 E F0
(estimate is stable and unchanging, but be adjusted to track mor)2.5 E
(e)-.18 E(dynamically during periods of variation with corr)93.6 334.8 Q
(espondingly shorter GR)-.18 E(TT collection)-.37 E(periods.)93.6 346.8
Q F1(GRTT)5 E F0(collection may also be coupled with collection of othe\
r information for)2.5 E(congestion contr)93.6 358.8 Q(ol purposes.)-.18
E(In summary)93.6 382.8 Q 2.5(,a)-1.11 G(lthough NORM r)-2.5 E
(epair cycle timeouts ar)-.18 E 2.5(eb)-.18 G(ased on)-2.5 E F1(GRTT)2.5
E F0 2.5(,i)C 2.5(ts)-2.5 G(hould be noted)-2.5 E(that conver)93.6 394.8
Q(gent operation of the pr)-.18 E
(otocol does not _strictly_ depend on highly accurate)-.18 E F1(GRTT)
93.6 406.8 Q F0 2.5(estimation. The)2.5 F(curr)2.5 E
(ent mechanism has pr)-.18 E(oved suf)-.18 E
(ficient in simulations and in the)-.18 E(envir)93.6 418.8 Q
(onments wher)-.18 E 2.5(eN)-.18 G(ORM-like pr)-2.5 E
(otocols have been deployed to date.)-.18 E(The estimate)5 E(pr)93.6
430.8 Q(ovided by the algorithm tracks the peak envelope of actual)-.18
E F1(GRTT)2.5 E F0(\(including operating)2.5 E(system ef)93.6 442.8 Q
(fect as well as network delays\) even in r)-.18 E
(elatively high loss connectivity)-.18 E 5(.T)-1.11 G(he)-5 E
(steady-state pr)93.6 454.8 Q
(obing/update interval may potentially be varied to accommodate dif)-.18
E(fer)-.18 E(ent)-.18 E(levels of expected network dynamics in dif)93.6
466.8 Q(fer)-.18 E(ent envir)-.18 E(onments.)-.18 E/F2 10
/Palatino-Bold@0 SF 2.5(3.7.2. One-to-Many)72 490.8 R(Receiver R)2.5 E
(TT Measurement)-.55 E F0(In this appr)93.6 506.4 Q(oach, r)-.18 E
(eceivers send messages with timestamps to the sender)-.18 E 5(.T)-.74 G
2.5(oc)-5.92 G(ontr)-2.5 E(ol the)-.18 E(volume of these r)93.6 518.4 Q
(eceiver)-.18 E(-generated messages, a suppr)-.18 E
(ession mechanism similar to that)-.18 E(described for NACK suppr)93.6
530.4 Q(ession my be used.)-.18 E(The "age" of r)5 E(eceivers' R)-.18 E
(TT measur)-.37 E(ement)-.18 E(should be kept by r)93.6 542.4 Q(eceiver\
s and used as a metric in competing for feedback opportunities in)-.18 E
(the suppr)93.6 554.4 Q(ession scheme.)-.18 E(For example, r)5 E
(eceiver who have not made any R)-.18 E(TT measur)-.37 E(ement)-.18 E
(or whose R)93.6 566.4 Q(TT measur)-.37 E
(ement has aged most should have pr)-.18 E(ecedence over other r)-.18 E
2.5(eceivers. In)-.18 F(turn the sender may have limited capacity to pr)
93.6 578.4 Q(ovide an "echo" of the r)-.18 E(eceiver timestamps)-.18 E
(back to the gr)93.6 590.4 Q(oup, and it could use this R)-.18 E
(TT "age" metric to determine which r)-.37 E(eceivers get)-.18 E(pr)93.6
602.4 Q 2.5(ecedence. The)-.18 F(sender can determine the)2.5 E F1(GRTT)
2.5 E F0(as described in 3.7.1 if it pr)2.5 E(ovides sender)-.18 E
(timestamps to the gr)93.6 614.4 Q 2.5(oup. Alternatively)-.18 F 2.5(,r)
-1.11 G(eceivers who note their R)-2.68 E(TT is gr)-.37 E
(eater than the)-.18 E(sender)93.6 626.4 Q F1(GRTT)2.5 E F0
(can compete in the feedback opportunity/suppr)2.5 E
(ession scheme to pr)-.18 E(ovide the)-.18 E(sender and gr)93.6 638.4 Q
(oup with this information.)-.18 E F2 2.5(3.7.3. Many-to-Many)72 662.4 R
-.55(RT)2.5 G 2.5(TM).55 G(easurement)-2.5 E F0(For r)93.6 678 Q(eliabl\
e multicast sessions that involve multiple senders, it may be useful to\
 have R)-.18 E(TT)-.37 E(measur)93.6 690 Q(ements occur on a tr)-.18 E
(ue "many-to-many" basis rather than have each sender)-.08 E
(independently tracking R)93.6 702 Q(TT)-.37 E 5(.S)-.74 G(ome pr)-5 E
(otocol ef)-.18 E(ficiency can be gained when r)-.18 E(eceivers can)-.18
E(infer an appr)93.6 714 Q(oximation of their R)-.18 E(TT with r)-.37 E
(espect to a sender based on R)-.18 E(TT information they)-.37 E
(Adamson, et al.)72 768 Q(Expir)96.06 E(es: 17 Mar)-.18 E(ch 2006)-.18 E
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(Building Blocks)2.5 E(October 2005)106.015 E
(have on another sender and that other sender)93.6 120 Q('s R).74 E
(TT with r)-.37 E(espect to the new sender of)-.18 E(inter)93.6 132 Q
2.5(est. For)-.18 F(example, for r)2.5 E(eceiver ")-.18 E/F1 10
/Courier@0 SF(a)A F0 2.5("a)C(nd sender)-2.5 E('s ").74 E F1(b)A F0 2.5
("a)C(nd ")-2.5 E F1(c)A F0(", it is likely that:)A F1
(RTT\(a<->b\) <= RTT\(a<->c\)\) + RTT\(b<->c\))187.8 156 Q F0(Further r)
93.6 180 Q(efinement of this estimate can be conducted if R)-.18 E
(TT information is available to a)-.37 E(node concerning its own R)93.6
192 Q(TT to a small subset of other gr)-.37 E(oup members and R)-.18 E
(TT)-.37 E(information among those other gr)93.6 204 Q
(oup members it learns during pr)-.18 E(otocol operation.)-.18 E/F2 10
/Palatino-Bold@0 SF 2.5(3.7.4. Sender)72 228 R(GR)2.5 E
(TT Advertisement)-.55 E F0 1.84 -.92(To f)93.6 243.6 T
(acilitate deterministic NORM pr).92 E
(otocol operation, the sender should r)-.18 E(obustly advertise)-.18 E
(its curr)93.6 255.6 Q(ent estimation of)-.18 E F1(GRTT)2.5 E F0
(to the r)2.5 E(eceiver set.)-.18 E(Common, r)5 E
(obust knowledge of the)-.18 E -1.76(sender 's)93.6 267.6 R(curr)2.5 E
(ent operating)-.18 E F1(GRTT)2.5 E F0(estimate among the gr)2.5 E
(oup will allow the pr)-.18 E(otocol to)-.18 E(pr)93.6 279.6 Q(ogr)-.18
E(ess in its most ef)-.18 E(ficient manner)-.18 E 5(.T)-.74 G(he sender)
-5 E('s).74 E F1(GRTT)2.5 E F0(estimate can be r)2.5 E
(obustly advertised)-.18 E(to the gr)93.6 291.6 Q(oup by simply embeddi\
ng the estimate into all pertinent messages transmitted by)-.18 E
(the sender)93.6 303.6 Q 5(.T)-.74 G(he over)-5 E
(head of this can be made quite small by quantizing \(compr)-.18 E
(essing\) the)-.18 E F1(GRTT)93.6 315.6 Q F0
(estimate to a single byte of information.)2.5 E
(The following C-language functions allows)5 E
(this to be done over a wide range \()93.6 327.6 Q F1(RTT_MIN)A F0(thr)
2.5 E(ough)-.18 E F1(RTT_MAX)2.5 E F0 2.5(\)o)C(f)-2.5 E F1(GRTT)2.5 E
F0(values while)2.5 E(maintaining a gr)93.6 339.6 Q(eater range of pr)
-.18 E(ecision for small)-.18 E F1(GRTT)2.5 E F0(values and less pr)2.5
E(ecision for lar)-.18 E(ge)-.18 E 2.5(values. V)93.6 351.6 R
(alues of 1.0e-06 seconds and 1000 seconds ar)-.92 E 2.5(eR)-.18 G
(ECOMMENDED for R)-2.5 E(TT_MIN and)-.37 E -.37(RT)93.6 363.6 S(T_MAX r)
.37 E(espectively)-.18 E 5(.N)-1.11 G
(ORM applications may wish to place an additional, smaller upper)-5 E
(limit on the)93.6 375.6 Q F1(GRTT)2.5 E F0
(advertised by senders to meet application data delivery latency)2.5 E
(constraints at the expense of gr)93.6 387.6 Q
(eater feedback volume in some network envir)-.18 E(onments.)-.18 E F1
(unsigned char QuantizeGrtt\(double grtt\))97 411.6 Q({)97 423.6 Q
(if \(grtt > RTT_MAX\))121 435.6 Q(grtt = RTT_MAX;)145 447.6 Q
(else if \(grtt < RTT_MIN\))121 459.6 Q(grtt = RTT_MIN;)145 471.6 Q
(if \(grtt < \(33*RTT_MIN\)\))121 483.6 Q
(return \(\(unsigned char\)\(grtt / RTT_MIN\) - 1\);)145 495.6 Q(else)
121 507.6 Q(return \(\(unsigned char\)\(ceil\(255.0 -)145 519.6 Q
(\(13.0 * log\(RTT_MAX/grtt\)\)\)\)\);)289 531.6 Q(})97 543.6 Q
(double UnquantizeRtt\(unsigned char qrtt\))97 567.6 Q({)97 579.6 Q
(return \(\(qrtt <= 31\) ?)122 591.6 Q
(\(\(\(double\)\(qrtt+1\)\)*\(double\)RTT_MIN\) :)172 603.6 Q
(\(RTT_MAX/exp\(\(\(double\)\(255-qrtt\)\)/\(double\)13.0\)\)\);)171
615.6 Q(})97 627.6 Q F0
(Note that this function is useful for quantizing)93.6 655.2 Q F1(GRTT)
2.5 E F0(times in the range of 1 micr)2.5 E(osecond to)-.18 E
(1000 seconds.)93.6 667.2 Q(Of course, NORM pr)5 E
(otocol implementations may wish to further constrain)-.18 E(advertised)
93.6 679.2 Q F1(GRTT)2.5 E F0
(estimates \(e.g., limit the maximum value\) for practical r)2.5 E
(easons.)-.18 E(Adamson, et al.)72 768 Q(Expir)96.06 E(es: 17 Mar)-.18 E
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/F0 10/Palatino-Roman@0 SF 99.635(Internet-Draft NORM)72 66 R
(Building Blocks)2.5 E(October 2005)106.015 E/F1 10/Palatino-Bold@0 SF
(3.8.)72 120 Q/F2 12/Palatino-Bold@0 SF
(Group Size Determination/Estimation)5 E F0(When NORM pr)93.6 135.6 Q
(otocol operation includes mechanisms that excite feedback fr)-.18 E
(om the gr)-.18 E(oup)-.18 E(at lar)93.6 147.6 Q
(ge \(e.g., congestion contr)-.18 E(ol\), it may be possible to r)-.18 E
(oughly estimate the gr)-.18 E(oup size based)-.18 E
(on the number of feedback messages r)93.6 159.6 Q(eceived with r)-.18 E
(espect to the distribution of the)-.18 E(pr)93.6 171.6 Q
(obabilistic suppr)-.18 E(ession mechanism used.)-.18 E(Note the timer)5
E(-based suppr)-.18 E(ession mechanism)-.18 E
(described in this document does not r)93.6 183.6 Q(equir)-.18 E 2.5
(eav)-.18 G(ery accurate estimate of gr)-2.5 E(oup size to)-.18 E
(perform adequately)93.6 195.6 Q 5(.T)-1.11 G(hus, a r)-5 E
(ough estimate, particularly if conservatively managed, may)-.18 E(suf)
93.6 207.6 Q 2.5(fice. Gr)-.18 F
(oup size may also be determined administratively)-.18 E 5(.I)-1.11 G
2.5(na)-5 G(bsence of a gr)-2.5 E(oup size)-.18 E
(determination mechanism a default gr)93.6 219.6 Q
(oup size value of 10,000 is RECOMMENDED for)-.18 E -.18(re)93.6 231.6 S
(asonable management of feedback given the scalability of expected NORM\
 usage.).18 E F1(3.9.)72 255.6 Q F2(Congestion Control Operation)5 E F0
(Congestion contr)93.6 271.2 Q(ol that fairly shar)-.18 E
(es available network capacity)-.18 E(with other r)5 E(eliable)-.18 E(m\
ulticast and TCP instantiations is REQUIRED for general Internet operat\
ion.)93.6 283.2 Q(The TCP-)5 E(Friendly Multicast Congestion Contr)93.6
295.2 Q(ol \(TFMCC\) [17] or Pragmatic General Multicast)-.18 E
(Congestion Contr)93.6 307.2 Q
(ol \(PGMCC\) techniques [18] may be applied to NORM operation to meet)
-.18 E(this r)93.6 319.2 Q(equir)-.18 E(ement.)-.18 E F1(3.10.)72 343.2
Q F2(Router/Intermediate System Assistance)5 E F0(NACK-oriented pr)93.6
358.8 Q(otocols may benefit fr)-.18 E(om general purpose r)-.18 E
(outer assistance.)-.18 E(In particular)5 E(,)-.74 E
(additional NACK suppr)93.6 370.8 Q(ession wher)-.18 E 2.5(er)-.18 G
(outers or intermediate systems can aggr)-2.68 E(egate NACK)-.18 E
(content \(or filter duplicate NACK content\) fr)93.6 382.8 Q(om r)-.18
E(eceivers as it is r)-.18 E(elayed towar)-.18 E 2.5(dt)-.18 G
(he sender)-2.5 E(could enhance NORM gr)93.6 394.8 Q
(oup size scalability)-.18 E 5(.F)-1.11 G(or NORM pr)-5 E
(otocols using FEC, it is possible)-.18 E
(that intermediate systems may be able to filter FEC r)93.6 406.8 Q
(epair messages to pr)-.18 E(ovide an intelligent)-.18 E("subcast" of r)
93.6 418.8 Q(epair content to dif)-.18 E(fer)-.18 E
(ent legs of the multicast topology depending on the r)-.18 E(epair)-.18
E(needs learned fr)93.6 430.8 Q(om pr)-.18 E(evious r)-.18 E
(eceiver NACKs.)-.18 E(Both of these types of assist functions would)5 E
-.18(re)93.6 442.8 S(quir).18 E 2.5(er)-.18 G(outer interpr)-2.68 E
(etation of transport data unit content identifiers and flags.)-.18 E F1
(3.1)72 466.8 Q(1.)-.37 E F2(NORM Applicability)5 E F0
(The NORM building block applies to pr)93.6 482.4 Q
(otocols wishing to employ negative)-.18 E(acknowledgement to achieve r)
93.6 494.4 Q(eliable data transfer)-.18 E 5(.P)-.74 G -.18(ro)-5 G
(perly designed negative-).18 E(acknowledgement \(NACK\)-oriented r)93.6
506.4 Q(eliable multicast \(NORM\) pr)-.18 E(otocols of)-.18 E
(fer scalability)-.18 E
(advantages for applications and/or network topologies wher)93.6 518.4 Q
(e, for various r)-.18 E(easons, it is)-.18 E(pr)93.6 530.4 Q
(ohibitive to constr)-.18 E(uct a higher or)-.08 E
(der delivery infrastr)-.18 E(uctur)-.08 E 2.5(ea)-.18 G
(bove the basic Layer 3 IP)-2.5 E(multicast service \(e.g., unicast or \
hybrid unicast/multicast data distribution tr)93.6 542.4 Q(ees\).)-.18 E
(Additionally)93.6 554.4 Q 2.5(,t)-1.11 G(he scalability pr)-2.5 E
(operty of NACK-oriented pr)-.18 E(otocols [19], [20] is applicable)-.18
E(wher)93.6 566.4 Q 2.5(eb)-.18 G -.18(ro)-2.5 G(ad "fan-out" is expect\
ed for a single network hop \(e.g., cable-TV data delivery).18 E(,)-1.11
E(satellite, or other br)93.6 578.4 Q(oadcast communication services\).)
-.18 E(Furthermor)5 E(e, the simplicity of a)-.18 E(pr)93.6 590.4 Q
(otocol based on "flat" gr)-.18 E
(oup-wide multicast distribution may of)-.18 E(fer advantages for a br)
-.18 E(oad)-.18 E
(range of distributed services or dynamic networks and applications.)
93.6 602.4 Q(NORM pr)5 E(otocols can)-.18 E(make use of r)93.6 614.4 Q
(ecipr)-.18 E(ocal \(among senders and r)-.18 E
(eceivers\) multicast communication under the)-.18 E(Any-Sour)93.6 626.4
Q(ce Multicast \(ASM\) model defined in RFC 1)-.18 E -.55(11)-.55 G 2.5
(2[).55 G(2], and ar)-2.5 E 2.5(ec)-.18 G(apable of scalable)-2.5 E
(operation in asymmetric topologies such as Single-Sour)93.6 638.4 Q
(ce Multicast \(SSM\) [8] wher)-.18 E 2.5(et)-.18 G(her)-2.5 E(e)-.18 E
(may only be unicast r)93.6 650.4 Q(outing service fr)-.18 E(om the r)
-.18 E(eceivers to the sender\(s\).)-.18 E
(NORM operation is compatible with transport layer forwar)93.6 674.4 Q
2.5(de)-.18 G(rr)-2.5 E(or corr)-.18 E(ection coding)-.18 E
(techniques as described in [14] and congestion contr)93.6 686.4 Q
(ol mechanisms such as those described)-.18 E(in [17] and [18].)93.6
698.4 Q 2.5(Ap)5 G(rincipal limitation of NORM operation involves gr)
-2.5 E(oup size scalability)-.18 E(when network capacity for r)93.6
710.4 Q(eceiver feedback is very limited.)-.18 E(NORM operation is also)
5 E(governed by implementation buf)93.6 722.4 Q(fering constraints.)-.18
E(Buf)5 E(fering gr)-.18 E(eater than that r)-.18 E(equir)-.18 E(ed for)
-.18 E(Adamson, et al.)72 768 Q(Expir)96.06 E(es: 17 Mar)-.18 E(ch 2006)
-.18 E([Page 25])124.71 E 0 Cg EP
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/F0 10/Palatino-Roman@0 SF 99.635(Internet-Draft NORM)72 66 R
(Building Blocks)2.5 E(October 2005)106.015 E(typical point-to-point r)
93.6 120 Q(eliable transport \(e.g., TCP\) is r)-.18 E
(ecommended to allow for disparity in)-.18 E(the r)93.6 132 Q
(eceiver gr)-.18 E
(oup connectivity and to allow for the feedback delays r)-.18 E(equir)
-.18 E(ed to attain gr)-.18 E(oup)-.18 E(size scalability)93.6 144 Q(.)
-1.11 E/F1 10/Palatino-Bold@0 SF(4.)72 168 Q/F2 13/Palatino-Bold@0 SF
(Security Considerations)5 E F0(NORM pr)93.6 183.6 Q(otocols ar)-.18 E
2.5(ee)-.18 G
(xpected to be subject to the same sort of security vulnerabilities as)
-2.5 E(other IP and IP multicast pr)93.6 195.6 Q 2.5(otocols. NORM)-.18
F(is compatible with IP security \(IPsec\))2.5 E
(authentication mechanisms [21] that ar)93.6 207.6 Q 2.5(eR)-.18 G
(ECOMMENDED for pr)-2.5 E(otection against session)-.18 E(intr)93.6
219.6 Q(usion and denial of service attacks.)-.08 E 2.5(Ap)5 G
(articular thr)-2.5 E(eat for NACK based pr)-.18 E(otocols is that)-.18
E(of NACK r)93.6 231.6 Q(eplay attacks that would pr)-.18 E
(event a NORM sender fr)-.18 E(om making forwar)-.18 E 2.5(dp)-.18 G
-.18(ro)-2.5 G(gr).18 E(ess)-.18 E(in transmission.)93.6 243.6 Q
(Any standar)5 E 2.5(dI)-.18 G(Psec mechanisms that can pr)-2.5 E
(ovide pr)-.18 E(otection against such)-.18 E -.18(re)93.6 255.6 S
(play attacks ar).18 E 2.5(eR)-.18 G(ECOMMENDED for use.)-2.5 E
(Additionally)5 E 2.5(,N)-1.11 G(ORM pr)-2.5 E(otocol instantiations)
-.18 E(SHOULD consider pr)93.6 267.6 Q
(oviding support for their own NACK r)-.18 E(eplay attack pr)-.18 E
(otection when)-.18 E(network layer mechanisms ar)93.6 279.6 Q 2.5(en)
-.18 G(ot available.)-2.5 E(The IETF Multicast Security \(msec\) W)5 E
(orking)-.92 E(Gr)93.6 291.6 Q(oup is also developing solutions which m\
ay be applicable to NORM in the futur)-.18 E(e.)-.18 E F1(5.)72 315.6 Q
F2(Acknowledgements)5 E/F3 10/Palatino-Italic@0 SF(\(and these ar)2.5 E
2.5(en)-.18 G(ot Negative\))-2.5 E F0
(The authors would like to thank Rick Jones, and Joer)93.6 331.2 Q 2.5
(gW)-.18 G(idmer for their valuable comments)-3.05 E(on this document.)
93.6 343.2 Q(The authors would also like to thank the RMT working gr)5 E
(oup chairs,)-.18 E(Roger Kermode and Lor)93.6 355.2 Q(enzo V)-.18 E
(icisano, for their support in development of this specification,)-.55 E
(and Sally Floyd for her early inputs into this document.)93.6 367.2 Q
F1(6.)72 391.2 Q F2(References)5 E F1(6.1.)72 415.2 Q/F4 12
/Palatino-Bold@0 SF(Normative References)5 E F0([1] Bradner)93.6 430.8 Q
2.5(,S)-.74 G(., "Key wor)-2.5 E(ds for use in RFCs to Indicate Requir)
-.18 E(ement Levels", BCP 14, RFC)-.18 E(21)93.6 442.8 Q(19, Mar)-.55 E
(ch 1997.)-.18 E
([2] Deering, S., "Host Extensions for IP Multicasting", STD 5, RFC 1)
93.6 466.8 Q -.55(11)-.55 G(2, August 1989.).55 E F1(6.2.)72 490.8 Q F4
(Informative References)5 E F0([3] Mankin, A., Romanow)93.6 506.4 Q 2.5
(,A)-.92 G(., Bradner)-2.5 E 2.5(,S)-.74 G(., and V)-2.5 E 2.5(.P)-1.29
G(axson, "IETF Criteria for Evaluating)-2.5 E(Reliable Multicast T)93.6
518.4 Q(ransport and Application Pr)-.9 E
(otocols", RFC 2357, June 1998.)-.18 E([4] Clark, D. and D. T)93.6 542.4
Q(ennenhouse, "Ar)-.92 E
(chitectural Considerations for a New Generation of)-.18 E(Pr)93.6 554.4
Q 2.5(otocols". In)-.18 F(Pr)2.5 E 2.5(oc. ACM)-.18 F
(SIGCOMM, pages 201--208, September 1990.)2.5 E
([5] Kermode, R. and L. V)93.6 578.4 Q
(icisano, "Author Guidelines for Reliable Multicast T)-.55 E
(ransport \(RMT\))-.9 E(Building Blocks and Pr)93.6 590.4 Q
(otocol Instantiation documents", RFC 3269, April 2002.)-.18 E
([6] Nonnenmacher)93.6 614.4 Q 2.5(,J)-.74 G 2.5(.a)-2.5 G
(nd E. Biersack, "Optimal Multicast Feedback," in IEEE Infocom , San)
-2.5 E(Francisco, California, p. 964, Mar)93.6 626.4 Q(ch/April 1998.)
-.18 E([7] Macker)93.6 650.4 Q 2.5(,J)-.74 G
(., and R. Adamson, "Quantitative Pr)-2.5 E
(ediction of Nack Oriented Reliable Multicast)-.18 E
(\(NORM\) Feedback", Pr)93.6 662.4 Q
(oc. IEEE MILCOM 2002, October 2002.)-.18 E([8] Holbr)93.6 686.4 Q
(ook, H., "A Channel Model for Multicast", Ph.D. Dissertation, Stanfor)
-.18 E 2.5(dU)-.18 G(niversity)-2.5 E(,)-1.11 E
(Department of Computer Science, Stanfor)93.6 698.4 Q
(d, California, August 2001.)-.18 E(Adamson, et al.)72 768 Q(Expir)96.06
E(es: 17 Mar)-.18 E(ch 2006)-.18 E([Page 26])124.71 E 0 Cg EP
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(Building Blocks)2.5 E(October 2005)106.015 E([9] Luby)93.6 120 Q 2.5
(,M)-1.11 G(., V)-2.5 E(icisano, L., Gemmell, J., Rizzo, L., Handley)
-.55 E 2.5(,M)-1.11 G(., and J. Cr)-2.5 E(owcr)-.18 E(oft, "Forwar)-.18
E(d)-.18 E(Err)93.6 132 Q(or Corr)-.18 E
(ection \(FEC\) Building Block", RFC 3452, December 2002.)-.18 E
([10] Floyd, S., Jacobson, V)93.6 156 Q
(., McCanne, S., Liu, C., and L. Zhang. "A Reliable Multicast)-1.29 E
(Framework for Light-weight Sessions and Application Level Framing", Pr)
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(1] W)-.55 E(atson, M., "Basic Forwar)-.92 E 2.5(dE)-.18 G(rr)-2.5 E
(or Corr)-.18 E(ection \(FEC\) Schemes", Internet-Draft draft-ietf-)-.18
E(rmt-bb-fec-basic-schemes-r)93.6 216 Q(evised-00, July 2005.)-.18 E
([12] Metzner)93.6 240 Q 2.5(,J)-.74 G(., "An Impr)-2.5 E(oved Br)-.18 E
(oadcast Retransmission Pr)-.18 E(otocol", IEEE T)-.18 E(ransactions on)
-.9 E(Communications, V)93.6 252 Q 2.5(ol. Com-32,)-1.11 F
(No.6, June 1984.)2.5 E([13] Macker)93.6 276 Q 2.5(,J)-.74 G
(., "Reliable Multicast T)-2.5 E(ransport and Integrated Erasur)-.9 E
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(ection", Pr)-.18 E(oc. IEEE MILCOM 97, October)-.18 E(1997.)5 E
([14] Luby)93.6 312 Q 2.5(,M)-1.11 G(., V)-2.5 E
(icisano, L., Gemmell, J., Rizzo, L., Handley)-.55 E 2.5(,M)-1.11 G
(., and J. Cr)-2.5 E(owcr)-.18 E(oft, "The Use of)-.18 E(Forwar)93.6 324
Q 2.5(dE)-.18 G(rr)-2.5 E(or Corr)-.18 E
(ection \(FEC\) in Reliable Multicast", RFC 3453, December 2002.)-.18 E
([15] Gossink, D., and J. Macker)93.6 348 Q 2.5(,")-.74 G
(Reliable Multicast and Integrated Parity Retransmission)-2.5 E
(with Channel Estimation", IEEE GLOBECOM 98'.)93.6 360 Q([16] Ozdemir)
93.6 384 Q 2.5(,V)-.74 G
(., Muthukrishnan, S., and I. Rhee, "Scalable, Low-Over)-3.79 E
(head Network Delay)-.18 E(Estimation", NCSU/A)93.6 396 Q
(T&T White Paper)-.74 E 2.5(,F)-.74 G(ebr)-2.5 E(uary 1999.)-.08 E
([17] W)93.6 420 Q(idmer J., and M. Handley)-.55 E 2.5(,")-1.11 G
(Extending Equation-Based Congestion Contr)-2.5 E(ol to)-.18 E
(Multicast Applications", Pr)93.6 432 Q
(oc ACM SIGCOMM 2001, San Diego, August 2001.)-.18 E([18] Rizzo, L., "p\
gmcc: A TCP-Friendly Single-Rate Multicast Congestion Contr)93.6 456 Q
(ol Scheme",)-.18 E(Pr)93.6 468 Q
(oc ACM SIGCOMM 2000, Stockholm, August 2000.)-.18 E
([19] Pingali, S., T)93.6 492 Q(owsley)-.92 E 2.5(,D)-1.11 G
(., and J. Kur)-2.5 E(ose, "A Comparison of Sender)-.18 E
(-Initiated and Receiver)-.18 E(-)-.18 E
(Initiated Reliable Multicast Pr)93.6 504 Q 2.5(otocols". In)-.18 F(Pr)
2.5 E 2.5(oc. INFOCOM,)-.18 F(San Francisco, CA, October)2.5 E(1993.)
93.6 516 Q([20] Levine, B., and J.J. Gar)93.6 540 Q
(cia-Luna-Aceves, "A Comparison of Known Classes of Reliable)-.18 E
(Multicast Pr)93.6 552 Q(otocols", Pr)-.18 E 2.5(oc. International)-.18
F(Confer)2.5 E(ence on Network Pr)-.18 E(otocols \(ICNP-96\),)-.18 E
(Columbus, Ohio, Oct 29--Nov 1, 1996.)93.6 564 Q
([21] Kent, S. and R. Atkinson, "Security Ar)93.6 588 Q(chitectur)-.18 E
2.5(ef)-.18 G(or the Internet Pr)-2.5 E(otocol", RFC 2401,)-.18 E
(November 1998.)93.6 600 Q(Adamson, et al.)72 768 Q(Expir)96.06 E
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/F0 10/Palatino-Roman@0 SF 99.635(Internet-Draft NORM)72 66 R
(Building Blocks)2.5 E(October 2005)106.015 E/F1 10/Palatino-Bold@0 SF
(7.)72 120 Q/F2 13/Palatino-Bold@0 SF(Authors' Addresses)5 E F0
(Brian Adamson)93.6 135.6 Q(Naval Resear)93.6 147.6 Q(ch Laboratory)-.18
E -.92(Wa)93.6 159.6 S(shington, DC).92 E(20375)5 E
(EMail: adamson@itd.nrl.navy)93.6 183.6 Q(.mil)-1.11 E(Carsten Bormann)
93.6 219.6 Q(Universitaet Br)93.6 231.6 Q(emen TZI)-.18 E
(Postfach 330440)93.6 243.6 Q(D-28334 Br)93.6 255.6 Q(emen, Germany)-.18
E(EMail: cabo@tzi.or)93.6 279.6 Q(g)-.18 E(Mark Handley)93.6 315.6 Q
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93.6 339.6 Q(Gower Str)93.6 351.6 Q(eet)-.18 E(London)93.6 363.6 Q
(WC1E 6BT)93.6 375.6 Q(UK)93.6 387.6 Q(EMail: M.Handley@cs.ucl.ac.uk)
93.6 411.6 Q(Joe Macker)93.6 447.6 Q(Naval Resear)93.6 459.6 Q
(ch Laboratory)-.18 E -.92(Wa)93.6 471.6 S(shington, DC).92 E(20375)5 E
(EMail: macker@itd.nrl.navy)93.6 495.6 Q(.mil)-1.11 E F1(8.)72 519.6 Q
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