Wspólnotowy Serwis Informacyjny Badan i Rozwoju - CORDIS

Modification of the Mad application

It is very common to do file mirroring on the Internet. The most common example is the mirroring of contents on FTP and Web sites. One example is the different Linux distributions that are accessed by thousands of users every day. To conserve bandwidth, CPU load, etc. volunteers set up public mirrors. There are also cases where a small company may have their own mirror instead of having all their computers access one single server over a possibly narrowband Internet connection.

The mirroring described above is generally done by unicast transmissions. An alternative for populating both large public mirrors and smaller internal ones could be multicast which further reduces the bandwidth consumed. When using multicast it could also be possible for end-hosts (not mirrors) to subscribe to updates and receive them as soon as they become available. This could in practice reduce the need for public mirrors. When receiving multicast contents like this, one should have some control of who is sending data, which means that it is natural to use SSM (source-specific multicast).

Multicast is not widely deployed on the Internet today. However it is available in academic communities and in NRENs and networks like GÉANT and Abilene. IPv6 multicast has some advantages over IPv4 multicast, and there is hope that it will be more widely deployed. For IPv4 multicast, the deployment of NAT boxes and some issues with layer-2 devices are 2 major problems. For IPv6, layer-2 multicast is a requirement for unicast to work, so this helps IPv6 multicast deployment in general. By adhering to the end-to-end model and avoiding inter-domain solutions like MSDP, IPv6 multicast should be easier to manage. IPv6 multicast is also easier to manage due to the well-defined scoping architecture.

The application MAD-FLUTE ( based on draft-ietf-rmt-flute-07.txt fulfils many of the needs above. The work in 6NET was to build a surrounding framework that can run the application at appropriate times, handle errors, cope with retransmissions or use IPv6 unicast for initial mirroring or filling in large blocks of missing data. The tool was deployed at some locations in 6NET, and later outside 6NET. It also evolved into a showcase demonstration.

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United Kingdom
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