The Three Ghosts of Multicast: Past, Present, and Future

1. The Three Ghosts of Multicast:Past, Present, and Future Kevin Almeroth (almeroth@cs.ucsb.edu) University of California—Santa Barbara 22-May 2007 TNC 2007

2. “Multicast could be the poster child for the irrelevance of the networking research community. Few other technologies (quality of service springs to mind) have generated so many research papers while yielding so little real-world deployment.” • Bruce Davies, public review of ACM Sigcomm 2006 accepted paper, • “Revisiting IP Multicast” by S. Ratnasamy, A. Ermolinskiy, S. Shenker • http://www.sigcomm.org/sigcomm2006/discussion/

3. Multicast’s failure… quantitatively • Methodology: • Look at MBGP (BGP4+) prefixes advertised (these prefixes are used by receivers to send join messages toward sources) • Assumption is that such an advertisement indicates support for multicast • Metrics: • Percentage of address space • Percentage of prefixes • Percentage of ASes

4. Multicast’s Failure… Quantitatively Data by Marshall Eubanks, Multicast Technologies http://multicasttech.com/status/

5. Multicast’s failure was because… • Multicast never become a ubiquitously deployed, revenue generating, native, one-to-many and many-to-many service capable of securely and robustly supporting: • (1) all manner of streaming media (TCP-friendly adaptation), • (2) reliable, TCP-friendly file transfer, and • (3) audio/video conferencing (with minimum jitter and delay) • all with only minimal additional router complexity, deployment effort, management needs, or cost.

6. Multicast’s failure was because… • Multicast never become a ubiquitously deployed, revenue generating, native, one-to-many and many-to-many service capable of securely and robustly supporting: • (1) all manner of streaming media (TCP-friendly adaptation), • (2) reliable, TCP-friendly file transfer, and • (3) audio/video conferencing (with minimum jitter and delay) • all with only minimal additional router complexity, deployment effort, management needs, or cost. So, is multicast really a failure?

7. The Success of Multicast… • The real use of multicast is not widely visible • High speed research and education networks • Plus, some campuses distribute CableTV/IPTV using multicast • Enterprises • Major companies using a wide variety of apps • Exchanges and securities trading companies • Other edge networks • Often called “walled gardens” • Examples: DSL and Cable TV (triple/quad play) • Military networks • One statistic: “60% of our traffic is going to be multicast”

8. In Fact… • Multicast, as an academic-style research area, has been one of the more successful recent research areas • Original idea was generated in academia • Academic-based research has led to the standardization and deployment of protocols, industry/academia collaboration, start-ups, new technology, products, revenue, jobs, etc. • And these efforts continue…

9. A Quick Aside… Replace “multicast” with “IPv6” or “QoS” (and maybe “ad hoc networks”) (okay, not really)

10. Why the Perception Disconnect? • Multicast evolved with simultaneous research, prototyping, deployment, testing, and use • Too many changes in direction (e.g., ASM v. SSM) • At some point, too much deployed infrastructure and too hard to make major changes • A lack of discipline among academics • Too many irrelevant papers and projects • A lack of foresight about the scope of the problem, the groups involved, and group interaction • A lack of the right expectations

11. The Interconnected Community • Users • App developers (socket interface) • OS companies (socket/network interface) • Router vendors • Network administrators • Content providers • Researchers

12. The Interconnected Community • Users • App developers (socket interface) • OS companies (socket/network interface) • Router vendors • Network administrators • Content providers • Researchers Becomes one big chicken farm and omelet problem!

13. Two of the Biggest Early Problems • Service just didn’t work • Remember, multicast started before there was a significant web presence and really even before inter-domain routing • Little consideration for large-scale deployments • Especially the economies of deployment • Especially monitoring/management/accounting

14. It was Doomed Soon After the Start • Original architecture was based on Deering PhD dissertation which was for LAN-based multicast • We never got away from many of those assumptions • The first step was a small one and it worked… • No scalability (broadcast and prune…), minimal requirements, but it worked! • …but the second step was too big • Would only accept (nearly-)infinite scalability • “Small group multicast” was dismissed out-of-hand

15. What was Deployed did not Work • Routing problems persisted • Trying to join dense with sparse • Mis-configuration (that’s what the vendors said) • Poor interface (that’s what the users said) • Proper deployment was arcane and hard to debug • Academics didn’t understand the problem • Hard for users to even know if it was working • Try-it-and-see mentality… • …and if it wasn’t working, it was nearly impossible to debug • Two experiments • What do users see? • What do the backbone routers see?

17. The Routers’ View

18. The Challenge of Economics • Users • Don’t care how they get content, they just want it • ISPs • Never figured out how to charge: UUNet (UUcast) tried, but the billing model wasn’t consistent with what multicast did • Odd “sweet spot” on the economics curve • Sold as a “reduction in traffic”, but wasn’t • Content providers • L-O-V-E multicast because they pay less… • Application developers • Good AAA requires implementing some non-scalable features, for example, tracking membership • The lesson of Starbust

19. A Litany of Other Problems • Inter-domain and source discovery • SSM fixes the problem, but too little too late • Reliability and congestion control • Firewall support • Authentication/Authorization/Accounting (AAA) • State scalability and router CPU processing • Security • Data security and protocol operation security • Monitoring/Troubleshooting/Management

20. Current Adjustments • IRTF SAM Research Group has a good mission • Continue work towards a hybrid solution • Solutions must be incrementally deployable • For example: Automatic Multicast Tunneling (AMT) • Even Application Layer Multicast (ALM) is okay • Convince academic community to re-accept multicast • They still are in many cases (even Sigcomm did), but what they consider interesting are monolithic solutions • Need a place that accepts good, deployable solutions • Interest by the funding agencies would also help

21. Automatic Multicast Tunneling • Allows multicast content to reach unicast-only receivers • The benefits of multicast wherever multicast is deployed • Hybrid solution • Multicast networks get the benefit of multicast but unicast users still get the benefit of the content • Works seamlessly with existing applications • Requires only client-side shim (somewhere on client) and router support in some places

22. Ucast Stream Automatic Multicast Tunneling Content Owner Mcast Enabled ISP Unicast-Only Network Mcast Traffic Greg Shepherd, Cisco Mcast Enabled Local Provider

23. Ucast Stream Automatic Multicast Tunneling Content Owner Mcast Enabled ISP Creates an expanding radius of incentive to deploy multicast. Unicast-Only Network Mcast Traffic Greg Shepherd, Cisco Mcast Enabled Local Provider

24. The Original MBone was Tunnels

25. Wrapping Up: More Directions • Continued development • Clearly room for more monitoring/management/accounting • Mobility support (as if the problem wasn’t hard enough already!) • Continued deployment efforts • Plus requires more apps and more content (as always) • Continued engineering work • Not necessarily by the academics but by the high-speed network operators/engineers • Keep multicast a de facto part of IPv6