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E -.25(va)54 552 S(ry between).25 E(lo)5 E 2.5(wn)-.25 G(umbers of kbit\
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s, with v)-2.5 E(arying)-.25 E(de)54 564 Q
(grees of contention from other \215o)-.15 E 2.5(ws. Recently)-.25 F 2.5
(,an)-.65 G(umber of asymmetric netw)-2.5 E
(ork services including 56K/ADSL modems,)-.1 E(CA)54 576 Q(TV Internet \
service, satellite and other wireless communication services ha)-1.11 E
.3 -.15(ve b)-.2 H -.15(eg).15 G(un to proliferate.).15 E(Man)7.5 E 2.5
(yo)-.15 G 2.5(ft)-2.5 G(hese are)-2.5 E
(inherently broadcast media with potentially lar)54 588 Q 2.5(ge "f)-.18
F(anouts" to which IP multicast service is highly applicable.)-.1 E
(Additionally)5 E(,)-.65 E(polic)54 600 Q 2.5(ya)-.15 G(nd/or technical\
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(\(SSM\) model from a speci\214c source [17].)54 612 Q(Recei)5 E -.15
(ve)-.25 G(rs in the group may be restricted to unicast feedback for N)
.15 E -.4(AC)-.35 G(Ks and).4 E(other messages.)54 624 Q
(Consideration must be gi)5 E -.15(ve)-.25 G(n, in b).15 E
(uilding block de)-.2 E -.15(ve)-.25 G
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/F0 10/Times-Roman@0 SF(Internet Draft)36 48 Q(NORM Building Blocks)
155.605 E(June 2003)169.475 E/F1 10/Times-Bold@0 SF
(2.7 Router/Intermediate System Assistance)36 84 Q F0
(While intermediate assistance from de)54 108 Q
(vices/systems with direct kno)-.25 E(wledge of the underlying netw)-.25
E(ork topology may be used)-.1 E(to le)54 120 Q -.15(ve)-.25 G(rage the\
 performance and scalability of reliable multicast protocols, there wil\
l continue to be a number of instances).15 E(where this is not a)54 132
Q -.25(va)-.2 G(ilable or practical.).25 E(An)5 E 2.5(yb)-.15 G
(uilding block components for N)-2.7 E -.4(AC)-.35 G
(K-oriented reliable multicast SHALL be).4 E
(capable of operating without such assistance.)54 144 Q(Ho)5 E(we)-.25 E
-.15(ve)-.25 G .8 -.4(r, i).15 H 2.5(ti).4 G 2.5(sR)-2.5 G
(ECOMMENDED that such protocols also be capable of)-2.5 E
(utilizing these features when a)54 156 Q -.25(va)-.2 G 2.5(ilable. The)
.25 F(Generic Router Assist b)2.5 E
(uilding block documents address this type of)-.2 E
(functionality for reliable multicast protocols [15].)54 168 Q F1
(3.0 Functionality)36 192 Q F0(The pre)54 216 Q
(vious section has presented the role of protocol b)-.25 E
(uilding blocks and some of the criteria that may af)-.2 E(fect NORM)
-.25 E -.2(bu)54 228 S
(ilding block identi\214cation/design. This section describes dif).2 E
(ferent b)-.25 E(uilding block areas applicable to NORM protocols.)-.2 E
(Some of these areas are speci\214c to N)54 240 Q -.4(AC)-.35 G
(K-oriented protocols.).4 E(Detailed descriptions of such)5 E
(areas are pro)5 E 2.5(vided. In)-.15 F(other)2.5 E
(cases, the areas \(e.g., node identi\214ers, forw)54 252 Q(ard error c\
orrection \(FEC\), etc\) may be applicable to other forms of reliable)
-.1 E 2.5(multicast. In)54 264 R(those cases, the discussion belo)2.5 E
2.5(wd)-.25 G(escribes requirements placed on those other general b)-2.5
E(uilding block areas)-.2 E(from the standpoint of N)54 276 Q -.4(AC)
-.35 G(K-oriented reliable multicast.).4 E(Where applicable, other b)5 E
(uilding block documents are referenced)-.2 E(for possible contrib)54
288 Q(ution to NORM protocols.)-.2 E -.15(Fo)54 312 S 2.5(re).15 G
(ach b)-2.5 E(uilding block, a notional "interf)-.2 E
(ace description" is pro)-.1 E(vided to illustrate an)-.15 E 2.5(yd)-.15
G(ependencies of one b)-2.5 E(uilding block)-.2 E
(component upon another or upon other protocol parameters.)54 324 Q 2.5
(Ab)5 G(uilding block component may require some form of "input")-2.7 E
(from another b)54 336 Q
(uilding block component or other source to perform its function.)-.2 E
(An)5 E 2.5(y")-.15 G(inputs" required by a b)-2.5 E(uilding block)-.2 E
(component and/or an)54 348 Q 2.5(yr)-.15 G(esultant "output" pro)-2.5 E
(vided will be de\214ned and described in each b)-.15 E
(uilding block components')-.2 E(s)-.55 E(interf)54 360 Q
(ace description.)-.1 E(Note that the set of b)5 E
(uilding blocks presented here do not fully satisify each other')-.2 E
2.5(s")-.55 G(input" and)-2.5 E("output" needs.)54 372 Q
(In some cases, "inputs" for the b)5 E
(uilding blocks here must come from other b)-.2 E(uilding blocks e)-.2 E
(xternal to this)-.15 E(document \(e.g., congestion control or FEC\).)54
384 Q(In other cases NORM b)5 E
(uilding block "inputs" must be satis\214ed by the speci\214c)-.2 E(pro\
tocol instantiation or implementation \(e.g., application data and cont\
rol\).)54 396 Q(The follo)54 420 Q(wing b)-.25 E
(uilding block components are described belo)-.2 E(w:)-.25 E/F2 10
/Times-BoldItalic@0 SF(\(NORM-Speci\214c\))54 444 Q F0 25.17(1\) Sender)
90 456 R -.35(Tr)2.5 G(ansmission).35 E 25.17(2\) NORM)90 468 R
(Repair Process)2.5 E 25.17(3\) Recei)90 480 R -.15(ve)-.25 G 2.5(rJ).15
G(oin Policies)-2.5 E F2(\(General Purpose\))54 504 Q F0 25.17(4\) Node)
90 516 R(\(member\) Identi\214cation)2.5 E 25.17(5\) Data)90 528 R
(Content Identi\214cation)2.5 E 25.17(6\) F)90 540 R(orw)-.15 E
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(Ti)2.5 G(ming Collection).35 E 25.17(8\) Group)90 564 R
(Size Determination/Estimation)2.5 E 25.17(9\) Congestion)90 576 R
(Control Operation)2.5 E 20.17(10\) Router/Intermediate)90 588 R
(System Assistance)2.5 E 20.17(11\) Ancillary)90 600 R
(Protocol Mechanisms)2.5 E(Figure 1 pro)54 624 Q(vides an pictoral o)
-.15 E -.15(ve)-.15 G(rvie).15 E 2.5(wo)-.25 G 2.5(ft)-2.5 G(hese b)-2.5
E(uilding block areas and some of their relationships.)-.2 E -.15(Fo)5 G
2.5(re).15 G(xample, the)-2.65 E(content of the data messages that send\
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Content)54 636 Q(Identi\214cation", and "FEC" components whil the rate \
of message transmission will generally depend upon the "Congestion)54
648 Q(Adamson, Bormann, et al.)36 696 Q(Expires December 2003)105.89 E
([P)124.09 E(age 4])-.15 E EP
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/F0 10/Times-Roman@0 SF(Internet Draft)36 48 Q(NORM Building Blocks)
155.605 E(June 2003)169.475 E(Control" component.)54 84 Q(Subsequently)5
E 2.5(,t)-.65 G(he recei)-2.5 E -.15(ve)-.25 G
(rs' response to these transmissions \(e.g., N).15 E -.4(AC)-.35 G
(King for repair\) will depend).4 E
(upon the data message content and inputs from other b)54 96 Q
(uilding block components.)-.2 E(Finally)5 E 2.5(,t)-.65 G(he sender')
-2.5 E 2.5(sp)-.55 G(rocessing of recei)-2.5 E -.15(ve)-.25 G(r).15 E
(responses will feed back into its transmission strate)54 108 Q(gy)-.15
E(.)-.65 E/F1 10/Courier@0 SF(Application Data and Control)258 132 Q(|)
330 144 Q(v)330 156 Q 66
(.---------------------. .-----------------------.)60 168 R 6(|N)60 180
S(ode Identification |----------->|)-6 E(Sender Transmission)12 E
(|<------.)12 E 36(`---------------------' _.-')60 192 R 36
(`-----------------------' |)6 F 12(.---------------------. _.-')60 204
R 66(.' |)6 F 18(.--------------. |)6 F 6(|D)60 216 S
(ata Identification |--')-6 E 72(.'' |)18 F 12(|J)6 G(oin Policy |)-12 E
(|)24 E 18(`---------------------' .')60 228 R 84('v)6 G 18
(`--------------' |)-78 F 6(.---------------------. .' ')60 240 R 30
(.------------------------. |)30 F(.->| Congestion Control)42 252 Q 12
(|-' ')12 F 6(|R)36 G(eceiver NACK)-6 E 36(||)60 G 12(|`)42 264 S 12
(---------------------' .')-12 F 6(|R)42 G(epair Process)-6 E 36(||)54 G
12(|.)42 276 S(---------------------. .')-12 E 6(|.)54 G 12
(------------------. |)-6 F(|)36 E 18 12(|| F)42 288 T 54(EC |'. |)-12 F
6(|N)6 G(ACK Initiation)-6 E -6 18(|| |)12 H 12(|`)42 300 S
(---------------------'` `._)-12 E 6(|`)42 G 12(------------------' |)-6
F(|)36 E 12(|.)42 312 S(---------------------. ``. `-._)-12 E 6(|.)18 G
12(------------------. |)-6 F(|)36 E 18(`--| RTT)42 324 R 12
(Collection |._`)6 F 24(``)6 G(->| | NACK Content)-24 E -6 18(|| |)30 H
(`---------------------' .`- `)60 336 Q 6(|`)36 G 12
(------------------' |)-6 F(|)36 E 6(.---------------------. \\)60 348 R
12(`-`._ |)6 F 12(.------------------. |)6 F(|)36 E 24(|G)60 360 S
(roup Size Est.)-24 E(|---.-`---`->| | NACK Suppression |)12 E 36(||)18
G 6(`---------------------'`. `)60 372 R 30(`|)6 G 12
(`------------------' |)-24 F(|)36 E 6(.---------------------. ` `)60
384 R 24(``)6 G 30(------------------------' |)-24 F 42(|O)60 396 S 48
(ther |)-42 F 12(``)18 G 78(`|)-6 G(.-----------------. |)-72 E 18
(`---------------------' `)60 408 R 54 6(`` ||)12 H
(Router Assistance| |)-6 E(`. ` `)228 420 Q 12(v`)66 G
(----------------' |)-12 E(`.`' .-------------------------.)240 432 Q(|)
30 E(`>| Sender NACK Processing)258 444 Q(|_____/)12 E 6(|a)270 456 S
(nd Repair Response)-6 E(|)30 E(`-------------------------')270 468 Q
150(^^)156 492 S 150(||)156 504 S(.-----------------------------.)144
516 Q 54(|\()144 528 S 54(Security\) |)-54 F
(`-----------------------------')144 540 Q/F2 10/Times-Italic@0 SF -.45
(Fi)210.06 564 S .3 -.15(g. 1 - N).45 H(ORM Building Bloc).15 E 2.5(kF)
-.2 G -.15(ra)-3.05 G(me).15 E(work)-.15 E F0(The components on the lef\
t side of this \214gure are areas that may be applicable be)54 588 Q
(yond NORM.)-.15 E(The most sign\214cant of these)5 E
(components, FEC and Congestion Control, are discussed in other b)54 600
Q(uilding block documents [13], [14].)-.2 E 2.5(Ab)5 G(rief description)
-2.5 E(of these areas and their role in the NORM protocol is gi)54 612 Q
-.15(ve)-.25 G 2.5(nb).15 G(elo)-2.5 E 3.8 -.65(w. T)-.25 H
(he components on the right are seen as speci\214c to).65 E
(NORM protocols, most notably the N)54 624 Q -.4(AC)-.35 G 2.5(Kr).4 G
(epair process.)-2.5 E(These areas are discussed in detail belo)7.5 E
3.8 -.65(w. S)-.25 H(ome other).65 E
(components \(e.g., "Security"\) impact man)54 636 Q 2.5(ya)-.15 G(spec\
ts of the protocol, and others such as "Router Assistance" may be more)
-2.5 E(transparent to the core protocol processing.)54 648 Q
(The sections belo)5 E 2.5(wd)-.25 G(iscuss issues with re)-2.5 E -.05
(ga)-.15 G(rds to these b).05 E(uilding block)-.2 E
(Adamson, Bormann, et al.)36 696 Q(Expires December 2003)105.89 E
([P)124.09 E(age 5])-.15 E EP
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/F0 10/Times-Roman@0 SF(Internet Draft)36 48 Q(NORM Building Blocks)
155.605 E(June 2003)169.475 E(components and their relationships.)54 84
Q(Where applicable, speci\214c technical recommendations are made for m\
echanisms that)5 E
(will properly satisfy the goals of NORM transport for the Internet.)54
96 Q/F1 10/Times-Bold@0 SF(3.1 Sender T)36 120 Q(ransmission)-.74 E F0
(Senders will transmit data content to the multicast session.)54 144 Q
2.5(The data)5 F(content will be application dependent.)2.5 E
(The sender will)5 E(transmit data content at a rate, and with message \
sizes, determined by application and/or netw)54 156 Q
(ork architecture requirements.)-.1 E(An)54 168 Q 2.5(yF)-.15 G(EC enco\
ding of sender transmissions SHOULD con\214rm with the guidelines of [1\
3].)-2.5 E(When congestion control)5 E(mechanisms are needed \(REQ)54
180 Q(UIRED for general Internet operation\), NORM transmission SHALL b\
e controlled by the)-.1 E(congestion control mechanism.)54 192 Q(In an)5
E 2.5(yc)-.15 G(ase, it is RECOMMENDED that all data transmissions from)
-2.5 E(NORM senders be)5 E(subject to rate limitations determined by th\
e application or congestion control algorithm.)54 204 Q(The sender')5 E
2.5(st)-.55 G(ransmissions)-2.5 E(SHOULD mak)54 216 Q 2.5(eg)-.1 G
(ood utilization of the a)-2.5 E -.25(va)-.2 G(ilable capacity \(which \
may be limited by the application and/or by congestion).25 E 2.5
(control\). As)54 228 R 2.5(ar)2.5 G(esult, it is e)-2.5 E
(xpected there will be o)-.15 E -.15(ve)-.15 G(rlap and multiple).15 E
(xing of ne)-.15 E 2.5(wd)-.25 G(ata content transmission with repair)
-2.5 E 2.5(content. Other)54 240 R -.1(fa)2.5 G(ctors related to applic\
ation operation may determine sender transmission formats and methods.)
.1 E -.15(Fo)5 G(r).15 E -.15(ex)54 252 S
(ample, some consideration needs to be gi).15 E -.15(ve)-.25 G 2.5(nt)
.15 G 2.5(ot)-2.5 G(he sender')-2.5 E 2.5(sb)-.55 G(eha)-2.5 E
(vior during intermittent idle periods when it has no data)-.2 E
(to transmit.)54 264 Q(In addition to data content, other sender messag\
es or commands may be emplo)54 288 Q(yed as part of protocol operation.)
-.1 E(These)5 E
(messages may occur outside of the scope of application data transfer)54
300 Q 5(.I)-.55 G 2.5(nN)-5 G
(ORM protocols, reliability of such protocol)-2.5 E
(messages may be attempted by redundant transmission when positi)54 312
Q .3 -.15(ve a)-.25 H(ckno).15 E(wledgement is prohibiti)-.25 E .3 -.15
(ve d)-.25 H(ue to group size).15 E(scalablity concerns.)54 324 Q
(Note that protocol design SHOULD pro)5 E
(vide mechanisms for dealing with cases where such messages)-.15 E
(are not recei)54 336 Q -.15(ve)-.25 G 2.5(db).15 G 2.5(yt)-2.5 G
(he group.)-2.5 E(As an e)5 E(xample, a command message might be redund\
antly transmitted by a sender to indicate)-.15 E
(that it is temporarily \(or permanently\) halting transmission.)54 348
Q(At this time, it may be appropriate for recei)5 E -.15(ve)-.25 G
(rs to respond with).15 E -.35(NA)54 360 S(CKs for an)-.05 E 2.5(yo)-.15
G(utstanding repairs the)-2.5 E 2.5(yr)-.15 G(equire follo)-2.5 E
(wing the rules of the NORM N)-.25 E -.4(AC)-.35 G 2.5(Kp).4 G 2.5
(rocedure. F)-2.5 F(or ef)-.15 E(\214cienc)-.25 E 1.3 -.65(y, t)-.15 H
(he).65 E(sender should allo)54 372 Q 2.5(ws)-.25 G(uf)-2.5 E
(\214cient time between the redundant transmissions to recei)-.25 E .3
-.15(ve a)-.25 H .3 -.15(ny N).15 H -.4(AC)-.2 G
(K-oriented responses from the).4 E(recei)54 384 Q -.15(ve)-.25 G
(rs to this command.).15 E(In general, when there is an)54 408 Q 2.5(yr)
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E(messages issued by a sender and other NORM protocol timeouts should b\
e dependent upon the group greatest round trip)54 420 Q(timing \()54 432
Q/F2 10/Courier@0 SF(GRTT)A F0 2.5(\)e)C(stimate and an)-2.5 E 2.5(ye)
-.15 G(xpected resultant N)-2.65 E -.4(AC)-.35 G 2.5(Ko).4 G 2.5(ro)-2.5
G(ther feedback operation.)-2.5 E(The NORM)5 E F2(GRTT)2.5 E F0
(is an estimate of)2.5 E(the w)54 444 Q
(orst-case round-trip timing from a sender to an)-.1 E 2.5(yr)-.15 G
(ecei)-2.5 E -.15(ve)-.25 G(rs in the group.).15 E
(It is assumed that the)5 E F2(GRTT)2.5 E F0(interv)2.5 E(al is a)-.25 E
(conserv)54 456 Q(ati)-.25 E .3 -.15(ve e)-.25 H(stimate of the maximum\
 span \(with respect to delay\) of the multicast group across a netw).15
E(ork topology with)-.1 E(respect to gi)54 468 Q -.15(ve)-.25 G 2.5(ns)
.15 G(ender)-2.5 E 5(.N)-.55 G(ORM instantiations SHOULD be able to dyn\
amically adapt to a wide range of multicast netw)-5 E(ork)-.1 E
(topologies.)54 480 Q(Adamson, Bormann, et al.)36 696 Q
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155.605 E(June 2003)169.475 E/F1 10/Times-BoldItalic@0 SF(Sender T)54 84
Q(ransmission Interface Description:)-.37 E/F2 10/Times-Italic@0 SF
(Inputs:)54 108 Q F0 25.17(1\) Application)90 132 R(data and control)2.5
E 25.17(2\) Sender)90 144 R(node identi\214er)2.5 E 25.17(3\) Data)90
156 R(identi\214ers)2.5 E 25.17(4\) Se)90 168 R
(gmentation and FEC parameters)-.15 E 25.17(5\) T)90 180 R
(ransmission rate)-.35 E 25.17(6\) Application)90 192 R(controls)2.5 E
25.17(7\) Recei)90 204 R -.15(ve)-.25 G 2.5(rf).15 G
(eedback messages \(e.g., N)-2.5 E -.4(AC)-.35 G(Ks\)).4 E F2(Outputs:)
54 228 Q F0 25.17(1\) Controlled)90 252 R(transmission of messages with\
 headers uniquely identifying data or repair content within the)2.5 E
(conte)126 264 Q(xt of the NORM session.)-.15 E 25.17(2\) Commands)90
276 R(indicating sender')2.5 E 2.5(ss)-.55 G
(tatus or other transport control actions to be tak)-2.5 E(en.)-.1 E/F3
10/Times-Bold@0 SF(3.2 NORM Repair Pr)36 300 Q(ocess)-.18 E F0 2.5(Ac)54
324 S(ritical component of NORM protocols is the N)-2.5 E -.4(AC)-.35 G
2.5(Kr).4 G(epair process.)-2.5 E(This includes the recei)5 E -.15(ve)
-.25 G(r').15 E 2.5(sr)-.55 G(ole in detecting and)-2.5 E
(requesting repair needs, and the sender')54 336 Q 2.5(sr)-.55 G
(esponse to such requests.)-2.5 E
(There are four primary elements of the NORM repair)5 E(process:)54 348
Q 25.17(1\) Recei)90 372 R -.15(ve)-.25 G 2.5(rN).15 G -.4(AC)-2.85 G
2.5(Kp).4 G(rocess initiation,)-2.5 E 25.17(3\) N)90 384 R -.4(AC)-.35 G
2.5(Ks).4 G(uppression,)-2.5 E 25.17(2\) N)90 396 R -.4(AC)-.35 G 2.5
(Km).4 G(essage content,)-2.5 E 25.17(4\) Sender)90 408 R -.35(NA)2.5 G
(CK processing and response.)-.05 E F1(3.2.1 Receiv)36 432 Q(er N)-.15 E
-.65(AC)-.3 G 2.5(KP).65 G(rocess Initiation)-2.5 E F0(The NORM N)54 456
Q -.4(AC)-.35 G 2.5(Kp).4 G(rocess \(c)-2.5 E
(ycle\) will be initiated by recei)-.15 E -.15(ve)-.25 G
(rs that detect a need for repair transmissions from a speci\214c).15 E
(sender to achie)54 468 Q .3 -.15(ve r)-.25 H(eliable reception.).15 E
(When FEC is applied, a recei)5 E -.15(ve)-.25 G 2.5(rs).15 G
(hould initiate the N)-2.5 E -.4(AC)-.35 G 2.5(Kp).4 G
(rocess only when it is)-2.5 E(kno)54 480 Q
(wn its repair requirements e)-.25 E
(xceed the amount of pending FEC transmission for a gi)-.15 E -.15(ve)
-.25 G 2.5(nc).15 G(oding block of data content.)-2.5 E(This can be det\
ermined at the end of the current transmission block \(if it is indicat\
ed\) or upon the start of reception of a)54 492 Q
(subsequent coding block or transmission object.)54 504 Q
(This implies the NORM data content is mark)5 E
(ed to identify its FEC block)-.1 E
(number and that ordinal relationship is preserv)54 516 Q
(ed in order of transmission.)-.15 E(Alternati)54 540 Q -.15(ve)-.25 G
(ly).15 E 2.5(,i)-.65 G 2.5(ft)-2.5 G(he sender')-2.5 E 2.5(st)-.55 G
(ransmission adv)-2.5 E(ertises the quantity of repair pack)-.15 E
(ets it is already planning to send for a block,)-.1 E(the recei)54 552
Q -.15(ve)-.25 G 2.5(rm).15 G(ay be able to initiate the N)-2.5 E -.4
(AC)-.35 G 2.5(Kp).4 G(rocessor earlier)-2.5 E 5(.A)-.55 G(llo)-5 E
(wing recei)-.25 E -.15(ve)-.25 G(rs to initiate N).15 E -.4(AC)-.35 G
2.5(Kc).4 G(ycles at an)-2.65 E 2.5(yt)-.15 G(ime the)-2.5 E(y)-.15 E
(detect their repair needs ha)54 564 Q .3 -.15(ve ex)-.2 H
(ceeded pending repair transmissions may result in slightly quick).15 E
(er repair c)-.1 E 2.5(ycles. Ho)-.15 F(we)-.25 E -.15(ve)-.25 G .8 -.4
(r, i).15 H(t).4 E(may be useful to limit N)54 576 Q -.4(AC)-.35 G 2.5
(Kp).4 G(rocess initiation to speci\214c e)-2.5 E -.15(ve)-.25 G
(nts such as at the end-of-transmission of an FEC coding block).15 E
(or upon detection of subsequent coding blocks.)54 588 Q(This can allo)5
E 2.5(wr)-.25 G(ecei)-2.5 E -.15(ve)-.25 G(rs to aggre).15 E -.05(ga)
-.15 G(te N).05 E -.4(AC)-.35 G 2.5(Kc).4 G
(ontent into a smaller number)-2.5 E(of N)54 600 Q -.4(AC)-.35 G 2.5(Km)
.4 G(essages and pro)-2.5 E
(vide some implicit loose synchronization among the recei)-.15 E -.15
(ve)-.25 G 2.5(rs).15 G(et to help f)-2.5 E(acilitate ef)-.1 E(fecti)
-.25 E -.15(ve)-.25 G(probabilistic suppression of N)54 612 Q -.4(AC)
-.35 G 2.5(Kf).4 G 2.5(eedback. The)-2.5 F(recei)2.5 E -.15(ve)-.25 G
2.5(rM).15 G(UST maintain a history of data content recei)-2.5 E -.15
(ve)-.25 G 2.5(df).15 G(rom the)-2.5 E
(sender to determine its current repair needs.)54 624 Q
(When FEC is emplo)5 E(yed, it is e)-.1 E
(xpected that the history will correspond to a)-.15 E
(record of pending or partially-recei)54 636 Q -.15(ve)-.25 G 2.5(dc).15
G(oding blocks.)-2.5 E(Adamson, Bormann, et al.)36 696 Q
(Expires December 2003)105.89 E([P)124.09 E(age 7])-.15 E EP
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/F0 10/Times-Roman@0 SF(Internet Draft)36 48 Q(NORM Building Blocks)
155.605 E(June 2003)169.475 E -.15(Fo)54 84 S 2.5(rp).15 G
(robabilistic, timer)-2.5 E(-base suppression of feedback, the N)-.2 E
-.4(AC)-.35 G 2.5(Kc).4 G(ycle should be)-2.65 E(gin with recei)-.15 E
-.15(ve)-.25 G(rs observing back).15 E(of)-.1 E(f)-.25 E 2.5
(timeouts. In)54 96 R(conjunction with initiating this back)2.5 E(of)-.1
E 2.5(ft)-.25 G(imeout, it is important that the recei)-2.5 E -.15(ve)
-.25 G(rs record the current position in).15 E(the sender')54 108 Q 2.5
(st)-.55 G(ransmission sequence at which the)-2.5 E 2.5(yi)-.15 G
(nitiate the N)-2.5 E -.4(AC)-.35 G 2.5(Kc).4 G 2.5(ycle. When)-2.65 F
(the suppression back)2.5 E(of)-.1 E 2.5(ft)-.25 G(imeout e)-2.5 E
(xpires,)-.15 E(the recei)54 120 Q -.15(ve)-.25 G(rs should only consid\
er their repair needs up to this recorded transmission position in maki\
ng the decision to).15 E(transmit or suppress a N)54 132 Q -.4(AC)-.35 G
2.5(K. W).4 F(ithout this restriction, suppression is greatly reduced a\
s additional content is recei)-.4 E -.15(ve)-.25 G 2.5(df).15 G(rom)-2.5
E(the sender during the time a N)54 144 Q -.4(AC)-.35 G 2.5(Km).4 G
(essage propag)-2.5 E(ates across the netw)-.05 E
(ork to the sender and other recei)-.1 E -.15(ve)-.25 G(rs.).15 E/F1 10
/Times-BoldItalic@0 SF(Receiv)54 168 Q(er N)-.15 E -.65(AC)-.3 G 2.5(KP)
.65 G(rocess Initiation Interface Description:)-2.5 E/F2 10
/Times-Italic@0 SF(Inputs:)54 192 Q F0 25.17(1\) Sender)90 216 R
(data content with sequencing identi\214ers from sender transmissions.)
2.5 E 25.17(2\) History)90 228 R(of content recei)2.5 E -.15(ve)-.25 G
2.5(df).15 G(rom sender)-2.5 E(.)-.55 E F2(Outputs:)54 252 Q F0 25.17
(1\) N)90 276 R -.4(AC)-.35 G 2.5(Kp).4 G(rocess initiation decision)
-2.5 E 25.17(2\) Recorded)90 288 R
(sender transmission sequence position.)2.5 E F1(3.2.2 N)36 312 Q -.65
(AC)-.3 G 2.5(KS).65 G(uppression)-2.5 E F0(An ef)54 336 Q(fecti)-.25 E
.3 -.15(ve N)-.25 H
(ORM feedback suppression mechanism is the use of random back).15 E(of)
-.1 E 2.5(ft)-.25 G(imeouts priot to N)-2.5 E -.4(AC)-.35 G 2.5(Kt).4 G
(ransmission by)-2.5 E(recei)54 348 Q -.15(ve)-.25 G
(rs requiring repairs[6].).15 E(Upon e)5 E(xpiration of the back)-.15 E
(of)-.1 E 2.5(ft)-.25 G(imeout, a recei)-2.5 E -.15(ve)-.25 G 2.5(rw).15
G(ill request repairs unless its pending)-2.5 E(repair needs ha)54 360 Q
.3 -.15(ve b)-.2 H(een completely superseded by N).15 E -.4(AC)-.35 G
2.5(Km).4 G(essages heard from other recei)-2.5 E -.15(ve)-.25 G
(rs \(when recei).15 E -.15(ve)-.25 G(rs are).15 E(multicasting N)54 372
Q -.4(AC)-.35 G(Ks\) or from some indicator from the sender).4 E 5(.W)
-.55 G(hen recei)-5 E -.15(ve)-.25 G(rs are unicasting N).15 E -.4(AC)
-.35 G 2.5(Km).4 G(essages, the sender)-2.5 E(may f)54 384 Q
(acilitate N)-.1 E -.4(AC)-.35 G 2.5(Ks).4 G(uppression by forw)-2.5 E
(arding a representation of N)-.1 E -.4(AC)-.35 G 2.5(Kc).4 G
(ontent it has recei)-2.5 E -.15(ve)-.25 G 2.5(dt).15 G 2.5(ot)-2.5 G
(he group at lar)-2.5 E(ge or)-.18 E(pro)54 396 Q(vide some other indic\
ator of the repair information it will be subsequently transmitting.)
-.15 E -.15(Fo)54 420 S 2.5(re).15 G -.25(ff)-2.5 G(ecti).25 E .3 -.15
(ve a)-.25 H(nd scalable suppression performance, the back).15 E(of)-.1
E 2.5(ft)-.25 G(imeout periods used by recei)-2.5 E -.15(ve)-.25 G
(rs should be independently).15 E(,)-.65 E(randomly pick)54 432 Q
(ed by recei)-.1 E -.15(ve)-.25 G(rs with a truncated e).15 E
(xponential distrib)-.15 E(ution [7].)-.2 E
(This results in the majority of the recei)5 E -.15(ve)-.25 G 2.5(rs).15
G(et)-2.5 E(holding of)54 444 Q 2.5(ft)-.25 G(ransmission of N)-2.5 E
-.4(AC)-.35 G 2.5(Km).4 G(essages under the)-2.5 E
(assumption that the smaller number of "early N)5 E -.4(AC)-.35 G -.25
(Ke).4 G(rs" will).25 E
(supersede the repair needs of the remainder of the group.)54 456 Q
(The mean of the distrib)5 E
(ution should be determined as a function of)-.2 E
(the current estimate of sender<->group)54 468 Q/F3 10/Courier@0 SF
(GRTT)2.5 E F0(and a group size estimate that is determined by other me\
chanisms within the)2.5 E
(protocol or preset by the multicast application.)54 480 Q 2.5(As)54 504
S(imple algorithm can be constructed to generate random back)-2.5 E(of)
-.1 E 2.5(ft)-.25 G(imeouts with the appropriate distrib)-2.5 E 2.5
(ution. Additionally)-.2 F(,)-.65 E
(the algorithm may be designed to optimize the back)54 516 Q(of)-.1 E
2.5(fd)-.25 G(istrib)-2.5 E(ution gi)-.2 E -.15(ve)-.25 G 2.5(nt).15 G
(he number of recei)-2.5 E -.15(ve)-.25 G
(rs \(R\) potentially generating).15 E 2.5(feedback. This)54 528 R
("optimization" minimizes the number of feedback messages \(e.g., N)2.5
E -.4(AC)-.35 G(K\) in the w).4 E(orst-case situation where)-.1 E
(all recei)54 540 Q -.15(ve)-.25 G(rs generate a N).15 E -.4(AC)-.35 G
(K. The maximum back).4 E(of)-.1 E 2.5(ft)-.25 G(imeout \()-2.5 E F3
(T_maxBackoff)A F0 2.5(\)c)C(an be set to control reliable deli)-2.5 E
-.15(ve)-.25 G(ry).15 E(latenc)54 552 Q 2.5(yv)-.15 G(ersus v)-2.65 E
(olume of feedback traf)-.2 E 2.5(\214c. A)-.25 F(lar)2.5 E(ger v)-.18 E
(alue of)-.25 E F3(T_maxBackoff)2.5 E F0(will result in a lo)2.5 E
(wer density of feedback)-.25 E(traf)54 564 Q(\214c for a gi)-.25 E -.15
(ve)-.25 G 2.5(nr).15 G(epair c)-2.5 E 2.5(ycle. A)-.15 F(smaller v)2.5
E(alue of)-.25 E F3(T_maxBackoff)2.5 E F0(results in shorter latenc)2.5
E 2.5(yw)-.15 G(hich also reduces the)-2.5 E -.2(bu)54 576 S -.25(ff).2
G(ering requirements of senders and recei).25 E -.15(ve)-.25 G
(rs for reliable transport.).15 E(Adamson, Bormann, et al.)36 696 Q
(Expires December 2003)105.89 E([P)124.09 E(age 8])-.15 E EP
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155.605 E(June 2003)169.475 E(Gi)54 84 Q -.15(ve)-.25 G 2.5(nt).15 G
(he recei)-2.5 E -.15(ve)-.25 G 2.5(rg).15 G(roup size \()-2.5 E/F1 10
/Courier@0 SF(R)A F0(\), and maximum allo)A(wed back)-.25 E(of)-.1 E 2.5
(ft)-.25 G(imeout \()-2.5 E F1(T_maxBackoff)A F0(\), random back)A(of)
-.1 E 2.5(ft)-.25 G(imeouts)-2.5 E(\()54 96 Q F1(t')A F0 2.5(\)w)C
(ith a truncated e)-2.5 E(xponential distrib)-.15 E(ution can be pick)
-.2 E(ed with the follo)-.1 E 2.5(wing algorithm:)-.25 F 25.17
(1\) Establish)90 120 R(an optimal mean \()2.5 E F1(L)A F0 2.5(\)f)C
(or the e)-2.5 E(xponential back)-.15 E(of)-.1 E 2.5(fb)-.25 G
(ased on the group size:)-2.5 E F1 6(L=l)126 144 S(n\(R\) + 1)-6 E F0
25.17(2\) Pick)90 168 R 2.5(ar)2.5 G(andom number \()-2.5 E F1(x)A F0
2.5(\)f)C(rom a uniform distrib)-2.5 E(ution o)-.2 E -.15(ve)-.15 G 2.5
(rar).15 G(ange of:)-2.5 E F1 162(LL)162 192 S(L)-48 E 6
(-------------------- to)114 204 R 6(-------------------- + ----------)
18 F 18(T_maxBackoff*\(exp\(L\)-1\) T_maxBackoff*\(exp\(L\)-1\))108 216
R(T_maxBackoff)12 E F0 25.17(3\) T)90 240 R(ransform this random v)-.35
E(ariate to generate the desired random back)-.25 E(of)-.1 E 2.5(ft)-.25
G(ime \()-2.5 E F1(t')A F0 2.5(\)w)C(ith the follo)-2.5 E(wing)-.25 E
(equation:)126 252 Q F1
(t' = T_maxBackoff/L * ln\(x * \(exp\(L\) - 1\) * \(T_maxBackoff/L\)\))
126 276 Q F0(This)54 300 Q F1(C)2.5 E F0
(language function can be used to generate an appropriate random back)
2.5 E(of)-.1 E 2.5(ft)-.25 G(ime interv)-2.5 E(al:)-.25 E F1
(double RandomBackoff\(double maxTime, double groupSize\))54 324 Q({)54
336 Q(double lambda = log\(groupSize\) + 1;)78 348 Q
(double x = UniformRand\(lambda/maxTime\) +)78 360 Q
(lambda / \(maxTime*\(exp\(lambda\)-1\)\);)144 372 Q
(return \(\(maxTime/lambda\) *)78 384 Q
(log\(x*\(exp\(lambda\)-1\)*\(maxTime/lambda\)\)\);)126 396 Q 12(}/)54
408 S 6(/e)-12 G(nd RandomBackoff\(\))-6 E F0(where)54 432 Q F1
(UniformRand\(double max\))2.5 E F0
(returns random numbers with a uniform distrib)2.5 E
(ution from the range of)-.2 E F1(0..max)2.5 E F0(.)A -.15(Fo)54 444 S
2.5(re).15 G(xample, based on the POSIX ")-2.65 E F1(rand\(\))A F0 2.5
("f)C(unction, the follo)-2.5 E(wing C code can be used:)-.25 E F1(doub\
le UniformRand\(double max\) {return \(max * \(\(double\)rand\(\)/\(dou\
ble\)RAND_MAX\)\);})54 468 Q F0(The number of e)54 492 Q(xpected N)-.15
E -.4(AC)-.35 G 2.5(Km).4 G(essages generated \()-2.5 E F1(N)A F0 2.5
(\)w)C(ithin the \214rst round trip time for a single feedback e)-2.5 E
-.15(ve)-.25 G(nt is).15 E(approximately:)54 504 Q F1 6(N=e)184.2 528 S
(xp\(1.2 * L / \(2*T_maxBackoff/GRTT\)\))-6 E F0(Thus the maximum back)
54 552 Q(of)-.1 E 2.5(ft)-.25 G(ime can be adjusted to tradeof)-2.5 E
2.5(fw)-.25 G(orst-case N)-2.6 E -.4(AC)-.35 G 2.5(Kf).4 G(eedback v)
-2.5 E(olume v)-.2 E(ersus latenc)-.15 E 3.8 -.65(y. T)-.15 H(his is).65
E(deri)54 564 Q -.15(ve)-.25 G 2.5(df).15 G(rom [7] and assumes)-2.5 E
F1(T_maxBackoff >= GRTT)5 E F0 2.5(,a)C(nd)-2.5 E F1(L)2.5 E F0
(is the mean of the distrib)2.5 E(ution optimized for the gi)-.2 E -.15
(ve)-.25 G(n).15 E(group size as sho)54 576 Q(wn in the algorithm abo)
-.25 E -.15(ve)-.15 G 5(.N).15 G
(ote that other mechanisms within the protocol may w)-5 E
(ork to reduce redundant)-.1 E -.35(NA)54 588 S(CK generation further)
-.05 E 5(.I)-.55 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 inte)2.5 E
(ger multiple of the sender')-.15 E 2.5(sc)-.55 G(urrent)-2.5 E(adv)54
600 Q(ertised)-.15 E F1(GRTT)2.5 E F0(estimate such that:)2.5 E F1
(T_maxBackoff = K * GRTT)199.345 624 Q F0(;where)6 E F1 6(K>)2.5 G 6(=1)
-6 G F0 -.15(Fo)54 648 S 2.5(rg).15 G(eneral Internet operation, a def)
-2.5 E(ault v)-.1 E(alue of)-.25 E F1(K=4)2.5 E F0
(is RECOMMENDED for an)2.5 E 2.5(ys)-.15 G
(ource multicast \(ASM\) operation and a)-2.5 E
(Adamson, Bormann, et al.)36 696 Q(Expires December 2003)105.89 E
([P)124.09 E(age 9])-.15 E EP
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/F0 10/Times-Roman@0 SF(Internet Draft)36 48 Q(NORM Building Blocks)
155.605 E(June 2003)169.475 E -.25(va)54 84 S(lue of).25 E/F1 10
/Courier@0 SF(K=6)2.5 E F0(for SSM.)2.5 E(Alternate v)5 E
(alues may be used to for b)-.25 E(uf)-.2 E
(fer utliization, reliable deli)-.25 E -.15(ve)-.25 G(ry latenc).15 E
2.5(ya)-.15 G(nd group size)-2.5 E(scalability tradeof)54 96 Q(f.)-.25 E
(Gi)54 120 Q -.15(ve)-.25 G 2.5(nt).15 G(hat \()-2.5 E F1(K*GRTT)A F0
2.5(\)i)C 2.5(st)-2.5 G(he maximum back)-2.5 E(of)-.1 E 2.5(ft)-.25 G
(ime used by the recei)-2.5 E -.15(ve)-.25 G(rs to initiate N).15 E -.4
(AC)-.35 G 2.5(Kt).4 G(ransmission, other timeout)-2.5 E
(periods related to the N)54 132 Q -.4(AC)-.35 G 2.5(Kr).4 G
(epair process can be scaled accordingly)-2.5 E 5(.O)-.65 G
(ne of those timeouts is the amount of time a)-5 E(recei)54 144 Q -.15
(ve)-.25 G 2.5(rs).15 G(hould w)-2.5 E(ait after generating a N)-.1 E
-.4(AC)-.35 G 2.5(Km).4 G(essage before allo)-2.5 E
(wing itself to initiate another N)-.25 E -.4(AC)-.35 G 2.5(Kb).4 G(ack)
-2.5 E(of)-.1 E(f/transmission)-.25 E -.15(cy)54 156 S(cle \().15 E F1
(T_rcvrHoldoff)A F0 2.5(\). This)B(delay should be suf)2.5 E
(\214cient for the sender to respond to the recei)-.25 E -.15(ve)-.25 G
2.5(dN).15 G -.4(AC)-2.85 G 2.5(Kw).4 G(ith repair)-2.5 E 2.5
(messages. An)54 168 R(appropriate v)2.5 E
(alue depends upon the amount of time for the N)-.25 E -.4(AC)-.35 G 2.5
(Kt).4 G 2.5(or)-2.5 G(each the sender and the sender to)-2.5 E(pro)54
180 Q(vide a repair response.)-.15 E(This MUST include an)5 E 2.5(ya)
-.15 G(mount of sender N)-2.5 E -.4(AC)-.35 G 2.5(Ka).4 G(ggre)-2.5 E
-.05(ga)-.15 G(tion period during which possible).05 E(multiple N)54 192
Q -.4(AC)-.35 G(Ks are accumulated to determine an ef).4 E
(\214cient repair response.)-.25 E
(These timeouts are further discussed in the)5 E(section belo)54 204 Q
2.5(wo)-.25 G 2.5(n")-2.5 G(Sender N)-2.5 E -.4(AC)-.35 G 2.5(KP).4 G
(rocessing and Repair Response".)-2.5 E
(There are also secondary measures that can be applied to impro)54 228 Q
.3 -.15(ve t)-.15 H(he performance of feedback suppression.).15 E -.15
(Fo)5 G 2.5(re).15 G(xample,)-2.65 E(the sender')54 240 Q 2.5(sd)-.55 G
(ata content transmissions can follo)-2.5 E 2.5(wa)-.25 G 2.5(no)-2.5 G
(rdinal sequence of transmission.)-2.5 E
(When repairs for data content occur)5 E(,)-.4 E(the recei)54 252 Q -.15
(ve)-.25 G 2.5(rc).15 G(an note that the sender has "re)-2.5 E -.1(wo)
-.25 G(und" its data content transmission position by observing the dat\
a object, FEC).1 E(block number)54 264 Q 2.5(,a)-.4 G
(nd FEC symbol identi\214ers. Recei)-2.5 E -.15(ve)-.25 G
(rs SHOULD limit transmission of N).15 E -.4(AC)-.35 G
(Ks to only when the sender').4 E(s)-.55 E
(current transmission position e)54 276 Q
(xceeds the point to which the recei)-.15 E -.15(ve)-.25 G 2.5(rh).15 G
(as incomplete reception. This reduces premature)-2.5 E
(requests for repair of data the sender may be planning to pro)54 288 Q
(vide in response to other recei)-.15 E -.15(ve)-.25 G 2.5(rr).15 G 2.5
(equests. This)-2.5 F(mechanism can)2.5 E(be v)54 300 Q(ery ef)-.15 E
(fecti)-.25 E .3 -.15(ve f)-.25 H(or protocol con).15 E -.15(ve)-.4 G
-.18(rg).15 G(ence in high loss conditions when transmissions of N).18 E
-.4(AC)-.35 G(Ks from other recei).4 E -.15(ve)-.25 G(rs \(or).15 E
(indicators from the sender\) are lost.)54 312 Q(Another mechanism \(pa\
rticularly applicable when FEC is used\) is for the sender to)5 E
(embed an indication of impending repair transmissions in current pack)
54 324 Q(ets sent.)-.1 E -.15(Fo)5 G 2.5(re).15 G
(xample, the indication may be as)-2.65 E(simple as an adv)54 336 Q
(ertisment of the number of FEC pack)-.15 E
(ets to be sent for the current applicable coding block.)-.1 E(Finally)
54 360 Q 2.5(,s)-.65 G(ome consideration might be gi)-2.5 E -.15(ve)-.25
G 2.5(nt).15 G 2.5(ou)-2.5 G(sing the N)-2.5 E -.4(AC)-.35 G
(King history of recei).4 E -.15(ve)-.25 G
(rs to weight their selection of N).15 E -.4(AC)-.35 G(K).4 E(back)54
372 Q(of)-.1 E 2.5(ft)-.25 G(imeout interv)-2.5 E 2.5(als. F)-.25 F
(or e)-.15 E(xample, if a recei)-.15 E -.15(ve)-.25 G 2.5(rh).15 G
(as historically been)-2.5 E -.15(ex)5 G(periencing the greatest de).15
E(gree of loss, it may)-.15 E(promote itself to)54 384 Q
(statistically N)5 E -.4(AC)-.35 G 2.5(Ks).4 G(ooner than other recei)
-2.5 E -.15(ve)-.25 G 2.5(rs. Note).15 F
(this requires there is correlation o)2.5 E -.15(ve)-.15 G 2.5(rs).15 G
(uccessi)-2.5 E -.15(ve)-.25 G(interv)54 396 Q
(als of time in the loss e)-.25 E(xperienced by a recei)-.15 E -.15(ve)
-.25 G 3.6 -.55(r. S).15 H(uch correlation MA).55 E 2.5(Yn)-1.05 G
(ot be present in multicast netw)-2.5 E 2.5(orks. This)-.1 F
(adjustment of back)54 408 Q(of)-.1 E 2.5(ft)-.25 G
(imeout selection may require the creation of an "early N)-2.5 E -.4(AC)
-.35 G(K" slot for these historical N).4 E -.4(AC)-.35 G -.25(Ke).4 G
(rs.).25 E(This additional slot in the N)54 420 Q -.4(AC)-.35 G 2.5(Kb)
.4 G(ack)-2.5 E(of)-.1 E 2.5(fw)-.25 G(indo)-2.5 E 2.5(ww)-.25 G
(ill result in a longer repair c)-2.5 E
(ycle process that may not be desirable for)-.15 E(some applications.)54
432 Q(The resolution of these trade-of)5 E
(fs may be dependent upon the protocol')-.25 E 2.5(st)-.55 G(ar)-2.5 E
(get application set or)-.18 E(netw)54 444 Q(ork.)-.1 E
(After the random back)54 468 Q(of)-.1 E 2.5(ft)-.25 G(imeout has e)-2.5
E(xpired, the recei)-.15 E -.15(ve)-.25 G 2.5(rw).15 G(ill mak)-2.5 E
2.5(ead)-.1 G(ecision on whether to generate a N)-2.5 E -.4(AC)-.35 G
2.5(Kr).4 G(epair)-2.5 E
(request or not \(i.e., it has been suppressed\).)54 480 Q(The N)5 E -.4
(AC)-.35 G 2.5(Kw).4 G(ill be suppressed when an)-2.5 E 2.5(yo)-.15 G
2.5(ft)-2.5 G(he follo)-2.5 E(wing conditions has)-.25 E(occurred:)54
492 Q 25.17(1\) The)90 516 R(accumulated state of N)2.5 E -.4(AC)-.35 G
(Ks heard from other recei).4 E -.15(ve)-.25 G(rs \(or forw).15 E
(arding of this state by the sender\) is)-.1 E
(equal to or supersedes the repair needs of the local recei)126 528 Q
-.15(ve)-.25 G 3.6 -.55(r. N).15 H(ote that the local recei).55 E -.15
(ve)-.25 G 2.5(rs).15 G(hould consider)-2.5 E(its repair needs only up \
to the sender transmission position recorded at the N)126 540 Q -.4(AC)
-.35 G 2.5(Kc).4 G(ycle initiation \(when)-2.65 E(the back)126 552 Q(of)
-.1 E 2.5(ft)-.25 G(imer w)-2.5 E(as acti)-.1 E -.25(va)-.25 G(ted\).)
.25 E(Adamson, Bormann, et al.)36 696 Q(Expires December 2003)105.89 E
([P)119.09 E(age 10])-.15 E EP
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155.605 E(June 2003)169.475 E 25.17(2\) The)90 84 R(sender')2.5 E 2.5
(sd)-.55 G(ata content transmission position "re)-2.5 E
(winds" to a point ordinally less than that of the lo)-.25 E(west)-.25 E
(sequence position of the local recei)126 96 Q -.15(ve)-.25 G(r').15 E
2.5(sr)-.55 G(epair needs. \(This detection of sender "re)-2.5 E
(wind" indicates the)-.25 E(sender has already responded to other recei)
126 108 Q -.15(ve)-.25 G 2.5(rr).15 G
(epair needs of which the local recei)-2.5 E -.15(ve)-.25 G 2.5(rm).15 G
(ay not ha)-2.5 E .3 -.15(ve b)-.2 H(een).15 E -2.3 -.15(aw a)126 120 T
2.5(re\). This).15 F("re)2.5 E(wind" e)-.25 E -.15(ve)-.25 G
(nt can occur an).15 E 2.5(yt)-.15 G(ime between 1\) when the N)-2.5 E
-.4(AC)-.35 G 2.5(Kc).4 G(ycle w)-2.65 E(as initiated with the)-.1 E
(back)126 132 Q(of)-.1 E 2.5(ft)-.25 G(imeout acti)-2.5 E -.25(va)-.25 G
(tion and 2\) the current moment when the back).25 E(of)-.1 E 2.5(ft)
-.25 G(imeout has e)-2.5 E(xpired to suppress the)-.15 E -.35(NA)126 144
S 2.5(CK. Another)-.05 F -.35(NA)2.5 G(CK c)-.05 E
(ycle must be initiated by the recei)-.15 E -.15(ve)-.25 G 2.5(rw).15 G
(hen the sender')-2.5 E 2.5(st)-.55 G(ransmission sequence)-2.5 E
(position e)126 156 Q(xceeds the recei)-.15 E -.15(ve)-.25 G(r').15 E
2.5(sl)-.55 G -.25(ow)-2.5 G(est ordinal repair point.).25 E
(Note it is possible that the local recei)5 E -.15(ve)-.25 G 2.5(rm).15
G(ay)-2.5 E(ha)126 168 Q .3 -.15(ve h)-.2 H
(ad its repair needs satis\214ed as a result of the sender').15 E 2.5
(sr)-.55 G(esponse to the repair needs of other recei)-2.5 E -.15(ve)
-.25 G(rs).15 E(and no further N)126 180 Q -.4(AC)-.35 G
(King is required.).4 E(If these conditions ha)54 204 Q .3 -.15(ve n)-.2
H(ot occurred and the recei).15 E -.15(ve)-.25 G 2.5(rs).15 G
(till has pending repair needs, a N)-2.5 E -.4(AC)-.35 G 2.5(Km).4 G
(essage is generated and)-2.5 E 2.5(transmitted. The)54 216 R -.35(NA)
2.5 G
(CK should consist of an accumulation of repair needs from the recei)
-.05 E -.15(ve)-.25 G(r').15 E 2.5(sl)-.55 G -.25(ow)-2.5 G
(est ordinal repair point up).25 E
(to the current sender transmission sequence position.)54 228 Q 2.5(As)5
G(ingle N)-2.5 E -.4(AC)-.35 G 2.5(Km).4 G
(essage should be generated and the N)-2.5 E -.4(AC)-.35 G 2.5(Km).4 G
(essage)-2.5 E(content should be truncated if it e)54 240 Q
(xceeds the payload size of single protocol message.)-.15 E(When such N)
5 E -.4(AC)-.35 G 2.5(Kp).4 G(ayload limits)-2.5 E(occur)54 252 Q 2.5
(,t)-.4 G(he N)-2.5 E -.4(AC)-.35 G 2.5(Kc).4 G
(ontent SHOULD contain requests for the ordinally lo)-2.5 E
(west repair content needed from the sender)-.25 E(.)-.55 E/F1 10
/Times-BoldItalic@0 SF -.3(NA)54 276 S
(CK Suppression Interface Description)-.35 E/F2 10/Times-Italic@0 SF
(Inputs:)54 300 Q F0 25.17(1\) N)90 324 R -.4(AC)-.35 G 2.5(Kp).4 G
(rocess initiation decision.)-2.5 E 25.17(2\) Recorded)90 336 R
(sender transmission sequence position.)2.5 E 25.17(3\) Sender)90 348 R
(GR)2.5 E(TT)-.6 E(.)-.74 E 25.17(4\) Sender)90 360 R
(group size estimate.)2.5 E 25.17(5\) Application-de\214ned)90 372 R
(bound on back)2.5 E(of)-.1 E 2.5(ft)-.25 G(imeout period.)-2.5 E 25.17
(6\) N)90 384 R -.4(AC)-.35 G(Ks from other recei).4 E -.15(ve)-.25 G
(rs.).15 E 25.17(7\) Pending)90 396 R
(repair indication from sender \(may be forw)2.5 E(arded N)-.1 E -.4(AC)
-.35 G(Ks\).).4 E 25.17(8\) Current)90 408 R
(sender transmission sequence position.)2.5 E F2(Outputs:)54 432 Q F0
25.17(1\) Y)90 456 R(es/no decision to generate N)-1 E -.4(AC)-.35 G 2.5
(Km).4 G(essage upon back)-2.5 E(of)-.1 E 2.5(ft)-.25 G(imer e)-2.5 E
(xpiration.)-.15 E F1(3.2.3 N)36 480 Q -.65(AC)-.3 G 2.5(KC).65 G
(ontent)-2.5 E F0(The content of N)54 504 Q -.4(AC)-.35 G 2.5(Km).4 G
(essages generated by reliable multicast recei)-2.5 E -.15(ve)-.25 G
(rs will include information detailing their current).15 E
(repair needs.)54 516 Q(The speci\214c information depends on the use a\
nd type of FEC in the NORM repair process.)5 E(The identi\214cation)5 E
(of repair needs is dependent upon the data content identi\214cation \(\
See Section 3.5 belo)54 528 Q 2.5(w\). At)-.25 F(the highest le)2.5 E
-.15(ve)-.25 G 2.5(lt).15 G(he N)-2.5 E -.4(AC)-.35 G(K).4 E
(content will identify the sender to which the N)54 540 Q -.4(AC)-.35 G
2.5(Ki).4 G 2.5(sa)-2.5 G(ddressed and the data transport object \(or s\
tream\) within the sender')-2.5 E(s)-.55 E
(transmission that needs repair)54 552 Q 5(.F)-.55 G
(or the indicated transport entity)-5.15 E 2.5(,t)-.65 G(he N)-2.5 E -.4
(AC)-.35 G 2.5(Kc).4 G(ontent will then identify the speci\214c FEC)-2.5
E(coding blocks and/or se)54 564 Q
(gments it requires to reconstruct the complete transmitted data.)-.15 E
(This content may consist of FEC)5 E(block erasure counts and/or e)54
576 Q(xplicit indication of missing blocks or se)-.15 E
(gments of data and FEC content.)-.15 E(It should also be)5 E
(noted that NORM can be ef)54 588 Q(fecti)-.25 E -.15(ve)-.25 G
(ly instantiated without a requirement for reliable N).15 E -.4(AC)-.35
G 2.5(Kd).4 G(eli)-2.5 E -.15(ve)-.25 G(ry using the techniques).15 E
(discussed here.)54 600 Q F1(3.2.3.1 N)54 624 Q -.65(AC)-.3 G 2.5(Ka).65
G(nd FEC Repair Strategies)-2.5 E F0
(Where FEC-based repair is used, the N)54 648 Q -.4(AC)-.35 G 2.5(Km).4
G(essage content will minimally need to identify the coding block\(s\) \
for which)-2.5 E(Adamson, Bormann, et al.)36 696 Q
(Expires December 2003)105.89 E([P)119.09 E(age 11])-.15 E EP
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/F0 10/Times-Roman@0 SF(Internet Draft)36 48 Q(NORM Building Blocks)
155.605 E(June 2003)169.475 E
(repair is needed and a count of erasures \(missing pack)54 84 Q
(ets\) for the coding block.)-.1 E
(Note that this assumes the FEC algorithm is)5 E
(capable of repairing _an)54 96 Q(y_ loss combination within the coding\
 block and that the quantity of unique FEC parity pack)-.15 E(ets the)
-.1 E(serv)54 108 Q(er has a)-.15 E -.25(va)-.2 G
(ilable to transmit is essentially unlimited \(i.e., the serv).25 E
(er will al)-.15 E -.1(wa)-.1 G(ys be able to pro).1 E(vide ne)-.15 E
1.3 -.65(w, u)-.25 H(nique,).65 E(pre)54 120 Q
(viously unsent parity pack)-.25 E(ets in response to an)-.1 E 2.5(ys)
-.15 G(ubsequent repair requests for the same coding block\).)-2.5 E
(In other cases,)5 E(the N)54 132 Q -.4(AC)-.35 G 2.5(Kc).4 G
(ontent will need to also _e)-2.5 E(xplicitly_ identify which se)-.15 E
(gments \(information and/or parity\) the recei)-.15 E -.15(ve)-.25 G
2.5(rr).15 G(equires to)-2.5 E
(successfully reconstruct the content of the coding block.)54 144 Q
(This will be true of man)5 E 2.5(ya)-.15 G
(pplicable small to medium size block)-2.5 E
(codes \(e.g., Reed Solomon\) that are capable of pro)54 156 Q
(vided a limited number of parity se)-.15 E
(gments per FEC coding block.)-.15 E(When FEC is not used as part of th\
e repair process, or the protocol instantiation is required to pro)54
180 Q(vide reliability e)-.15 E -.15(ve)-.25 G 2.5(nw).15 G(hen)-2.5 E
(the sender has transmitted all a)54 192 Q -.25(va)-.2 G
(ilable parity for a gi).25 E -.15(ve)-.25 G 2.5(nc).15 G
(oding block \(or the sender')-2.5 E 2.5(sa)-.55 G(bility to b)-2.5 E
(uf)-.2 E(fer transmission history)-.25 E(is e)54 204 Q(xceeded by the)
-.15 E/F1 10/Courier@0 SF(delay*bandwidth*loss)2.5 E F0
(characteristics of the netw)2.5 E(ork topology\), the N)-.1 E -.4(AC)
-.35 G 2.5(Kc).4 G(ontent will need to)-2.5 E(contain _e)54 216 Q 2.5
(xplicit_ coding)-.15 F(block and/or se)2.5 E
(gment loss information so that the sender can pro)-.15 E
(vide appropriate repair pack)-.15 E(ets)-.1 E
(and/or data retransmissions.)54 228 Q(Explicit loss information in N)5
E -.4(AC)-.35 G 2.5(Kc).4 G(ontent may also potentially serv)-2.5 E 2.5
(eo)-.15 G(ther purposes.)-2.5 E -.15(Fo)5 G(r).15 E -.15(ex)54 240 S(a\
mple, it may be useful for decorrelating loss characteristics among a g\
roup of recei).15 E -.15(ve)-.25 G(rs to help dif).15 E
(ferentiate candidate)-.25 E
(congestion control bottlenecks among the recei)54 252 Q -.15(ve)-.25 G
2.5(rs).15 G(et.)-2.5 E(When FEC is used and N)54 276 Q -.4(AC)-.35 G
2.5(Kc).4 G(ontent is designed to contain e)-2.5 E
(xplicit repair requests, there is a strate)-.15 E(gy where the recei)
-.15 E -.15(ve)-.25 G(rs).15 E(can N)54 288 Q -.4(AC)-.35 G 2.5(Kf).4 G
(or speci\214c content that will help f)-2.5 E(acilitate N)-.1 E -.4(AC)
-.35 G 2.5(Ks).4 G(uppression and repair ef)-2.5 E(\214cienc)-.25 E 3.8
-.65(y. T)-.15 H(he assumptions for this).65 E(strate)54 300 Q
(gy are that sender may potentially e)-.15 E(xhaust its supply of ne)
-.15 E 1.3 -.65(w, u)-.25 H(nique parity pack).65 E(ets a)-.1 E -.25(va)
-.2 G(ilable for a gi).25 E -.15(ve)-.25 G 2.5(nc).15 G(oding block)-2.5
E(and be required to e)54 312 Q
(xplicitly retransmit some data or parity se)-.15 E
(gments to complete reliable transfer)-.15 E 5(.A)-.55 G
(nother assumption is)-5 E(that an FEC algorithm where an)54 324 Q 2.5
(yp)-.15 G(arity pack)-2.5 E(et can \214ll an)-.1 E 2.5(ye)-.15 G
(rasure within the coding block \(e.g., Reed Solomon\) is used.)-2.5 E
(The goal of this strate)54 336 Q(gy is to mak)-.15 E 2.5(em)-.1 G
(aximum use of the a)-2.5 E -.25(va)-.2 G(ilable parity and pro).25 E
(vide the minimal amount of data and repair)-.15 E
(transmissions during reliable transfer of data content to the group.)54
348 Q(When systematic FEC codes are used, the sender transmits the data\
 content of the coding block \(and optionally some)54 372 Q
(quantity of parity pack)54 384 Q(ets\) in its initial transmission.)-.1
E(Note that a systematic FEC coding block is considered to be logically)
5 E(made up of the contiguous set of data v)54 396 Q
(ectors plus parity v)-.15 E(ectors for the gi)-.15 E -.15(ve)-.25 G 2.5
(nF).15 G(EC algorithm used.)-2.5 E -.15(Fo)5 G 2.5(re).15 G
(xample, a coding)-2.65 E(scheme that pro)54 408 Q(vides for 64 data se)
-.15 E(gments and 32 parity se)-.15 E(gments per coding block w)-.15 E
(ould contain FEC symbol identi\214ers in)-.1 E(the range of 0 to 95.)54
420 Q(Recei)54 444 Q -.15(ve)-.25 G(rs then can construct N).15 E -.4
(AC)-.35 G 2.5(Km).4 G(essages requesting suf)-2.5 E
(\214cient content to satisfy their repair needs.)-.25 E -.15(Fo)5 G 2.5
(re).15 G(xample, if the)-2.65 E(recei)54 456 Q -.15(ve)-.25 G 2.5(rh)
.15 G(as three erasures in a gi)-2.5 E -.15(ve)-.25 G 2.5(nr).15 G(ecei)
-2.5 E -.15(ve)-.25 G 2.5(dc).15 G
(oding block, it will request transmission of the three lo)-2.5 E
(west ordinal parity)-.25 E -.15(ve)54 468 S
(ctors in the coding block. In our e).15 E
(xample coding scheme from the pre)-.15 E(vious paragraph, the recei)
-.25 E -.15(ve)-.25 G 2.5(rw).15 G(ould e)-2.6 E(xplicitly)-.15 E
(request parity se)54 480 Q
(gments 64 to 66 to \214ll its three erasures for the coding block.)-.15
E(Note that if the recei)5 E -.15(ve)-.25 G(r').15 E 2.5(sl)-.55 G
(oss for the coding)-2.5 E(block e)54 492 Q(xceeds the a)-.15 E -.25(va)
-.2 G(ilable parity quantity \(i.e., greater than 32 missing se).25 E
(gments in our e)-.15 E(xample\), the recei)-.15 E -.15(ve)-.25 G 2.5
(rw).15 G(ill be)-2.5 E(required to construct a N)54 504 Q -.4(AC)-.35 G
2.5(Kr).4 G(equesting all \(32\) of the a)-2.5 E -.25(va)-.2 G
(ilable parity se).25 E(gments plus some additional portions of its)-.15
E(missing data se)54 516 Q(gments in order to reconstruct the block.)
-.15 E(If this is done consistently across the recei)5 E -.15(ve)-.25 G
2.5(rg).15 G(roup, the resulting)-2.5 E -.35(NA)54 528 S(CKs will compr\
ise a minimal set of sender transmissions to satisfy their repair needs\
.)-.05 E(In summary)54 552 Q 2.5(,t)-.65 G(he rule is to request the lo)
-2.5 E(wer ordinal portion of the parity content for the FEC coding blo\
ck to satisfy the)-.25 E(erasure repair needs on the \214rst N)54 564 Q
-.4(AC)-.35 G 2.5(Kc).4 G 2.5(ycle. If)-2.65 F(the a)2.5 E -.25(va)-.2 G
(ilable number of parity se).25 E(gments is insuf)-.15 E
(\214cient, the recei)-.25 E -.15(ve)-.25 G 2.5(rw).15 G(ill also)-2.5 E
(request the subset of ordinally highest missing data se)54 576 Q
(gments to co)-.15 E -.15(ve)-.15 G 2.5(rw).15 G(hat the parity se)-2.5
E(gments will not \214ll.)-.15 E(Note this)5 E(strate)54 588 Q
(gy assumes FEC codes such as Reed-Solomon for which a single parity se)
-.15 E(gment can repair and erased se)-.15 E 2.5(gment. This)-.15 F
(strate)54 600 Q(gy w)-.15 E(ould need minor modi\214cation to tak)-.1 E
2.5(ei)-.1 G
(nto account the possibly limited repair capability of other FEC types.)
-2.5 E(On)5 E(subsequent N)54 612 Q -.4(AC)-.35 G 2.5(Kr).4 G(epair c)
-2.5 E(ycles where the recei)-.15 E -.15(ve)-.25 G 2.5(rm).15 G(ay ha)
-2.5 E .3 -.15(ve r)-.2 H(ecei).15 E -.15(ve)-.25 G 2.5(ds).15 G
(ome portion of its pre)-2.5 E(viously requested repair)-.25 E
(content, the recei)54 624 Q -.15(ve)-.25 G 2.5(rw).15 G
(ill use the same strate)-2.5 E(gy)-.15 E 2.5(,b)-.65 G(ut only N)-2.7 E
-.4(AC)-.35 G 2.5(Kf).4 G(or the set of parity and/or data se)-2.5 E
(gments it has not yet)-.15 E(recei)54 636 Q -.15(ve)-.25 G 2.5
(d. Optionally).15 F 2.5(,t)-.65 G(he recei)-2.5 E -.15(ve)-.25 G
(rs could also pro).15 E(vide a count of erasures as a con)-.15 E -.15
(ve)-.4 G(nience to the sender or intermediate).15 E
(systems assisting N)54 648 Q -.4(AC)-.35 G 2.5(Ko).4 G(peration.)-2.5 E
(Adamson, Bormann, et al.)36 696 Q(Expires December 2003)105.89 E
([P)119.09 E(age 12])-.15 E EP
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/F0 10/Times-Roman@0 SF(Internet Draft)36 48 Q(NORM Building Blocks)
155.605 E(June 2003)169.475 E(After receipt and accumulation of N)54 84
Q -.4(AC)-.35 G 2.5(Km).4 G(essages during the aggre)-2.5 E -.05(ga)-.15
G(tion period, the sender can be).05 E(gin transmission of fresh)-.15 E
(\(pre)54 96 Q(viously untransmitted\) parity se)-.25 E
(gments for the coding block based on the highest recei)-.15 E -.15(ve)
-.25 G 2.5(re).15 G(rasure count _if_ it has a)-2.5 E(suf)54 108 Q
(\214cient quantity of parity se)-.25 E(gments that were _not_ pre)-.15
E(viously transmitted.)-.25 E(Otherwise, the sender MUST resort to)5 E
(transmitting the e)54 120 Q(xplicit set of repair v)-.15 E
(ectors requested.)-.15 E -.4(Wi)5 G
(th this approach, the sender needs to maintain v).4 E
(ery little state on)-.15 E(requests it has recei)54 132 Q -.15(ve)-.25
G 2.5(df).15 G(rom the group without need for synchronization of repair\
 requests from the group.)-2.5 E(Since all)5 E(recei)54 144 Q -.15(ve)
-.25 G(rs use the same consistent algorithm to e).15 E(xpress their e)
-.15 E(xplicit repair needs, N)-.15 E -.4(AC)-.35 G 2.5(Ks).4 G
(uppression among recei)-2.5 E -.15(ve)-.25 G(rs is).15 E
(simpli\214ed o)54 156 Q -.15(ve)-.15 G 2.5(rt).15 G
(he course of multiple repair c)-2.5 E 2.5(ycles. The)-.15 F(recei)2.5 E
-.15(ve)-.25 G(rs can simply compare N).15 E -.4(AC)-.35 G
(Ks heard from other recei).4 E -.15(ve)-.25 G(rs).15 E(ag)54 168 Q
(ainst their o)-.05 E
(wn calculated repair needs to determine whether the)-.25 E 2.5(ys)-.15
G(hould transmit or suppress their pending N)-2.5 E -.4(AC)-.35 G(K).4 E
(messages.)54 180 Q/F1 10/Times-BoldItalic@0 SF(3.2.3.2 N)54 204 Q -.65
(AC)-.3 G 2.5(KC).65 G(ontent F)-2.5 E(ormat)-.7 E F0(The format of N)54
228 Q -.4(AC)-.35 G 2.5(Kc).4 G(ontent will depend on the protocol')-2.5
E 2.5(sd)-.55 G
(ata service model and the format of data content identi\214cation)-2.5
E(the protocol uses.)54 240 Q(This N)5 E -.4(AC)-.35 G 2.5(Kf).4 G
(ormat also depends upon the type of FEC encoding \(if an)-2.5 E
(y\) is used.)-.15 E(Figure 2 illustrates a)5 E(logical, hierarchical t\
ransmission content identi\214cation scheme, denoting that the notion o\
f objects \(or streams\) and/or FEC)54 252 Q
(blocking is optional at the protocol instantiation')54 264 Q 2.5(sd)
-.55 G 2.5(iscretion. Note)-2.5 F
(that the identi\214cation of objects is with respect to a gi)2.5 E -.15
(ve)-.25 G(n).15 E(sender)54 276 Q 5(.I)-.55 G 2.5(ti)-5 G 2.5(sr)-2.5 G
(ecommended that transport data content identi\214cation is done within\
 the conte)-2.5 E(xt of a sender in a gi)-.15 E -.15(ve)-.25 G 2.5(ns)
.15 G(ession.)-2.5 E(Since the notion of session "streams" and "blocks"\
 is optional, the frame)54 288 Q -.1(wo)-.25 G(rk de).1 E
(generates to that of typical transport data)-.15 E(se)54 300 Q
(gmentation and reassembly in its simplest form.)-.15 E/F2 10/Courier@0
SF(Session_)54 336 Q(\\_)108 348 Q(Sender_)126 360 Q(\\_)174 372 Q
([Object/Stream\(s\)]_)192 384 Q(\\_)306 396 Q([FEC Blocks]_)324 408 Q
(\\_)402 420 Q(Segments)420 432 Q/F3 10/Times-Italic@0 SF -.45(Fi)
192.455 456 S(gur).45 E 2.5(e2)-.37 G 2.5(:N)-2.5 G
(ORM Data Content Identi\214cation Hier)-2.5 E(ar)-.15 E -.15(ch)-.37 G
(y).15 E F0(The format of N)54 480 Q -.4(AC)-.35 G 2.5(Km).4 G
(essages should meet the follo)-2.5 E(wing goals:)-.25 E 25.17(1\) Able)
90 504 R(to identify transport data unit transmissions required to repa\
ir a portion of the recei)2.5 E -.15(ve)-.25 G 2.5(dc).15 G(ontent,)-2.5
E(whether it is an entire missing object/stream \(or range\), entire FE\
C coding block\(s\), or sets of se)126 516 Q(gments,)-.15 E 25.17
(2\) Be)90 540 R(simple to process for N)2.5 E -.4(AC)-.35 G 2.5(Ka).4 G
(ggre)-2.5 E -.05(ga)-.15 G(tion and suppression,).05 E 25.17(3\) Be)90
564 R(capable of including N)2.5 E -.4(AC)-.35 G
(Ks for multiple objects, FEC coding blocks and/or symbols in a single)
.4 E 2.5(message. FEC)126 576 R(erasure counts may also be desirable.)
2.5 E 25.17(4\) Ha)90 600 R .3 -.15(ve a r)-.2 H
(easonably compact format, and).15 E 25.17(5\) Be)90 624 R(capable of w)
2.5 E(orking with the Generic Router Assist \(GRA\) b)-.1 E
(uilding block.)-.2 E
(If the NORM transport object/stream is identi\214ed with an)54 648 Q F3
(<objectId>)2.5 E F0(and the FEC se)2.5 E
(gment being transmitted is identi\214ed)-.15 E
(Adamson, Bormann, et al.)36 696 Q(Expires December 2003)105.89 E
([P)119.09 E(age 13])-.15 E EP
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/F0 10/Times-Roman@0 SF(Internet Draft)36 48 Q(NORM Building Blocks)
155.605 E(June 2003)169.475 E(with and)54 84 Q/F1 10/Times-Italic@0 SF
(<fecP)2.5 E(ayloadId>)-.8 E F0 2.5(,t)C(he concatenation of)-2.5 E F1
(<objectId::fecP)2.5 E(ayloadId>)-.8 E F0
(comprises a basic transport protocol data unit)2.5 E
(\(TPDU\) identi\214er for se)54 96 Q(gments from a gi)-.15 E -.15(ve)
-.25 G 2.5(ns).15 G 2.5(ource. N)-2.5 F -.4(AC)-.35 G 2.5(Kc).4 G
(ontent can be composed of lists and/or ranges of these TPDU)-2.5 E
(identi\214ers to b)54 108 Q(uild up N)-.2 E -.4(AC)-.35 G 2.5(Km).4 G
(essages to describe the recei)-2.5 E -.15(ve)-.25 G(rs repair needs.)
.15 E(If no hierarchical object delineation or FEC)5 E(blocking is used\
, the TPDU is a simple linear representation of the data se)54 120 Q
(gments transmitted by the sender)-.15 E 5(.W)-.55 G(hen the)-5 E
(TPDU represents a hierarch)54 132 Q 2.5(yf)-.05 G
(or purposes of object/stream delineation and/or FEC blocking, the N)
-2.5 E -.4(AC)-.35 G 2.5(Kc).4 G(ontent unit may)-2.5 E
(require \215ags to indicate which portion of the TPDU is applicable.)54
144 Q -.15(Fo)5 G 2.5(re).15 G
(xample, if an entire "object" \(or range of objects\) is)-2.65 E
(missing in the recei)54 156 Q -.15(ve)-.25 G 2.5(dd).15 G
(ata, the recei)-2.5 E -.15(ve)-.25 G 2.5(rw).15 G
(ill not necessarily kno)-2.5 E 2.5(wt)-.25 G(he appropriate range of)
-2.5 E F1(<sour)2.5 E(ceBloc)-.37 E(kNumber)-.2 E(s>)-.1 E F0(or)2.5 E
F1(<encodingSymbolIds>)54 168 Q F0(for which to request repair and thus\
 requires some mechanism to request repair \(or retransmission\) of)2.5
E(the entire unit represented by an)54 180 Q F1(<objectId>)2.5 E F0 5
(.T)C(he same is true if entire FEC coding blocks represented by one or\
 a range of)-5 E F1(<sour)54 192 Q(ceBloc)-.37 E(kNumber)-.2 E(s>)-.1 E
F0(ha)2.5 E .3 -.15(ve b)-.2 H(een lost.).15 E/F2 10/Times-BoldItalic@0
SF -.3(NA)54 216 S(CK Content Interface Description)-.35 E F1(Inputs:)54
240 Q F0 25.17(1\) Sender)90 264 R(identi\214cation.)2.5 E 25.17
(2\) Sender)90 276 R(data identi\214cation.)2.5 E 25.17(3\) Sender)90
288 R(FEC Object T)2.5 E(ransmission Information.)-.35 E 25.17
(4\) Recorded)90 300 R(sender transmission sequence position.)2.5 E
25.17(5\) Current)90 312 R(sender transmission sequence position.)2.5 E
25.17(5\) History)90 324 R(of repair needs for this sender)2.5 E(.)-.55
E F1(Outputs:)54 348 Q F0 25.17(1\) N)90 372 R -.4(AC)-.35 G 2.5(Km).4 G
(essage with repair requests.)-2.5 E F2(3.2.4 Sender Repair Response)36
396 Q F0(Upon reception of a repair request from a recei)54 420 Q -.15
(ve)-.25 G 2.5(ri).15 G 2.5(nt)-2.5 G
(he group, the sender will initiate a repair response procedure.)-2.5 E
(The)5 E(sender may wish to delay transmission of repair content until \
it has had)54 432 Q(suf)5 E
(\214cient time to accumulate potentially multiple)-.25 E -.35(NA)54 444
S(CKs from the)-.05 E(recei)5 E -.15(ve)-.25 G 2.5(rs).15 G 2.5
(et. This)-2.5 F(allo)2.5 E(ws the sender to determine the most ef)-.25
E(\214cient repair strate)-.25 E(gy for a gi)-.15 E -.15(ve)-.25 G 2.5
(nt).15 G(ransport)-2.5 E(stream/object or FEC coding block.)54 456 Q(D\
epending upon the approach used, some protocols may \214nd it bene\214c\
ial for the sender)5 E(to pro)54 468 Q(vide an indicator of pending rep\
air transmissions as part of the its current transmitted message conten\
t.)-.15 E(This can aid)5 E(some N)54 480 Q -.4(AC)-.35 G 2.5(Ks).4 G
(uppression mechanisms.)-2.5 E(The amount of time to perform this N)5 E
-.4(AC)-.35 G 2.5(Ka).4 G(ggre)-2.5 E -.05(ga)-.15 G(tion should be suf)
.05 E(\214cient to allo)-.25 E(w)-.25 E(for the maximum recei)54 492 Q
-.15(ve)-.25 G 2.5(rN).15 G -.4(AC)-2.85 G 2.5(Kb).4 G(ack)-2.5 E(of)-.1
E 2.5(fw)-.25 G(indo)-2.5 E 2.5(w\()-.25 G(")-2.5 E/F3 10/Courier@0 SF
(T_maxBackoff)A F0 2.5("f)C(rom Section 3.2.2\) and propag)-2.5 E
(ation of N)-.05 E -.4(AC)-.35 G(K).4 E(messages from the recei)54 504 Q
-.15(ve)-.25 G(rs to the sender).15 E 5(.N)-.55 G
(ote the maximum transmission delay of a message from a recei)-5 E -.15
(ve)-.25 G 2.5(rt).15 G 2.5(ot)-2.5 G(he sender)-2.5 E
(may be approximately)54 516 Q F3(\(1*GRTT\))2.5 E F0(in the case of v)
2.5 E(ery asymmetric netw)-.15 E
(ork topology with respect to transmission delay)-.1 E(.)-.65 E
(Thus, if the maximum recei)54 528 Q -.15(ve)-.25 G 2.5(rN).15 G -.4(AC)
-2.85 G 2.5(Kb).4 G(ack)-2.5 E(of)-.1 E 2.5(ft)-.25 G(ime is)-2.5 E F3
(T_maxBackoff = K*GRTT)2.5 E F0 2.5(,t)C(he sender N)-2.5 E -.4(AC)-.35
G 2.5(Ka).4 G(ggre)-2.5 E -.05(ga)-.15 G(tion period).05 E
(should be equal to at least:)54 540 Q F3
(T_sndrAggregate = T_maxBackoff + 1*GRTT = \(K+1\)*GRTT)148.2 564 Q F0
(Immediately after the sender N)54 588 Q -.4(AC)-.35 G 2.5(Ka).4 G(ggre)
-2.5 E(gration period, the sender will be)-.15 E
(gin transmitting repair content determined from)-.15 E(the aggre)54 600
Q -.05(ga)-.15 G(te N).05 E -.4(AC)-.35 G 2.5(Ks).4 G
(tate and continue with an)-2.5 E 2.5(yn)-.15 G .5 -.25(ew t)-2.5 H 2.5
(ransmission. Also,).25 F(at this time, the sender should observ)2.5 E
2.5(ea")-.15 G(holdof)-2.5 E(f")-.25 E
(period where it constrains itself from initiating a ne)54 612 Q 2.5(wN)
-.25 G -.4(AC)-2.85 G 2.5(Ka).4 G(ggre)-2.5 E -.05(ga)-.15 G
(tion period to allo).05 E 2.5(wp)-.25 G(ropag)-2.5 E(ation of the ne)
-.05 E(w)-.25 E
(transmission sequence position due to the repair response to the recei)
54 624 Q -.15(ve)-.25 G 2.5(rg).15 G 2.5(roup. T)-2.5 F 2.5(oa)-.8 G
(llo)-2.5 E 2.5(wf)-.25 G(or w)-2.5 E(orst case asymmetry)-.1 E 2.5(,t)
-.65 G(his)-2.5 E("holdof)54 636 Q(f" time should be:)-.25 E
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/F0 10/Times-Roman@0 SF(Internet Draft)36 48 Q(NORM Building Blocks)
155.605 E(June 2003)169.475 E/F1 10/Courier@0 SF(T_sndrHoldoff = 1*GRTT)
238.2 84 Q F0(Recall that the recei)54 108 Q -.15(ve)-.25 G
(rs will also emplo).15 E 2.5(ya")-.1 G(holdof)-2.5 E
(f" timeout after generating a N)-.25 E -.4(AC)-.35 G 2.5(Km).4 G
(essage to allo)-2.5 E 2.5(wt)-.25 G(ime for the)-2.5 E(sender')54 120 Q
2.5(sr)-.55 G 2.5(esponse. Gi)-2.5 F -.15(ve)-.25 G 2.5(nas).15 G(ender)
-2.5 E F1(<T_sndrAggregate>)2.5 E F0(plus)2.5 E 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)-2.5 E(recei)54
132 Q -.15(ve)-.25 G(rs should use holdof).15 E 2.5(ft)-.25 G
(imeouts of:)-2.5 E F1
(T_rcvrHoldoff = T_sndrAggregate + T_sndrHoldoff = \(K+2\)*GRTT)124.2
156 Q F0(This allo)54 180 Q(ws for a w)-.25 E(orst-case propag)-.1 E
(ation time of the recei)-.05 E -.15(ve)-.25 G(r').15 E 2.5(sN)-.55 G
-.4(AC)-2.85 G 2.5(Kt).4 G 2.5(ot)-2.5 G(he sender)-2.5 E 2.5(,t)-.4 G
(he sender')-2.5 E 2.5(sa)-.55 G(ggre)-2.5 E -.05(ga)-.15 G
(tion time and).05 E(propag)54 192 Q(ation of the sender')-.05 E 2.5(sr)
-.55 G(esponse back to the recei)-2.5 E -.15(ve)-.25 G 3.6 -.55(r. A).15
H(dditionally).55 E 2.5(,i)-.65 G 2.5(nt)-2.5 G
(he case of unicast feedback from the recei)-2.5 E -.15(ve)-.25 G 2.5
(rs).15 G(et,)-2.5 E(it may be useful for the sender to forw)54 204 Q
(ard \(via multicast\) a representation of its aggre)-.1 E -.05(ga)-.15
G(ted N).05 E -.4(AC)-.35 G 2.5(Kc).4 G(ontent to the group to)-2.5 E
(allo)54 216 Q 2.5(wf)-.25 G(or N)-2.5 E -.4(AC)-.35 G 2.5(Ks).4 G
(uppression when there is not multicast connecti)-2.5 E
(vity among the recei)-.25 E -.15(ve)-.25 G 2.5(rs).15 G(et.)-2.5 E
(At the e)54 240 Q(xpiration of the)-.15 E F1(<T_sndrAggregate>)2.5 E F0
(timeout, the sender will be)2.5 E
(gin transmitting repair messages according to)-.15 E
(the accumulated content of N)54 252 Q -.4(AC)-.35 G(Ks recei).4 E -.15
(ve)-.25 G 2.5(d. There).15 F(are some guidelines with re)2.5 E -.05(ga)
-.15 G(rds to FEC-based repair and the ordering).05 E
(of the repair response from the sender that can impro)54 264 Q .3 -.15
(ve r)-.15 H(eliable multicast ef).15 E(\214cienc)-.25 E(y:)-.15 E 25.17
(1\) When)90 288 R
(FEC is used, it is bene\214cial that the sender transmit pre)2.5 E
(viously untransmitted parity content as repair)-.25 E(messages whene)
126 300 Q -.15(ve)-.25 G 2.5(rp).15 G 2.5(ossible. This maximizes)-2.5 F
(the recei)2.5 E(ving nodes' ability to reconstruct the entire)-.25 E
(transmitted content from their indi)126 312 Q(vidual subsets of recei)
-.25 E -.15(ve)-.25 G 2.5(dm).15 G(essages.)-2.5 E 25.17(2\) The)90 336
R(transmitted object and/or stream data and repair content should be in\
de)2.5 E -.15(xe)-.15 G 2.5(dw).15 G 2.5(ith monotonically)-2.5 F
(increasing sequence numbers \(within a reasonably lar)126 348 Q
(ge ordinal space\).)-.18 E(If the sender observ)5 E(es the)-.15 E
(discipline of)126 360 Q
(transmitting repair for the earliest content \(e.g., ordinally lo)5 E
(west FEC blocks\) \214rst, the)-.25 E(recei)126 372 Q -.15(ve)-.25 G
(rs can use a strate).15 E(gy of witholding repair requests for later c\
ontent until the sender once ag)-.15 E(ain)-.05 E
(returns to that point in the object/stream transmission sequence.)126
384 Q(This can increase o)5 E -.15(ve)-.15 G(rall message).15 E(ef)126
396 Q(\214cienc)-.25 E 2.5(ya)-.15 G(mong the group and help w)-2.5 E
(ork to k)-.1 E(eep repair c)-.1 E(ycles relati)-.15 E -.15(ve)-.25 G
(ly synchronized without).15 E
(dependence upon strict time synchronization among the sender and recei)
126 408 Q -.15(ve)-.25 G 2.5(rs. This).15 F(also helps minimize)2.5 E
(the b)126 420 Q(uf)-.2 E(fering requirements of recei)-.25 E -.15(ve)
-.25 G(rs and senders and reduces redundant transmission of data to the)
.15 E(group at lar)126 432 Q(ge.)-.18 E/F2 10/Times-BoldItalic@0 SF
(Sender Repair Response Interface Description)54 456 Q/F3 10
/Times-Italic@0 SF(Inputs:)54 480 Q F0 25.17(1\) Recei)90 504 R -.15(ve)
-.25 G 2.5(rN).15 G -.4(AC)-2.85 G 2.5(Km).4 G(essages)-2.5 E 25.17
(2\) Group)90 516 R(timing information)2.5 E F3(Outputs:)54 540 Q F0
25.17(1\) Repair)90 564 R
(messages \(FEC and/or Data content retransmission\))2.5 E 25.17
(1\) Adv)90 576 R
(ertisement of current pending repair transmissions when unicast recei)
-.15 E -.15(ve)-.25 G 2.5(rf).15 G(eedback is detected.)-2.5 E/F4 10
/Times-Bold@0 SF(3.3 Gr)36 600 Q(oup "J)-.18 E(oin" P)-.15 E
(olicies/ Pr)-.2 E(ocedur)-.18 E(es)-.18 E F0
(Consideration should be gi)54 624 Q -.15(ve)-.25 G 2.5(nt).15 G 2.5(ot)
-2.5 G(he policies and procedures by which ne)-2.5 E 2.5(wr)-.25 G(ecei)
-2.5 E -.15(ve)-.25 G(rs join a group \(perhaps where reliable).15 E
(transmission is already in progress\) and be)54 636 Q
(gin requesting repair)-.15 E 2.5(.I)-.55 G 2.5(fr)-2.5 G(ecei)-2.5 E
-.15(ve)-.25 G 2.5(rj).15 G
(oins are unconstrained, the dynamics of group)-2.5 E
(membership may impede the application')54 648 Q 2.5(sa)-.55 G
(bility to meet its goals for forw)-2.5 E
(ard progression of data transmission.)-.1 E(Policies)5 E
(Adamson, Bormann, et al.)36 696 Q(Expires December 2003)105.89 E
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/F0 10/Times-Roman@0 SF(Internet Draft)36 48 Q(NORM Building Blocks)
155.605 E(June 2003)169.475 E(limiting the opportunities when recei)54
84 Q -.15(ve)-.25 G(rs be).15 E(gin participating in the N)-.15 E -.4
(AC)-.35 G 2.5(Kp).4 G(rocess may be used to achie)-2.5 E .3 -.15(ve t)
-.25 H(he desired).15 E(beha)54 96 Q(vior)-.2 E 5(.F)-.55 G(or e)-5.15 E
(xample, it may be bene\214cial for recei)-.15 E -.15(ve)-.25 G
(rs to attempt reliable reception from a ne).15 E
(wly-heard sender only upon)-.25 E(non-repair transmissions of data in \
the \214rst FEC block of an object or logical portion of a stream.)54
108 Q(The sender may also)5 E(implement policies limiting the recei)54
120 Q -.15(ve)-.25 G(rs from which it will accept N).15 E -.4(AC)-.35 G
2.5(Kr).4 G(equests, b)-2.5 E(ut this may be prohibiti)-.2 E .3 -.15
(ve f)-.25 H(or).15 E(scalability reasons in some situations.)54 132 Q
(Alternati)5 E -.15(ve)-.25 G(ly).15 E 2.5(,i)-.65 G 2.5(tm)-2.5 G
(ay be desirable to ha)-2.5 E .3 -.15(ve a l)-.2 H
(ooser transport synchronization polic).15 E(y)-.15 E(and rely upon ses\
sion management mechanisms to limit group dynamics that can cause poor \
performance , in some types of)54 144 Q -.2(bu)54 156 S
(lk transfer applications \(or for potential interacti).2 E .3 -.15
(ve r)-.25 H(eliable multicast applications\).).15 E/F1 10
/Times-BoldItalic@0 SF(Group J)54 180 Q(oin P)-.4 E
(olicy Interface Description)-.55 E/F2 10/Times-Italic@0 SF(Inputs:)54
204 Q F0 25.17(1\) Current)90 228 R(object/stream data/repair content a\
nd sequencing identi\214ers from sender transmissions.)2.5 E F2
(Outputs:)54 252 Q F0 25.17(1\) Recei)90 276 R -.15(ve)-.25 G 2.5(ry).15
G(es/no decision to be)-2.5 E(gin recei)-.15 E(ving and N)-.25 E -.4(AC)
-.35 G(King for reliable reception of data).4 E/F3 10/Times-Bold@0 SF
(3.4 Reliable Multicast Member Identi\214cation)36 300 Q F0(In a NORM p\
rotocol \(or other multicast protocols\) where there is the potential f\
or multiple sources of data, it is necessary to)54 324 Q(pro)54 336 Q(v\
ide some mechanism to uniquely identify the sources \(and possibly some\
 or all recei)-.15 E -.15(ve)-.25 G(rs in some cases\) within the).15 E
2.5(group. Identity)54 348 R(based on arri)2.5 E(ving pack)-.25 E
(et source addresses is insuf)-.1 E(\214cient for se)-.25 E -.15(ve)-.25
G(ral reasons.).15 E(These reasons include routing)5 E
(changes for hosts with multiple interf)54 360 Q
(aces that result in dif)-.1 E(ferent pack)-.25 E
(et source addresses for a gi)-.1 E -.15(ve)-.25 G 2.5(nh).15 G(ost o)
-2.5 E -.15(ve)-.15 G 2.5(rt).15 G(ime, netw)-2.5 E(ork)-.1 E
(address translation \(N)54 372 Q -1.11(AT)-.35 G 2.5(\)o)1.11 G 2.5
<728c>-2.5 G(re)-2.5 E -.1(wa)-.25 G(ll de).1 E
(vices, or other transport/netw)-.25 E(ork bridging approaches.)-.1 E
(As a result, some type of)5 E(unique source identi\214er)54 384 Q F2
(<sour)2.5 E(ceId>)-.37 E F0(\214eld should be present in pack)2.5 E
(ets transmitted by reliable multicast session members.)-.1 E F3
(3.5 Data Content Identi\214cation)36 408 Q F0(The data and repair cont\
ent transmitted by a NORM sender requires some form of identi\214cation\
 in the protocol header)54 432 Q 2.5(\214elds. This)54 444 R
(identi\214cation is required to f)2.5 E(acilitate the reliable N)-.1 E
-.4(AC)-.35 G(K-oriented repair process.).4 E
(These identi\214ers will also be)5 E(used in N)54 456 Q -.4(AC)-.35 G
2.5(Km).4 G(essages generated.)-2.5 E(This b)5 E
(uilding block document assumes tw)-.2 E 2.5(ov)-.1 G
(ery general types of data that may)-2.65 E(comprise b)54 468 Q
(ulk transfer session content.)-.2 E
(One type is static, discrete objects of)5 E
(\214nite size and the other is continuous non-)5 E(\214nite streams.)54
480 Q 2.5(Ag)5 G -2.15 -.25(iv e)-2.5 H 2.5(na).25 G 2.5(pplication may)
-2.5 F(wish to reliably multicast data content using either one or both\
 of these paradigms.)2.5 E(While it may be possible for some applicatio\
ns to further generalize this model and pro)54 492 Q
(vide mechanisms to encapsulate)-.15 E
(static objects as content embedded within a stream, there are adv)54
504 Q(antages in man)-.25 E 2.5(ya)-.15 G(pplications to pro)-2.5 E
(vide distinct support for)-.15 E(static b)54 516 Q
(ulk objects and messages with the conte)-.2 E
(xt of a reliable multicast session.)-.15 E
(These applications may include content)5 E(caching serv)54 528 Q
(ers, \214le transfer)-.15 E 2.5(,o)-.4 G 2.5(rc)-2.5 G(ollaborati)-2.5
E .3 -.15(ve t)-.25 H(ools with b).15 E(ulk content.)-.2 E
(Applications with requirements for these static object)5 E
(types can then tak)54 540 Q 2.5(ea)-.1 G(dv)-2.5 E
(antage of transport layer mechanisms \(i.e., se)-.25 E
(gmentation/reassembly)-.15 E 2.5(,c)-.65 G(aching, inte)-2.5 E
(grated forw)-.15 E(ard)-.1 E
(error correction coding, etc\) rather than being required to pro)54 552
Q(vide their o)-.15 E(wn mechanisms for these functions at the)-.25 E
(application layer)54 564 Q(.)-.55 E
(As noted, some applications may alternati)54 588 Q -.15(ve)-.25 G
(ly desire to transmit b).15 E
(ulk content in the form of one or more streams of non-)-.2 E
(\214nite size.)54 600 Q(Example streams include continuous quasi-realt\
ime message broadcasts \(e.g., stock tick)5 E
(er\) or some content types)-.1 E(that are part of collaborati)54 612 Q
.3 -.15(ve t)-.25 H(ools or other more comple).15 E 2.5(xa)-.15 G 2.5
(pplications. And,)-2.5 F(as indicated abo)2.5 E -.15(ve)-.15 G 2.5(,s)
.15 G(ome applications may)-2.5 E(wish to encapsulate other b)54 624 Q(\
ulk content \(e.g., \214les\) into one or more streams within a multica\
st)-.2 E(session.)5 E(The components described within this b)54 648 Q
(uilding block draft document are en)-.2 E
(visioned to be applicable to both of these models)-.4 E
(Adamson, Bormann, et al.)36 696 Q(Expires December 2003)105.89 E
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/F0 10/Times-Roman@0 SF(Internet Draft)36 48 Q(NORM Building Blocks)
155.605 E(June 2003)169.475 E(with the)54 84 Q
(potential for a mix of both types within a single multicast session.)5
E 1.6 -.8(To s)5 H(upport this requirement, the normal data).8 E(conten\
t identi\214cation should include a \214eld to uniquely identify the ob\
ject or stream)54 96 Q/F1 10/Times-Italic@0 SF(<objectId>)2.5 E F0
(within some reasonable)2.5 E(temporal or ordinal interv)54 108 Q 2.5
(al. Note)-.25 F(that it is _not_ e)2.5 E(xpected that this data conten\
t identi\214cation will be globally unique.)-.15 E(It is)5 E -.15(ex)54
120 S(pected that the object/stream identi\214er will be unique with re\
spect to a gi).15 E -.15(ve)-.25 G 2.5(ns).15 G
(ender within the reliable multicast session)-2.5 E(and during the time\
 that sender is supporting a speci\214c transport instance of that obje\
ct or stream.)54 132 Q(Since the "b)54 156 Q
(ulk" object/stream content usually requires se)-.2 E
(gmentation, some form of se)-.15 E(gment identi\214cation must also be)
-.15 E(pro)54 168 Q 2.5(vided. This)-.15 F(se)2.5 E
(gment identi\214er will be relati)-.15 E .3 -.15(ve t)-.25 H 2.5(oa).15
G .3 -.15(ny o)-2.5 H(bject or stream identi\214er that has been pro).15
E 2.5(vided. Thus,)-.15 F(in some)2.5 E
(cases, NORM protocol instantiations may be able to recei)54 180 Q 2.8
-.15(ve t)-.25 H
(ransmissions and request repair for multiple streams and one).15 E
(or more sets of static objects in parallel.)54 192 Q -.15(Fo)5 G 2.5
(rp).15 G(rotocol instantiations emplo)-2.5 E(ying FEC the se)-.1 E
(gment identi\214cation portion of the)-.15 E(data content identi\214er\
 may consist of a logical concatenation of a coding block identi\214er)
54 204 Q F1(<sour)2.5 E(ceBloc)-.37 E(kNumber>)-.2 E F0(and an)2.5 E
(identifer for the speci\214c data or parity symbol)54 216 Q F1
(<endcodingSymbolId>)2.5 E F0(of the code block.)2.5 E
(The FEC Building Block document)5 E([13] pro)54 228 Q(vides a standard\
 message format for identifying FEC transmission content. NORM protocol\
 instantiations using FEC)-.15 E(SHOULD follo)54 240 Q 2.5(wt)-.25 G
(hat document')-2.5 E 2.5(sg)-.55 G(uidelines.)-2.5 E(Additionally)54
264 Q 2.5<2c8d>-.65 G(ags to determine the usage of the content identi\
\214er \214elds \(e.g., stream vs. object\) may be applicable.)-2.5 E
(Flags)7.5 E(may also serv)54 276 Q 2.5(eo)-.15 G
(ther purposes in data content identi\214cation.)-2.5 E(It is e)5 E
(xpected that an)-.15 E 2.5<798d>-.15 G
(ags de\214ned will be dependent upon)-2.5 E(indi)54 288 Q
(vidual protocol instantiations.)-.25 E(In summary)54 312 Q 2.5(,t)-.65
G(he follo)-2.5 E(wing data content identi\214cation \214elds may be re\
quired for NORM protocol data content messages:)-.25 E 25.17(1\) Source)
90 336 R(node identi\214er \()2.5 E F1(<sour)A(ceId>)-.37 E F0(\))A
25.17(2\) Object/Stream)90 348 R(identi\214er \()2.5 E F1(<objectId>)A
F0(\), if applicable.)A 25.17(3\) FEC)90 360 R(Block identi\214er \()2.5
E F1(<sour)A(ceBloc)-.37 E(kNumber>)-.2 E F0(\), if applicable.)A 25.17
(4\) FEC)90 372 R(Symbol identi\214er \()2.5 E F1(<encodingSymbolId>)A
F0(\))A 25.17(5\) Flags)90 384 R(to dif)2.5 E(ferentiate interpretation\
 of identi\214er \214elds or identi\214er structure that implicitly ind\
icates usage.)-.25 E 25.17(6\) Additional)90 396 R
(FEC transmission content \214elds per FEC Building Block)2.5 E
(These \214elds ha)54 420 Q .3 -.15(ve b)-.2 H
(een identi\214ed because an).15 E 2.5(yg)-.15 G(enerated N)-2.5 E -.4
(AC)-.35 G 2.5(Km).4 G
(essages will use these identi\214ers in requesting repair or)-2.5 E
(retransmission of data.)54 432 Q(NORM protocols that use these data co\
ntent \214elds should be compatible with planned support for)5 E
(Generic Router Assist \(GRA\) for reliable multicast operation [15].)54
444 Q/F2 10/Times-Bold@0 SF(3.6 F)36 468 Q(orward Err)-.25 E(or Corr)
-.18 E(ection \(FEC\))-.18 E F0(Multiple forw)54 492 Q
(ard error correction \(FEC\) approaches ha)-.1 E .3 -.15(ve b)-.2 H
(een identi\214ed that can pro).15 E
(vide great performance enhancements)-.15 E(to the repair process of N)
54 504 Q -.4(AC)-.35 G
(K-oriented and other reliable multicast protocols [9],[13].).4 E
(NORM protocols can reap additional)5 E
(bene\214ts since FEC-based repair does not _generally_ require e)54 516
Q(xplicit kno)-.15 E(wledge of repair content within the bounds of its)
-.25 E(coding block size \(in se)54 528 Q 2.5(gments\). In)-.15 F
(NORM, parity repair pack)2.5 E
(ets generated will generally be transmitted only in response to)-.1 E
-.35(NA)54 540 S(CK repair requests from recei)-.05 E(ving nodes.)-.25 E
(Ho)5 E(we)-.25 E -.15(ve)-.25 G .8 -.4(r, t).15 H
(here are bene\214ts in some netw).4 E(ork en)-.1 E
(vironments for transmitting)-.4 E
(some predetermined quantity of FEC repair pack)54 552 Q(ets multiple)
-.1 E -.15(xe)-.15 G 2.5(dw).15 G(ith the re)-2.5 E(gular data se)-.15 E
(gment transmissions [8].)-.15 E(This can)7.5 E(reduce the amount of N)
54 564 Q -.4(AC)-.35 G 2.5(Kt).4 G(raf)-2.5 E
(\214c generated with relati)-.25 E -.15(ve)-.25 G 2.5(ly little).15 F
-.15(ove)2.5 G(rhead cost when group sizes are v).15 E(ery lar)-.15 E
(ge or the)-.18 E(netw)54 576 Q 2.5(ork connecti)-.1 F(vity has a lar)
-.25 E(ge)-.18 E/F3 10/Courier@0 SF(delay*bandwidth)2.5 E F0
(product with some nominal le)2.5 E -.15(ve)-.25 G 2.5(lo).15 G 2.5(fe)
-2.5 G(xpected pack)-2.65 E(et loss.)-.1 E(While the)5 E(application of\
 FEC is not unique to NORM, these sorts of requirements may dictate the\
 types of algorithms and protocol)54 588 Q
(approaches that are applicable.)54 600 Q 2.5(As)54 624 S(peci\214c iss\
ue related to the use of FEC with NORM is the mechanism used to identif\
y which portion\(s\) of transmitted)-2.5 E
(data content to which speci\214c FEC pack)54 636 Q(ets are applicable.)
-.1 E(It is e)5 E
(xpected that FEC algorithms will be based on generating a)-.15 E
(set of parity repair pack)54 648 Q
(ets for a corresponding block of transmitted data pack)-.1 E 2.5
(ets. Since)-.1 F(data content pack)2.5 E(ets are uniquely)-.1 E
(Adamson, Bormann, et al.)36 696 Q(Expires December 2003)105.89 E
([P)119.09 E(age 17])-.15 E EP
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/F0 10/Times-Roman@0 SF(Internet Draft)36 48 Q(NORM Building Blocks)
155.605 E(June 2003)169.475 E(identi\214ed by the concatenation of)54 84
Q/F1 10/Times-Italic@0 SF(<sour)2.5 E(ceId::objectId::sour)-.37 E
(ceBloc)-.37 E(kNumber::encodingSymbolId>)-.2 E F0
(during transport, it is)2.5 E -.15(ex)54 96 S(pected that FEC pack).15
E(ets will be identi\214ed in a similar manner)-.1 E 5(.T)-.55 G
(he FEC Building Block speci\214cation [13] pro)-5 E(vides)-.15 E(detai\
led recommendations concerning application of FEC and standard formats \
for related reliable multicast protocol)54 108 Q(messages.)54 120 Q/F2
10/Times-Bold@0 SF(3.7 Round-trip T)36 144 Q(iming Collection)-.18 E F0
(The measurement of pack)54 168 Q(et propag)-.1 E
(ation round-trip time \(R)-.05 E
(TT\) among members of the group is required to support timer)-.6 E(-)
-.2 E(based N)54 180 Q -.4(AC)-.35 G 2.5(Ks).4 G(uppression algorithms,\
 timing of sender commands or certain repair functions, and congestion \
control)-2.5 E 2.5(operation. The)54 192 R(nature of the round-trip inf\
ormation collected is dependent upon the type of interaction among the \
members)2.5 E(of the group.)54 204 Q(In the case where only "one-to-man)
5 E
(y" transmission is required, it may be that only the sender require R)
-.15 E(TT)-.6 E(kno)54 216 Q(wledge of the greatest R)-.25 E(TT \(GR)-.6
E(TT\) among the recei)-.6 E -.15(ve)-.25 G 2.5(rs).15 G(et and/or R)
-2.5 E(TT kno)-.6 E(wledge of only a portion of the group.)-.25 E(Here,)
5 E(the GR)54 228 Q
(TT information might be collected in a reasonably scalable manner)-.6 E
5(.F)-.55 G(or congestion control operation, it is possible)-5.15 E
(that R)54 240 Q(TT information may be required by each recei)-.6 E -.15
(ve)-.25 G 2.5(ri).15 G 2.5(nt)-2.5 G(he group.)-2.5 E
(In this case, an alternati)5 E .3 -.15(ve R)-.25 H
(TT collection scheme may)-.45 E(be utilized where recei)54 252 Q -.15
(ve)-.25 G(rs collect indi).15 E(vidual R)-.25 E
(TT measurements with respect to the sender and adv)-.6 E
(ertise them to the group)-.15 E(or sender)54 264 Q 5(.W)-.55 G
(here it is lik)-5 E(ely that e)-.1 E(xchange of reliable multicast dat\
a will occur among the group on a "man)-.15 E(y-to-man)-.15 E(y" basis,)
-.15 E(there are alternati)54 276 Q .3 -.15(ve m)-.25 H
(easurement techniques that might be emplo).15 E(yed for increased ef)
-.1 E(\214cienc)-.25 E 2.5(y[)-.15 G 2.5(12]. And)-2.5 F
(in some cases, there)2.5 E
(might be absolute time synchronization among hosts that may simplify R)
54 288 Q(TT measurement.)-.6 E(There are trade-of)5 E(fs in multicast)
-.25 E(congestion control design that require further consideration bef\
ore a uni)54 300 Q -.15(ve)-.25 G(rsal recommendation on R).15 E
(TT \(or GR)-.6 E(TT\))-.6 E(measurement can be speci\214ed.)54 312 Q
(Re)5 E -.05(ga)-.15 G(rdless of ho).05 E 2.5(wt)-.25 G(he R)-2.5 E
(TT information is collected \(and more speci\214cally GR)-.6 E
(TT\) with)-.6 E(respect to congestion control or other requirements, t\
he sender will need to adv)54 324 Q(ertise its current GR)-.15 E
(TT estimate to the group)-.6 E(for v)54 336 Q
(arious timeouts used by recei)-.25 E -.15(ve)-.25 G(rs.).15 E/F3 10
/Times-BoldItalic@0 SF(3.7.1 One-to-Many Sender GR)36 360 Q
(TT Measurement)-.3 E F0(The goal of this form of R)54 384 Q
(TT measurement is for the sender to learn the GR)-.6 E
(TT among the recei)-.6 E -.15(ve)-.25 G(rs who are acti).15 E -.15(ve)
-.25 G(ly).15 E(participating in NORM operation.)54 396 Q
(The set of recei)5 E -.15(ve)-.25 G(rs participating in this process m\
ay be the entire group or some subset).15 E(of the group determined fro\
m another mechanism within the protocol instantiation.)54 408 Q
(An approach to collect this GR)5 E(TT)-.6 E(information follo)54 420 Q
(ws.)-.25 E(The sender periodically polls the group with a message \(in\
dependent or "piggy-back)54 444 Q
(ed" with other transmissions\) containing)-.1 E(a)54 456 Q/F4 10
/Courier@0 SF(<sendTime>)2.5 E F0(timestamp relati)2.5 E .3 -.15(ve t)
-.25 H 2.5(oa).15 G 2.5(ni)-2.5 G(nternal clock at the sender)-2.5 E 5
(.U)-.55 G(pon reception of this message, the recei)-5 E -.15(ve)-.25 G
(rs will).15 E(record this)54 468 Q F4(<sendTime>)2.5 E F0
(timestamp and the time \(referenced to their o)2.5 E
(wn clocks\) at which it w)-.25 E(as recei)-.1 E -.15(ve)-.25 G(d).15 E
F4(<recvTime>)2.5 E F0(.)A(When the recei)54 480 Q -.15(ve)-.25 G 2.5
(rp).15 G(ro)-2.5 E(vides feedback to the sender \(either e)-.15 E
(xplicitly or as part of other feedback messages depending upon)-.15 E(\
protocol instantiaon speci\214cation\), it will construct a "response" \
using the formula:)54 492 Q F4
(grttResponse = sendTime + \(currentTime - recvTime\))154.2 516 Q F0
(where the)54 540 Q F4(<sendTime>)2.5 E F0
(is the timestamp from the last probe message recei)2.5 E -.15(ve)-.25 G
2.5(df).15 G(rom the source and the \()-2.5 E F4(currentTime)A 6(-<)54
552 S(recvTime)-6 E F0 2.5(\)i)C 2.5(st)-2.5 G(he amount of time dif)
-2.5 E(ferential since that request w)-.25 E(as recei)-.1 E -.15(ve)-.25
G 2.5(du).15 G(ntil the recei)-2.5 E -.15(ve)-.25 G 2.5(rg).15 G
(enerated the response.)-2.5 E(The sender processes each recei)54 576 Q
-.15(ve)-.25 G 2.5(rr).15 G(esponse by calculating a current R)-2.5 E
(TT measurement for the recei)-.6 E -.15(ve)-.25 G 2.5(rf).15 G
(rom whom the)-2.5 E(response w)54 588 Q(as recei)-.1 E -.15(ve)-.25 G
2.5(du).15 G(sing the follo)-2.5 E(wing formula:)-.25 E F4
(RTT_rcvr = currentTime - grttResponse)193.2 612 Q F0
(During the each periodic GR)54 636 Q(TT probing interv)-.6 E
(al, the source k)-.25 E(eeps the peak round trip timing measurement \()
-.1 E F4(RTT_peak)A F0(\))A(from the set of responses it has recei)54
648 Q -.15(ve)-.25 G 2.5(d. A).15 F(conserv)2.5 E(ati)-.25 E .3 -.15
(ve e)-.25 H(stimate of).15 E F4(GRTT)2.5 E F0(is k)2.5 E
(ept to maximize the ef)-.1 E(\214cienc)-.25 E 2.5(yr)-.15 G(edundant)
-2.5 E(Adamson, Bormann, et al.)36 696 Q(Expires December 2003)105.89 E
([P)119.09 E(age 18])-.15 E EP
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/F0 10/Times-Roman@0 SF(Internet Draft)36 48 Q(NORM Building Blocks)
155.605 E(June 2003)169.475 E -.35(NA)54 84 S
(CK suppression and repair aggre)-.05 E -.05(ga)-.15 G 2.5(tion. The).05
F(update to the source')2.5 E 2.5(so)-.55 G(ngoing estimate of)-2.5 E/F1
10/Courier@0 SF(GRTT)2.5 E F0(is done observing the)2.5 E(follo)54 96 Q
(wing rules:)-.25 E 25.17(1\) If)90 120 R 2.5(ar)2.5 G(ecei)-2.5 E -.15
(ve)-.25 G(r').15 E 2.5(sr)-.55 G(esponse round trip time \()-2.5 E F1
(RTT_rcvr)A F0 2.5(\)i)C 2.5(sg)-2.5 G(reater than the current)-2.5 E F1
(GRTT)2.5 E F0(estimate, the)2.5 E F1(GRTT)2.5 E F0
(is immediately updated to this ne)126 132 Q 2.5(wp)-.25 G(eak v)-2.5 E
(alue:)-.25 E F1(GRTT = RTT_rcvr)295.2 156 Q F0 25.17(2\) At)90 180 R
(the end of the response collection period \(i.e., the GR)2.5 E
(TT probe interv)-.6 E(al\), if the recorded "peak")-.25 E(response)126
192 Q F1(RTT_peak)2.5 E F0 2.5(\)i)C 2.5(sl)-2.5 G
(ess than the current GR)-2.5 E(TT estimate, the GR)-.6 E
(TT is updated to:)-.6 E F1(GRTT = MAX\(0.9*GRTT, RTT_peak\))250.2 216 Q
F0 25.17(3\) If)90 240 R(no feedback is recei)2.5 E -.15(ve)-.25 G
(d, the sender).15 E F1(GRTT)2.5 E F0(estimate remains unchanged.)2.5 E
25.17(4\) At)90 264 R
(the end of the response collection period, the peak tracking v)2.5 E
(alue \()-.25 E F1(RTT_peak)A F0 2.5(\)i)C 2.5(sr)-2.5 G(eset to ZER)
-2.5 E 2.5(Of)-.4 G(or)-2.5 E(subsequent peak detection.)126 276 Q(The)
54 300 Q F1(GRTT)2.5 E F0(collection period \(i.e., period of probe tra\
nsmission\) could be \214x)2.5 E(ed at a v)-.15 E
(alue on the order of that e)-.25 E(xpected for)-.15 E
(group membership and/or netw)54 312 Q(ork topology dynamics.)-.1 E -.15
(Fo)5 G 2.5(rr).15 G(ob)-2.5 E
(ustness, more rapid probing could be used at protocol startup)-.2 E
(before settling to a less frequent, steady-state interv)54 324 Q 2.5
(al. Optionally)-.25 F 2.5(,a)-.65 G 2.5(na)-2.5 G(lgorithm may be de)
-2.5 E -.15(ve)-.25 G(loped to adjust the).15 E F1(GRTT)2.5 E F0
(collection period dynamically in response to the current)54 336 Q F1
(GRTT)2.5 E F0(estimate \(or v)2.5 E
(ariations in it\) and to an estimation of pack)-.25 E(et)-.1 E 2.5
(loss. The)54 348 R -.15(ove)2.5 G
(rhead of probing messages could then be reduced when the).15 E F1(GRTT)
2.5 E F0(estimate is stable and unchanging, b)2.5 E(ut be)-.2 E
(adjusted to track more dynamically during periods of v)54 360 Q
(ariation with correspondingly shorter GR)-.25 E(TT collection periods.)
-.6 E F1(GRTT)54 372 Q F0(collection may also be coupled with collectio\
n of other information for congestion control purposes.)2.5 E
(In summary)54 396 Q 2.5(,a)-.65 G(lthough NORM repair c)-2.5 E
(ycle timeouts are based on)-.15 E F1(GRTT)2.5 E F0 2.5(,i)C 2.5(ts)-2.5
G(hould be noted that con)-2.5 E -.15(ve)-.4 G -.18(rg).15 G
(ent operation of the).18 E
(protocol does not _strictly_ depend on highly accurate)54 408 Q F1
(GRTT)2.5 E F0 2.5(estimation. The)2.5 F(current mechanism has pro)2.5 E
-.15(ve)-.15 G 2.5(ds).15 G(uf)-2.5 E(\214cient in)-.25 E
(simulations and in the en)54 420 Q(vironments where NORM-lik)-.4 E 2.5
(ep)-.1 G(rotocols ha)-2.5 E .3 -.15(ve b)-.2 H(een deplo).15 E
(yed to date.)-.1 E(The estimate pro)5 E(vided by the)-.15 E
(algorithm tracks the peak en)54 432 Q -.15(ve)-.4 G(lope of actual).15
E F1(GRTT)2.5 E F0(\(including operating system ef)2.5 E
(fect as well as netw)-.25 E(ork delays\) e)-.1 E -.15(ve)-.25 G 2.5(ni)
.15 G(n)-2.5 E(relati)54 444 Q -.15(ve)-.25 G(ly high loss connecti).15
E(vity)-.25 E 5(.T)-.65 G(he steady-state probing/update interv)-5 E
(al may potentially be v)-.25 E(aried to accommodate)-.25 E(dif)54 456 Q
(ferent le)-.25 E -.15(ve)-.25 G(ls of e).15 E(xpected netw)-.15 E
(ork dynamics in dif)-.1 E(ferent en)-.25 E(vironments.)-.4 E/F2 10
/Times-BoldItalic@0 SF(3.7.2 One-to-Many Receiv)36 480 Q(er R)-.15 E
(TT Measurement)-.3 E F0(In this approach, recei)54 504 Q -.15(ve)-.25 G
(rs send messages with timestamps to the sender).15 E 5(.T)-.55 G 2.5
(oc)-5.8 G(ontrol the v)-2.5 E(olume of these recei)-.2 E -.15(ve)-.25 G
-.2(r-).15 G(generated).2 E
(messages, a suppression mechanism similar to that described for N)54
516 Q -.4(AC)-.35 G 2.5(Ks).4 G(uppression my be used.)-2.5 E
(The "age" of recei)5 E -.15(ve)-.25 G(rs').15 E -.6(RT)54 528 S 2.5(Tm)
.6 G(easurement should be k)-2.5 E(ept by recei)-.1 E -.15(ve)-.25 G
(rs and used as a metric in competing for feedback opportunities in the)
.15 E(suppression scheme.)54 540 Q -.15(Fo)5 G 2.5(re).15 G
(xample, recei)-2.65 E -.15(ve)-.25 G 2.5(rw).15 G(ho ha)-2.5 E .3 -.15
(ve n)-.2 H(ot made an).15 E 2.5(yR)-.15 G(TT measurement or whose R)
-3.1 E(TT measurement has aged)-.6 E(most should ha)54 552 Q .3 -.15
(ve p)-.2 H(recedence o).15 E -.15(ve)-.15 G 2.5(ro).15 G(ther recei)
-2.5 E -.15(ve)-.25 G 2.5(rs. In).15 F(turn the sender may ha)2.5 E .3
-.15(ve l)-.2 H(imited capacity to pro).15 E(vide an "echo" of the)-.15
E(recei)54 564 Q -.15(ve)-.25 G 2.5(rt).15 G
(imestamps back to the group, and it could use this R)-2.5 E
(TT "age" metric to determine which recei)-.6 E -.15(ve)-.25 G
(rs get precedence.).15 E(The sender can determine the)54 576 Q F1(GRTT)
2.5 E F0(as described in 3.7.1 if it pro)2.5 E
(vides sender timestamps to the group.)-.15 E(Alternati)5 E -.15(ve)-.25
G(ly).15 E(,)-.65 E(recei)54 588 Q -.15(ve)-.25 G(rs who note their R)
.15 E(TT is greater than the sender)-.6 E F1(GRTT)2.5 E F0
(can compete in the feedback opportunity/suppression scheme)2.5 E
(to pro)54 600 Q(vide the sender and group with this information.)-.15 E
(It should be noted that the TFMCC Congestion Control b)5 E(uilding)-.2
E(block described a similar approach to recei)54 612 Q -.15(ve)-.25 G
2.5(rR).15 G
(TT measurement as part of its congestion control operation [14].)-3.1 E
(Adamson, Bormann, et al.)36 696 Q(Expires December 2003)105.89 E
([P)119.09 E(age 19])-.15 E EP
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/F0 10/Times-Roman@0 SF(Internet Draft)36 48 Q(NORM Building Blocks)
155.605 E(June 2003)169.475 E/F1 10/Times-BoldItalic@0 SF
(3.7.3 Many-to-Many R)36 84 Q(TT Measurement)-.3 E F0 -.15(Fo)54 108 S
2.5(rr).15 G(eliable multicast sessions that in)-2.5 E -.2(vo)-.4 G(lv)
.2 E 2.5(em)-.15 G(ultiple senders, it may be useful to ha)-2.5 E .3
-.15(ve R)-.2 H(TT measurements occur on a true)-.45 E("man)54 120 Q
(y-to-man)-.15 E(y" basis rather than ha)-.15 E .3 -.15(ve e)-.2 H
(ach sender independently tracking R).15 E(TT)-.6 E 5(.S)-.74 G
(ome protocol ef)-5 E(\214cienc)-.25 E 2.5(yc)-.15 G(an be g)-2.5 E
(ained)-.05 E(when recei)54 132 Q -.15(ve)-.25 G
(rs can infer an approximation of their R).15 E
(TT with respect to a sender based on R)-.6 E(TT information the)-.6 E
2.5(yh)-.15 G -2.25 -.2(av e)-2.5 H(on)2.7 E
(another sender and that other sender')54 144 Q 2.5(sR)-.55 G
(TT with respect to the ne)-3.1 E 2.5(ws)-.25 G(ender of interest.)-2.5
E -.15(Fo)5 G 2.5(re).15 G(xample, for recei)-2.65 E -.15(ve)-.25 G 2.5
(r").15 G/F2 10/Courier@0 SF(a)-2.5 E F0 2.5("a)C(nd)-2.5 E(sender')54
156 Q 2.5(s")-.55 G F2(b)-2.5 E F0 2.5("a)C(nd ")-2.5 E F2(c)A F0
(", it is lik)A(ely that:)-.1 E F2
(RTT\(a<->b\) <= RTT\(a<->c\)\) + RTT\(b<->c\))193.2 180 Q F0
(Further re\214nement of this estimate can be conducted if R)54 204 Q
(TT information is a)-.6 E -.25(va)-.2 G
(ilable to a node concerning its o).25 E(wn R)-.25 E(TT to a)-.6 E
(small subset of other group members and R)54 216 Q(TT information amon\
g those other group members it learns during protocol)-.6 E(operation.)
54 228 Q F1(3.7.4 Sender GR)36 252 Q(TT Adv)-.3 E(ertisement)-.15 E F0
1.6 -.8(To f)54 276 T
(acilitate deterministic NORM protocol operation, the sender should rob)
.7 E(ustly adv)-.2 E(ertise its current estimation of)-.15 E F2(GRTT)2.5
E F0(to)2.5 E(the recei)54 288 Q -.15(ve)-.25 G 2.5(rs).15 G 2.5
(et. Common,)-2.5 F(rob)2.5 E(ust kno)-.2 E(wledge of the sender')-.25 E
2.5(sc)-.55 G(urrent operating)-2.5 E F2(GRTT)2.5 E F0
(estimate among the group will allo)2.5 E(w)-.25 E
(the protocol to progress in its most ef)54 300 Q(\214cient manner)-.25
E 5(.T)-.55 G(he sender')-5 E(s)-.55 E F2(GRTT)2.5 E F0
(estimate can be rob)2.5 E(ustly adv)-.2 E(ertised to the group by)-.15
E(simply embedding the estimate into all pertinent messages transmitted\
 by the sender)54 312 Q 5(.T)-.55 G(he o)-5 E -.15(ve)-.15 G
(rhead of this can be made).15 E
(quite small by quantizing \(compressing\) the)54 324 Q F2(GRTT)2.5 E F0
(estimate to a single byte of information.)2.5 E(The follo)5 E
(wing C-lanquage)-.25 E(functions allo)54 336 Q(ws this to be done o)
-.25 E -.15(ve)-.15 G 2.5(raw).15 G(ide range \()-2.5 E F2(RTT_MIN)A F0
(through)2.5 E F2(RTT_MAX)2.5 E F0 2.5(\)o)C(f)-2.5 E F2(GRTT)2.5 E F0
-.25(va)2.5 G(lues while maintaining a).25 E
(greater range of precision for small)54 348 Q F2(GRTT)2.5 E F0 -.25(va)
2.5 G(lues and less precision for lar).25 E(ge v)-.18 E 2.5(alues. V)
-.25 F(alues of 1.0e-06 seconds and 1000)-1.11 E
(seconds are RECOMMENDED for R)54 360 Q(TT_MIN and R)-.6 E
(TT_MAX respecti)-.6 E -.15(ve)-.25 G(ly).15 E 5(.N)-.65 G
(ORM applications may wish to place an)-5 E
(additional, smaller upper limit on the)54 372 Q F2(GRTT)2.5 E F0(adv)
2.5 E(ertised by senders to meet application data deli)-.15 E -.15(ve)
-.25 G(ry latenc).15 E 2.5(yc)-.15 G(onstraints at the)-2.5 E -.15(ex)54
384 S(pense of greater feedback v).15 E(olume in some netw)-.2 E(ork en)
-.1 E(vironments.)-.4 E F2(unsigned char QuantizeGrtt\(double grtt\))108
408 Q({)108 420 Q(if \(grtt > RTT_MAX\))132 432 Q(grtt = RTT_MAX;)156
444 Q(else if \(grtt < 1.0e-06\))132 456 Q(grtt = RTT_MIN;)156 468 Q
(if \(grtt < \(33*RTT_MIN\)\))132 480 Q
(return \(\(unsigned char\)\(grtt * RTT_MIN\) - 1\);)156 492 Q(else)132
504 Q(return \(\(unsigned char\)\(ceil\(255.0.-)156 516 Q
(\(13.0 * log\(RTT_MAX/grtt\)\)\)\)\);)300 528 Q(})108 540 Q
(double UnquantizeRtt\(unsigned char qrtt\))108 564 Q({)108 576 Q
(return \(\(qrtt < 31\) ?)144 588 Q
(\(\(\(double\)\(qrtt+1\)\)/\(double\)RTT_MIN\) :)144 600 Q
(\(RTT_MAX/exp\(\(\(double\)\(255-qrtt\)\)/\(double\)13.0\)\)\);)168 612
Q(})108 624 Q F0(Note that this function is useful for quantizing)54 648
Q F2(GRTT)2.5 E F0(times in the range of 1 microsecond to 1000 seconds.)
2.5 E(Of course,)5 E(Adamson, Bormann, et al.)36 696 Q
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/F0 10/Times-Roman@0 SF(Internet Draft)36 48 Q(NORM Building Blocks)
155.605 E(June 2003)169.475 E
(NORM protocol implementations may wish to further constrain adv)54 84 Q
(ertised)-.15 E/F1 10/Courier@0 SF(GRTT)2.5 E F0
(estimates \(e.g., limit the maximum v)2.5 E(alue\))-.25 E
(for practical reasons.)54 96 Q/F2 10/Times-Bold@0 SF(3.8 Gr)36 120 Q
(oup Size Determination/Estimation)-.18 E F0
(When NORM protocol operation includes mechanisms that e)54 144 Q
(xcite feedback from the group at lar)-.15 E(ge \(e.g., congestion)-.18
E(control\), it may be possible to roughly estimate the group size base\
d on the number of feedback messages recei)54 156 Q -.15(ve)-.25 G 2.5
(dw).15 G(ith)-2.5 E(respect to the distrib)54 168 Q
(ution of the probabilistic suppression mechanism used.)-.2 E
(Note the timer)5 E(-based suppression mechanism)-.2 E
(described in this document does not require a v)54 180 Q
(ery accurate estimate of group size to perform adequately)-.15 E 5(.T)
-.65 G(hus, a rough)-5 E(estimate, particularly if conserv)54 192 Q(ati)
-.25 E -.15(ve)-.25 G(ly managed, may suf).15 E 2.5(\214ce. Group)-.25 F
(size may also be determined administrati)2.5 E -.15(ve)-.25 G(ly).15 E
5(.I)-.65 G(n)-5 E
(absence of a group size determination mechanism a def)54 204 Q
(ault group size v)-.1 E(alue of 10,000 is RECOMMENDED for)-.25 E
(reasonable)5 E(management of feedback gi)54 216 Q -.15(ve)-.25 G 2.5
(nt).15 G(he scalability of e)-2.5 E(xpected NORM usage.)-.15 E F2
(3.9 Congestion Contr)36 240 Q(ol Operation)-.18 E F0
(Congestion control that f)54 264 Q(airly shares a)-.1 E -.25(va)-.2 G
(ilable netw).25 E(ork capacity)-.1 E
(with other reliable multicast and TCP instantiations is)5 E(REQ)54 276
Q(UIRED for general Internet operation.)-.1 E
(The TCP-Friendly Multicast Congestion Control [14])5 E
(or PGMCC speci\214cation)5 E
([18] may be applied to NORM operation to meet this requirement.)54 288
Q F2(3.10 Router/Intermediate System assistance)36 312 Q F0 -.35(NA)54
336 S(CK-oriented protocols may bene\214t from general purpose router a\
ssistance.)-.05 E(In particular)5 E 2.5(,a)-.4 G(dditional N)-2.5 E -.4
(AC)-.35 G 2.5(Ks).4 G(uppression)-2.5 E
(where routers or intermediate systems can aggre)54 348 Q -.05(ga)-.15 G
(te N).05 E -.4(AC)-.35 G 2.5(Kc).4 G(ontent \(or \214lter duplicate N)
-2.5 E -.4(AC)-.35 G 2.5(Kc).4 G(ontent\) from recei)-2.5 E -.15(ve)-.25
G(rs as it is).15 E(relayed to)54 360 Q -.1(wa)-.25 G
(rd the sender could enhance NORM group size scalability).1 E 5(.F)-.65
G(or NORM protocols using FEC, it is possible that)-5.15 E(intermediate\
 systems may be able to \214lter FEC repair messages to pro)54 372 Q
(vide an intelligent "subcast" of repair content to)-.15 E(dif)54 384 Q
(ferent le)-.25 E(gs of the multicast toplogy depending on the repair n\
eeds learned from pre)-.15 E(vious recei)-.25 E -.15(ve)-.25 G 2.5(rN)
.15 G -.4(AC)-2.85 G 2.5(Ks. Both).4 F(of these)2.5 E
(types of Generic Router Assist \(GRA\) functions w)54 396 Q(ould requi\
re router interpretation of transport data unit content identi\214ers)
-.1 E(and \215ags.)54 408 Q(Additionally)5 E 2.5(,t)-.65 G
(he GRA router should observ)-2.5 E 2.5(eN)-.15 G -.4(AC)-2.85 G 2.5(Kr)
.4 G(epair process timeouts based on the NORM sender')-2.5 E(s)-.55 E F1
(GRTT)2.5 E F0(adv)54 420 Q(ertisement.)-.15 E F2(4.0 NORM A)36 444 Q
(pplicability)-.25 E F0(The NORM b)54 468 Q
(uilding block applies to protocols wishing to emplo)-.2 E 2.5(yn)-.1 G
-2.25 -.15(eg a)-2.5 H(ti).15 E .3 -.15(ve a)-.25 H(ckno).15 E
(wledgement to achie)-.25 E .3 -.15(ve r)-.25 H(eliable data).15 E
(transfer)54 480 Q 5(.P)-.55 G(roperly designed ne)-5 E -.05(ga)-.15 G
(ti).05 E -.15(ve)-.25 G(-ackno).15 E(wledgement \(N)-.25 E -.4(AC)-.35
G(K\)-oriented reliable multicast \(NORM\) protocols of).4 E(fer)-.25 E
(scalability adv)54 492 Q(antages for applications and/or netw)-.25 E
(ork topologies where, for v)-.1 E(arious reasons, it is prohibiti)-.25
E .3 -.15(ve t)-.25 H 2.5(oc).15 G(onstruct a)-2.5 E(higher order)54 504
Q(deli)5 E -.15(ve)-.25 G(ry infrastructure abo).15 E .3 -.15(ve t)-.15
H(he basic Layer 3 IP multicast service \(e.g., unicast or h).15 E
(ybrid unicast/multicast)-.05 E(data distrib)54 516 Q(ution trees\).)-.2
E(Additionally)5 E 2.5(,t)-.65 G(he scalability property of N)-2.5 E -.4
(AC)-.35 G(K-oriented protocols [2, 3] is applicable where broad).4 E
("f)54 528 Q(anout" is e)-.1 E(xpected for a single netw)-.15 E
(ork hop \(e.g., cable-TV data deli)-.1 E -.15(ve)-.25 G(ry).15 E 2.5
(,s)-.65 G(atellite, or other broadcast communication)-2.5 E
(communication services\).)54 540 Q(Furthermore, the simplicity of a pr\
otocol based on "\215at" group-wide multicast distrib)5 E(ution may)-.2
E(of)54 552 Q(fer adv)-.25 E(antages for a broad range of distrib)-.25 E
(uted services or dynamic netw)-.2 E(orks and applications.)-.1 E
(NORM protocols can mak)5 E(e)-.1 E
(use of reciprocal \(among senders and recei)54 564 Q -.15(ve)-.25 G
(rs\) multicast communication under the An).15 E
(y-Source Multicast \(ASM\) model)-.15 E(de\214ned in RFC 1112 [5], and\
 are capable of scalable operation in asymmetric topologies such as Sin\
gle-Source Multicast)54 576 Q(\(SSM\) [17] where there may only be unic\
ast routing service from the recei)54 588 Q -.15(ve)-.25 G
(rs to the sender\(s\).).15 E
(NORM operation is compatible with transport layer forw)54 612 Q
(ard error correction coding techniques as described in [19] and)-.1 E
(congestion control mechanisms described in [14] and [18].)54 624 Q 2.5
(Ap)5 G(rinciple limitation of NORM operation in)-2.5 E -.2(vo)-.4 G(lv)
.2 E(es group size)-.15 E(scalability when netw)54 636 Q
(ork capacity for recei)-.1 E -.15(ve)-.25 G 2.5(rf).15 G(eedback is v)
-2.5 E(ery limited.)-.15 E(NORM operation is also go)5 E -.15(ve)-.15 G
(rned by).15 E(implementation b)54 648 Q(uf)-.2 E(fering constraints.)
-.25 E(Buf)5 E(fering greater than that required for typical point-to-p\
oint reliable transport \(e.g.,)-.25 E(Adamson, Bormann, et al.)36 696 Q
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/F0 10/Times-Roman@0 SF(Internet Draft)36 48 Q(NORM Building Blocks)
155.605 E(June 2003)169.475 E(TCP\) is recommended to allo)54 84 Q 2.5
(wf)-.25 G(or disparity in the recei)-2.5 E -.15(ve)-.25 G 2.5(rg).15 G
(roup connecti)-2.5 E(vity and to allo)-.25 E 2.5(wf)-.25 G
(or the feedback delays required)-2.5 E
(to attain group size scalability)54 96 Q(.)-.65 E/F1 10/Times-Bold@0 SF
(5.0 Security Considerations)36 120 Q F0(NORM protocols are e)54 144 Q(\
xpected to be subject to same sort of security vulnerabilities as other\
 IP and IP multicast protocols.)-.15 E(NORM is compatible with IP secur\
ity \(IPSEC\) authentication mechanisms [20] that are RECOMMENDED for p\
rotection)54 156 Q(ag)54 168 Q
(ainst session intrusion and denial of service attacks.)-.05 E 2.5(Ap)5
G(articular threat for N)-2.5 E -.4(AC)-.35 G 2.5(Kb).4 G
(ased protocols is that of N)-2.5 E -.4(AC)-.35 G 2.5(Kr).4 G(eplay)-2.5
E(attacks that w)54 180 Q(ould pre)-.1 E -.15(ve)-.25 G
(nt a NORM sender from making forw).15 E(ard progress in transmission.)
-.1 E(An)5 E 2.5(ys)-.15 G(tandard IPSEC)-2.5 E(mechanisms that can pro)
54 192 Q(vide protection ag)-.15 E
(ainst such replay attacks are RECOMMENDED for use.)-.05 E(Additionally)
5 E 2.5(,N)-.65 G(ORM)-2.5 E
(protocol instantiations SHOULD consider pro)54 204 Q
(viding support for their o)-.15 E(wn N)-.25 E -.4(AC)-.35 G 2.5(Kr).4 G
(eplay attack protection when netw)-2.5 E(ork)-.1 E
(layer mechanisms are not a)54 216 Q -.25(va)-.2 G(ilable.).25 E F1
(6.0 Ackno)36 240 Q(wledgements \(and these ar)-.1 E 2.5(en)-.18 G
(ot Negati)-2.5 E -.1(ve)-.1 G(\)).1 E F0(The authors w)54 264 Q
(ould lik)-.1 E 2.5(et)-.1 G 2.5(ot)-2.5 G(hank Rick Jones, and Joer)
-2.5 E 2.5(gW)-.18 G(idmer for their v)-2.9 E
(aluable comments on this document.)-.25 E(The authors)5 E -.1(wo)54 276
S(uld also lik).1 E 2.5(et)-.1 G 2.5(ot)-2.5 G(hank the RMT w)-2.5 E
(orking group chairs, Roger K)-.1 E(ermode and Lorenzo V)-.25 E
(icisano, for their support in)-.6 E(de)54 288 Q -.15(ve)-.25 G
(lopment of this speci\214cation, and Sally Flo).15 E
(yd for her early inputs into this document.)-.1 E F1(7.0 Refer)36 312 Q
(ences)-.18 E F0([1])59 342 Q(A. Mankin, A. Romano)122.398 342 Q 1.3
-.65(w, S)-.25 H 5(.B).65 G(radner)-5 E 2.5(,V)-.4 G 5(.P)-3.79 G
(axson, "IETF Criteria for Ev)-5.15 E(aluating Reliable Multicast)-.25 E
-.35(Tr)122.398 354 S
(ansport and Application Protocols", RFC 2357, June 1998.).35 E([2])59
378 Q(S. Ping)122.398 378 Q(ali, D. T)-.05 E -.25(ow)-.8 G(sle).25 E 1.3
-.65(y, J)-.15 H 5(.K).65 G(urose, "A Comparison of Sender)-5.15 E
(-Initiated and Recei)-.2 E -.15(ve)-.25 G -.2(r-).15 G
(Initiated Reliable).2 E(Multicast Protocols".)122.398 390 Q(In Proc.)5
E(INFOCOM, San Francisco, CA, October 1993.)5 E([3])59 414 Q(B.N. Le)
122.398 414 Q(vine, J.J. Garcia-Luna-Ace)-.25 E -.15(ve)-.25 G
(s, "A Comparison of Kno).15 E
(wn Classes of Reliable Multicast Protocols",)-.25 E 2.5
(Proc. International)122.398 426 R(Conference on Netw)2.5 E
(ork Protocols \(ICNP-96\), Columb)-.1 E(us, Ohio, Oct 29--No)-.2 E 2.5
(v1)-.15 G 2.5(,1)-2.5 G(996.)-2.5 E([4])59 450 Q(D. Clark, D. T)122.398
450 Q(ennenhouse, "Architectural Considerations for a Ne)-.7 E 2.5(wG)
-.25 G(eneration of Protocols".)-2.5 E(In Proc.)5 E -.4(AC)122.398 462 S
2.5(MS).4 G(IGCOMM, pages 201--208, September 1990.)-2.5 E([5])59 486 Q
2.5(S. Deering,)122.398 486 R
("Host Extensions for IP Multicasting". Internet RFC1112, August 1989.)
2.5 E([6])59 510 Q(S. Flo)122.398 510 Q(yd, V)-.1 E 5(.J)-1.29 G
(acobson, S.)-5 E(McCanne, C.)5 E(Liu, and L.)5 E
(Zhang. "A Reliable Multicast Frame)5 E -.1(wo)-.25 G(rk for Light-).1 E
(weight Sessions and Application Le)122.398 522 Q -.15(ve)-.25 G 2.5(lF)
.15 G(raming", Proc.)-2.5 E -.4(AC)5 G 2.5(MS).4 G(IGCOMM, August 1995.)
-2.5 E([7])59 546 Q(J. Nonnenmacher and E. W)122.398 546 Q 2.5(.B)-.92 G
(iersack, "Optimal Multicast Feedback," in IEEE Infocom , \(San Francis\
co,)-2.5 E(California\), p. 964, March/April 1998.)122.398 558 Q([8])59
582 Q(D. Gossink, J.)122.398 582 Q(Mack)5 E(er)-.1 E 2.5(,")-.4 G
(Reliable Multicast and Inte)-2.5 E(grated P)-.15 E
(arity Retransmission with Channel)-.15 E
(Estimation", IEEE GLOBECOM 98'.)122.398 594 Q([9])59 618 Q(J. Metzner)
122.398 618 Q 2.5(,")-.4 G(An Impro)-2.5 E -.15(ve)-.15 G 2.5(dB).15 G
(roadcast Retransmission Protocol", IEEE T)-2.5 E
(ransactions on Communications,)-.35 E -1.29(Vo)122.398 630 S 2.5
(l. Com-32,)1.29 F(No.6, June 1984.)2.5 E(Adamson, Bormann, et al.)36
696 Q(Expires December 2003)105.89 E([P)119.09 E(age 22])-.15 E
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155.605 E(June 2003)169.475 E([10])54 84 Q(J. Mack)122.398 84 Q(er)-.1 E
2.5(,")-.4 G(Inte)-2.5 E
(grated Erasure-Based Coding for Reliable Multicast T)-.15 E
(ransmission", IR)-.35 E(TF Meeting)-.6 E(presentation, March 1997.)
122.398 96 Q([11])54 120 Q(J. Mack)122.398 120 Q(er)-.1 E 2.5(,")-.4 G
(Reliable Multicast T)-2.5 E(ransport and Inte)-.35 E 2.5
(grated Erasure-based)-.15 F -.15(Fo)2.5 G(rw).15 E
(ard Error Correction", Proc.)-.1 E(IEEE MILCOM 97, October)122.398 132
Q(1997.)5 E([12])54 156 Q 2.58 -1.29(V. O)122.398 156 T(zdemir)1.29 E
2.5(,S)-.4 G 2.5(.M)-2.5 G(uthukrishnan, I. Rhee, "Scalable, Lo)-2.5 E
(w-Ov)-.25 E(erhead Netw)-.15 E(ork Delay Estimation",)-.1 E(NCSU/A)
122.398 168 Q(T&T White P)-1.11 E(aper)-.15 E 2.5(,F)-.4 G
(ebruary 1999.)-2.5 E([13])54 192 Q(M. Luby)122.398 192 Q 2.5(,L)-.65 G
2.5(.V)-2.5 G(icisano, J. Gemmell, L. Rizzo, M. Handle)-3.1 E 1.3 -.65
(y, a)-.15 H(nd J. Cro).65 E(wcroft, "F)-.25 E(orw)-.15 E
(ard Error Correction)-.1 E
(\(FEC\) Building BLock", RFC 3452, December 2002.)122.398 204 Q([14])54
228 Q(J. W)122.398 228 Q(idmer)-.4 E 2.5(,M)-.4 G 2.5(.H)-2.5 G(andle)
-2.5 E 1.3 -.65(y, ")-.15 H(TCP-Friendly Multicast Congestion Control \
\(TFMCC\) Protocol Speci\214cation",).65 E
(Internet Draft draft-ietf-rmt-bb-tfmcc-01.txt, No)122.398 240 Q -.15
(ve)-.15 G(mber 2002, w).15 E(ork in progress.)-.1 E
(Citation for informational)5 E(purposes only)122.398 252 Q(.)-.65 E
([15])54 276 Q 1.48 -.74(T. S)122.398 276 T(peakman, L. V).74 E
(icisano, "Reliable Multicast T)-.6 E
(ransport Building Block Generic Roouter Assist -)-.35 E(Signalling Pro\
tocol Speci\214cation", Internet Draft draft-ietf-rmt-bb-gra-signalling\
-01.txt, January 2003,)122.398 288 Q -.1(wo)122.398 300 S
(rk in progress.).1 E(Citation for informational purposes only)5 E(.)
-.65 E([16])54 324 Q(J. Mack)122.398 324 Q(er)-.1 E 2.5(,R)-.4 G 2.5(.A)
-2.5 G(damson, "Quantitati)-2.5 E .3 -.15(ve P)-.25 H
(rediction of Nack Oriented Reliable Multicast \(NORM\) Feedback",).15 E
(Proc. IEEE MILCOM 2002, October 2002.)122.398 336 Q([17])54 360 Q
(Holbrook, H. W)122.398 360 Q
(., "A Channel Model for Multicast", Ph.D. Dissertation, Stanford Uni)
-.92 E -.15(ve)-.25 G(rsity).15 E 2.5(,D)-.65 G(epartment of)-2.5 E
(Computer Science, Stanford, California, August 2001.)122.398 372 Q
([18])54 396 Q(Rizzo, L., V)122.398 396 Q(icisano, L, Handle)-.6 E 1.3
-.65(y, M)-.15 H 2.5(,").65 G
(PGMCC Single Rate Multicast Congestion Control Protocol)-2.5 E(Speci\
\214cation", Internet Draft draft-ietf-rmt-bb-pgmcc-01.txt, June 2002, \
w)122.398 408 Q(ork in progress.)-.1 E(Citation for)5 E
(informational purposes only)122.398 420 Q(.)-.65 E([19])54 444 Q(Luby)
122.398 444 Q 2.5(,M)-.65 G(., V)-2.5 E
(icisano, L., Gemmell, J., Rizzo, L., Handle)-.6 E 1.3 -.65(y, M)-.15 H
2.5(.a).65 G(nd J. Cro)-2.5 E(wcroft, "The Use of F)-.25 E(orw)-.15 E
(ard Error)-.1 E
(Correction \(FEC\) in Reliable Multicast", RFC 3453, December 2002.)
122.398 456 Q([20])54 480 Q(S. K)122.398 480 Q(ent and R. Atkinson, "Se\
curity Architecture for the Internet Protocol", RFC 2401, No)-.25 E -.15
(ve)-.15 G(mber 1998.).15 E(Adamson, Bormann, et al.)36 696 Q
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155.605 E(June 2003)169.475 E/F1 10/Times-Bold@0 SF(8.0 A)36 84 Q
(uthors' Addr)-.5 E(esses)-.18 E F0(Brian Adamson)54 108 Q
(adamson@itd.nrl.na)54 120 Q(vy)-.2 E(.mil)-.65 E(Na)54 132 Q -.25(va)
-.2 G 2.5(lR).25 G(esearch Laboratory)-2.5 E -.8(Wa)54 144 S
(shington, DC, USA, 20375).8 E(Carsten Bormann)54 168 Q
(cabo@tellique.de)54 180 Q -.7(Te)54 192 S(llique K).7 E
(ommunikationstechnik GmbH)-.35 E(Gusta)54 204 Q(v-Me)-.2 E(yer)-.15 E
(-Allee 25 Geb ude 12)-.2 E(D-13355 Berlin, German)54 216 Q(y)-.15 E
(Mark Handle)54 240 Q(y)-.15 E(mjh@aciri.or)54 252 Q(g)-.18 E
(1947 Center Street, Suite 600)54 264 Q(Berk)54 276 Q(ele)-.1 E 1.3 -.65
(y, C)-.15 H 2.5(A9).65 G(4704)-2.5 E(Joe Mack)54 300 Q(er)-.1 E(mack)54
312 Q(er@itd.nrl.na)-.1 E(vy)-.2 E(.mil)-.65 E(Na)54 324 Q -.25(va)-.2 G
2.5(lR).25 G(esearch Laboratory)-2.5 E -.8(Wa)54 336 S
(shington, DC, USA, 20375).8 E(Adamson, Bormann, et al.)36 696 Q
(Expires December 2003)105.89 E([P)119.09 E(age 24])-.15 E EP
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