> As far as I know, the operators prefer native multicast for IPTV > applications, for a good reason. > It seem like this is the application that Mark has in mind. > >>So, yes, it is a fairly good idea to study how multicast delivery could be >>accomplished by a series of unicast transmission. There are two solutions today: multicast all the way, from the source to the various destinations; and, unicast all the way. The multicast solution suffers from very poor performance on the 802.11 network. The unicast solution prevents bandwidth optimization in the distribution network. The "best" solution would combine unicast on 802.11 networks and multicast on the distribution network. That requires protocol changes, so that an 802.11 node that subscribes to a multicast group effectively gets unicast delivery from the wireless router, while the wireless router gets multicast delivery from the network router. That's what Mark's draft is attempting to define. That seems like a fine project.
Of course that's not an easy project, and there are many details that need to get solved. For example, allowing multicast delivery to arrive over unicast addresses may well have some interesting security implications. Then there is the matter of "multiplying" the multicast packets, which is prone to create instant congestion in the router. Then there is the decision logic on when to choose multicast versus unicast delivery. Oh, and doing all that without an explosion in complexity... Of course, we can observe that unicast delivery can be implemented today using end-to-end procedures. Makes you really wonder whether the right way to optimize bandwidth for multicast content delivery is a new version of IP forwarding standards, or instead some form of compression on the distribution links. -- Christian Huitema -------------------------------------------------------------------- IETF IPv6 working group mailing list ipv6@ietf.org Administrative Requests: https://www.ietf.org/mailman/listinfo/ipv6 --------------------------------------------------------------------
