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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
(lopment and protocol design, to the nature of the).15 E
(underlying netw)54 636 Q(orks o)-.1 E -.15(ve)-.15 G 2.5(rw).15 G
(hich the protocols may be operating.)-2.5 E(Adamson, Bormann, et al.)36
696 Q(Expires September 2003)105.05 E([P)123.25 E(age 3])-.15 E
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/F0 10/Times-Roman@0 SF(Internet Draft)36 48 Q(NORM Building Blocks)
155.605 E(March 2003)161.705 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 \(e.g.)54 252 Q 2.5(node identi\214ers,)5 F
(FEC, etc\) may be applicable to other forms of reliable multicast.)2.5
E(In those cases, the)5 E(discussion belo)54 264 Q 2.5(wd)-.25 G
(escribes requirements placed on those other general b)-2.5 E
(uilding block areas from the standpoint of N)-.2 E -.4(AC)-.35 G(K-).4
E(oriented reliable multicast.)54 276 Q(Where applicable, other b)5 E
(uilding block documents are referenced for possible contrib)-.2 E
(ution to)-.2 E(NORM protocols.)54 288 Q -.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 the an)-.15 E 2.5(yd)
-.15 G(ependencies of one b)-2.5 E(uilding)-.2 E
(block component upon another or upon other protocol parameters.)54 324
Q 2.5(Ab)5 G(uilding block component may require some form of)-2.7 E
("input" 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 each)-2.5 E -.2(bu)54 348 S
(ilding block component and/or an).2 E 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)
-.2 E(components')54 360 Q 2.5(si)-.55 G(nterf)-2.5 E(ace description.)
-.1 E(The follo)54 384 Q(wing b)-.25 E
(uilding block components are described belo)-.2 E(w:)-.25 E/F2 10
/Times-BoldItalic@0 SF(\(NORM-Speci\214c\))54 408 Q F0 25.17(1\) Sender)
90 420 R -.35(Tr)2.5 G(ansmission).35 E 25.17(2\) N)90 432 R -.4(AC)-.35
G(K-Oriented Repair Process).4 E 25.17(3\) "Late-Joining")90 444 R
(Recei)2.5 E -.15(ve)-.25 G 2.5(rP).15 G(olicies and Mechanisms)-2.5 E
F2(\(General Purpose\))54 468 Q F0 25.17(4\) Node)90 480 R
(\(member\) Identi\214cation)2.5 E 25.17(5\) Data)90 492 R
(Content Identi\214cation)2.5 E 25.17(6\) F)90 504 R(orw)-.15 E
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(ming Collection).35 E 25.17(8\) Group)90 528 R
(Size Determination/Estimation)2.5 E 25.17(9\) Congestion)90 540 R
(Control Operation)2.5 E 20.17(10\) Router/Intermediate)90 552 R
(System Assistance)2.5 E 20.17(11\) Ancillary)90 564 R
(Protocol Mechanisms)2.5 E(Figure 1 pro)54 588 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 their relationships.)-.2 E -.15(Fo)5 G 2.5(re)
.15 G(xample, the content of the)-2.65 E(data messages that sender init\
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Identi\214cation", "FEC" ,)54 600 Q(and "Congestion Control components \
\(Note that the rate of message transmission will generally depend upon\
 the)54 612 Q("Congestion Control" component\).)54 624 Q(Subsequently)5
E 2.5(,t)-.65 G(he recei)-2.5 E -.15(ve)-.25 G
(rs response to these transmissions \(e.g. N).15 E -.4(AC)-.35 G
(King for repair\)).4 E(will depend upon the content of these transmiss\
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(Finally)5 E 2.5(,t)-.65 G(he sender')-2.5 E(s)-.55 E(processing of the\
se responses will feed back into its transmission strate)54 648 Q(gy)
-.15 E(.)-.65 E(Adamson, Bormann, et al.)36 696 Q
(Expires September 2003)105.05 E([P)123.25 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(March 2003)161.705 E/F1 10/Courier@0 SF(Application Data)294
84 Q(|)330 96 Q(v)330 108 Q 66
(.---------------------. .-----------------------.)60 120 R 6(|N)60 132
S(ode Identification |----------->|)-6 E(Sender Transmission)12 E
(|<------.)12 E 36(`---------------------' _.-')60 144 R 36
(`-----------------------' |)6 F 12(.---------------------. _.-')60 156
R 66(.' |)6 F 18(.--------------. |)6 F 6(|D)60 168 S
(ata Identification |--')-6 E 72(.'' |)18 F 6(|J)6 G(oin Policy" |)-6 E
(|)24 E 18(`---------------------' .')60 180 R 84('v)6 G 18
(`--------------' |)-78 F 6(.---------------------. .' ')60 192 R 30
(.------------------------. |)30 F(.->| Congestion Control)42 204 Q 12
(|-' ')12 F 6(|R)36 G(eceiver NACK-oriented |)-6 E(|)36 E 12(|`)42 216 S
12(---------------------' .')-12 F 6(|R)42 G(epair Process)-6 E 36(||)54
G 12(|.)42 228 S(---------------------. .')-12 E 6(|.)54 G 12
(------------------. |)-6 F(|)36 E 18 12(|| F)42 240 T 54(EC |'. |)-12 F
6(|N)6 G(ACK Initiation)-6 E -6 18(|| |)12 H 12(|`)42 252 S
(---------------------'` `._)-12 E 6(|`)42 G 12(------------------' |)-6
F(|)36 E 12(|.)42 264 S(---------------------. ``. `-._)-12 E 6(|.)18 G
12(------------------. |)-6 F(|)36 E 18(`--| RTT)42 276 R 12
(Collection |._`)6 F 24(``)6 G(->| | NACK Content)-24 E -6 18(|| |)30 H
(`---------------------' .`- `)60 288 Q 6(|`)36 G 12
(------------------' |)-6 F(|)36 E 6(.---------------------. \\)60 300 R
6(`-`._ |)6 F 12(.------------------. |)6 F(|)36 E 24(|G)60 312 S
(roup Size Est.)-24 E(|---.-`---`->| | NACK Suppression |)12 E 36(||)18
G 6(`---------------------'`. `)60 324 R 30(`|)6 G 12
(`------------------' |)-24 F(|)36 E 6(.---------------------. ` `)60
336 R 24(``)6 G 30(------------------------' |)-24 F 42(|O)60 348 S 48
(ther |)-42 F 12(``)18 G 78(`|)-6 G(.-----------------. |)-72 E 18
(`---------------------' `)60 360 R 54 6(`` ||)12 H
(Router Assistance| |)-6 E(`. ` `)228 372 Q 12(v`)66 G
(----------------' |)-12 E(`.`' .-------------------------.)240 384 Q(|)
30 E(`>| Sender NACK Processing)258 396 Q(|_____/)12 E 6(|a)270 408 S
(nd Repair Response)-6 E(|)30 E(`-------------------------')270 420 Q
150(^^)156 444 S 150(||)156 456 S(.-----------------------------.)144
468 Q 54(|\()144 480 S 54(Security\) |)-54 F
(`-----------------------------')144 492 Q/F2 10/Times-Italic@0 SF -.45
(Fi)210.06 516 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)38.5 540 Q
(yond NORM.)-.15 E(The most sign\214cant of these)5 E
(components, FEC and Congestion Control, are discussed in other b)38.5
552 Q(uilding block documents [13], [14].)-.2 E 2.5(Ab)5 G
(rief description of)-2.5 E
(these areas and their role in NORM protocol operation is gi)38.5 564 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.)38.5 576 Q(These areas are discussed in detail belo)7.5
E 3.8 -.65(w. S)-.25 H
(ome other components \(e.g. "Security"\) impact man).65 E 2.5(ya)-.15 G
(spects of)-2.5 E(the protocol and others such as "Router Assistance" m\
ay be more transparent to the core protocol processing.)38.5 588 Q
(The sections)5 E(belo)38.5 600 Q 2.5(wd)-.25 G(iscuss issues with re)
-2.5 E -.05(ga)-.15 G(rds to these b).05 E
(uilding block components and their relationships.)-.2 E
(Where applicable, speci\214c)5 E(technical recommendations are made fo\
r mechanisms that will properly satisfy the goals of NORM transport for\
 the Internet.)38.5 612 Q/F3 10/Times-Bold@0 SF(3.1 Sender transmission)
36 636 Q F0(Adamson, Bormann, et al.)36 696 Q(Expires September 2003)
105.05 E([P)123.25 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(March 2003)161.705 E
(Senders will transmit data content to the multicast session.)38.5 84 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 pack)38.5
96 Q(et sizes determined by application and/or netw)-.1 E
(ork architecture requirements.)-.1 E(An)5 E(y)-.15 E(FEC encoding of s\
ender transmissions SHOULD con\214rm with the guidelines of [13].)38.5
108 Q(When congestion control mechanisms are)5 E(needed \(REQ)38.5 120 Q
(UIRED for general Internet operatoin\), NORM transmission SHALL be con\
trolled by the congestion control)-.1 E 2.5(mechanism. In)38.5 132 R(an)
2.5 E 2.5(yc)-.15 G
(ase, it is RECOMMENDED that all data transmissions from)-2.5 E
(NORM senders be subject to rate limitations)5 E
(determined by the application or congestion control algorithm.)38.5 144
Q(The sender')5 E 2.5(st)-.55 G(ransmissions SHOULD mak)-2.5 E 2.5(eg)
-.1 G(ood utilization of)-2.5 E(the a)38.5 156 Q -.25(va)-.2 G(ilable c\
apacity \(which may be limited by the application and/or by congestion \
control\).).25 E(As a result, it is e)5 E(xpected there)-.15 E
(will be o)38.5 168 Q -.15(ve)-.15 G(rlap and multiple).15 E(xing of ne)
-.15 E 2.5(wd)-.25 G(ata content transmission with repair content.)-2.5
E(Other f)5 E(actors related to application)-.1 E
(operation may determine sender transmission formats and methods.)38.5
180 Q -.15(Fo)5 G 2.5(re).15 G
(xample, some consideration needs to be gi)-2.65 E -.15(ve)-.25 G 2.5
(nt).15 G 2.5(ot)-2.5 G(he)-2.5 E(sender')38.5 192 Q 2.5(sb)-.55 G(eha)
-2.5 E
(vior during intermittent idle periods when it has no data to transmit.)
-.2 E(In addition to data content, other sender messages or commands ma\
y be emplo)38.5 216 Q(yed as part of protocol operation.)-.1 E(These)5 E
(messages may occur outsided of the scope of application data transfer)
38.5 228 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)38.5
240 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.)38.5 252 Q
(Note that protocol design SHOULD pro)5 E
(vide mechanisms for dealing with cases where such messages are)-.15 E
(not recei)38.5 264 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 that it)-.15 E
(is temporarily \(or permanently\) halting transmission.)38.5 276 Q
(At this time, it may be appropriate for recei)5 E -.15(ve)-.25 G
(rs to respond with N).15 E -.4(AC)-.35 G(Ks).4 E(for an)38.5 288 Q 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 sender should).65 E(allo)38.5 300 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 recei).4 E -.15(ve)-.25 G(rs to this).15
E(command.)38.5 312 Q(In general, when there is an)38.5 336 Q 2.5(yr)
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eedback operation, the timing of redundant transmission of control)-2.5
E(messages issued by a sender and other NORM protocol timeouts should b\
e dependent upon the group greatest round trip timing)38.5 348 Q(\()38.5
360 Q/F1 10/Courier@0 SF(GRTT)A F0 2.5(\)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 F1(GRTT)2.5 E F0
(is an estimate of the w)2.5 E(orst-)-.1 E
(case round-trip timing from a sender to an)38.5 372 Q 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 F1(GRTT)2.5 E F0(interv)2.5 E
(al is a conserv)-.25 E(ati)-.25 E -.15(ve)-.25 G(estimate of the maxim\
um span \(with respect to delay\) of the multicast group across a netw)
38.5 384 Q(ork topology with respect to gi)-.1 E -.15(ve)-.25 G(n).15 E
(sender)38.5 396 Q 5(.N)-.55 G(ORM instantiations SHOULD be able to dyn\
amically adapt to a wide range of multicast netw)-5 E(ork topologies.)
-.1 E/F2 10/Times-BoldItalic@0 SF(Interface Description)38.5 420 Q/F3 10
/Times-Italic@0 SF(Inputs:)38.5 444 Q F0 25.17(1\) Application)90 468 R
(data content)2.5 E 25.17(2\) Se)90 480 R(gmentation size)-.15 E 25.17
(3\) FEC)90 492 R(parameters)2.5 E 25.17(4\) T)90 504 R
(ransmission rate)-.35 E 25.17(5\) Application)90 516 R(controls)2.5 E
25.17(6\) Recei)90 528 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 F3(Outputs:)54
552 Q F0 25.17(1\) Controlled)90 576 R(transmission of messages with he\
aders uniquely identifying data or repair content within the)2.5 E
(conte)126 588 Q(xt of the NORM session.)-.15 E 25.17(2\) Commands)90
600 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/F4
10/Times-Bold@0 SF(3.2 N)36 624 Q -.55(AC)-.2 G(K-Oriented Repair Pr).55
E(ocess)-.18 E F0 2.5(Ac)54 648 S
(ritical component of the NORM protocol b)-2.5 E(uilding block is the N)
-.2 E -.4(AC)-.35 G 2.5(Kr).4 G(epair process.)-2.5 E
(There are four primary elements of)5 E(Adamson, Bormann, et al.)36 696
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155.605 E(March 2003)161.705 E 2.5(ag)54 84 S(eneral N)-2.5 E -.4(AC)
-.35 G 2.5(Kr).4 G(epair process:)-2.5 E 25.17(1\) Recei)90 108 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)90 120 R -.4(AC)-.35 G 2.5(Ks).4 G(uppression,)-2.5 E
25.17(2\) N)90 132 R -.4(AC)-.35 G 2.5(Km).4 G(essage content,)-2.5 E
25.17(4\) Sender)90 144 R -.35(NA)2.5 G(CK processing and response.)-.05
E/F1 10/Times-BoldItalic@0 SF(3.2.1 N)36 168 Q -.65(AC)-.3 G 2.5(KP).65
G(rocess Initiation)-2.5 E F0(The NORM N)54 192 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)54 204 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)54 216 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)54 228 Q
(subsequent coding block or transmission object.)54 240 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)54 252 Q
(ed in order of transmission.)-.15 E(Alternati)54 276 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)54 288
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)54 300 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)54 312 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.)54 324 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)54 336 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)54 348 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.)54 360 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)54 372 Q -.15(ve)-.25 G 2.5(dc).15
G(oding blocks.)-2.5 E -.15(Fo)54 396 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)54 408 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')54 420 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)54 432 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)54 444 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)54 456 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
(Interface Description)54 480 Q/F2 10/Times-Italic@0 SF(Inputs:)54 504 Q
F0 25.17(1\) Sender)90 528 R
(data content with sequencing identi\214ers from sender transmissions.)
2.5 E 25.17(2\) History)90 540 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:)54 564 Q F0 25.17
(1\) N)90 588 R -.4(AC)-.35 G 2.5(Kc).4 G(ycle initiation decision)-2.65
E 25.17(2\) Recorded)90 600 R(sender transmission sequence position.)2.5
E F1(3.2.2 N)36 624 Q -.65(AC)-.3 G 2.5(KS).65 G(uppression Mec)-2.5 E
(hanisms)-.1 E F0 2.5<418d>54 648 S -.15(ex)-2.5 G
(ible NORM feedback suppression mechanism is the use of initial back).15
E(of)-.1 E 2.5(ft)-.25 G(imeouts by recei)-2.5 E -.15(ve)-.25 G
(rs wishing to transmit).15 E(Adamson, Bormann, et al.)36 696 Q
(Expires September 2003)105.05 E([P)123.25 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(March 2003)161.705 E -.35(NA)54 84 S(CK messages[6].)-.05 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 transmit a)-2.5
E(unless the content of the pending)10 E(repair request is completely)54
96 Q(superseded by N)5 E -.4(AC)-.35 G 2.5(Km).4 G
(essages heard from other recei)-2.5 E -.15(ve)-.25 G(rs \(when recei)
.15 E -.15(ve)-.25 G(rs are multicasting).15 E -.35(NA)54 108 S
(CKs\) or from some indicator from the sender)-.05 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 may f)-2.5 E(acilitate)-.1 E -.35(NA)54
120 S(CK suppression by forw)-.05 E 2.5(arding a)-.1 F
(representation of N)2.5 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 pro)-.18 E(vide some)-.15 E(other indicat\
or of the repair information it will be subsequently transmitting.)54
132 Q -.15(Fo)54 156 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)54 168 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)54 180 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.)54 192 Q
(The mean of the distrib)5 E
(ution should be determined as a function of)-.2 E
(the current estimate of sender<->group)54 204 Q/F1 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.)54 216 Q 2.5(As)54 240
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)54 252 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)54 264 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)54 276 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 \()-2.5 E F1
(T_maxBackoff)A F0 2.5(\)c)C(an also be controlled to allo)-2.5 E 2.5
(wt)-.25 G(he)-2.5 E(application control reliable deli)54 288 Q -.15(ve)
-.25 G(ry latenc).15 E 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 F1(T_maxBackoff)2.5 E F0(will)2.5 E(result in a lo)54
300 Q(wer density of feedback traf)-.25 E(\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 F1(T_maxBackoff)2.5 E F0(results in shorter)2.5 E
(latenc)54 312 Q 2.5(yw)-.15 G(hich also reduces the b)-2.5 E(uf)-.2 E
(fering requirements of senders and recei)-.25 E -.15(ve)-.25 G
(rs for reliable transport.).15 E(Gi)54 336 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 \()-2.5 E F1(R)A
F0(\), 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(\()54 348 Q F1(t')A F0 2.5(\)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)90 372 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)301.2 396 S(n\(R\) + 1)-6 E F0
25.17(2\) Pick)90 420 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)162 444 S(L)-48 E 6
(-------------------- to)114 456 R 6(-------------------- + ----------)
18 F 18(T_maxBackoff*\(exp\(L\)-1\) T_maxBackoff*\(exp\(L\)-1\))108 468
R(T_maxBackoff)12 E F0 25.17(3\) T)90 492 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:)126 504 Q F1
(t' = T_maxBackoff/L * ln\(x * \(exp\(L\) - 1\) * \(T_maxBackoff/L\)\))
157.2 528 Q F0(Adamson, Bormann, et al.)36 696 Q(Expires September 2003)
105.05 E([P)123.25 E(age 8])-.15 E EP
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/F0 10/Times-Roman@0 SF(Internet Draft)36 48 Q(NORM Building Blocks)
155.605 E(March 2003)161.705 E(This is a C language function that can b\
e used to perform this function:)38.5 84 Q/F1 10/Courier@0 SF
(double RandomBackoff\(double maxTime, double groupSize\))38.5 108 Q({)
38.5 120 Q(double lambda = log\(groupSize\) + 1;)62.5 132 Q
(double x = UniformRand\(lambda/maxTime\) +)62.5 144 Q
(lambda / \(maxTime*\(exp\(lambda\)-1\)\);)128.5 156 Q
(return \(\(maxTime/lambda\) *)62.5 168 Q
(log\(x*\(exp\(lambda\)-1\)*\(maxTime/lambda\)\)\);)110.5 180 Q 12(}/)
38.5 192 S 6(/e)-12 G(nd RandomBackoff\(\))-6 E F0(where)38.5 216 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 5(.F)C(or)-5.15 E -.15
(ex)38.5 228 S(ample, based on the POSIX ").15 E F1(rand\(\))A F0 2.5
("f)C(unction, the follo)-2.5 E(wing C code can be used:)-.25 E F1(inli\
nedouble UniformRand\(double max\) {return \(max * \(\(double\)rand\(\)\
/\(double\)RAND_MAX\)\);})38.5 252 Q F0(The number of e)38.5 276 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:)38.5 288 Q F1 6(N=e)176.45 312 S
(xp\(1.2 * L / \(2*T_maxBackoff/GRTT\)\))-6 E F0(Thus the maximum back)
38.5 336 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 deri).65 E -.15(ve)-.25 G(d).15 E(from [7] and assumes)38.5 348
Q 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 2.5(ng).15 G(roup size as)-2.5 E(sho)38.5 360 Q
(wn in the algorithm abo)-.25 E -.15(ve)-.15 G 5(.N).15 G
(ote that other mechanisms within protocol may w)-5 E
(ork to reduce redundant N)-.1 E -.4(AC)-.35 G 2.5(Kg).4 G(eneration)
-2.5 E(further)38.5 372 Q 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 adv)-2.5 E
(ertised)-.15 E F1(GRTT)2.5 E F0(estimate such that:)38.5 384 Q F1
(T_maxBackoff = K * GRTT)191.595 408 Q F0(;where)6 E F1 6(K>)2.5 G 6(=1)
-6 G F0 -.15(Fo)38.5 432 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 -.25(va)38.5 444 S
(lue of).25 E F1(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 scalability)-2.5 E(tradeof)38.5 456 Q(f.)
-.25 E(Gi)38.5 480 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 periods)-2.5
E(related to the N)38.5 492 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 recei)-5 E -.15(ve)-.25 G
2.5(rs).15 G(hould)-2.5 E -.1(wa)38.5 504 S(it 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 c)-.25 E(ycle)-.15 E(\()38.5 516 Q F1
(T_rcvrHoldoff)A F0 2.5(\). 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 messages.)-2.5 E(An)5
E(appropriate v)38.5 528 Q
(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 pro)-2.5 E
(vide a repair)-.15 E 2.5(response. This)38.5 540 R(MUST include an)2.5
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 multiple N).05 E
-.4(AC)-.35 G(Ks are).4 E(accumulated to determine an ef)38.5 552 Q
(\214cient repair response.)-.25 E
(These timeouts are further discussed in the section belo)5 E 2.5(wo)
-.25 G 2.5(n")-2.5 G(Sender)-2.5 E -.35(NA)38.5 564 S
(CK Processing and Repair Response".)-.05 E
(There are also secondary measures that can be applied to impro)38.5 588
Q .3 -.15(ve t)-.15 H(he performance of feedback suppression.).15 E -.15
(Fo)5 G 2.5(re).15 G(xample, the)-2.65 E(sender')38.5 600 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 2.5(,t)-.4 G(he)-2.5 E(recei)
38.5 612 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 obs\
erving the data object, FEC block).1 E(number)38.5 624 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 2.5(sc)-.55 G(urrent)-2.5 E
(transmission position e)38.5 636 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 requests for)-2.5 E
(repair of data the sender may be planning to pro)38.5 648 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 be v)2.5 E(ery)-.15 E
(Adamson, Bormann, et al.)36 696 Q(Expires September 2003)105.05 E
([P)123.25 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(March 2003)161.705 E(ef)38.5 84 Q(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 \(or indicators).15 E
(from the sender\) are lost.)38.5 96 Q(Another mechanism \(particularly\
 applicable when FEC is used\) is for the sender to embed an)5 E
(indication of impending repair transmissions in current pack)38.5 108 Q
(ets sent.)-.1 E -.15(Fo)5 G 2.5(re).15 G
(xample, the indication may be as simple as an)-2.65 E(adv)38.5 120 Q
(ertisment of the number of FEC pack)-.15 E
(ets to be sent for the current applicable coding block.)-.1 E(Finally)
38.5 144 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)38.5
156 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)38.5 168 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 .3 -.15(ve i)-.25 H(nterv).15 E(als)-.25 E
(of time in the loss e)38.5 180 Q(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)2.5 E(back)38.5 192 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
2.5(rs. This).25 F(additional slot in)2.5 E(the N)38.5 204 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 some applications.)-.15 E
(The)5 E(resolution of these trade-of)38.5 216 Q
(fs may be dependent upon the protocol')-.25 E 2.5(st)-.55 G(ar)-2.5 E
(get application set or netw)-.18 E(ork.)-.1 E(After the random back)
38.5 240 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 request)-2.5 E(or not \(i.e. it has been suppressed\).)38.5 252 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 occurred:)-.25 E 25.17(1\) The)90 276 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)126 288 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)126 300 Q -.4(AC)
-.35 G 2.5(Kc).4 G(ycle initiation \(when)-2.65 E(the back)126 312 Q(of)
-.1 E 2.5(ft)-.25 G(imer w)-2.5 E(as acti)-.1 E -.25(va)-.25 G(ted\).)
.25 E 25.17(2\) The)90 348 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)126 360 Q -.15(ve)-.25 G(r').15 E
2.5(sr)-.55 G(epair needs. \(This detection of sender "re)-2.5 E
(wind" indicates the)-.25 E(sender has already responded to other recei)
126 372 Q -.15(ve)-.25 G 2.5(rr).15 G
(epair needs of which the local recei)-2.5 E -.15(ve)-.25 G 2.5(rm).15 G
(ay not ha)-2.5 E .3 -.15(ve b)-.2 H(een).15 E -2.3 -.15(aw a)126 384 T
2.5(re\). 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)126 396 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)126 408
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)126 420 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)126 432 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)126 444 Q -.4(AC)-.35 G
(King is required.).4 E(If these conditions ha)38.5 468 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)38.5 480 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 to).25 E
(the current sender transmission sequence position.)38.5 492 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)38.5 504 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 occur)-2.5 E(,)-.4 E(the N)
38.5 516 Q -.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
(Adamson, Bormann, et al.)36 696 Q(Expires September 2003)105.05 E
([P)118.25 E(age 10])-.15 E EP
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/F0 10/Times-Roman@0 SF(Internet Draft)36 48 Q(NORM Building Blocks)
155.605 E(March 2003)161.705 E/F1 10/Times-BoldItalic@0 SF
(Interface Description)38.5 84 Q/F2 10/Times-Italic@0 SF(Inputs:)38.5
108 Q F0 25.17(1\) Group)90 132 R(greatest round trip time estimate \()
2.5 E/F3 10/Courier@0 SF(GRTT)A F0(\).)A 25.17(2\) Group)90 144 R
(size estimate.)2.5 E 25.17(3\) Application-de\214ned)90 156 R
(bound on back)2.5 E(of)-.1 E 2.5(ft)-.25 G(imeout period.)-2.5 E 25.17
(4\) N)90 168 R -.4(AC)-.35 G(Ks from other recei).4 E -.15(ve)-.25 G
(rs.).15 E 25.17(5\) Pending)90 180 R
(repair indication from sender \(may be forw)2.5 E(arded N)-.1 E -.4(AC)
-.35 G(Ks\).).4 E 25.17(6\) Recorded)90 192 R
(sender transmission sequence position.)2.5 E 25.17(7\) Current)90 204 R
(sender transmission sequence position.)2.5 E F2(Outputs:)54 228 Q F0
25.17(1\) Y)90 252 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)36 276 Q -.65(AC)-.3 G 2.5(KC).65 G
(ontent)-2.5 E F0(The content of N)54 300 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.)54 312 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 \(\
See Section 3.5 belo)54 324 Q 2.5(w\). 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)54 336 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)54 348 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)54 360 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
372 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)54 384 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.)54 396 Q F1(3.2.3.1 N)54 420 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)54 444 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
(repair is needed and a count of erasures \(missing pack)54 456 Q
(ets\) for the coding block.)-.1 E
(Note that this assumes the FEC algorithm is)5 E
(capable of repairing _an)54 468 Q(y_ loss combination within the codin\
g block and that the quantity of unique FEC parity pack)-.15 E(ets the)
-.1 E(serv)54 480 Q(er has a)-.15 E -.25(va)-.2 G
(ilable to transmit is essentially unlimited \(i.e. the serv).25 E
(er will al)-.15 E -.1(wa)-.1 G(ys be able to pro).1 E(vide ne)-.15 E
1.3 -.65(w, u)-.25 H(nique, pre).65 E(viously)-.25 E(unsent parity pack)
54 492 Q(ets in response to an)-.1 E 2.5(ys)-.15 G
(ubsequent repair requests for the same coding block\).)-2.5 E
(In other cases, the N)5 E -.4(AC)-.35 G(K).4 E
(content will need to also _e)54 504 Q(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.)54 516 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)54 528 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)54 552
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)54 564 Q -.25(va)-.2 G
(ilable parity for a gi).25 E -.15(ve)-.25 G 2.5(nc).15 G
(oding block \(or the sender')-2.5 E 2.5(sa)-.55 G(bility to b)-2.5 E
(uf)-.2 E(fer transmission history)-.25 E(is e)54 576 Q
(xceeded by the delay*bandwidth*loss characteristics of the netw)-.15 E
(ork topology\), the N)-.1 E -.4(AC)-.35 G 2.5(Kc).4 G
(ontent will need to contain)-2.5 E(_e)54 588 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 and/or)-.1 E
(data retransmissions.)54 600 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 2.5(re).15 G(xample, it)-2.65 E
(may be useful for decorrelating loss characteristics among a group of \
recei)54 612 Q -.15(ve)-.25 G(rs to help dif).15 E
(ferentiate candidate congestion)-.25 E
(control bottlenecks among the recei)54 624 Q -.15(ve)-.25 G 2.5(rs).15
G(et.)-2.5 E(When FEC is used and N)54 648 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(Adamson, Bormann, et al.)36 696 Q
(Expires September 2003)105.05 E([P)118.25 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(March 2003)161.705 E(can N)54 84 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 96 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)54 108 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)54 120 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)54 132 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
144 Q(When systematic FEC codes are used, the sender transmits the data\
 content of the coding block \(and optionally some)54 168 Q
(quantity of parity pack)54 180 Q(ets\) 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)54 192 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)54 204 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
216 Q(Recei)54 240 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)54 252 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)54 264 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)54 276 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)54 288 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)54 300 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)54 312 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)54 324 S(CKs will compr\
ise a minimal set of sender transmissions to satisfy their repair needs\
.)-.05 E(In summary)54 348 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)54 360 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)54 372 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)54 384 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)54 396 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)54 408 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)54 420 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)54 432 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)54 444 Q -.4(AC)-.35 G 2.5(Ko).4 G(peration.)-2.5 E
(After receipt and accumulation of N)54 468 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
(\(pre)54 480 Q(viously untransmitted\) 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)54 492 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)54 504 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)54 516 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)54 528 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)54 540 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)54 552 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.)54 564 Q/F1 10/Times-BoldItalic@0 SF(3.2.3.2 N)54 588 Q -.65
(AC)-.3 G 2.5(KC).65 G(ontent F)-2.5 E(ormat)-.7 E F0(The format of N)54
612 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.)54 624 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)54 636 Q
(blocking is optional at the protocol instantiation')54 648 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(Adamson, Bormann, et al.)36 696 Q
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155.605 E(March 2003)161.705 E(sender)54 84 Q 5(.I)-.55 G 2.5(ti)-5 G
2.5(sr)-2.5 G(ecommended that transport data content identi\214cation i\
s 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 96 Q -.1(wo)-.25 G(rk de).1 E
(generates to that of typical transport data)-.15 E(se)54 108 Q
(gmentation and reassembly in its simplest form.)-.15 E/F1 10/Courier@0
SF(Session_)102 144 Q(\\_)156 156 Q(Sender_)174 168 Q(\\_)222 180 Q
([Object/Stream\(s\)]_)240 192 Q(\\_)354 204 Q([FEC Blocks]_)372 216 Q
(\\_)450 228 Q(Segments)468 240 Q/F2 10/Times-Italic@0 SF -.45(Fi)
192.455 264 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)54 288 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)
90 312 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)126 324 Q(gments,)-.15 E 25.17
(2\) Be)90 348 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
372 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)126 384 R(erasure counts may also be desirable.)
2.5 E 25.17(4\) Ha)90 408 R .3 -.15(ve a r)-.2 H
(easonably compact format, and).15 E 25.17(5\) Be)90 432 R(capable of w)
2.5 E(orking with the Generic Router Assist \(GRA\) b)-.1 E
(uilding block.)-.2 E(The concatenation of)54 456 Q F2(objectId::bloc)
2.5 E(kId::se)-.2 E(gmentId)-.4 E F0(comprises a basic transport protoc\
ol data unit \(TPDU\) identi\214er of)2.5 E(se)54 468 Q
(gments transmitted 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 li\
sts and/or ranges of these TPDU identi\214ers)-2.5 E(to b)54 480 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 blocking is)5 E
(used, the TPDU is a simple linear representation of the data se)54 492
Q(gments transmitted by the sender)-.15 E 5(.W)-.55 G
(hen the TPDU represents)-5 E 2.5(ah)54 504 S(ierarch)-2.5 E 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 require \215ags to)-2.5
E(indicate which portion of the TPDU is applicable.)54 516 Q -.15(Fo)5 G
2.5(re).15 G
(xample, if an entire "object" \(or range of objects" is missing in the)
-2.65 E(recei)54 528 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(<blockIds>)2.5 E F0(or)2.5 E F1
(<symbolIds>)2.5 E F0(for which to)2.5 E(request repair and thus requir\
es some mechanism to request repair \(or retransmission\) of the entire\
 unit represented by an)54 540 Q F1(<objectId>)54 552 Q F0 5(.T)C(he sa\
me is true if entire FEC coding blocks represented by one or a range of)
-5 E F1(<blockIds>)2.5 E F0(is missing for)2.5 E 2.5(ar)54 564 S(ecei)
-2.5 E -.15(ve)-.25 G -.55(r.).15 G/F3 10/Times-BoldItalic@0 SF
(3.2.4 Sender N)36 588 Q -.65(AC)-.3 G 2.5(KP).65 G
(rocessing and Repair Response)-2.5 E F0
(Upon reception of a repair request from a recei)54 612 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)54 624 Q(suf)5 E
(\214cient time to accumulate potentially multiple)-.25 E -.35(NA)54 636
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.)54 648 Q(D\
epending upon the approach used, some protocols may \214nd it bene\214c\
ial for the sender)5 E(Adamson, Bormann, et al.)36 696 Q
(Expires September 2003)105.05 E([P)118.25 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(March 2003)161.705 E(to pro)54 84 Q(vide an indicator of pend\
ing repair transmissions as part of the its current transmitted message\
 content.)-.15 E(This can aid)5 E(some N)54 96 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)54 108 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\()-.25 G(")-2.5 E/F1 10/Courier@0 SF
(T_maxBackoff)A F0 2.5("f)C(rom Section 3.2.2\) and propag)-2.5 E
(ation of N)-.05 E -.4(AC)-.35 G(K).4 E(messages from the recei)54 120 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)54 132 Q F1(\(1*GRTT\))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)54 144 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 F1
(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:)54 156 Q F1
(T_sndrAggregate = T_maxBackoff + 1*GRTT = \(K+1\)*GRTT)148.2 180 Q F0
(Immediately after the sender N)54 204 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)54 216
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)54 228 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)
54 240 Q -.15(ve)-.25 G 2.5(rg).15 G 2.5(roup. This)-2.5 F("holdof)2.5 E
(f" time should be)-.25 E F1(\(1*GRTT)2.5 E F0(to)2.5 E(allo)54 252 Q
2.5(wf)-.25 G(or w)-2.5 E(orst case asymmetry:)-.1 E F1
(T_sndrHoldoff = 1*GRTT)238.2 276 Q F0(Recall that the recei)54 300 Q
-.15(ve)-.25 G(rs' will emplo).15 E 2.5(yah)-.1 G(oldof)-2.5 E 2.5(ft)
-.25 G(imeout after generating a N)-2.5 E -.4(AC)-.35 G 2.5(Km).4 G
(essage to allo)-2.5 E 2.5(wt)-.25 G(ime for the sender')-2.5 E(s)-.55 E
2.5(response. Gi)54 312 R -.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 recei)-2.5 E -.15(ve)-.25 G
(rs should use).15 E(holdof)54 324 Q 2.5(ft)-.25 G(imeouts of:)-2.5 E F1
(T_rcvrHoldoff = T_sndrAggregate + T_sndrHoldoff = \(K+2\)*GRTT)124.2
348 Q F0(This allo)54 372 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)54 384 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)54 396 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)54 408 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)54 432 Q(xpiration of the "T_sndrAggre)-.15 E -.05(ga)-.15 G
(te" timeout, the sender will be).05 E
(gin transmitting repair messages according to the)-.15 E
(accumulated content of N)54 444 Q -.4(AC)-.35 G(Ks recei).4 E -.15(ve)
-.25 G 2.5(d. There).15 F(are a couple of guidelines with re)2.5 E -.05
(ga)-.15 G(rds to FEC-based repair and the).05 E
(ordering of the repair response from the sender that can impro)54 456 Q
.3 -.15(ve r)-.15 H(eliable multicast ef).15 E(\214cienc)-.25 E -.65(y.)
-.15 G
(When FEC is used, it is bene\214cial that the sender transmit pre)54
480 Q(viously untransmitted parity content as repair messages)-.25 E
(whene)54 492 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 tr\
ansmitted content from their)-.25 E(indi)54 504 Q
(vidual subsets of recei)-.25 E -.15(ve)-.25 G 2.5(dm).15 G(essages.)
-2.5 E(The transmitted object and/or stream data and repair content sho\
uld be inde)54 528 Q -.15(xe)-.15 G 2.5(dw).15 G 2.5(ith monotonically)
-2.5 F(increasing sequence)2.5 E(numbers \(within a reasonably lar)54
540 Q(ge ordinal space\).)-.18 E(If the sender observ)5 E
(es the discipline of)-.15 E(transmitting repair for the)5 E
(earliest content \(e.g. ordinally lo)54 552 Q
(west FEC blocks\) \214rst, the recei)-.25 E -.15(ve)-.25 G
(rs can use a strate).15 E(gy of witholding repair requests for later)
-.15 E(content until the sender once ag)54 564 Q
(ain returns to that point in the object/stream transmission sequence.)
-.05 E(This can increase)5 E -.15(ove)54 576 S(rall message ef).15 E
(\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 dependence).15 E
(upon strict time synchronization among the sender and recei)54 588 Q
-.15(ve)-.25 G 2.5(rs. This).15 F(also helps minimize the b)2.5 E(uf)-.2
E(fering requirements of)-.25 E(recei)54 600 Q -.15(ve)-.25 G(rs and se\
nders and reduces redundant transmission of data to the group at lar).15
E(ge.)-.18 E(Adamson, Bormann, et al.)36 696 Q(Expires September 2003)
105.05 E([P)118.25 E(age 14])-.15 E EP
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/F0 10/Times-Roman@0 SF(Internet Draft)36 48 Q(NORM Building Blocks)
155.605 E(March 2003)161.705 E/F1 10/Times-BoldItalic@0 SF
(Interface Description)54 84 Q/F2 10/Times-Italic@0 SF(Inputs:)54 108 Q
F0 25.17(1\) Recei)90 132 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)90 144 R(timing information)
2.5 E F2(Outputs:)54 168 Q F0 25.17(1\) Repair)90 192 R
(messages \(FEC and/or Data content retransmission\))2.5 E/F3 10
/Times-Bold@0 SF(3.3 Gr)36 216 Q(oup "J)-.18 E(oin" P)-.15 E
(olicies/ Pr)-.2 E(ocedur)-.18 E(es)-.18 E F0
(Consideration should be gi)54 240 Q -.15(ve)-.25 G 2.5(nt).15 G 2.5(oh)
-2.5 G .5 -.25(ow n)-2.5 H .5 -.25(ew r).25 H(ecei).25 E -.15(ve)-.25 G
(rs join a group \(perhaps where reliable transmission is already in pr\
ogress\)).15 E(and be)54 252 Q(ging N)-.15 E -.4(AC)-.35 G(King for an)
.4 E 2.5(yr)-.15 G(epair needs. If this is unconstrained, the dynamics \
of group membership may impede the)-2.5 E(application')54 264 Q 2.5(sa)
-.55 G(bility to meet it goals in progressing the transmission of data.)
-2.5 E(Policies limiting the opportunities when)5 E(recei)54 276 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 beha).15 E(vior)-.2 E 5(.F)-.55 G(or e)-5.15 E
(xample, it may be)-.15 E(bene\214cial if recei)54 288 Q -.15(ve)-.25 G
(rs only attempt reliable reception from a ne).15 E
(wly-heard sender when upon non-repair transmissions of data)-.25 E
(in the \214rst FEC block of an object or logical portion of a stream.)
54 300 Q(The sender may also implement policies limiting the)5 E(recei)
54 312 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 scalability reasons in some situations.).15 E(In)5 E
(some types of b)54 324 Q
(ulk transfer applications \(and for potential interacti)-.2 E .3 -.15
(ve a)-.25 H(pplications\), it may alternati).15 E -.15(ve)-.25 G
(ly desirable to ha).15 E .3 -.15(ve a)-.2 H
(looser transport synchronization polic)54 336 Q 2.5(ya)-.15 G(nd rely \
upon session management mechanisms to limit group dynamics that can)-2.5
E(cause poor performance.)54 348 Q F1(Interface Description)54 372 Q F2
(Inputs:)54 396 Q F0 25.17(1\) Current)90 420 R(object/stream data/repa\
ir content and sequencing identi\214ers from sender transmissions.)2.5 E
F2(Outputs:)54 444 Q F0 25.17(1\) Recei)90 468 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
(3.4 Reliable Multicast Member Identi\214cation)36 492 Q F0
(In a NORM protocol \(or other multicast)54 516 Q(protocols\) where the\
re is the potential for multiple sources of data, it is necessary to)5 E
(pro)54 528 Q(vide some mechanism to uniquely identify the sources \(an\
d possibly some or all recei)-.15 E -.15(ve)-.25 G
(rs in some cases\) within the).15 E 2.5(group. Identity)54 540 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)54 552 Q(aces that result 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 \(N)54 564 Q -1.11(AT)-.35 G 2.5(\)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 <sourceId> \
\214eld should be present in pack)54 576 Q
(ets transmitted by reliable multicast session members.)-.1 E F3
(3.5 Data Content Identi\214cation)36 600 Q F0(The data and repair cont\
ent transmitted by a NORM sender requires some form of identi\214cation\
 in the protocol header)54 624 Q 2.5(\214elds. This)54 636 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 be used)5 E(in N)54 648 Q -.4(AC)-.35 G 2.5
(Km).4 G 2.5(essages generated. There)-2.5 F(are tw)2.5 E 2.5(ov)-.1 G
(ery general types of data that may comprise b)-2.65 E
(ulk transfer session content.)-.2 E(Adamson, Bormann, et al.)36 696 Q
(Expires September 2003)105.05 E([P)118.25 E(age 15])-.15 E EP
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/F0 10/Times-Roman@0 SF(Internet Draft)36 48 Q(NORM Building Blocks)
155.605 E(March 2003)161.705 E
(These data types are static, discrete objects of)54 84 Q
(\214nite size and continuous non-\214nite streams.)5 E 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)2.5 E(to r\
eliably multicast data content using either one or both of these data m\
odels.)54 96 Q(While it may be possible for some)5 E
(applications to further generalize this model and pro)54 108 Q
(vide mechanisms to encapsulate static objects as content embedded)-.15
E(within a stream, there are adv)54 120 Q(antages to man)-.25 E 2.5(ya)
-.15 G(pplications to pro)-2.5 E(vide distinct support for static b)-.15
E(ulk objects and messages)-.2 E(with the conte)54 132 Q
(xt of a reliable multicast session.)-.15 E
(These applications may include content caching serv)5 E
(ers, \214le transfer or)-.15 E(collaborati)54 144 Q .3 -.15(ve t)-.25 H
(ools with b).15 E(ulk content.)-.2 E(Applications with requirements fo\
r these static object types can then tak)5 E 2.5(ea)-.1 G(dv)-2.5 E
(antage of)-.25 E(transport layer mechanisms \(i.e.)54 156 Q(se)5 E
(gmentation/reassembly)-.15 E 2.5(,c)-.65 G(aching, inte)-2.5 E
(grated forw)-.15 E(ard error correction coding, etc\) rather)-.1 E
(than being required to pro)54 168 Q(vide their o)-.15 E
(wn mechanisms for these functions at the application layer)-.25 E(.)
-.55 E(As noted, some applications may alternati)54 192 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.)54 204 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)54 216 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)54 228 Q
(ulk content \(e.g. \214les\) into one more streams within a multicast)
-.2 E(session.)5 E(The components described within this b)54 252 Q
(uilding block draft document are en)-.2 E
(visioned to be applicable to both of these models)-.4 E(with the)54 264
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 <objectId> within some reasonable)54 276 Q
(temporal or ordinal interv)54 288 Q 2.5(al. Note)-.25 F
(that it is _not_ e)2.5 E(xpected that this data content identi\214cati\
on will be globally unique.)-.15 E(It is)5 E -.15(ex)54 300 S(pected th\
at the object/stream identi\214er will be unique with respect 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.)54 312 Q(Since the "b)54 336 Q
(ulk" object/stream content usually require)-.2 E(se)5 E
(gmentation, some form of se)-.15 E(gment identi\214cation must also be)
-.15 E(pro)54 348 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)54 360 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.)54 372 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 \
<blockId> and an identifer for the)54 384 Q
(speci\214c data or parity symbol <symbolId> of the code block.)54 396 Q
(The FEC Building Block document [13] pro)5 E(vides a standard)-.15 E(m\
essage format for identifying FEC transmission content. NORM protocol i\
nstantiations using FEC SHOULD follo)54 408 Q 2.5(wt)-.25 G(hat)-2.5 E
(document')54 420 Q 2.5(sg)-.55 G(uidelines.)-2.5 E(Additionally)54 444
Q 2.5<2c8d>-.65 G
(ags to determine the usage of the content identi\214er \214elds \(e.g.)
-2.5 E(stream vs.)5 E(object\) may be applicable.)5 E(Flags)7.5 E
(may also serv)54 456 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)54 468 Q
(vidual protocol instantiations.)-.25 E(In summary)54 492 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)
90 516 R(node identi\214er \(<senderId>\))2.5 E 25.17(2\) Object/Stream)
90 528 R(identi\214er \(<objectId>\), if applicable.)2.5 E 25.17
(3\) FEC)90 540 R(Block identi\214er \(<blockId>\), if applicable.)2.5 E
25.17(4\) FEC)90 552 R(Symbol identi\214er \(<symbolId>\))2.5 E 25.17
(5\) Flags)90 564 R(to dif)2.5 E(ferentiate interpretation of identi\
\214er \214elds or identi\214er structure that implicitly indicates usa\
ge.)-.25 E 25.17(6\) Additional)90 576 R
(FEC transmission content \214elds per FEC Building Block)2.5 E
(These \214elds ha)54 600 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.)54 612 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
624 Q/F1 10/Times-Bold@0 SF(3.6 F)36 648 Q(orward Err)-.25 E(or Corr)
-.18 E(ection \(FEC\))-.18 E F0(Adamson, Bormann, et al.)36 696 Q
(Expires September 2003)105.05 E([P)118.25 E(age 16])-.15 E EP
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/F0 10/Times-Roman@0 SF(Internet Draft)36 48 Q(NORM Building Blocks)
155.605 E(March 2003)161.705 E(Multiple forw)54 84 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 96 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)54 108
Q(xplicit kno)-.15 E(wledge of repair content within the bounds of its)
-.25 E(coding block size \(in se)54 120 Q 2.5(gments\). In)-.15 F
(NORM, parity repair pack)2.5 E
(ets generated will generally be transmitted only in response to)-.1 E
-.35(NA)54 132 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)54 144 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)
54 156 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)54 168 Q 2.5(ork connecti)-.1 F(vity has a lar)
-.25 E(ge delay*bandwidth product with some nominal le)-.18 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)54 180 Q
(approaches that are applicable.)54 192 Q 2.5(As)54 216 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)54 228 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)54 240 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
(identi\214ed by the concatenation of)54 252 Q/F1 10/Courier@0 SF
(sourceId::objectId::blockId::symbolId)2.5 E F0
(during transport, it is e)2.5 E(xpected that)-.15 E(FEC pack)54 264 Q
(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 detailed)-.15
E(recommendations concerning application of FEC and standard formats fo\
r related reliable multicast protocol messages.)54 276 Q/F2 10
/Times-Bold@0 SF(3.7 Round-trip T)36 300 Q(iming Collection)-.18 E F0
(The measurement of pack)54 324 Q(et propag)-.1 E
(ation round-trip time \(R)-.05 E
(TT\) among members of the group is required to support N)-.6 E -.4(AC)
-.35 G(K).4 E(suppression algorithms, timing of sender commands or cert\
ain repair functions, and congestion control operation.)54 336 Q(The)5 E
(nature of the round-trip information collected is dependent upon the t\
ype of interaction among the members of the group.)54 348 Q(In)5 E
(the case where only "one-to-man)54 360 Q(y" transmission is required, \
it may be necessary that only the sender require R)-.15 E(TT)-.6 E(kno)
54 372 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)54 384 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)54 396 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)54 408 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 \(or an)-.15 E(competed subset\) to the group or sender)54
420 Q 5(.W)-.55 G(here it is lik)-5 E(ely that e)-.1 E
(xchange of reliable multicast data will occur among the)-.15 E
(group on a "man)54 432 Q(y-to-man)-.15 E(y" basis, there are alternati)
-.15 E .3 -.15(ve m)-.25 H(easurement techniques that might be emplo).15
E(yed for increased)-.1 E(ef)54 444 Q(\214cienc)-.25 E 2.5(y[)-.15 G 2.5
(12]. And)-2.5 F(in some cases, there might be absolute time synchroniz\
ation among hosts that may simplify R)2.5 E(TT)-.6 E 2.5
(measurement. There)54 456 R(are trade-of)2.5 E(fs in multicast congest\
ion control design that need further consideration before a uni)-.25 E
-.15(ve)-.25 G(rsal).15 E(recommendation on R)54 468 Q(TT \(or GR)-.6 E
(TT\) measurement can be speci\214ed.)-.6 E(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)-.6 E(\(and more speci\214cally GR)54 480 Q
(TT\) with respect to congestion control or other requirements, the sen\
der will need to adv)-.6 E(ertise its)-.15 E(current GR)54 492 Q
(TT estimate to the group for v)-.6 E(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)36 516 Q(TT Measurement)-.3 E F0
(The goal of this form of R)54 540 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.)54 552 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.)54 564 Q
(An approach to collect this GR)5 E(TT)-.6 E(information follo)54 576 Q
(ws.)-.25 E(The sender periodically polls the group with a message \(in\
dependent or "piggy-back)54 600 Q
(ed" with other transmissions\) containing)-.1 E(a)54 612 Q F1
(<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)54 624 Q F1(<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
F1(<recvTime>)2.5 E F0(.)A(When the recei)54 636 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:)54 648 Q(Adamson, Bormann, et al.)36 696 Q
(Expires September 2003)105.05 E([P)118.25 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(March 2003)161.705 E/F1 10/Courier@0 SF
(grttResponse = sendTime + \(currentTime - recvTime\))154.2 84 Q F0
(where the)54 108 Q F1(<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 \()-2.5 E F1(currentTime)A 6(-<)54
120 S(recvTime)-6 E F0 2.5(\)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)54 144 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)54 156 Q(as recei)-.1 E -.15(ve)-.25 G
2.5(du).15 G(sing the follo)-2.5 E(wing formula:)-.25 E F1
(receiverRtt = currentTime - grttResponse)184.2 180 Q F0
(During the each periodic GR)54 204 Q(TT probing interv)-.6 E
(al, the source k)-.25 E
(eeps the peak round trip estimate from the set of responses it)-.1 E
(has recei)54 216 Q -.15(ve)-.25 G 2.5(d. The).15 F(GR)2.5 E
(TT estimate should be \214ltered to be conserv)-.6 E(ati)-.25 E .3 -.15
(ve t)-.25 H -2.1 -.25(ow a).15 H(rds maintaining an estimate biased to)
.25 E -.1(wa)-.25 G(rds the).1 E(greatest recei)54 228 Q -.15(ve)-.25 G
2.5(rR).15 G(TT measurements recei)-3.1 E -.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 GR).15 E
(TT maximizes the ef)-.6 E(\214cienc)-.25 E 2.5(yr)-.15 G(edundant N)
-2.5 E -.4(AC)-.35 G(K).4 E(suppression and repair aggre)54 240 Q -.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 GR)-2.5 E(TT is done observing the follo)-.6 E(wing)
-.25 E(rules:)54 252 Q 25.17(1\) If)90 276 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 calculation is greater than the)-2.5 E(current GR)5
E(TT estimate AND current)-.6 E(peak, the response v)126 288 Q
(alue is immediately fed into the GR)-.25 E 2.5(TT update)-.6 F
(\214lter gi)2.5 E -.15(ve)-.25 G 2.5(nb).15 G(elo)-2.5 E 3.8 -.65(w. I)
-.25 H 2.5(na).65 G .3 -.15(ny c)-2.5 H(ase, the).15 E
(source records the "peak" recei)126 300 Q -.15(ve)-.25 G 2.5(rR).15 G
(TT measurement for the current probe interv)-3.1 E(al.)-.25 E 25.17
(2\) At)90 324 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" response)-.25 E
(is less than the current GR)126 336 Q
(TT estimate AND this is the third consecuti)-.6 E .3 -.15(ve c)-.25 H
(ollection period with a peak less).15 E(than the current GR)126 348 Q
(TT estimate the recorded peak is fed into the GR)-.6 E
(TT update. \(Implicitly)-.6 E 2.5(,R)-.65 G(ule #1 w)-2.5 E(as)-.1 E
(applied otherwise so no ne)126 360 Q 2.5(wu)-.25 G
(pdate is required\).)-2.5 E 25.17(3\) At)90 384 R
(the end of the response collection period, the peak tracking v)2.5 E
(alue is set to either ZER)-.25 E 2.5(Oi)-.4 G 2.5(ft)-2.5 G
(he "peak" is)-2.5 E(greater than or equal to the current GR)126 396 Q(\
TT estimate \(i.e. Already incorporated into the \214lter under Rule #1\
\))-.6 E(or k)126 408 Q(ept the same if its v)-.1 E
(alue is less than the current GR)-.25 E(TT estimate AND w)-.6 E
(as not yet incorporated into the)-.1 E(GR)126 420 Q(TT update \214lter\
 according to Rule #2. Thus for decreases in the source')-.6 E 2.5(se)
-.55 G(stimate of GR)-2.5 E(TT)-.6 E 2.5(,t)-.74 G(he "peak")-2.5 E
(is track)126 432 Q(ed across three consecuti)-.1 E .3 -.15(ve p)-.25 H
(robe interv).15 E(als.)-.25 E(The follo)41 456 Q(wing GR)-.25 E
(TT update \214lter is used to incorporate ne)-.6 E 2.5(wp)-.25 G
(eak responses into the the GR)-2.5 E(TT estimate:)-.6 E F1
(if \(peak > current_estimate\))108 480 Q
(current_estimate = 0.25 * current_estimate + 0.75 * peak;)132 492 Q
(else)108 504 Q
(current_estimate = 0.75 * current_estimate + 0.25 * peak;)132 516 Q F0
(This update method is biased to)54 540 Q -.1(wa)-.25 G
(rds maintaining an estimate of the w).1 E(orst-case round trip delay)
-.1 E 5(.T)-.65 G(he reason the GR)-5 E(TT)-.6 E
(estimate is reduced only after 3 consecuti)54 552 Q .3 -.15(ve c)-.25 H
(ollection periods with smaller response peaks is to be conserv).15 E
(ati)-.25 E .3 -.15(ve w)-.25 H(here).15 E(pack)54 564 Q(et loss may ha)
-.1 E .3 -.15(ve r)-.2 H(esulted in lost response messages.).15 E
(And then the reduction is additionally conserv)5 E(ati)-.25 E -.15(ve)
-.25 G(ly weighted).15 E(using the a)54 576 Q -.15(ve)-.2 G
(raging \214lter from abo).15 E -.15(ve)-.15 G(.).15 E(The GR)54 600 Q(\
TT collection period \(i.e. period of probe transmission\) could be \
\214x)-.6 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)54 612 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)54 624 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 GR).15 E(TT)-.6 E
(collection period dynamically in response to the current GR)54 636 Q
(TT estimate \(or v)-.6 E
(ariations in it\) and to an estimation of pack)-.25 E(et)-.1 E 2.5
(loss. The)54 648 R -.15(ove)2.5 G
(rhead of probing messages could then be reduced when the GR).15 E
(TT estimate is stable and unchanging, b)-.6 E(ut be)-.2 E
(Adamson, Bormann, et al.)36 696 Q(Expires September 2003)105.05 E
([P)118.25 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(March 2003)161.705 E
(adjusted to track more dynamically during periods of v)54 84 Q
(ariation with correspondingly shorter GR)-.25 E(TT collection periods.)
-.6 E(In summary)54 108 Q 2.5(,a)-.65 G(lthough NORM repair c)-2.5 E
(ycle timeouts are based on GR)-.15 E(TT)-.6 E 2.5(,i)-.74 G 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 GR)54 120 Q
(TT estimation.)-.6 E(The current mechanism has pro)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
132 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)54 144 Q -.15(ve)-.4 G
(lope of actual GR).15 E(TT \(including operating system ef)-.6 E
(fect as well as netw)-.25 E(ork delays\) e)-.1 E -.15(ve)-.25 G 2.5(ni)
.15 G(n)-2.5 E(relati)54 156 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)54 168 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/F1 10
/Times-BoldItalic@0 SF(3.7.2 One-to-Many Receiv)36 192 Q(er R)-.15 E
(TT Measurement)-.3 E F0(In this approach, recei)54 216 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
228 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)54 240 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.)54 252 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 not made an)-2.5 E
2.5(yR)-.15 G(TT measurement or whose R)-3.1 E(TT measurement has aged)
-.6 E(most should ha)54 264 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)54 276
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)54 288 Q/F2 10
/Courier@0 SF(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)54 300 Q -.15(ve)-.25 G(rs who note their R)
.15 E(TT is greater than the sender)-.6 E F2(GRTT)2.5 E F0
(can compete in the feedback opportunity/suppression scheme)2.5 E
(to pro)54 312 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)54 324 Q -.15(ve)-.25 G
2.5(rR).15 G
(TT measurement as part of its congestion control operation [14].)-3.1 E
F1(3.7.3 Many-to-Many R)36 348 Q(TT Measurement)-.3 E F0 -.15(Fo)54 372
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)54 384 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)54 396 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')54 408 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(a)-2.5 E F0 2.5("a)C(nd)-2.5 E(sender')54 420 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
444 Q F0(Further re\214nement of this estimate can be conducted if R)54
468 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)54 480 Q(TT information amon\
g those other group members it learns during protocol)-.6 E(operation.)
54 492 Q F1(3.7.4 Sender GR)36 516 Q(TT Adv)-.3 E(ertisement)-.15 E F0
1.6 -.8(To f)54 540 T
(acilitate deterministic NORM protocol operation, the sender should rob)
.7 E(ustly adv)-.2 E(ertise its current estimation of GR)-.15 E(TT to)
-.6 E(the recei)54 552 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 GR)-2.5 E(TT estimate among the group will allo)-.6 E
(w)-.25 E(the protocol to progress in its most ef)54 564 Q
(\214cient manner)-.25 E 5(.T)-.55 G(he sender')-5 E 2.5(sG)-.55 G -.6
(RT)-2.5 G 2.5(Te).6 G(stimate 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)54 576 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 GR)54 588 Q
(TT estimate to a single byte of information.)-.6 E(The follo)5 E
(wing C-lanquage)-.25 E(function algorithm allo)54 600 Q
(ws this to be done o)-.25 E -.15(ve)-.15 G 2.5(raw).15 G
(ide range of GR)-2.5 E(TT v)-.6 E
(alues while maintaining a greater range of precision)-.25 E
(for small GR)54 612 Q(TT v)-.6 E(alues and less precision for lar)-.25
E(ge v)-.18 E(alues:)-.25 E(Adamson, Bormann, et al.)36 696 Q
(Expires September 2003)105.05 E([P)118.25 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(March 2003)161.705 E/F1 10/Courier@0 SF
(unsigned char QuantizeGrtt\(double grtt\))108 84 Q({)108 96 Q
(if \(grtt > 1.0e03\))132 108 Q(grtt = 1.0e03;)156 120 Q
(else if \(grtt < 1.0e-06\))132 132 Q(grtt = 1.0e-06;)156 144 Q
(if \(grtt < 3.3e-05\))132 156 Q
(return \(\(unsigned char\)\(grtt * 1.0e06\) - 1\);)156 168 Q(else)132
180 Q(return \(\(unsigned char\)\(ceil\(255.0.-)156 192 Q
(\(13.0 * log\(1.0e03/grtt\)\)\)\)\);)300 204 Q(})108 216 Q F0
(Note that this function is useful for quantizing GR)54 240 Q
(TT times in the range of 1 microsecond to 1000 seconds.)-.6 E
(Of course,)5 E
(NORM protocol implementations may wish to further constrain adv)54 252
Q(ertised GR)-.15 E(TT estimates \(e.g. limit the maximum v)-.6 E
(alue\))-.25 E(for practical reasons.)54 264 Q/F2 10/Times-Bold@0 SF
(3.8 Gr)36 288 Q(oup Size Determination/Estimation)-.18 E F0
(When NORM protocol operation includes mechanisms that e)54 312 Q
(xcite feedback from the groupat lar)-.15 E
(ge \(e.g. congestion control\),)-.18 E(it may be possible to roughly e\
stimate the group size based on the number of feedback messages recei)54
324 Q -.15(ve)-.25 G 2.5(dw).15 G(ith respect to the)-2.5 E(distrib)54
336 Q(ution of the probabilistic suppression mechanism used.)-.2 E
(Note the timer)5 E(-based suppression mechanism described in this)-.2 E
(document do not require a v)54 348 Q
(ery accurate estimate of group size to perform adequately)-.15 E 5(.T)
-.65 G(hus, a rough estimate, particularly if)-5 E(conserv)54 360 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 2.5(na)-5 G(bsence of a group size)-2.5 E
(determination mechanism a def)54 372 Q(ault group size v)-.1 E
(alue of 10,000 is RECOMMENDED for)-.25 E(reasonable management of)5 E
(feedback gi)54 384 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)36 408 Q
(ol Operation)-.18 E F0(Congestion control that f)54 432 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)54 444
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.)54 456
Q F2(3.10 Router/Intermediate System assistance)36 480 Q F0 -.35(NA)54
504 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)54 516 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)54 528 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)54 540 Q
(vide an intelligent "subcast" of repair content to)-.15 E(dif)54 552 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)54 564 Q(ould requi\
re router interpretation of transport data unit content identi\214ers)
-.1 E(and \215ags.)54 576 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)54 588 Q(ertisement.)-.15 E F2(4.0 NORM A)36 612 Q
(pplicability)-.25 E F0(The NORM b)54 636 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)54 648 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
(Adamson, Bormann, et al.)36 696 Q(Expires September 2003)105.05 E
([P)118.25 E(age 20])-.15 E EP
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/F0 10/Times-Roman@0 SF(Internet Draft)36 48 Q(NORM Building Blocks)
155.605 E(March 2003)161.705 E(scalability adv)54 84 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 96
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 \(e.g. unicast or h).15 E
(ybrid unicast/multicast)-.05 E(data distrib)54 108 Q(ution trees\).)-.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)54 120 Q(anout" is e)-.1 E(xpected for a single netw)-.15 E
(ork hop \(e.g.)-.1 E(cable-TV data deli)5 E -.15(ve)-.25 G(ry).15 E 2.5
(,s)-.65 G(atellite, or other broadcast communication)-2.5 E
(communication services\).)54 132 Q(Furthermore, the simplicity of a pr\
otocol based on "\215at" group-wide multicast distrib)5 E(ution may)-.2
E(of)54 144 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 \(among senders and recei)54 156 Q -.15(ve)-.25 G
(rs\) 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)54 168 Q(\(SSM\) [17] where there may only be unic\
ast routing service from the recei)54 180 Q -.15(ve)-.25 G
(rs to the sender\(s\).).15 E
(NORM operation is compatible with transport layer forw)54 204 Q
(ard error correction coding techniques as described in [19] and)-.1 E
(congestion control mechanisms described in [14] and [18].)54 216 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)54 228 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)54 240 Q(uf)-.2 E(fering constraints.)
-.25 E(Buf)5 E(fering greater than that required for typical point-to-p\
oint reliable transport \(e.g.)-.25 E(TCP\) is recommended to allo)54
252 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)54 264 Q(.)-.65 E/F1 10/Times-Bold@0
SF(5.0 Security Considerations)36 288 Q F0(NORM protocols are e)54 312 Q
(xpected to be subject to same sort of security vulnerabilities as othe\
r IP and IP multicast protocols.)-.15 E(NORM is compatible with IP secu\
rity \(IPSEC\) authentication mechanisms [20] that are RECOMMENDED for \
protection)54 324 Q(ag)54 336 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)54 348 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)
54 360 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)54 372 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)54 384 Q -.25(va)-.2 G(ilable.).25 E F1
(6.0 Refer)36 408 Q(ences)-.18 E F0([1])59 438 Q(A. Mankin, A. Romano)
122.398 438 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)122.398 450 S
(ansport and Application Protocols", RFC 2357, June 1998.).35 E([2])59
474 Q(S. Ping)122.398 474 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".)122.398 486 Q(In Proc.)5
E(INFOCOM, San Francisco, CA, October 1993.)5 E([3])59 510 Q(B.N. Le)
122.398 510 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)122.398 522 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])59 546 Q(D. Clark, D. T)122.398
546 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)122.398 558 S
2.5(MS).4 G(IGCOMM, pages 201--208, September 1990.)-2.5 E([5])59 582 Q
2.5(S. Deering,)122.398 582 R
("Host Extensions for IP Multicasting". Internet RFC1112, August 1989.)
2.5 E([6])59 606 Q(S. Flo)122.398 606 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)122.398 618 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(Adamson, Bormann, et al.)36 696 Q(Expires September 2003)105.05 E
([P)118.25 E(age 21])-.15 E EP
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/F0 10/Times-Roman@0 SF(Internet Draft)36 48 Q(NORM Building Blocks)
155.605 E(March 2003)161.705 E([7])59 84 Q(J. Nonnenmacher and E. W)
122.398 84 Q 2.5(.B)-.92 G(iersack, "Optimal Multicast Feedback," in IE\
EE Infocom , \(San Francisco,)-2.5 E
(California\), p. 964, March/April 1998.)122.398 96 Q([8])59 120 Q
(D. Gossink, J.)122.398 120 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'.)122.398 132 Q([9])59 156 Q(J. Metzner)
122.398 156 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)122.398 168 S 2.5
(l. Com-32,)1.29 F(No.6, June 1984.)2.5 E([10])54 192 Q(J. Mack)122.398
192 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.)
122.398 204 Q([11])54 228 Q(J. Mack)122.398 228 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)122.398 240
Q(1997.)5 E([12])54 264 Q 2.58 -1.29(V. O)122.398 264 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)
122.398 276 Q(T&T White P)-1.11 E(aper)-.15 E 2.5(,F)-.4 G
(ebruary 1999.)-2.5 E([13])54 300 Q(M. Luby)122.398 300 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.)122.398 312 Q([14])54
336 Q(J. W)122.398 336 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)122.398 348 Q -.15
(ve)-.15 G(mber 2002, w).15 E(ork in progress.)-.1 E
(Citation for informational)5 E(purposes only)122.398 360 Q(.)-.65 E
([15])54 384 Q 1.48 -.74(T. S)122.398 384 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,)122.398 396 Q -.1(wo)122.398 408 S
(rk in progress.).1 E(Citation for informational purposes only)5 E(.)
-.65 E([16])54 432 Q(J. Mack)122.398 432 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.)122.398 444 Q([17])54 468 Q
(Holbrook, H. W)122.398 468 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.)122.398 480 Q
([18])54 504 Q(Rizzo, L., V)122.398 504 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)122.398 516 Q(ork in progress.)-.1 E(Citation for)5 E
(informational purposes only)122.398 528 Q(.)-.65 E([19])54 552 Q(Luby)
122.398 552 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.)
122.398 564 Q([20])54 588 Q(S. K)122.398 588 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
(Expires September 2003)105.05 E([P)118.25 E(age 22])-.15 E EP
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/F0 10/Times-Roman@0 SF(Internet Draft)36 48 Q(NORM Building Blocks)
155.605 E(March 2003)161.705 E/F1 10/Times-Bold@0 SF(7.0 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 September 2003)105.05 E([P)118.25 E(age 23])-.15 E EP
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