Global Internet 2005 A Comparative Study of Multicast Protocols: Top, Bottom, or In the Middle? Li Lao (UCLA), Jun-Hong Cui (UCONN) Mario Gerla (UCLA), Dario Maggiorini (Uni. of Milano)

Global Internet Why Another Study? Multicast solutions have been evolving from “bottom” to “top”  IP multicast, application layer multicast, overlay multicast  Incredible amount of research … Little research has been done to systematically compare the performance of different layer protocols  How much worse are upper layer solutions?  Are they long-term substitute to IP multicast or temporary solutions?  How will overlay design impact overlay multicast performance?  Which architecture should we choose in which scenario?

Global Internet Outline Multicast Overview Experimental Methodology Simulation Studies Conclusions

Global Internet Multicast Overview IP Multicast Application Layer MulticastOverlay Multicast

Global Internet IP Multicast Relies on network routers Pros  Bandwidth efficiency Cons  Lack of scalable inter-domain multicast routing protocols  Require global deployment of multicast-capable routers  Lack of practical pricing models Examples:  DVMRP/PIM-DM, CBT, PIM-SM, MOSPF, PIM-SSM, …

Global Internet Application Layer Multicast (ALM) Relies on end systems only Pros  Ease of deployment Cons  Lower bandwidth efficiency and higher end-to-end delay  Heavy control overhead  Challenges for large groups Examples:  Yoid, ESM, ALMI, NICE, TAG, HyperCast, …

Global Internet Overlay Multicast (OM) Relies on intermediate proxies to form a “backbone” overlay Pros Implicitly gains knowledge about the network topology More efficient group management Reduced control overhead Support multiple groups/applications simultaneously Cons Deployment and maintenance cost of overlay proxies Requires careful design of the overlay network Examples:  Scattercast, Overcast, RMX, AMCast, OMNI, …

Global Internet A Qualitative Comparison MetricsIPALMOM Ease of DeploymentLowHighMedium Multicast EfficiencyHighLowMedium Control OverheadLowHighMedium

Global Internet Experimental Methodology (I) Topology graphs  Router-level: Rocketfuel (University of Washington)  AS-level: Route Views (University of Oregon) Group membership generation  Uniform distribution Multicast Protocols  IP multicast: PIM-SSM  Application layer multicast: Narada and NICE  Overlay multicast: POM (Pure Overlay Multicast) End users connect to proxies via unicast

Global Internet Experimental Methodology (II) Overlay design  Overlay proxies: nodes with the highest degree  Overlay links: adjacent connection Performance Metrics  Multicast tree quality Tree cost: number of physical links in multicast tree End-to-end delay: # of hops between source & receivers  Control overhead Tree setup/tear-down, tree refresh, overlay link measurement For a single group and multiple groups  Reliability, stability, security, etc.

Global Internet Multicast Tree Cost OM has lower cost than ALM Among ALM, NARADA outperforms NICE for small groups, but not for larger groups Tree cost of POM increases faster than IP and ALM  Can use IP or ALM instead of unicast between proxies and end users

Global Internet End-to-End Delay OM has slightly higher latency than IP multicast Among ALM, the delay of NARADA remains fairly constant, and the delay of NICE increases very rapidly Trade-off between multicast tree cost and end-to-end delay

Global Internet Control Overhead (I) IP multicast has lowest overhead overall ALM has less overhead than OM for small groups, but its overhead exceeds OM when group size increases beyond a point OM curve has a smaller slope than ALM curves  Backbone overlay maintenance overhead is independent of group size

Global Internet Control Overhead (II) Backbone overlay maintenance overhead is independent of the number of groups Control overhead of ALM is proportional to the number of groups

Global Internet Impact of Overlay Parameters A larger number of proxies help to reduce multicast tree cost

Global Internet Impact of Overlay Parameters Backbone overlay maintenance overhead increases with the number of proxies

Global Internet Conclusions Application layer multicast  A suitable solution for immediate deployment  Good for small groups Overlay multicast  Could achieve performance comparable to IP multicast  A good choice for large numbers of groups  Could serve as a long-term solution Future work  Reliability, stability, security…  Different group membership models  Overlay network design

Global Internet No more questions, please!