Post on 25-Feb-2016
description
The Three Ghosts of Multicast:Past, Present, and Future
Kevin Almeroth (almeroth@cs.ucsb.edu)University of California—Santa Barbara
22-May 2007TNC 2007
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“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/
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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
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Multicast’s Failure… Quantitatively
Data by Marshall Eubanks, Multicast Technologieshttp://multicasttech.com/status/
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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.
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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?
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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”
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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…
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A Quick Aside…
Replace “multicast” with “IPv6” or “QoS”
(and maybe “ad hoc networks”)(okay, not really)
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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
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The Interconnected Community
Users App developers (socket interface) OS companies (socket/network interface) Router vendors Network administrators Content providers Researchers
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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!
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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
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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
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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?
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The Routers’ View
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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
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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
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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
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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
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Automatic Multicast TunnelingMcast Enabled ISP
Unicast-Only Network
Content Owner
Mcast Enabled Local Provider
Mcast Traffic
Ucast Stream
Greg Shepherd, Cisco
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Automatic Multicast TunnelingMcast Enabled ISP
Unicast-Only Network
Content Owner
Mcast Enabled Local Provider
Creates an expanding radius of incentive to deploy multicast.
Greg Shepherd, Cisco
Mcast Traffic
Ucast Stream
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The Original MBone was Tunnels
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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