Re: Quality of BBC Internet radio to overtake DAB

Boltar wrote:


As I mentioned in another thread last week , multicasting is a network
and router killer. The chances of there being hundreds or thousands of
multicast streams to choose from in the future will be zero. There is
currently no way (at least on IP4 , don't know about IP6) for a
machine listening on a given multicast subnet to tell a router N hops
down the line that it is/isn't listening to it. Ergo every router at
every stage will have to forward every multicast packet to every
network its connected to in all directions just in case any machine
anywhere wants it. You might aswell just switch the internet off and
go home.

Thinking about this some more. There is no need for IP4 to know anything about multicasting, provided that that the multicasting standards are implemented at a higher layer than the IP4 standard.

To illustrate what I mean consider the situation of setting up 1000s of servers all connected to the internet. Any server can send any information it needs to, to any other server, just by putting the information into IP4 packets. There is no need for IP4 to understand the data in these packets, it just needs to deliver them.

Now supposing we set up a system where we organise these servers into a multicast system. One server could communicate with a few of it's neighbours sending them the broadcast data, and each of these can send it to a few more, and so on. So you can end up sending the broadcast data to 1000s of servers, but no one server is sending any large amount of data. If one server doesn't need to receive he stream any more it can just communicate with whichever other servers are appropriate to switch off that route.

In this arrangement IP4 still doesn't need to know anything about the multicasting standards being used by the servers. It only needs to route packets between servers, as requested by the servers. The servers would be able to organise whatever multicasting logic was appropriate, just as long as they can communicate with each other. IP4 allows them to do that, it is simply being used as a data transport system.

Now I seem to remember reading in this NG about routers needing to be multicast enabled. If this is true then obviously multicasting must be being built into the routers. However this still doesn't have to affect the IP4 standard. It could be done at a higher layer, which would effectively be like taking the servers, as explained in my illustration above, but simply having these servers built into the router. Obviously only the multicast functionality would be built into the routers (not the whole server), but it would still work in the same way. The multicasting part of the routers would talk to the multicast part of other routers, by sending IP4 packets. It would be able to send any appropriate commands, by putting them into IP4 packets. IP4 would not need to know anything about the contents of these packets, it would simply route them to the appropriate destinations.

Richard E.
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