Multicast Matthew Wolf College of Computing Georgia Institute

Multicast Matthew Wolf College of Computing Georgia Institute of Technology www. cercs. gatech. edu

Overview I. Why Multicast? A user’s perspective. II. The ABC’s of Multicast – some important acronyms and what they mean.

I. Why Multicast? • The last time Bill Gates gave a web-cast speech, how many simultaneous connections did they need to use? – OK, I don’t know, but it was lots. • Multicast supports a group communication model. – Everyone who’s interested in the web-cast is a group → only one outgoing video feed. • Huge reductions in bandwidth!

Example: Access Grid • The Access Grid – – http: //www. accessgrid. org A large-group teleconferencing facility The human interactions interface to grid computing Core middleware with support for multimedia streams, interfaces to grid data, and data visualizations • Summary: The futuristic Internet 2 application you can use to justify whatever upgrades you want.

Access Grid (cont) • Realities: Mainly video & audio right now, along with distributed Power. Point. • This isn’t a bad thing – Bandwidth consumption can hit 45 Mb on big conferences just with this set. • 90+ nodes, 4 or more video streams + audio per node

A Day in the Lobby:

A Typical Day in the Lobby

Multicast to the Rescue • Multicast tools (vic & rat) make the largescale collaboration possible • End-users only need to know a multicast address to send to, which defines the group. – This is handled through a web interface • The networking hardware manages getting the data to everyone else in the group.

II. The ABC’s of Multicast Flood & Prune Messages automatically go everywhere, except where excluded. Router builds table from prune messages.

PIM Protocol Independent Multicast • PIM uses the unicast routing tables rather than building its own – hence “independent” • PIM-DM (dense mode) – Uses the Flood and Prune idea • PIM-SM (sparse mode) – Messages only go where explicitly requested – Client host uses IGMP (Internet group management protocol) to signal interest in multicast group to the lasthop router.

PIM-SM MSDP Sparse Mode RP IGMP Client specifies interest with IGMP. The RP (rendezvous point) acts as a clearing house for requests within a domain. MSDP allows RPs to talk between domains.

Routing • MSDP (multicast source discovery protocol) allows peered Rendezvous Points to share group memberships. • You still need a routing table to tell you how to get from one zone to another • m. BGP (multiprotocol Border Gateway Protocol) provides the solution – Allows for different unicast & multicast routes • ISM (Internet Standard Multicast) is based on these protocols

Problems with ISM • Provides a good service model, but… – Lots of state gets held in the routers • Discovery, updated delivery lists, etc – Makes unintentional Do. S attacks easier • 100 MB host talking through a 10 MB hub. • CS networking class projects. . .

PIM-SSM • SSM (Source-Specific Multicast) extends the IGMP message format. • Application submits a (Source, Group) pair • Router only builds tree to specified source • IGMP v 3 is required to support this – V 3 will add the ability to explicitly include or exclude a source (when it gets here)

Discovery of Resources • Finding the proper multicast address for particular content can be difficult – With SSM, you need a multicast address and a (list of) source(s). • SDAP (session directory announcement protocol) and SDP (session description protocol) give you tools to announce and describe your multicast group. • Access Grid Virtual Venue is an example of an http-based discovery method.

Miscellaneous Future Developments • BGMP (border gateway multicast protocol) is a next generation replacement for MSDP – Lacks the single point of failure – a whole domain acts as the root of the broadcast tree, not just a single RP.

For More Information • Internet 2 WG – at http: //www. internet 2. edu/multicast • Two upcoming events: – 1 st I 2 Multicast Hands-On Workshop. (In Eugene, most likely 19 -21 June. ) – An "Ask the Experts" In-depth session the afternoon of 31 July as part of the next NLANR/Interent 2 Techs Workshop in Boulder.