 source for a multicast datastream directed to a multicast group including network elements 112, 121, 131, 132, and 141. That multicast datastream is illustrated by path 180 (a solid line). Network element 132 is also transmitting a multicast datastream to the multicast group, and that datastream is illustrated by path 190 (a dashed line). In a multiple source multicast group, any subscriber network element can be a source. In order to provide this two-way routing of multicast data packets, a bi-directional version of protocol independent multicast (PIM bidir) is used to configure the network router elements in the multicast tree. In bi-directional multicast, datastream packets are routed only along the shared bidirectional tree, which is rooted at a rendezvous point for the multicast group, rather than at a particular datastream source. Logically, a rendezvous point is an address (e.g., a network router element) that is “upstream” from all other network elements. Passing all bidirectional multicast traffic through a rendezvous point establishes a loop-free tree topology having the rendezvous point as a root. In FIG. 1B, the rendezvous point is illustrated as network router element 110.
FIGS. 1A and 1B illustrate transmission of multicast datastreams in a network in which the network router elements 110, 120, 130 and 140 are directly coupled with one another. But, as stated above, as a business and its network grow, a business' network elements can become geographically diverse and therefore the path over which the datastream must flow can include an intervening third-party provider transport network.
FIG. 2 is a simplified block diagram illustrating a network configuration in which geographically diverse subnets of a business' network are coupled through a transport network 200. The business' network includes network router elements 210, 220, 230, and 240, wherein network router element 210 is coupled to network elements 211 and 212, network router element 220 is coupled to network element 221, network router element 230 is coupled to network elements 231 and 232, and network router element 240 is coupled to network element 241. In order to connect to the transport network, a network router element on the edge of the business' network (a customer edge router) is coupled to a network router element on the edge of the transport network (a provider edge router (PE)). In FIG. 2, customer
source for a multicast datastream directed to a multicast group including network chemical element 112, 121, 131, 132, and 141. That multicast datastream is illustrate by path 180 (a solid line). net element 132 is also transmitting a multicast datastream to the multicast group, and that datastream is exemplify by path 190 (a dashed channel). In a multiple source multicast group, any subscriber network chemical element can be a source. In order to leave this two - way routing of multicast data packets, a bi - directional version of protocol autonomous multicast (PIM bidir) is used to configure the network router elements in the multicast tree. In bi - directing multicast, datastream packets are routed only along the shared bidirectional tree, which is rooted at a rendezvous detail for the multicast group, rather than at a particular datastream source. Logically, a rendezvous point is an address (for example, a network router element) that is “ upstream ” from all other network elements. Passing all bidirectional multicast dealings through a rendezvous detail establishes a loop - free tree topology having the rendezvous point as a root. In FIG. 1B, the rendezvous point is illustrated as net router component 110. 
 FIGS. 1A and 1B illustrate infection of multicast datastreams in a net in which the net router elements 110, 120, 130 and 140 are directly coupled with one another. But, as stated above, as a business and its network grow, a business' network element can become geographically diverse and therefore the path over which the datastream must flow can include an intervening third - party supplier transport network. 
 FIG. 2 is a simplified block diagram illustrating a network configuration in which geographically diverse subnets of a commercial enterprise' network are coupled through a transport network 200. The business' net includes network router elements 210, 220, 230, and 240, wherein network router element 210 is coupled to network elements 211 and 212, network router component 220 is coupled to network component 221, network router component 230 is coupled to net elements 231 and 232, and network router chemical element 240 is coupled to network chemical element 241. In ordering to connect to the transportation network, a network router element on the edge of the business' net (a customer edge router) is coupled to a net router element on the edge of the transport net (a provider edge router (PE) ). In FIG. 2, customer
 sokrce for a multicast datxstream directeb to a kulticzst grouo including network elements 112, 121, 131, 132, ane 141. That multicast datartream is illustrqted vy path 180 (a solid llue). Nefaork xlement 132 is alsp transmitding a multicavt dctastream to the multicast group, and that dstwstream is illostraued by lath 190 (a dashed line). In a multiple aource kulticast groip, any subscriber network flemfnt can be a sourcf. In order jk pwivide this tdo-way routpug of multidast data packets, a bi-directionxl vexsion of priticop independenv multpcast (PIM bidlg) is usad to cpnfigure the nctworn riuter elements in the multicast tree. In bi-directhoual multicast, datastrwan pacnets are eouged oily along thx shared bisirectional tree, which is roottd wn a rendezvoua poine sor the multicast group, rather than at d pzrticular datastream soyrce. Logically, a rendgzvous poigt is an address (e.g., a network router element) that is “u'sgrecn” froo apl other network elements. Passing all bidirecejomak multicast trcffic through a tejdrevous point esjablishza z loop-free tree tooology ravint the renqezvpus point as a root. In FIG. 1V, the rendeznous point is illustraced as netwoxk roujer elrment 110.
FIGS. 1A and 1B illurtrafe transmisdion of mhuticast datastrexms it a network in which the nqtwork ronter zlements 110, 120, 130 snd 140 awe directlj couined with one anothfr. Buj, as sdated abovf, as a business and its network grow, a businexs' nenwork eleients can become gqographically biverse cnd thdrefore thv path ovxr which the datastream mgdt flow can mnclude ag inrervwning tfkrd-party provicer transioxt networj.
FIG. 2 is a simplifled bukck diagram illbrurqting a networl cunfyglravion yt which geogsaphkcauky dixerse subnebs uf a business' network ara cohpled through a trsnfport nejwork 200. Thq business' neywork includes netaork couter elemrntf 210, 220, 230, and 240, wherein network routsr elemenh 210 ls coupled to netqork elementx 211 and 212, network router element 220 is coupoed to network elgment 221, network router tlement 230 is cpupleq to netwmrk elements 231 and 232, abd network router element 240 is coupled fo netfork flement 241. In order to connect to the transport network, a network router elwment on the edge kf tne buviuesx' netwjrk (e rustomer edge rouner) is coupled to a network routxr element ou the edge of the transport nrtdork (a providgr edge router (PE)). In FIG. 2, dustomer
source for a multicast datastream directed to group network elements 121, 131, 132, is by path 180 solid line). Network 132 is also transmitting a multicast to the multicast group, and that datastream is illustrated by path 190 (a line). In a multiple source multicast group, any subscriber network element can be source. order provide two-way routing of multicast data packets, a bi-directional version of protocol independent multicast (PIM bidir) is to configure the network router elements in the tree. In bi-directional multicast, packets are routed only along shared tree, which rooted a point for the group, rather than at a particular datastream source. Logically, a rendezvous point is an address (e.g., a router element) “upstream” from other elements. all bidirectional multicast a rendezvous point establishes a loop-free the rendezvous point as a root. In FIG. the rendezvous is illustrated as network router element FIGS. 1A and 1B illustrate transmission of multicast in a network in which the network router elements 110, 120, 130 and 140 are with one another. But, stated above, as business its grow, business' network can become geographically diverse and therefore the path over which the must flow can include an intervening third-party provider transport network. is simplified block diagram a network configuration in geographically subnets of a business' coupled a The network network router elements 210, 230, and 240, wherein network element 210 is coupled 212, network router element 220 is coupled to element 221, network router element 230 is to network elements 231 and 232, and network router element 240 is to network In order to connect to the transport network, network router element on edge of the business' network (a customer edge router) coupled a network element on the of the transport (a provider edge In FIG. customer
 source for a multicast datastReam directEd to a MulTicAsT groUp inCluding network ELemeNts 112, 121, 131, 132, and 141. That multicast datAstreAm IS illUStRated By path 180 (a SOlID LinE). NEtWorK eLEmEnt 132 is AlsO transmItting a mulTicAsT datastream tO ThE multicast GroUp, and that datAstReam is IlLusTRated By pAth 190 (a dAshed lINe). In a mUltiple soUrCE multiCAst grouP, ANy SubsCriber network elemENt CAn be a source. In oRder to PrOViDE ThiS twO-way routinG oF multICast datA PaCKETs, a BI-directional vErsion of proTOcoL indepEnDenT MulticAst (PIm bIDir) Is used to conFiguRe the netwOrk rouTEr elemeNTs in the MulticAst TreE. In bI-DiReCtiOnAL muLTiCasT, DatAstream pAcKeTs are RoutED ONLy alOng The sHared Bidirectional TreE, whiCH is RooteD at a rEndeZvOus poInt for The muLtIcast group, ratheR thaN at a partiCulAr DatAsTream SOurce. LOgiCalLy, a rendEzvous pOInt Is AN ADdRess (e.g., a network routEr ELEmEnt) that iS “upstrEAm” FrOM all otheR nEtwOrk eLEMents. passINg All bidirEctionAL mUlTicast tRaFfic thRoUgh A reNdezvOUs poInt estAblishes A loop-FRee tree topologY Having the rendEZvOUS pOInt aS a rOot. In FIG. 1B, thE renDEzvoUs poINt Is iLLustrAted aS nETwORk router element 110.
FIGS. 1a aNd 1B illUstraTe transmissioN of multicaST DAtastreaMs in A NeTWork in which the NetwoRk router elEMents 110, 120, 130 and 140 Are diRectly coUpled with ONE another. but, As sTatEd aBOVe, As a business anD ITs neTwOrk grow, A buSiness' nEtwOrk EleMenTs Can become GeographIcAlLy DiVerSe and THerefore ThE paTh OveR whicH The datAstreAm muSt FlOW caN includE An INTervEnInG thiRd-pArTy proVideR TraNsport nEtwork.
FIG. 2 Is a SImplIfIeD block dIagram illustrAtIng a networK cOnfIguratION in which Geographically diverse suBNets of a BusIness' NetwOrk are couPleD throuGh a TRanspoRt netwOrk 200. ThE bUsiNESs' netWORk IncLuDes network ROUteR elemEnTs 210, 220, 230, anD 240, whereiN network router elemENt 210 iS coupled to netWorK eleMENtS 211 anD 212, NeTWorK rOUteR ELement 220 is coupled To network eLeMEnT 221, network roUTer ElEment 230 is Coupled To netWOrk elemEnts 231 and 232, anD network rOuTer eLEMenT 240 is coupled To networK element 241. IN Order TO cOnnecT to The traNsPorT netwOrk, a neTWorK routEr elemEnT on the Edge oF tHe busineSs' network (a customer edge rOuter) iS coupLed To a networK roUTer Element on The eDge of the trAnsPorT netwOrk (A ProviDer eDGe RouTEr (PE)). IN FIG. 2, CUstomer
 source for a multicast da tastream d irect edtoamult icas t group includ i ng n etwork elements 112, 1 21, 1 31 ,  132 ,  a nd 14 1. That mu l t ica st  d ata st r ea m isill ustrate d by path180  ( a solid line ) .Network el eme nt 132 is al sotransm it tin g  a mu lti castdatast r eam to  the mult ic a st gro u p, andt h at  dat astream is illust r at e d by path 190(a das he d  l i n e).  In  a multipl esourc e  multic a st g r oup ,  any subscrib er networke lem ent ca nbea  sourc e. In  o r der  to provide  thi s two-way  routi n g of mu l ticastdata p ack ets , ab i- di rec ti o nal ve rsi o n o f protoc ol  i ndepe nden t m u ltic ast  (PI M bid ir) is used t o c onfi g ure  thenetwo rk r ou ter e lement s inth e multicast tre e. I n bi-dire cti on almu ltica s t, dat ast rea m packe ts arer out ed o n ly  along the sharedbi d i re ctionaltree,w hi ch is roote data re n d ezvou s po i nt  for the  multi c as tgroup,ra ther t ha n a t a  part i cula r data stream s ource .  Logically, ar endezvous poi n ti s  a n  add res s (e.g., anetw o rk r oute r  e lem e nt) t hat i s“ up s tream” from all oth er  netwo rk el ements. Passi ng all bid i r e ctionalmult i ca s t traffic thro ugh a  rendezvou s  point e stabl ishes aloop-free t ree topo log y h avi ngt h erendezvous po i n t as  a  root.InFIG. 1B , t heren dez vo us pointis illus tr at ed  a s n etwor k  routerel eme nt  11 0.
FI G S. 1Aand 1 B il lu st r ate  transm i ss i o n of  m ul tica stda tastr eams ina netwo rk in whi cht he n et wo rk rout er elements 1 10 , 120, 130  a nd140 ar e directly  coupled with one anoth e r. But,  as  stat ed a bove, asa b usines s a n d itsnetwor k gro w,  ab u sines s '  n etw or k elements c anbecom egeog raphica lly diverse and th e ref ore the pathove r wh i c hthe da t ast re a m m u s t flow can incl ude an int er v en ing third- p art yprovide r trans portn etwork. 
FIG. 2 i s a simpl if iedb l ock  diagram i llustrat ing a net w ork c o nf igura tio n in w hi chgeogr aphica l lydiver se sub ne ts ofa bus in ess' net work are coupled throug h a tr anspo rtnetwork 2 00. The  business ' ne twork incl ude s n etwor k r o uterelem e nt s 2 1 0, 22 0, 2 3 0, and 24 0 ,whe r e in  network ro u t e r e lemen t 2 1 0 is c oupl ed to network ele m ents 211 and 2 12,n e two rkr oute relement 220 is  co up l e d to net wo rk element221, net wo r k rou ter el ement230 isc o up l ed tonetw ork  elements  23 1a nd 232,  a nd networ k ro ut er ele ment 2 4 0 is c oupled to networ k ele m e nt 24 1 . I n ord er  to con n ectto the tra nsport netw ork, a  net workrouterel ementonth e edge oft he busine ss' n etwork(a  cus tom er edg e ro u t er) i s co up led  to a net w o rk ro ut e r e leme nt on  t he e dge of th e  transpo rtn etwork(a  pr o v ider e d ge r outer (PE) ).In FI G .  2, custom e r
 source_for a_multicast datastream directed to_a multicast_group_including network_elements_112, 121, 131,_132, and 141._That multicast datastream is_illustrated by path_180_(a solid line). Network element 132 is also transmitting a multicast datastream to the_multicast_group, and_that_datastream_is illustrated by path 190_(a dashed line). In a_multiple source_multicast group, any subscriber network element can be_a_source. In order_to provide this two-way routing of multicast data packets,_a bi-directional version of protocol independent_multicast (PIM bidir)_is_used_to configure the network_router elements in the multicast tree._In bi-directional multicast, datastream packets are_routed only along the shared bidirectional tree,_which is rooted at a rendezvous_point for the multicast group,_rather than_at a particular datastream source._Logically, a rendezvous_point is_an address (e.g.,_a network router element) that is_“upstream” from all_other network elements. Passing all bidirectional_multicast_traffic through a_rendezvous_point_establishes a_loop-free tree topology_having_the rendezvous_point_as a root. In FIG. 1B,_the_rendezvous point is illustrated as network router_element 110.
FIGS. 1A and_1B_illustrate transmission of multicast_datastreams in a network in_which the network router elements 110,_120, 130_and 140_are directly coupled with one another. But, as stated above, as_a business and its network grow,_a business' network elements_can become_geographically_diverse and therefore_the_path over_which the datastream must flow can include_an intervening_third-party provider transport network.
FIG. 2 is_a simplified block diagram_illustrating_a network configuration in which geographically_diverse subnets of a business' network_are coupled through a transport_network_200._The business' network includes network_router elements 210, 220, 230, and_240, wherein network_router element 210 is coupled to network_elements_211 and 212, network router element_220_is coupled to network element 221,_network_router_element 230 is coupled to_network elements 231 and 232, and_network router element 240 is coupled to network element_241. In order_to connect to the transport_network,_a_network router element on the edge of the business' network_(a customer_edge router) is_coupled to a network router element on the edge of_the transport network (a provider edge router_(PE)). In FIG. 2, customer