[75] Inventors: Paul T. Francis, Morristown, N.J.; [75] Inventors: Paul T. Francis, Morristown, N.J.; Anthony J. Ballardie, Alstonefield; Anthony J. Ballardie, Alstone?eld; Jonathan A. Crowcroft, London, Jonathan A. Crowcroft, London, both of England both of England [73] Assignee: Bell Communications Research, Inc., [73] Assignee: Bell Communications Research, Inc., Livingston, N.J. Livingston, NJ.

Alternatively, the packet may contain voice data 1) or routers a, b, c, d, e, f, g, h, i, j, k, l, m, n, o, p, q, r, of a speaking teleconference participant at a source s (shown as squares in FIG. 1).

The router r7 transmits a copy of the received packet to the destination node d3 5 uses a modified reverse path forwarding algorithm to copy of the received packet to the destination node d3 uses a modi?ed reverse path forwarding algorithm to via the routers r9 and rlO.

The copies of the packet are then transmitted ing table is indexed by the multicast address of the core via the appropriate links to the member nodes.

FIG. 7 depicts a forwarding table at a node of the communicates a request to join the particular multicast communicates a request to join the particular multicast FIG. 7 depicts a forwarding table at a node of the internet of FIG. 6 in the process of being added to a group to a designated router.

Viewed this way, the majority of what gets transmitted over the internet is distribution: mail, news, web pages (HTML) and files of all types (jpg, mp3, etc.), chat, channels, DNS records, audio-video broadcasts, and so on.

In addition to open standards like NNTP, IRC, ICP, RFC822 mail headers, and so on, many companies offer proprietary server-based systems: Pointcast for its channels, Tivoli for its software distribution, Tibco for its publish/subscribe stuff, RealNetworks for its audio-video broadcasts, and on and on.

In fact, a key objective of most reliable transport protocols for IP multicast is to build a tree (among routers or among hosts, depending on the scheme) over which acks or naks can be sent.

Recently the IETF chartered an ad hoc group, called maddogs, to explore ways to overcome the problems of IP multicast and to make it more suitable for commercial products and services.

All other intent to joins are stamped as rejected and replicated, with one copy going back the way it came over the reverse path to flush it from the loop detection maps, and the other going directly to the originator.

Most LANs and more recent wide-area network tech nologies such as SMDS (12) and ATM [7) specify mul ticast as part of their service, but perhaps the most apparent and widespread growth in multicast applica tions is being experienced in the IP Internet.

IP Module ,ll 11, Local Network Service Interface Figure 2: Protocol Relationships CBT operation is invoked whenever a router receives a group membership report as part of IGMP from some host on a directly attached subnetwork.

owever, a ne~~t1ve ac owledgement (JOIN-NACK) may be sent 1n reply to a Join request for various reasons, for example, in the event of loop detection, or simply because the router does not wish to become part of a CBT tree for that group.

We consider the development of a dedicated mul ticast directory service which would be responsible for all aspects of group management, a long term goal of internetwork multi casting in general.

Also, Joel Halpern (Network Systems Corpora tion), Steve Deering (Xerox Pare), and Scott Brim (Cor nell University) for their general constructive comments and suggestions since the conception of CBT.

The majority of users indicate that the textual content is of greatest value, however, a somewhat higher quality reproduction could be made from "photographs" if essential to the understanding of the dissertation.

My f e llo w s tu d e n ts a t th e D i g i t a l Systems Lab, Dick Karp, Ron C rane, Jim M ath is, Judy E s t r i n and D a rry l Rubin have h elped in many ways.

My re s e a r c h has b een su p p o rte d by th e Advanced R esearch P r o je c t s Agency o f th e Department o f D efen se, under ARPA O rder No. 2494, C o n tra c t No. MDA903-76C-0093, and th e N a tio n a l S cience F o u n d atio n , under r e s e a r c h g r a n t MCS73-07973-Al,2.

4 .1 2 Lower Bound on B roadcast Cost f o r M u lti- D e s tin a tio n A ddressing and Source Based Forw arding

140 4 .1 3 Upper Bound on th e Number o f P ack ets T ran sm itte d f o r Hot P o ta to Forwarding w ith D iscard T h resh o ld

Existing broadcast routing algorithms, including multidestination addressing, constrained flooding, mini­ multidestination addressing, constrained ?ooding, mini mum spanning tree forwarding, and reverse path for­ mum spanning tree forwarding, and reverse path for warding, suffer from an excessive use of bandwidth, a warding, suffer from an excessive use of bandwidth, a poor choice of routes, or a costly need for memory or poor choice of routes, or a costly need for memory or computing power.

It may be necessary to broadcast a packet of data from a sensor node in the high earth orbit equal to the number of reachable destinations.

strained ?ood; Also, links must be flooded with packet copies in the FIGS. 12 and 13 graphically compare transmission Also, links must be ?ooded with packet copies in the FIGS. 12 and 13 graphically compare transmission hope that neighbors that are not part of the tree will 60 delays between a broadcast in accordance with the hope that neighbors that are not part of the tree will delays between a broadcast in accordance with the stop the flood, although this undesirable situation can be present invention and a broadcast utilizing a constrained stop the ?ood, although this undesirable situation can be present invention and a broadcast utilizing a constrained corrected by having neighbors exchange their routing corrected by having neighbors exchange their routing flood; ?ood; , tables.

The present invention is a broadcast routing algo­ The present invention is a broadcast routing algo rithm that closely matches the delay performance of rithm that closely matches the delay performance of constrained flooding and that provides optimal band- constrained ?ooding and that provides optimal band

A point on the CDF curve shows Broadcast routes are extracted from Ack Scout pack the network included.

For these reasons, and as described in greater detail below, it is my opinion that the methods recited in the subject claims were known and obvious to one of ordinary skill in the art prior to the filing of the ’069 patent.

In my opinion, a person of ordinary skill in the art seeking to improve or modify the system taught in Francis would have looked to similar concepts discussed in Gilbert for inspiration.

Additionally, a person of ordinary skill in the art seeking to further improve the system in Francis by increasing the efficiency of the join process would have also been inspired by Gilbert’s use of a network manager to identify and contact an existing member node.

A person of ordinary skill in the art would have been further inspired by the efficiencies achieved by Gilbert’s teachings of having the portal computer sending the connection request to existing nodes on the network.

A person of ordinary skill in the art seeking to advance Francis’s objective that “each member establishes the same number of mesh links” would have looked to Gilbert for inspiration on how to maintain such a topology while adding new nodes.