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Application Layer Multicast for Small Groups:
Status and Research Direction
Bobby Bhattacharjee
University of Maryland
John Buford
Panasonic Digital Networking Laboratory
March 16, 2006
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Topics
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Problem statement
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Background and summary of current ALM research
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A. Garyfalos and K. Almeroth, A Flexible Overlay Architecture for Mobile IPv6
Multicast", J on Sel Areas in Communications Special Issue on Wireless Overlay
Networks Based on Mobile IPv6, vol. 23, num. 11, pp. 2194-2205, Nov 2005.
A. Garyfalos, K. Almeroth, and J. Finney. A comparison of network and
application layer multicast for mobile IPv6 networks. MSWIM '03.
Hybrid multi-destination and host-group multicast
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Yang-hua Chu, Sanjay G. Rao, Srinivasan Seshan and Hui Zhang. A Case for
End System Multicast. IEEE J on Selected Areas in Communications, 2002
Suman Banerjee, Bobby Bhattacharjee. A Comparative Study of Application Layer
Multicast Protocols. Submitted.
ALM and Mobile IP
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Mostafa Ammar. Why Johnny Can’t Multicast Lessons about the Evolution of the
Internet. Keynote - NOSDAV 03.
Qi He, Mostafa Ammar, "Dynamic Host-Group/Multi-Destination Routing for
Multicast Sessions," J. of Telecommunication Systems, vol. 28, pp. 409-433,
2005.
Research issues for proposed SSGM activity
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Problem Statement
Mostafa Ammar. Why Johnny Can’t Multicast Lessons about the Evolution of the Internet.
Keynote - NOSDAV 03..
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Application Layer Multicast (End System Multicast)
Y. Chu, S. Rao and H. Zhang. A Case for End System Multicast. IEEE Journal on Selected Areas in Communications, 2002
Y. Chu, S. Rao and H. Zhang. A Case for End System Multicast. (Keynote) ACM SIGMETRICS Performance Evaluation Review, 2000
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Scalability with number of groups
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Routers maintain per-group state
Analogous to per-flow state for QoS
guarantees
Aggregation of multicast addresses is
complicated
Supporting higher level functionality is
difficult
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IP Multicast: best-effort multi-point delivery service
End systems responsible for handling higher level
functionality
Reliability and congestion control for IP Multicast
complicated
Deployment is difficult and slow
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ISP’s reluctant to turn on IP Multicast
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Application Layer Multicast
Y. Chu, S. Rao and H. Zhang. A Case for End System Multicast. IEEE Journal on Selected Areas in Communications, 2002
Y. Chu, S. Rao and H. Zhang. A Case for End System Multicast. (Keynote) ACM SIGMETRICS Performance Evaluation Review, 2000
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Potential Benefits
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Scalability
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Easier to deploy
Potentially simplifies support for higher level functionality
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Leverage computation and storage of end systems
For example, for buffering packets, transcoding, ACK aggregation
Leverage solutions for unicast congestion control and reliability
End System Multicast is a promising alternative approach for multi-point delivery
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Routers do not maintain per-group state
End systems do, but they participate in very few groups
Narada: A distributed protocol for constructing efficient overlay trees among end systems
Simulation and Internet evaluation results to demonstrate that Narada can achieve good
performance
Consider applications with small and sparse groups
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Around tens to hundreds of members
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Application Layer Multicast
Y. Chu, S. Rao and H. Zhang. A Case for End System Multicast. IEEE Journal on Selected Areas in Communications, 2002
Y. Chu, S. Rao and H. Zhang. A Case for End System Multicast. (Keynote) ACM SIGMETRICS Performance Evaluation Review, 2000
Internet measurements (SIGMETRICS 2000)
3 topologies, various group sizes
simulation results (JSAC 2002)
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Application Layer Multicast
Suman Banerjee, Bobby Bhattacharjee. A Comparative Study of Application Layer Multicast Protocols. Submitted
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Mesh-first protocols are efficient for small multicast groups, while implicit
protocols scale well with increasing group sizes.
Tree-first protocols are less suited for latency sensitive (e.g. real-time)
applications but are useful to implement for high-bandwidth data transfers.
Implicit protocols are particularly beneficial when the size of the multicast
group is very large, and can be adapted for both latency-sensitive
applications (due to their short path lengths) and high-bandwidth
applications (due to low tree degree).
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ALM & Mobile IP
A. Garyfalos and K. Almeroth, A Flexible Overlay Architecture for Mobile IPv6 Multicast", J on Selected Areas in
Communications Special Issue on Wireless Overlay Networks Based on Mobile IPv6, vol. 23, num. 11, pp. 21942205, November 2005.
A. Garyfalos, K. Almeroth and J. Finney, "A Comparison of Network and Application Layer Multicast for Mobile
IPv6 Networks", ACM Workshop on Modeling, Analysis and Simulation of Wireless and Mobile Systems
(MSWiM), San Diego, California, USA, September 2003.
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Mobility introduces several new challenges for ALM that do not exist in
wired networks.
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System stability,heterogeneity and node capability become critical problems since
mobile nodes may be less capable or more constrained in their ability to act as
ALM end hosts.
Moreover, in terms of network performance IP Multicast outperforms ALM
both for low and high speeds.
Approach
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hybrid system in which inter-domain multicast support is provided using ALM and
intra-domain support is provided using native multicast.
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ALM & Mobile IP
A. Garyfalos and K. Almeroth, A Flexible Overlay Architecture for Mobile IPv6 Multicast", J on Selected Areas in
Communications Special Issue on Wireless Overlay Networks Based on Mobile IPv6, vol. 23, num. 11, pp. 21942205, November 2005.
A. Garyfalos, K. Almeroth and J. Finney, "A Comparison of Network and Application Layer Multicast for Mobile
IPv6 Networks", ACM Workshop on Modeling, Analysis and Simulation of Wireless and Mobile Systems
(MSWiM), San Diego, California, USA, September 2003.
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In terms of throughput, low mobility gives no major advantage to IP
multicast. However, as nodes start to increase their speed, ALM
experiences additional packet loss.
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In terms of RDP (Relative Delay Penalty),
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At its worst, ALM suffers about 4 times the loss of IP multicast.
Low mobility causes IP multicast to perform much better: on the order of 4 to 5
times better than ALM.
High mobility, IP multicast still performs better, but the improvement is less: an
RDP ratio of 2 to 1.
Overall, ALM suffers both when mobility is low and when it is high.
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Low mobility gives better robustness but very high RDP.
High mobility gives better RDP values, but robustness is poor.
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Hybrid Multi-Destination & Host-group Multicast Routing
Qi He, Mostafa Ammar, "Dynamic Host-Group/Multi-Destination Routing for Multicast Sessions,"
Journal of Telecommunication Systems, vol. 28, pp. 409-433, 2005.
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Assume Internet support for both hostgroup multicast routing to very large
groups and multi-destination routing to
small and medium size groups
Protocol to switch between SGM and
PIM-SSM (Single Source Multicast)
Protocol for dynamic join/leave using
tunnel management
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“One criticism against Xcast is that it involves more
router processing due to multiple unicast route
lookups. The Xcast community(Xcast (2004)) has
argued that the cost would not be substantial given
the small session sizes Xcast is intended for. On
the other hand, Xcast developers strive to optimize
the processing cost in their designs, tunneling being
one of the approaches they adopt. Given that most
(80% according to (Chalmers and Almeroth
(2001))) of the routers on typical multicast trees
are non-branching, tunneling between
branching routers could reduce the SGM
processing cost by a large fraction. It should be
clear from the description of the transition
protocol how we exploit the tunnels to save
processing costs.” (p. 12)
Future work:
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Target an implementation of the dynamic SGM/splitgroup SGM/PIM routing system. Our goal will be to
investigate issues in router performance and
processing overheads.
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Hybrid Multi-Destination & Host-group Multicast Routing
Qi He, Mostafa Ammar, "Dynamic Host-Group/Multi-Destination Routing for Multicast Sessions,"
Journal of Telecommunication Systems, vol. 28, pp. 409-433, 2005.
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Research Issues for Proposed SSGM Activity
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For small groups, topology optimization/adaptation is not as
crucial
Assume millions of groups, then different set of assumptions
drive solutions for
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Bootstrapping
Group management and group formation
Group level churn
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Questions?