[icecast] A large streaming project

Michael Smith msmith at labyrinth.net.au
Thu Feb 27 13:26:55 UTC 2003

> Michael Smith wrote:
>  > The only major thing is this: do they require RTP (multicast)?
> Can you explain what this is and it's benefits?  I tried googling it but 
> didn't find anything useful.

<p>In brief: unicast (what icecast currently does) sends a copy of the stream to
every listener. Thus, for a 32 kbps stream, your total bandwidth usage is
approximately (there are a few little extras, but they end up being
insignificant) number-of-listeners * 32 kbps. That adds up to a lot if you
have thousands of listeners.

With multicast, you basically send out only one copy of the stream (though you
have overhead from each client reporting that it's connected, etc, so total
bandwidth usage still scales upwards, just much slower), and the network
infrastructure (routers, etc.) copies that to all the clients that are
listening (description much simplified here, of course). The downside is that
many ISPs don't have routers that are capable of multicast, and/or they don't
have it enabled. So for really wide deployment you need both unicast and
multicast available, ideally.


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