By Dr Kim Chin Australian Catholic University, North Sydney, New South Wales, Australia

1. By Dr Kim ChinAustralian Catholic University, North Sydney,New South Wales, Australia Multicast Networking

2. Outline • What is Multicast? • Unicast vs Broadcast vs Multicast • Why Multicast? • IP Multicast Model • MBone and its growth • Multicast Trees • Some Logical Multicast Trees generated when the MBone experienced an explosive growth

3. Outline (continue…) • IP Multicast deployment status • Factors that hinder deployment • Beyond IP multicast • Application layer multicast • Overlay multicast • Summary and the future of Multicast

4. What is multicast? • a receiver-based concept • is the sending of messages from one-to-many receivers or many-to-many receivers • is a subset of broadcast

5. Broadcast vs Unicast • Broadcast • sends data to everyone whether they want them or not • Unicast • the common way of transmitting data across the Internet • sending a single copy of the message to anyone who requests it

6. UC Berkeley Multimedia Seminar law (California) edgar (Washington) tove (Maryland) erlang (Massachusetts) alps (Georgia) float (Virginia) cedar (Texas) ursa (Germany) anhur (Sweden) Network Network Network node Data packets replicated by this node Audio packet

7. Problem with Unicast • The Internet has traditionally been built to send information to one person (or computer) at a time--unicast • consider sending information simultaneously to more than one person • e.g. e-mail message to which you've attached a graphics file • unicast--to one person • multicast--to many at the same time

8. Why Multicast? • “The unicast delivery paradigm predominant in today’s Internet does not scale to support the widespread use of video.” [Edwards et. al.] • “Multicast is becoming important because it enables desired applications to scale, ... Widespread use of these applications would be virtually impossible without the scaling provided by multicast services” [Miller] • “push” services of PointCast -- traffic clogged up networks

9. Why Multicast? (continue 1…) • Large-scale events: • (1998), latest version of Microsoft explorer--meltdown • landing of Pathfinder on Mars--”surfers” overwhelm NASA’s Web site

10. Why Multicast? (continue 2…) • September 11 tragedy, at Northern University, CNN was rebroadcast using multicast on the Internet--over 2000 viewers • “users on multicast-enabled networks were able to watch real-time video accounts throughout the entire day.” [Edwards et al.]

11. Video Transmission in Unicast & Multicast Networks (from http://www.mcclellanconsulting.com/)

12. Multicast Applications

13. The IP Multicast Model Deering’s standard multicast model for IP networks is as follows: • IP-style semantics: source sends UDP/IP packets • no need to register • no schedule transmission • send at any time • best effort

14. The IP Multicast Model (continue...) • Open groups: • multicast address known by sender only • need not know group membership • need not be a member of the multicast group they send packets to • group can have any number of sources

15. The IP Multicast Model (continue...) • Dynamic group: • members can join and leave a group • no need to register • no need to synchronize • no need to negotiate with any centralized group management entity

18. The IP Multicast backbone (MBone) • The “virtual network backbone” which joins together the multicast-capable portion of the Internet was the MBone. • Originated from DARTNet (DARPA Research Testbed network) • the success of the weekly DARTNet meetings resulted in extending the multicast infrastructure:

19. MBone (continue…) • multicast routing function provided by mrouted • a daemon process--received encapsulated multicast packets-- incoming interface outgoing interface • tunnels (multicast routers at the edge of a multicast-capable portion of the Internet) • each tunnel connected two end-points via one logical link--crossed several Internet routers • multicast packet received at a tunnel endpoint--broadcast on a local network • DVMRP (Distance Vector Routing Protocol)

22. Multicast Trees • multicast routing was a controlled form of flooding • no pruning initially -- pruning was deployed several years later • broadcast & prune used to create multicast trees • reverse shortest path tree --rooted the source

23. Multicast Trees (continue 1…) 4 steps to creating a multicast tree: • source broadcasts packets on its local network • an attached router receives the packets • sends them through all outgoing interfaces • router receiving a packet performs a RPF (Reverse Path Forwarding) check • router checks incoming interface (packet received) is used as the outgoing interface to reach the source

24. Multicast Trees (continue 2…) • When a packet reaches a router (leaf router) with attached hosts • leaf router checks if there are known group members on its attached subnets • IGMP queries issued periodically to discover group members • leaf router: • does nothing if there are group members • no group members--leaf router sends a prune towards the source on the RPF interface

25. Multicast Trees (continue 3…) • Prune packets sent back to the source • routers create prune state for the interface receiving the prune

26. anhur (Sweden) World Radio Network (Washington D.C) zen (Missouri) cedar (Texas) law (California) tove (Maryland) willow (Arizona) collage (California) erlang (Massachusetts) ursa (Germany) alps (Georgia) float (Virginia)

28. erlang (Massachusetts) ocarina (Kentucky) pax (France) cedar (Texas) anhur (Sweden) World Radio Network (Washington DC) alps (Georgia) tove (Maryland)

30. spiff (Sweden) erlang (Massachusetts) ursa (Germany) pax (France) cedar (Texas) float (Virginia) Radio Free Vat (California) artemis (France) edgar (Washington) tove (Maryland) bagpipe (Kentucky) excalibur (California) Logical Multicast Tree (April 19th, 1996). It is adapted from Yajnik et al.

32. lupus (Germany) erlang (Massachusetts) tove (Maryland) cedar (Texas) spiff (Sweden) law (California) float (Virginia) edgar (California) Radio Free Vat(California) ganef (California) excalibur (California) Logical Multicast Tree (May 8th, 1996). It is adapted from Yajnik et al. The bold lines represent the connections between backbone routers. All other lines are branches of the tree and they are on the edge of the network, leading to the receiving hosts.  is the backbone router and is the local LAN router.

33. Deployment Status Deployment has been very slow even though multicast is an old concept by Internet standards—compare with WWW & HTTP • Jan 1992—the MBone, did not exist—in 1995, it made up 20% of all the Internet data bytes at one research lab—40% at another and more than 50% at yet another---but traffic overshadowed by Web soon after.

34. Deployment Status (continue…) • the Web was quite unknown until late 1992 --then a “stunning pattern of growth set in”: “a research site’s Web traffic began to double every 6 weeks, and continued to do so for 2 full years!!!” by 1994, Web traffic wholly dominated the site’s activities [Paxson,1996]. • Web traffic has overshadowed MBone traffic ever since

35. Factors that hinder deployment • multicast lacks the “killer” applications • most popular multimedia applications access the content via multicast then falling over to unicast • lack of scalable inter-domain routing protocol • state scalability issue with a large number of groups • how to charge for Multicast services—lack of appropriate pricing model • loss of revenues from unicast bandwidth • issue of end-to-end connectivity

36. Factors that hinder deployment (continue…) • can the Internet ever have prime-time television quality video? • lack of test tools for trouble-shooting • Denial of Service attacks—ASM (Any-Source-Multicast) • lack of security support • multicast protocols are complex and may break the unicast network

37. Beyond IP Layer Multicast • Application layer multicast • group membership, tree construction, data forwarding controlled by end hosts, thus requiring no support from intermediate nodes such routers • Overlay multicast • Multicast functionalities supported by some additionally deployed intermediate nodes forming an overlay network

38. Taken from [Lao et al, 2005]

39. Application Layer Multicast • ALMI (Application Level Multicast Infrastructure) [Pendarakis et al] • provides a multicast middleware which is implemented above the socket layer • scales for a large number of groups with number of members small • independent of multicast support in routers

40. ALMI • An ALMI session consists of a session controller and multiple members • a session controller is in a location where it is easily accessible by members • session members are organized into a multicast tree • unicast connection between 2 members is represented by a link

41. Application Layer Multicast Approach • Multicast related features are implemented at end hosts • Data packets are transmitted between end-hosts via unicast and replicated at end hosts • Can be deployed with ease because it does not require infrastructure support from intermediate nodes [Lao et al]

42. Disadvantages of Application-layer Multicast • Not scalable to support large multicast groups due to its rather low bandwidth efficiency • Tree maintenance at end hosts causes heavy control overhead • Difficult for ISPs to have an effective profit-making service model because group membership and multicast trees managed at end hosts—hard to have member access control as well as knowledge of a group’s bandwidth usage [Lao et al]

43. Overlay Multicast • Two-tier Overlay Multicast (TOM) [Lao et al] • A key feature is its backbone service domain, MSON (Multicast Service Overlay Network), consisting of service nodes or proxies strategically deployed by MSON provider (ISP) • The design of MSON relies on well-defined relationship between: • the MSON provider; • the network service provider; and • the group coordinators

44. Summary • Multicast is a more efficient mode of transmitting packets, especially video packets, than unicast and broadcast • Microsoft supports Multicast project in China

45. Summary (continue 1…) • “Microsoft to “fully support” and “co-operate” with IP-Set-Top-Box manufacturer World Multicast China, on first ever direct to home IP Multicast service. This test to take place in the city of Shaoxing China beginning in early 2005.” [http://www.ipmulticast.com/]

46. Summary (continue 2…) • “Any time you are dealing with an emerging technology that has infinite potential you are going to have interested parties, our secure reliable IP multicast technology is the toolbox of missing links that have thus far hindered Inter-domain IP Multicast from proliferation. Now this test will change all of that. “

47. Summary (continue 3…) • “IP Multicast is the only technology built-into the current inter-domain routing infrastructure that addresses mass media on the Internet.We have dubbed our technology “Infinicast” because of its ability to support an infinite number of users from just one stream of video or audio.”[World Multicast Technology inventor Ian A. Stewart ]

48. The file size required to represent about one minute of media (taken from ASTD’s source for E-learning)

49. Summary (continue 4…) • IP Multicast Model • IP Multicast Routing Protocols • The MBone and its growth • Multicast trees • IP multicast deployment status • Factors hindering IP multicast deployment

50. Summary (continue 5…) • Beyond IP multicast • Application layer multicast • Overlay multicast