How to do high-speed multicast right!
Section snippets
Brave new world of high-speed multicast
Multicast is a widespread technology enabling a broad range of applications such as the distribution of stock quotations and video conferencing to effectively send data to groups of receivers. In the past, multicast has been accomplished mainly by software, by processor-based forwarding mechanisms and by the distribution of multicast packets as broadcast in layer 2 networks like Ethernet. Thus, the bandwidth available to multicast applications has been restricted to several megabits.
This has
Practical high-speed multicast technologies
Three technologies currently dominate the high-speed networking market: ATM; (used in LAN and WAN), gigabit Ethernet (LAN), and Packet-Over-Sonet (POS; used in IP routers for WAN). High-speed interfaces for end systems are available for gigabit Ethernet and ATM (622 Mbit/s).
Multicast data distribution in these networks typically takes place via IP multicast, which is supported by most application program interfaces (APIs) for IP in end systems. It is also possible to use native ATM connections
Avoid small packets!
Looking at Table 1, one can become quite optimistic about the bandwidth, which will be available to our multicast application. Something between 500 and 900 Mbit/s seems to be possible. So what limits the server mentioned in our multicast disaster to throughput rates of 100 Mb/s or even less?
One possible reason can be found in the diagrams Fig. 2, Fig. 3, Fig. 4, which show some of the measurements we did on a Sun E250. For XTI, LANE and GE we chose a set of packet sizes and for each of them
Summary
Today, modern hardware allows high-speed multicast with hundreds of megabits. In practice the following methods may be used for multicast distribution:
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APIs for native layer 2 usage (like the ATM extension for the XTI API)
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IP multicast over single layer 2 networks (based on gigabit Ethernet or ATM/LANE)
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Router-based IP multicast networks.
The main lessons we learned in our environment are:
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There is no clear winner, but every technology has its advantages and drawbacks.
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You have to carefully separate
Acknowledgements
We would like to thank our colleagues of the High Speed Networking Group at GMD. The German Research Network (DFN) supported this research as part of the Gigabit Testbed West.
Gundula Dörries received a Diploma in Physics from the University of Düsseldorf in 1994. After working for Hewlett-Packard as Systems Engineer, she joined the High Speed Networking group (HSN; now NetMedia) in the Institute for Media Communication (IMK) of the German National Research Center for Information Technology (GMD) in 1999. Her main interests are multimedia networking and QoS issues.
References (8)
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IP Multicasting
(1998)- B. Williamson, Developing IP Multicast Networks, vol. 1, CISCO Press, Indianapolis, IN,...
- The Open Group: Networking Services (XNS), Issue 5.2, X/Open Transport Interface (XTI), January 2000,...
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Gundula Dörries received a Diploma in Physics from the University of Düsseldorf in 1994. After working for Hewlett-Packard as Systems Engineer, she joined the High Speed Networking group (HSN; now NetMedia) in the Institute for Media Communication (IMK) of the German National Research Center for Information Technology (GMD) in 1999. Her main interests are multimedia networking and QoS issues.
Lothar Zier received his Diploma in Computer Science from the University of Bonn in 1991. He worked as a Scientist at GMD in the Networking Department from 1991 to 2001. His research topics were IP and ATM based networking. He has been working as consultant for DETECON GmbH (a subsidiary of Deutsche Telekom AG) since July 2001.